Can I grease my DMM selector with SILICONE oil?

[joeqsmith]

Don't waste your time, we're being trolled!

Yep. 

[coromonadalix]

yep +1

[Trader]

... experiments showed that the absence of lubricant did not affect the durability of the contacts.

My RM303 was reading ~1.5 Ohms with shorted probes, after rotating the selector a couple of times decreased to ~0.1 Ohms.  I opened it and see a grease/vaseline in the PCB traces, after cleaning with isopropyl alcohol solved the problem, now is ~0.07 Ohms always.

ps: I also found recommendations to use "Silicone Dielectric Grease", but  I think this insulation property is the culprit for the extra +1.5 Ohms.

[helius]

I'm not too sure you have improved the accuracy. Most DMM leads have ~0.5 ohm each and the contact itself is rather small.
Did you use an actual shorting bar across the + and COM sockets, or just touch the probes together? Only the first is going to be ~0 ohms.

[Trader]

"touch the probes together". Each probe has 0.03 Ohms (in a 4-wire measure).

Before cleaning was always around 1.5R and now ~0.07R.

Yes, I know the accuracy is not good for low ohms, but I measured exactly 1.00R (a 1 Ohm resistor).

[helius]

There is a wide variation in lead resistance, even with quality brands. Using the Fluke 8060A, I measured from 0.07 ohms to 3.50 ohms (!) on a half dozen pairs of probes. The 3.50 leads were echt Fluke, and the lowest was a set that came with an HP-Yokogawa meter.

Interesting that your DMMs were so heavily greased. Silicone dielectric grease is most commonly used for contacts that are exposed to the weather, for example, spark plug wires or lamp bulbs/sockets in wet or outside locations. It works very well to prevent the contacts from corroding together and becoming hard to remove. It also has applications to prevent flashover in medium-voltage circuits, although the DMM itself should be designed to safely absorb such events. I think if I had to restore any lubrication in the switch wipers, I would use a very small amount of contact enhancing oil, not grease.

[Trader]

There is a wide variation in lead resistance, even with quality brands. Using the Fluke 8060A, I measured from 0.07 ohms to 3.50 ohms (!) on a half dozen pairs of probes. The 3.50 leads were echt Fluke, and the lowest was a set that came with an HP-Yokogawa meter.

Yes, same thing here, I have a lot of multimeter probes, I tested each one and I kept only the best ones, around 0.025 Ohms.

Interesting that your DMMs were so heavily greased. Silicone dielectric grease is most commonly used for contacts that are exposed to the weather, for example, spark plug wires or lamp bulbs/sockets in wet or outside locations. It works very well to prevent the contacts from corroding together and becoming hard to remove. It also has applications to prevent flashover in medium-voltage circuits, although the DMM itself should be designed to safely absorb such events. I think if I had to restore any lubrication in the switch wipers, I would use a very small amount of contact enhancing oil, not grease.

This site shows some DMMs teardowns, look at the Aneng AN870 PCB, they also use grease/vaseline.  Seems the high-end DMMs don't use that.

https://lygte-info.dk/pic/Aneng/AN870/DSC_7499a.jpg

[nukie]

Your dmm has a high impedance input in the megaohm range, if your grease conducts then it would mess up the sensitivity and also introduce errors in the measurements.

I say leave the dmm  dial in the setting you use most often and let the autooff do its job. This way you can prevent wear in expense of battery life. You have Eneloop right?

If you are switching the dial too often consider getting a second dmm for the second most used mode. You can never have enough dmm.

[helius]

The lowest resistance is not necessarily the "best" for all purposes. Some of the probes may be designed for lower reactance at the expense of having a couple of ohms that need nulling out at low ranges.