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Products => Test Equipment => Topic started by: balage on April 03, 2019, 12:38:14 pm

Title: Leakage current measurement with Keithely 237 high voltage SMU
Post by: balage on April 03, 2019, 12:38:14 pm
Hi Guys,

I have bought a Keithley 237 high voltage source measure unit. I haven't got massive experience in the world of low level measurements. But everybody started somewhere.

So I would like to ask you opinion on my first measurements. I am measuring the leakage current of a high voltage 4,7 nF MLCC (https://hu.mouser.com/datasheet/2/212/KEM_C1051_GOLDMAX_Z5U-1140498.pdf (https://hu.mouser.com/datasheet/2/212/KEM_C1051_GOLDMAX_Z5U-1140498.pdf)). I have simply connected the two terminals of the cap to the FORCE HI and the Groung banana on the SMU. I have set a source voltage of 1000 Volts.

At the begining I can measure around 8-10 nA and this value settled down to 2 nA slowly. It is expected based on what is the written in Keithley's Low Level Measurements Handbook. You can see the copied image below. So the average looks good for me. The thing I cannot understand is that the momentary measured value is always changing, e.g. between 1,99 - 2,24 nA. The resulted resistance is 502 GOhm to 446 GOhm at this point.

It is clear that a proper measurement chamber should be used to isolate the environment. One is under construction. I am using the experience shared here: https://www.eevblog.com/forum/metrology/my-triax-cable-shielded-box-project-for-keithley-instruments/ (https://www.eevblog.com/forum/metrology/my-triax-cable-shielded-box-project-for-keithley-instruments/)

Generally my question is that this variation in the momentary measured values is expected? Why can I see this?
How do you think the AC current caused by the ripple of source voltage affects the leakage resistance measurement? I assume the source voltage has ripple. I will measure it.

Cheers,