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DMMCheck Plus Multimeter Reference(and other References) - Experiences..

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tomud:

--- Quote from: alm on July 07, 2023, 08:29:05 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.


--- Quote from: tomud on July 07, 2023, 05:46:48 pm ---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).

--- End quote ---
No argument there :)

--- End quote ---

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).

KungFuJosh:

--- Quote from: Martin72 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.

--- End quote ---

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.

Martin72:
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.

jchw4:

--- Quote from: Martin72 on July 07, 2023, 03:29:26 pm ---
--- Quote from: Martin72 on July 04, 2023, 06:49:45 pm ---Should arrive this week.

--- End quote ---

Has arrived... 8)

--- End quote ---


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.
--- End quote ---

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.

KungFuJosh:

--- Quote from: Martin72 on July 07, 2023, 10:51:40 pm ---How about to buy the L/C option  board ?

--- End quote ---

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.

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