Old SR1 standard resistors from ESI - Page 1
Forum section: electronics / general

author: TimFox
author_rank: Super Contributor
timestamp: March 19, 2022, 03:02:21 pm
content: I have several SR1 resistors in good condition that I purchased through eBay, originally from an OSHA laboratory, where they were treated well. The screw-in gold-plated banana plugs are also in good condition.The manufacturer's dates are 1977, and the last OSHA calibrations were done in 1978. I would like to get newer measurements on three units: 1k, 10k, and 100k.Can anyone speak from experience on the longevity of these units, and what an independent calibration lab (in US) is likely to charge for measurements to the original tolerance (0.001% = 10 ppm)?

author: Villain
author_rank: Regular Contributor
timestamp: March 19, 2022, 04:16:27 pm
content: I would rather send the units to a friendly eevblog forum member that has a reference resistor that is characterized to a few ppm's and maybe a 3458A, that should be good enough for what you want to achieve. Then it would only be shipping cost. I would offer to do it but germany seems to be a bit far away.

author: TimFox
author_rank: Super Contributor
timestamp: March 19, 2022, 04:20:16 pm
content: I would gladly accept that measurement, within reasonable shipping distance from Chicago, if anyone cares to offer it.It should be practicable at the 10 ppm level.

author: TiN
author_rank: Super Contributor
timestamp: March 19, 2022, 06:23:33 pm
content: Problem with SR1 is non-metrology grade interface. So this limits reproduction of accurate resistance quite a bit. You can have anyone with calibrated 7.5 or 8.5 digit meter should give the ballpark value. I wouldn't waste gold sending SR1 to accredited lab.

author: martinr33
author_rank: Frequent Contributor
timestamp: March 19, 2022, 08:13:00 pm
content: Why do you say that? I know that they are not great resistors by recent standards, but they do at least have a 4-wire interface.

author: TiN
author_rank: Super Contributor
timestamp: March 19, 2022, 08:18:52 pm
content: I'm not seeing 4-wire?

author: martinr33
author_rank: Frequent Contributor
timestamp: March 19, 2022, 08:38:48 pm
content: Here's my 10k. The posts look optional and can be unscrewed. They have acrylic insulating rings for the jacks. . I don't have a current reading on this one, I should do that.

author: MK
author_rank: Regular Contributor
timestamp: March 19, 2022, 11:06:48 pm
content: That is two wire and ground. No easy way to get a 4 terminal measurement from that.

author: bck
author_rank: Contributor
timestamp: March 19, 2022, 11:34:40 pm
content: https://www.eevblog.com/forum/metrology/esi-sr1-standard-resistor-current-rating/msg1256040/#msg1256040if your resistor is like the one linked above you can easily get a 4-wire reading from it, just plug it into a DMM and connect 2 wires from the binding posts to the sense ports...

author: TimFox
author_rank: Super Contributor
timestamp: March 20, 2022, 04:22:53 am
content: These resistors have true four-wire connections. There are three binding posts on the top (one for case) and three corresponding banana plugs that screw into the plastic insulators on the bottom.

author: lowimpedance
author_rank: Super Contributor
timestamp: March 21, 2022, 03:07:13 am
content: Quote from: TimFox on March 20, 2022, 04:22:53 amJust for reference I have attached the data/marketing info from an ESI catalogue for the SR1 ... FYIClearly stating 4 terminal measurement possible, with photo of underside showing terminals as well.

author: dietert1
author_rank: Super Contributor
timestamp: March 21, 2022, 07:49:52 am
content: About longevity:Two weeks before i went to the Stuttgart Metrology meeting in 2019 i got a SR1010 12x 1K resistor box, that has very similar resistors inside (mylar wire wound with those strong terminals, about same size). I did some cleaning but without solvents. During the lab session we confirmed its original calibration from 1960 for a 10 KOhm string, with uncertainty of some ppm and with no significant deviation. So except if yours are broken and unless you want to calibrate to better precision, i think you can just use them as standard. They are probably better than anything else you have.Of course Dr. Frank will say: A standard resistor needs a DUT temperature sensor. Yet those resistors have low TC of about 1 ppm/K or so, so again it depends on what you want to achieve.Regards, DieterEdit: Original calibration date of our SR1010 was 1969-09-29. A Keithley 2700 i got recently reads a stable 22 ppm high after some hours of heating up. Its 24 hour spec is 26 ppm and its calibration due date is 2005-12-13 ...

author: alm
author_rank: Super Contributor
timestamp: March 21, 2022, 09:50:25 pm
content: Quote from: dietert1 on March 21, 2022, 07:49:52 amReadingthis post from Edwin Pettis, and in the absence of hard data about the treatment of the resistors, I'd take his opinion over pretty much anyone else in the world if it concerns wire wound resistors, the SR1 isn't made the same as the SR1010. The post processing after winding is apparently quite different, and this plays a major role in relieving stress and hence improving stability, and may also affect temperature coefficient. Manganin (the wire used in the SR1) is especially sensitive to this.They may well meet the 50 ppm long term accuracy spec, but I wouldn't count on them being within a few ppm of its calibration value like your SR1010. Plus, I'm not sure if they have their calibration written on them as often as the SR1010 has its table.

author: martinr33
author_rank: Frequent Contributor
timestamp: March 22, 2022, 01:57:13 am
content: You can see an ESI calibration sticker on my unit. It says:Initial value 9.999.1Recalibration 10,000.07 8/19/78I'll get a better number on that later in the week. I'm not expecting anything shocking.

author: dietert1
author_rank: Super Contributor
timestamp: March 22, 2022, 06:57:17 am
content: Yes it makes complete sense to check a standard after 44 years. Probably most of the stress relieved during the 10 or 20 years from initial calibration to 1978..Regards, Dieter