Author Topic: DMMCheck Plus Multimeter Reference(and other References) - Experiences..  (Read 31899 times)

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Offline mendip_discovery

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #50 on: July 07, 2023, 04:58:32 pm »
Do some tests, and record the results. Do it again ina few months. Compare it to another TEA victim nearby. If you can find a nice lab that will do calibration for sensible money in the future do it and you can build up some confidence in the unit.

Thanks for sharing the cert btw. I like to see what others do.
Motorcyclist, Nerd, and I work in a Calibration Lab :-)
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So everyone is clear, Calibration = Taking Measurement against a known source, Verification = Checking Calibration against Specification, Adjustment = Adjusting the unit to be within specifications.
 

Offline tomud

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #51 on: July 07, 2023, 05:46:48 pm »
It might be a bit of a challenge for a 6.5 or 8.5 as they are much better than the specs of the DMMCheck.

6 and 1/2 digits is ok, 8 and 1/2 digits make absolutely no sense. While buying such a multimeter is real, keeping it in good condition, including calibration, is not easy fun. These are high costs, not all laboratories can calibrate such an 8 1/2 multimeter. On the other hand, buying 8 and 1/2 of some old one, which has no known accuracy, does not make any sense. Well, unless I just boast that I have such a multimeter.

In fact, if I wanted to become independent, I'd build my own real calibrator, although it's expensive fun. Right now it's cheaper for me to calibrate my 6 1/2 digit multimeters (non-ISO 17025 certified) - as it's not terribly expensive. However, as standards in my home laboratory, they are sufficient - I absolutely do not need 8 1/2 digits to calibrate a multimeter bought for around 200 euros (6 1/2 is fully sufficient).


« Last Edit: July 07, 2023, 05:57:14 pm by tomud »
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Offline Steve77

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #52 on: July 07, 2023, 06:04:31 pm »
The International Vocabulary of Metrology (VIM) was first published in 1984 and has had many revisions since.  The VIM of course pushes the separate definitions of calibration and adjustment among other specific terms, but it's not a guarantee that everyone just adopts such things immediately.  Plenty of older manuals consider calibration to include adjusting the instrument if necessary, and I still see this used in modern times as well:  https://www.ianjohnston.com/index.php/onlineshop/handheld-precision-digital-voltage-source-2-mini-detail

J-R: Thank you for mentioning this document.  I did a quick Google search and came up with a 2021 version that I will archive.  It will be nice to use standard language in procedures and test documents so I can pretend that I know what I am talking about. 



 
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Offline alm

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #53 on: July 07, 2023, 08:29:05 pm »
6 and 1/2 digits is ok, 8 and 1/2 digits make absolutely no sense. While buying such a multimeter is real, keeping it in good condition, including calibration, is not easy fun. These are high costs, not all laboratories can calibrate such an 8 1/2 multimeter. On the other hand, buying 8 and 1/2 of some old one, which has no known accuracy, does not make any sense. Well, unless I just boast that I have such a multimeter.
Adjustment is actually quite straight-forward for a certain popular 8.5 digit meter (3458A), all it requires is a good short, an accurate 10 kOhm resistor and an accurate 10 V source. Costs about €130 here (forum user AP). That's actually much easier than adjusting something like a HP/Agilent 34401A which requires a whole bunch of voltages, currents and resistances to calibrate and adjust it.

Resolution, stability and linearity has value beyond accuracy. For example, you might compare two resistors by putting them in series, putting a voltage across them and then comparing the voltage across the two resistors. If the meter has good short term stability and linearity, you can measure the ratio of the two resistors very accurately without needing any absolute accuracy.

Right now it's cheaper for me to calibrate my 6 1/2 digit multimeters (non-ISO 17025 certified) - as it's not terribly expensive. However, as standards in my home laboratory, they are sufficient - I absolutely do not need 8 1/2 digits to calibrate a multimeter bought for around 200 euros (6 1/2 is fully sufficient).
No argument there :)

Online Martin72Topic starter

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #54 on: July 07, 2023, 08:38:31 pm »
I have already tried something, the L/C/R section.
The meter was the ET4410 (LCR Bridge).
This is exactly how I imagined it, I now have a reference with which I can compare different devices, this makes things easier in the future.
The next device will be the Brymen 869s, then possibly the Oscilloscope, a Hioki LCR, and so on.
I will always post here.

