[volt-nuts] Fluke 883AB differential voltmeter
Dr. Frank Stellmach
drfrank.stellmach at freenet.de
Fri Mar 19 21:57:12 UTC 2010
>>..Final problem was it would not zero properly.
The zero circuit uses two diodes to make a +/- 0.6V supply driving the offset pot.
The unit was offset so that you could not reach zero and the offset pot had fairly little range.
Adjusting the chopper didn't help.
I replaced the diodes with three 1.2V reference chips (making a -1.2 to +2.4V supply).
This centered the zero adjustment and gave better range...
this problem seems to be related to the mechanical, reed contact chopper.
This device had to be replaced very often, when I worked in a cal lab about 30 years ago..
I wonder if the unit realy works oK after your modification.
Try to replace the mechanical contact by a FET., like in later Fluke designs..
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