[volt-nuts] Newer Fluke 845ab manual with chopper mod?

Charles Steinmetz csteinmetz at yandex.com
Tue May 6 14:06:07 EDT 2014

Dallas wrote:

>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.

Best regards,


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