Offline tomud

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #55 on: July 07, 2023, 08:40:25 pm »
Adjustment is actually quite straight-forward for a certain popular 8.5 digit meter (3458A), all it requires is a good short, an accurate 10 kOhm resistor and an accurate 10 V source. Costs about €130 here (forum user AP). That's actually much easier than adjusting something like a HP/Agilent 34401A which requires a whole bunch of voltages, currents and resistances to calibrate and adjust it.

Resolution, stability and linearity has value beyond accuracy. For example, you might compare two resistors by putting them in series, putting a voltage across them and then comparing the voltage across the two resistors. If the meter has good short term stability and linearity, you can measure the ratio of the two resistors very accurately without needing any absolute accuracy.

Right now it's cheaper for me to calibrate my 6 1/2 digit multimeters (non-ISO 17025 certified) - as it's not terribly expensive. However, as standards in my home laboratory, they are sufficient - I absolutely do not need 8 1/2 digits to calibrate a multimeter bought for around 200 euros (6 1/2 is fully sufficient).
No argument there :)

I'm talking about a normal approach according to the art, not trying to figure out how to do it cheaply. You don't have standards a class above an 8 1/2 digit multimeter your approach is just for fun, not a serious approach to calibration. That's why I prefer calibrated in an accredited 6 and 1/2 lab which is relatively cheap than pretending to calibrate and validate an 8 1/2 digit multimeter at home.

I had the opportunity to buy an 8 1/2 digit multimeter but I didn't because it makes no sense to pay such large amounts for calibration in an accredited lab for something that I don't really need at home. Because seriously, explain to me the need to have 8 and 1/2 digits in the house? Unless we are collecting equipment, but it will only be a collection like in a museum - not a reliable measuring instrument.

So I still have more faith in the old Agilent 34401A and the newer Keysight 34465A that have up-to-date calibration from an accredited lab. Now the new Siglent SDM3065X has arrived, which will also be sent to the laboratory in a while (when the Siglent calibration period is over). Although to be honest, instead of the SDM3065X, I wanted to buy a second Keysight 34465A first. However, the currently unfavorable exchange rate of the Polish currency and the lack of availability of Keysight 34465A made me take a risk with the purchase. I decided to give DMM Siglent a chance (I don't know if it was a good choice, we'll see after a long time). Unfortunately, in such a combination, I doubt that the uncertain DMM 8 and 1/2 would be better (without current calibration in an accredited laboratory).

« Last Edit: July 07, 2023, 10:48:56 pm by tomud »
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Offline KungFuJosh

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #56 on: July 07, 2023, 10:13:03 pm »
I have already tried something, the L/C/R section.
The meter was the ET4410 (LCR Bridge).
This is exactly how I imagined it, I now have a reference with which I can compare different devices, this makes things easier in the future.
The next device will be the Brymen 869s, then possibly the Oscilloscope, a Hioki LCR, and so on.
I will always post here.

I started running through my LCRs with SMD resistors. It takes a long ass time. I will definitely be getting something like that device in the future. I saw on their website about some new high accuracy device coming soon.
"Right now I’m having amnesia and déjà vu at the same time. I think I’ve forgotten this before." - Steven Wright
 
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Online Martin72Topic starter

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #57 on: July 07, 2023, 10:51:40 pm »
Hi Josh,

How about to buy the L/C option  board ?

It´s passive, so you don´t need the "rest"..

https://dmmcheckplus.com/shop/ols/products/lc-board

Meanwhile I remember of my third LCR meter I got, a mastech MS8911 smart smd tester with testfrequencies up to 10khz..Must check it too.
 
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Offline jchw4

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #58 on: July 08, 2023, 01:51:32 am »
Should arrive this week.

Has arrived... 8)


You skipped the most interesting part of the certificate: the bottom. But let's look at my case.

I bought my DMMCheckplus long time ago from Doug. And sent it back for calibration several times.

But then at some point I wanted to get an L/C-board. So I decided to give the new brand owner a try and sent my device for recalibration and adding a new board.

Here you can compare the two calibration reports that I got: the previous one from Doug and the new one from the new brand owner.



First, the new report lacks the "as received" measurements.

All the previous reports showed slight drift of the DC reference value. Now it is simply missing the significant digit.

I asked the new owner whether they did any adjustments and they said they did. Which means the history is already lost too.
The damage was done. 


The new cert even has a funny "DCV temperature coefficient" measured +6uV/F but the value measured was specified to the hundreds of microvolts! Was it a joke?


Looking further, many (most?) of the values lost at least one significant digit. Starting from AC voltage and current.
My AC current has not drifted a single 10^-4 for several years, but now they simply specified it to 10^-3.

