NI PXI-4071 DMM Calibration - Page 1
Forum section: electronics / general

author: NANOJOLTS
author_rank: Contributor
timestamp: June 27, 2024, 10:58:43 pm
content: Here's my situation.Having accumulated a inventory of some 17 NI PXI-4071 7.5 digit DMM's.Some when acquired were found with recorded calibration dates still within their 2 year specs.Having compared the published specifications with other 7.5 dig. DMM'sE.g., Keithley, Fluke, Keysight, ect.These NI PXI DMM's seem to have "mostly better" Dc Volts and Ohms specificationsthen any of the other comparable brands E.g., Keithley, Fluke, Keysight, ect.Excluding the 8.5 dig. models for the moment.I thought I would, through Labview "calibrate" a batch of 5 of the these PXI DMM's and compare the results.The NI calibration procedure calls for a Fluke 5720a (90 day spec.) configured for the following outputs of+/-0.1 and +/-10 DC volts and 10K, 100K, 1.9M, 10M, 100M Ohms. Calibration coefficients stored to the DMM EEPROM.In lieu of the Fluke 5720a I utilized the following standards.For DC Voltage a (Krohn-Hite 523 source) and for resistance standards one IET SRL-1K and one IET SRL-100 Ohm inconjunction with and a dozen or so transfer standards consistingof the following ESI SR1010/SR1030/SR1050, configured to yield the required resistance standards.Although beyond the their calibration date, these DC voltage and resistance standards should remain stable enough todo a "relative calibration".The goal would be, after calibration, one could over time, compare the calibrated DMM'sto the standards and predominantly to one another and track how far they drift from one another and from thestandards. Could utilizing these data confer their relative accuracy/stability?As it turns out, after about a year, comparing the 10V measurements of 5 DMM's resulted in less than2ppm difference from one another. So what if any conclusions could be drawn?So having the DMM's calibrated to the same standards a later relative comparison of the DMM's measurementsshould remain within the DMM's specifications?Oh by the way these DMM's utilize something called a LTZ1000.

author: coromonadalix
author_rank: Super Contributor
timestamp: June 27, 2024, 11:07:09 pm
content: 17x pxi boards, you sit on a gold mine lollif you want a reference dmm, you need to calibrate it once a year, and not thru "non official standards" ..i dont understand your labview things ... labview help create interfaces for "your stuff", if you have access to calibration commands, yes you can build anything you wantNI-DMM offline is 2.6 gig of filecalibration documenthttps://www.ni.com/docs/en-US/bundle/pxi-4071-cal-pro/resource/371281h.pdfspecs and infoshttp://www.trinergy.co.th/pdf/ni-pxi-4071.pdfand finally seeing their used prices ... i would better go with an bench one, based on the same ltz 1000 reference ...

author: NANOJOLTS
author_rank: Contributor
timestamp: June 28, 2024, 12:38:10 am
content: Here's a picture chart of 3 of the dmm's 10v DC EDC 522 source.Anyone have something similar?

author: NANOJOLTS
author_rank: Contributor
timestamp: June 28, 2024, 12:40:55 am
content: Try post pic again.

author: CalibrationGuy
author_rank: Unknown
timestamp: June 28, 2024, 02:27:31 am
content: You did not say what your requirements are. What are the dmm cards being used for? Perhaps the easiest way to calibrate these is to send one in for calibration and use that one to calibrate all the others. You could also reach out to the cal club here.TomG.

author: NANOJOLTS
author_rank: Contributor
timestamp: June 28, 2024, 03:24:26 am
content: No requirements really, Actually I started comparing my PXI DMM's to the "DMM Noise comparison testing project". But I didn't find any PXI DMM's in the test.My PXI DMM's seem to have lower noise than all the other DMM's except the 3458a, and even at that they were very close. I'm working in a bubble so that mysetup could be of by a mile. I use Labview and it's close variants which seem to held in great disdain by many on this forum. I'm just curious how these PXIDMM's stack up in real world, there published specifications read very well.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 28, 2024, 05:58:41 am
content: The spec file shows low noise at low PLC, but also extra noise for 10 PLC and more. The shown curve also shows some lot frequency noise, though this could be just reference LF noise from 2 x LTZ.The extra LF noise can be thermal in nature and thus dependent on the case / environment. The orientation of the card could already make a difference in thermal noise.The ADC seems to be a SD type and this may mean that adjecent readings may not be independent. This can be decieving with the bandwith / effective integration time. So 1 PLC may not be fully comparable to 1 PLC on other meters.

author: zrq
author_rank: Frequent Contributor
timestamp: June 28, 2024, 09:48:33 am
content: Off topic but do you plan to sell some of the 17 cards? I regret that I missed out for the recent ebay auction...

author: NANOJOLTS
author_rank: Contributor
timestamp: June 28, 2024, 01:31:33 pm
content: I'll post comparison spec sheets 3458a and PXI-4071, apples to apples?I would need a $1000 to sale one PXI-4071.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 28, 2024, 06:23:37 pm
content: The specs file linked earlier showed quite some extra low frequency noise. The last graphs could be for an improved version with less noise or possibly just cacluated back from 1 PLC ignoring the possible and likely thermal LF noise.Another explaination could be that the other file is for true N PLC at a time, while the other is averaging over 1 PLC conversions instead and thus the theoretical square root N law going down.Another odd point is the noise multipliers. The 1000 V ranges should have a slight higher noise, like 5-10% more from the divider - maybe not enough to show.For the 100 V range things are odd too: the value of 2 for the 3458 looks a bit optimistic as the divider resistor alone should give about much noise.The factor of 6 for the NI card is rather high - maybe there is no true 1 or 100 V range (e.g. a gain of only 3 maybe) - the 100 mV range specs suggest a rather good amplifier and not much added noise from the protection.The noise level of 1 µV_RMS for 1 PLC in the 10 V range is actually not that difficult and unusual. The HP3446x are not much higher and the DMM7510 is also about there (though with problems for longer integration). For the 3458 most of the new units seem to be usually well better than the noise specs. Part of what makes it a 8 digit meter is the performance at longer integration (e.g. 100 PLC), actually getting to 0.01 ppm for the RMS noise. If the curve with LF noise is true the PXI-4071 never gets there and gets worse beyond some 20 PLC.

author: NANOJOLTS
author_rank: Contributor
timestamp: June 28, 2024, 08:37:27 pm
content: I generally use charts/graphs to compare the various DMM attributes and try to emulate the modes/function as described in the"DMM Noise comparison testing project".Oddly the HP3446x series seem be less noisy than the 7510 and many of the other DMM's, according to the comparison plots.It wound be nice to compare the various DMM's side by side. Published Specifications do not always tell the full story.I have some other DMM's a few PXI-4070 6.5 DMM. Also (10) Prema 6001 6.5 dig. and (4) Prema 5017 7.5. dig,very good specs, both Prema's incorporate the LM399. and one Agilent 34401a.NI claims there newer PXIe-4081 DMM 7.5 dig. has the highest accuracy DMM?