I am trying to do simultaneous measurements with two 34401A's over GPIB. Each is setup identically (10V, no autozero, no qutorange, 0.02 NPLC, 4 digit resolution), and I am using GPIB (BUS) triggering (with a trigger delay of 2 ms). I am using 10 samples, but that doesn't affect the issue.
The two meters are identical except for firmware: one is HEWLETT-PACKARD,34401A,0,11-5-2, the other is HEWLETT-PACKARD,34401A,0,10-5-2.
I can't get the two to trigger simultaneously (by observing the VM complete signal on the back). They wander about +/- 100 us from each other, with the 10-5-2 one tending to be earlier than the other 90 % of the time (i.e. the variations aren't symmetrical). The 10 samples are usually, but not always equally spaced. Some other trigger delay settings (e.g. 1.333 ms) cause larger meter-meter variations.
There is no spec for this performance for the meter (there is for the newer 34461A range of meters).
Has anyone seem similar behaviour ? Any ideas ?
FYI -- I'm using pyvisa, and after setup I loop:
HP34401A_DMM1.write("INIT")
HP34401A_DMM2.write("INIT")
time.sleep(0.2)
GPIB_BUS.group_execute_trigger(HP34401A_DMM1, HP34401A_DMM2)
I saw the same thing until I turned the display off. Then it worked as expected and the samples occurred simultaneously.