Author Topic: DMM linearity comparison  (Read 30416 times)

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Offline TiN

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Re: DMM linearity comparison
« Reply #100 on: April 10, 2021, 06:54:15 pm »
krasimir.k

Since you have two calibrations, what was calculated drift of your LTZ1000 standard?

Quote
The Fluke 7009N itself was calibrated in BIPM France in 20.12.2017.

Wait here a second, so standard was never calibrated since end of 2017? I didn't expect this from NMI lab, to be honest.

I'd say going for 100K modification was a good choice, I can only wish to see more people who do not need full +50°C ambient functionality ability do it. 1.5 months for settling is usually enough for LTZ1000A A9 reference. You do have to keep 3458A permanently powered on, however.

Could be best if BIM would adjust your 3458A for you vs JJ, so you could know internal LTZ1000A A9 value with very good confidence. Then you could "transport" that value to your LTZ1000 reference at home, using 3458A as a transfer box (I know, many in EU will throw tomatoes at me on this suggestion, but it's better than nothing).

Perhaps next step would be to evaluate thermal stability of your 3458A (you can cycle on/off airconditioner in the room, while logging data over few days), so you can estimate TC error of your 10V measurements as well.

Looking forward to hear more about your results.
« Last Edit: April 10, 2021, 06:56:07 pm by TiN »
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Offline krasimir.k

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Re: DMM linearity comparison
« Reply #101 on: April 11, 2021, 05:12:00 am »
Hi TiN
The drift based on absolute calibration values between June 2019 and June 2020 was 2uV only, but the uncertainty increased from 21uV in 2019 to 34uV in 2020. You can see in the attached screenshots.
Yes, they calibrated their voltage references and resistance references on 3 years base.
Now they have JJA, so they will stop sending the Fluke 7009N to France and probably will start calibration every year.
I can not keep running the 3458a 24/7 because the DMM it is located next to my bed :-). But I'm running the last 3 months at least 12-14 hours per day.

Regards,
Krasi
 
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Offline krasimir.k

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Re: DMM linearity comparison
« Reply #102 on: April 11, 2021, 05:56:01 am »
Hello,
Here are the charts, based on raw data from the Supracon's programmable Josephson junction array system.

The Agilent 3458a is within the spec according the "Transfer Accuracy/Linearity" table in the 3458a datasheet document for 10V and 1V range and out of spec for 0.1V range.

The INL of the HP 34401a is within the datasheet spec : 2ppm of reading and 1ppm of the range.
The INL of the HP 34401 is about 4 times better then the spec for 10V and 1V range.

Regards,
Krasi
« Last Edit: May 29, 2021, 06:10:05 pm by krasimir.k »
 
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Online Kleinstein

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Re: DMM linearity comparison
« Reply #103 on: April 11, 2021, 07:55:03 am »
The specs for the 3458 in the 10 V range are for 0.05 ppm of the range plus 0.05 ppm of the reading. So the measured current curve is still inside this.
The spec limits for the 1 V and 0.1 V range are even higher (0.3 +0.1 ppm and 0.5+0.5 ppm). This is natural as this includes amplifcation, that can add some INL errors.
Also the measurement curve likely shows more noise effects.  The 100 mV range may be effected by noise quite a bit.
Even though the JJA source may be near perfect, there can still be noise from the distribution system and the DMM reference can also show noise / short time drift during the time for the measurements.  The  difference from the ideal line is quite small and thus just the random DMM noise can be significant.  The deviation from the straight line is not only INL error but also includes ADC noise, amplifer noise, source noise (likely small) and DMM reference noise.

Especially the LM399 ref in the 34401 can really limit the results, if the measurement is done in one run and not by repeating the squence several times. It is not so uncommon for a LM399 reference to show popcorn type jumps of some 0.5 ppm (3.5 µV) at some random times. If this happens during the measurement it can really though of the whole curve.
 
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Offline krasimir.k

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Re: DMM linearity comparison
« Reply #104 on: April 11, 2021, 08:38:00 am »
Thank you very much, Kleinstein!
I really forgot the "Transfer Accuracy/Linearity table" and only remember the number 0.05ppm.
I will update my post with the correct data.
Regards,
Krasi
 

Offline rf-design

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Re: DMM linearity comparison
« Reply #105 on: April 16, 2021, 08:52:42 am »
If the linearity measurement is a sequential procedure why it is exercised in the most error covering manner?

