NI-4060 giving invalid 1st reading after switching from or to LOW Resistance Measurements

[Simon_Holman]

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?

Thanks
Simon Holman

[Mike_T]

I tried it here on my machine and didn't have any problem. How is your switch and DMM communicating? Has your switch settled by the time the DMM takes the reading?
Are you doing two-wire handshaking or synchronous handshaking?
Are you changing the range of the DMM for each mode?
AC measurements take longer than voltage or resistance measurements, so if anything happens, (i.e. switch settling) you will get faulty measurements
Do you still get inaccurate results when you measure DC voltage after the resistance measurement, instead of AC?
Good luck,
Mike

[Simon_Holman]

Thanks, after playing with a few more settings I found if I turned the Cacheing off niDMMInitWithOptions, with "Cache=0" that everything worked fine, but it would take a couple of seconds to get the first AC measurement after switching from resistance.
Simon