Chapter 4 Analog Input
NI USB-621x User Manual 4-10 ni.com
Analog Input Digital Triggering
Analog input supports three different triggering actions:
• Start trigger
• Reference trigger
•Pause trigger
Refer to the AI Start Trigger Signal, AI Reference Trigger Signal, and
AI Pause Trigger Signal sections for information about these triggers.
A digital trigger can initiate these actions. All USB-621x devices support
digital triggering. USB-621x devices do not support analog triggering.
Field Wiring Considerations
Environmental noise can seriously affect the measurement accuracy of the
device if you do not take proper care when running signal wires between
signal sources and the device. The following recommendations apply
mainly to AI signal routing to the device, although they also apply to signal
routing in general.
Minimize noise pickup and maximize measurement accuracy by taking the
following precautions:
• 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 signals attached to the positive
and negative input channels 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.
Refer to the NI Developer Zone document, Field Wiring and Noise
Considerations for Analog Signals, for more information. To access this
document, go to
ni.com/info and enter the info code rdfwn3.
Caution Electromagnetic interference can adversely affect the measurement accuracy of
this product. Refer to the NI USB-621x Specifications for more information about the
performance of this product.
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