Chapter 4
Theory of Operation
4-4
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If the E/M Series DAQ device scans the cabled module, the module routes
its input signals through the CH 0 pin on its rear signal connector to the
E/M Series DAQ device CH 0.
Multiplexed mode scanning acquisition rates have limitations that are
determined based on the hardware in the system, and the mode of
operation. The maximum multiplexing rate of SCXI is 333 kHz. If the
E/M Series DAQ device can sample more quickly than 333 kHz, then the
maximum multiplexing rate of SCXI is the limiting factor. If the E/M Series
DAQ device cannot sample at 333 kS/s, the sample rate of the E/M Series
DAQ device is the limiting factor on the maximum acquisition rate of the
system.
Since you must scan the SCXI-1102/B/C sequentially, the driver
automatically scans channels not included in the scan list if a sequential
order is not maintained. When this happens, the maximum sample rate is
also factored into the channels that are scanned and discarded for the
purpose of completing the scan list.
For measurement accuracy of 0.012% of full scale, the minimum scan
interval is 3
µ
s, which is the smallest interval in which you can switch
between analog channels on the module and still measure accurate
voltages. The 3
µ
s scan interval gives you a maximum sampling rate of
333 kHz. For better accuracy, you must increase the scan interval in
accordance with the specifications, which will reduce the maximum
aggregate sample rate.
