Author Topic: how do you calibrate a dvm with 6.5 digits?  (Read 5014 times)

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Offline Joop01Topic starter

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how do you calibrate a dvm with 6.5 digits?
« on: May 01, 2023, 02:40:41 pm »
I'm planning the layout of my own lab, I planned for a R&S dvm HMC8012, but unfortunately it is no longer manufactured, that is that all shops no longer deliver the meter. So refocus. The HMC was 5 3/4 digit, it must be the same or better. If you make a list you end up with 5.5 or 6.5 digits meters. If you look at the specs you can read that its valid for a year. After that it won't be off that much, but after some time you need to re-calibrate, but how do you calibrate  those meters? Send it back for calibration?, which has the risk that the box is dropped on the floor or so when its send to the manufacturer (or what's available) or returned to you. This is the reason I want to do it myself, but with what? I have designed calibration stuff, but that's 0,1% at best. Those 5.5 or 6.5digit meters have a lot more 0 figures behind the decimal point. Buy two meters (from different manufacturers)?
 

Offline BeBuLamar

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #1 on: May 01, 2023, 02:53:26 pm »
If I were you I either send it to the manufacturer for calibration or not having it calibrated as I don't think they change much over the years. I think you can buy the equipment to calibrate it but then they are very expensive and they need to be calibrated too.
 

Offline Fungus

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #2 on: May 01, 2023, 03:08:37 pm »
This is the reason I want to do it myself, but with what? I have designed calibration stuff, but that's 0,1% at best. Those 5.5 or 6.5digit meters have a lot more 0 figures behind the decimal point.

You don't need zeros after the decimal point to see if it's changing. Measure the most stable reference you own using the meter when it arrives. Measure it again every six months using the same reference under the same conditions, see how much it changes (if at all). You might need an oven to get a stable temperature for this. :popcorn:

These meters are designed to not change with time, and they usually don't. The best bet is just to monitor it and take no action unless you think it needs it.

You could spend the first few days of ownership messing around with a trimmable voltage reference in your oven. See how many zeros you can get after the decimal point using the circuit in the datasheet.
« Last Edit: May 01, 2023, 03:34:56 pm by Fungus »
 
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Offline nctnico

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #3 on: May 01, 2023, 03:13:05 pm »
I'm planning the layout of my own lab, I planned for a R&S dvm HMC8012, but unfortunately it is no longer manufactured, that is that all shops no longer deliver the meter. So refocus. The HMC was 5 3/4 digit, it must be the same or better. If you make a list you end up with 5.5 or 6.5 digits meters. If you look at the specs you can read that its valid for a year. After that it won't be off that much, but after some time you need to re-calibrate, but how do you calibrate  those meters? Send it back for calibration?, which has the risk that the box is dropped on the floor or so when its send to the manufacturer (or what's available) or returned to you.
You are overreacting here. Test equipment is shipped around all the time for calibration. Just make sure to ship it in the box + packaging it came in; that has been designed to survive any kind of transport. IOW: just send it to the manufacturer for calibration and be done with it.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline coromonadalix

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #4 on: May 01, 2023, 03:26:48 pm »
Exactly same toughts,  to build you own cal lab  you need control over humidity / temperatures   etc ....   you can not play god

i always heard for a 6.5 digit    you need at least 7.5 or even 8.5 digit calibrators, and check all their used prices  lolll

better send it,  you receive the cal sheet  etc ...   and way less costly  in time or ressources
 

Offline Joop01Topic starter

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #5 on: May 01, 2023, 03:45:30 pm »
I'm planning the layout of my own lab, I planned for a R&S dvm HMC8012, but unfortunately it is no longer manufactured, that is that all shops no longer deliver the meter. So refocus. The HMC was 5 3/4 digit, it must be the same or better. If you make a list you end up with 5.5 or 6.5 digits meters. If you look at the specs you can read that its valid for a year. After that it won't be off that much, but after some time you need to re-calibrate, but how do you calibrate  those meters? Send it back for calibration?, which has the risk that the box is dropped on the floor or so when its send to the manufacturer (or what's available) or returned to you.
You are overreacting here. Test equipment is shipped around all the time for calibration. Just make sure to ship it in the box + packaging it came in; that has been designed to survive any kind of transport. IOW: just send it to the manufacturer for calibration and be done with it.
May be, last shipment on my door had a harmonica shape. Double boxes, so box in a box! Power supply casing split in two. Got a new one. Last time on tv, some footage of tntpost, three packages on the edge of the van floor and they dropped on the street. So I have some mixed feelings about that.
 

