Advantech PCI-1713U, Руководство пользователя

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17 Chapter 3
External Trigger Source Connection
In addition to pacer triggering, the PCI-1713U card also allows external
triggering for A/D conversions. A low-to-high edge coming from
EXT_TRG will trigger an A/D conversion on the PCI-1713U board.
Note: Don't connect any signal to the EXT_TRG pin when the external
trigger function is not being used.
Note: If you use external triggering for A/D conversions, we recommend
you choose differential mode for all analog input signals, so as to reduce
the cross-talk noise caused by the external trigger source.
3.4 Field Wiring Considerations
When you use the PCI-1713U card to acquire outside data, environmental
noise can seriously affect the accuracy of your measurements if you don’t
provide any protection. The following suggestions will be helpful when
running signal wires between signal sources and the PCI-1713U card.
•
Please make sure that you have carefully routed signal cables to the
card. You must separate the cabling from noise sources. Try to keep
video monitors far away from the analog signal cables, because
these are a common noise source in a PCI data acquisition system.
• If you want to reduce common-mode noise, try to use differential
analog input connections.
• If you do not want your signals to be affected when travelling
through areas with high electromagnetic interference or large mag-
netic fields, try the following routing techniques: Use
individually shielded, twisted-pair wires to connect analog input
signals to the board, i.e. the signals connected to the High and Low
inputs aretwisted together and covered with a shield. Finally,
connect the shield only to one point at the signal source ground.
• Make sure that your signal lines do not travel through conduits,
because these may contain power lines. Also, keep your signals far
from electric motors, breakers or welding equipment, as these can
create magnetic fields.
• Keep a reasonable distance between high-voltage (or high-current)
lines and signal cables connected to the PCI-1713U card if the
cables run parallel, or route signal cables at right angles to high
voltage/current cables.