Easy way to test the calibration of a DMM (Fluke 45)?

[Fried Chicken]

Hah.

So now I have the slightest stupidest insight into what makes pushing the boundaries of metrology difficult.
I have three or four multimeters or multimeter-like devices capable of reading voltages, but I'm not sure the accuracy of any of them.

So what around the house options to I have to verify/test what's accurate and what's not?  Fresh alkaline batteries?  Stick the probes in an outlet and compare with what the power company is reporting?  USB power from computers?

I have two relatively nice DMMs (Fluke 45 and a Hioki handheld), along with other DMM-like devices (o-scope, chinese LCR meter with DMM capabilities, a chinese function generator that let's me dial in a voltage, the mtester thing)...  Resistance notwithstanding.

Are there any reliable around-the-house ways I can test these multimeters?  Reliable resistors?  Pencil lead?  The nicest resistor I have laying around?

[bdunham7]

Do the Hioki and the Fluke 45 disagree on anything you've measured?

[Fungus]

I imagine the Fluke/Hioki won't drift much from spec.

Simple check: Do they agree with each other on things?

eg. A battery? USB power? A resistor?

[adinsen]

Been there... I texted a friend who had gotten himsels an almost new bench meter, we had coffee, discussed life, work and other stuff, and I got my meters checked against his. Recently I got myself one of those small TL431 based voltage references with hand written values on the pcb which are available on eBay, but it drifts a little with temperature and it doesn't say what temperature it was calibrated on, so I can't trust it.

[J-R]

My first thought was this: https://dmmcheckplus.com/shop/ols/products/dmm-check-plus-fully-loaded-with-all-options-lc-board-enclosure-and-dual-frequency

But given the cost and the equipment you have, I am not sure if it makes a ton of sense to spend that kind of money.

If not, maybe an option could be to go the route of sanity cross-checking combined with multiple DMMs and other test equipment.
Different ranges and functions use different paths/configurations.  Different resistor dividers, offset and gain calibrations for each individual range/function, etc.

So apply 3V to the Fluke 45 and Hioki, then manually range up to 30V, 300V, 1000V, and see if everything is consistent.  In some devices it's worth reversing the leads.  The Fluke 45 seems to have multiple negative DC V performance tests but only a single -90mV calibration point.  If you look at the theory of operation of some DMMs, this method isn't always overly useful if the same passives are used in multiple ranges and they've drifted.  But if things align, then that provides some level of confidence I'd think.

You could get some 0.1% resistors from DigiKey/Mouser and use them with Ohm's law.  I picked up a pile some time ago and perhaps since they are designed to hold that spec through various temperature ranges, I found that at room temperature they were typically far better than spec.  So a 1K 0.1% resistor is probably going to easily be between 999.5K and 1000.5K.  Cross check the voltage drop with the current flow and resistor value and see if it all lines up.

If it DOESN'T line up, then you have more work to do, but I suspect things will come out pretty good given your test equipment's pedigree.

[Fried Chicken]

Do the Hioki and the Fluke 45 disagree on anything you've measured?

I imagine the Fluke/Hioki won't drift much from spec.

Simple check: Do they agree with each other on things?

eg. A battery? USB power? A resistor?

Yes they do unfortunately.  The Fluke reads lower than the Hioki when measuring a battery, power supply... not sure how resistors are but they don't completely agree either.

[bdunham7]

Yes they do unfortunately.  The Fluke reads lower than the Hioki when measuring a battery, power supply... not sure how resistors are but they don't completely agree either.

So the first thing you do is quantify that disagreement.  You just need a reasonably stable source for voltage that you measure with the meters in parallel.  Resistors you have to measure sequentially but that shouldn't be a problem at your precision level.  Do this several times with each meter so you get an idea of how repeatable your measurements are.  Then look at the specified tolerances of the meter and make sure your repeatability error (difference between measurements of the same source with the same meter) is much less than the meter's spec.  Once you have measurements that are stable and repeatable, you can see how far off one meter is relative to the other.  Compare that with the specified tolerances to see whether their disagreement is expected and within specs or excessive and out of specs.

You can use a 9V battery, mains power from a wall socket and any random resistor of 1k to 10k as sources to start out.  Calibrators come later.

[CatalinaWOW]

There is another step you should take.  To control the time and money spent on this you should take this step first.

How much accuracy and precision do you need.  Note that those are two different questions.  And in a hobby context want is effectively a need.

For the majority of applications one part in a hundred is good enough.  Only a rare few require one part in ten million which pushes the limits of what can be achieved hard.

If your meters agree to the level of your needs you are done.  Except for training yourself to ignore those other digits on the right of the display.  As you add digits you will have to think about more things.  Leads, contacts, and a bunch of others.

[shapirus]

Yes they do unfortunately.  The Fluke reads lower than the Hioki when measuring a battery, power supply...

How much lower?

[Fried Chicken]

Consistently 0.02v ish

[bdunham7]

You didn't state the Hioki model, but assuming you have a DT4252 (my best guess) the specified tolerance is 0.3% of the reading plus 5 digits.  That works out to +/- 0.020V.  The specified 1-year tolerance of the Fluke 45 is 0.025%/rdg plus 2 digits in the 30V range that you are using which comes to about 0.003V.  So either the Hioki as at the extreme upper end of its tolerance range or the Fluke 45 is out of spec.

You could try using the slow reading 10V range on the Fluke 45 and see if anything changes.  Beyond that, it is going to be difficult to judge which meter(s) are within spec with just what you have on hand.

[shapirus]

Consistently 0.02v ish

Well, even if that may still be within spec (I don't know what is the accuracy spec for these, that's on you to check), a 20 mV difference sounds a bit too much.

There are some good relatively inexpensive voltage references like DMMCheck plus, which are adjusted and calibrated using well-known equipment with valid calibration certificates. One option is to use these to check which of your meters is (or are) off.

Another option is much cheaper, it's to use one of these LM399 boards from Ali. The equipment with which the as-measured values written on them were obtained, and the calibration status of that equipment, are questionable, but reportedly these boards are quite decent, and in most cases good to at least 1 mV. I have one of these, and it's been staying consistently in agreement with my Brymen BM869s within 500uV in the 5V range and 1.5 mV in the 50V range, which is well within the accuracy spec of the BM869s. The question is whether the numbers written on the board are trustworthy remains, and that may be a problem in your case: ideally you would need to check this board with some trusted recently calibrated voltmeter before using it to find out which of your meters is off :).

[Fried Chicken]

You didn't state the Hioki model, but assuming you have a DT4252 (my best guess) the specified tolerance is 0.3% of the reading plus 5 digits.  That works out to +/- 0.020V.  The specified 1-year tolerance of the Fluke 45 is 0.025%/rdg plus 2 digits in the 30V range that you are using which comes to about 0.003V.  So either the Hioki as at the extreme upper end of its tolerance range or the Fluke 45 is out of spec.

You could try using the slow reading 10V range on the Fluke 45 and see if anything changes.  Beyond that, it is going to be difficult to judge which meter(s) are within spec with just what you have on hand.

Oh shoot, I thought the model would appear on the picture.  It's the DT4251 (same as DT4252 afaik, except no current functionality).

So this is where the challenge comes in, what reliable voltage source might I have laying around...  Else as shapirus suggested, one of those aliexpress/ebay voltage sources...  Unless there's some creative way to find a reliable voltage source.  Maybe from a PC computer that might have a built in multimeter for its 5v USB rail?

[shapirus]

Maybe from a PC computer that might have a built in multimeter for its 5v USB rail?

Nope, you wouldn't expect anything like that to have the required accuracy.

You need either a voltage source that is sufficiently stable and has been measured with a sufficiently accurate (preferably better than your DMMs) calibrated (aka verified) meter, or access to such a meter to compare its readings with those of your DMMs on an arbitrary voltage source like a battery.

Realistically, DMMCheck Plus sounds like the best option (but yeah, $225, oh well), since if you get that cheap Chinese board, you still don't have a trusted DMM to verify it and use that initial verification as your reference point. Yes it is done by the manufacturer, but to what extent can that manufacturer be trusted? In case of DMMCheck Plus it is as trustworthy as the calibration certificates published on the manufacturer's website, and that's more than sufficient for your use case.

[bdunham7]

So this is where the challenge comes in, what reliable voltage source might I have laying around... 

This is where/how USA Cal Club got started, albeit at a few more digits of precision.  You aren't likely to have anything "laying around" nearly accurate enough to exceed the Fluke 45 specs.  And a one-point voltage source isn't really all that much help when you want to verify the meter entirely.  If you really care, you need an official or trusted unofficial calibration.  The question is whether you care enough to worry about that level of discrepancy. 

[Majorassburn]

So this is where the challenge comes in, what reliable voltage source might I have laying around...  Else as shapirus suggested, one of those aliexpress/ebay voltage sources...  Unless there's some creative way to find a reliable voltage source.  Maybe from a PC computer that might have a built in multimeter for its 5v USB rail?

Shamelessly self-promoting my products.....

https://www.ebay.com/itm/285781907875

Plus, I have precision resistors, etc....

[Fried Chicken]

So this is where the challenge comes in, what reliable voltage source might I have laying around...  Else as shapirus suggested, one of those aliexpress/ebay voltage sources...  Unless there's some creative way to find a reliable voltage source.  Maybe from a PC computer that might have a built in multimeter for its 5v USB rail?

Shamelessly self-promoting my products.....

https://www.ebay.com/itm/285781907875

Plus, I have precision resistors, etc....

I shall keep this in mind, but right now I've spent so much money on stuff I'm waiting before selling anything.

[bdunham7]

Shamelessly self-promoting my products.....

As I stated earlier, a single-point source is of rather limited usefulness here.  Besides that, is your reference here sufficiently accurate to test or calibrate a Fluke 45?   Does the trim pot adjust the 10V or 6V output?

[bdunham7]

I've spent so much money on stuff I'm waiting before selling anything.

Worrying about anything past the second place after the decimal point can get expensive in a hurry, so be careful!

If you like, I can unofficially calibrate your Fluke 45 for the cost of postage both ways.  I'll post the process and results to the forum here.  PM me if interested.  I don't have and can't find calibration info for the Hioki, so I'd be unable to adjust it, but it can be characterized so that you know how far it is off.

[Fried Chicken]

If you like, I can unofficially calibrate your Fluke 45 for the cost of postage both ways.  I'll post the process and results to the forum here.  PM me if interested.  I don't have and can't find calibration info for the Hioki, so I'd be unable to adjust it, but it can be characterized so that you know how far it is off.

That's very generous, and would be fantastic! assuming you have the right equipment.  I toyed with replacing any recommended wear components (electrolytic capacitors, carbon composition resistors, etc.) prior to having some sort of calibration done at some point.

Unfortunately Hioki has terrible support for their instruments, providing neither schematics, repair manuals, or even calibration instructions.  I was quite fond of Hioki, bordering on fanboyism, until I found this out.  It's a damn shame.

[Majorassburn]

Shamelessly self-promoting my products.....

As I stated earlier, a single-point source is of rather limited usefulness here.  Besides that, is your reference here sufficiently accurate to test or calibrate a Fluke 45?   Does the trim pot adjust the 10V or 6V output?

You just love to pick apart a reply and mis-state the context in which it was offered!
READ WHAT FriedChicken ASKED FOR: a low cost reference like the cheap Chinese devices on AliExpress, right?

So, you want to turn my reply into an argument and compare my $30 device with your favorite DMM Check for $250? Is the DMM Check sufficiently accurate to calibrate a Fluke 45? No F**king way and you know it! So why imply that my ad suggests that mine is? AGAIN and AGAIN in your multiple posts about my devices.

And, with all your expertise, if you read my description of my 10V references, it is CLEARLY EXPLAINED THAT THE TRIM POT TRIMS THE OUTPUT OF THE REFERENCE!

Does my ad anywhere say or imply or suggest that the pot adjusts the 6V tap?  Look closely and you'll see the 0.1% resistor divider that is FIXED at 6V as a "CONVENIENCE" and not a separate reference!

I'm sick of your arrogant sideswipes about most of my posts as I try to be a good participant in this forum. To hell with guys that want to flex their arrogance and inundate us inferior individuals with their self-proclaimed expertise. That's the kind of attitudinal presence that chase away forum participants and narrows the focus of an otherwise limitless exchange of ideas and experience.