1. Starting with the most negative input voltage
2. Progress with lowest positive increments
3. Only a single measurement for a single INL point

What are the practical reasons against a random voltage point and a number of measurment points above 1?
 

Online Kleinstein

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Re: DMM linearity comparison
« Reply #106 on: April 16, 2021, 09:24:27 am »
The INL test usually does a larger number of readings. The data  krasimir.k showed include a stdDev column, and this needs more readings to calculate. From the scattering of the RMS values I would guess some 20-100 readings.

I agree that a simple sequence startung at one end going up is not the best. There is nothing wrong with starting at one end an than go to one direction, as this would make a linear drift of the meter look like a change in gain only. The other possible reason is to have small steps and thus less settling time (DMM and source) needed.
The problem is having 1 pass and thus quite some sensitivity to drift and low frequency noise.

It is likely better to do multiple passes, so more like 10 readings each and than 10 passes instead of 200 readings at each point. This would allow averaging also to suppress lower frequency reference noise, which can be an issue especially for some meters like the 34401.
It often takes some settling time, so it is a compromise between reference noise suppression ( more passes, less data at a time) and overall noise from more averaging.

The test can not work with lowest increments  - it would just take too much time with a slow (e.g. 1 Minute for each point) and high resolution DMM (e.g. > 1 million counts). So the INL test is allways only a partial test checking on a small fraction of the possible readings.
 

Offline Pipelie

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Re: DMM linearity comparison
« Reply #107 on: March 24, 2022, 05:58:24 am »
it seems that there is no DMM7510 INL plot on the forum yet, I've tested the INL of the units in my lab. Here it's the result. |O
1. Source: Fluke 5700EP
2. DMM 2xDMM7510, and one 3458A as a comparison.
3. setup on 7510: filter off, auto-zero on, >10G impedance.  NPLC 2(I took 50 samples at each point and got the mean value in my script)

as you can see in the plot below, the Positive input is pretty good, better than I expected(as good as my 34401 :) ).
The INL of negative input is very different.  :-//

and the Spec of ADC INL is 1ppm of reading + 1ppm of range.
 
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Online Andreas

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Re: DMM linearity comparison
« Reply #108 on: March 24, 2022, 07:37:13 am »
Hmm,

what are the comp1 and comp2 measurements?

with best regards

Andreas
 

Offline HighVoltage

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Re: DMM linearity comparison
« Reply #109 on: March 24, 2022, 07:50:19 am »
I also don't understand comp1 and comp2

Also, you mentioned your 34401A can you add that one to your graph, if you have the numbers.
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Online MegaVolt

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Re: DMM linearity comparison
« Reply #110 on: March 24, 2022, 08:32:51 am »
 
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Offline Pipelie

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Re: DMM linearity comparison
« Reply #111 on: March 24, 2022, 09:30:31 am »
@Andreas and @HighVoltage

the 7510#1 and 7510#2 are the INL of two DMM 7510 I measured.
and then I did poly fit on those curves in excel for fun, and I labeled them as  7510#1Comp. 1, 7510#2Comp. 2.  :-DMM
 

Offline Pipelie

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Re: DMM linearity comparison
« Reply #112 on: March 24, 2022, 09:32:17 am »
I also don't understand comp1 and comp2

Also, you mentioned your 34401A can you add that one to your graph, if you have the numbers.

HighVoltage, you can find it here.
https://www.eevblog.com/forum/metrology/dmm-linearity-comparison/75/
 

Offline e61_philTopic starter

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Re: DMM linearity comparison
« Reply #113 on: March 24, 2022, 11:00:40 am »
it seems that there is no DMM7510 INL plot on the forum yet, I've tested the INL of the units in my lab. Here it's the result. |O
1. Source: Fluke 5700EP
2. DMM 2xDMM7510, and one 3458A as a comparison.
3. setup on 7510: filter off, auto-zero on, >10G impedance.  NPLC 2(I took 50 samples at each point and got the mean value in my script)

as you can see in the plot below, the Positive input is pretty good, better than I expected(as good as my 34401 :) ).
The INL of negative input is very different.  :-//

and the Spec of ADC INL is 1ppm of reading + 1ppm of range.

