Vishay VHP101 out of tolerance? (or HP 3458A) - Page 1
Forum section: electronics / general

author: e61_phil
author_rank: Frequent Contributor
timestamp: June 01, 2016, 06:26:42 pm
content: Hi,today my VHP101 10k 0.001% resistors arrived (2 pieces). I tried to measure the resistors with a HP 3458A and the result was 0.0018% (0.0019%) below 10k. The reading was very stable. The 1-year specification for the 3458A is 10.5ppm for 10k. I had a look into the calibration sheet from last year (10 montah ago) and the meter had 7ppm difference to the calibrator. The calibration uncertainty was 0.12R (12ppm) (Isn't it to bad for a 3458A calibration?).I'm very suprised with this result.Whats going wrong here? Is the resistor out of spec or the meter? Or is this the sum of tolerances? In this case both have to be in the same direction with maximum tolerance.3458A settings: 4W, 100NPLC, Offset Compensation ON, the meter was running till days, the fan is clean and I performed a AUTOCAL before the measurementThanks in advancePhilipp

author: e61_phil
author_rank: Frequent Contributor
timestamp: June 01, 2016, 08:44:51 pm
content: I will try another 3458A in the next days. If the resistors is out of tolerance I would ask Vishay whats going on.

author: Dr. Frank
author_rank: Super Contributor
timestamp: June 01, 2016, 08:47:57 pm
content: In 2010, I also ordered several VHP202Z, 9k9998, 0.001%, complete with a measurement protocol.First problem was a stable environment, a stable 4W assembly, and reliable measurement of temperature.You can't trust Vishay for their claimed low T.C. (VHP101 maybe better, anyhow)Without that, you can already have several ppm deviation by temperature.Later, when I compared my finished 10k standard against 'quarks' one, it turned out, that all resistors were 10ppm lower than measured by Vishay, so that even the +/-10ppm spec was not met.Second problem, Vishay might have cycled the resistors to +125°C to check the butterfly T.C.This caused about +5ppm hysteresis to both resistors, which I sent in for re-check.Do you have a measurement protocol from Vishay?For the 3458A, Keysight offers several, very different level of calibration.I have lurked into several calibration certificates, and one of them also contained a detailed Test Report.The standards used were really bad, and they could really not definitely test to the original 1 yr. limits..So your test report should tell, which references they used, and maybe they also gave you the as found values/deviation, so you might find out, in which direction your instrument deviates.(This is normally not given, very strange).Also, take into account any temperature deviation from cal temperature.. might be as high as 1..2ppm/K!What is the vintage of your 3458a?If it's before about 1995, you might have the old, less stable 40k reference inside. After 1995, it should also be a VHP101, so T.C. and ageing is much lower than specification.If you dare to open your unit and have a peek on this resistor, you might tell for sure.In the end, I agree to DiligentMinds, that everything is inside spec, especially as you did not tell anything about the direction of your 3458As deviations.In the end, a practical and straight forward proposal, to decide what's going on:I could measure your resistor under controlled temperature conditions, for a 2nd opinion.I estimate my own reference resistors to have about 1ppm uncertainty.Frank

author: e61_phil
author_rank: Frequent Contributor
timestamp: June 01, 2016, 09:15:44 pm
content: Unfortunately, I have no protocol from Vishay.I think even with the old resistor the 3458A should meet the specs? I'll try to find out how old the units are (both HP brand).

author: zlymex
author_rank: Frequent Contributor
timestamp: June 02, 2016, 05:22:18 am
content: I don't trust my 3458A, I use it mainly for linearity, repeatability and low noise.I don't trust Vishay neither, so I buy 0.1% only for their hermetic foils when ever possible.

author: ap
author_rank: Frequent Contributor
timestamp: June 02, 2016, 09:01:17 am
content: It is not unusual that precision gear (such as the 3458A or calibrators like the Datron 4808) are calibrated using standards that are just inadequate. And certainly e.g. a 5700 is not good enough to verify a 3458A. I saw a Datron 4808 that was AC-calibrated with a HP8903. Keysight iirc specifies (3458A cal. manual) uncertainties for the 10V and 10k of 2 respectively 3ppm. Not very precise given the price of calibration. With a few well maintained standards and some other gear such as a KV-divider one can do better.I maintain 10k and 10V/1V calibrated to in the range of 1ppm, and other gear derived from that. Could check your resistor if you want (no charge).

