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

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unseenninja:
For anyone looking to make their own cables, I can confirm that the Huber & Suhner G_02330_HT cable mates very nicely with the Pomona 5056 two lug triax connector. Just don't try to push the cone inside the cable's outer sheath like I did, it's enough to just engage the tip of the cone underneath the trimmed outer shield when you screw the plug together after fitting the pin and soldering the guard shield to the guard tube.

I also found the H&S cable really easy to work with. 20 AWG wire strippers will remove the the black, conductive layer cleanly from the inner dielectric and you can then strip the inner dielectric from the centre conductor with 22 AWG strippers. That way, you don't need to deform the inner dielectric or nick the inner conductor when you prepare the cable. For the outer shield and dielectric, a scalpel and care was sufficient. You'll need to cut along the outer sheath and dielectric from your cut as they will not pull off the cable.

Although I ordered 3m of cable from Mouser, they supplied me with three feet instead.  :palm:  Hopefully, by the time I try to order again, their pick and pack people might be more observant of the fact that it says, in capital letters, "Coaxial Cables SOLD IN METERS" on the product listing page!
 

BD1QMP:
Today, I received my  Keithley 617 with very good condition. it was made in 1991 or 1992, and last cal time is 1999. when I power on it, on current and 2pA mode, no input, the read is change from 20 counts to 300. Now, I have work to do. ;D. maybe need clean the pcb first and change the capacitors .

Kosmic:

--- Quote from: BD1QMP on April 24, 2024, 07:12:11 am ---Today, I received my  Keithley 617 with very good condition. it was made in 1991 or 1992, and last cal time is 1999. when I power on it, on current and 2pA mode, no input, the read is change from 20 counts to 300. Now, I have work to do. ;D. maybe need clean the pcb first and change the capacitors .

--- End quote ---

I would only attempt cleaning if the PCB is really dirty and changing capacitor if you really suspect them to be bad. Also always wear clean cloves when manipulating the input board.

But what is the problem exactly with your unit ? if it's simply a offset after removing Zero Check, check the manual page 7-5 chapter 7.4.8 "Input Offset Adjustment".

HighVoltage:

--- Quote from: BD1QMP on April 24, 2024, 07:12:11 am ---Today, I received my  Keithley 617 with very good condition. it was made in 1991 or 1992, and last cal time is 1999. when I power on it, on current and 2pA mode, no input, the read is change from 20 counts to 300. Now, I have work to do. ;D. maybe need clean the pcb first and change the capacitors .

--- End quote ---

Maybe just place a short on the input and watch it again.
Some charge can caused this,

Alex Nikitin:

--- Quote from: HighVoltage on April 24, 2024, 08:24:40 pm ---Maybe just place a short on the input and watch it again.
Some charge can caused this,

--- End quote ---

You don't place a short on the input of a transimpedance amplifier (such as an electrometer in the current measuring mode), you use a screening cap over the input (or just a bit of an aluminium foil) !

Cheers

Alex

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