Cleaning Yokogawa Standard Resistor 2792  - Page 1
Forum section: electronics / general

author: tfm
author_rank: Contributor
timestamp: November 13, 2020, 10:48:02 pm
content: Hi, long time reader here, just posting now.I've scored these 2 Yokogawa Standard Resistor 2792.Higher resolution photos here:https://ibb.co/ypH7XZphttps://ibb.co/j5DWSbyhttps://ibb.co/TT0GrQpAlso attached some specs for these units.Note that these are not the newer 2792A, but the 2792.So one of them came with some oil inside, even had a piece of paper towel wrapped around the center hole, apparently preventing oil from leaking. You can see dust stuck to a layer of oil.Probably it was bathed in oil, can't say for how long. Is it advisable to open it and clean it with IPA, preventing possible further chemical changes or better to keep it this way and avoid any mechanical stress by dismounting it?A quick check with a ready 34401A (out of cal) showed that the 1ohm unit was 5,0mohm out and the 1mohm unit was 5,4mohm out. So it seems at least there is no greater physical damage, considering these units came from Japan.BTW, this is a somewhat related thread, might be useful for someone that eventually gets here in the future and wants to know more:https://www.eevblog.com/forum/metrology/teardown-standard-resistors/

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: November 14, 2020, 04:38:26 am
content: Nice! I'm no expert but I wouldn't clean them with any sort of solvent. I'd change the oil and then maybe change it again in a few months. First, do no harm.

author: tfm
author_rank: Contributor
timestamp: November 14, 2020, 01:27:55 pm
content: I couldn't find any document showing that these units are supposed to work bathed in oil or just air.According to 2792A(not mine) spec sheet:However, according to page 7 of this document, also 2792A:Full document attached, might be useful for someone in the future.One could infer that the previous model, 2792, the unit I have, is supposed to be bathed in oil for accurate temperature control and stability during calibration. But then, after calibration, what is the good practice, clean it? Just leave it?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: November 14, 2020, 02:07:54 pm
content: Ah, didn't see that! Hopefully there's no contamination of the windings, just oil on the outside. Is it possible oil was used in the thermometer hole?

author: antintedo
author_rank: Contributor
timestamp: November 14, 2020, 02:34:42 pm
content: Storing in air without any cleaning seems to be the most common practice. I assume the manual refers to water dissolved in oil and corrosive degradation products. Fresh high quality oil should not damage them. Pharmaceutical mineral or regular silicone oil might not be good enough. Oil can be kept dry with molecular sieves, there are lots of papers about that. Keep outside surfaces clean from debris that can dissolve in oil when you put resistors into the bath. I would definitely avoid cleaning the inside with anything but oil. To remove corrosive stuff building up over time you can periodically flush them with fresh oil and then store in air. For maximum nuttery you can use a sealed container filled with oil and inert gas. Argon is very practical for this as it sinks in air. For your convenience it might be a good idea to acquire some sealed resistors instead or just accept slightly increased yearly drift.

author: tggzzz
author_rank: Super Contributor
timestamp: November 14, 2020, 02:38:57 pm
content: Not the same, but similar:https://www.eevblog.com/forum/metrology/oil-for-a-leaking-tinsley-standard-resistor/msg2761572/#msg2761572

author: tfm
author_rank: Contributor
timestamp: November 14, 2020, 05:35:59 pm
content: Quote from: Conrad Hoffman on November 14, 2020, 02:07:54 pmYes, I believe that is the case, although I have not opened it yet. Since there is no cal data, I believe it wouldn't hurt to open it up and have a look inside.

author: dl1640
author_rank: Regular Contributor
timestamp: November 16, 2020, 12:24:48 am
content: 2792 can be used in oil bath for higher power dissipation and temperature stability, it is not hermetically sealed wirewound type, you can take it apart and see.While 2792A is metal foil type and iirc it is designed to be used in air.