Fluke 732a noise - Page 1
Forum section: electronics / general

author: martinr33
author_rank: Frequent Contributor
timestamp: April 30, 2018, 12:51:56 am
content: Has anybody measured the actual noise on a Fluke 732a?My perception is that they seem very quiet. On an 8.5 digit meter, I am seeing noise SD of 170nV on the 10V output, which is about as good as the meter ever reads on its own. Now, that's over a few minutes and there could obviously be longer-term noise, but the base level seems so low that it would be hard to separate out longer-term noise without a thermally and electrically quiet environment.I guess this is what you get when you put high-end parts in an oven and run it for a couple of decades.

author: zhtoor
author_rank: Frequent Contributor
timestamp: April 30, 2018, 01:03:22 am
content: maybe use the method described in this paper.best regards.-zia

author: chuckb
author_rank: Frequent Contributor
timestamp: April 30, 2018, 01:44:21 am
content: Quote from: chuckb on June 03, 2017, 12:35:18 amIn this previous post I provided F732A - F732A noise data for 100 hours. It has an attached pdf.

author: kj7e
author_rank: Frequent Contributor
timestamp: April 30, 2018, 01:45:51 am
content: Pipelie also provided some 732a noise measurements here;https://www.eevblog.com/forum/metrology/kx-reference/msg1375033/#msg1375033Here is the link to chuckb's measurement referenced above;https://www.eevblog.com/forum/metrology/more-than-one-reference-all-together-why/msg1224132/#msg1224132

author: martinr33
author_rank: Frequent Contributor
timestamp: April 30, 2018, 04:44:53 am
content: Thanks, those links are perfect, and are consistent with what I am seeing, at least in the short term.There's no doubting that nanovoltmeter and the differential method.Interesting that the noise on the 732a roughly matches that of the 3458a.

author: HighVoltage
author_rank: Super Contributor
timestamp: April 30, 2018, 09:22:09 am
content: Quote from: Flinstone on April 30, 2018, 09:00:57 amWhat settings did you use for NPLC?What is the best settings for the Keithley DMM7510 to detect noise?May be low NPLC and no filter?

author: Kleinstein
author_rank: Super Contributor
timestamp: April 30, 2018, 01:35:44 pm
content: Quote from: HighVoltage on April 30, 2018, 09:22:09 amAs the DMM7510 uses averaging sorter conversions to get the very long integration time, I would suspect to use a PLC setting similar to that for internal averaging (e.g. 1, 3 or 5 PLC). No filter is a good idea, and also using AZ is likely needed for longer times.However it also depends in which noise frequencies you are interested. In the simple case of using RMS calculation the data rate and sample length set the frequency range. To get close to the common 0.1 -10 Hz range, I would expect about 1 PLC with sync AZ (and thus 24 / 29 reading per second) and than a set of data to cover 10 seconds.

author: kj7e
author_rank: Frequent Contributor
timestamp: April 30, 2018, 03:42:03 pm
content: For the 7510, hidden in the 1000+ page reference manual (sitting in front of me) NPLC of 2 or 5 for lowest noise. I usually use 5. I found no difference with the Line Sync on or off in my case. Also be sure to use Auto Z. Math filtering will only mask noise, not reduce it.

author: alm
author_rank: Super Contributor
timestamp: April 30, 2018, 08:01:45 pm
content: How would you describe the difference between reducing noise and masking noise? Is a low-pass filter reducing or masking noise? Or analog averaging (integration)? What about a DSP implementation of that same filter?

author: kj7e
author_rank: Frequent Contributor
timestamp: April 30, 2018, 08:37:57 pm
content: Quote from: alm on April 30, 2018, 08:01:45 pmIdeally, the measuring device would have zero noise so only the DUT noise would be measured. You can optimize the instrument for minimal noise, but the math averaging functions will mask the noise of the DUT.

author: Andreas
author_rank: Super Contributor
timestamp: May 01, 2018, 07:02:57 pm
content: Quote from: Flinstone on May 01, 2018, 03:56:43 amHello,if you want to measure noise then you should ever define the kind of noise and the bandwidth.so what kind of noise do you want to measure?- wideband noise (uVeff) (e.g. 10Hz-100kHz)example measurement setup with a AN83 (LT) amplifier (1000:1) and a digital scope (RMS) or AC RMS millivoltmeter.- 1/f noise (uVpp) (e.g. 0.1 - 10 Hz)example measurement setup with a LNA (10000:1) and a scope (2mV/div resulting in 0.2uV/Div)- popcorn noise (uVpp)(usually below 1 Hz)longer pulses could be measured with a >= 6.5 digit DMM (if below 1uV resolution can be obtained by HPIB/RS232)shorter can be observed with a 1/f measurement setupof course you should always determine noise floor of your setup (e.g. measuring 8 AA NiCd/NiMH cells at constant temperature).with best regardsAndreasEdit: be aware that AN83 contains a bug regarding frequency response.To get a flat frequency range you have to change R9 = 5K19

author: blackdog
author_rank: Frequent Contributor
timestamp: May 02, 2018, 07:27:34 am
content: Hi Andreas,Allready a long time i have the components on stock for building the AN83 amplifier.You mention this:To get a flat frequency range you have to change R9 = 5K19I cant find a R9 in this schematic, it is not the alcohol, but maybe my old ageCan you explane please.Kind regards,Bram

author: Andreas
author_rank: Super Contributor
timestamp: May 02, 2018, 06:46:32 pm
content: ok my faultR9 refers to the PCB of branadic that I use.In AN83 it is the 5.62 K resistor.with best regardsAndreas

author: blackdog
author_rank: Frequent Contributor
timestamp: May 02, 2018, 07:54:59 pm
content: Hi Andreas,Thanks!Bram

author: czgut
author_rank: Contributor
timestamp: July 20, 2018, 02:12:50 am
content: Re. 732A noise:When I compared 10V between two Fluke 732A units with Solartron 7081 multimeter, Avg change of difference of voltage was about 0,155uV std dev; 0,918uV p-p/12hours.7081 at 0.1V level has noise about 25nV std dev, so it seems that one 732A unit (assuming their noise is similar) generates about 0,108uV std dev, 0,68uV p-p/12 hours.Integration time of single measurement was 51.2s , so this noise was for frequency (0.02 Hz. ..0,00002 Hz).