author: EEVblog
author_rank: Unknown
timestamp: June 02, 2016, 09:20:42 am
content: Quote from: e61_phil on June 01, 2016, 06:26:42 pm10ppm is already 0.001% so you are within the basic uncertainty of your meter + resistor.

author: e61_phil
author_rank: Frequent Contributor
timestamp: June 02, 2016, 10:03:58 am
content: Quote from: EEVblog on June 02, 2016, 09:20:42 amOnly when both are at maximum tolerance and in the same direction.Quote from: e61_phil on June 01, 2016, 06:26:42 pm

author: Alex Nikitin
author_rank: Super Contributor
timestamp: June 02, 2016, 10:14:41 am
content: Quote from: e61_phil on June 01, 2016, 06:26:42 pmHi Philipp,Did you add a delay? It is required to add a 1s delay for this kind of Ohms measurement, otherwise you may get additional errors. It is described in the short (1 page) user's guide to the 3458A Front Panel Operation.Google finds that guidehere, for example.CheersAlex

author: e61_phil
author_rank: Frequent Contributor
timestamp: June 02, 2016, 10:49:45 am
content: Quote from: Alex Nikitin on June 02, 2016, 10:14:41 amNo, but I read a thread from Dr. Frank with this issues, but I couldn't find the setting in the manual under Offset Compensation.Your link is great. THANKS!

author: Alex Nikitin
author_rank: Super Contributor
timestamp: June 02, 2016, 02:20:04 pm
content: Quote from: e61_phil on June 02, 2016, 10:49:45 amThank you, it would be interesting to know it the delay makes a difference in your case or not?CheersAlex

author: Dr. Frank
author_rank: Super Contributor
timestamp: June 02, 2016, 03:26:25 pm
content: Great find in this 1 sheet user guide.. this hint totally misses in all other documents..Though, the effect (dielectric absorption) is still not sufficiently understood there, as it's depending on the Ohm range, correlated with the measuring current AND the resistance of DUT.For the 10k range, one needs >=1sec, otherwise errors on the order of 1ppm may occur.For the 100k range, >= 5sec is needed, otherwise 10..30ppm can be observed.For ranges <= 1kOhm, the normal delay of 30msec is sufficient, no essential error will be seen.In this case, the missing delay will not play a role.Frank

author: e61_phil
author_rank: Frequent Contributor
timestamp: June 02, 2016, 06:01:08 pm
content: I did some further measurements today. I also tried our Keysight 34470A's (I didn't try this units earlier, because even their 24h specification isn't suitable to verify the tolerance).The delay on the meter I used at first (3458A#2) didn't change the reading enough to bring the reading close enough to 10k (see attachment).The spec of the 34470A is quite bad, but the readings look very good. These meters are all younger than one year and only factory calibrated. All the meters showed 0ppm deviation from the 5720A at Keysight.Both 3458A showed the same value at last calibration (and therefore both 2.7ppm higher than the standard). And now the reading seems to be at bit low compared to the 34470A's.I'm very curious about the next calibration of the 3458A's.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: June 02, 2016, 06:45:25 pm
content: Quote from: Dr. Frank on June 02, 2016, 03:26:25 pmAs you may see, Philipp has measured 4 to 5ppm difference on both his 3458A meters.CheersAlex

author: Dr. Frank
author_rank: Super Contributor
timestamp: June 02, 2016, 07:04:53 pm
content: Your thread is getting more & more interesting..Concerning the Ohm-uncertainty of the 34465A/470A, I did a review:https://www.eevblog.com/forum/testgear/keysight's-new-34465a-(6-5-digit)-and-34470a-(7-5-digit)-bench-multimeters/msg889215/#msg889215These (practically identical) instruments are really better than their specification, so you can rely on their Test Report.~1ppm uncertainty for a freshly calibrated instrument can be expected.In another thread, I found out, that the 34465A/470A, using OCOMP, did not necessarily need 1 sec delay like the 3458A, as the APERTURE equals 1sec at NPLC100, which already provided sufficient long settling time. Anyhow, you might also use several seconds delay on the 34470A, to cancel this relaxation error even further.You may also set the 3458A explicitly to APER 1, instead of NPLC 50, to improve its accuracy further.Concerning the 3458As, the calibration standard obviously had +/- 8.5ppm uncertainty already, so that the deviation from the measured Vishay value can very well be explained.By first subtracting these +2.7ppm, and then adding 8.5ppm, the 3458A #1 and 34470A #3, #4 from February do agree.It's very probable, that the Vishay resistor has about -5ppm deviation from default value.Concerning the drift of the 3458As over 1/2 year, this may depend on their vintage. TiN just opened a thread about the A1 board, and its DCI resistors.https://www.eevblog.com/forum/metrology/3458a's-current-shuntsresistance-current-source-tempco-study/msg952201/#msg952201If the instrument is produced between 1989 and ~ 1994, it will contain the initial 40k Ohm reference from Vishay, which defined the original specification, 10ppm/year and 1ppm/°C in this case.If it's a later instrument, it will contain VHP101 resistors, which are specified by Vishay as 0.3ppm/K and 2ppm/6years.. so being much more stable. agilent and Keysight marked instruments for sure contain VHP101 already.If you would publish the serial numbers, maybe blanking the last two digits , their date of production could be determined, and their assumed stability.Frank

