Why does SMU has larger measurement result than current limit/range in voltage mode?

Updated Mar 19, 2026

Reported In

Hardware

  • PXIe-4135
  • PXI Source Measure Unit
  • Power Supply
  • PXIe-4137

Software

  • LabVIEW
  • InstrumentStudio

Issue Details

When I use two SMU to test a resistance, both of the two PXIe-4135 use Hi port. The Hi of one SMU work as HI, another SMU works as LO. In some special scenario, I found the measured current is more than current limit/range. For example, I set current limit to 10mA, but the measured result of the SMU is 12mA. Why does SMU has larger measurement result than current limit/range in voltage mode?

Solution

The reason is caused by using two SMU. If there is only one SMU to source and measure, the issue will not happen.

When using two SMU in a measurement, the SMU used for souring can be proctected by current limit.

But for the SMU used for measuring, it can't be protected by current limit settings. Even the current is more than current limit setting,  it can't adjust the voltage to protect the SMU. That's why the reading of SMU is more than current limit.

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