So, I may as well get banned forever for saying this but I offer it with a cool head and considerate forethought...

bdunham7.....FUCK OFF! 

[Fried Chicken]

Can both of y'all chill.

Major, your little voltage reference is exactly what I was looking for.  I didn't want to get one of the chinese aliexrpress ones because I don't trust something mass produced out of China.  The only reason I was holding off is because I wouldn't just want the voltage reference, but every reference you have available in one fell order... and I just spent money frivolously on other stuff, so I'm waiting here slightly.

bdunham, your offer to calibrate my multimeter is very generous and something I will take up on, assuming shipping is within the United States and available reasonably, which it should be through whatever freight forwarder service I use.  I can include the return label in the box....  I am curious about what equipment you have in your lab that you might test it with, so I can gloat about know to what standard it's been calibrated to.

[bdunham7]

READ WHAT FriedChicken ASKED FOR: a low cost reference like the cheap Chinese devices on AliExpress, right?

No, he wants to know which of his meters are correct and presumably in spec and which are not.  Neither your device or the cheap AliExpress AD584-based references are likely to be very helpful when it comes to the Fluke 45.  I'm not the one that advocated the DMM Check and it has the same issue regarding only having a single point for DCV.  Its stated uncertainties are marginal for the Fluke 45, but at least would be helpful in determining whether it was in the ballpark.

bdunham7.....FUCK OFF! 

Yikes!  This is a simple discussion involving math and facts, no need to be offended if I don't agree with you.

[J-R]

It might be a bummer to see that your two DMMs disagree that much, but let's analyze a bit.  The Hioki DT4251 is a 6,000 count DMM and you are near the top of the range at 5V.  The Fluke 45 is 99,999 counts but only in slow mode.  In medium mode you are limited to 30,000 counts which means you are in the 30V range.  Try setting it to slow mode in the 10V range.  You could also check the 100V slow range to gather more intel.

Also, was the Fluke 45 allowed to stay powered on for some hours before taking that measurement?

I disagree, the DMMCheckPlus is absolutely good enough to check those DMMs, and in another thread I mentioned leveraging the current source and resistors to generate additional values.  Sure, it's not going to allow you to check everything and the cost for this purpose is iffy as I also mentioned.  Also, the specs are worse case between calibrations, so right after receipt/calibration it is going to be better and that is a common metrology tactic.

Paying some money to get the Fluke 45 calibrated/adjusted seems like a reasonable path at the moment.  Although I wonder if it would be better to snag a calibrated 6.5 digit DMM instead if you're already worried about such things.

[Majorassburn]

To Bdunham7:
OK. I'm never offended when you disagree with me. But, I don't like your seemingly pickiness and taking things out of context regarding my device claims.  I really strive to UNDER-state their capabilities and I would never try to inflate or scam anyone who trusts in me and buys one.

Look, I know that you are a valuable and expert contributor in this forum. I have admired many of your posts and contributions. But, you seem to have a bug up your ass about some of my devices that I offer on eBay. I wish I could resolve that with you because I know that I could learn a lot from you.

I will do my best to eliminate any sensitivity that i have developed about your "disagreeing" with me if you can try to frame your "concerns" about my posts in a more helpful and constructive manner.

I really do appreciate folks questioning my claims and raising questions as to performance, etc. so don't hold back.

TRUCE on my part. I'll probably get banned anyway for engaging in the nasty manner as I have in this post so, if or when I do, Best Regards to all and I'll see you on eBay (SQWARREL) in case I have anything you might be interested in.

Thank You.

[shapirus]

Is the DMM Check sufficiently accurate to calibrate a Fluke 45? No F**king way and you know it!

Yes of course it is, albeit only at a single voltage value (5V). It's accurate to ±0.007% (DCV output) and it's aged and then adjusted to exactly 5.0V as measured by a calibrated DMM with 0.0008% accuracy.

Quite obviously (on second thought -- maybe not so obviously; how much more accurate should the reference be compared to the DUT?) good enough for calibration of a 0.025% base DCV accuracy meter. But if we were to speak about adjustment (alignment), then it wouldn't be suitable, as you'd need more than one reference voltage, and probably more precise one than 0.007%.

I'm sick of your arrogant sideswipes about most of my posts as I try to be a good participant in this forum.

You see, the issue with your device is not the quality of the device itself -- it may very well be just fine and suitable for many applications -- but lack of information. To be better than the chinese sellers, you should at least specify what device was used to measure output voltage of each reference you sell (I believe you specified this in at least one post) and present a calibration certificate for that device. To be much better than the chinese sellers (and this will almost inevitably lead to a price increase), you need to measure and specify more data: long-term stability, temperature stability, noise level etc. Aging them will also be a plus.

The value of a voltage reference is not so much in its components and design, but in the reference to which its output voltage can be linked. This is an important aspect where the DMMCheck Plus is good and chinese references are poor.

[bdunham7]

assuming shipping is within the United States and available reasonably, which it should be through whatever freight forwarder service I use.  I can include the return label in the box....  I am curious about what equipment you have in your lab that you might test it with, so I can gloat about know to what standard it's been calibrated to.

I'm in California and I'd recommend UPS or USPS with good packing.  FedEx seems to be air-dropping stuff right from the plane from the looks of the packages.

As for equipment, not much to gloat about.  I use an assortment of things to get the stimuli needed and a Fluke 45 is at the beginning of the area where things get slightly challenging.  I've managed to calibrate 6.5-digit meters that later passed a 'real' calibration without adjustment, but in reality that's a stretch.  The ideal situation is to have a good enough uncertainty ratio (TUR) that you can adjust the meter to within the limits of its short term stability.  On your meter I would use:

Fluke 5100B multifunction calibrator, repaired and calibrated by me.  50ppm DCV basic accuracy, but no cert.

Fluke 8846A 6.5-digit DMM, calibrated by Fluke (cert attached below)

Fluke 5220A current amplifier, calibrated by Transcat (but more than a year ago) no cert available as I just have the sticker.

Fluke 8506A Thermal-RMS DMM, AC ranges informally calibrated by using a 5200A with an in-cal 3458A in parallel.  This meter has a 1-year basic spec of 200ppm on AC and it probably is within that, but it only needs to be somewhat close in order to be more than good enough.  In reality this is overkill, but I have it and need an excuse to use it.

A set of L&N NBS-style standard resistors from 1R to 1M.

Siglent SDG2042X signal generator

I use the calibrator as source for most ranges and then one of the DMMs in parallel (or series for current) to characterize the 5100B output.  IOW, I fine-tune the 5100B using the more accurate meter.  The Siglent AWG is for the 100kHz frequency test.  For resistance, the decade resistors in the calibrator are accurate enough for your DMM and I'd check them immediately beforehand with the 8846A.

I've also attached the calibration procedure for the service manual.  You can look at each test or adjustment point and see what the tolerances are and then compare them to the tolerances of the calibration equipment.  For example, the third peformance test point is 900.00mVDC and the tolerance is +/- 290µV.   If you look up and calculate the tolerance for the 8846A (1-year spec) at 900mV, it is +/- 30µV.   And so forth.  Those are good ratios, certainly good enough that I'm confident that your meter will be accurate, but probably no bragging rights.

[bdunham7]

But, you seem to have a bug up your ass about some of my devices that I offer on eBay.

I'm not claiming that you are dishonest or that your devices are overpriced, but rather that you don't seem to fully understand where they would be appropriate and where they aren't helpful.  You're starting with a 0.05% device and trimming it to some unstated uncertainty and not further characterizing it or indicating how stable it might be over time.  The descriptions and claims just aren't very precise.  Your listing says 10.000V in one spot and 10.0000V in another.  The maximal implied precision of first might be just adequate for a sanity check on the Fluke 45 if it were perfectly stable.  The second claim of 10.0000V is preposterous if you are implying that level of accuracy with that device.  If you trim it to that number using a particular meter or method, you should specify those particulars and give some idea of the actual uncertainty.  Otherwise your specs are misleading, even if you don't intend them to be.

The problem in the context of the OPs issue is that when you have a particular device that you have doubts about, checking it with another device of similar uncertainty and no independent verification just leads to more uncertainty--if they disagree you just have two things that you're not sure of.  In this case, your device is probably good for spot-checking the Hioki, but not adequate for the Fluke, IMO. 

That's about the whole issue I have in this context.  I realize it is a very inexpensive device and it would be silly to hold it to the same standard as a VREF10 or even a DMMCheck, but that also implies that its applicability is more limited.  If you want a better idea of how your device performs and aren't ready to start logging temperature vs voltage and so forth, send me one (I'll send it back) and I'll give you a chart.  Maybe it will do better than anyone thinks.

[Fried Chicken]

To be honest, if I have two units with agree with a calibrator, and a fluke that doesn't, that definitely points to the fluke being problematic.  It would serve to see if I need calibration... assuming my other voltmeter devices are accurate enough.

[shabaz]

Very kind, generous offer to unofficially calibrate.

Just to put some sample numbers out there, for the AD584 cheap references (sub-$10 on AliExpress), by chance, a friend and I have both measured these devices (one sample each, purchased separately at different times) using two separate DMM6500 meters.

The label on it, claiming to have been measured with HP 3458A, is, of course, completely untrue (unless it's a completely broken HP 3458A!). They probably used (at best) a 6.5-digit meter, perhaps not even calibrated, and even then, they have typos in the printed values (the label on mine had a noticeably erroneous extra digit for one of the values!).

However, on the plus side, it turned out that the nominal voltage values (2.5V, 5V, 7.5V, 10V, were actually close enough to the real values, that it's very likely that one would be able to tell if that 0.02V discrepancy you're seeing between multimeters is a problem with one meter or the other, or both. In other words, a 20 mV discrepancy should be identifiable if it's present at one of those four voltages (2.5/5/7.5/10V).

Beyond three digits, you can't really rely on it with no measurement with a known calibrated instrument. Nevertheless, for the price (under $10) with no further measurement, it is a crude finger-in-the-air type of check if absolutely nothing better is available.

Just in case this helps, this was my sample result:
Label              My measurement
-------            ---------------
2.49954            2.49963
4.999501           4.99964
7.39875            7.49899
9.99823            9.99854

[Fried Chicken]

Here's a guy with a Fluke 8842a and a cheap chinese voltage standard:

[Fried Chicken]

assuming shipping is within the United States and available reasonably, which it should be through whatever freight forwarder service I use.  I can include the return label in the box....  I am curious about what equipment you have in your lab that you might test it with, so I can gloat about know to what standard it's been calibrated to.

I'm in California and I'd recommend UPS or USPS with good packing.  FedEx seems to be air-dropping stuff right from the plane from the looks of the packages.

As for equipment, not much to gloat about.  I use an assortment of things to get the stimuli needed and a Fluke 45 is at the beginning of the area where things get slightly challenging.  I've managed to calibrate 6.5-digit meters that later passed a 'real' calibration without adjustment, but in reality that's a stretch.  The ideal situation is to have a good enough uncertainty ratio (TUR) that you can adjust the meter to within the limits of its short term stability.  On your meter I would use:

Fluke 5100B multifunction calibrator, repaired and calibrated by me.  50ppm DCV basic accuracy, but no cert.

Fluke 8846A 6.5-digit DMM, calibrated by Fluke (cert attached below)

Fluke 5220A current amplifier, calibrated by Transcat (but more than a year ago) no cert available as I just have the sticker.

Fluke 8506A Thermal-RMS DMM, AC ranges informally calibrated by using a 5200A with an in-cal 3458A in parallel.  This meter has a 1-year basic spec of 200ppm on AC and it probably is within that, but it only needs to be somewhat close in order to be more than good enough.  In reality this is overkill, but I have it and need an excuse to use it.

A set of L&N NBS-style standard resistors from 1R to 1M.

Siglent SDG2042X signal generator

I use the calibrator as source for most ranges and then one of the DMMs in parallel (or series for current) to characterize the 5100B output.  IOW, I fine-tune the 5100B using the more accurate meter.  The Siglent AWG is for the 100kHz frequency test.  For resistance, the decade resistors in the calibrator are accurate enough for your DMM and I'd check them immediately beforehand with the 8846A.