author: e61_phil
author_rank: Frequent Contributor
timestamp: June 02, 2016, 09:32:50 pm
content: Quote from: e61_phil on June 01, 2016, 06:26:42 pmSorry for confusing. That was the wrong line in the calibration sheet (it was for 2W). The +2.7ppm ist the right value for 4W.Tomorow, I will have a look at the serial numbers and I will test the APER 1 setting.@Frank and ap: How do you reach 1ppm uncertainty? Direct calibration at the PTB? I haven't seen any callab which provides 1ppm of uncertainty.

author: Dr. Frank
author_rank: Super Contributor
timestamp: June 02, 2016, 10:19:28 pm
content: It's an estimation only. That means, no certificate. Nobody (nearly) could afford a PTB cal, or else.In fact, it's a conglomerate of quarks, acbern, and 2-3 34465/470A calibrated instruments, all were within 1ppm, not by chance, obviously.Frank

author: acbern
author_rank: Frequent Contributor
timestamp: June 02, 2016, 10:53:04 pm
content: There are a couple of labs out there that can do better than 1ppm at reasonable costs. Had a 10k resistor calibrated at to less than 1ppm (ISO). This may vary though, last cal was only to slightly above 1ppm. 10V was about 0.3ppm.

author: e61_phil
author_rank: Frequent Contributor
timestamp: June 03, 2016, 08:25:23 am
content: The HP 3458A serial numbers are:2823A009XX2823A002XXHow do you find out, how old the units are?

author: EEVblog
author_rank: Unknown
timestamp: June 03, 2016, 09:01:01 am
content: Quote from: e61_phil on June 02, 2016, 10:03:58 amHow do you know they aren't?

author: e61_phil
author_rank: Frequent Contributor
timestamp: June 03, 2016, 09:17:24 am
content: Quote from: EEVblog on June 03, 2016, 09:01:01 amI can't know it. But it is very unlikely. Even the tolerances from the 3458 are only 99% sure...

author: Kleinstein
author_rank: Super Contributor
timestamp: June 03, 2016, 09:37:11 am
content: Its not that unlikely the tolerances are in the same direction. There are only the two possibilities of same and different direction. If they where same direction the measured value would be rather close to nominal - something less people care about and remember.Its also not that surprising that the two new resistors are that close to each other. That is common because they are made the same way and checked / adjusted with the same instruments.

author: e61_phil
author_rank: Frequent Contributor
timestamp: June 03, 2016, 10:09:31 am
content: Now with 15ppm I can believe it. But at the beginning I measured 19ppm. Therefore, not only both tolerances have to be in the same direction, they also have to be at the maximum.I talked to our calibration partner and he is very sure, that the uncertainty of the Fluke calibrator is much much better than 8.5ppm. Next month the 3458A will go to the calibration lab. In the meantime I will improve my setup.

