Field Wiring Considerations

Environmental noise can seriously affect the measurement accuracy of the device if you do not take proper care when running signal wire between signal sources and the device. The following recommendations mainly apply to AI signal routing to the device, as well as signal routing in general.

Take the following precautions to minimize noise pickup and maximize measurement accuracy:
  • Use differential AI connections to reject common-mode noise.
  • Use individually shielded, twisted-pair wires to connect AI signals to the device. With this type of wire, the signal attached to the positive and negative inputs are twisted together and then covered with a shield. You then connect this shield only at one point to the signal source ground. This kind of connection is required for signals traveling through areas with large magnetic fields or high electromagnetic interference.
  • Route signals to the device carefully. Keep cabling away from noise sources, such as video monitors and analog signals.
Use the following recommendations for all signal connections to the NI PXIe-7862:
  • Separate NI PXIe-7862 signal lines from high-current or high-voltage lines. These lines can induce currents in or voltages on the NI PXIe-7862 signal lines if they run in parallel paths at a close distance. To reduce the magnetic coupling between lines, separate them by a reasonable distance if they run in parallel or run the lines at right angles to each other.
  • Do not run signal lines through conduits that also contain power lines.
  • Protect signal lines from magnetic fields caused by electric motors, welding equipment, breakers, or transformers by running them through special metal conduits.
  • To minimize signal-to-signal skew within each digital channel, maintain signal lines' length within 1 inch of difference.