From the previous calibrations I know that my 1kOhm resistor used to drift for 0.01ohm annually (1.00023k, next year 1.00024k) but there is no that last digit anymore.

Low and high oscillator duty cycle was never the same for me. They are suspiciously equal in the new report. And one digit is lost.


So I feel that the new cert is basically saying "in specs" and does not give any more details. Which is a very different product from what Doug created.

The attention to details is what built trust in this product. Now it is different. And I feel that the new owners are basically reusing old product reviews (see the happy Doug customers above).
I would not apply Doug's reputation to the new product. It's not what it used to be.


But why dream of what was gone? New age, new trust, new products! Don't be the old guy!


Let's look at the new product built by these guys. The L/C board.

https://dmmcheckplus.com/shop/ols/products/lc-board still says:
Quote
giving you .001, .01, .1 and 1 uF reference capacitors AND .001, .01, .1 and 1 mH inductors, all tested to within .05% of their value.

Great! 0.05% is a pretty high margin. What did they use to measure it? BK 891.

It's a nice meter, but 0.05% is the very best accuracy it can provide. BK Precision even makes a special "LCR Accuracy Calculator" software to calculate the actual measurement accuracy.
Page 6 of the datasheet https://bkpmedia.s3.us-west-1.amazonaws.com/downloads/datasheets/en-us/891_datasheet.pdf specifies the basic accuracy, but the user manual has the actual formulas and their software is capable of calculating the actual accuracy.

For example, if I read this chart correctly the basic accuracy for a 1uF capacitor measured at 10kHz with this meter is on the edge between 0.5% and 1%.

So it was worth asking about the measurement accuracy of their setup, wasn't it?

And... they replied me with the chart above. Saying that "BK lays it out on this chart". And attached the chart. That was it.

Which basically means they do not have more data and probably never paid attention to.



To sum it all up: I think it's unfair to reference Doug work on this product anymore. The attention to details and confidence was the product that Doug built. (And hopefully he is still doing good with his voltagestandard references!)

The schematics is not complicated, you can easily build one yourself. You can even measure it with some random calibrated meter, but it won't get you the Doug experience and passion.
 
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Offline KungFuJosh

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #59 on: July 08, 2023, 02:13:18 am »
How about to buy the L/C option  board ?

I emailed them asking what the fancy new device is supposed to be. I'll likely either get the new thing, or just order the whole kit. It will take significantly less time than fussing with the SMD fixture and stuff I have right now...which isn't certified or anything anyway.
"Right now I’m having amnesia and déjà vu at the same time. I think I’ve forgotten this before." - Steven Wright
 

Offline J-R

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #60 on: July 08, 2023, 03:03:12 am »
The "recalibration" of the DC voltage references from VoltageStandard.com is also the same.  All the references are tweaked to be as close to the desired value as possible before being sent back to the customer.

FWIW, Doug puts the as-received value on the certificate as well.
Yes, that is correct.  My statement was aimed at the point that "calibration" included an adjustment, unlike the strict definition from the VIM.
 

Offline bdunham7

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #61 on: July 08, 2023, 03:11:10 am »
The attention to details is what built trust in this product. Now it is different. And I feel that the new owners are basically reusing old product reviews (see the happy Doug customers above).
I would not apply Doug's reputation to the new product. It's not what it used to be.

I don't want to pile on or suggest the DMMCheck+ is a bad value or inadequate for it's obvious intended purpose (which IMO doesn't include calibration or precise checking of meters past the 4.5 digit mark), but as for the detail part here's the link to the calibration certificate for their 3458A.

https://img1.wsimg.com/blobby/go/c544540f-524c-4b38-8d0c-cbfda88bf37a/downloads/2022%203458A%20Calibration.pdf?ver=1688384167316
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 J-R

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #62 on: July 08, 2023, 04:24:07 am »
I have the original calibration cert from the DMMCheck Plus I purchased from Doug in 2018 and it only has the DCV listed to the 100uV, no further.  I would make the guess that by that point he decided the extra digits can provide a false impression to the customer, so he reduced the resolution to make it clear what can be reasonably trusted and what can't, especially in between calibrations.

The voltage references are designed to be adjusted, that is why there is a trimmer pot installed.  If you want something different, the metrology forum is full of folks running references and tracking standards for years straight, noting every tiny fluctuation.  The DMMCheck Plus is just not a good solution for this.  The passives aren't good enough and nothing is sealed so you can bump things with your fingers, probes, etc.  The PDVS2mini is the superior voltage reference, but you'll pay $400USD for it.

I am not seeing the point of an "as-received" for the passives!

