Products > Test Equipment
Fun With Low Leakage/Bias Current: Femtompere, Electrometer, Keithley 617
BD1QMP:
after 2 days power on. the meter become stable.
from noon to night, room temperature changed from 25 degree c to 21 degree C, the no input, the read change from +75 to -50.
--- 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 ---
ZhuraYuk:
For those looking for cheap Keithley cables/connectors. Recently a wery cheap triaxial equipment apeared on ebay, I bought few items and the quality is good. The connectors are precise and fit nicely, the cable have triple PTFE (FEP) insulation, really low leakage
https://www.ebay.com/itm/276059871116
ZhuraYuk:
Question to everyone, how much time it takes for your Keithley 617 to settle down to at least 15fA when zero check disabled? My input circuitry seems to be very contaminated, because input current start from 150 fA and goes to 15fA in 20 minutes. Tried to wash input connector but did not helped.
David Hess:
--- Quote from: ZhuraYuk on May 08, 2024, 08:07:34 pm ---Question to everyone, how much time it takes for your Keithley 617 to settle down to at least 15fA when zero check disabled? My input circuitry seems to be very contaminated, because input current start from 150 fA and goes to 15fA in 20 minutes. Tried to wash input connector but did not helped.
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If construction is on a substrate, then I think that level of leakage could be caused by circuit board hook, which is sort of like dielectric absorption. Circuit board hook can be caused by contamination of the substrate and the solution is usually to clean and then bake out the substrate.
If it was just leakage, then I would not expect it to get better as the circuit warms up.
Alex Nikitin:
--- Quote from: ZhuraYuk on May 08, 2024, 08:07:34 pm ---Question to everyone, how much time it takes for your Keithley 617 to settle down to at least 15fA when zero check disabled? My input circuitry seems to be very contaminated, because input current start from 150 fA and goes to 15fA in 20 minutes. Tried to wash input connector but did not helped.
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Takes about 20 seconds to settle below 5fA. The input connector is the last thing to touch. The main sources of leakage in the 617 in my experience are the relays and the input FET. The relays can be a real problem as a good replacement is not easy to find. The only option from stock I know of is the MEDER HI05-1A66, available from Mouser. These relays are not quite as good as the original though much better than any standard relays. I've measured the leakage across the open relay contacts at 20fA for 100V. A really good low leakage relay (as some Crydom custom made relays I have in my lab) leak
less than 3fA at 100V (see the graph below, 0V for 5min, than 100V for 5min and back to 0V for 5min) and have considerably smaller DA, settling in seconds rather than in minutes.
Cheers
Alex
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