Avoid Using PXI Chassis Ground as a Measurement Reference

Updated Sep 1, 2026

Reported In

Hardware

  • PXI Chassis

Issue Details

I have external floating signals that need an electrical reference point for measurement with my PXI module.
 
Can I use the ground lug on the rear of the PXI chassis as the measurement reference plane?
 
Can I use the PXI module front-panel mounting screws to reference my floating signals to the chassis?

Solution

The PXI chassis ground, which is accessible through the enclosure, backplane chassis connections, rear grounding screw, and module mounting hardware, serves as a safety earth ground. Its primary purpose is to provide a path to earth ground for safety, electrostatic discharge (ESD) shunting, and shielding. It is not intended to be used as a precision measurement reference.
 
Using the chassis ground as a signal reference can introduce measurement error because the chassis may be exposed to common-mode noise sources, including:
  • Internal switching power supplies
  • PXI backplane activity
  • Cooling fan noise
 
This noise can couple into the measurement signal path when the chassis ground is used directly as a reference.
 
To minimize measurement noise:
  1. Reference floating signals to the appropriate ground connection on the measurement device, such as:
    • AI GND
    • AO GND
    • COM
  2. Consult the module specifications to determine whether the module is isolated from the PXI backplane or chassis ground.
 

Additional Information

The PXI chassis grounding system is intended for safety grounding and grounding continuity throughout the chassis. Some PXI modules provide electrical isolation from chassis ground, while others reference signal ground to the backplane and chassis. The backplane ground signal eventually travels back to a common chassis ground point.  But the ground signal on those individual paths will be less noisy than the common ground at the chassis ground lug or the chassis enclosure.

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