We've been using TestStand & LabView to test various Circuit board. On series of test involves checking for a short circuit (Measure Low Resistance 4-wire) then measuring for a 3.5Vrms signal on another part of the board.
For each measurement, the following NI-DMM VI's are used in order:
niDMMInit, niDMMAutoZero, niDMMConfigure, niDMMMeasure, niDMMClose.
If we do the Low Resistance 4WR measurement, then a AC V measurement, the 1st reading from the DMM is approx 10x too high, if a 2nd reading it done it is then OK.
It doesn't matter how long a delay is before we take the 1st measurement, it's always approx a factor of 1E+1 out.
If however we don't do a Low Restance prior to
the AC V measurement, then the measurement is always correct.
I expermented with turning AutoZero on & off, and various resolution settings, however none of these seem to have an effect on the result.
Can anyone explain these strange results?
Certified LabVIEW Developer
Certified TestStand Developer
measX GmbH & Co. KG.