31 Chapter 3
Figure 3.4: Isolated Digital Input Channel Connections
3.6 Field Wiring Considerations• When you use USB-4718 to acquire data from outside, noises in the
environment might significantly affect the accuracy of your measure-
ments if due cautions are not taken. The following measures will be
helpful to reduce possible interference running signal wires between
signal sources and the USB-4718.
• The signal cables must be kept away from strong electromagnetic
sources such as power lines, large electric motors, circuit breakers or
welding machines, since they may cause strong electromagnetic inter-
ference. Keep the analog signal cables away from any video monitor,
since it can significantly affect a data acquisition system.
• If the cable travels through an area with significant electromagnetic
interference, you should adopt individually shielded, twisted-pair wires
as the analog input cable. This type of cable has its signal wires twisted
together and shielded with a metal mesh. The metal mesh should only
be connected to one point at the signal source ground.
• Avoid running the signal cables through any conduit that might have
power lines in it.