optimal configuration of HP 3458A to measure 10k - Page 1
Forum section: electronics / general

author: e61_phil
author_rank: Frequent Contributor
timestamp: March 01, 2018, 09:16:19 am
content: Hi,I know, we discussed that already severeal times, but it is hidden in various threads.So the question is: "How to configure the 3458A to get the most accurate 10k reading"My current configuration is the following:OHMFRANGE 10000OCOMP ONDELAY 2APER 1NDIG 8Is there anything to improve?I take several measurements with this configuration and calculate the average.BestPhilipp

author: TiN
author_rank: Super Contributor
timestamp: March 01, 2018, 10:24:39 am
content: DELAY depends on cable, some cables might need as high as 5, but most high quality cables are fine with 1-3 sec.you may want to NULL meter with short prior to DUT if possible.Or notAlso beware tempco, 3458A (at least mine) are not that great in this respect, so you either run ACAL every 0.5c or characterize tempco of the meter itself by using thermally anchored DUT resistor first.Keithley 2002 is much better for tempco in this respect on 10K range.

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 01, 2018, 11:20:19 am
content: Singular measurement samples will have too big an error, as the noise / standard deviation in Ohm mode is at least 0.2ppm of range.Therefore it's mandatory to invoke the statistics function for measurements.By measuring the StD also, you will have control over possible erroneous measurements, as can happen easily by external disturbance. If you observe an excessive StD value, just skip the measurement.With these above settings, take 16 readings and use mean value for the Ohm value, and the StD value as its uncertainty value (plus calibration uncertainty, of course).The setting for my 10k resistors and cabling, and the 'workflow' for taking measurements is therefore:OHMFRANGE 10000NDIG 8OCOMP ONDELAY 1APER 1NRDGS 16TRIG HOLDMATH STATTRIG SGL or TRIG=>RMATH NSAMPRMATH MEANRMATH SDEVI have stored the settings in the first block to a State, to be accessed by e.g. RSTATE 2, and the MATH functions are assigned to several Keys, copied that configuration from the FLUKE 3458A/HFL.A single measurement then lasts about one minute.Once configured that way, you can easily repeat the measurement, or measure the next resistor by pressingMATH STATTRIGPS:MATH NULL is not recommended, because OCOMP and 4W function already compensate NULL errors. Additionally, for using NULL, you would have to change the cabling configuration and would probably subtract a residual Offset which has nothing to do with your 10k DUT.Also, MATH NULL will delete the STAT function, and it's difficult to invoke both functions in a logically correct manner.Frank

author: PartialDischarge
author_rank: Super Contributor
timestamp: March 01, 2018, 11:27:41 am
content: Add AZERO ON

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 01, 2018, 11:32:22 am
content: Quote from: MasterTech on March 01, 2018, 11:27:41 amAZERO is on by default, but is not necessary due to OCOMP ON, as this automatically subtracts voltage offsets from the DUTs wires, but also internal voltage offsets.If you select OCOMP ON, the 3458A does not use a dedicated AZERO cycle any more, I strongly suppose, because the measurement time is not increased over about 4 seconds / sample.

author: PartialDischarge
author_rank: Super Contributor
timestamp: March 01, 2018, 11:44:24 am
content: Quote from: Dr. Frank on March 01, 2018, 11:32:22 amTrueQuoteAre you sure?? I'm not that sure about that, and the manual does not suggest that exclusive behaviour anywhere. Someone even posted this question regarding his suspicion on the inner workings of OCOMP and AZEROhttps://community.keysight.com/thread/20408

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 01, 2018, 11:53:32 am
content: Quote from: MasterTech on March 01, 2018, 11:44:24 amI'm pretty sure, because I wondered, why the sampling time did not double by using OCOMP ON.The manual is lacking some information at several instances

author: e61_phil
author_rank: Frequent Contributor
timestamp: March 01, 2018, 12:10:11 pm
content: Thanks for your comments!It seems to be already the right setup, that I used.Quote from: Dr. Frank on March 01, 2018, 11:20:19 amI do all statistics on the computer.As an example I attached a measurement of my SR1010-1k Transfer Standard (R1-R10).Std. Deviation is 0.38ppm over 1000 MeasurementsTemperature was well within 22°C +/- 0.1°CBestPhilipp

author: Alex Nikitin
author_rank: Super Contributor
timestamp: March 01, 2018, 12:43:09 pm
content: Quote from: TiN on March 01, 2018, 10:24:39 amYes, the tempco of our 3458A on 10K is somewhere between 1 and 2 ppm/C. It is about the same on my 3456A meter at 10K.CheersAlex

author: Dr. Frank
author_rank: Super Contributor
timestamp: March 01, 2018, 01:08:01 pm
content: Quote from: Alex Nikitin on March 01, 2018, 12:43:09 pmI assume, that's the T.C. w/o ACAL?It's specified 3.1ppm/K, but 1ppm/K with (or right after) ACALFrank

author: TiN
author_rank: Super Contributor
timestamp: March 01, 2018, 01:15:50 pm
content: Yes, of course. ACAL helps, but not very practical if ambient is unstable due to 860 seconds wait time.

