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Fun With Low Leakage/Bias Current: Femtompere, Electrometer, Keithley 617

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Alex Nikitin:
You can use a ceramic NP0 from TDK, for example:
this one
Cheers

Alex

Kosmic:
Hmm looking at my pictures, I think I need to change C307 in my unit too. Completely missed that last time it was open.

ZhuraYuk:
Does anyone had an issue when barely deforming or knocking on electromer's chassis or housing makes measurement go crazy for few seconds? I rechecked electrometer board but cant find any cold joint there. Resoldered few suspicions places but that not helped.
Maybe there is a place that fails often? My second K617 not doing such thing so it is for sure an issue.

David Hess:

--- Quote from: ZhuraYuk on May 14, 2024, 09:43:29 pm ---Does anyone had an issue when barely deforming or knocking on electromer's chassis or housing makes measurement go crazy for few seconds? I rechecked electrometer board but cant find any cold joint there. Resoldered few suspicions places but that not helped.
--- End quote ---

That is common with sensitive high impedance circuits.  Vibrating wires cause movement of charge.  Mechanically securing the parts and wires helps.

I would tap around with an insulated poker or something to see if any areas are more sensitive than others.

ZhuraYuk:

--- Quote from: David Hess on May 15, 2024, 09:56:25 am ---That is common with sensitive high impedance circuits.  Vibrating wires cause movement of charge.  Mechanically securing the parts and wires helps.

I would tap around with an insulated poker or something to see if any areas are more sensitive than others.

--- End quote ---

I have 6 electrometers of different vendors including second K617 and non of them is doing that. There is some drift when you shake the device but just a little.
The one I have issues with, goes to higher range even from lightly knocking on the housing.

Anyway, I was able to remove old reed switches from the relays. Some are easily sliding out, some require desoldering the relay and poling the switch with tweezers.
Replaced only first 4 relays and now input current goes to 5fA in 5-10 seconds after switching to amps. Easily can be compensated to zero current.
The original look of the board was  preserved.


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