Removing Guarding Pins in SMU Cables

Updated Oct 3, 2018

Reported In


  • PXI Source Measure Unit

Issue Details

Are the guard pins of my SMU really needed? What happens if I avoid using them with a custom cable?


The guard pins are needed to prevent leakage currents and parasitic capacitances. (i.e pings 1, 4, 7, 10 in a PXIe-4140).

Although you might not use them, it's possible that the accuracy specifications of your device canĀ“t be met without them.

Additional Information

Guarding is specially important in low voltage measurements. Although cable insulation impedance is typically high, it can have a significant effect when measuring small currents from high-impedance loads.

You can find a list of the SMUs that support guarding in Related Links.