I've also attached the calibration procedure for the service manual.  You can look at each test or adjustment point and see what the tolerances are and then compare them to the tolerances of the calibration equipment.  For example, the third peformance test point is 900.00mVDC and the tolerance is +/- 290µV.   If you look up and calculate the tolerance for the 8846A (1-year spec) at 900mV, it is +/- 30µV.   And so forth.  Those are good ratios, certainly good enough that I'm confident that your meter will be accurate, but probably no bragging rights.

I'll send you a PM tomorrow.  I think I'll take you up on this offer!  Would definitely be thrilled to see the process documented!  Happy Easter!

[J-R]

The problem with the Chinese eBay references is that you can't really apply any trust to them.  Sure, one person might get one that is OK, but the next may not be.  Or you could have blatant fakes, as has been shown already with the copied calibration labels.

Also, a random video of someone showing how close their DMM is to a reference can be suspect because it's possible they used it to calibrate the DMM earlier and are hiding that fact.  You just can't be sure.

Compare this to the references from Doug and Russ where they have been active here for a while and their products are well regarded.  Although really the King of hobby DCV references is the PDVS2mini in my opinion.  Really hoping it comes back soon so I can get a second one.  I also plan to get a second 10V reference from Doug because his updated model has some great improvements.  I have quite a bit of equipment that can leverage a 10V calibration point.

But the bdunham7/Majorassburn conversation has got me thinking that what the hobby really could use right now is a budget-friendly calibration service.  There is a gap between getting a professional calibration and trying to do a DIY calibration with references on hand.  I don't see the USA Cal Club being a solution since it's more in the metrology space.

[alm]

But the bdunham7/Majorassburn conversation has got me thinking that what the hobby really could use right now is a budget-friendly calibration service.  There is a gap between getting a professional calibration and trying to do a DIY calibration with references on hand.  I don't see the USA Cal Club being a solution since it's more in the metrology space.

The problem I see that this is capital and time intensive. I would imagine buying all the equipment that bdunham7 listed now might cost you maybe $5k, if not more. And calibration of even just the 8846A (which will give you uncertainties that are plenty good for 4.5 digit like the Fluke 45 but not for 6.5 digit like HP 34401A) will be a few hundred USD per year. This figure can easily get into thousands per year if you need to have multiple pieces of equipment calibrated. And also, correctly if I'm wrong, I'm guessing that bdunham7 has not set up an automated calibration for the Fluke 45, so calibration, and particularly adjustment, might easily take hours in changing connections and settings, waiting for things to stabilize, etc. Expecting someone to do this regularly for a low fee is a lot to ask. Would you like to be spending every Saturday doing calibrations for say $100 per day?

Even the production of products like the Geller Labs voltage references, DMMCheck Plus and PVDS2Mini does not seem very sustainable given how often the stop production or change hands.

[robert.rozee]

one could probably go a long way with just a DIY hamon divider http://conradhoffman.com/HamonResistor.html and the raw output from a simple LM399 reference. first send the LM399 off to someone with a good 6.5 digit meter to measure it, then use the LM399 and hamon divider to calibrate low DC voltage ranges at 7v, 700mv, 70mv. if desired, 70v and 700v points can be calibrated using the same gear plus an adjustable HV supply and a little creativity.

i dare say resistance ranges can similarly be calibrated using similar methods to scale up/down and just a single precision resistor that has been measured with a good 6.5 digit meter.

sending off a small PCB (containing LM399 + CC source) and a single resistor through the post should be relatively cheap, and the time expended by the recipient making measurements relatively short.


cheers,
rob   :-)

[Majorassburn]

But, you seem to have a bug up your ass about some of my devices that I offer on eBay.

snip -
You're starting with a 0.05% device and trimming it to some unstated uncertainty and not further characterizing it or indicating how stable it might be over time.  The descriptions and claims just aren't very precise.  Your listing says 10.000V in one spot and 10.0000V in another.  The maximal implied precision of first might be just adequate for a sanity check on the Fluke 45 if it were perfectly stable.  The second claim of 10.0000V is preposterous if you are implying that level of accuracy with that device.  If you trim it to that number using a particular meter or method, you should specify those particulars and give some idea of the actual uncertainty.  Otherwise your specs are misleading, even if you don't intend them to be.
snip -
If you want a better idea of how your device performs and aren't ready to start logging temperature vs voltage and so forth, send me one (I'll send it back) and I'll give you a chart.  Maybe it will do better than anyone thinks.

OK, Thank You for that advice. Let me respond:
1) For your first comment about the 10Vref and trimming, the "10.0000" you refer to was a typo on an early eBay ad where that ad had both 10.000 and 10.0000 in the specs. That was corrected several ads ago to read "10.000". So, you are correct about the typo conflict.

2) I built a typical 10Vref, like my eBay ads, and that device is trimmed to an actual value of 10.0000 with a new DMM6500 that I have occasional access to. That device is then "compared" to my new Sig SDM3065 and the eBay devices are then trimmed to 10.000 based upon the Sig. Crude but very effective, so far. Read the eBay feedback from those who have bought them and tested them for accuracy.

I'm not saying that's the best way to operate but at this point, it keeps costs low and makes the low-end buyer happier than spending $250+ for a DMM Check, etc. if they are even in stock. Not knocking DMMChecks but whenever I wanted to buy one in the recent past they were never available.

3)  As for the SPECS issue, I agree with you that my devices are very short on "specs" but my devices are also very short on CLAIMED specs, like so many phony Chinese devices. I don't want a volt-nut to buy one of my devices and then scream that it missed listed specs by .0005ppm after it was lit up in an oven for 6 months.   

The specs for my devices are the data sheet from Linear Tech (Analog Devices) for the AD1236-10 voltage ref IC that my device is based upon. I include the data sheet with every sale so that each buyer can decide how much faith he/she/it  should place on the long-term accuracy/usability of the device. Of course, I could list the fact that in the trim circuit, I use all selected 1% 15-25ppm metal film resistors but the Bourns trim pot blows that up into another spec argument, right? Or, I could hand trim each device with selected low-ppm resistors and eliminate the easy-adjust trimpot. Hmmmm.

Now, you may begin to appreciate why I purposely avoid "over-specifying" my devices. For those serious buyers, like yourself and myself, who eat & sleep specs before we buy stuff, my devices amount to no more than curiosity or novelty. But, to anyone who wants to simply and quickly and affordably verify the DC or AC or Resistance accuracy of their DMM, I honestly believe that my devices fulfil that kind of need.

Do I compare my devices to a DMMCheck or other superior engineered devices? NO, not at all. I'm not in that league. I'm making hobby-grade stuff for amateurs, homeowners, DIYers, students, hobbyists and guys like us that now have something new to talk about and slice and dice in forums. 

Here's what I would like to do:  I'd like to start a thread where I list reasonably concise specs for each of my hand-made devices and encourage fellow forum participants like you to evaluate, correct, criticize and comment on which would help me arrive at some happy medium in my ads.

Where in this forum should I do that?  What category?  Test Equipment? Metrology/ (I love that category because there are no sane individuals there at all - I feel at home there just browsing!) 

Let me know what you suggest and I'll do it.
Thanks and Happy Easter, all.

[bdunham7]

Where in this forum should I do that?  What category?  Test Equipment? Metrology/ (I love that category because there are no sane individuals there at all - I feel at home there just browsing!) 

Just reuse this post with a little background added and post it in the metrology forum.  I'm sure you'll get comments and some might actually be helpful.  Include everything  you've written here as I'd like to respond without cluttering up this thread any more.

[shapirus]

...and I wish you good luck (without irony), because having yet another option for an inexpensive voltage reference is a good thing, especially if it comes with an honest specification which lists its parameters and allows to clearly understand the limits of its applicability.

[Fungus]

Just to put some sample numbers out there, for the AD584 cheap references (sub-$10 on AliExpress), by chance, a friend and I have both measured these devices (one sample each, purchased separately at different times) using two separate DMM6500 meters.

Those cheapo references on Aliexpress are a mixed bag.

Some are genuinely measured, some aren't. Several people on EEVBLOG have ordered one and received the exact same "calibration"sheet.

https://www.eevblog.com/forum/metrology/are-cheap-ad584-units-worth-it/msg920924/#msg920924

[shabaz]

Hehe yeah zero trust there with that sticker : ) I had the access to be able to test it against a known DMM, but most people purchasing that won't.

I think it's fine as a quick check for those seeing large discrepancies (tens of mV) to try to narrow down which of the instruments is most in need of a health-check, and definitely expectations need to be low and not trust the device (at least not without confirming) much further than 3-digits (i.e. 2 decimal places) or so!

[alm]

one could probably go a long way with just a DIY hamon divider http://conradhoffman.com/HamonResistor.html and the raw output from a simple LM399 reference. first send the LM399 off to someone with a good 6.5 digit meter to measure it, then use the LM399 and hamon divider to calibrate low DC voltage ranges at 7v, 700mv, 70mv. if desired, 70v and 700v points can be calibrated using the same gear plus an adjustable HV supply and a little creativity.

i dare say resistance ranges can similarly be calibrated using similar methods to scale up/down and just a single precision resistor that has been measured with a good 6.5 digit meter.

sending off a small PCB (containing LM399 + CC source) and a single resistor through the post should be relatively cheap, and the time expended by the recipient making measurements relatively short.

Yes, that could certainly work. That's how metrology labs did it before instruments like the HP 3458A and Fluke 5700A automated it. They would have 1.018V standard cells and 1 Ohm standard resistors and derive everything from those. There's no reason why you couldn't do the same artifact calibration by hand if you had ways of scaling voltage and resistance (note that the ratio of the voltage across two resistors in series is proportional to the resistance ratio). ACV and ACI is more tricky, though maybe there you could use a trick like ratio transformers. Solutions like the cal club could be useful for importing the cardinal points like 10V and 10k that you can scale to any other value.

[J-R]

Of course the calibration service I'm proposing is not going to be making the owner rich, and I'm confident Doug/Russ/Ian are not doing what they do for the money.  As long as you're close to breaking even then you are doing fine because you're investing in yourself and probably having some fun at the same time.

And I would suggest this basic service would be just a verification of the calibration points listed in the service manual.  There is no need to get carried away with the more mundane metrology aspects.  If you need that then go with an accredited lab.

$5k or even $10k plus hundreds per year for an external cal is really nothing for a dedicated hobbyist.  It just comes down to what you choose to spend your money on.

[BILLPOD]

Shamelessly self-promoting my products.....

https://www.ebay.com/itm/285781907875

Plus, I have precision resistors, etc....
[/quote]

Good Morning Majorassburn, when I went to E-Bay to look at your module, it indicates it is sold and no others are available???

[Majorassburn]

Removed listings:
Deleted

BTW, you can always do an advanced search on eBay for SQWARREL to see my listings.

[EEVblog]

Here are a few of today's listings:

Please do not spam these in existing threads, use the Buy/Sell section.

[Majorassburn]

Thank you.  I should have known better. Sorry.

[CalibrationGuy]

DISCLAIMER: I don't know Doug, just bought one of his 10V references from voltagestandard.com. Base cost is $140. I dusted the unit off and measured it. Attached is the picture.

Just to put things in perspective for those perusing threads like this one. First of all, I paid over $2,700.00 to calibrate that meter. The cable attached to the meter and the reference box costs more than the reference.

People measuring the Chinese/Asian boxes do NOT (most likely) have the capabilities that my lab has, so PLEASE take their observations with a grain of salt. They are well meaning, but measurement procedures/traceability DO matter. As a hobby, it is great to share experiences, but observations may be misleading without intending to be misleading.

Final thoughts, I'm impressed with Doug's device, I know it's out of the OP's price range, but I just thought I would show you how mine held up as measured with a calibrated, certified, accurate 3458A.

TomG.

[shabaz]

It would be a complete waste of time and money spending $140 plus £2700, when the OP could simply send his meter in for a calibration check for under $100.

You'd need to be calibrating a _lot_ of equipment per year before that made any sense.

The OP observed a 20 mV discrepancy between meters. That doesn't require a 10.0000V standard to determine which instrument is faulty.

The OP could simply buy several calibrated meters, new, each year, and it would be cheaper than that.

[KungFuJosh]

It would be a complete waste of time and money spending $140 plus £2700, when the OP could simply send his meter in for a calibration check for under $100.

That wasn't his point at all. His point was that the reference for $140 is surprisingly accurate.

