Omega OMB-DAQBOARD-3000 Series User Manual page 21

Example 3: Analog and digital channel scanning, once per scan mode
The figure below shows a more complicated acquisition. The scan is programmed pre-acquisition and is
made up of 6 analog channels (Ch0, Ch2, Ch5, Ch11, Ch22, Ch25) and 4 digital channels (16-bits of
digital IO, 3 counter inputs.) Each of the analog channels can have a different gain and each of the counter
channels can be put into a different mode (totalizing, pulsewidth, encoder, etc.) The acquisition is
triggered and the samples stream to the PC via DMA. Each analog channel requires one microsecond of
scan time therefore the scan period can be no shorter than 6 us for this example. All of the digital channels
are sampled at the start of scan and do not require additional scanning bandwidth as long as there is at least
one analog channel in the scan group. 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.
The counter channels could be returning only the lower 16-bits of count value if that is sufficient for the
application. They could also be returning the full 32-bit result if necessary. Similarly, the digital input
channel could be the full 24 bits if desired or only 8 bits if that is sufficient. If the 3 counter channels are
all returning 32 bit values and the digital input channel is returning a 16 bit value, then 13 samples are
being returned to the PC every scan period, each sample being 16-bits. 32-bit counter channels are divided
into two 16-bit samples, one for the low word and the other for the high word. If the maximum scan
frequency is 166,666 Hz then the data bandwidth streaming into the PC is 2.167 MSamples per second.
Some slower PCs may have a problem with data bandwidths greater than 6 MSamples per second.
DaqBoard/3000 Series User's Manual Daq Systems and Device Overviews 1-7
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