May it be an artifact of the fitting? Could you also publish raw data?
 

Offline Pipelie

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Re: DMM linearity comparison
« Reply #114 on: March 24, 2022, 12:13:24 pm »
it seems that there is no DMM7510 INL plot on the forum yet, I've tested the INL of the units in my lab. Here it's the result. |O
1. Source: Fluke 5700EP
2. DMM 2xDMM7510, and one 3458A as a comparison.
3. setup on 7510: filter off, auto-zero on, >10G impedance.  NPLC 2(I took 50 samples at each point and got the mean value in my script)

as you can see in the plot below, the Positive input is pretty good, better than I expected(as good as my 34401 :) ).
The INL of negative input is very different.  :-//

and the Spec of ADC INL is 1ppm of reading + 1ppm of range.

May it be an artifact of the fitting? Could you also publish raw data?

Sure, It could be.
I've uploaded the raw data.  have fun!

the file name with #1 is the data of my first DMM7510, #2 is the second one.

there is no 3458A data in the files, I've measured 3458 INL over 5700 many times, there is no need to do it again.
the 3458A curve on the plot is one of the typical INL of 3458A for reference only.



« Last Edit: March 26, 2022, 03:45:16 am by Pipelie »
 

Online MegaVolt

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Re: DMM linearity comparison
« Reply #115 on: March 25, 2022, 11:15:00 am »
I've uploaded the raw data.  have fun!
I have processed one of the files. The error reaches 3 ppm. On the graphs above, the error is much smaller. Am I forgetting something?
 

Online Kleinstein

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Re: DMM linearity comparison
« Reply #116 on: March 25, 2022, 11:37:03 am »
The curve gets a little better if a common slope is subtracted. The INL still does not look that great, reaching 0.9 ppm FS
Part of the jump around zero may be due to the calibrator - there is at least a chance to have some offset error there before polarity change.

The positive side on it's own looks quite good, but the negative side does not look good. Also the combination is odd: at least the INL contributions I am aware of tend to not change so abrupt at around zero. So the square and cubic part would more be expected to effect both side about equally.
This makes me wonder a little how much numerical correction of the INL is alread included.

Edit:
I just realized that there are 3 curves for 2 x DMM7510, so the 3 rd curve seems to be more like the 3458. makes me susepect that the odd curve is to a large part an effect of the calibrator and not the DMMs.
« Last Edit: March 25, 2022, 11:41:23 am by Kleinstein »
 

Online MegaVolt

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Re: DMM linearity comparison
« Reply #117 on: March 25, 2022, 11:40:30 am »
The curve gets a little better if a common slope is subtracted.
To what extent it applies to measurements? After all, we consider the devices calibrated. Those should they be in tolerance without any additional amendments?

An additional correction makes the graph look nice. But at the same time it says that there is a problem with the devices.
 

Offline e61_philTopic starter

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Re: DMM linearity comparison
« Reply #118 on: March 25, 2022, 11:51:09 am »

Sure, It could be.
I've uploaded the raw data.  have fun!

Thanks, but it seems that all DUTs are in the same file, but not measured at the same time? Especially measuring the 3458A against the 7510 at the same moment in time would be interesting.

And it is not fun to parse the data with several headers..

Which DUT is which? duta is what?
 

Offline macaba

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Re: DMM linearity comparison
« Reply #119 on: March 25, 2022, 12:10:23 pm »
On the graphs above, the error is much smaller. Am I forgetting something?

It seems to me that you should pick the fitting that makes the most sense for the situation (and state the fit you used in the chart title, e.g. "Endpoint fit INL"). In my opinion, that's usually endpoint linear fit (y=mx+c on first and last points to make the first and last points have 0PPM error on the chart) as this reflects a "perfect calibration to extremes" (because the actual calibration always drifts). In Pipelie's data, it looks like it would be better to use 0V and most positive value due to the defect in the negative region. I don't think it makes sense to do a general linear fit in most cases.
« Last Edit: March 25, 2022, 12:21:30 pm by macaba »
 

Offline e61_philTopic starter

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Re: DMM linearity comparison
« Reply #120 on: March 25, 2022, 02:08:35 pm »
On the graphs above, the error is much smaller. Am I forgetting something?

