Electronics

LabMonkey · Guest

Ran into some problems:

the meter has an auto off feature which I can't turn off (at least I
couldn't find anything in the instruction manual). So after 10 minutes
it turns itself off. So with the capacitor experiment this only rules
out internal resistance with time constants less than 10 minutes. If
the internal resistance were 300M and the capacitor was 0.9mF, then the
time constant would be 4.5 minutes - which is not what I saw. After ten
minutes it had decayed to 0.200mV instead of 0.230mV.

As for the other experiment, the electrometer I use to measure the
voltage on the 100M resistor has some problems. I consistently got out
that the experimental equivalent parallel resistance was greater than
Rx, which naturally can't be.

I will try and find an electrometer which is more reliable, but as it
is the weekend I will not be able to get my hands on anything until
Monday.

Thanks for all of the help :)

LabMonkey

LabMonkey · Guest

I found out how to trick the meter in staying on: quickly press the
"hold" button twice and it resets the clock for the 10 minute
inactivity.

Only problem is, when I did that I didn't get an internal resistance of
1.4G. The time constant would have been about 20 minutes and I had it
running for 4.5 hours with it only decreasing to 160mV from 257mV.

So either the capacitors were doing something funny, or the internal
resistance some how changes between even higher resistors when on the
"mV" range.

I am still trying to get a hold of an electrometer

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