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OT Deoxit performance on extremely low level switches? OFF-list only

Ed Breya
 

First, please respond directly to me only OFF-list, and only with relevant info. I don't want to get off on another huge Deoxit good/bad/whatever discussion, which has been covered many times. I would just like any feedback or experience info on whether Deoxit would help to improve mechanical switch contact performance used in very low level circuits.

One of my projects involves boxing up some special transformers and a switching system, for isolating and dividing down AC signals by large factors (E-3 to E-6), down as far as the 1 nV RMS region. A fair number of switching elements are needed to route and select various transformer output taps to send to the single output connection. There are two transformers to cover two frequency bands 10 Hz-1 kHz, and 1 kHz-100 kHz, and each has four outputs for the decade dividing. The switching elements need to have as low an on resistance (<< 1 ohm) as possible, and function well at extremely low levels. Since this is an AC system, I'm not worried about Seebeck effects, just the low level contacting ability. The primary sides of the transformers are at more normal levels, so the switches there are not critical.


I have all sorts of nice low level regular and Hg reed relays that would do the job, but since the output side is to be isolated, to minimize interference, it would be much better to do all the switching passively with mechanical switches. This would avoid needing electricity, and the proximity problems of having relay coils and capacitance in the low level environment, and power supply and line noise and ground loops (no power cord), or messing with battery power. Especially, there would be no power transformer emissions to worry about.

I have lots of mechanical switches of all sorts. I'd like to go with a rotary wafer type to select the transformer taps and frequency ranges. I have mostly standard Ag plated type contact ones and some Au ones. I can usually build a switch from pieces for almost any arrangement.

Another, but quite complicated option is to use low level reeds actuated by a mechanically driven magnet, but doing that would be a big project in itself, so scratch that, unless a simple way pops up. Another way is to make heavy analog switches with big MOSFETs, but that's a lot of parts, a battery, and issues with capacitance and crosstalk. So, good old mechanical switching seems the best way to go - if only it can actually be done.

The big question then, is how to get a regular, environmentally exposed contact to be usable in the nV region. Wetting the contacts with Deoxit is the only practical thing I can picture so far. There is another class of contact "protectors" based on synthetic oils, but I think I need chemical action too, so these may not work - I'll have to investigate that too.

So anyway, does anyone have experience or knowledge of how Deoxit would behave for low level contacts? It may boil down to a "try it and see" scenario, but it would be nice to have some info in advance. OFF-list only, please.

Ed

Daveolla
 

Sorry Ed this is on list, I couldn't find your email addy in your post. Dont know if it mentions Deoxit but may be useful.
A google should find this,
What Designers Need to Know About Low Voltage Contacts.pdf
by Samuel Garte 1.415KB
If you cant find it I can send it you.

Dave

At 01:28 PM 5/23/2020, you wrote:
First, please respond directly to me only OFF-list, and only with relevant info. I don't want to get off on another huge Deoxit good/bad/whatever discussion, which has been covered many times. I would just like any feedback or experience info on whether Deoxit would help to improve mechanical switch contact performance used in very low level circuits.

One of my projects involves boxing up some special transformers and a switching system, for isolating and dividing down AC signals by large factors (E-3 to E-6), down as far as the 1 nV RMS region. A fair number of switching elements are needed to route and select various transformer output taps to send to the single output connection. There are two transformers to cover two frequency bands 10 Hz-1 kHz, and 1 kHz-100 kHz, and each has four outputs for the decade dividing. The switching elements need to have as low an on resistance (<< 1 ohm) as possible, and function well at extremely low levels. Since this is an AC system, I'm not worried about Seebeck effects, just the low level contacting ability. The primary sides of the transformers are at more normal levels, so the switches there are not critical.


I have all sorts of nice low level regular and Hg reed relays that would do the job, but since the output side is to be isolated, to minimize interference, it would be much better to do all the switching passively with mechanical switches. This would avoid needing electricity, and the proximity problems of having relay coils and capacitance in the low level environment, and power supply and line noise and ground loops (no power cord), or messing with battery power. Especially, there would be no power transformer emissions to worry about.

I have lots of mechanical switches of all sorts. I'd like to go with a rotary wafer type to select the transformer taps and frequency ranges. I have mostly standard Ag plated type contact ones and some Au ones. I can usually build a switch from pieces for almost any arrangement.

