Chapter 4 Relay Ladder Logic Programming 64
Timer Mode 7 (FLASH Cascade without Reset)
Mode 7 Timer is a Flash timer without reset that uses two timers in a cascade configuration. The cascade
configuration connects the timer status bit of first timer to enable the second timer. The second timer will time up
to its preset value then flash and its timer status bit will enable the first timer. Additionally, the current time value is
non-retentive and will reset to zero on a loss of power to the smart relay. In the example below, timer status bit T1
will be ON after it completes its timing sequence of 2.5 seconds. Timer 2 will then begin its timing sequence of 1
second. When the current time value of Timer 2 reaches its preset of 1 second, its status bit T2 will flash and
Timer 1 will begin timing again. This type of cascade timer is of ten used in combination with a counter in
applications where it is necessary to count the number of time cycles completed.
Note:
Timer
Mode
7
uses
two
timers.
These
timers
cannot
be
reused
as
timers
for
other
modes
in
other
areas
of
the program.
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