IOtech DaqBoard/3000USB Series, User Manual

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An Example of Timing Mode
The following example represents one channel in timing mode. The time desired is between the rising
edge on the input channel and the falling edge on the mapped channel . Zeroes are returned, in the scan,
until one complete time measurement has been taken. At that point, the value (time in ticks) is latched and
logged by the /3000USB Series board until the next time measurement has been completed. Rising edges
on the input channel will clear the counter and falling edges on the mapped channel will latch the output of
the counter at that time. If the scan period is much slower than the rate of time-frames coming [available on
the two channels] then the data will miss some time-frames. The scan period can be decreased to capture
more time-frames.
The data returned is interpreted as time measured in ticks. This data represents the number of ticksize
intervals counted during the timing measurement. There are four timebase settings: 20.833 ns, 208.33 ns,
2.083 µs, and 20.83 µs. These are often referred to as tick-sizes. The 3000USB Series board uses a
48 MHz, 50 ppm oscillator as a timing source.
If the input signal has a poor slew rate the timing mode will provide variant results,
dependant upon the input switching threshold.
Example of One Channel in Timing Mode
TIMING: OPT2: This determines whether the time is to be measured with a 16-bit (Counter Low), or
32-bit (Counter High) counter. Since time measurements always have the “stop at the top” option enabled,
this option dictates whether the measurement has a range of 0 to 65535 ticks or 0 to 4,294,967,295 ticks.
5-14 Counter Input Modes
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DaqBoard/3000USB Series User’s Manual