Electronics > Metrology

Oil for a leaking Tinsley standard resistor

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tggzzz:
I've got a Tinsley 1659 oil-filled 10ohm standard resistor, and some of the oil has leaked out. The datasheet indicates that "the standards are not filled with oil when supplied. The recommended oil is Castrol Whitemor WOM14 or if it is not obtainable any high-quality non-corrosive oil can be used such as Transformer Oil".

Firstly I have to clean the leaked oil off the outside, then decide whether or not to top up or refil the oil. The latest calibration markings are from 1995, so I think it is reasonable to assume there are no PCBs in the oil!

Thereafter I could just leave the remaining oil in the resistor with a 1-2cm airgap at the top, or drain the oil. Either would imply not putting 1A(!) through the coil, but I don't see any real problem with that.

Alternatively I could drain the oil and replace it. I've looked for Castrol Whitemor WOM14 (now called optileb wom 14), which turns out to be a "medicinal white oil" available in 208l drums - i.e. about 103 times too much!

Fleabay has sellers of Shell Diala B "transformer oil", but it isn't clear that it is suitable. In particular it contains potassium hydroxide and (unsurprisingly) the electrical properties are changed if stored in non-airtight containers. The standard resistor will never be airtight! Having said that, in my application I'm more concerned about any corrosive properties of the KOH.

I'm aware of Ralf Richard Ohmberger's 1659 teardown at https://www.amplifier.cd/Test_Equipment/other/Tinsley-1659-Standard-Resistor.html , but he is careful to avoid claiming that oil is suitable.

I'd appreciate any comments on sources of Whitemor/Optileb oil, or alternatives that are known to be suitable.

Gyro:
"medicinal white oil"  sounds a bit like medical grade liquid paraffin - used as a laxative (among other things).

tggzzz:
Well, it is a "food grade lubricant", tasteless, and "complies with all of the purity requirements ... for Liquid Paraffin"!
https://www.kernow-oils.co.uk/food-grade-lubricants/castrol-whitemor-wom-14-medicinal-white-oils-6920/c-6920/

Gyro:
I certainly remember hearing that Liquid Paraffin was used to lubricate the blades of industrial bread slicing (as in sliced loaf) machines... with slight laxative effect if you ate enough! It looks as if they've found a fancy brand name substitute.

picburner:
If it were not for the addition of perfume and Isopropyl palmitate, you could use Johnson's baby oil which is exactly liquid paraffin in even 500ml bottles.
I don't know how much these additives can affect electrical properties.

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