Timer and Counter Instructions
Chapter 5
53
All three timers differ in the way they set and reset status bits, respond to
rung logic continuity and reset the accumulated value. With each timer, the
programmer must select one of the following time bases:
1.0 second
0.1 second
0.01 second (10 milliseconds)
Bit 16 of the timer accumulated value word reflects the time base. It will
go on and off at the selected time base rate acting as a pulse train
(Figure 5.2) except for 10 ms timers.
The Timer On-Delay instruction (TON) can be used to turn a device on or
off once an interval is timed out (Figure 5.3).
When rung conditions for a Timer On-Delay instruction (rung 1) become
true, the timer begins to count time-base intervals. As long as conditions
remain true, it increments its accumulated value word for each counted
interval. When the accumulated value equals the programmed preset value,
the timer stops incrementing its accumulated value and sets the timed bit,
bit 15, of this word on. Bit 15 may then be used to turn an output device on
or off (rung 2).
Bit 17 of the accumulated value word is termed the enabled bit. It is set on
whenever the rung conditions are true and the timer is enabled.
Whenever the rung conditions for the TON instruction go false, the
accumulated value is reset to 000 and bits 15 and 17 of that word are reset
to zero. The accumulated value and status bits are also reset when the
mode select switch is turned to the program position or when there is a loss
of power.
5.1.1
Timer OnDelay Instruction
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
