HP-4145B Parameter Analyser

We have an HP-4145B Parameter Analyser, and we are trying to
programatically (in user mode) apply a current of over 10 mA from one
of the SMU's. We have found that applying currents of less than 10 mA
works fine, but for 10 mA or above, no current is applied. However in
manual mode, we can apply currents well above 10 mA.
Is this a feature of the old Parameter Analysers? Does the same apply
to the later models? Or have I got a fault with my equipment?
Does anybody know?

 

1. 10 mA may be the threshold for the safety interlock. All
HP/Agilent SMU boxes have these interlocks. With voltage forcing you
hit it at 42V. I don't have a 4145 manual handy to check for forcing
current limit but 10 mA is about the level where you can cause cardiac
arrest through electrocution. Check the manual for how to create your
own interlock switch cable.

2. Other possibility would be wrong compliance but normally that only
limits output rather than kicking it off altogether. On the other
hand being in compliance limiting might simply seem like it shutdown.
Check that you are programming the force parameters, especially
compliance, correctly.

The fact you can get higher current from the front panel suggests the
latter or both of these. The instrument is probably working fine.

MM