Advantech USB-4702, Руководство пользователя

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USB-4702 User Manual 16
3.5 External Trigger Source Connections
In addition to pacer triggering, USB-4702 also allows external triggering
for A/D conversions. The external trigger function is thereby disabled.
And the external trigger function will be enabled once the +5V DC source
is removed.A low-to-high edge coming from TRIG will trigger an A/D
conversion on the USB-4702 board.
3.6 Field Wiring Considerations
• When you use USB-4702 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-4702.
• 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.
• If you have to place your signal cable parallel to a power line that has a
high voltage or high current running through it, try to keep a safe dis-
tance between them. Or place the signal cable in a right angle to the
power line to minimize the undesirable effect.