ESI Resistance Standard SR1010 and Standard Resistor SR104 - Page 1
Forum section: electronics / general

author: quarks
author_rank: Frequent Contributor
timestamp: December 13, 2012, 08:18:22 pm
content: Hello all,because I am kind of crazy about stuff/gear related to metrology/calibration, I always try to get better accuracy than I already can achieve. I know this is stupid, because it will never be possible to have absolute accuracy. It always will be about the level of uncertainty and only confidence is what counts. But nevertheless I have fun with this kind of stuff and that keeps me going forward.Right now I am after resistance measurement accuracy and already asked for suggestions around that topic. My dream gear would still be Fluke 8508A but this seems to be hopeless. Therefore I decided to look for good resistor references. And the SR1010 and SR104 were the once I picked. I hope and I feel confident that this is a good choice for many, many years of fun with it.In Reply 42 of an old thread (Re: interested in hobbyist voltage reference standards?https://www.eevblog.com/forum/chat/interested-in-hobbyist-voltage-reference-standards/msg14369/#msg14369) saturation posted this very interesting link:http://translate.googleusercontent.com/translate_c?hl=en&sl=zh-CN&tl=en&u=http://www.hellocq.net/forum/showthread.php%3Ft%3D139719%26page%3D1%26pp%3D30&rurl=translate.google.com&usg=ALkJrhiE1Yx0OUNwnWa_mTxlFYkyoh49wQIn there I saw a chart named "Drift of 5 SR104 standard resistors at 23°C" that showed graphs with a recorded timeline from 1973 to 2008. The reported annual drift is around 0.07ppm over many years.Now I wonder if anyone has experience with Tegam/ESI/IET SR1010/1030/1050 and SR104 and likes to share it?I would like to know if anyone came across a similar drift information for SR1010 and if the drift of (only) this 5 SR104 is representative and this really can be expected.Also I have not yet understood how this resistance transfer really works, especially because I do not have the "Model 242D resistance Measuring System" mentioned as required equipment in the "User and Service manual".I hope someone is able and willing to share some knowledge or can give some hints.thxQuarksedit:finalized my research on this topic (meassured 14x SR1010s, result of 168 resistors, almost all were well in spec after at least 10 years of age, but drift is mixed, some drift positive some negative and allmost all with different rates (even within one idividual SR1010).Also meassured 2 SR104, both showed positive drift, like in the Chart mentioned above, but different rates.

author: doktor pyta
author_rank: Frequent Contributor
timestamp: January 11, 2016, 06:02:41 pm
content: Hi,I use SR104 in my lab. I needed to have quite well calibrated 100ohms standard resistor, so I've bought ESI SR1010 and got also parallel compensating network. The only missing part was SB 103 shorting bars, so I did it myself.Pomona 3770 terminals were used.Below You will find a link to my website and a .dwg file for those who want to use it.I used 2 mm thick copper base material, then 0,1um of silver plated layer and 0,3um of gold plated layer.The silver layer aim is to stop diffusion of gold into copper (and vice versa).Maybe there is to little gold on it but I wanted the bars to be quite inexpensive.More here:http://rfscientific.eu/esi-sb103-shorting-bars

author: alanambrose
author_rank: Frequent Contributor
timestamp: January 11, 2016, 10:11:43 pm
content: Wow, how did you do the plating?Regards, Alan

author: branadic
author_rank: Super Contributor
timestamp: January 11, 2016, 10:17:49 pm
content: Pretty uncommon putting silver as barrier between copper and gold, standard is a nickel - gold system, isn't it?

author: doktor pyta
author_rank: Frequent Contributor
timestamp: January 12, 2016, 06:48:43 pm
content: @alanambrose: Nope, I found a company which does electroplating since 1958. Gold plating requires a lot of experience and harmful chemicals.@branadic: as we all know, a typical buffer layer consists of nickel which is cheap however I was worried about thermal emf (as the gold layer is very thin in my case -may not be very reliable if the gold layer is scratched). The guys from electroplating company told me that they sometimes use high purity silver as a buffer layer with good results. The time will tell if this solution is suitable for protecting electric stuffPS. The users of SR1010 transfer standards should notice that when using it with SB103 and SPC102 (or PC101) theratiotransfer accuracy is independent from ageing of the internal resistors.PS2. Could someone measure the thickness of the original SB103 bar?PS3. SR1010 utilizes Hamon transfer scheme

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: January 13, 2016, 02:54:42 am
content: @doktor pytaI measure 1.70mm (from several locations) on the SB103 bar.

author: quarks
author_rank: Frequent Contributor
timestamp: January 13, 2016, 05:19:08 pm
content: good to see this old topic is still of interestabout the plating, Fluke uses gold plating over silver plating (contains no nickel) in the "Low Thermal Test Leads" 5730A-7003BTW very nice job, original looks like this (see att. pic)

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: January 14, 2016, 01:18:46 am
content: @QuarksThis is OT but ESI used lots of gold plating inside the SR-1050 too. They certainly are impressive to look at. Let me know, and I will post a few photos of mine in need of repair.