Offline Joop01Topic starter

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #6 on: May 01, 2023, 03:50:10 pm »
Exactly same toughts,  to build you own cal lab  you need control over humidity / temperatures   etc ....   you can not play god
Last is true, but controlling humidity and temperature is way easier then most think. One of the tricks is too wait for the right conditions. You need of course two meters for that, one for humidity and one for temperature. 
 

Offline nctnico

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #7 on: May 01, 2023, 03:51:35 pm »
I'm planning the layout of my own lab, I planned for a R&S dvm HMC8012, but unfortunately it is no longer manufactured, that is that all shops no longer deliver the meter. So refocus. The HMC was 5 3/4 digit, it must be the same or better. If you make a list you end up with 5.5 or 6.5 digits meters. If you look at the specs you can read that its valid for a year. After that it won't be off that much, but after some time you need to re-calibrate, but how do you calibrate  those meters? Send it back for calibration?, which has the risk that the box is dropped on the floor or so when its send to the manufacturer (or what's available) or returned to you.
You are overreacting here. Test equipment is shipped around all the time for calibration. Just make sure to ship it in the box + packaging it came in; that has been designed to survive any kind of transport. IOW: just send it to the manufacturer for calibration and be done with it.
May be, last shipment on my door had a harmonica shape. Double boxes, so box in a box! Power supply casing split in two. Got a new one. Last time on tv, some footage of tntpost, three packages on the edge of the van floor and they dropped on the street. So I have some mixed feelings about that.
Ofcourse you'd ship equipment with UPS or Fedex. Not regular postal service  8) Nevertheless, equipment should be packed well enough to survive a drop from 1 meter high (which IIRC is part of a standard for packaging requirements).
« Last Edit: May 01, 2023, 04:14:07 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Fungus

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #8 on: May 01, 2023, 03:56:39 pm »
Ofcourse you'd ship equipment with UPS or Fedex. Not regular postal service

There's a difference in how they treat things?
 

Offline NoisyBoy

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #9 on: May 01, 2023, 05:14:08 pm »
If you are truly serious about calibration to bring it within spec, it simply isn’t feasible for most labs, let alone home labs. There are numerous calibration point within each function, each requiring an extreme stable source.  My 6.5 digit meters requires Fluke 5720A and 5725A or later for proper calibration, these equipment would far exceeds the cost of most home labs.

It depends on where you live, in the US, I am fortunate to have Keysight.  They have a service depot locally, they come out in their padded equipment van to pick up the equipment from my lab for calibration.  It is always fun to peek inside their van to see what other exotic test equipment is on the way back for calibration or repair.  I read they may not serve home labs, if that is the case, look for other local cal labs.  My local third party cal labs also do pick up and delivery, which minimize the risk due to shipping damage.

 

Offline Joop01Topic starter

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #10 on: May 01, 2023, 06:17:37 pm »
If you are truly serious about calibration to bring it within spec, it simply isn’t feasible for most labs, let alone home labs. There are numerous calibration point within each function, each requiring an extreme stable source.  My 6.5 digit meters requires Fluke 5720A and 5725A or later for proper calibration, these equipment would far exceeds the cost of most home labs.
What amazes me is how difficult they do about what a product cost. With some trouble I found the 5720A, way above my head or what I want to  spend on it. Didn't found 5725A. Did found that the 6.5 digit is no longer in catalog. They have now only a 5.5 digit Bench meter. Back to my question, if it is not possible to calibrate your own equipment, then what is the point in having, say, a 6.5 digit bench multi meter?. What I looking at?
 

Offline alm

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #11 on: May 01, 2023, 07:11:08 pm »
What amazes me is how difficult they do about what a product cost. With some trouble I found the 5720A, way above my head or what I want to  spend on it. Didn't found 5725A. Did found that the 6.5 digit is no longer in catalog. They have now only a 5.5 digit Bench meter. Back to my question, if it is not possible to calibrate your own equipment, then what is the point in having, say, a 6.5 digit bench multi meter?. What I looking at?
Calibration is about having readings that are traceable to national standards. For many applications you need resolution (to determine how much a value changes with temperature, for example), but not necessarily accuracy. Also, good quality 6.5 digits like the classic HP/Agilent/Keysight 34401A are known to stay within their stated 1 year accuracy or most ranges for years, though if you want to certify this, you will need to have it calibrated every year. But for many hobbyists, knowing that a voltage is 5V +/- 1% but it's varying at most 0.5 mV over load or temperature is good enough.

If you need traceability, for example because your customers demand it, then you'd send it to a cal lab at the interval the manufacturer recommends (often 1 year, sometimes if you want higher accuracy). I haven't kept track of prices, but I'd think that calibration of a 6.5 digit meter would be in the ball park of $200.