Also, where can he get his DMM calibrated for under $100? (besides bdunham7 that offered to do it for free)

[CalibrationGuy]

I think you completely missed the point of my reply. As I said, it's out of range of the original poster's budget but I was just showing a contrast to the expense required to definitively get precision data.

TomG.

[CalibrationGuy]

Yes, what Josh said.

[shabaz]

No, you're missing the point, when you stated:

People measuring the Chinese/Asian boxes do NOT (most likely) have the capabilities that my lab has, so PLEASE take their observations with a grain of salt.

Those cheap boxes are actually usable to 3 digits, for an identification of which instrument has the 20 mV discrepancy. It's a very successful way of seeing which instrument has a significant discrepancy. It makes zero sense to expend a lot more on such a check when you'd have to calibrate your device anyway, if you need accuracy.

Perhaps the OP has a lab full of instruments or wishes to go into the calibration business and willing to spend $2700 per year.

I was simply focussed on addressing the OP's problem. He doesn't need to expend anywhere near that amount to get measurement to the specification of his instrument, once it has been properly calibrated by actually shelling out for it (or a calibrated meter purchased, for a tiny fraction of that cost). Thanks for your perspective, but you missed my point regarding how low-cost it can be for an initial identification of which instrument is wildly out of spec. Only an idiot would assume it was in any way close to an actual calibration.

As for Josh, I'm surprised you can't find a way to get a half-price calibration?
You seemed pretty proud of the unethical practice of hacking instruments beyond what you'd paid for them, on another thread.

[CalibrationGuy]

No, I'm not missing the point. Without traceability, those numbers mean NOTHING. I have friends who have boards like these and the numbers were the same for every board. Your usability claims have no credibility because there is no verification of said values.

My point is that counting on these values is problematic at best.

TomG.

[shabaz]

Well now you're just trying to swing the discussion into something else.

"Without traceability, those numbers mean NOTHING"

If you need $2700 of traceability to figure out which instrument is off by 20 mV or so, then there's something wrong with the way you do engineering.

[KungFuJosh]

As for Josh, I'm surprised you can't find a way to get a half-price calibration?

I actually do have a half-price calibration waiting for me from the manufacturer of one of my DMMs. 🤣

[KungFuJosh]

Well now you're just trying to swing the discussion into something else.

"Without traceability, those numbers mean NOTHING"

If you need $2700 of traceability to figure out which instrument is off by 20 mV or so, then there's something wrong with the way you do engineering.

I don't know what your first language is, but there seems to be something lost in translation with you. He never said anybody else should spend that money on calibration. The dude's name is "CalibrationGuy" you might infer from that that he's somewhat into calibration.

[CalibrationGuy]

I'm going to reply because there are people who will read this thread and misunderstand what is being said. So, let me be clear.

1) I pay top dollar because I must be sure of my data.
2) Using a newly calibrated meter verified that a very reasonably priced voltage reference achieved excellent results.
3) You cannot verify with any certainty, 20mV which meter is off using a reference from unknown sources without proof of calibration.
4) To tell the OP that it's a good idea to rely on an unknown reference to test his meters is bad advice.

TomG.

[shapirus]

If you need $2700 of traceability to figure out which instrument is off by 20 mV or so, then there's something wrong with the way you do engineering.

The wonders of metrology. Yes you actually do need to spend a lot of money, if you want to have a definite, expressed in numbers, and certified amount of certainty uncertainty in the readings displayed by your test equipment.

But once you can be satisfied by qualitative expressions "most likely" and "good enough", or have a friend or someone who offers to use their calibrated (officially or unofficially) equipment out of their good will for you, then it can be done much, much cheaper.

[shabaz]

Regarding:
"Yes you actually do need to spend a lot of money, if you want to have a definite, expressed in numbers, and certified amount of certainty in the readings displayed by your test equipment"

No one is arguing with that - although with the slight caveat that some would say it's not a lot of money to pay to get a 5-digit DMM calibrated. Everyone has a different perspective on pricing, of course, and it would vary by region.

[shabaz]

"3) You cannot verify with any certainty, 20mV which meter is off using a reference from unknown sources without proof of calibration."

That's demonstrably untrue. Modern silicon comes factory-trimmed to a greater precision. You could pick up a $5 voltage reference (half the cost of the AliExpress one!) and with little care (a couple of capacitors) end up with a result accurate to within single-digit millivolts.

So yes, it is certainly possible to identify which of two multimeters (or both, or any number of them) are faulty, if their discrepancy is 20 mV.

[CalibrationGuy]

You quote me but don't understand my words. I said unknown sources. Do you know what factory seconds are? How about counterfeit goods that pervade the sources you mentioned.

Where in anything I said did you get the idea that I meant you cannot get an idea of approximate voltage using parts from a reputable manufacturer?

In fact, I went out of my way to mention a device that is reasonably priced yet has remarkable performance.

I mentioned my equipment and cost of calibration to emphasize that the result I posted was in fact true, NOT that the OP should waste his money for no reason.

Go take your distortions elsewhere.

TomG.

[shapirus]

"3) You cannot verify with any certainty, 20mV which meter is off using a reference from unknown sources without proof of calibration."

That's demonstrably untrue. Modern silicon comes factory-trimmed to a greater precision. You could pick up a $5 voltage reference (half the cost of the AliExpress one!) and with little care (a couple of capacitors) end up with a result accurate to within single-digit millivolts.

So yes, it is certainly possible to identify which of two multimeters (or both, or any number of them) are faulty, if their discrepancy is 20 mV.

If, and only if, the reference has been measured with a trusted voltmeter!

Otherwise, you have three devices, DMM 1, DMM 2, and voltage reference, showing the same or different readings, and you have no way of telling which reading is true, because none of the devices have been verified against a known-good reference.

That's exactly the problem with the Chinese references. They aren't that bad in terms of design and parts. But how do we know whether their output voltages match what's written on the sticker, and if it does, then with what exactly degree of uncertainty?

Oh and regarding the modern silicon... What did you have in mind? If we take, for example, LM399, then its initial tolerance is specified at 2%. That's 0.139V at its nominal 6.95V output. Definitely not good for checking DMMs out of the box without measuring and adjusting. What's the highest precision single-chip reference? Is there anything that has at least a 0.05% tolerance?

[J-R]

Recommending that someone buy the cheap/unknown references to check their equipment is an indefensible position.  You will go down with that ship...  It's been well established here on the forums that those cannot be trusted and that is essentially their only job.  Someone who is new to this might try to calibrate their TE or apply attributes to the reference that it cannot support.  So it's more dangerous to have one than not.  Fine, if you're bored and want to play around with them go ahead, but don't suggest anything further.

[shabaz]

Oh, so a $5 reference chip is totally fine?
Now you agree!

There's every chance that there could be a fault with a reference from a reputable manufacturer too.
If it was drifty, or in fact had an error greater than 20 mV, you'd easily be able to detect it.

You literally created an argument that wasn't there. You dreamt it up. No-one stated that a $10 board should be relied on (or a $5 one for that matter) for trusting your multimeter is performing to spec. That would be an idiotic thing to do.

It was simply to determine if a multimeter had a significant discrepancy or not, so that you'd know which one to send for calibration.

[CalibrationGuy]

"3) You cannot verify with any certainty, 20mV which meter is off using a reference from unknown sources without proof of calibration."

That's demonstrably untrue. Modern silicon comes factory-trimmed to a greater precision. You could pick up a $5 voltage reference (half the cost of the AliExpress one!) and with little care (a couple of capacitors) end up with a result accurate to within single-digit millivolts.

So yes, it is certainly possible to identify which of two multimeters (or both, or any number of them) are faulty, if their discrepancy is 20 mV.

If, and only if, the reference has been measured with a trusted voltmeter!

Otherwise, you have three devices, DMM 1, DMM 2, and voltage reference, showing the same or different readings, and you have no way of telling which reading is true, because none of the devices have been verified against a known-good reference.

That's exactly the problem with the Chinese references. They aren't that bad in terms of design and parts. But how do we know whether their output voltages match what's written on the sticker, and if it does, then with what exactly degree of uncertainty?

That's exactly my point. There were numerous discussions about certain suppliers who were writing random numbers on the included "calibration" sheets. You need to start with a known good reference. It doesn't have to be as accurate as ours, that wasn't the point, the point was that it has to be of known values which meets your needs, tolerance wise.

TomG.

[shabaz]

"but don't suggest anything further."

I don't see that I suggested anything dangerous. I caveated each time that one cannot rely on it as a calibration.

[shabaz]

LM399 has low drift hence the price, but there are other ICs with higher initial accuracy (higher drift). REF50xx could be an option (sub-$5) that would easily determine if a meter had a 20mV discrepancy (at the spot(nominal) voltage of the chip).

[shapirus]

So it's more dangerous to have one than not. Fine, if you're bored and want to play around with them go ahead, but don't suggest anything further.

As usual, they may be useful if you know what you're doing and understand the limitations.

For example, I bought one of those Chinese LM399 boards and measured it with my then freshly purchased Brymen BM869s and used that measurement as a reference point. They still stay in agreement today, after 3 years or so, which may mean one of: a) neither of them have drifted; b) they both have drifted by the same amount. By comparing this to my other meters I conclude that the former is much more likely, and that's more than good enough for my hobby. Of course I'd like to re-measure that LM399 thingy with a more precise meter, but I don't have access to any.

The important point here is that I had a known-good meter to compare that reference against.

In the case of two meters, neither of which is known-good, such a board wouldn't work, especially given that there are reports of bogus values on the stickers that some people received, especially when those stickers are printed. Mine was hand-written, which kinda invites to trust it a little more.

[KungFuJosh]

Here's some simple solutions.

Buy a $20 ref, and pay $100 (plus shipping) to have it calibrated (after hundreds of hours of runtime to confirm stability).

Or buy a $140 ref that comes calibrated and reliable.

Or spend a lot more money, build a ref yourself, and still need to send it out for calibration (after hundreds of hours of runtime to confirm stability).

Or just send both meters out for calibration. Simple. 😉

[Fungus]

No, I'm not missing the point. Without traceability, those numbers mean NOTHING. I have friends who have boards like these and the numbers were the same for every board. Your usability claims have no credibility because there is no verification of said values.

OTOH lots of people have a good one where the numbers are good.

eg. Me. I've measured mine on a few different high-end multimeters and the numbers seem good to at least three decimal places.

Traceability or not, that's very unlikely to be luck.

[shabaz]

"Or spend a lot more money, build a ref yourself, and still need to send it out for calibration (after hundreds of hours of runtime to confirm stability)."

Or, spend $5! and not send it for calibration, nor wait hundreds of hours (a ridiculous suggestion) because it will immediately tell you which of the two multimeters has the 20 mV discrepancy. Then, you know which multimeter might actually be functioning, and you can send it for a cal, at less than the cost of a calibrated reference.

[shapirus]

REF50xx could be an option (sub-$5) that would easily determine if a meter had a 20mV discrepancy (at the spot(nominal) voltage of the chip).

Now, this lengthy discussion has finally produced a second result that may be useful not only to the OP.

To answer this:

Are there any reliable around-the-house ways I can test these multimeters?  Reliable resistors?  Pencil lead?  The nicest resistor I have laying around?

REF50xx is specified (standard grade) at +/- 0.1%, which is, for REF5050 that outputs 5V, +/- 0.005V, which is almost good enough for the initial problem. If we get a high grade type (the "I" suffix), then precision is 0.05% which I think gets rid of the "almost".

This can be considered, I think, an acceptable solution for an in-house basic verification of DMMs to what, say ~10 mV uncertainty? Doesn't sound too bad!

Is there anything better than REF50xx and still reasonably cheap?

[shapirus]

OTOH lots of people have a good one where the numbers are good.

eg. Me. I've measured mine on a few different high-end multimeters and the numbers seem good to at least three decimal places.

Traceability or not, that's very unlikely to be luck.

Yeah but still you don't know if you received a good one or a bad one until you measure it with a known-good meter. That was the point. Once you do such a measurement, whatever its accuracy is, you have a decent reference point (of a long-term stability that remains unclear though) with about that accuracy. But if you don't have a known-good meter to do it, then the reference is useless.

[shabaz]

I've not kept up-to-date on the latest reference chips unfortunately, but I do have a few REF50xx parts here (not kept sealed though, they are a few years old), I could check a few samples of them, if a lashed-up circuit would in practice have that accuracy, I think there's a chance they would, those are excellent chips for ADC references. I could check at 4.5V and possibly 2.048V (I think those are the ones I've got). But there may be better chip options than this at a similar price.

