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. The result is divided by the actual
measurement period to obtain the rate display value. If the unit does not receive a
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.
Note: The minimum update time must be equal to or less than 65536 divide by the
maximum operating frequency (in Hz) or the internal rate counter will overflow.
For example: If the maximum 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
AVERAGE CYCLE MEASUREMENT
ONE COUNT CYCLE MEASUREMENT