Direction Detection - Allen-Bradley FLEX I/O 1794-IJ2 User Manual

1-8 Overview of the Frequency Input Module
Allen-Bradley Replacements
Publication 1794-6.5.11 - November 1997
Missing Pulse Multiplier
Missing Pulse Alarm Would be Reported After Last Window, If No Pulse Occurs
Minimum Sampling Time
Frequency Input
Pulses
first pulse in window,
T1 time stored

Direction Detection

Direction detection is accomplished by using the Frequency input, Gate
input, and two sensors. The module expects to see a Low to High
transition on the Frequency input, followed by a Low to High transition
on the Gate input. This assumes both input polarity select bits are the
same selection.
This corresponds to Clockwise rotation (see figure). If a Low to High
transition occurs on the Gate input, followed by one on the Frequency
input, the rotation is CounterClockwise.
Direction Detection - Principle of Operation
2 x M
M
Frequency Reported at
First Pulse in Extended Time =
extended windows added one at time, until
pulse occurs or multiplied windows exceeded
2 = pulses counted
first pulse in an extended window,
T2 time stored
Clockwise Rotation
Sensor 0
Sensor 1
Sensor 0 (F)
Sensor 1 (G)
Sensor 0 (F)
Sensor 1 (G)
2 - 1
T2 - T1
possible extended window
Gate Input Frequency Input
IJ2 Module
Clockwise
Rotation
Counter
Clockwise
Rotation