[Fungus]

Yeah but still you don't know if you received a good one or a bad one until you measure it with a known-good meter. That was the point.

Correct, but what's the worst thing that could possibly happen? That you have to return it?

[shapirus]

Correct, but what's the worst thing that could possibly happen? That you have to return it?

That you end up with N+1 devices about which you're not certain as to whether they're up to spec. Returning it and ordering another does not solve the problem of needing a known-good meter to perform the initial sanity check of the reference.

[Fungus]

Correct, but what's the worst thing that could possibly happen? That you have to return it?

Returning it and ordering another does not solve the problem of needing a known-good meter to perform the initial sanity check of the reference.

That's why we all own several meters. 

My BM857s and my Fluke 187 both agree (to within a digit) with what's written on the sticker.

Neither have been calibrated, but what are the odds of that?

(that they agree with each other and with the randomly-purchased reference to three or four decimal places)

[Fungus]

If you only own a single meter and there's a disagreement then it doesn't help, but that doesn't apply to anybody here...

If it agrees then it's 1000:1 that it's just dumb luck.

[shapirus]

If you only own a single meter and there's a disagreement then it doesn't help, but that doesn't apply to anybody here...

If it agrees then it's 1000:1 that it's just dumb luck.

In the OP's situation, if the reference agrees with one of the meters, but not the other, then it's very likely, or, maybe, likely enough, that the one that it agrees with is the good one, however the chance that both the reference and that meter are off is not zero.

If, however, both meters don't agree, then we end up with three untrusted devices instead of just two :).

But yeah your point is valid. Once again, know the limitations and know what you're doing, and you can get useful results out of any crap.

[KungFuJosh]

"Or spend a lot more money, build a ref yourself, and still need to send it out for calibration (after hundreds of hours of runtime to confirm stability)."

Or, spend $5! and not send it for calibration, nor wait hundreds of hours (a ridiculous suggestion) because it will immediately tell you which of the two multimeters has the 20 mV discrepancy. Then, you know which multimeter might actually be functioning, and you can send it for a cal, at less than the cost of a calibrated reference.

Not a ridiculous suggestion as thermal regulation and drift over time are things that exist. There's a reason some people leave their DMMs on 24/7.

This is the part you don't seem to understand: if the POS $5 ref you buy agrees with one of your meters, it doesn't tell you anything without valid calibration. 2 items agreeing only matters if the results are repeatable on calibrated devices. 2 devices can be equally out of spec. If both meters agree with the ref, then you might be lucky. As was mentioned, most of those $5 refs come with bullshit cal sheets that are copied over and over again and are completely useless.

[shapirus]

As was mentioned, most of those $5 refs come with bullshit cal sheets that are copied over and over again and are completely useless.

"Most" is either ambiguous, or has to be proved. Since this thread has a slight hint of metrology, I would reword it like so: there is a significant number of bogus cal sheet reports on certain types of those ref boards. At the same time, many appear to be legit, but none seem like they can be traced to an instrument with a valid calibration certificate.

[Fungus]

As was mentioned, most of those $5 refs come with bullshit cal sheets that are copied over and over again and are completely useless.

"Most" is either ambiguous, or has to be proved. Since this thread has a slight hint of metrology, I would reword it like so: there is a significant number of bogus cal sheet reports on certain types of those ref boards. At the same time, many appear to be legit, but none seem like they can be traced to an instrument with a valid calibration certificate.

There's many threads discussing these references, eg.
https://www.eevblog.com/forum/metrology/are-cheap-ad584-units-worth-it/
https://www.eevblog.com/forum/testgear/cheap-chinese-ad584-voltage-reference-legit-cal-data-let_s-find-out!/
https://www.eevblog.com/forum/metrology/cheap-ebay-ad584-voltage-references-my-experiences/

[shabaz]

"if the POS $5 ref you buy agrees with one of your meters, it doesn't tell you anything without valid calibration"

I'm almost speechless that you can't engineer a way to determine a 20 mV discrepancy without "valid calibration".
It's really not rocket science.

[shabaz]

Really ugly prototype, but it seems to indicate that even an unrecommended layout of the REF50xx chip will perform for the use-case being discussed.

I didn't have many through-hole parts, so I've used SMD capacitors with wires soldered on.
The parts used are:
REF5045AID (stored in an unsealed packet with humidity indicator indicating humidity is present, and the purchase date on the sticker is Dec 2014, i.e. 9 years old).
Input capacitor: 22uF, TPSB226K010R0700
Output capacitor: 4.7uF, TPSA475K010R1400
Noise reduction capacitor: 1uF, TPSA105K035R3000
Input supply: 9V PP3 battery

Just a quick measurement with a Fluke 87V was 4.503V, so it certainly appears to be a good result, but I'll measure with a DMM6500 tomorrow (and will also try some more samples of that part, plus some REF5020AID.

[KungFuJosh]

As was mentioned, most of those $5 refs come with bullshit cal sheets that are copied over and over again and are completely useless.

"Most" is either ambiguous, or has to be proved. Since this thread has a slight hint of metrology, I would reword it like so: there is a significant number of bogus cal sheet reports on certain types of those ref boards. At the same time, many appear to be legit, but none seem like they can be traced to an instrument with a valid calibration certificate.

Most by definition means more than 51%. I was being generous since from the numerous threads and examples I've seen, only one had a seemingly valid cal sheet. I also have purchased a bunch of these, and know from experience most of them are not worth the $2 shipping fee. I also mentioned the $20 range, because this ~$22 example was the best of all the shitty refs I bought from any only retailer for less than $100: https://www.aliexpress.us/item/3256804431053626.html

ETA: Another reason I don't like non-calibrated sources is because I find it pretty easy to have multiple DMMs disagree with a ref that one DMM might agree with. Hence the need for calibration.

[Fungus]

REF5045AID (stored in an unsealed packet with humidity indicator indicating humidity is present, and the purchase date on the sticker is Dec 2014, i.e. 9 years old).

Humidity doesn't really matter if you're hand-soldering. It's more for ovens.

And if you're putting it in a socket, then... 

[Fungus]

Most by definition means more than 51%. I was being generous since from the numerous threads and examples I've seen, only one had a seemingly valid cal sheet. I also have purchased a bunch of these, and know from experience most of them are not worth the $2 shipping fee.

Seems to me like somebody here could buy a bunch of them, calibrate them properly, and resell them.

[CatalinaWOW]

Lots of trash talking here, backed with pedantic accuracy.

Yes, you do have to have traceability to assure accuracy, and history to assure accuracy over time.

I will be the first to admit that my array of meters all have long outdated calibrations and my similar array of sources are mostly worse, although I do have actual paperwork on my DMMcheck.  My meters are stable to several parts per million compared to the USA cal club reference, which is not formally calibrated, but TiN thoroughly evaluated it against multiple calibrated 3458s.  I can't truly claim that my equipment is calibrated or truly traceable.  But I am actually pretty confident that I know how good they are and feel that they do meet their specs (5.5 digit in several cases, 6.5 in one case).

 Maybe I got lucky on my cheap chinese reference, but it is stable relative to the other references, and the values on its sticker are in within a couple dozen ppm of the observed value. 

Labeling these things as junk in the context of a 3.5 digit meter is extreme.  Without additional measurement and calibration they are inadequate for much higher accuracy meters, and perhaps few of them are useful even with additional care.  So maybe in that context they are junk.

Perhaps the right way to ask the question is: If your budget is ~$20 dollars are they as good as anything else in the price range?  Are you better off with nothing than with one of them?  Are you better off using a pile of fresh alkaline batteries than with one of them?  Do you really believe that more than half are not within parts per 1000 (or even 10,000) of their stated output?

[J-R]

The higher-quality references from Doug/Russ/Ian don't have any reports of fake calibration certificates.  They list out the specific calibrated equipment that was used and when they were last calibrated.  All three have been active here on the forums and many reviews have been published about their products.  (I use their names because we have them and also it's easier than pasting a huge line of URLs.)

Side note, Doug has some budget $35 single-voltage references that could be of interest to some: https://voltagestandard.com/01%25-voltage-references


It's true that not everyone needs the same level of performance from their test equipment, but these random unknown references really are bad no matter how you look at it.  The technical shortcomings have already been well discussed (and perhaps somewhat ignored), but a different point is that you are frequently contributing to people who would be totally fine scamming you wherever possible.  Instead, send your money to individuals who are not really doing it for the money but for the love of the hobby.  Win/win for everyone.


And again my main point about why these cheap references are "dangerous" is that they have specific voltages printed on them and are sold as "references" so buyers apply additional weight to them.  What ratio of buyers do we think have adjusted their DMM based on the "reference" compared to adjusting the "reference" based on their DMM?

[tggzzz]

"Or spend a lot more money, build a ref yourself, and still need to send it out for calibration (after hundreds of hours of runtime to confirm stability)."

Or, spend $5! and not send it for calibration, nor wait hundreds of hours (a ridiculous suggestion) because it will immediately tell you which of the two multimeters has the 20 mV discrepancy. Then, you know which multimeter might actually be functioning, and you can send it for a cal, at less than the cost of a calibrated reference.

When responding please use the "quote" button, and proceed from there. Doing that reduces ambiguity and increases comprehension.

Why spend $5? I'll sell you one for $0.50.

[CalibrationGuy]

Everything is relative and it all begins with your requirements. My clients produce military and space hardware. When you're flying in an aircraft, I'm pretty sure you wouldn't want it serviced or tested by people who have uncalibrated equipment of unknown origin.

Having said that, let's see what we could do with a minimal budget.

As suggested above, we could use a AA battery for the 1 volt range. A new battery would be in the 1.5v range. A 9 volt battery could test the 10vdc range. Put 10 9v batteries in series to test the 100vdc range. You could even select 10 resistors that are the closest match and build a divider circuit to test the millivolt range. Plug the meter into the socket and measure 120vac, but observe all cautions when working with line voltage.

By being creative with a few resistors and batteries, you can accomplish a lot. Remember that ratios and relative measurements can get you very close to your goals.

TomG.

[shapirus]

Side note, Doug has some budget $35 single-voltage references that could be of interest to some: https://voltagestandard.com/01%25-voltage-references

Unfortunately he doesn't.
All the products in the "shop" section have been out of stock for a good while.

[KungFuJosh]

Plug the meter into the socket and measure 120vac, but observe all cautions when working with line voltage.

I don't know anybody with wall voltage that's reliably on point, or stable throughout the day. I have to use a variac when I do circuit testing.

[CatalinaWOW]

Everything is relative and it all begins with your requirements. My clients produce military and space hardware. When you're flying in an aircraft, I'm pretty sure you wouldn't want it serviced or tested by people who have uncalibrated equipment of unknown origin.

Having said that, let's see what we could do with a minimal budget.

As suggested above, we could use a AA battery for the 1 volt range. A new battery would be in the 1.5v range. A 9 volt battery could test the 10vdc range. Put 10 9v batteries in series to test the 100vdc range. You could even select 10 resistors that are the closest match and build a divider circuit to test the millivolt range. Plug the meter into the socket and measure 120vac, but observe all cautions when working with line voltage.

By being creative with a few resistors and batteries, you can accomplish a lot. Remember that ratios and relative measurements can get you very close to your goals.

TomG.

Those battery combinations can hit the right voltage ranges.  But my observations indicate that new batteries have variability in their output of a few parts per thousand.  Is that good enough?  Only the user can say.

[J-R]

Side note, Doug has some budget $35 single-voltage references that could be of interest to some: https://voltagestandard.com/01%25-voltage-references

Unfortunately he doesn't.
All the products in the "shop" section have been out of stock for a good while.

That's common for small, one-man shops, just check back later.

[Fried Chicken]

Plug the meter into the socket and measure 120vac, but observe all cautions when working with line voltage.

I don't know anybody with wall voltage that's reliably on point, or stable throughout the day. I have to use a variac when I do circuit testing.

I noticed this, and it occurred to me that a wall socket will not be accurate, as it will be different behind every transformer, and depending on the copper you have, any resistances along the way.

That said, it can act as a reliable signal source.  ERCOT publishes the current grid conditions, including the frequency to three decimal places.  This should be the same wherever you measure from afaik, but AC is witchcraft.

