Chapter 4 Signal ConnectionsAT-MIO/AI E Series User Manual4-58 National Instruments CorporationField Wiring ConsiderationsEnvironmental noise can seriously affect the accuracy of measurementsmade with your AT E Series board if you do not take proper care whenrunning signal wires between signal sources and the board. Thefollowing recommendations apply mainly to analog input signal routingto the board, although they also apply to signal routing in general.You can minimize noise pickup and maximize measurement accuracyby taking the following precautions:• Use differential analog input connections to reject common-modenoise.• Use individually shielded, twisted-pair wires to connect analoginput signals to the board. With this type of wire, the signalsattached to the CH+ and CH- inputs are twisted together and thencovered with a shield. You then connect this shield only at onepoint to the signal source ground. This kind of connection isrequired for signals traveling through areas with large magneticfields or high electromagnetic interference.• Route signals to the board carefully. Keep cabling away from noisesources. The most common noise source in a PC data acquisitionsystem is the video monitor. Separate the monitor from the analogsignals as much as possible.The following recommendations apply for all signal connections toyour AT E Series board:• Separate AT E Series board signal lines from high-current orhigh-voltage lines. These lines are capable of inducing currents inor voltages on the AT E Series board signal lines if they run inparallel paths at a close distance. To reduce the magnetic couplingbetween lines, separate them by a reasonable distance if they run inparallel, or run the lines at right angles to each other.• Do not run signal lines through conduits that also contain powerlines.• Protect signal lines from magnetic fields caused by electric motors,welding equipment, breakers, or transformers by running themthrough special metal conduits.For more information, refer to the application note, Field Wiring andNoise Consideration for Analog Signals, available from NationalInstruments.
