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Programming PLC Applications
gram cycle. This ensures that the gate cannot be blocked if the button sticks or of the operator
does not release it.
It must be ensured that the drive can only be switched on when it is not already turning in the
opposite direction. This is implemented by programming the PLC so that M1 can only be set
when M2 is not set.
NOTE
The motor direction interlock must also be complemented by an additional interlock with
physical contactors outside the PLC (see wiring diagram).
A similar approach is used to process the signals from buttons S4 and S5 for closing the gate.
Here, M1 is polled for a signal state of "0" to ensure that M1 and M2 cannot both be set at the
same time.
b Close gate automatically after 20 seconds
Ladder Diagram
X003
14
T0
18
When the gate is open limit switch S3 activates and input X3 is switched off. (For safety reasons
S3 is a break contact.) When this happens timer T0 starts the 20s delay (K200 = 200 x 0.1s =
20s). When the timer reaches 20s relay M2 is set and the gate is closed.
b Stop gate with STOP switch
Ladder Diagram
X000
20
Pressing the STOP button (S0) resets relays M1 and M2, stopping the gate motor.
b Identifying obstacles with the photoelectric barrier
Ladder Diagram
X007
23
If an obstacle is registered by the photoelectric barrier while the gate is closing relay M2 is
reset and the close operation is halted. After this relay M1 is set, opening the gate again.
3 – 30
RST
RST
M2
RST
An Introduction to Programming
Instruction List
K200
14 LDI
T0
15 OUT
18 LD
SET
M2
19 SET
Instruction List
M1
20 LDI
21 RST
22 RST
M2
Instruction List
23 LD
M2
24 AND
25 RST
SET
M1
26 SET
X003
T0
K200
T0
M2
X000
M1
M2
X007
M2
M2
M1
MITSUBISHI ELECTRIC
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