Author Topic: DMM Noise comparison testing project  (Read 133915 times)

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Online maxwell3e10

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Re: DMM Noise comparison testing project
« Reply #525 on: July 10, 2018, 12:14:23 am »
I fixed a couple of errors in the plot in the previous post, going back to the raw data when possible.
 

Offline serg-el

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Re: DMM Noise comparison testing project
« Reply #526 on: July 12, 2018, 09:33:00 am »
Хмм.

У меня получились другие данные.

I got other data.

Edit: added data
WTF!!!

Edit2: ManateeMafia HP3458A пересчитано
« Last Edit: July 13, 2018, 07:45:18 am by serg-el »
 

Online maxwell3e10

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Re: DMM Noise comparison testing project
« Reply #527 on: July 12, 2018, 05:27:17 pm »
Проверьте что вы вычисляити стандартное отклонение а не среднее, у Тина есть ошибки в таблице
 

Offline serg-el

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Re: DMM Noise comparison testing project
« Reply #528 on: July 12, 2018, 05:39:58 pm »
В каких данных ошибка?
Я пока не нашёл.
Вычислял stddev (rms).
СТАНДОТКЛОН в русской версии exel.

Edit: нашел.
Новые данные выше.
« Last Edit: July 13, 2018, 07:13:36 am by serg-el »
 

Offline TiN

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Re: DMM Noise comparison testing project
« Reply #529 on: July 12, 2018, 06:04:07 pm »
EEVBlog fixed unicode support for forum? Wowski :)

I had two versions of Excel file, with older peak-peak values and then later with RMS Stddev.
Also there was issue of double division by range on some test.
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Online maxwell3e10

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Re: DMM Noise comparison testing project
« Reply #530 on: July 12, 2018, 09:27:28 pm »
Old neutrons 34461A, pilelie 34420A - analyze original data, summary table shows rms, not stddev.
barnacle2k Solartron -shows integration time in seconds, not nplc

 

Offline serg-el

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Re: DMM Noise comparison testing project
« Reply #531 on: July 12, 2018, 09:56:33 pm »
https://xdevs.com/datashort/Pipelie/
Вычислял сам.

https://xdevs.com/datashort/OldNeurons/
Вычислял сам.


barnacle2k Solartron это, да. Неправильно. Но график не сильно изменится, если пересчитать 3,2 сек. в plc. Будет равно 160 PLC. Если 50 Гц.
Или 192 PLC если 60 Гц.

RMS это и есть stdev ;)

Edit: OldNeurons_RAW_25_344641A вычислено заново.
Edit: ManateeMafia_HP3458A__ID111 вычислено заново.
« Last Edit: July 13, 2018, 07:46:50 am by serg-el »
 

Online maxwell3e10

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Re: DMM Noise comparison testing project
« Reply #532 on: July 12, 2018, 10:11:07 pm »
нет, Stddev=sqrt(rms^2-ave^2)
 

Offline serg-el

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Re: DMM Noise comparison testing project
« Reply #533 on: July 12, 2018, 10:19:25 pm »
Physical scientists often use the term "root mean square" as a synonym for standard deviation when it can be assumed the input signal has zero mean, i.e., referring to the square root of the mean squared deviation of a signal from a given baseline or fit.[5][6] This is useful for electrical engineers in calculating the "AC only" RMS of a signal. Standard deviation being the root mean square of a signal's variation about the mean, rather than about 0, the DC component is removed (i.e. RMS(signal) = Stdev(signal) if the mean signal is 0).

https://en.m.wikipedia.org/wiki/Root_mean_square
 

Offline dl1640

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Re: DMM Noise comparison testing project
« Reply #534 on: July 19, 2018, 10:05:01 am »
checked my 6.5 digit DMM today.
with copper short on hi to lo.

setting:
dcv 200mV range, AZON, 25PLC (500ms, 50Hz line), 25 is the largest settable number.
sampling interval 1100ms, single trigger on each and every 1.3s with totally 3600 data.

STDEV for the last 1800 data around 0.102uV, the display resolution is only 0.1uV, not bad.

 :popcorn:
 

Offline knightzdw

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Re: DMM Noise comparison testing project
« Reply #535 on: December 23, 2018, 09:49:15 am »
What meter is used in this case if you don't mind to share?
 

Offline MiDi

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Re: DMM Noise comparison testing project
« Reply #536 on: May 29, 2019, 03:49:30 pm »
Is there ootb script/tool for 3458A and Solartron 7081 for Linux/RPI awailable?
Or at least sourcecode, so that it is easy to derive script?
 

Offline 3roomlab

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Re: DMM Noise comparison testing project
« Reply #537 on: May 29, 2019, 05:25:52 pm »
What meter is used in this case if you don't mind to share?

Im guessing from the file, its yokogawa 7562?
getting 0.1uV @ 25NPLC is nice
Im curious to see 1 2 4 8 16 32 NPLC. it could tell alot more

but how can it be? no teardown photos in eevblog?  :-DD
« Last Edit: May 29, 2019, 05:29:21 pm by 3roomlab »
spheres of influence, example linustechtips. can you feel the brainwashing? showing off equipment, etc. were you swayed and baited? with immense popularity (and social "titles"), can you afford to disagree?
 

Offline MiDi

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Re: DMM Noise comparison testing project
« Reply #538 on: June 04, 2019, 03:30:55 pm »
Is there ootb script/tool for 3458A and Solartron 7081 for Linux/RPI awailable?
Or at least sourcecode, so that it is easy to derive script?