author: Vgkid
author_rank: Super Contributor
timestamp: January 14, 2016, 02:23:38 am
content: Nice job doktor pyta. The closest thing to a SR1010 i have is a SR1 resistor, plus 2 decade resistors.

author: quarks
author_rank: Frequent Contributor
timestamp: January 14, 2016, 09:40:46 am
content: Quote from: ManateeMafia on January 14, 2016, 01:18:46 amyes, please share it with us

author: acbern
author_rank: Frequent Contributor
timestamp: January 14, 2016, 04:05:23 pm
content: Moving all this into the new metrology folder has the nice effect that it is kind of reviving.Anyway, a few comments:SR104: I bought one around 2 years ago, it was built in the 70ties, to replace my home-brew 10k reference resistor (VPG hermetic, which has a track record so far to drift about 0,2ppm/a). At the time, I did not have a meter with a guaranteed ohms transfer accuracy (the 3458A does not have that). So I decided that I would apply a stable voltage to the SR104 in series with my 10k ref and compare the voltages (the 3458A is pretty good at that). That resulted in a deviation of less than 1ppm between the two, so by coincidence, they were more or less equal (at the 23C I measured them). I then, about 1+ year later, got other meters (a 7071, 1ppm resistance transfer accuracy, and a 1281, well below 1ppm transfer acc.), so I decided to redo the measurement, and in comparison also with a 3458A in ohms mode. To my surprise, I measured about 7ppm delta. I also redid the voltage drop method described above, essentially same result. That eliminated the dielectric absorption issue (known from the 3458A, using OCOMP, but I did use a delay anyway, and switching OCOMP off did not make considerable changes, and so I had not expect this to be the issue anyhow; see also Dr Franks story about this here). Conclusion was, something has drifted, rather than the current measurement being wrong, too many equal results with different meters. A SR104 does not drift 7ppm in about a year (actually, if the last measurement was right, it would have drifted less than 5ppm in 40 years). I had the suspicion that my SR104 maybe had lost its sealing, so I decided (yes, I know the comments that I will be getting) to look inside (I just lifted the lid a bit, so not much stress applied). It had no history, other than its original value, and it needs to be call'ed now anyway, so this was not a loss for me. And at the moment I cannot use it. No leak recognized though. So next third party cal. , due soon, needs to tell what drifted (it could of course as well be that my initial measurement was wrong for unclear reasons, we will see).What surprised me was the wiring. This is supposed to be a 4-wire resistor, so each lead at the resistor terminals being connected by two wires to two binding posts. That way the wire resistance is eliminated. What they had done though was to connect the two binding posts of each side directly, and then connect two wires to that pair. That does not make any sense. I changed this, the change in resistance was marginal (0.6ppm less, one would expect a slightly lower resistance as the copper cable resistance is eliminated; ma hope was a bad solder joint too, explaining the 7ppm above when I saw the strange wiring, but that was not the case).SR1010: This is normally used to transfer resistances, rather than as a reference. So normally, before their use, they are calibrated (important is their deviation). I bought a couple for them (10R, 1k, 100k, 10M; per resistor) with bars recently, for the purpose of transfering 10k to a range of 1 ohm to 100M with better accuracy than I do so far. So what I want to do in specific is going from the 1k (10 in series is 10k, 10 in parallel 100R) and measure each one with a (non-calibrated, at least not to that accuracy) meter in transfer mode. That gives certain deviations. Then, with 10 in series, I would compare this value to the precisely known 10k standard and transfer the total deviation measured to each of the single deviations I had determined before (relative, but not absolute). That way, although I do not have a 10k SR1010, I still can do a proper transfer from the 10k standard to the 1k SR1010. Al this with an error propagation calc should give a good transfer within the abilities of the SR1010 as per manual. Any objections to this?

author: Dr. Frank
author_rank: Super Contributor
timestamp: January 14, 2016, 05:47:47 pm
content: Quote from: acbern on January 14, 2016, 04:05:23 pmWhat level of voltage did you apply?I assume, you had <= 20V over both resistors, so that the 3458A measured at about 10V over each individually , not having to change its range, and also that the power dissipation was small enough.. <= 10mWDid you numerically remove offset voltages, by measuring with and without driving voltage?Quote from: acbern on January 14, 2016, 04:05:23 pmSame setup as above?That's again the Man-With-Only-Two-Clocks problem!You urgently need a third (..fourth, fifth..) stable 10k resistor standard!The VHPxy had not been heated for some reason, I assume, so that these 7ppm difference would origin from hysteresis?Quote from: acbern on January 14, 2016, 04:05:23 pmHuh? Why? Lost some oil? ("Auslaufmodell"?)Quote from: acbern on January 14, 2016, 04:05:23 pmThe SR1010 allows 100:1 transfers of about 1ppm uncertainty.. what about 10:1 transfers, is that more precise (due to Hammon divider principle?)As the 3458A allows 10:1 transfers of 0.3ppm at least, I would also verify the SR1010 transfer with that alternative technique.I was doing a similar thing, see my post inside Daves eevblogthread about the Fluke 5450A. That seemed to work very well.Finally, a 752A Hammon like 10:1 / 100:1 divider might be an additional, independent verification method.Or as you have the 1281, you could use this as a third independent instrument.Frank

