Red Lion LEGEND - Manual (Page 17)

PROGRAMMING 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. The unit will
update the rate display at the end of the measurement period. 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 or less than 65536 divided 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