Red Lion LEGEND - Manual (Page 20)

PROGRAM RATE MODULE
MINIMUM AND MAXIMUM UPDATE TIME
The Minimum and Maximum Update Times are programmed in the Rate
module. The update times can range from 0.1 to 99.9 seconds. The following
flowchart shows only the Rate portion:
The Rate value is calculated using the time measured between the first and
last pulse as the measurement period. The measurement period ends when the
minimum update time has expired, and the next negative edge occurs. The
number of pulses that occurred during the measurement period are counted and
multiplied 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 period between the
minimum update time and the maximum update time from the start of the
measurement period, the time period ends and the rate display goes to zero. At
very slow count rates the measurement period is 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 only uses the falling edge of the Input A signal.
Note: The minimum update time must be equal to 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 KHz, the
minimum update time must be less than 6.5 sec (65,535 ÷ 10,000 = 6.5).
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ONE COUNT CYCLE MEASUREMENT
AVERAGE CYCLE MEASUREMENT
BASIC TIMING DIAGRAMS FOR RATE OPERATION