Some computer chassis can induce ground loop noise in measurements taken with instruments having grounded input connectors. Spurious DC and low-frequency content can result. The cause is usually power supply return currents from the motherboard that partially flow through the computer chassis to the power supply housing rather than entirely through the power supply cabling.

Follow these guidelines to mitigate the ground loop noise for PCI devices:

  1. Ensure that the motherboard is tightly screwed down to the chassis so that chassis return currents will flow though the chassis under the motherboard and not in the vicinity of the PCI boards.
  2. Ensure that the power supply cable is well seated on the motherboard.
  3. Locate analog input cards in slots furthest away from the power supply.
  4. Locate video cards and other high power PCI boards in slots furthest removed from the analog input cards.

Follow these guidelines to mitigate the ground loop noise for PXI devices:

  1. Ensure that the screws on the front panel of the device are tightened down.
  2. Ensure that any external equipment that is providing a signal, and is not floating with respect to ground (for example, it is not a passive sensor or a battery-operated device), is connected to the same ground as the chassis.
  3. On rack mounted systems, ground the chassis to the metal rack mount to reduce ground loop currents.