Red Lion LEGEND - Manual (Page 8)

BASIC OPERATION (Cont’d)
The signal at Input A is also used for the Rate
indicator portion. The rate indicator uses a time
interval method (1/tau) to calculate the rate value. The
unit counts on the negative edge of the input pulses.
After the programmed minimum update time elapses
and the next negative edge occurs, the unit saves the
number of edges that occurred during the elapsed time.
The number of edges is multiplied by the Rate Scale
Factor, Rate Scale Multiplier, and the Rate Conversion
Factor to calculate the rate value. Averaging can be
accomplished by programming the Rate Minimum
Update Time for the desired response. Extensive
scaling capabilities allow practically any desired
reading at very slow count rates. The following is a
Block Diagram overview of the basic operation.
The Counter should not be allowed to operate in an overflow condition. As
soon as, or before the counter overflows, the information should be recorded
and the counter reset.
INHIBIT
When the Inhibit terminal is low, connected to common, all input pulses
will be ignored by the counter. The rate input, however, is unaffected by the
Inhibit terminal and will continue to indicate the rate of the signal at input A.
When the Inhibit terminal is high, the signal for the counter will be sensed and
counted.
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OVERFLOW INDICATION
The Legend will flash the word “OVERFLOW” in the appropriate display
when an overflow condition occurs. An overflow occurs if the capacity of the
display (6 digits) is exceeded or if the internal count capacity (9 digits) is
exceeded. The use of an extremely small Scale Multiplier and a Scale Factor
Value can cause the internal count capacity to overflow before the displayed
value will overflow.
For example, if a Scale Factor of 0.0001 and a Scale Multiplier of 0.001 is
used, for every 10,000,000 count edges received, the display will increment
by 1. Before the display reaches 215, the internal counter will overflow.
When the capacity of the display is exceeded, the count value will be
maintained and will be valid. But if the internal count capacity is exceeded,
then this value will no longer be valid. It should be noted that the use of a
Scale Factor larger than “1” could cause the displayed count value to
overflow before 999,999 counts are accumulated. Also the use of a Rate Scale
Factor, Scale Multiplier, and Rate Conversion Factor larger than “1” can
cause the rate display to be in an overflow condition.