Hi group ! After long waiting for cheap listing with possibility to european delivery, at last win 200$ ebay "parts" hp3457a meter. Now only now need to find someone local with better equipment to check calibration :-} Meter works fine, but I'm not sure how meter must behave in low voltage bands. If I short leads it show ~1uV, thats Ok. But if leads not connected then voltage slowly creep up from zero and after about 5 min grow to +3v and meter start to click relays trying to autorange. So look like somewhere inside is ~15GOhm leak to + voltage, i try to clean board with isopropyl , but no big changes. So is it normal (I doubt...) , because 10GOhm input impedance, or something is wrong and need to repair ? Any input will be appreciated! Juris yl3cb

It's normal. Maybe yours has a little bit higher I-offset than most. But it is > infinity input impedance on the lowest ranges. You might stick a parallel 1 G resistor across the input and see what you get. They are nice meters though. Tom ----- Original Message ----- From: "J L" <juris.l@gmail.com> To: <volt-nuts@febo.com> Sent: Tuesday, September 03, 2013 7:55 AM Subject: [volt-nuts] hp3457a low voltage range behavior > Hi group ! > > After long waiting for cheap listing with possibility to european > delivery, > at last win 200$ ebay "parts" hp3457a meter. > Now only now need to find someone local with better equipment to check > calibration :-} > > Meter works fine, but I'm not sure how meter must behave in low voltage > bands. > If I short leads it show ~1uV, thats Ok. > But if leads not connected then voltage slowly creep up from zero and > after > about 5 min > grow to +3v and meter start to click relays trying to autorange. > So look like somewhere inside is ~15GOhm leak to + voltage, i try to clean > board with isopropyl , but no big changes. > > So is it normal (I doubt...) , because 10GOhm input impedance, or > something > is wrong and need to repair ? > Any input will be appreciated! > > Juris > yl3cb > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

The more important parameter is Ibias, the input current, vs. the input capcitance. Neither Input Resistance, nor input bias current, nor input capacitance are specified for the 3457A. Input current is on the order of a few pA, up to 20pA, and input capacitance, I would guess, several dozen pF, or you'll have to study the CLIP, if there's a bigger cap in the front end. Even this would be 100nF, you can calculate, that the input will charge quickly with open input jacks, and then will actuate the 100:1 divider by relais, if 3V were exceeded. The 10MOhm then will quickly discharge the input cap again. Frank