« Reply #9 on: November 20, 2016, 08:03:48 pm »
You can test this waving your hand near some unshielded wire that is connected to an instrument that has a noise floor well below 1nA.
I once tried to measure insulation resistance of a piece of ceramic substrate. I set the bias voltage to 1kV, and my meter reads as low as a couple tens of nA. Forget about moving hands or any conductive metal parts around, even only blowing air can cause displacement current of air dielectric, which considerably alters readings by up to hundreds of nA, so one word or suggestion: shield your DUT, not only electrically, but also mechanically. Don't let air to pass by it, or any thing that can carry charges.
Exactly. Air can carry charge from HI to LO. That is why having a hermetically sealed enclosure around the DUT and energizing that enclosure to GUARD potential is an important technique. All of the air inside of the sealed enclosure is charged to GUARD potential creating a fluid that insulates against leakage from HI to LOW.
I set one of these up and measured some wire. During one of the tests I encountered a very large current which was traced to a thumbprint that spanned the wire insulation and the copper core. Cleaning the sample restored the low current. I then purposely added a thumbprint to verify the cause and the measurement was ruined as I expected.
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working instruments :Keithley 260,261,2750,7708, 2000 (calibrated), 2015, 236, 237, 238, 147, 220, Rigol DG1032 PAR Model 128 Lock-In amplifier, Fluke 332A, Gen Res 4107 KVD, 4107D KVD, Fluke 731B X2 (calibrated), Fluke 5450A (calibrated)