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616 volt/ampere measurements

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geda7325
Posts: 7
Joined: May 24th, 2012, 2:56 am
Country: Italy

616 volt/ampere measurements

Post by geda7325 » February 6th, 2013, 12:08 am

I'm trying to measure voltage and current across a source that allegedly has an output impedance always matching that of the electrometer. I have chosen the 10^-11 ampere range (and thus an input impedance of 10^11 ohms) and before performing the measurements I have disconnected the tri-axial cable and disabled zero check to see how much is the noise. I got a reading of about +0.00300. Then I enable zero check, connected the tri-axial cable and disabled again zero check. This time I got the following reading: about +0.00600. Then, I repeated the above procedure after having inverted the alligators (the polarity) on the DUT. This time I got: -0.00018. May I say that the measured value is nearly plus (or minus) 0.00300. Namely, may I take the open input reading (the first one) as a kind of offset to be subtracted to the actual readings from the DUT?

Thank you very much for your attention,

Geda7325

Dale C
Keithley Applications
Keithley Applications
Posts: 2849
Joined: June 10th, 2010, 6:22 am
Country: United States
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Re: 616 volt/ampere measurements

Post by Dale C » February 6th, 2013, 6:51 am

Look at page 8 of the Model 616 instruction manual.
It talks about low current measurements and using the ZERO control.
Here is the link to the manual on the Keithley web site.
http://www.keithley.com/support/data?asset=5258

geda7325
Posts: 7
Joined: May 24th, 2012, 2:56 am
Country: Italy

Re: 616 volt/ampere measurements

Post by geda7325 » February 7th, 2013, 11:45 pm

Dear Dale,

Thanks. I carefully followed the instructions ( included the two hour warmup time) but I seemingly still have a high offset current. I tried to measure voltage with volt function (input impedance > 2x10^14 Ohms) and with clips not connected to the DUT (but still shielded in a Faraday cage) I get a reading of +0.0220 volts. Does 616 need calibration? Or can I safely make measurements by exchanging the polarity (by making two measurements exchanging the clips) and then by taking the measured value as the semi-difference?

Thank you,

Geda7325

Dale C
Keithley Applications
Keithley Applications
Posts: 2849
Joined: June 10th, 2010, 6:22 am
Country: United States
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Re: 616 volt/ampere measurements

Post by Dale C » February 8th, 2013, 5:36 am

It could have a high offset current. The unit is probably close to 35 years old.
Keithley does not service this old of a product.
You could follow the cal procedure and see if that helps, but that is about it.
I would recommend the Model 6514 to replace the Model 616.

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