IOtech DaqBoard/3000USB Series, User Manual

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Another synchronous mode allows digital inputs to be scanned every time an analog input channel is
scanned. For example, if eight analog inputs are scanned at 1 µsec per channel continuously, and 24 bits of
digital inputs are enabled, then the 24 bits of digital inputs will be scanned at 24 bits per 1 µsec. If counters
are enabled in this mode, they will be scanned at once per scan, in the same manner as in the first example
above.
Note : It is not necessary to read counters as often as it is to read digital inputs. This is because counters
continue to count pulses regardless of whether or not they are being read by the PC.
Example 1: Analog channel scanning of voltage inputs
The figure below shows a simple acquisition. The scan is programmed pre-acquisition and is made up of 6
analog channels (Ch0, Ch2, Ch5, Ch11, Ch22, Ch25.) Each of these analog channels can have a different
gain. The acquisition is triggered and the samples stream to the PC via USB2. Each analog channel
requires one microsecond of scan time therefore the scan period can be no shorter than 6 us for this
example. The scan period can be made much longer than 6 us, up to 19 hours. The maximum scan
frequency is one divided by 6us or 166,666 Hz.
All analog channels are sampled at the same rate of 1us.
DaqBoard/3000USB Series User’s Manual
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