If Doug thought the current owners of the DMMCheck Plus were no good, I'm confident he would not have their web site address plastered across the top of his own web site.  But I don't see the point in idolizing Doug either.  At the end of the day, Doug and Russ are selling hobby products.  If you want to be serious, then buy the serious stuff for tens of thousands of dollars and forget these "toys", relatively speaking.


When I received my L/C board I did notice the fact they were using the BK 891 and wasn't super-impressed.  But on the flip side DMMs and LCR meters are known to use different test methods so it's already going to be a tricky situation to get useful numbers.

100% agree with regard to the "all tested to within .05% of their value" on the L/C board description.  I think there was just a misunderstanding on their part.  Now that the issue is out in the open, I'm sure it will be addressed.
 

Offline jchw4

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #63 on: July 08, 2023, 04:43:13 am »
I have the original calibration cert from the DMMCheck Plus I purchased from Doug in 2018 and it only has the DCV listed to the 100uV, no further.  I would make the guess that by that point he decided the extra digits can provide a false impression to the customer, so he reduced the resolution to make it clear what can be reasonably trusted and what can't, especially in between calibrations.

My original cert is from 2018 too. And it lists DCV to the 100uV too. But later recalibration certificates are more precise. So I would guess the opposite.

Quote
But I don't see the point in idolizing Doug either.

Sure. I just demonstrated the two certificates that present attention to details.

Quote
When I received my L/C board I did notice the fact they were using the BK 891 and wasn't super-impressed.  But on the flip side DMMs and LCR meters are known to use different test methods so it's already going to be a tricky situation to get useful numbers.

100% agree with regard to the "all tested to within .05% of their value" on the L/C board description.  I think there was just a misunderstanding on their part.  Now that the issue is out in the open, I'm sure it will be addressed.

To me the main issue is ignoring the tool specification that they base their claim on. I wonder what Martin's cerificate says about the meter though.

Quote
Now that the issue is out in the open,

Are you serious?
 

Offline J-R

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #64 on: July 08, 2023, 05:38:54 am »
My first cert is from December 2018 (Doug), next cert is from March 2020 (Russ), neither have more than 100uV, nor do subsequent ones.

Not sure about your comment regarding my comment to the issue being out in the open.  You said you e-mailed them but they blew you off or whatever, but now you've pointed it out in the forums for everyone to see and we agree with you.  So we should expect them to have to deal with it at some point.
 

Offline jchw4

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #65 on: July 08, 2023, 06:18:36 am »
I have the original calibration cert from the DMMCheck Plus I purchased from Doug in 2018 and it only has the DCV listed to the 100uV, no further.  I would make the guess that by that point he decided the extra digits can provide a false impression to the customer, so he reduced the resolution to make it clear what can be reasonably trusted and what can't, especially in between calibrations.

My original cert is from 2018 too. And it lists DCV to the 100uV too. But later recalibration certificates are more precise. So I would guess the opposite.

Quote
But I don't see the point in idolizing Doug either.

Sure. I just demonstrated the two certificates that present attention to details.


I feel that I look too aggressive here, but this story just blew me away.


But let me explain which details I had in mind here.

As you can see from my certificate from Doug, these references are often more stable than stated.  I.e. both "before" and "after" DCV values start with "5.0000".
To see the behavior of the reference you need to get into the unstable area, this is why (at least) the next digit is important.

But it is also only important if stated before and after the adjustments too. This way I could estimate how precise my measurements were just before sending it for recalibration.
If it was "5.5000" before the adjustments I would need to double-check what I did just before sending it for recalibration. If it was "5.00001" - probably not.

I have only one DMMCheckplus, so I don't have the total statistics, but looking at the annual stability of all the values, losing the "before adjustments" part and a significant digit is a major loss.
I believe they should know that stability of the values are often better than what they measured.

So I am not saying it is not useful or suitable for this or another purpose. I am just saying that it's a different product now.
Before I could predict the actual value, now I am not sure. There is no information on where the uncertainty area of this particular reference starts.

It used to be a reference (not extremely precise, but with known behavior), now it's just "Check your DMM pass/fail".

The device price is still good, so I would recommend the hardware itself (but I don't have a new version, so I just hope they did not "improve" the hardware part). Hopefully it's just the measurements setup that is now different.

Quote
Not sure about your comment regarding my comment to the issue being out in the open.

If you noticed the issue with the L/C board too, then it's fair to assume that we are not alone and many other people have also noticed it.
Do you mean that the issue has to go public to be addressed?

