Rockwell Automation DeviceLogix System User Manual - Manual (Page 39)

Publication RA-UM003B-EN-P - February 2010 39
Navigate the Function Block Editor Interface Chapter 2
Off Delay Timer
The Off-Delay Timer works the same way as the On-Delay Timer but
instead of delaying the TRUE status of the output, it delays the FALSE
status of the output. The input to this timer is a level sensitive FALSE
with an edge-triggered reset on the FALSE to TRUE transition. This
means that when the input is FALSE, the timer increments the
accumulator and when the input goes TRUE the timer resets the
accumulator. For each time base unit of time, the timer increments the
accumulator.
When the accumulator reaches the preset value, the timer sets the
output to FALSE. The timer maintains the output FALSE status as long
as the input remains FALSE. When the input changes from FALSE to
TRUE, the timer sets the output to TRUE and resets the accumulator. If
the input goes TRUE before the time period specified by the time base
and preset, the output remains TRUE, and the accumulator is cleared,
essentially ignoring the input.
If the timer senses a TRUE level on the reset input at any time during
the operation of the timer, it resets the output to FALSE and clears the
accumulator. Because the reset line is level sensitive, the timer
remains reset until the timer detects a FALSE on the reset input. Also,
because the input is level sensitive, the timer again begins to
increment the accumulator if the reset line goes FALSE while the input
remains FALSE. However, because the reset logic already set the
output to FALSE, the time delay causes no effect because the output is
already FALSE. If the input is TRUE when the reset goes FALSE, the
timer sets the output to TRUE.