Rockwell Automation 1794-IJ2XT FLEX I/O Frequency Input Modules User Manual - Manual (Page 21)

Publication 1794-6.5.11 - September 2011
Overview of the Frequency Input Module 11
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 illustration, Direction Detection –
Principle of Operation, on page 12. If a Low to High transition occurs on the
Gate input, followed by one on the Frequency input, the rotation is
counterclockwise.
Missing pulse multiplier
Frequency reported at
first pulse in extended
time 2 - 1
T2 - T1
=
Missing pulse alarm would be reported after last window, if no pulse occurs
Extended windows added one at time, until
pulse occurs or multiplied windows exceeded
Minimum sampling time
2 = pulses counted
Possible extended window
Frequency input
pulses
First pulse in window,
T1 time stored
First pulse in an extended
window, T2 time stored
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