The problem with calibrating it yourself is a) that you need another reference with traceable calibration with lower uncertainty than the desired uncertainty of the calibration and b) that you need stable sources for all signals that the meter needs, unless you want to do a limited calibration of only DCV and Ohms, let's say. For a full calibration might need DC voltages from 100 mV to 1000 V, resistance from 100 Ohm to 100 MOhm, DC currents from 10 mA to 2 A, AC voltages from 100 mV to 750 V from 10 Hz to 50 kHz and AC currents at 1 A and 2 A at 1 kHz (this is for the 34401A, check the service/calibration procedure for your DMM). Especially high frequency, high voltage AC is often difficult in your average lab. This all needs to have a stability much better than the desired uncertainty. So a basic 1/4W resistor will definitely not be stable enough for this comparison.

So either you would need a more accurate DMM that was calibrated before and stable sources for all these signals, or a calibrated multi-function calibrator that can source all these signs with a low enough uncertainty. This is how the cal labs do it, but they might be investing $100k in equipment and another $10k or so for yearly calibration. They make this back in the volume of equipment they calibrate.

Offline bdunham7

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #12 on: May 01, 2023, 07:49:55 pm »
Back to my question, if it is not possible to calibrate your own equipment, then what is the point in having, say, a 6.5 digit bench multi meter?.

If you actually need a current traceable calibration certificate then you have to ship it to a certified (to whatever standard you require) calibration lab.  To actually set that up yourself for a typical 6.5-digit bench meter like Keithley DMM6500 or Keysight 34465A would take an enormous investment in equipment and then you'd still have to get whatever accreditation you require--and then you'd still have to have that equipment calibrated periodically at an exponentially higher cost.  Nobody does that unless they have hundreds or thousands of instruments to calibrate.  The point of having a calibrated 6.5-digit meter is that you can take measurements with the meter and be fairly sure that the are accurate within the specifications of the meter.

Now if you wanted to check the calibration unofficially, you could get a few standards or DMM-check type units that would at least verify that your meter is not broken and hasn't drifted grossly out of spec.  However, to get the precise high-voltage and high-frequency calibration stimuli that is required for a full calibration would still be a very daunting task.  Some of us do this sort of thing as hobby, but I would never guarantee results although I'm pretty sure I can get pretty close.

I have no idea why you think that nothing can ever be shipped--how do you get your new meters?  If getting a new meter is the only way you can get something without it being smashed, just buy a new meter every year or two, depending on your calibration cycle.  It will be way cheaper, especially if you sell your old one.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Offline Fungus

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #13 on: May 01, 2023, 08:01:14 pm »
Yeah, is this calibration needed for legal reasons or are you just doing it as a hobby?

As noted, these things are designed not to go out of calibration. Maybe all you need is a way to convince yourself of that fact.

Adjusting it if it ever goes out of spec usually needs a lot of fancy equipment. You usually need several very precise references, one for each range.
 

Offline David Hess

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #14 on: May 01, 2023, 09:02:45 pm »
I usually settle for periodically checking the calibration as best I can against my best references and my best other multimeter.
 

Offline Joop01Topic starter

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #15 on: May 01, 2023, 10:09:03 pm »
have no idea why you think that nothing can ever be shipped--how do you get your new meters?  If getting a new meter is the only way you can get something without it being smashed, just buy a new meter every year or two, depending on your calibration cycle.  It will be way cheaper, especially if you sell your old one.
First question, jump in my car and drive to the reseller. I have a special floor in the car for transporting equipment. Second remark, thanks, figured out the same thing. I have downloaded a service manual for a dvm and what you need to do the job. As said before, that's way above what I want to spend. Second hand somewhere between 60.000 and 75000 dollars, so new will be much more. Also with so much figures behind the decimal point I think you can safely ommit the last two. Also I agree with you that you can buy a new every two years, prices are dropping due to some genius in China who put all in one chip. 
 

Offline Joop01Topic starter

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #16 on: May 01, 2023, 10:14:40 pm »
Yeah, is this calibration needed for legal reasons or are you just doing it as a hobby?
As noted, these things are designed not to go out of calibration. Maybe all you need is a way to convince yourself of that fact.
No, I'm just a hobbyist who happens to have a hobby with equipment which is not available on the market. Your second remark, I could not find specs  for a period longer than 1 year. I think your right.
 

Online Martin72

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #17 on: May 01, 2023, 10:26:43 pm »
Quote
Back to my question, if it is not possible to calibrate your own equipment, then what is the point in having, say, a 6.5 digit bench multi meter?

It never occurred to me to calibrate my measuring instruments myself, because I simply do not have the means to do so and do not want to buy them.
It is much easier and cheaper to have them calibrated externally.
If it were necessary in the hobby area.
I had once exemplary done and my Brymen 869S calibrated externally (cost 79 €).
In the "Pro" area it looks different, we have to calibrate all our measuring equipment annually.
If we had them calibrated to the DakkS standard, we could extend the time between calibrations.
But it is enough to have them calibrated according to ISO with equipment calibrated according to DakkS.
Why do you need the accuracy of a 6.5 digit meter in the private sector, that is another question.
If I have to measure something to three decimal places, then it doesn't matter whether my 6.5 digit meter is calibrated or not.

