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Timers
4.3
Timers
When you are controlling processes you will often want to program a specific delay before
starting and stopping certain operations. In hard-wired controllers this is achieved with timer
relays. In PLCs this is achieved with programmable internal timers.
Timers are really just counters that count the PLCs internal clock signals (e.g. 0.1s pulses).
When the counter value reaches the setpoint value the timer's output is switched on.
All timers function as make delay switches and are activated with a "1" signal. To start and reset
timers you program them in the same way as outputs. You can poll the outputs of timers as
often as you like in your program.
Ladder Diagram
X0
0
T200
4
In the above example timer T200 is started when input X0 is switched on. The setpoint value is
123 x 10ms = 1.23 s, so T200 switches on output Y0 after a delay of 1.23 s. The signal
sequence generated by the following program example is as follows:
X0
T200
Y0
You can also specify the timer setpoint value indirectly with a decimal value stored in a data
register. See section 4.6.1 for details.
4 – 6
K123
T200
Y0
1,23 s
The timer continues to count the internal
10ms pulses as long as X0 remains on.
When the setpoint value is reached the
output of T200 is switched on.
If input X0 or the power supply of the PLC
are switched off the timer is reset and its
output is also switched off.
Devices in Detail
Instruction List
0
LD
X0
1
OUT
T200
4
LD
T200
5
OUT
Y0
MITSUBISHI ELECTRIC
K123
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