Question- DMM grease

[martinuy]

Hello!

I recently bought a great used Fluke 87 (old model)...

Disassembly required for cleanup of the display contacts and turn-dial contacts...

The question is: what kind of grase is recomended to put in the turndial mechanism?

Thankyou!
Best Regards
Martin

[andyg]

I usually use Electrolube SGB on sliding contacts like that. Seems to work okay. I don't know if its what you're "suppose" to use though...

[Psi]

Yeah, there's special 'switch contact' grease you can buy.

However, typical white bicycle grease has worked fine for me in an emergency.

[robrenz]

Caig Deoxit Gold is made for gold contacts

[sotos]

Here is what Fluke uses.

[deephaven]

I have some difficulty imagining how this grease works. Looking at the data on the grease, it says it's conductive. If that's the case why doesn't it interfere with connections round the switch by providing a resistance between them?

[sotos]

I have some difficulty imagining how this grease works. Looking at the data on the grease, it says it's conductive. If that's the case why doesn't it interfere with connections round the switch by providing a resistance between them?

Did you see this one, from the Fluke manual?

 Because I don’t see that’s its conductive.

[deephaven]

I have some difficulty imagining how this grease works. Looking at the data on the grease, it says it's conductive. If that's the case why doesn't it interfere with connections round the switch by providing a resistance between them?

Did you see this one, from the Fluke manual?

 Because I don’t see that’s its conductive.

If it's not conductive, the converse argument is that isn't there a danger of it getting between the wiper and the PCB pad and causing an open circuit? Or is there enough pressure on the wiper to guarantee to overcome this?

[sotos]

As I understand from the manual, all the Flukes have this grease in their rotary switches.

[sotos]

But because this stuff is expensive, I use dielectric grease and I’m happy with this.

[Monkeh]

I have some difficulty imagining how this grease works. Looking at the data on the grease, it says it's conductive. If that's the case why doesn't it interfere with connections round the switch by providing a resistance between them?

Where does it say it's conductive?

Contact pressure on the switch is more than sufficient to displace light greases and oils.

[deephaven]

Where does it say it's conductive?

In the manufacturer's data, but that may have been a different product from the one Fluke used.

[Monkeh]

Where does it say it's conductive?

In the manufacturer's data, but that may have been a different product from the one Fluke used.

Please elaborate, because nothing posted in this thread says anywhere that it is conductive.

[deephaven]

Where does it say it's conductive?

In the manufacturer's data, but that may have been a different product from the one Fluke used.

Please elaborate, because nothing posted in this thread says anywhere that it is conductive.

No, I just looked up the manufacturer and saw a general description their products which mentioned conductivity. I had wrongly assumed that they were all conductive but now know this isn't the case. Sorry for the confusion.

[MikeO]

Certainly, there is no risk in using what fluke recommends.  Barring that being a convenient option, I would recommend silicone dielectric grease.

In my opinion, there is no issue with it getting between conductors.  As previously mentioned, there is sufficient contact pressure to displace the grease.  What little will remain will be so fine in cross section, it will fail to insulate the contacts.  And as it is non-conductive, and (generally) displaces water, there is no issue with it getting where you don't want it.  If you need to solder in that location later, you'll need to clean aggressively with strong isopropyl, as silicone is the ultimate contaminant.

Don't forget, non-conductive just means high resistance, which equals electrical resistivity per length, multiplied by length of specimen (thickness seems more logical here), divided by cross sectional area of specimen (Pouillet's Law).  So, imagine a glob of grease between the contacts, and surrounding them.  The electrons must flow through the grease.  There is a path directly between that has a small cross section, but a very small length (the numerator in the equation, making the resulting resistivity very small and therefore, sufficiently conductive to break down from even a small voltage).  There is also a path through the glob, which is a greater risk, as it contacts other terminals.  But, this glob has a length (thickness) orders of magnitude larger, so despite the larger cross sectional area, has high resistance, preventing spurious signals from getting through.

In my neighborhood, the most convenient way to get it is at the auto parts store, where it is sold as silicone dielectric grease or tune-up grease.  I just looked in my tool bag, and the here is what I'm currently using:

Permatex, part number 22058.

Regards,
Mike O'

[sotos]

In my neighborhood, the most convenient way to get it is at the auto parts store, where it is sold as silicone dielectric grease or tune-up grease.  I just looked in my tool bag, and the here is what I'm currently using:

Permatex, part number 22058.

Regards,
Mike O'

I use  LOCTITE® Dielectric Grease, which I think is the same as yours.

[MikeO]

In my neighborhood, the most convenient way to get it is at the auto parts store, where it is sold as silicone dielectric grease or tune-up grease.  I just looked in my tool bag, and the here is what I'm currently using:

Permatex, part number 22058.

Regards,
Mike O'

I use  LOCTITE® Dielectric Grease, which I think is the same as yours.

I think you're right.

[Monkeh]

I think it's silicone grease like any other.

[robrenz]

I don't think dielectric grease should be used on contacts as stated in this quote from wikipedia. It is intended for the rubber or elastomeric parts of electrical connections not the actual contacts

"Another common use of dielectric grease is on the rubber mating surfaces or gaskets of multi-pin electrical connectors used in automotive and marine engines. The grease again acts as a lubricant and a sealant on the nonconductive mating surfaces of the connector. It is not recommended to be applied to the actual electrical conductive contacts of the connector because it could interfere with the electrical signals passing through the connector in cases where the contact pressure is very low. Products designed as electronic connector lubricants, on the other hand, should be applied to such connector contacts and can dramatically extend their useful life. Polyphenyl Ether, rather than silicone grease, is the active ingredient in some such connector lubricants.
 
