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Keithley 6517A electrometer fault

JD
John Devereux
Thu, Aug 2, 2012 6:20 PM

Hi, hope this is not off topic - well it does measure volts...

I just received a 6517A electrometer but it appears to have a fault.

On volts, with shorted input, the reading usually drifts rapidly
upwards. For example 10mV in 10 seconds on the 2V range.

It is usually OK (stable to 10uV) at power-up, but the fault can be
provoked by tapping it lightly with e.g. a finger. Then it runs
away.

I can hear a faint noise, very like a relay switching when the unit is
tilted. Nothing obviously loose or rattling inside...

Has anyone seen this? Could a reed relay fail like that?

--

John Devereux

Hi, hope this is not off topic - well it does measure volts... I just received a 6517A electrometer but it appears to have a fault. On volts, with shorted input, the reading usually drifts rapidly upwards. For example 10mV in 10 seconds on the 2V range. It is usually OK (stable to 10uV) at power-up, but the fault can be provoked by tapping it lightly with e.g. a finger. Then it runs away. I can hear a faint noise, very like a relay switching when the unit is tilted. Nothing obviously loose or rattling inside... Has anyone seen this? Could a reed relay fail like that? -- John Devereux
JD
John Devereux
Thu, Aug 2, 2012 7:10 PM

John Devereux john@devereux.me.uk writes:

Hi, hope this is not off topic - well it does measure volts...

I just received a 6517A electrometer but it appears to have a fault.

On volts, with shorted input, the reading usually drifts rapidly
upwards. For example 10mV in 10 seconds on the 2V range.

It is usually OK (stable to 10uV) at power-up, but the fault can be
provoked by tapping it lightly with e.g. a finger. Then it runs
away.

I can hear a faint noise, very like a relay switching when the unit is
tilted. Nothing obviously loose or rattling inside...

(replying to myself)

OK, seems like the noise was a red herring. It is caused by the front
panel bezel assembly flexing, there are metal grounding fingers that
make the noise when they slide a bit!

Has anyone seen this? Could a reed relay fail like that?

I poked around a bit more and I do think it is the relays inside the
internal shield - not sure whether to attempt a repair or not.

John

--

John Devereux

John Devereux <john@devereux.me.uk> writes: > Hi, hope this is not off topic - well it does measure volts... > > I just received a 6517A electrometer but it appears to have a fault. > > On volts, with shorted input, the reading usually drifts rapidly > upwards. For example 10mV in 10 seconds on the 2V range. > > It is usually OK (stable to 10uV) at power-up, but the fault can be > provoked by tapping it lightly with e.g. a finger. Then it runs > away. > > I can hear a faint noise, very like a relay switching when the unit is > tilted. Nothing obviously loose or rattling inside... (replying to myself) OK, seems like the noise was a red herring. It is caused by the front panel bezel assembly flexing, there are metal grounding fingers that make the noise when they slide a bit! > Has anyone seen this? Could a reed relay fail like that? I poked around a bit more and I do think it is the relays inside the internal shield - not sure whether to attempt a repair or not. John -- John Devereux