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6485 - noise

2502, 6485, 6487 - Support
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[email protected]
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6485 - noise

Post by [email protected] » July 22nd, 2016, 1:58 pm

Hi
I am trying to capture a current pulse reading that occurrs within 1 second. The reading is expected to be in nA or lower. However the initial noise is of the order of micro amperes. So I want the noise to be as low as possible. What should I do?

brian.d.smith
Keithley Applications
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Re: 6485 - noise

Post by brian.d.smith » July 22nd, 2016, 7:13 pm

Disconnect the input cable of the 6485 and see what the noise is. Chances are the reading will be below 1 nA. The noise is probably your cables and/or your device or lack of shielding.

Please post a snapshot of your cables and device with fixture.

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Re: 6485 - noise

Post by [email protected] » July 23rd, 2016, 8:43 am

As soon as I disconnect the ammeter, the reading go down and range from 0.07 to 0.1 nA (attached image). I am using the 4801 Low Noise BNC Input Cable (4 ft) that came along the ammeter. While I fix the rest o my setup, is this the lowest the stand alone ammeter noise can be suppressed to?
Also, I hear these 'ticks' from the ammeter even when its in the auto-range mode. Why would that be the case? The readings kind of stuck during those ticks.
Attachments
IMG_20160723_200958.jpg
IMG_20160723_200958.jpg (736.68 KiB) Viewed 23196 times

Andrea C
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Re: 6485 - noise

Post by Andrea C » July 27th, 2016, 9:28 am

Your front panel shows 75pA when using the 2nA range. Is this for an open circuit condition?
If this is open circuit, this is a very large offset.

Were you on the 2nA range when you did the zero correct? Please double check the zero correct procedure in the manual.

When was last time the 6485 was calibrated?

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