Hi All,
Have a 3455A 6.5 digit multimeter that I have finally gotten up and running after some hiccups.? While trying to go through some of the cal procedures, I have found the unit does not stay zero'ed.? The "Auto Cal" function seems to do its job well, that is not the issue here.? With Auto Cal OFF and a nice shiny copper strap placed between the hi/low terminals, the unit reads .000000V in hi-accuracy mode.? HOWEVER, that reading slowly creeps DOWNWARD in time, and have seen it as low as .000050V.? It takes only a minute or so for the first couple uV drop.? This also seems to happen in 2 wire resistance mode, but to a lesser extent.? Not sure about 4 wire mode, and resolution is such that it doesn't register in ACV modes. ?
HERE'S where it gets weird though...? If I hit Auto-Cal (or change mode/range which automatically enables Auto-Cal again) the unit reads 0 after a couple of counts, as it should, being corrected.? When turning Auto-Cal back off again, the unit stays at 0, and starts creeping downward again. ?
Does this sound like something is faulty with the input DC amplifier, something funky with the A/D converter, or perhaps something else??? I'm a little dumbfounded by this and at a loss where to even begin. ?
OR is this perfectly normal behavior for these meters???? It has been on 24/7 for about a week now, so this is certainly not a matter of it not having enough time to stabilize. ?
Incidentally, this exercise has made me realize that Auto-Cal apparently does not function in my 3456A, that Simco just cal'd earlier this year.? Ugh. ?
Any input at all with this?? ?
Regards,
Chris
