Analog Input Digital Triggering; Field Wiring Considerations - National Instruments Data Acquisition Device NI USB-621x User Manual

Chapter 4 Analog Input

Analog Input Digital Triggering

Field Wiring Considerations

NI USB-621x User Manual
Analog input supports three different triggering actions:
• Start trigger
• Reference trigger
• Pause trigger
Refer to the AI Start Trigger
AI Pause Trigger Signal
A digital trigger can initiate these actions. All USB-621x devices support
digital triggering. USB-621x devices do not support analog triggering.
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 DIFF 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
Signal, AI Reference Trigger
sections for information about these triggers.
and enter the info code
4-10
Signal, and
.
rdfwn3
ni.com