[volt-nuts] Fluke 343 arrived, trip behaviour

Frank Stellmach frank.stellmach at freenet.de
Thu May 10 22:27:51 UTC 2012


as far as I remember back 30 years, the behaviour of your 343A is 
perfectly ok.

The trip behaviour on downranging or even on reducing the output setting 
on the high voltage ranges is caused by the "crowbar driver" and "sink 
supply". (see manual)
This circuitry protects the output driver transistors, because those 
suddenly see excessive voltage if downranging occurs.
The protection circuit quickly discharges the capacitors following the 
voltage doubler, and shunts the series voltage regulator transistors.

If the 343A stays stable on the high volatge ranges, if the setting is 
not changed, everything is fine.

The 343A is a very nice unit for resolving 7 digits of voltage, although 
it is not extraordinarily stable.


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