author: ltz2000
author_rank: Regular Contributor
timestamp: January 14, 2016, 06:02:23 pm
content: Quote from: acbern on January 14, 2016, 04:05:23 pmThere is four wire cabling inside connected in two wire style. The reason was getting better 2-wire compatibility. At the time the SR104 was introduced, still a number of two wire bridges were in use. The hermetic feed through is also two wire...Quote from: acbern on January 14, 2016, 04:05:23 pmDid you forget to let it dry the top lid open after shipping? Or did you possibly cleaned it with a damp cloth?If any humidity gets under/inside the binding posts, it stays there a long time and you will get readings several ppm low.That is why I always measured the leak resistance before any SR104 calibrations.

author: acbern
author_rank: Frequent Contributor
timestamp: January 14, 2016, 06:12:34 pm
content: Interesting, the drying may really have been an issue. I do not remember exactly, but I think it may have been maybe 2 to 4 weeks between when I received it (it came through air freight, so condensation possible) and I did the test. I opened the lid for a couple hours only in that time, but certainly not days, essentially when I did the test. No cleaning with wet cloth. No removal of the aluminium plate. I did not measure leakage.So are you saying this was not enough and may have caused it?Dr Frank, re. your questions:voltage below 20V to limit load, did reversal measurement and zero-comp, so offset should not have been an issue. I took special care to not overlaod the standard, to keep the load below 10mW, unless for any mistake I unknowingly made, should not be an issue. Thought about that too. Need to have the thing calibrated. The reason why I cannot use it is because it just has no valid calibration, and I cannot even calibrate it against my standard, because this may be the problem (dont know which clock is wrong). But this will be resolved soon once I have it calibrated.Re. the SR1010, I will probably use the 1281, it is the fastest way to get there. In fact so far I did my 10:1 transfers with a 3458A in voltage divider mode (as described above), but error propagation calc shows that the SR1010 should lead to better results.

author: ltz2000
author_rank: Regular Contributor
timestamp: January 14, 2016, 06:26:21 pm
content: Quote from: acbern on January 14, 2016, 06:12:34 pmPlease post your relative measurements (and also the absolute ones made with the 3458A). Makes it easier to see the whole picture.Did you measure the tempco? If there is a problem inside the hermetic container, it usually affects the resistor matching.

author: doktor pyta
author_rank: Frequent Contributor
timestamp: January 14, 2016, 10:03:49 pm
content: Quote from: acbern on January 14, 2016, 04:05:23 pm@ Dr. Frankhttp://www.ietlabs.com/pdf/Manuals/SR-1010_im.pdfPages 11, 25, 31.From the IET website "Transfer Accuracy:±(1 ppm + 0.1u ohm) at parallel value for 100:1 transfer±(1 ppm + 1u ohm) at series-parallel value for 10:1 transfer".This is slightly different from data shown on the manual, page 11 (see attachment), but I could omit something.

author: acbern
author_rank: Frequent Contributor
timestamp: January 15, 2016, 09:05:59 am
content: Quote from: ltz2000 on January 14, 2016, 06:26:21 pmSo I measured (indirect method through voltage measurement with 3458A and a Fluke 5440 as source) 9.999,962 kohms back in 2014.Recently I measured 10.000,032 kohms (with a Datron 1281). That is + 7.0ppm. I also measured a 6,8ppm increase in voltage measurement mode with a 3458A as part of a control measurement which confirms the Datron result within limits of acc.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: January 15, 2016, 09:14:38 am
content: Here are some pics. The unit was received with a bad resistor. The 10M resistance is made using three 3.3M resistors and a small trim mica resistor. On mine, one of the 3.3M resistors is open. It is currently awaiting repair by someone who works with custom wirewound resistors.

author: Dr. Frank
author_rank: Super Contributor
timestamp: January 15, 2016, 09:27:18 am
content: Quote from: doktor pyta on January 14, 2016, 10:03:49 pmThanks for that information; I already had that in mind, but always wondered why 10:1 uncertainty is 1ppm only.For a 40k / 400k / 4M Hamon divider, like the Fluke 752A, you usually get about 0.2ppm of output for 10:1 and also for 100:1 (neglecting self heating effects), which is better than the HP3458A.Frank

author: Dr. Frank
author_rank: Super Contributor
timestamp: January 15, 2016, 09:36:05 am
content: Quote from: acbern on January 14, 2016, 06:12:34 pmI'm confused a bit, which one do you regard as your actual standard? Is it the Vishay VHPxxx?If you want to have one of your standards calibrated, wouldn't it be better to send the SR104 to the cal lab?Frank

author: ltz2000
author_rank: Regular Contributor
timestamp: January 15, 2016, 12:27:36 pm
content: Quote from: ManateeMafia on January 15, 2016, 09:14:38 amAnd for comparison a later unit manufactured by IET labs.It is so sad what has happened to many classic ESI and General Radio products after adopted by IET.

