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Voltage and charge measurement problem

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catniper
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Joined: November 13th, 2014, 9:46 pm
Country: United States

Voltage and charge measurement problem

Post by catniper » November 13th, 2014, 10:15 pm

Hi, I use keithley electrometer 6514 to measure our sample's voltage. Before I measure it, I use a multi-meter to measure it's voltage. The value is 0.8V. However when I use keithley electrometer to measure it. The reading is only 0.0008 and the reading isn't very consistent. I don't know why.

Again, I use electrometer 6514 to measure the charge of our sample. At first, I chose 2uc range. When I connected my sample to electrometer, the reading is overflow. However, I chose 20uc range. At first few seconds, the reading changes very quickly and a few seconds latter, it goes overflow. The charge of my sample is only 1 E-8 or even less than this.

We just did the same measurement last week. And the result was fine. But this time, the reading beyond our expectation. I don't know why. I think there might be some problem with the electrometer 6514. Are there anyone who can help me?

Dale C
Keithley Applications
Keithley Applications
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Joined: June 10th, 2010, 6:22 am
Country: United States
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Re: Voltage and charge measurement problem

Post by Dale C » November 14th, 2014, 10:23 am

1.If you used the Model 6514 before to make this measurement and now you are trying to duplicate the measurement with the same piece of gear and it is not making the measurement then something is wrong.
Are you using the same cables?
Is the measurement being performed in the same environment?
Can you input a known voltage into the input of the Model 6514 and see if it makes the proper measurement?
2. To check the Model 6514 in Coulombs mode I suggest the following.
a. Set the Model 6514 to charge mode.
b. Charge up a 1nF(1e-9F) capacitor to 10V.
c. Connect the capacitor to the input of the Model 6514.
d. Disable zero check.
e. Model 6514 should display about 10nC on the 20nC range.
since Q=CV this should work.
If not then maybe the 6514 is in need of service.

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