Products > Test Equipment
Fun With Low Leakage/Bias Current: Femtompere, Electrometer, Keithley 617
HighVoltage:
--- Quote from: Alex Nikitin on April 24, 2024, 10:00:39 pm ---
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
--- End quote ---
Very true, my mind was somewhere else, thanks for pointing this out!
BD1QMP:
when I was testing it, I put a copper foil on it.
BD1QMP:
You are totally right. I measured 2 capacitors, the ESR and capacity are normal. Then I changed the traxial connector. the offset become much worse |O. Maybe my cloves are not clean :(,or the connector from Taobao(Aliexpress) is bad >:(
Next week is labor day, we will have 5 days holiday, I want to clean the original connector and put it back.
--- Quote from: Kosmic on April 24, 2024, 12:54:12 pm ---
--- 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".
--- End quote ---
BD1QMP:
After put back the original BNC connector, I recorded the offset. Is it normal or not? thanks
Alex Nikitin:
--- Quote from: BD1QMP on April 28, 2024, 01:47:57 pm ---After put back the original BNC connector, I recorded the offset. Is it normal or not? thanks
--- End quote ---
If that is the drift when switching on from cold, it might be normal. According to the manual, the warm up time to rated accuracy is 2 hours. There are two trimmers on the input board, one to adjust the DC offset (in the Voltage measuring mode) and the second is to compensate the input current (in the Current measuring mode), so it can be adjusted to zero. Both are not easy adjustments, mostly because you need to keep the top cover on to get the temperature stable and correct, than open the cover (thus upsetting the thermal equilibrium) to do the adjustments, only to close it quickly and see if you hit the spot after the temperature settles again :palm: . Both the offset and the input current will drift noticeably when you open/close the cover however by several iterations it is possible to get a reasonable result.
Cheers
Alex
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