author: ltz2000
author_rank: Regular Contributor
timestamp: January 15, 2016, 12:53:22 pm
content: Quote from: acbern on January 15, 2016, 09:05:59 am+3...4 ppm is typical for an SR104 of that era.Let the unit cool down to +15...18 C and after that warm back to the room temparature while measuring the main resistor and the thermistor. The tempco should be very close match to the original chart. And there shouln't be any hystereresis left after reaching the original temperature.

author: quarks
author_rank: Frequent Contributor
timestamp: January 15, 2016, 03:25:03 pm
content: Quote from: ManateeMafia on January 15, 2016, 09:14:38 amthanks a lot for sharingthat looks very nice and totally diff. to my SR1010s

author: quarks
author_rank: Frequent Contributor
timestamp: January 15, 2016, 03:27:05 pm
content: Quote from: ltz2000 on January 15, 2016, 12:27:36 pmLooks by far not as impressive as the ESI design

author: ltz2000
author_rank: Regular Contributor
timestamp: January 15, 2016, 03:56:00 pm
content: Quote from: quarks on January 15, 2016, 03:25:03 pmAt 10 Mohm level the contact resistances are not the main problem anymore allowing to use switches. The real problems are leakage resistance related instead.

author: acbern
author_rank: Frequent Contributor
timestamp: January 15, 2016, 05:21:42 pm
content: Quote from: Dr. Frank on January 15, 2016, 09:36:05 amWell, I do have a history with the homebrew one. So I will get that cal'ed to verify. I will then transfer this to the SR104. Since it has changed its value so much, I am hesitant to use it and want to veryfy it has settled. How do I know it does not change again when shipped (I may actually hand cary it there) to the cal lab (always assuming of course that the homebrew low drift rate is confirmed).

author: acbern
author_rank: Frequent Contributor
timestamp: January 15, 2016, 05:38:42 pm
content: Quote from: ltz2000 on January 15, 2016, 12:53:22 pmSo you say since its build date it should have drifted 3-4ppm until today, right? The 7 ppm drift I meaured was within a year or so.From its build date until today (always provided my current measurement is right and my homebrew reference is not bad) it would have drifted from 10.000,005kOhm to 10.000,032 kOhm, or 2,7ppm, which looks ok.I will do the measurement you propose soon (currently my thermal chamber is occupied with some other stuff). I am not expecting any deviation though, the current value measured looks nice, and I hope it will be confirmed when I have my standard re-cal'ed. The main problem is, whay was my measurement so much off when done in 2014. Your explanation re. humidity sounds valid, but how do I proof (if possible at all) and how did it happen?

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: January 15, 2016, 06:15:04 pm
content: @acbernSince your SR-104 was made before 1990, have you taken into account the +1.69ppm correction in 1990? Not that it is relevant to the apparent drift, but my SR-104 was made in 1969 and I plan on sending it in for its first cal (for me). I was wondering what to expect on its calculated drift since its original calibration value 46 years ago.

author: ltz2000
author_rank: Regular Contributor
timestamp: January 15, 2016, 06:39:51 pm
content: Quote from: acbern on January 15, 2016, 05:38:42 pm10 kohm (1990) + 3...4 ppm nowadays.When calculating the total drift you should include the drift of the US legal ohm from the date of manufacture until 1990 plus the 1990 change of definition already mentioned.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: January 15, 2016, 06:47:32 pm
content: Thanks.It looks like PTB only adjusted by +0.56 ppm. I was referencing the NIST correction.

author: lars
author_rank: Regular Contributor
timestamp: January 16, 2016, 08:01:18 am
content: About the SR1010: I have an SR1010-10LTC and an SR1010-1k from the sixties. I think they are excellent ratio transfer standards between 1:10 and 1:100 but absolute value suffers from seasonal variations. Both my SR1010´s have about 8-10ppm seasonal variations for about 30-40%RH variations. A regression on the 1k series (10k) for the last 5 years give +0.3ppm/%RH +2ppm/C and -0.5ppm/year against a GR1440-10k. The individual resistors in the SR1010-1k is between -1ppm/C and +6ppm/C.Lars

author: ltz2000
author_rank: Regular Contributor
timestamp: January 16, 2016, 11:03:42 am
content: Quote from: lars on January 16, 2016, 08:01:18 amThat is normal. The SR1010 is atransferstandard.ESI made also an oil filled sister version, which was much better from that point of view.A proven trick with the dry version is to seal the enclosure and put silica gel bags under a perforated fake bottom.

author: zlymex
author_rank: Frequent Contributor
timestamp: February 23, 2016, 05:12:05 am
content: That chart of "Drift of 5 SR104 standard resistors at 23°C" was plotted by me more than 8 years ago when I only had two SR104s.I've been trying to keep track of every SR104 I can find and now I updated the chart to ten SR104sEdit: update chart to 12 SR104s.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: February 23, 2016, 05:24:55 am
content: I hope to get my 1969 era SR-104 sent in for its first cal (by me). I will gladly pass that on to you.On a side note, do you know if any of the owners of these resistors ever had the alpha and beta constants recalculated? I have read conflicting information that they change as they get older. The SR-104 would be a good candidate to confirm or debunk this theory.