author: Dr. Frank
author_rank: Super Contributor
timestamp: June 03, 2016, 12:35:51 pm
content: Quote from: e61_phil on June 03, 2016, 08:25:23 amJoe Gellers site still contains several hints about this subject.http://www.gellerlabs.com/HP%203458A%20DMM.htmUnfortunately, he already removed the ser. no. list.The numbering for the 3458A changed several times, either when HP became agilent, or when manufacturing was transferred from U.S. to Singapore, and at last to Malaysia:The Prefix is accordingly: 2832Axxxxx => US280xxxxx => SG450xxxxx => MY450xxxxx.xxxxx is an incrementing number, starting at about 100 (in 1988/1989), and several thousand numbers missing, whenever they changed the prefix.Therefore, this xxxxx is a direct measure of an instruments vintage. Yours are very old, the 002xx being from 1989, the 009xx one or two years later, at most.Therefore, both contain the original 40k resistor, being not so stable.TiNs instrument contains the VHP101 already, and it is from about 1995, ser no 133xx.So they sold about 2000 instrument per year in the beginning, therefore 009xx very probable is from the very first production year, which is 1989, as this is the first appearance in the HP catalogue.Since several years, Keysight publishes all calibration certificates online, so you can peek, how many instruments are produced, and the approximate manufacturing date.The latest instrument as of today is 52790, calibrated on 31.5.2016.Older instruments are not contained, only if it gets re-calibrated at Keysight.Mine reads 2823A257xx, is marked "HP", and is not contained in the database.Adjacent serial numbers were produced in August 2000, that fits the date codes inside my instrument.Frank

author: e61_phil
author_rank: Frequent Contributor
timestamp: June 03, 2016, 07:24:03 pm
content: @Frank: Thanks for the information and the link. Our units have both this old dust filter. They seem really old.@Flintstone: Thanks. Our cal certs look quite simillar. Unfortuntely our cal partner use a Fluke 5700A instead of the 5720 as in your cert. But the report with the 5700A is more or less only an automated function test. For calibration/adjustment they use a good 10k reference (don't know which) and a 732B.

author: Dr. Frank
author_rank: Super Contributor
timestamp: June 04, 2016, 09:20:40 am
content: In this context, I'd like to recommend this Keysight channel about metrology and their different facilities:https://www.youtube.com/user/KeysightCalRepairBob Stern, their chief metrologist, presents a series of videos, including several virtual lab tours.Especially the video about Loveland Standards Laboratory is very interesting, which had been built in the 1980ties, exclusively for the verification of the 3458A.They have their JJA inside, and all 3458A in U.S., were calibrated there.Recently, a web based seminar covered these subjects also, "Accuracy matters: Calibration Options for Lab Standards Webcast":http://www.keysight.com/main/eventDetail.jspx?ckey=2689915&nid=-11143.0.00&id=2689915The Q&A session afterwards also was very instructiveFrank

author: quarks
author_rank: Frequent Contributor
timestamp: June 07, 2016, 08:36:59 am
content: unfortunately this is another topic I missed until now.afaik VPG is using a Keithley 2002 to meassure their tolerances and if you do not ask for data when ordering the resistors you do not get any data from them. I doubt that they are able/willing to give you the data afterwards.If you do not have a better reference to compare it to, you unfortunately cannot know if your resistor really is in tolerance or not.

author: e61_phil
author_rank: Frequent Contributor
timestamp: June 07, 2016, 09:04:38 am
content: I ask Vishay for some data, but they didn't respond until now.

author: Dr. Frank
author_rank: Super Contributor
timestamp: June 07, 2016, 10:07:07 am
content: In the measurement report, which I ordered in advance for my 10ppm resistors, they did not reveal the method, but obviously used a 1kOhm reference resistor, specified -2ppm. The designator of this standard is '1500 G 103', maybe something from ESI.I assume, they used sort of a bridge, but that would be a 11:1 relationship, maybe explaining the extra error.They measured each resistor three times, adding 2ppm for each value.Everything inside three times of plus or minus 10ppm was accepted.For my 5 resistors, they produced a total of 27, and 20 were 'good'.Maybe they are using a DMM for bigger tolerance resistors.FrankPS: I ordered 9k9998 resistors. Vishay measured them to have values of +7 , +8, and three times +6ppm, greater than the default value.The relative deviations were correct, but it turned out after several comparisons with calibrated resistors (quarks, acbern), that these all deviated in the other direction, i.e. instead they must have had about -14/-13/-15ppm of nominal. Something went completely wrong there.

author: ap
author_rank: Frequent Contributor
timestamp: June 07, 2016, 01:15:42 pm
content: First, i would not trust vishay here, simply because its a manufactured part, and not a calibration. Any cal report is probably more expensive than this resistor.Secondly, somewhere i think i remember having read they use a DCC current comparator bridge. One would expect that, by the way. That however would contradict the bad results. Maybe they just own one