author: e61_phil
author_rank: Frequent Contributor
timestamp: March 01, 2018, 01:26:42 pm
content: Why is the K2002 that much better? Is the VHP101-40k only used for the ACAL and not for 10k in the 3458A? Or is it the circuit around?And how is it done in the K2002?

author: TiN
author_rank: Super Contributor
timestamp: March 01, 2018, 01:43:32 pm
content: It's kinda obvious if one look at2002 current sourceand 3458A current source schematics and resistors used.And no, 40K not used in resistance measurement directly.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: March 01, 2018, 01:53:05 pm
content: Quote from: Dr. Frank on March 01, 2018, 01:08:01 pmYes, without ACAL. ACAL helps but doesn't remove the temperature dependency completely (so even after ACAL the measured value somewhat depends on the ambient temperature).CheersAlex

author: dl1640
author_rank: Regular Contributor
timestamp: March 13, 2018, 12:35:59 pm
content: I'd rather wonder how to make a correct null on 3458 before measuring a voltage source, 1) null by copper short on 3458 binding posts, 2) null by shorting measurement leads, 3) null by measuring voltage source set at 0V and output on, 4) dont null..

author: TiN
author_rank: Super Contributor
timestamp: March 13, 2018, 01:20:52 pm
content: Depends on what you trying to do. Usually it's 3.

author: CalMachine
author_rank: Frequent Contributor
timestamp: March 13, 2018, 01:40:24 pm
content: Quote from: dl1640 on March 13, 2018, 12:35:59 pmDepends on where you want your plane of reference to be. At the end of your leads? At the front of your meter? At the front of your source?

author: cellularmitosis
author_rank: Unknown
timestamp: March 13, 2018, 11:09:30 pm
content: Quote from: CalMachine on March 13, 2018, 01:40:24 pmWhat might determine that? Perhaps, "Am I shipping the cables with this reference, or not?"

author: CalMachine
author_rank: Frequent Contributor
timestamp: March 14, 2018, 12:25:04 am
content: Quote from: cellularmitosis on March 13, 2018, 11:09:30 pmGenerally personal preference.

author: dl1640
author_rank: Regular Contributor
timestamp: March 14, 2018, 12:35:17 am
content: IMO it is good to use method 3 if check "gain", but to check "zero" output from the source, one would consider to null out any cabling effect and/or DMM "residual" reading beforehand. Some would use method 2, to short two leads and let them hanging in the air, or short them at either of the source terminal, then take a null, then change the cable config to gain measurement, this means the cable config at null measurement and gain measurement are diffierent, I am not sure if such null is correct for precise application. Most of time I do not have to measure down to a few or sub ppm, so I do not null, method 4.Please correct me if I'm wrong.Also, I think method 1 can be used to check the "true" null of DMM, but need a good copper short.

author: CalMachine
author_rank: Frequent Contributor
timestamp: March 14, 2018, 02:11:39 am
content: Quote from: dl1640 on March 14, 2018, 12:35:17 amYes, as you pointed out, each scenario is applicable to certain situations!

author: dl1640
author_rank: Regular Contributor
timestamp: March 14, 2018, 03:15:29 am
content: For precise DCV measurement, I would consider a remote controlled switch to form and release a short at DUT end. This is method 2.For Ohm measurement, I use 4-wire, OCOMP ON, and Delay 1, NPLC 20~100.

author: e61_phil
author_rank: Frequent Contributor
timestamp: March 14, 2018, 05:12:14 pm
content: Quote from: dl1640 on March 14, 2018, 03:15:29 amThis controlled switch should be very good. Most relay contacts I know are specified with around 2µV.

author: dl1640
author_rank: Regular Contributor
timestamp: March 15, 2018, 12:22:20 am
content: Or, if the source has binding posts, then just leave the cable config as gain measurement (Hi-Hi, Lo-Lo), and place a good copper short in between the binding posts, I think this is a good null, then remove copper short and measure gain.