Another, but quite complicated option is to use low level reeds actuated by a mechanically driven magnet, but doing that would be a big project in itself, so scratch that, unless a simple way pops up. Another way is to make heavy analog switches with big MOSFETs, but that's a lot of parts, a battery, and issues with capacitance and crosstalk. So, good old mechanical switching seems the best way to go - if only it can actually be done.

The big question then, is how to get a regular, environmentally exposed contact to be usable in the nV region. Wetting the contacts with Deoxit is the only practical thing I can picture so far. There is another class of contact "protectors" based on synthetic oils, but I think I need chemical action too, so these may not work - I'll have to investigate that too.

So anyway, does anyone have experience or knowledge of how Deoxit would behave for low level contacts? It may boil down to a "try it and see" scenario, but it would be nice to have some info in advance. OFF-list only, please.

Ed

 

Hi Dave,
When you click on a post to read it (assuming you receive each post in a
separate email) you will see this line at the top like the one at the top of
your post as I was reading it just now:
TekScopes@groups.io; on behalf of; Daveolla <grobbins@...>

Sometimes, as in your case it is obvious what your address is. Other times
you have to do a little bit of guesswork.

This was what was at the top of Ed Breya's original post:
to:TekScopes@groups.io; on behalf of; Ed Breya via groups.io
<edbreya=yahoo.com@groups.io>

In this case you can guess what his email address is by simply removing the
equal sign Groups.io put in it to confuse bots.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Daveolla
Sent: Saturday, May 23, 2020 4:50 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] OT Deoxit performance on extremely low level
switches? OFF-list only

Sorry Ed this is on list, I couldn't find your email addy in your post. Dont
know if it mentions Deoxit but may be useful.
A google should find this,
What Designers Need to Know About Low Voltage Contacts.pdf
by Samuel Garte 1.415KB
If you cant find it I can send it you.

Dave

At 01:28 PM 5/23/2020, you wrote:
First, please respond directly to me only OFF-list, and only with
relevant info. I don't want to get off on another huge Deoxit
good/bad/whatever discussion, which has been covered many times. I
would just like any feedback or experience info on whether Deoxit would
help to improve mechanical switch contact performance used in very low
level circuits.

One of my projects involves boxing up some special transformers and a
switching system, for isolating and dividing down AC signals by large
factors (E-3 to E-6), down as far as the 1 nV RMS region. A fair number
of switching elements are needed to route and select various
transformer output taps to send to the single output connection. There
are two transformers to cover two frequency bands
10 Hz-1 kHz, and 1 kHz-100 kHz, and each has four outputs for the
decade dividing. The switching elements need to have as low an on
resistance (<< 1 ohm) as possible, and function well at extremely low
levels. Since this is an AC system, I'm not worried about Seebeck
effects, just the low level contacting ability. The primary sides of
the transformers are at more normal levels, so the switches there are
not critical.


I have all sorts of nice low level regular and Hg reed relays that
would do the job, but since the output side is to be isolated, to
minimize interference, it would be much better to do all the switching
passively with mechanical switches. This would avoid needing
electricity, and the proximity problems of having relay coils and
capacitance in the low level environment, and power supply and line
noise and ground loops (no power cord), or messing with battery power.
Especially, there would be no power transformer emissions to worry
about.

I have lots of mechanical switches of all sorts. I'd like to go with a
rotary wafer type to select the transformer taps and frequency ranges.
I have mostly standard Ag plated type contact ones and some Au ones. I
can usually build a switch from pieces for almost any arrangement.

Another, but quite complicated option is to use low level reeds
actuated by a mechanically driven magnet, but doing that would be a big
project in itself, so scratch that, unless a simple way pops up.
Another way is to make heavy analog switches with big MOSFETs, but
that's a lot of parts, a battery, and issues with capacitance and
crosstalk. So, good old mechanical switching seems the best way to go -
if only it can actually be done.

The big question then, is how to get a regular, environmentally exposed
contact to be usable in the nV region. Wetting the contacts with Deoxit
is the only practical thing I can picture so far. There is another
class of contact "protectors" based on synthetic oils, but I think I
need chemical action too, so these may not work - I'll have to
investigate that too.

So anyway, does anyone have experience or knowledge of how Deoxit would
behave for low level contacts? It may boil down to a "try it and see"
scenario, but it would be nice to have some info in
advance. OFF-list only, please.

Ed







--
Dennis Tillman W7pF
TekScopes Moderator