Offline bdunham7

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #18 on: May 01, 2023, 10:34:12 pm »
First question, jump in my car and drive to the reseller. I have a special floor in the car for transporting equipment.

Well, depending on where you are, Tektronix Eindhoven seems driveable, at least to me, and they likely can recalibrate your meter.  If that isn't driveable, buy a Pelican case for it.  I have these for my better handheld and my best bench meter so that they can travel with an almost indestructable shield.  I doubt any reasonable courier service would destroy a fairly light and well protected package like that on such a short trip--it's usually the heavy ones that get slammed.

https://www.tek.com/en/calibration-services/netherlands/eindhoven

If you buy a new Keithley DMM6500, it has a 2-year calibration cycle (at slightly worse specs than 1 year) and is actually pretty unlikely to go out of spec even over a decade.  One ISO-17025 calibration after two years should convince you of that.

https://download.tek.com/datasheet/1KW-61315-1_DMM6500_Datasheet_072121.pdf
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline Someone

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #19 on: May 01, 2023, 10:58:36 pm »
In the "Pro" area it looks different, we have to calibrate all our measuring equipment annually.
all ? at places I have worked the safety and compliance bits were kept calibrated but the rest didn't matter. Where "the rest" could be 99% of the equipment and never less than half.
 

Online Martin72

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #20 on: May 01, 2023, 11:05:49 pm »
OK, not all... ;)
Multimeter, current clamps, current probes for scopes, oscilloscopes, poweranalyzer, high voltage tester, isolation tester, current shunts, temperature sensors, frequency counters, spectrumanalyzer, data logger/recorder, frequency generators, pressure gauge, test pumps  for testfield.
Crimp tools, torque wrench and soldering stations in the production area.


« Last Edit: May 01, 2023, 11:24:19 pm by Martin72 »
 

Offline BeBuLamar

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #21 on: May 01, 2023, 11:30:42 pm »
Yeah, is this calibration needed for legal reasons or are you just doing it as a hobby?
As noted, these things are designed not to go out of calibration. Maybe all you need is a way to convince yourself of that fact.
No, I'm just a hobbyist who happens to have a hobby with equipment which is not available on the market. Your second remark, I could not find specs  for a period longer than 1 year. I think your right.

I have sent some Fluke meters in for repair. Some of them are like 10 years old and after the repair they did the calibration and sent me the reports. All of them said in specs no adjustment needed and thus I don't worry about having my meter calibrated every year.
 

Offline BeBuLamar

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #22 on: May 01, 2023, 11:32:28 pm »
have no idea why you think that nothing can ever be shipped--how do you get your new meters?  If getting a new meter is the only way you can get something without it being smashed, just buy a new meter every year or two, depending on your calibration cycle.  It will be way cheaper, especially if you sell your old one.
First question, jump in my car and drive to the reseller. I have a special floor in the car for transporting equipment. Second remark, thanks, figured out the same thing. I have downloaded a service manual for a dvm and what you need to do the job. As said before, that's way above what I want to spend. Second hand somewhere between 60.000 and 75000 dollars, so new will be much more. Also with so much figures behind the decimal point I think you can safely ommit the last two. Also I agree with you that you can buy a new every two years, prices are dropping due to some genius in China who put all in one chip.

Let assume that you have the money for the calibration equipment but those eqeipment need calibration too right?
 

Online Martin72

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #23 on: May 01, 2023, 11:39:21 pm »
Quote
All of them said in specs no adjustment needed and thus I don't worry about having my meter calibrated every year.

Meh.... ;)
Fluke I agree immediately, we have a fluke 87 from 1992, until now every year calibrating without any re-adjustments needing.
My brymen 869s was external calibrated a few weeks after buying it new and needed some re-adjustments while calibrating.
My hint in general:
Buy a "cheap" reference and when something suspicous occurs while measuring, give the meter away for calibrating.
https://www.welectron.com/DMMCheck-Plus-Multimeter-Calibration-Reference

Offline Tony_G

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Re: how do you calibrate a dvm with 6.5 digits?
« Reply #24 on: May 02, 2023, 12:40:58 am »
Just wanted to add that if you're in the US then you can get the unit that Martin referenced from https://dmmcheckplus.com/ - They used to be made by https://voltagestandard.com/ here in WA state but I seem to remember that the volume rate was too low or something like that and they sold off that part of the business.

I have one and have been pretty happy with it over the years.

TonyG


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