author: zlymex
author_rank: Frequent Contributor
timestamp: February 23, 2016, 07:07:40 am
content: Quote from: ManateeMafia on February 23, 2016, 05:24:55 amOne of my SR104 tested by NBS in Dec 1982, alpha=-0.10ppm/C, beta=-0.028ppm/C2, as shown in green line.I tested it in Dec 2009, alpha=-0.09ppm/C, beta=-0.033ppm/C2, as shown in red line.ref:http://bbs.38hot.net/thread-1352-1-1.html

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: February 23, 2016, 02:18:56 pm
content: Thanks for the information.

author: jfphp
author_rank: Regular Contributor
timestamp: June 11, 2016, 04:41:51 pm
content: I have a 40 years old SR104 and I am very interested by the comparison chart of 10 SR104 but I have 2 questions :1. Why some SR104 show no drift at all ? Mesurement errors ?2. Most important, how do you insert in the graph the 1990 change in the ohm definition ?"The U.S. representation of the ohm based on the quantum Hall effect to be maintained at NIST starting January 1, 1990, using the internationally agreed-upon or conventional value of the von Klitzing constant RK-90 = 25 512.807 ? exactly. From quantized Hall resistance measurements it is calculated that ?(NIST-90) will exceed ?(NBS-48)01/01/90 by 1.69 ppm"There must be a jump in the various drift lines or did you recalculate the drift without the jump???

author: zlymex
author_rank: Frequent Contributor
timestamp: June 12, 2016, 01:33:39 am
content: Quote from: jfphp on June 11, 2016, 04:41:51 pm1. I could be the combination of low drift(or right drift) of the resistors with the change in the definition. It is for certain that most good wire-wound resistors are drifting upwards(value increase) if properly made and not constrained.2. If a very stable resistor is constantly compared to the NBS/NIST standard, there should be a jump in 1990 when graphed.NBS Ohm was based on the mean value of five Thomas resistors before 1990, and this definition is not constant by nature.According to an IEEE paper in 1989(http://www.nist.gov/calibrations/upload/eee-38-2.pdf), the drift rate of NBS Ohm was -0.053ppm per year, which means that the five resistors were drifting at +0.053ppm per year before 1990. That change of 1.69ppm in 1990 is not random value in my opinion, rather, it is the correction of NBS Ohm back to the right track.If a stable resistor was placed into dormancy during 1980 to 1995 for 15 years, it will not aware of all these changes. That is exactly the case for most of the SR104s in my chart. I plotted the chart with dots of data and connect them in straight lines.Someone has asked me before how I obtain those data on the chart, it is simple, I gather data from the web. Sometime it is already charted like that Japanese SR104(http://www20.tok2.com/home/daisuken/esisr10401.html) but most other times I extract data from calibration stickers(http://lionelectroniclabs.com/esi-sr-104-10k-resistance-standard/) or descriptions(http://www.amplifier.cd/Test_Equipment/other/Widerstands_Normal.htm).

author: ap
author_rank: Frequent Contributor
timestamp: June 12, 2016, 09:26:50 am
content: @zlymexNice work on this overview. What you could do is to take the 1.69 ppm into account in a second version of your chart on the pre-1990 data, so that the real drift would be shown.

author: zlymex
author_rank: Frequent Contributor
timestamp: June 12, 2016, 12:57:26 pm
content: Quote from: ap on June 12, 2016, 09:26:50 amOf course, I should have done that long time agoHere it is.The formula is: =IF(S1>=32874,U1,U1+1.69-(32874-S1)/365.24*0.053)Where 32874 is the date code of 1-Jan-1990 when the -1.69ppm, U1 is the value calibrated on S1

author: ap
author_rank: Frequent Contributor
timestamp: June 12, 2016, 01:38:21 pm
content: That was fast! Thx!

author: doktor pyta
author_rank: Frequent Contributor
timestamp: August 27, 2018, 08:28:15 am
content: Sad things also need to be posted. Below pictures of my DIY shorting bars after over 2 years. Bars were used maybe 10 times and were always touched by the edges.I think the gold and silver layers were too thin.Also there is interesting .pdf in the attachment. Guildline 'borrowed' a picture from my website and put it into their brochure.That's not elegant for such company. Haven't they resources to take their own photo ?

author: MK
author_rank: Regular Contributor
timestamp: November 04, 2018, 05:33:21 pm
content: Quote from: doktor pyta on August 27, 2018, 08:28:15 amWhy not send them the fee for using your photo?

author: dietert1
author_rank: Super Contributor
timestamp: May 22, 2019, 06:10:57 pm
content: Today we received a SR1010 with 12x 1K from ebay. Internally it looks similar to the 100 Ohm unit shown above. It has the original calibration dated 1969-09-29 attached and perfectly readable.My first measurements using a HP 3456A resulted in the data below.Resistance measurements are 17 ppm off on average, a mixture of DVM misalignment and drift of the resistors. Somebody determined 0,07 ppm/year, that would be 3.5 ppm after 50 years. So probably DVM misalignment is the bigger part of the difference.The original deviation pattern is clearly present and subtracting the common shift, only about 3 ppm remain as standard deviation of a single resistor. Great after 50 years.Regards, Dieter

author: 0.01C
author_rank: Regular Contributor
timestamp: August 21, 2019, 01:44:50 pm
content: Quote from: ltz2000 on January 15, 2016, 12:27:36 pmYour picture does not show the most important resistors.

