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Diff. conductance with 2635A

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alpaq40
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Joined: November 2nd, 2010, 7:51 am
Country: Canada

Diff. conductance with 2635A

Post by alpaq40 » November 2nd, 2010, 8:01 am

Hello,

Your description for Differential Conductance Keithley Method involved a current source and a nanovoltmeter.

Is there any way to perform this measurement with only a sourcemeter unit model A2635?

Thank you

Alex

Dale C
Keithley Applications
Keithley Applications
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Re: Diff. conductance with 2635A

Post by Dale C » November 2nd, 2010, 11:03 am

Yes. You can make this measurement with a Source Meter or SMU.
The trouble is the voltmeter capability of the SMU or Source Meter is not as sensitive or accurate as a standalone voltmeter.
For the high conductance devices the voltage drop is usually small, say mV(0.001V) and below.
The SMUs and source meters all have several hundred micro volts of uncertainty on the most sensitive range.
If this does not bother your measurement then by all means use the SMU or Source Meter.
Then follow the procedure and formulas for differential conductance criteria in the Model 6221 reference manual.
Look in section 5.
It is generally recommended to use a separate current source and a separate voltmeter to do differential conductance.

alpaq40
Posts: 2
Joined: November 2nd, 2010, 7:51 am
Country: Canada

Re: Diff. conductance with 2635A

Post by alpaq40 » November 4th, 2010, 7:45 am

Hello Dale,

I tried to apply delta operation from front pannel control. On model A2635, I don't think we have the possibility to do any of delta measurement (2 points, 3 points, or diff. conduct).

Am I right? If I can't do this, I guess I'll have to program to do it remotly.

I want to measure resistor in the order of 50k. I want to avoid any selfheating. Below 60nA my measurent is noisy and seems to have bias error. Is there any solution with this source meter, or I have to go with an external voltmeter.

Best regards,

Alex

Dale C
Keithley Applications
Keithley Applications
Posts: 2849
Joined: June 10th, 2010, 6:22 am
Country: United States
Contact:

Re: Diff. conductance with 2635A

Post by Dale C » November 4th, 2010, 12:03 pm

Alex,
The Model 2635A does not have a "Delta" mode.
You could write a script to do this and down load it into the unit.
But you would have to write it.
The Model 2635A 200mV voltage measure range has an uncertainty of about 225uV. Check the voltage measure specs.
That is probably the noise and offset you are seeing. You could null this out but it could still drift to about the level over time.
If you need better than that I would recommend a separate voltmeter.
Model 2000 DMM hs a 100mV range and is good to about 3uV.
That should help.
Dale

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