Electronics > Metrology

Keithley 182 leakage

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e61_phil:
Hi all,

in another thread we discussed how well a Hamon divider (like Fluke 752A) could be self-calibrated using anything other than a proper Null-meter.

In my opinion the most critical parameter is the leakage of the instrument, when floating in the middle of the bridge on half the supply voltage.

My Keithley 182 showed ~100Gig at 10V. That is way better than specified, but other voltnuts measured better values. Maybe we can collect some data from different Keithley 182 here.

There is no need for a fancy SMU, electrometer or something like that. A simple meter with 10Meg input impedance, low enough input current and sensitivity will do the job. I appended an example using a HP 34401A. The 10V source could be a simple lab power supply.

In this setup my 34401A reads ~0.8mV.

0.8mV / 10Meg = 80pA

10V / 80pA = 125Gig

It will take a bit of time to settle. It makes also sense to swap the polarity on the source. Keep in mind, that the GUARD/SHIELD of the K182 is tight to Mains earth.

Thanks for your help!
Philipp

HighVoltage:
Hello Philipp

No 182 here but 2 Keithley 181

Your setup with an external PSU at 10V and 10 MOhm DMM in series does not reveal any usable data for me. The measurements are all over the place. Maybe I have too much noise today in my lab.

So, I used a Keithley 617 Electrometer with the internal 10V output of the 617.

Keithley 181 #1: 26 to 28 pA
Keithley 181 #2: 5 to 6 pA

These readings are taken after about 10 min stabilization time and me being 3 m away.

e61_phil:
Hi Ulf,

thank you very much! It seems that my K182 is a unit with higher leakage than usual (even if it is way better than specified).

Interesting, that your DMM setup was all over the place. The unshielded part of my cable was rather short (see picture) and I used 100NPLC. My currents are higher than yours, but it should work even with lower currents.

Just for fun I also compared the 34401A setup against my Keithley 617 at 10pA (100Gig 1V). There is some offset in the 34401A measurement, but it is ok for a rough idea.

gamalot:
Sorry to get off topic, how did you guys connect the shield of the cable and the plug together?  :-//

The Soulman:
Also, for a simpler/easier/cheaper and (arguably) better setup one could use 9V alkaline battery as a source and a handheld meter
for lower noise and truly floating measurement.
Add more batteries in series for a higher test voltage if needed.

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