Quote
You said you e-mailed them but they blew you off or whatever, but now you've pointed it out in the forums for everyone to see and we agree with you.  So we should expect them to have to deal with it at some point.

No, they did not. We had a very polite discussion. I just learned that they could not provide the data that I needed and stopped.
I don't see any point arguing with them because the lost data won't magically come back, and my knowledge is definitely less than theirs. They want their product to look like this for some reason, whatever.

My point is just that the prior Doug-era experience may not be relevant to the current device. So when comparing it to cheap Chinese references we should not take prior experience into account.
 

Online Martin72Topic starter

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #66 on: July 08, 2023, 05:55:11 pm »
Today my Brymen BM869s..
« Last Edit: July 08, 2023, 06:03:09 pm by Martin72 »
 

Offline tomud

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #67 on: July 08, 2023, 06:23:18 pm »
Today my Brymen BM869s..

Chinese reference voltage for a few dollars, on a relatively poor AD584  :popcorn:
« Last Edit: July 08, 2023, 06:25:19 pm by tomud »
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Online Martin72Topic starter

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #68 on: July 08, 2023, 06:40:27 pm »
Looks good.  8)

Offline bdunham7

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #69 on: July 08, 2023, 07:03:59 pm »
When I received my L/C board I did notice the fact they were using the BK 891 and wasn't super-impressed.  But on the flip side DMMs and LCR meters are known to use different test methods so it's already going to be a tricky situation to get useful numbers.

IMO the 891 is more than adequate for this type of low-cost standard given it's objectives and the fact that it is on a small PCB and not some sort of fixture.  The only problem is the 0.05% claim--that's not an easy spec to meet even at much higher cost.  They need to get real about that, although there will be howling if they revise it downwards.

The issue of DMMs and LCR meters giving different results due to the differences in their test methods is a result of the type of capacitor used.  A very high quality, low-D, low-ESL/ESR and low leakage unit--polypropylene, polystyrene, wet tantalum or silver mica--will give similar results on different instruments and to an extent, with different test frequencies. 
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.
 

Online Martin72Topic starter

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #70 on: July 08, 2023, 07:48:22 pm »
I hope that it is clear to everyone that neither this "reference" nor any other, even cheaper to get, are to be used seriously for calibration purposes.
You can use them as a comparison, as a kind of guide.
But regular what calibrate or adjust with it, in this state, you should leave it, if you take the matter seriously.
Sure, if you need something accurate to 2..3 digits, then that may be enough.
But actually a reference must be unequally "better", more accurate, more stable.
At work, we thought for many years that we could calibrate some of our measuring instruments ourselves, because we have measuring equipment calibrated according to ISO.
Until auditors once taught us otherwise, and they were still friendly about it. ;)
All this was of no value.
To be able to calibrate according to ISO, the references must have a higher calibration standard.
That is, e.g. calibrated according to DakkS (very expensive).
And even then it would not be valid, because we have no accreditation for being able to calibrate something according to the standard and bring it into circulation.
So... ;)
That's why this little piece of paper that came with the device is hardly worth anything.
At least until I have it calibrated again and then by an accredited laboratory (and then it depends on what means they have used for calibration).
This costs about the same if not more than the device itself, so I still have to think very well. 8)
Until then, I use it as something with which I can quickly compare devices with each other and that's already good. :)

Offline 4thDoctorWhoFan

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #71 on: July 08, 2023, 08:03:51 pm »
I have one and I mainly use it for a sanity check.  Because sometimes you need a sanity check.  :)
 
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Offline KungFuJosh

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #72 on: July 08, 2023, 10:29:11 pm »
I have one and I mainly use it for a sanity check.  Because sometimes you need a sanity check.  :)

That statement next to your profile picture is pretty funny. 😉
"Right now I’m having amnesia and déjà vu at the same time. I think I’ve forgotten this before." - Steven Wright
 

Offline 4thDoctorWhoFan

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #73 on: July 08, 2023, 10:32:30 pm »
I have one and I mainly use it for a sanity check.  Because sometimes you need a sanity check.  :)

That statement next to your profile picture is pretty funny. 😉

Yep! You got that right.  :-+
 
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Online Martin72Topic starter

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Re: DMMCheck Plus Multimeter Calibration Reference - Experiences ?
« Reply #74 on: July 08, 2023, 10:39:18 pm »
I must smile a little bit as I recognize what LCR they have used to measure the L/C board.
A BK891..
https://de.rs-online.com/web/p/lcr-messgerate/1217581

Our calibrated ST2830 also have 0.05%, so I´m curious about the results when I take the box to work on monday. 8)

 
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