It seems to me that you should pick the fitting that makes the most sense for the situation (and state the fit you used in the chart title, e.g. "Endpoint fit INL"). In my opinion, that's usually endpoint linear fit (y=mx+c on first and last points to make the first and last points have 0PPM error on the chart) as this reflects a "perfect calibration to extremes" (because the actual calibration always drifts). In Pipelie's data, it looks like it would be better to use 0V and most positive value due to the defect in the negative region. I don't think it makes sense to do a general linear fit in most cases.

One should do a least-square fit against the reference. In that case the gain and offset of the DUT doesn't matter.
 
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Offline Pipelie

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Re: DMM linearity comparison
« Reply #121 on: March 26, 2022, 03:46:49 am »
I forgot to mention.

here it's the info of files.
the file name with #1 is the data of my first DMM7510, #2 is the second one.
there is no 3458A data in the files, I've measured 3458 INL over 5700 many times, there is no need to do it again.
the 3458A curve on the plot is one of the typical INL of 3458A for reference only.

I also used gain and offset correction on the INL plot.
« Last Edit: March 26, 2022, 03:48:36 am by Pipelie »
 

Online Kleinstein

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Re: DMM linearity comparison
« Reply #122 on: March 27, 2022, 07:54:22 am »
The gain and offset correction (which is the same as subtracting a fitted straight line) should be done for the whole curve, not seprate for the positive and negative side.
The way the data are shown, as some smooth curve is confusing - it should be some point like symbols and not a smooth curve suggsting there would be a smooth curve. A good part of the scattering may very well be noise. The average over 50 readings of 2 PLC is not very much and the DMM7510 does have a problem with extra low frequency noise for about that time scale.

It is a bit surprising to get such a poor linearity only for the negative side, and than 2 meters behaving nearly identical. Could there be a problem with settling ? It may be worth taking more data at each step and look at the frist and later data separate.

For noise the averaging over multiple 2 PLC readings may be best, but the INL could be better for true 10 PLC at a piece.
 

Offline Pipelie

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Re: DMM linearity comparison
« Reply #123 on: March 27, 2022, 04:53:57 pm »
The gain and offset correction (which is the same as subtracting a fitted straight line) should be done for the whole curve, not seprate for the positive and negative side.
The way the data are shown, as some smooth curve is confusing - it should be some point like symbols and not a smooth curve suggsting there would be a smooth curve. A good part of the scattering may very well be noise. The average over 50 readings of 2 PLC is not very much and the DMM7510 does have a problem with extra low frequency noise for about that time scale.

It is a bit surprising to get such a poor linearity only for the negative side, and than 2 meters behaving nearly identical. Could there be a problem with settling ? It may be worth taking more data at each step and look at the frist and later data separate.

For noise the averaging over multiple 2 PLC readings may be best, but the INL could be better for true 10 PLC at a piece.

the DMM itself usually uses different gain and offset for the positive and negative input, however, the F5700 doesn't. that's why I did the correction separated.
Keithley's ADC has the best performance while it runs at 1~5PLC, I've calculated the SDEV of 50 samples and printed it in log files, you can check the SDEV in the files.
I don't think there is a problem in my setting and it's not worth the effort to test it again at this point.
 

Offline e61_philTopic starter

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Re: DMM linearity comparison
« Reply #124 on: March 27, 2022, 05:27:00 pm »
Here is what I get without any smoothing or differentiation between positive and negative.

INL is calculated this way:

def ppm_inl(dut, ref):
    slope, intercept, rvalue, pvalue, stderr = stats.linregress(dut, ref)
    return (ref - (dut * slope + intercept)) / 10 * 1e6

Simple linear regression

I took the first measurement of one file
data = pd.read_csv("DCV_10vdc_F5700EP_DMM7510_2PLC_avg50_2.csv.txt", nrows = 219)
 


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