IEC 1131-3 Timers
It is not the intent of this course to cover all S7-200 instructions, but timer instructions provide an opportunity to understand some of the differences between the SIMATIC and IEC 1131-3 instruction sets. The timers previously discussed were SIMATIC timers. The IEC 1131-3 instruction set also includes three timers, On-Delay Timer (TON), Off-Delay Timer (TOF), and Pulse Timer (TP). The same three resolutions (1 ms, 10, ms, and 100 ms) are available as for the SIMATIC timers, and the resolution is determined by the timer number as shown in the following illustration. IEC 1131-3 Timers Number (TO to T255)
%Txxx
%Txxx TON
IN
PT xxx ms On-Delay Resolution (1 ms, 10 ms, 100 ms)
ET
.
Timer\
Elapsed Time
IN
%Txxx
TOF
PT XX( ms
ET
Off -Delay Timer
IN
TP
PT xxx ms
ET
Pulse Timer
lassOuateAssailaMgarmiliim T32, T96 1 ms T33 to T36, T97 to T100 10 ms T37 to T63, T101 lo T255_ 100 ms
32.767 seconds 327 67 seconds 3276 7 seconds
The On-Delay Timer (TON) begins timing when its enable input (IN) turns on. When the elapsed time (ET) equals the preset time (PT), the timer stops timing, and the output (0) turns on. The timer is reset, when IN turns off.
The Off-Delay Timer (TOF) output (0) turns on immediately when IN turns on. When IN turns off, the timer begins timing. When ET equals PT, Q turns off. The elapsed time is maintained until the next time IN turns on. If IN turns on before ET equals PT, Q remains on.
The Pulse Timer (TP) generates pulses of a preset duration. When IN turns on, 0 turns on, and the timer begins timing. When ET equals PT, Q turns off. The elapsed time is maintained until IN turns off.
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