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Chapter 4
Theory of Operation
Data Acquisition Timing
DAQCard-1200 User Manual
A DAQ operation refers to the process of taking a sequence of A/D
conversions when the sample interval, or the time between successive A/D
conversions, is carefully timed. A finite DAQ operation acquires a finite
number of samples, while a continuous DAQ operation acquires an infinite
number of samples. The DAQCard-1200 can perform both single-channel
data acquisition and multiple-channel, or scanned, data acquisition in two
modes—round-robin and interval.
The DAQ timing circuitry consists of various clocks and timing signals that
control the DAQ operation. DAQ timing consists of signals that initiate a
DAQ operation, time the individual A/D conversions, gate the DAQ
operation, and generate scan clocks. The DAQ operation can either be
timed by the timing circuitry or by externally generated signals. These
two modes are software configurable.
Data Acquisition Operation
DAQ operations are initiated either externally through EXTTRIG or
through software control. The DAQ operation is terminated either
internally by counter A1 of the 82C53A counter/timer circuitry, which
counts the total number of samples taken during a finite operation, or
through software control in a continuous operation.
Round-Robin Data Acquisition
In a round-robin DAQ operation, samples are taken at regular sample
intervals without any delays. Therefore, each sample is taken with the same
sample interval. This sample interval applies to both single-channel and
multiple-channel data acquisition in either continuous or finite operation.
The sample interval is either controlled externally by EXTCONV* or
internally by counter A0 of the timing circuitry.
Interval Data Acquisition
In an interval DAQ operation, a period called the scan interval is defined.
Within each scan interval, a predefined number of samples is taken at
regular intervals, and conversions are stopped for the remainder of the
interval cycle. A DAQ operation consists of back-to-back interval cycles.
In single-channel interval data acquisition, you select the number of
samples in each interval cycle from a single channel. In multiple-channel
interval data acquisition, the channels are scanned once during each
interval cycle. The scan interval timing can be externally controlled
through OUTB1 or internally by counter B1 of the timing circuitry.
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