Campbell Scientific SDM-INT8 8-Channel Interval Timer - Manual (Page 23)

SDM-INT8 8 Channel Interval Timer
Assume the input frequency is 0.5 Hz, and the execution interval of Instruction
101 is 10 Hz. The datalogger input location is updated at about 0.5 Hz if a
change occurred, not every time the INT8 is addressed.
An example of an intermittent signal is a Cub Scout Pinewood Derby where
the measured event is the elapsed time of a race, but several minutes separate
each heat. Three cars per heat are gravity powered down a straight track. The
start of the race triggers an edge on INT8 channel 1. The three cars each
trigger an edge on separate channels as they cross the finish line. Function 4 is
used to measure "time since channel 1" to provide the elapsed time for each
car. The datalogger can be addressing the INT8 as often as desired with this
option, but variables or input locations will only be updated at the finish of a
new heat.
The Continuous Averaging Option is used for totalizing counts (Function 7)
because the INT8 continues to measure and store events even when
communicating with the datalogger. However, counts will be missed if the
measuring/storing task exceeds the processing task (see Table 3).
6.4.4 Option nnnn or XXXX: Specified Averaging Interval
Option nnnn or XXXX is used to average over an exact interval when the
instruction is executed. The averaging interval is specified in units of
milliseconds. The datalogger program is delayed for the specified interval
while the INT8 captures, edges, plus the extra time required for processing if
the processing task lags behind the measuring/storing task. After returning the
results to the datalogger, the INT8 enters the low power standby mode (400
microamp current drain), increasing battery life.
Like Option 0, this option will return 0 for frequency and count functions and
99999 for all functions if no result is available during the specified interval, i.e.
the signal was too slow.
6.4.5 Option –nnnn or XXXX--: Capture All Events Until nnnn or XXXX
Edges On Channel 1
6.4.5.1 Option –nnnn
Option –nnnn instructs the INT8 to capture all events until “nnnn” edges have
occurred on channel 1, until the datalogger addresses the INT8 with the
Capture Trigger argument true, or until 8000 events have been captured.
When the CaptureTrig argument is true, the INT8 will return up to the last
nnnn events for each of the programmed channels, reset its memory, and begin
capturing the next nnnn events. The INT8 waits for the first edge on channel 1
as a trigger to start making measurements. The Dest parameter must be
dimensioned large enough to receive the captured events.
6.4.5.2 Option XXXX--
Option XXXX-- outputs all available timing information with no averaging.
"All events" means that every occurrence of each programmed functions is
recorded, i.e., each period, each pulse width, etc. as opposed to one averaged
value.
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