author: dietert1
author_rank: Super Contributor
timestamp: September 26, 2019, 09:04:10 am
content: The recommendation to put desiccant into a normal "dry" SR1010 worked for me.When using our SR1010 in a resistance measurement bridge (3 resistors as voltage divider and 1 resistor as current source) i found a TC of -1.9 ppm/K at room temperature and a 8 ppm drift after inserting about 1 cm of silica gel at the bottom. The drying process started at 44 % HR and took about 18 hours. I mounted a PT1000 sensor on the inside of the SR1010 top plate in order to correct ambient temperature variations numerically. There is a heat conduction delay of about 4 to 5 minutes from temperature variations as seen by the temperature sensor to TC effects on the bridge. Now i got stable results at a +/- 0,05 ppm level over several days.Another exercise will be looking at the copper wires between the SR1010 and the DUT (Alpha Electronics HCZ500R00T).Regards, Dieter

author: dietert1
author_rank: Super Contributor
timestamp: September 27, 2019, 06:47:02 am
content: About thermal EMF with the SR1010: I did some measurements, that yielded a 0,34 uV/K slope of my setup under ambient temperature changes. And i noticed that a copper spade on one of the binding posts yielded up to 3 uV when heating it between two fingers, so the binding posts don't seem to be copper.Before i start scratching parts - maybe somebody did that before.Another question with respect to desiccant: It was recommended to "seal" the SR1010. Anybody with an image?Regards, Dieter

author: SvanGool
author_rank: Regular Contributor
timestamp: September 27, 2019, 08:47:26 am
content: Quote from: dietert1 on September 27, 2019, 06:47:02 amIf you can compensate the leakage by the amount of desiccant, as is mentioned inthis report, you maybe don't need to seal at all. But you do need to find a way of roughly estimating the leakage.

author: dietert1
author_rank: Super Contributor
timestamp: September 28, 2019, 09:26:34 pm
content: Yes, and nowadays it's quite simple to supervise humidity using integrated sensors. Since i have a lot of desiccant in that SR1010, i won't touch it any more, but observe humidity inside.I made a closed box around it including 20 mm of styrofoam thermal insulation to reduce leakage and temperature changes. Hope to reduce the binding post thermal EMF by keeping everything at the same temperature, thus avoiding expenses for another 26 low thermal binding posts. Now the SR1010 temperature sensor indicates a thermal time constant of about 1 hour - much better than before. Thermals seem to be down by a factor of 10 in comparison to before. I guess oil may be necessary when running the precision resistors at varying loads, but it does not help with the thermals.Regards, Dieter

author: guenthert
author_rank: Frequent Contributor
timestamp: September 29, 2019, 10:54:44 pm
content: Quote from: dietert1 on September 28, 2019, 09:26:34 pmIf you don't intend to replace the "consumed" (or "spoiled") desiccant, but just observe the internal humidity, why use a non-zero amount of desiccant in the first place?

author: BradC
author_rank: Super Contributor
timestamp: September 30, 2019, 03:35:28 am
content: Quote from: guenthert on September 29, 2019, 10:54:44 pmThe dessicant isn't there to remove humidity, it's there to buffer it.

author: dietert1
author_rank: Super Contributor
timestamp: October 02, 2019, 04:47:17 am
content: Slowly i am coming to grip with our SR1010-1K and here is an example measurement. This is a resistance bridge with a voltage divider 10 V to 3.3 V (3x 1 KOhm) and one 1KOhm resistor serving as a 6.7 mA current source to the DUT, which is an Alpha Electronics HCZ500R00 (Vishay hermetic foil). The DUT has been in a 40 °C oven for about a week. Bridge is driven by our Geller reference.I logged the bridge voltage difference and the temperature of the dry and boxed SR1010 with our two HP 3456A. During the night the SR1010 temperature was following the decreasing room temperature for about 5 hours. Vertical axis is 1 ppm, horizontal is 0.5 K. Red line is a calculated filter, green a line fit.Now i can correct the SR1010 temperature dependence numerically (linear -1,84 ppm/K)Regards, Dieter

author: dietert1
author_rank: Super Contributor
timestamp: November 04, 2019, 08:32:21 am
content: After i got about 10 uV of thermal EMF by heating a copper lug between fingers, i checked the materials used in a SR1010. I think the binding posts are gold-plated steel as well as the nuts on them (front and back). The trapezoidal plates inside appear to be copper. This construction is prone to generate thermal EMF. The other SR1010 i am operating in a box, well protected from air movement, generates about 300 nV.Pomona 3770 copper binding posts fit, but their diameter in the back is about M4 and the holes in the plates are more like M6. And the Pomona posts come with steel nuts. So one needs to buy copper nuts and washers in addition.Regards, Dieter

author: splin
author_rank: Frequent Contributor
timestamp: November 04, 2019, 05:40:07 pm
content: Quote from: dietert1 on November 04, 2019, 08:32:21 amI'm having a very hard time believing that ESI would have used gold plated steel - these aren't cheap items. Have you checked with a magnet? Could someone have replaced them before they came into your possession?