[mawyatt]

The AC mains are an interesting source.

Here is US the grid frequency can drop during the day with all the heavy loads, but picks up at night and early morning so the average mains frequency over 24 hours is exact.

The voltage can vary and don't think there is any attempt to make the average over 24 hours an exact amount, just attempt regulation at the substations to a fixed amount using tap changes on the large transformers. With the usual large inductive (motor) loads, sometime capacitors are added to improve (tune out the inductive reactance) the Power Factor.

Also the waveform can be distorted from the non-linear loads such as AC to DC conversion, so assuming a pure Sinewave is questionable.

Best,

[shabaz]

I tried a total of five REF50XX samples (4.5V and 2.048V versions), all 2014 era.

Sample 1: 4.50228 V
Sample 2: 4.50254 V
Sample 3: 2.04845 V
Sample 4: 2.04867 V
Sample 5: 2.04852 V

The screenshot shows the graph/stats for about 7 minutes (started about 15 seconds after power-up) for the last sample.

The setup was the worst possible (see earlier photo), and the IC socket is squeezing on the chip. The chip factory trimming and general/mechanical stability are good enough for 10 mV levels of accuracy at a typical room temperature, with no calibration nor burn-in. It's an easy circuit to assemble properly, given the crude set-up performed adequately.

[shabaz]

Trying quoting for the first time:

It's true that not everyone needs the same level of performance from their test equipment, but these random unknown references really are bad no matter how you look at it.  The technical shortcomings have already been well discussed (and perhaps somewhat ignored), but a different point is that you are frequently contributing to people who would be totally fine scamming you wherever possible. 

That works both ways. There's no innocence on either side, with Westerners openly scamming by unlocking functionality that they have not paid for on Eastern test equipment. I don't choose to automatically mistrust every seller based on the occasional bad experience here or there.

Instead, send your money to individuals who are not really doing it for the money but for the love of the hobby.  Win/win for everyone.

Not everyone thinks the same. It is possible to "buy local" as well as to help others across the world, who might actually need the money.

And again my main point about why these cheap references are "dangerous" is that they have specific voltages printed on them and are sold as "references" so buyers apply additional weight to them.  What ratio of buyers do we think have adjusted their DMM based on the "reference" compared to adjusting the "reference" based on their DMM?

Let's guess at an extreme 90% of buyers adjusting their DMMs based on that board. Even if they did, so what? They would have a DMM that was possibly inaccurate by tens of mV at the most? What are the implications:

(a) For a hobbyist, if it affects their projects, it will be a great learning curve on what to trust. If something is worth doing, it's worth doing wrong.

(b) On the other hand, if you're a professional: a qualified engineer may well rely on prototype or 'uncalibrated' equipment when developing products; there's nothing abnormal in that. But equally, that engineer is in every way liable for trusting a $10 device over a calibration if they ignored a process, or were supposed to be working to a standard, or if a body of other professionals would not have done the same for that specific task.

[Fungus]

That said, it can act as a reliable signal source.  ERCOT publishes the current grid conditions, including the frequency to three decimal places.  This should be the same wherever you measure from afaik, but AC is witchcraft.

They make clocks that use the mains as an oscillator and they're very accurate.

Apparently the power companies make great efforts to keep the frequencies stable and even compensate them over the course of the day to keep the total number of cycles per 24 hours correct.

(I'm not sure why they'd do that, was it just so that people could have accurate clocks?)

I don't know what happens in a power cut. Do they have an internal backup oscillator?

[CalibrationGuy]

(I'm not sure why they'd do that, was it just so that people could have accurate clocks?)

In Ye Olden Days the 60Hz line was used for a whole lot of timing purposes. In cheaper devices, it eliminated an internal clock circuit. (Yes, I am that old.)

TomG.

[mawyatt]

(I'm not sure why they'd do that, was it just so that people could have accurate clocks?)

In Ye Olden Days the 60Hz line was used for a whole lot of timing purposes. In cheaper devices, it eliminated an internal clock circuit. (Yes, I am that old.)

TomG.

Ironically the 60Hz Power Grid was not that accurate short term, over the span of precisely a day it was dead on by design. As mentioned during the day the frequency would drop, this was caused by the on-line loads in the Grid (1/2 the US on each Grid, East and West coast). However during lighter loads late at night and early morning the grid would "Speed Up" to catch up time-wise (think of an old clock which was based upon a synchronous motor).

Exactly 60 cycles/sec * 60 seconds/min * 60 minutes/hr * 24 hours/day or 5,184,000 cycles/day were created by the Grid and "tuned" to such every day. This was why old wall clocks were always in time from day to day, week to week, month to month and only needed setting when power was interrupted. In fact, we used the wall clock to discover if we had a power interruption and how long this was by simply comparing the wall clock to our wristwatch which we synched up every day.

Back in ~1970 we made an instrument to monitor and plot the Grid Frequency. While giving a lecture on such the Nuclear Power Plant Turkey Point in South Florida tripped off-line and we all witnessed a large Dip in the Eastern US Grid Frequency, recall this Dip was something like ~30mHz!!

You could see the Grid "Speed Up" at night/early morning and the "Dip" mid day when viewing the instruments chart recorder output over a 24 hours period.

Best,

[J-R]

Trying quoting for the first time:

It's true that not everyone needs the same level of performance from their test equipment, but these random unknown references really are bad no matter how you look at it.  The technical shortcomings have already been well discussed (and perhaps somewhat ignored), but a different point is that you are frequently contributing to people who would be totally fine scamming you wherever possible. 

That works both ways. There's no innocence on either side, with Westerners openly scamming by unlocking functionality that they have not paid for on Eastern test equipment. I don't choose to automatically mistrust every seller based on the occasional bad experience here or there.

What about all the threads here for hacking the Agilent/Keysight scopes (one over 131 pages long)?  No need for any West/East nonsense... People will hack equipment in their possession for various reasons and it has nothing to do with where they or the equipment came from.  You're moving the goalposts now...
Back on topic: how ELSE would you describe an online seller that prints out duplicate copies of a calibration sheet and applies them to all the "references" they ship out?  That is an extremely solid definition of a scammer.

Instead, send your money to individuals who are not really doing it for the money but for the love of the hobby.  Win/win for everyone.

Not everyone thinks the same. It is possible to "buy local" as well as to help others across the world, who might actually need the money.

I don't know what you are arguing against here.  I never said anything about not buying local.  Support honest businesses.  Local as well.

And again my main point about why these cheap references are "dangerous" is that they have specific voltages printed on them and are sold as "references" so buyers apply additional weight to them.  What ratio of buyers do we think have adjusted their DMM based on the "reference" compared to adjusting the "reference" based on their DMM?

Let's guess at an extreme 90% of buyers adjusting their DMMs based on that board. Even if they did, so what? They would have a DMM that was possibly inaccurate by tens of mV at the most? What are the implications:

(a) For a hobbyist, if it affects their projects, it will be a great learning curve on what to trust. If something is worth doing, it's worth doing wrong.

(b) On the other hand, if you're a professional: a qualified engineer may well rely on prototype or 'uncalibrated' equipment when developing products; there's nothing abnormal in that. But equally, that engineer is in every way liable for trusting a $10 device over a calibration if they ignored a process, or were supposed to be working to a standard, or if a body of other professionals would not have done the same for that specific task.

Quite an incredible stance.  You are OK with people adjusting their previously factory calibrated test equipment with some random reference?  I think you should reconsider your position.

[shabaz]

What about all the threads here for hacking the Agilent/Keysight scopes (one over 131 pages long)?  No need for any West/East nonsense... People will hack equipment in their possession for various reasons and it has nothing to do with where they or the equipment came from.  You're moving the goalposts now...

No I didn't, except perhaps in the most minor of ways. You were the one that stated that buying from AliExpress means frequently contributing to scammers. I merely responded. But, now you mention Keysight, you think it makes it any better that the scammers that I mentioned in return, are perfectly willing to do the same to fellow colleagues in our own countries too?

Quite an incredible stance.  You are OK with people adjusting their previously factory calibrated test equipment with some random reference?  I think you should reconsider your position.

I'm perfectly OK with what I stated. Not my problem if you misinterpret. The text is there forever, and anyone can read it to judge for themselves.

[Finnaaah]

Not sure if it's that relevant or useful since it's only resistance, but I stumbled across this series of resistors when I last ordered from Mouser.
RNCF0805TKW
e.g. 1K would be RNCF0805TKW1K00

I definitely wouldn't use them to adjust calibration, but 2ppm/C and 0.01% for $4.50 AUD lets you pick up enough to check multiple ranges on a budget. I made a 4W measurement PCB for Vishay's hermetically sealed metal foil resistors and left a few SMD footprints on it, which I've attached. Not saying this is (remotely close to) the pinnacle of accuracy, but it's very handy to have a bunch laying around if you're buying second hand equipment or just want a quick n' dirty idea of your meters resistance accuracy   

[Fungus]

Quite an incredible stance.  You are OK with people adjusting their previously factory calibrated test equipment with some random reference?  I think you should reconsider your position.

The sort of person who would do that deserves to do it.

[tggzzz]

What about all the threads here for hacking the Agilent/Keysight scopes (one over 131 pages long)?  No need for any West/East nonsense... People will hack equipment in their possession for various reasons and it has nothing to do with where they or the equipment came from.  You're moving the goalposts now...

No I didn't, except perhaps in the most minor of ways. You were the one that stated that buying from AliExpress means frequently contributing to scammers. I merely responded. But, now you mention Keysight, you think it makes it any better that the scammers that I mentioned in return, are perfectly willing to do the same to fellow colleagues in our own countries too?

Quite an incredible stance.  You are OK with people adjusting their previously factory calibrated test equipment with some random reference?  I think you should reconsider your position.

I'm perfectly OK with what I stated. Not my problem if you misinterpret. The text is there forever, and anyone can read it to judge for themselves.

Yes, the text is there - but you have snipped the context so a new reader has to actively search out the text. Snipping too much of a conversation is a technique frequently used by those that use dodgy debating tactics, e.g. strawman arguments, moving goalposts, ignoring valid counter-arguments, etc. This isn't stackexchange or EDABoard; multi-level quoting is encouraged.

IMHO J-R comes out of this discussion better than you do.

[shapirus]

You could see the Grid "Speed Up" at night/early morning and the "Dip" mid day when viewing the instruments chart recorder output over a 24 hours period.

You have just boosted my motivation to finally implement visualization for the frequency data that I'm already collecting with my homemade mains voltage data logger. I plot voltage (which btw is not even remotely suitable to check the accuracy of any voltmeter), but not frequency, yet.

[tggzzz]

You could see the Grid "Speed Up" at night/early morning and the "Dip" mid day when viewing the instruments chart recorder output over a 24 hours period.

You have just boosted my motivation to finally implement visualization for the frequency data that I'm already collecting with my homemade mains voltage data logger. I plot voltage (which btw is not even remotely suitable to check the accuracy of any voltmeter), but not frequency, yet.

In the UK you could compare that with stats from official sources: http://gridwatch.templar.co.uk/download.php

(Great information, but appalling skeuomorphic GUI: click "white none" then click "white voltage" and "white frequency" and select the dates and times.)

[shabaz]

What about all the threads here for hacking the Agilent/Keysight scopes (one over 131 pages long)?  No need for any West/East nonsense... People will hack equipment in their possession for various reasons and it has nothing to do with where they or the equipment came from.  You're moving the goalposts now...

No I didn't, except perhaps in the most minor of ways. You were the one that stated that buying from AliExpress means frequently contributing to scammers. I merely responded. But, now you mention Keysight, you think it makes it any better that the scammers that I mentioned in return, are perfectly willing to do the same to fellow colleagues in our own countries too?

Quite an incredible stance.  You are OK with people adjusting their previously factory calibrated test equipment with some random reference?  I think you should reconsider your position.

I'm perfectly OK with what I stated. Not my problem if you misinterpret. The text is there forever, and anyone can read it to judge for themselves.

Yes, the text is there - but you have snipped the context so a new reader has to actively search out the text. Snipping too much of a conversation is a technique frequently used by those that use dodgy debating tactics, e.g. strawman arguments, moving goalposts, ignoring valid counter-arguments, etc. This isn't stackexchange or EDABoard; multi-level quoting is encouraged.

IMHO J-R comes out of this discussion better than you do.

