PXI-4132 SMU - Only works in remote sense mode

[Dan_Lauber]

We have four PXI-4132's that have worked fine for years in our automated test systems.  We sent them out for calibration and when we got them back, two of them seemed to stop working in local sense mode.

Using the MAX test panel, I can set it to output 10V in CV mode, and the internal meter reads 9.999V out, but there's only 70mV at the terminals measured by a multimeter.  I can switch to remote sense (with jumpers between the outputs and the sense terminals), and it works fine, 10V at the terminals.  I switch back to local sense and the output drops into the mV range again.  This is the same regardless of if it has a load attached or not.

I've run the self-check, and that says everything is fine, and I've done a device reset and that also didn't change this behavior.

What could be happening here?  I could send it back to the calibration folks, but I can't figure how this would be anything they could fix.

[johnr4]

Hello Dan_Lauber,

I have a few of questions for you:

1.  What is your test setup?

2.  When running your test setup, what are the expected values and what values do you receive?

3.  Have you contacted the calibration company and requested the calibration reports?

Hopefully, we can track down what is happening.  

Regards,

[Dan_Lauber]

Thanks for the response.  My best guess is that the output switch isn't closing (only in local sense mode though).  In local sense mode, with the output enabled and the voltage set to 5V, the output voltage (hi-lo) is 0V, but the guard voltage is 5V - looking at the basic schematic of the 4132, the only thing between these two paths is the output switch (and the unity gain amps on the guard).

Answering your questions:

1. Our test system has the SMU connected through a 4-wire MUX to one of several DUT's.  However, for troubleshooting I'm directly measuring the output of the SMU at its terminals (using a handheld DMM), and connecting the output terminals to their respective sense terminals with jumpers, so the MUX and DUT connections are out of the loop.

2a. In our automated test system, I expect the SMU to output a 15V waveform, but what I actually get is about 0V.  When I switch the SMU to remote sense mode, it correctly outputs the waveform.  This only affects 2 of the SMUs, the other two correctly output the waveform in both local and remote sense mode (and yes, we've tried swapping them between test systems, it follows the SMU, not the machine).

2b. In my troubleshooting test setup, I use the NI-Power front panel to ask it to apply 5V to a dummy load in local sense mode with output enabled, and the front panel shows 5V measured output but no current.  I measure across the SMU output terminals (hi & lo) and see 0V, and measure between the lo and guard terminals and get 5V.  I expect the output to be 5V.  I switch it to remote sense mode (and make no other changes), and the soft front panel measurement stays at 5V, but the current output displayed goes up as expected and probing the output terminals shows 5V out.

3.  We contacted the calibration vendor.  It seems that the calibration date stored in the SMU didn't get updated when the company performed the calibration, so they must've done something wrong in their procedure - we're sending them back for them to try again.  

Even if they did something wrong, this is a strange failure mode, for only local sense (i.e. the simpler option) to not work, and for all self-tests to pass, and the self-calibration and device resets not resolve the issue.  I'd expect if something went that wrong in the calibration, there'd be an error generated by the SMU to indicate it.

Regards, Dan.

[johnr4]

Hello Dan_Lauber,

Okay, thanks for giving me the details.  Please let me know what happens after they recalibrate the device.

Thanks,