Chapter 9 SCXI—Signal Conditioning

Note When you connect any type of SCXI module to a DAQ device, certain analog input and digital lines on the DAQ device are reserved for SCXI control. On MIO Series devices, lines 0, 1, and 2 are unavailable for general-purpose digital I/O. On MIO E Series devices, lines 0, 1, 2, and 4 are unavailable for general-purpose digital I/O.

For the fastest performance in parallel mode on digital modules, use the appropriate onboard port numbers instead of the SCXI channel string syntax in the digital VIs.

SCXI Gains

SCXI modules provide higher analog input gains than those available on most DAQ plug-in devices.

Enter the gain jumper settings in Measurement & Automation Explorer or the NI-DAQ Configuration utility for each channel on each module with jumpered gains. LabVIEW stores these gain settings and uses them to scale the input data. When you use the input limits control of the analog input VIs, LabVIEW chooses onboard gains that complement the jumpered SCXI gains to achieve the given input limits as closely as possible.

For analog input modules with programmable gains, LabVIEW uses the gain setting you enter in Measurement & Automation Explorer or the NI-DAQ Configuration utility for each module as the default gain for that module. LabVIEW uses the default gain for the module whenever you leave the input limits terminal to the analog input VIs unwired, or if you enter 0 for your upper and lower input limits.

When you use the input limits to specify non-zero limits for a module with programmable gains, LabVIEW chooses the most appropriate SCXI gain for the given limits. LabVIEW selects the highest SCXI gain possible for the given limits, and then selects additional DAQ device gains if necessary.

If your module has programmable gains and only one gain for all channels and you are using an MIO/AI DAQ device, you can specify different input limits for channels on the same module by splitting up your channel range over multiple elements of the channel array, and using a different set

of input limits for each element. LabVIEW selects one module gain suitable for all of the input limits for that module, then chooses different MIO/AI gains to achieve the different input limits. The last three examples in Table 9-2 illustrate this method. The last example shows a channel list with two modules.

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LabVIEW Measurements Manual