Seems I have to start from scratch or did I miss something in this long thread or elsewhere?

If there is enough interest, I would get some motivation to make a universal python script to adapt different DMMs easy.
Target is primary linux-gpib and perhaps COM-Port.
 

Online maxwell3e10

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Re: DMM Noise comparison testing project
« Reply #539 on: August 31, 2019, 05:10:21 am »
This thread has been dormant for a while, but it contains a lot of useful information. In particular, it had been noted here that the shorted input noise is quite small for DMM7510 on low DC voltage ranges, much smaller than for 34461-70 Keysight meters. It turns out a lot of the noise for Keysight meters is due to air flow over the input stage.
https://www.eevblog.com/forum/metrology/turning-fan-off-to-reduce-dmm-voltage-noise/
This effect was first pointed out by OldNeurons earlier in this thread. https://www.eevblog.com/forum/metrology/dmm-adc-noise-comparison-testing-project/msg665603/#msg665603
With proper air current shield or turning the fan off the noise can be reduced quite a bit. Here is a comparison of Allan deviation for DMM7510, DMM6500 and Keysight 34461 with air cover. One can see that for short averaging times DMM7510 is still the best. But because it does not average well, at longer times 34461 can do just as well.
« Last Edit: August 31, 2019, 05:14:57 am by maxwell3e10 »
 

Offline imo

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Re: DMM Noise comparison testing project
« Reply #540 on: August 31, 2019, 01:41:29 pm »
34401A shorted inputs.
Stddev 42.1nV.
« Last Edit: August 31, 2019, 01:54:10 pm by imo »
 

Offline 3roomlab

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Re: DMM Noise comparison testing project
« Reply #541 on: September 01, 2019, 12:22:27 am »
this pdf cpem-2016-keysight.pdf was mentioned in another thread about noise analysis
of interest is my incomplete understanding about the use of allan variance in finding a certain range of sampling which gives the best SNR
at some point in the 3458A plot, the SNR seem to get smaller

eg : for 10v, the best sampling is 10-20 samples? eye popping 150dB SNR
(150 SNR ~ 26 bits. 26bits @ 10v = 0.15uV per step. the best set of data I have is 0.6uV/24bits for similar range but needs 100x more averaging)
on most plots here in this thread contributed by users, it does not seem like 100NPLC is more noisy on 3458A than 10 NPLC
maybe theirs (on paper) is a different way of measuring?

on K2015, my previous messy data seem to suggest the best capture block is around 8NPLC. weird? but looking into the K2015 pdf, it also seem to suggest similar. with that, back then i then started to play in blocks of 2/4/8 binary increment NPLC blocks with interesting results.

in the other thread about the maths use, I used to think about the use of kurtosis. but after seeing allanvariance, i am imagining some kind of algorithm where there is a real time allanvariance calculation which adjusts NPLC as time progresses to get the most optimum sampling over time. or maybe the user specify a SNR and the software auto determines averaging and NPLC rate for fastest capture possible.
currently all of our captures are fixed NPLC.averaging, but noise and ambient intrusions are variables.

i found 2-3 xls online which has simple allan variance calculations. i tried to do something similar for noise but i could not get the allan variance to work. im sure my math is wrong somewhere  :-DD

lets hope keysight doesnt do this first before one of us does and names it "true-nplc" :-DD
« Last Edit: September 01, 2019, 01:44:32 am by 3roomlab »
spheres of influence, example linustechtips. can you feel the brainwashing? showing off equipment, etc. were you swayed and baited? with immense popularity (and social "titles"), can you afford to disagree?
 

Offline Kleinstein

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Re: DMM Noise comparison testing project
« Reply #542 on: September 01, 2019, 08:29:08 am »
It is quite normal that there is an optimal integration time to get the best SNR. This because there can be source of 1/f noise in the ADC. In auto zero mode, from some point on it is more effective to use shorter conversions and averaging than one (actually 2 for the AZ mode) long conversions.  The like many modern DMMs the 3458 uses this, and the normal 100 PLC setting is actually the average of 10 readings at 10 PLC. AFAIK there is a way to force it to do linger integration at a piece, but this gives more noise.
The lowest noise point may be even at shorter integrations, but INL may be better at 10 PLC than 1 PLC.
For my ADC design I get best block size at 1 PLC and the DMM7510  seems to be best more around 2 or 3 PLC. It is a balance between 1/f noise and limited resolution / error in reading the final charge.

There is no real need to do some complicates read time calculations to choose the best setting. Close to the optimum it does not make a big difference which setting is used and the best settings are fixed for a given instruments. So just using averaging from a certain point on (e.g. 10 PLC for the 3458) is a good enough solution.  Things get more interesting with those meters that include an extra analog low pass filter before the ADC (e.g. DA1281, Keithley 2182) - there using shorter conversions allows a faster settling analog filter. The filter helps reducing the noise bandwidth seen for the input signal - this does not help much with a short in the 10 V range, but it can help (get the same noise level in half the time) if the signal source itself is noisy or in the low ranges where the amplifier noise is more important than ADC noise.
 

Offline Dr. Frank

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Re: DMM Noise comparison testing project
« Reply #543 on: September 01, 2019, 09:04:53 am »
Using APER 1 instead of NPLC 50 gives a single conversion,  what you can directly observe in OHM mode, probably valid in DCV mode also.
 


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