[volt-nuts] Newer Fluke 845ab manual with chopper mod?
csteinmetz at yandex.com
Tue May 6 14:06:07 EDT 2014
>Did Fluke ever make the 845ab Null Meter with the optically-isolated
>Bilateral Analog FET chopper?
I have never seen an 845 with FET chopper, despite the engineering
change specification most 845 owners have seen. I've heard of one or
two 845s that may have been repaired (by Fluke) with a FET chopper
assembly (perhaps using 335D parts ??), but I'm not sure any 845s
left the factory that way.
These days, there are integrated chopper-stabilized ("zero offset")
op amps that can do better than chopper amplifiers (e.g., LTC1050,
LTC1052, LTC2054, LTC2057, LTC7652, ICL7650, MAX4238/4239). Randy
Evans started two threads here back in December 2013, one on
modifying the Fluke 887 and one on modifying the 845. He made
available his notes, which were quite thorough. Check the archives
starting on Dec. 22, 2013.
More information about the volt-nuts