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6487 unstable through autoranging

2502, 6485, 6487 - Support
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milkshake
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Joined: March 17th, 2017, 6:27 am
Country: United States

6487 unstable through autoranging

Post by milkshake » March 17th, 2017, 6:40 am

I've been using some 6487 for current measurements (typically 0.1nA up to 800nA-ish) for long time (since the 486 went obsolete). We’ve been using A06 firmware for a while and on some of new instruments have B02. Recently, with our new instruments out in the field, we’ve seen instances where the autoranging becomes unstable with excessive clicking as current is changing through the 0.2, 2, 20, 200nA ranges but doesn’t show any error codes. Even when turning zerocheck off, it’s still unstable. The signals don't have excessive noise and are from locations we've used before. We haven’t been able to reproduce it outside of measurements from the field to know for sure what the cause is. Has anyone else seen this issue on newer 6487’s?

Andrea C
Keithley Applications
Keithley Applications
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Re: 6487 unstable through autoranging

Post by Andrea C » March 23rd, 2017, 11:52 am

The firmware from A06 to B02 should not be causing such an issue. The B02 release is only for newer builds that utilize a different ROM and require different support for firmware flashing. The range change and other measurement features should be unchanged.

Some ideas:
when having the range changing instability, can you press the DAMP button to enable dampening. If cable or DUT capacitance is contributing to the issue, this could help.

Can you connect a scope to the analog output? If you have the range change relay clicking, try putting the instrument on a fixed range and look as the output of the I-to-V converter with a scope. If signal is noisy, this would tell you why the range changes are occurring.

What kind of cable are you connecting? Is it triax?

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