Red Lion LEGEND - Manual (Page 18)

PROGRAM RATE MODULE
In the Rate module the Minimum and Maximum Update Times are
programmed. The update times can range from 0.1 to 99.9 seconds. The
following flowchart shows only the Rate portion:
The Rate value calculation uses the method in which the time measured
between the first and last pulse is the measurement period. When the
minimum update time has expired, the unit will end the measurement period
on the next negative going edge. The unit will count the number of pulses that
occurred during the measurement period and multiply them by the rate scale
factor, scale multiplier, and rate conversion factor for the rate display value.
The unit will update the rate display at the end of the measurement period. If
the unit does not receive the negative edge within the maximum update time
from the start of the measurement period, the unit will end the time period and
the rate display will go to zero. At very slow count rates the measurement
period will be the actual period of one count cycle, as long as the input rate
frequency is not longer than the maximum update time. The rate indicator will
only use the falling edge of the Input A signal, due to the method of rate
indication used.
Note: The minimum update time must be equal to or less than 65536 divided by
maximum operating frequency (in Hz) or the internal rate counter will
overflow. For example: If the max. operating frequency is 10,000 Hz, the
minimum update time must be less than 6.5 sec. (65,535
10,000 6.5).
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BASIC TIMING DIAGRAMS FOR RATE OPERATION
ONE COUNT CYCLE
AVERAGE CYCLE MEASUREMENT