National Instruments NI USB-621x Field Wiring Considerations, Analog Input Timing Signals

Chapter 4 Analog Input

A digital trigger can initiate these actions. All NI 621x devices support digital triggering. NI 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 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 and enter the info code rdfwn3.

Analog Input Timing Signals

In order to provide all of the timing functionality described throughout this section, M Series devices have a flexible timing engine. Figure 4-4summarizes all of the timing options provided by the analog input timing engine.

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