Hello, 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. Frank

Frank Stellmach <frank.stellmach@freenet.de> ha scritto: > Hello, > > 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" Hello, Frank, thank you for your comment. I can hear the crowbar working, should be that slight rattling sound when I pass from an higher voltage to a lower? The problem is that I cannot set a voltage between 480 and 500V and less than 200V at all. The strange think is that the unit works ok in the >200...480V range and >500 to more than 1000V. I have to study better the manual, if i rmember correctly there is a circuitry that changes protection behaviour around 300V. Fabio. ---------------------------------------------------------------- This message was sent using IMP, the Internet Messaging Program.