author: voltampere
author_rank: Regular Contributor
timestamp: April 11, 2018, 06:50:50 pm
content: I hope the answer to my question is not just a trivial thing that i could have found in the manual myself!I am scratching my head regarding the use of the APER vs the NPLC command.According the manual it should have the same rersult! ( as far as i understood it ).Meaning if i set APER 1 then the integration time should be 1 second.And if i say NPLC 50 then it should also be 1 sec, right ( on a 50 Hz model ).I tried the APER command like thisDELAY 1APER 1NRDGS 15And it will take roughly 89 sec to complete the 15 readings. ( hand measured, +/- 1 sec ).If i useDelay 1NPLC 50NRDGS 15then it will take roughly 204 sec to complete 15 readings.OCOMP ON for both sessions.It is the first time i used the APER command because Dr. Frank mentioned it in his reply!Furthermore:If i command APER 1then i get the following results when querying:NPLC ? -> 50APER ? -> 1.0 E+0If i command NPLC 50i get the following results:NPLC ? -> 50.0 E+0APER ? -> 200.0 E-03I hope somebody can shine a light for me!RegardsJoergEDIT:Typo ; it looked like i used the same commands; instead it should read NPLC 50 on the second run ( with 204 sec )

author: Echo88
author_rank: Frequent Contributor
timestamp: April 11, 2018, 07:41:49 pm
content: Please take a look a Dr Franks nice summary in a related thread:https://www.eevblog.com/forum/metrology/hp3458a-ocomp-delay-related-problems/msg1464930/#msg1464930If you use a setting in which NPLC is greater than 10 NPLC, the 3458A just averages the samples of multiple 10 NPLC measurements. Also delay and OCOMP are used on every 10NPLC, so this leads to such a large measurement time. The APER-command integrates over the whole time instead of doing the mathematical 10NPLC/DELAY/OCOMP-averaging, therefore saving sample time.Here are a few measurements i did which show the timing on a 3458A:#OCOMP OFF, Delay default, NPLC 10,AZ OFF -> 0.2s#OCOMP OFF, Delay default, NPLC 10,AZ ON -> 0.4s#OCOMP OFF, Delay 1, NPLC 10,AZ ON -> 1.4s#OCOMP OFF, Delay 2, NPLC 10,AZ ON -> 2.4s#OCOMP ON, Delay default, NPLC 10, AZ OFF -> 0.4s#OCOMP ON, Delay default, NPLC 10,AZ ON -> 0.8s#OCOMP ON, Delay 1, NPLC 10,AZ ON -> 2.77s#OCOMP ON, Delay 1, NPLC 10,AZ OFF -> 2.38s#OCOMP ON, Delay 2, NPLC 10,AZ OFF -> 4.33s#OCOMP OFF, Delay default, NPLC 100,AZ ON -> 4.05s#OCOMP ON, Delay default, NPLC 100,AZ ON -> 8.25s#OCOMP ON, Delay 1, NPLC 100,AZ ON -> 27.26s#OCOMP ON, Delay 1, NPLC 50,AZ ON -> 13.65s#OCOMP ON, Delay 1, APER 1,AZ ON -> 5.97s

author: voltampere
author_rank: Regular Contributor
timestamp: April 11, 2018, 07:55:58 pm
content: Thank you for pointing!Should have found that by myselfThat makes sense and your numbers are equal to mine.But still it doesn´t explain why a query APER? gives an aperture of 0,2 sec after i set 50 NPLC.Any explanation for it?

author: dl1640
author_rank: Regular Contributor
timestamp: April 11, 2018, 10:18:39 pm
content: I didnt see difference between your 2 sets of cmds, APER is straightforward but it is only settable between 500ns to 1s.NPLC 50 is identical to APER 1 in 50Hz system, unless you specify by LFREQ LINE which will set integration time to a actually measured line frequency, dont if it really helps to improve any measurement.Yes, APER 1 saves time of measurenent than NPLC 50.QuoteI set NPLC=50, DELAY=1, measure dc currentthe data update rate is less than 3s, that is the DELAY is not inserted into each 10PLCso, 50PLC = average of 10PLC is true and the user manual does say thatbut DELAY is used on each 10PLC, is not true, for all conditions at leastalso, if I set 50PLC, the APER? is returned as 200ms, yes it is

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 12, 2018, 06:28:03 am
content: NPLC 50 overrides the APER 1 setting, and splits the continuous 1sec aperture.As NPLC 50 consists instead of 5 measurements, APER? delivers the 200ms aperture of each NPLC 10 measurement.I recommend to test a longer DELAY if using NPLC 50 instead of APER 1.Frank

author: aronake
author_rank: Frequent Contributor
timestamp: April 26, 2024, 05:03:22 pm
content: When making 10K ohm measurements on 3458a, can somehow usage of the guard terminal and guard switch be of any help?