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617 Guarded Low Current Measurement

200, 210, 220, 486/7, 60x, 61x, 64x Electrometers
409, 41x, 42x, 44x, 48x -
14x, 18x, 1801 Nanovoltmeters
15x, 18x Null Detectors/Microvoltmeters
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p.markus
Posts: 2
Joined: November 21st, 2011, 3:56 am
Country: Germany

617 Guarded Low Current Measurement

Post by p.markus » November 21st, 2011, 4:01 am

Hello,

I'm using a 617 Electrometer for the purpose of measuring low currents (<1nA). Reading the manual I was confused by the fact that it advises the user not to use the guarded mode in AMPS. Therefore my question, is it possible with the 617 Electrometer to conduct guarded Current-measurements?

Also, since this model is already quite old I was wondering if anyone can tell me how reliable these models still are?

Best regards,
Markus

Norbert W
Keithley Applications
Keithley Applications
Posts: 227
Joined: October 21st, 2010, 7:18 am
Country: Germany

Re: 617 Guarded Low Current Measurement

Post by Norbert W » November 24th, 2011, 12:16 am

By design the 617 uses a feedback technique to measure current; doing so reduces the
voltage across the input to a quite low level and ensures that the Lo potential is near the
Hi input potential, which in effect means the Lo is guarding the Hi.
So one do not have to (and must not) use the special input configuaration when using guarding for voltage measurements
(This guarding technique for current measurements would only be of use for even older electrometers where one could alternatively use
a shunt measurement technique. Again: not for the 617).

If you are interesed in more details please have a look at the 617 instruction manual.

The reliability will depend on the history of your specific model, e.g. the age when it was built, the
overall time it was in operation, applications (' used to specs', 'handled with care'), time to last adjustment &c.
I know units which still work very well.

p.markus
Posts: 2
Joined: November 21st, 2011, 3:56 am
Country: Germany

Re: 617 Guarded Low Current Measurement

Post by p.markus » November 28th, 2011, 3:21 am

Dear Norbert,

thank you for your reply, this was exactly what I needed to know.

Best,
Markus

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