author: dietert1
author_rank: Super Contributor
timestamp: November 04, 2019, 08:44:41 pm
content: Of course i can't guarantee the binding posts are original, but the web is full of images of SR1010 and they look like original. And they are identical on the two SR1010 we got from two different sources.I just checked it, the binding posts and nuts are non magnetic. They don't have the reddish shine of copper nor the golden color of brass inside, but appear white. Maybe silver? I'd prefer copper, since i am using copper lugs and copper cables.Best regards, Dieter

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: November 04, 2019, 11:54:58 pm
content: The normal material for ESI terminals is Tellurium Copper, it is a dull golden color usually, depends on the alloy's mix.

author: Kosmic
author_rank: Super Contributor
timestamp: November 05, 2019, 01:43:59 am
content: Personally I would not replace the binding post with Pomonas.What protocol and instruments (meter / cable / connectors) are you using to measure the thermal EMF ?

author: dietert1
author_rank: Super Contributor
timestamp: November 05, 2019, 07:58:50 am
content: I am not really measuring thermal EMF, since it's a dirt effect and i think it will be negligible once i have the correct materials. A simple test i always do is: Connect one of the resistors with four copper lugs and copper wires to the HP3456A input (input terminals are made of copper). After a minute or two i get a zero reading of -0,6 uV. This is "without" thermal EMF. Then i heat one of the lugs on the SR1010 terminal between my fingers, so there will be a 5 or 10 °C temperature increase. The HP 3456A reading slowly creeps up to about 10 uV and it slowly returns back to -0,6 uV as soon as i take my hand off. This may take two or three minutes. I can repeat that on the other terminal giving -10 uV.The binding posts are certainly not copper, they look white inside like steel or silver. I guess the SR1010 is from a time when users were satisfied with 1 or 2 ppm results, which are easy to get if you keep the lab at 23 °C and don't touch the setup. In my current bridge experiment i have 3.3 V across the DUT and see a 0.3 ppm difference on voltage reversal, so thermals appear at a 1 uV level.Regards, Dieter

author: Kosmic
author_rank: Super Contributor
timestamp: November 05, 2019, 03:01:37 pm
content: Quote from: dietert1 on November 05, 2019, 07:58:50 amInteresting, I will try to repro with my SR1010.Quote from: dietert1 on November 05, 2019, 07:58:50 amIn the manual of the SR1010, ESI don't specifically talk about the binding post but they explain in details how the resistor were made and how they selected materials that create low EMF when coupled to copper. I would be surprise if in the end they decided to use cheap steel binding post.Technically IET still sell binding post similar to the one used back in the days by ESI. Like Edwin mentioned, they are made of tellurium copper.https://www.ietlabs.com/binding-posts-bp-1000.html

author: dietert1
author_rank: Super Contributor
timestamp: November 05, 2019, 05:10:57 pm
content: The binding posts in our SR1010s look different. They have two different isolators (different shape and different color). The outside isolator looks dark brown and fits into the hole. The inside isolator looks like teflon and has a larger conical hole covering up the other isolators end.By the way, the tellurium copper of the Pomona 3770 body material appears reddish, similar to the trapezoidal sheets inside the SR1010. If something looks white, probably it has little copper. Even brass doesn't look white. I know this can't replace a chemical analysis.Meanwhile i ordered copper screws to test whether they work better and will report later.Regards, Dieter

author: MegaVolt
author_rank: Frequent Contributor
timestamp: November 06, 2019, 09:01:41 am
content: I checked my SR1010 100 kOhm with a magnet. If it is not disassembled, then the magnet has nothing to be attached to.

author: Kosmic
author_rank: Super Contributor
timestamp: November 06, 2019, 02:45:02 pm
content: Quote from: Kosmic on November 05, 2019, 03:01:37 pmSo I tried quickly with non ideal connectors (brass banana), non ideal meter (34401a, the 7.5 meters are sleeping). Heating for 30 sec with a hot air rework station at 100deg (the binding post was probably a lot cooler) I was able to get around 3uV offset. In 4W Ohm mode it's generating 1 to 2 ppm of noise.Look like it's less of a problem in my case.

