Red Lion LEGEND - Manual (Page 21)

PROGRAM COUNTER MODULE
In the Counter Module, the count mode, reset action, and automatic reset
capability are selected. The following flowchart shows only the Counter portion:
COUNT MODES (CNT. INPUT)
There are seven available count modes. User Input 4 programmed for the
count Inhibit function can be used with any count mode. Input A signal is used for
the count and rate input. Input B is used in combination with Input A for Count
Control Direction, Quadrature counting, Anti-coincidence Add/Subtract or
Anti-coincidence Add/Add counting applications.
CT+DIRX1 (X1 COUNTING WITH DIRECTION)
The unit counts one count on every negative edge of the input signal at Input
A. The direction of the count is determined by the logic state of Input B. A high
level at Input B causes the unit to count in a positive direction. A low level
causes the unit to count in a negative direction. The rate display is NOT affected
by the logic state of Input B.
CT+DIRX2 (X2 COUNTING WITH DIRECTION)
The unit counts one count on every negative edge of the input signal and one
count on every positive edge of the input signal at Input A. In this mode, the input
signal is effectively doubled. The direction of the count is determined by the
logic state of Input B. A high level at Input B causes the unit to count in a positive
direction. A low level causes the unit to count in a negative direction. The rate
display is NOT affected by the state of Input B.
QUAD X1 (QUADRATURE X1)
Quadrature counting modes are primarily used in positioning and anti-jitter
applications. This mode works due to the manner in which the two incoming
pulses are positioned relative to each other. The pulse signal on Input B is shifted
90º away from the pulse signal at Input A. These two signals are processed by the
Legend Plus as follows:
Input A serves as the count and rate input, while Input B serves as the quadrature
input. For quadrature with single edge counting, the counter counts in a positive
direction when Input A is a negative going edge and Input B is at a low level. The
counter counts in a negative direction when Input A is a positive going edge and
Input B is at a low level. All transitions on Input A are ignored when Input B is at a
high level. These logic rules provide the basis for anti-jitter operation which prevents
false counts from occurring due to back-lash, vibration, chatter, etc.
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