Silicone grease should not be applied to (or next to) any switch contact that might experience arcing, as silicone can convert to silicon-carbide under arcing conditions, and accumulation of the silicon-carbide can cause the contacts to prematurely fail."

[martinuy]

Thank you all for the replies!

The recomended grease is so expensive, I think that there should be no dielectric grease any, must be alien formulated compuound!
£39.98 for 10g!!!

But this isn't dielectric grease, is POTENTIOMETER CONTACT LUBE !!

Anyway, i used NYE lubricants (synthetic oil #179) here for electromechanic temperature/presure registrators (that wacky disc printers used in industry), it's recommended lubricant for ultra expensive Honeywell registrators, NYE must be high quality brands...

[Psi]

I think what they mean is the grease does have some resistance, (probably in the Mohms or Gohms), and may cause small current to flow that could pull high impedance inputs up or down.

If they don't put that into the datasheet, companies will complain when their 10Mohm signals are being disrupted by the so-called non conductive grease.

[Monkeh]

I think what they mean is the grease does have some resistance, (probably in the Mohms), and may cause small current to flow that could pull high impedance inputs up or down.

Silicone grease is a dielectric. It takes kilovolts to break it down.

[MikeO]

I don't think dielectric grease should be used on contacts as stated in this quote from wikipedia. It is intended for the rubber or elastomeric parts of electrical connections not the actual contacts

"Another common use of dielectric grease is on the rubber mating surfaces or gaskets of multi-pin electrical connectors used in automotive and marine engines. The grease again acts as a lubricant and a sealant on the nonconductive mating surfaces of the connector. It is not recommended to be applied to the actual electrical conductive contacts of the connector because it could interfere with the electrical signals passing through the connector in cases where the contact pressure is very low. Products designed as electronic connector lubricants, on the other hand, should be applied to such connector contacts and can dramatically extend their useful life. Polyphenyl Ether, rather than silicone grease, is the active ingredient in some such connector lubricants.
 
Silicone grease should not be applied to (or next to) any switch contact that might experience arcing, as silicone can convert to silicon-carbide under arcing conditions, and accumulation of the silicon-carbide can cause the contacts to prematurely fail."

This is interesting.  I work in the marine industry, and dielectric grease (silicone) is absolutely necessary to achieve any useful connector, or even bulb socket, life.  I do note, there is no reference in the wikipedia article.  On the other hand, there are references in wikipedia's general article on Silicone.  Doing some more poking around (very, very little actual research--under a minute), I note that the bulk of these claims come from Santolube and CRC's literature.  Santolube, meh.  CRC, well, that's quite the legitimate publisher when it comes to chemistry.  Further, it appears they drew all of their information from:

_A_Comparison_for_the_Effects_of_Various_Forms_of_Silicon_Contamination_on_Contact_Performance_ by Witter, G. (Published in "Components, Hybrids, and Manufacturing Technology, IEEE Transactions, Mar 1979)

I've let my IEEE membership lapse, so, I can't check the article.  Regardless, a bit of the CRC book that is available to me, from a google book review of the CRC press, that references Witter's work seems compelling.  I would note, it seems you need an arc to make this happen.  If I recall my physics, if it's DC, it arcs.  That being said, a small signal is a very, very small arc.

I'm going to try to learn more about this.  I'd like to do the best work, and advise my customers well.  I do believe though, based more upon experience than anything else, for the rotary switch in a DMM, your are fine with the silicone grease.

Nice work Robrenz!  Thanks!

Regards,
Mike O'

[robrenz]

More

Quote from Electrolube website
http://www.electrolube.com/docs/lubricantmain.asp?id=68

"Silicone contamination
As silicones can “creep” great distances, these products should not be used in switch assembly areas. When silicone is present between moving or vibrating contacts, they react under arcing conditions to form silicon carbide. These crystals abrade the contact surface and cause electrical breakdown."

Quote from Wikipedia
http://en.wikipedia.org/wiki/Silicone

"Silicone contamination of electrical switch contacts can lead to failures by causing an increase in contact resistance, often late in the life of the contact, well after any testing is completed.[10][11] Use of silicone-based spray products in electronic devices during maintenance or repairs can cause later failures."

Quote from Electrolube contact lubrication info page
http://www.contact-lubricants.com/061/the-benefits-of-contact-lubricants.html

"Silicone Contamination
Silicone contamination can be caused only if low molecular weight silicones (silicone oligomers) are present. Silicone oligomers exist in abundance in silicone oils, greases, pastes and materials such as furniture and floor polish, and hand creams. Its use as a mould release also means it is often present on moulded plastic components. As silicones creep amazing distance, silicone contamination can occur far from the point where the silicone material was used.
When free silicones are present between moving or vibrating electrical contacts – and as that includes fretting, all electrical contacts are included – and especially where arching occurs, then the free silicones will be transformed into hard crystals as silicone compounds, notably silicone carbide. These crystals, as well as rapidly abrading the contact surface, will cause breakdown.
Silicone contamination cannot be removed easily and should be avoided wherever possible. Silicone carbide crystals in particular are extremely difficult to remove other than with a file, which will of course damage the contacts. Certain contact lubricants can prevent the damage caused by silicones. A particularly effective treatment is Electrolubes Eltinert F range of contact lubricants which will remove silicone contamination even after silicone carbide crystals have formed. Eltinert F is a modified fluorinated oil which is believed to act by reacting with silicone carbide to form volatile silicone tetraflouride gas."

[T4P]

Hmm, do you ever see arcing on a meter's rotary switch anyway  Not that it ever could unless it's piss poor design