author: dietert1
author_rank: Super Contributor
timestamp: November 06, 2019, 08:58:07 pm
content: Kosmic, this was for a binding post like the ones on the IET website you linked?Meanwhile i found this table in a Keithley 2700 manual:Table E-1Material thermoelectric coefﬁcientsMaterial Thermoelectric potentialCopper-Copper 0.2 µV/°CCopper-Silver 0.3 µV/°CCopper-Gold 0.3 µV/°CCopper-Cadmium/Tin 0.3 µV/°CCopper-Lead/Tin 1–3 µV/°CCopper-Kovar 40 µV/°CCopper-Silicon 400 µV/°CCopper-Copper Oxide 1000 µV/°CSo it appears the thermal voltages i actual had in my setup (220 and 250 nV) are a good result even for a copper-to-copper contact.Can anyone explain why Pomona and others use Cu-Te? Tellurium is listed with 500 uV/°C, so i'd guess even a small fraction of Te could distort everything.Regards, Dieter

author: razvan784
author_rank: Regular Contributor
timestamp: November 06, 2019, 09:48:13 pm
content: Quote from: dietert1 on November 06, 2019, 08:58:07 pmI get around 3 uV with Pomona 5291A cables (supposedly CuTe bananas with CuBe springs) stuck into a 34401A (Cu sockets). This is when heating the cable end that sticks into the meter with my fingers. I also see the opposite polarity when heating the other cable, and the offsets take several minutes to decay - which is to be expected.I guess they are called "low emf" not "zero emf" for a reasonI get about the same behavior with Multi-Contact Multilam bananas (brass body, CuTe spring) and Multi-Contact LS4 (CuBe hollow bananas).Edit: for comparison, I get around 9 uV for a Pomona 5291A stuck into a Pomona 3770 binding post (also supposedly CuTe), and on the order of 100 uV for a copper-Kovar junction (made with a pin from a hermetic transistor package -- like the LTZ1000 uses). That is certainly not "low emf". So your binding posts are certainly not steel.Quote from: dietert1 on November 06, 2019, 08:58:07 pmIt's been discussed on this forum before, apparently the reason is mechanical. Pure Cu is hard to machine, CuTe is apparently much easier, while still retaining "low emf" characteristics.

author: Kosmic
author_rank: Super Contributor
timestamp: November 07, 2019, 04:57:03 am
content: Quote from: dietert1 on November 06, 2019, 08:58:07 pmNo, I got the old traditional ESI version.

author: MiDi
author_rank: Frequent Contributor
timestamp: November 07, 2019, 08:50:27 am
content: Quote from: dietert1 on November 06, 2019, 08:58:07 pmSomeone mentioned Cu-Te is used for better machinability and I guess it is harder than pure copper.For spring contacts e.g. in plugs there is often used Cu-Be, because it has better properties for that purpose.I had searched for infos about T-EMF for these materials, but could not find anything.Edit:The T-EMF for copper to copper should depend on differences of the purity.Theoretically if only copper from same batch is used the T-EMF would be 0.

author: MegaVolt
author_rank: Frequent Contributor
timestamp: November 08, 2019, 10:51:23 am
content: Quote from: MiDi on November 07, 2019, 08:50:27 amAny material is not only copper.

author: alligatorblues
author_rank: Regular Contributor
timestamp: May 09, 2022, 05:50:33 am
content: Responding to the OP, I have a SR104 that was manufactured in 1974, and I have a few reasons to believe that is authentic. The cal. Cert says so. The glue under the laminate failed on the back panel when I accidentally lost control of the cover, and let it flop open hard. The whole panel just broke loose.No big deal to put it back with 2-sided 3M adhesive material. And the binding posts have no banana jacks on top. They're solid. You have to loosen them up and screw them down on the leads. Which everyone should be doing anyway!We had Keysight calibrate it, I think to 0.2ppm, if that sounds right. It was something with a '2'. When we got it back we could confirm its drift from 1974 to 2019 was 0.3ppm. I researched to check if this is reasonable, and it is. For one thing, the drift could be in different directions over all that time, thereby offsetting itself.With no cal in between it's impossible to know. But that is my limited experience with the SR104.

author: manganin
author_rank: Regular Contributor
timestamp: May 11, 2022, 03:51:43 pm
content: Quote from: alligatorblues on May 09, 2022, 05:50:33 amDon't forget the 1990 correction and the drift of the US legal ohm before that.Quote from: alligatorblues on May 09, 2022, 05:50:33 amStress free Evanohm drifts upwards.

author: HighVoltage
author_rank: Super Contributor
timestamp: May 11, 2022, 04:22:20 pm
content: Quote from: manganin on May 11, 2022, 03:51:43 pmBut how do you know, you have it stress free installed?

author: manganin
author_rank: Regular Contributor
timestamp: May 11, 2022, 06:28:50 pm
content: Quote from: HighVoltage on May 11, 2022, 04:22:20 pmBecause the people at ESI knew what they were doing. They were able to release the mechanical stress so well that practically the only drift left was metallurgical.

author: alligatorblues
author_rank: Regular Contributor
timestamp: August 12, 2022, 10:02:40 pm
content: Quote from: manganin on May 11, 2022, 03:51:43 pmOk, how do I find out about the correction and drfft of the Ohm?

author: alm
author_rank: Super Contributor
timestamp: August 12, 2022, 11:37:33 pm
content: Quote from: alligatorblues on August 12, 2022, 10:02:40 pmSee this NIST document:Guidelines for Implementing the New Representations of the Volt and Ohm Effective January, 1, 1990. It describes the correction on page 3, and pages 13-18 talk about the drift about the Ohm as it was defined before 1990.