I might try multi-level quoting in the future, to see if it is helps. Others (like me) may well prefer not to see repeated walls of text nested. You can't please everyone.

It's up to the reader if they wish to read previous comments or to step in part-way. I've been speedy with the responses so one doesn't need to traverse too far back. Anyone freshly googling how to test their calibration will easily be able to see the discussion around various options. It's not a difficult discussion to follow. If anyone is really stuck, I'm happy to clarify my comments at least.

My contribution started on page 2, with the following entire text:

Very kind, generous offer to unofficially calibrate.

Just to put some sample numbers out there, for the AD584 cheap references (sub-$10 on AliExpress), by chance, a friend and I have both measured these devices (one sample each, purchased separately at different times) using two separate DMM6500 meters.

The label on it, claiming to have been measured with HP 3458A, is, of course, completely untrue (unless it's a completely broken HP 3458A!). They probably used (at best) a 6.5-digit meter, perhaps not even calibrated, and even then, they have typos in the printed values (the label on mine had a noticeably erroneous extra digit for one of the values!).

However, on the plus side, it turned out that the nominal voltage values (2.5V, 5V, 7.5V, 10V, were actually close enough to the real values, that it's very likely that one would be able to tell if that 0.02V discrepancy you're seeing between multimeters is a problem with one meter or the other, or both. In other words, a 20 mV discrepancy should be identifiable if it's present at one of those four voltages (2.5/5/7.5/10V).

Beyond three digits, you can't really rely on it with no measurement with a known calibrated instrument. Nevertheless, for the price (under $10) with no further measurement, it is a crude finger-in-the-air type of check if absolutely nothing better is available.

Just in case this helps, this was my sample result:
Label              My measurement
-------            ---------------
2.49954            2.49963
4.999501           4.99964
7.39875            7.49899
9.99823            9.99854

My last message in its entirety that you were referring to, which was on page 4:

Quote from: J-R on Yesterday at 08:26:43 am
It's true that not everyone needs the same level of performance from their test equipment, but these random unknown references really are bad no matter how you look at it.  The technical shortcomings have already been well discussed (and perhaps somewhat ignored), but a different point is that you are frequently contributing to people who would be totally fine scamming you wherever possible.

That works both ways. There's no innocence on either side, with Westerners openly scamming by unlocking functionality that they have not paid for on Eastern test equipment. I don't choose to automatically mistrust every seller based on the occasional bad experience here or there.

Quote from: J-R on Yesterday at 08:26:43 am
Instead, send your money to individuals who are not really doing it for the money but for the love of the hobby.  Win/win for everyone.

Not everyone thinks the same. It is possible to "buy local" as well as to help others across the world, who might actually need the money.

Quote from: J-R on Yesterday at 08:26:43 am
And again my main point about why these cheap references are "dangerous" is that they have specific voltages printed on them and are sold as "references" so buyers apply additional weight to them.  What ratio of buyers do we think have adjusted their DMM based on the "reference" compared to adjusting the "reference" based on their DMM?

Let's guess at an extreme 90% of buyers adjusting their DMMs based on that board. Even if they did, so what? They would have a DMM that was possibly inaccurate by tens of mV at the most? What are the implications:

(a) For a hobbyist, if it affects their projects, it will be a great learning curve on what to trust. If something is worth doing, it's worth doing wrong.

(b) On the other hand, if you're a professional: a qualified engineer may well rely on prototype or 'uncalibrated' equipment when developing products; there's nothing abnormal in that. But equally, that engineer is in every way liable for trusting a $10 device over a calibration if they ignored a process, or were supposed to be working to a standard, or if a body of other professionals would not have done the same for that specific task.

Not one person in the discussion suggested that it was a good idea to calibrate a test tool with a $10 device. In fact, everyone went out of their way to mention that their suggestions were a spot-check to determine any significant glaring error at best.

[tggzzz]

I might try multi-level quoting in the future, to see if it is helps. Others (like me) may well prefer not to see repeated walls of text nested. You can't please everyone.

True, but good taste goes a long way.

The same is true in creating electronic hardware and software.

It's up to the reader if they wish to read previous comments or to step in part-way.

Not entirely. Your position assumes that readers are devoting attention to your sub-thread, and are prepared to spend more their time than is necessary. Both represent bad taste.

It is polite and considerate to consider the readers. That's the opposite of most yootoob videos, which mainly consider how easy it is for the creator. Waste of my remaining life.

[shabaz]

(No quoting because I'm responding to the immediate message above):

I can't argue with that. I love learning from elegant designs, and hate seeing poor-quality circuits (or badly drawn schematics) or code, although sometimes one can learn a little from that too.

I am as considerate to readers as the next man and always try to speak in plain language, annotate, take photos, provide diagrams, or do whatever it takes to help the average reader. I am always genuinely happy to help clarify things because some comment style choices will please some readers and not others. But no one likes it when people try to put words in their mouths that they didn't state, e.g. strawman arguments etc. Sometimes, that's accidental, of course.

Same with YouTube videos; you can't please everyone, although there some additional compromises are needed from both creators and viewers because of the extraordinary length of time, learning curve, and skill set it could take for individuals. I believe I have just as negative an opinion about most YouTube content as you might, because I don't like the fact that the viewers are just a means to an end, advert delivery, have to sit through a lot for little information, and so on, for the majority of the content out there. Sometimes people want to see how things are done as if they were peering at a circuit or screen as if they were sitting next to a colleague, but it stinks for the remainder 95% of the time.

[mawyatt]

You could see the Grid "Speed Up" at night/early morning and the "Dip" mid day when viewing the instruments chart recorder output over a 24 hours period.

You have just boosted my motivation to finally implement visualization for the frequency data that I'm already collecting with my homemade mains voltage data logger. I plot voltage (which btw is not even remotely suitable to check the accuracy of any voltmeter), but not frequency, yet.

The technique we used way back in ~1970 was for measuring and plotting Frequency Deviation from ideal Mains (60Hz).

This involved starting with an isolation step down transformer, followed by passive and active BPF to remove noise, then zero crossing. This squared up signal was used in a low noise PLL that multiplied the Reference (60Hz) by 1000, so the output was now 60KHz, or 1000*Fmains.

An NBS traceable OCXO was divided down to 60KHz and the two signals were phase compared. The phase pulses were integrated and sampled on each cycle at 60KHz. This integrated & sampled phase signal was then filtered by two cascaded high order Elliptic LPFs with the 1st null located at 60KHz to remove the residual 60KHz. The signal then was precisely differentiated to yield the frequency deviation, as deltaF = K*dP/dt, where K is the Differential Scaling and Amplification/Attenuation as applied for range settings for display and chart plotting.

Very effective instrument at the time.

Anyway, hope this helps understand what we did way back then in measuring Mains Frequency Deviation.

Best,

[bdunham7]

The Fluke 45 arrived today and I had a bit of time between tasks to set it up atop the wreckage on my bench and take some initial readings.  It didn't get a full warmup, but that's probably not an issue.  Here's the numbers, read 'em and weep!  As posted elsewhere, my 5220A current amp has gone up in flames for the moment.  When it arises from the ashes, or at least I manage to get it off my bench, I'll get back to this meter. 

[J-R]

I think grid voltage is typically going to be highly variable these days since there is so much interconnectivity and buying/selling.  My grid-tied inverter claims to use frequency to control import/export and I wonder if that is used on the grid as well.  I don't have a way currently to track frequency, but here is a voltage graph for the last year:

[J-R]

The Fluke 45 arrived today and I had a bit of time between tasks to set it up atop the wreckage on my bench and take some initial readings.  It didn't get a full warmup, but that's probably not an issue.  Here's the numbers, read 'em and weep!  As posted elsewhere, my 5220A current amp has gone up in flames for the moment.  When it arises from the ashes, or at least I manage to get it off my bench, I'll get back to this meter. 

I think that this explains the 5.1V discrepency:
"In the medium and fast measurement rates, the a/d converter uses one of two ranges: ±300 mV and ±3 V full scale.
In the slow rate, the a/d converter uses one of two additional ranges (±100 mV and ±1000 mV full scale), for a total of four ranges."

[bdunham7]

I think that this explains the 5.1V discrepency:
"In the medium and fast measurement rates, the a/d converter uses one of two ranges: ±300 mV and ±3 V full scale.
In the slow rate, the a/d converter uses one of two additional ranges (±100 mV and ±1000 mV full scale), for a total of four ranges."

Possibly, but since it measures 10V using a scaled (divided) range (10V or 30V, not 3 as I wrote) it could be either the scaling constant for that range or the ADC calibration.

If I measure 1V using both the 1V and 3V ranges, I get 0.99460 and 0.9969 respectively.  0.99460 x 5.1 = 5.07246 and 0.9969 x 5.1 = 5.084.  So according to that, the range scaling factor is still way off on 10V but close on 30V.  And this is where it might get interesting as the DCV calibration adjustment process sets all 4 ADC ranges, but only sets range constants on the 30/300/1000V ranges not the 10/100. 

100.000 mV on the 100mV and 300mV ADC ranges gives me 96.535mV and 98.84mV respectively. 

So what now?  Does this patient need calibration (adjustment) or repair? 

[shapirus]

Anyway, hope this helps understand what we did way back then in measuring Mains Frequency Deviation.

Sounds like one hell of a complicated system, but I guess it was the way to go back then.

Mine is much more simple (by today's standards, of course): input divider -> MCP3304 -> single-board computer. Frequency measurement is as (in)accurate as the SBC's clock generator is, plus any inaccuracy added by the finite sampling rate, which is 100 kSa/s. I guess that's good enough for my home/hobby use. At least it agrees with my Brymen BM869s to within ~2 mHz. The latter's accuracy spec, however, is +/- 0.014 Hz at 50 Hz line frequency, so not an ideal comparison, but what are the odds of them both being off by the same amount? But I think I can verify this: I have a GPSDO, and I can build a frequency divider circuit to divide its 10 MHz to get a 50 Hz output, and measure that with the BM869s to see what it's showing.

p.s. whenever I measured AC line frequency, I don't remember seeing exactly 50 Hz. It was 49.98-ish every time. Right now its 3 a.m., and it's fluctuating around 49.97-49.99. I don't think I would want to sync my wall clock to that :).

p.p.s. I also log the value of the crest factor (\$\frac{|V_{peak}|}{V_{RMS}}\$) of the actual AC line waveform divided by the crest factor of the ideal sine wave to be used as a representation of how much the sine wave in the wall outlet is distorted. I'm usually seeing values around 0.97-0.98, which means that the wave's peaks are a bit flattened (and this can actually be observed with an oscilloscope). I guess this can be expected. I completely forgot that I had this value logged too -- will of course plot it along with frequency. Time to find (or rather remember) a suitable time-series data acquisition and storage backend for Grafana. There was one that I thought was a perfect fit for the job, but forgot it, maybe someone can remind me.

[J-R]

Repair or adjust...  I admit I'm on the fence.  It does seem a little odd that so many readings are low.  There is a decent amount of information in the service manual, so checking a few things out seems reasonable.

[bdunham7]

Before I take it apart and start poking at its guts, I'm going to test it for stability and linearity.  I wouldn't anticipate problems with either, but I may as well check.  I'll be logging a 10 reference overnight, although the amount it is off by is pretty ridiculous--it reads 9.7470, or 2.53% of nominal.  If that is stable, even being way off, that would be a good sign.

Looking at this meter closely, I'm seeing it is really a 30,000 count meter with a 100,000 count "hi-res" mode, similar to the Fluke 87 and relatives with their 6,000 counts and 20,000 counts in hi-res.  It is also the only meter I know of that has modern closed-case calibration but still uses a plain 6.3V zener (presumably a selected temperature compensated model) as a reference. 

[bdunham7]

And for one final interesting thing before I leave this project for a bit, the calibration constants can be retrieved over the remote connection (RS232 in this case) and so I did.  Here they are.  You can see that the first six are off by amounts similar to the errors I'm seeing.  IDK which way they work or whether they are the cause of the errors or if they are attempting to correct the errors. 

[Fried Chicken]

I am following this with interest!

This is thorough work!

It is also the only meter I know of that has modern closed-case calibration but still uses a plain 6.3V zener (presumably a selected temperature compensated model) as a reference. 

