Did Fluke ever make the 845ab Null Meter with the optically-isolated
Bilateral Analog FET chopper? Is so where's the schematic? The 335D is
not optically isolated. Will not having this isolation effect the
leakage? What is the part number of the optical-isolated Bi-FET?
My Fluke null meter new neon's are now starting to flicker with unstable
zero again.
I modified the meter to use curve tracer selected INS-1 Russian neon
dots. Selected for equal break down voltage and brightness. Worked well
for about two years. The NE2? with the isotope in it is impossible to find.
Has anyone used some type of circuit modification for this meter?
Dallas
On 5/3/2014 12:18 PM, Dallas Smith wrote:
Does anyone have the schematic for the Fluke 845 chopper modification
as stated in front of manual to be released approximately Dec 1993?
Manual statement:
'The new circuit now employs optically-isolated Bilateral Analog FETs,
and is fabricated on an additional circuit board.'
Frank, from Volt-Nuts 21 Mar 2010, suggested that: The 335A_D manual
contains the coil chopper for the calibrator circuitry, (page 119/120)
and the opto chopper version for the included Null volt meter, same
circuitry as of the 845A/B. Compare this with the 335_D manual,(page
169) where you can find the MOS FET version for the calibrator amplifier.
Has anyone tried this circuit for the Fluke 845ab?
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