IOtech DaqBoard/3000USB Series, Руководство пользователя

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Example 5: Analog channel scanning of voltage inputs and streaming analog outputs
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.
This example has all 4 DACs being updated and the 16-bits of digital IO. These updates are performed at
the same time as the acquisition pacer clock (also called the scan clock.) All 4 DACs and the 16-bits of
pattern digital output are updated at the beginning of each scan. Note that the DACs will actually take up
to 4 us after the start of scan to settle on the updated value. This is due to the amount of time to shift the
digital data out to the DACs plus the actual settling time of the digital to analog conversion.
The data for the DACs and pattern digital output comes from a PC-based buffer. The data is streamed
across the USB2 bus to the board.
It is possible to update the DACs and pattern digital output with the DAC pacer clock (either internally
generated or externally applied.) In this case, the acquisition input scans are not synchronized to the
analog outputs or pattern digital outputs. It is possible to synchronize everything (input scans, DACs,
pattern digital outputs) to one clock. That clock can be either internally generated or externally applied.
DaqBoard/3000USB Series User’s Manual
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Device Overviews 1-15