What do meters normally use?  It's my understanding these DMMs are stable in their calibration once calibrated

[Fungus]

It is also the only meter I know of that has modern closed-case calibration but still uses a plain 6.3V zener (presumably a selected temperature compensated model) as a reference. 

It doesn't really matter what the exact voltage is for digital calibration. All you need is something stable.

There's no need for laser trimming to an exact value or anything like that.

It does seem a little odd that so many readings are low.

They're probably all related in some way. At the end of the day everything comes down to measuring voltage (Ohms, amps, etc. are all done by measuring voltage and using Ohms law).

[CalibrationGuy]

It doesn't really matter what the exact voltage is for digital calibration. All you need is something stable.

There's no need for laser trimming to an exact value or anything like that.

It all comes down to your requirements. As an example, if you are using a 12bit DAC then a voltage reference trimmed to 4.096 Volts would be very convenient as each step would be 1mV, simplifying your math and eliminating scaling equations and their associated errors.

TomG.

[bdunham7]

It is also the only meter I know of that has modern closed-case calibration but still uses a plain 6.3V zener (presumably a selected temperature compensated model) as a reference. 

It doesn't really matter what the exact voltage is for digital calibration. All you need is something stable.

There's no need for laser trimming to an exact value or anything like that.

Sure, I'm not concerned about the value.  However, either buried zeners with temperature compensation or on-die heating are used in most decent bench meters these days or else a bandgap reference for those on the lower end.  For example, the 8808A which replaced the Fluke 45 uses an LM399 while the much older 8800A used the SZA263.  The Fluke 45 is a 1990's product, not 1960's.  The only digital meter I have with a plain temp-compensated zener is the 1968 era Fairchild 7000A which has surprisingly good specs--about the same as the 45--but needs a long warmup to acheive them.  In any case, I've run the Fluke 45 overnight and it seems completely stable with no signficant tempco over a 3-4C range.  Apparently the selected temp-comp zener does the job.

[bdunham7]

What do meters normally use?  It's my understanding these DMMs are stable in their calibration once calibrated

Typically either a buried zener for better models or a bandgap reference at ~1.2V for handhelds and lower end bench meters.  Both are supposed to have lower drift than typical zeners.  The zener used in the 45, Fluke p/n 857201, is listed as 6.3V +/- 3% @ 2mA bias current.  They don't even actually specify that it is temperature compensated--I'm just assuming that it is.  I cannot cross-reference or match it to any common part.  This appears to not be an issue as far as temperature stability but I don't know what the long term drift implications are.  In any case, I doubt reference drift has anything to do with whatever is going on with your meter.

[G0HZU]

I've got an old Fluke 45 meter here and I use it daily. I think I've had it for nearly 15 years. In all this time I've not seen any noticeable drift in the meter although I'm not a 'volt nut'. I've never sent it for calibration and I think it has not been calibrated since it was first sold.

I think it still reads just over 0.5mV low with a 5V input and this is quite impressive across this time span. I have never bothered to really put it through its paces other than to check its linearity is OK for my needs. With this in mind, the Fluke 45 owned by Fried Chicken does seem to have some significant issues.

I can post up some tests of mine if it helps? I've got some 6.5 digit DMMs here that are out of formal cal but two of them were UKAS calibrated when last calibrated a few years ago by the previous owners. I've also got a programmable PSU here that has 1mV resolution and good accuracy and this is usually good enough to do a basic health check on a meter across a huge range of test voltages and currents. It can also test current to 0.1mA up to several amps. It's not in the same class as a VI calibrator obviously but it is probably still better than most budget DMMs (and dodgy ebay references) in terms of accuracy. It's not quite accurate enough to actually calibrate a Fluke 45, but it is going to be close enough to prove it's still in pretty good shape...

[bdunham7]

Alright, progress!  I had almost no time to look at it earlier so I set it up to log a 10V reference for a while (overnight) in the 10V range and then I set it up with a 20V (19.99997-ish actually) source all day in the 30V range.  This tests the stability of the 100mV and 300mV ADC ranges as well as the x100 divider circuit.  Screenshots attached, the meter is perfectly stable to 1 count or less.  I did the same thing for a shorter period in the 1V and 3V ranges, no charts but the same result--perfectly stable. 

Looking at the calibration constants it appeared to me that all of the DCV-related constants were way off while all the others seemed to reflect a reasonable amount of correction.  Proceeding on the theory that this and the punctured calibration seal might indicate that someone has tried to calibrate it and failed badly, I ran it through just the DCV calibration steps.  After that I scanned through and checked for linearity and offset on all the ranges and they were good.  As I suspected from the design, the 30,000 count ranges are better than the 100,000 count ranges--the former were perfect while the latter were still good enough but not quite as perfect.  There was a 3-count discrepancy at the negative limit of those ranges. 

However, it appears that all of the other functions--ACV, DCA, ACA and Ohms are now in spec or at least very close to it.  That's all I've got for now, more later this weekend.

[CatalinaWOW]

Lots of good work there. Hope the owner appreciates the value he is getting.

[Fried Chicken]

Lots of good work there. Hope the owner appreciates the value he is getting.

I will be thrilled once it's safely back on my bench xD  But I am excited yes

[bdunham7]

OK, mission complete!  The only calibration constants changed were in the DCV sequence.  The results are pretty good, IMO.  I gave the meter the recommended 1-hour warmup, but it really seems to make very little difference.  that means you don't need to leave it on for extended periods which will extend display life.  There are three different options for testing the resistance ranges plus some extended high-resistance test points that don't have corresponding adjustments.  I did two sets--the decades of 3.0 and 1.0--and the extended tests in the 1.0 since I don't have reasonable 30M or 300M standards.

[KungFuJosh]

Great work!

[Fried Chicken]

Yoooooo the mighty Fluke 45 is back from it's California adventure!

This is some borderline professional work, papers included, packaging excellent, quick rundown of tests as follows (had to go crazy on the compression to get under the 8MB limit):

[J-R]

I think a table with the values would be easier for us to read.

Also, there are a lot of missing digits on the DT4251.  It's a 6,000 count DMM, so 5.3V can have two more digits of resolution, for example.

[bdunham7]

Yoooooo the mighty Fluke 45 is back from it's California adventure!

Also, there are a lot of missing digits on the DT4251.  It's a 6,000 count DMM, so 5.3V can have two more digits of resolution, for example.

I'm glad our friend made it home.  Just a quick pointer--don't use the Auto-V mode on the Hioki if you want any precision at all.  That's not auto-ranging, it is a low-impedance single-range check for voltage that has a specified 2% or worse basic accuracy.  It's appropriate for probing a wall socket or an SMPS primary.

[Fried Chicken]

Yes yes I noticed that.  I excitedly just got it mounted in my station and just took measurements right after having done a brake fluid flush on a car and had some beer.  I'm still running around like a chicken with its head cut off (lol bok bok).  I'll do some more testing stuff.

So professional, so nice.  Love the calibration sticker

[Fried Chicken]

And all these pictures came in a dogshit order.  I apologize, these pictures are probably meaningless.  I might format them properly, or host them myself.

[KungFuJosh]

I'm still running around like a chicken with its head cut off (lol bok bok).

Fried, I assume.

[J-R]

I vote for posting a couple photos because it's always fun to see people's setups, but make them smaller because they are grainy anyway and we don't need much detail.  The smiley sticker is fun, nice.

Then for the measurements, just make a table with values from both DMMs so we can compare, no need for those photos.  And as mentioned don't use the AutoV mode so you get all the digits of resolution on the Hioki.

[Fried Chicken]

Got some more time to dick with the unit.

The inexpensive but seemingly well built power supply I have has fixed outputs for useful voltages.  My guess is it intentionally errs on the conservative side for safety, but who knows.  Maybe now I can calibrate it that I have a calibrated and hopefully reliable multimeter.

DC Voltages:

Here it's measuring at "5 volts":

Hioki: 5.174v
Fluke: 5.163v



And at the "12 volts" output:

Hioki: 11.81v
Fluke: 11.804v



And at the "-12 volts" output:

Hioki: -12.10v
Fluke -12.086v



And I managed to get it in the mV scale using the variable voltage option on the cheap but seemingly well built DC power supply.  The Fluke 45 cuts out of the mV range relatively early, the Hioki goes up to 600mV:

Hioki: 276.1mV
Fluke: 275.58mV




High Voltage AC:

I don't have any good high voltage sources besides the wall, so that's what I used.  While I could have measured them simultaneously, I decided against doing stupid shit.

Hioki: 120.8v @ 59.98Hz
Fluke: 120.63v @ 60.02Hz
Ercot: 60.014Hz

Here is the Hioki:


And the Fluke:


And the power company:




Blah, the pictures didn't come out how I like them.  I wanted expanding thumbnails not links to full images.  I don't think I can do expanding thumbnails inline.

[Fried Chicken]

Resistors:

For the (presumably, I didn't read it) 470Ω resistor:
Hioki: 470.7Ω
Fluke: 469.9Ω

Hioki:



Fluke:



For the (again presumably) 1kΩ resistor:
Hioki: 0.998kΩ
Fluke 0.9973kΩ

Hioki:



Fluke:



And finally a (presumably) 220Ω Resistor (I just randomly grabbed these out of my misc. can of electronic stuff):

Hioki: 220.0Ω
Fluke: 219.61Ω

Hioki:



Fluke:




I have to say in doing all of this, it feels really weird to not trust the Hioki and instead trust this new (to me) Fluke.  The Hioki has been my companion for everything, being my only multimeter after someone stole my cheap-o craftsman (still angry/sad about this one).  The Hioki has this very endearing way of beeping at you when taking measurements.  It's also very fast, and been rock solid reliable whenever I've used it.  It's a weird thought to think that this Fluke 45 is now presumably my gold standard and I should trust it over my Hioki.  That said, after finding out about Hioki's after sales support/information including service manuals (it pretty much doesn't exist), I can't really recommend Hioki anymore.  That is a damn shame but oh well.

[Fried Chicken]

Frequency Counting

So now I gt to dicking with the frequency generator that I bought along with the Fluke 45, and trying out the Fluke's frequency counting capabilities.

It's a BK Precision 4040 (no 4040A, 4040B or anything, just the 4040).  This must be a pretty old unit, b/c I had a very hard time finding any information on it online.

The frequency generator's display and the Fluke are almost perfectly bang on all the way up to about 2.3MHz-ish on the Fluke that then got pissy and stopped reporting accurately.  This might have been b/c the signal became too weak, but when I hooked it up to the scope, I saw an appropriate p2p voltage, so I'm guessing it's just out of range for the Fluke?

Here is 10.004kHz:



And then at 1.6603MHz.  The scope is set to 5 volts per division, but the Fluke is only reading 45.58mV RMS.  It must be at its limit.  Also bonus Tektronix 2230 display.





I also just noticed that for many of the above voltage and resistance numbers I had the Fluke in auto ranging mode.  Forgive me, it got a bit finnicky taking these measurements.

[J-R]

I think all of those numbers look good.  You could further explore the minor disagreements by doing some additional cross-checking of different values and ranges (and the slow mode of the Fluke 45).  Use Ohm's law for further calculated verifications.  Although odds are that the Fluke 45 is right and the Hioki is slightly off.  But as mentioned before, if such things are bothering you then you're headed for some kind of higher-end bench DMM with frequent calibrations...

The Fluke 45 ACV accuracy is not specified above 100kHz, and frequency measurements are not defined above 1MHz.  So any displayed values above that are for entertainment only!

[bdunham7]

Here it's measuring at "5 volts":

Hioki: 5.174v
Fluke: 5.163v

So calibrating the Fluke 45 has only reduced your ~20mV discrepancy to 11mV--but at least you know which is which.  The tolerances for the Hioki work out to 19 counts, so 11 is OK.  Welcome to the "within specs but not as good as you hoped" zone!

[Fried Chicken]

Here it's measuring at "5 volts":

Hioki: 5.174v
Fluke: 5.163v

So calibrating the Fluke 45 has only reduced your ~20mV discrepancy to 11mV--but at least you know which is which.  The tolerances for the Hioki work out to 19 counts, so 11 is OK.  Welcome to the "within specs but not as good as you hoped" zone!

This is more than adequate for my needs.  The Hioki has similarly always been more than adequate for my needs.  This is by no means a way to verify the calibration of the Fluke.... that question... and the original inspiration for this whole thread I have no way to test your calibration   I gotta trust your work, but I do