Chapter 6 PLC Programming 127
This section described how you could use the force instruction to
turn instructions on and off using the computer keyboard. However,
the force instruction must be used with extreme caution. Even though
the force instruction is a powerful tool for troubleshooting, using the
force instruction in an industrial plant has the potential of causing
fatal accidents.
0000
0002
0001
Red
pushbutton
Green
pushbutton
I:0
1
Stop
I:0
0
1747-L20A
1747-L20A 1747-
Motor #1
O:0
0
1747-L20A
Motor #1
O:0 I:0
0
1747-L20A
I:0
2
1747-L20A
Motor #1
O:0
0
1747-L20A
Stop
I:0
0
Red
pushbutton
1747-L20A
I:0
1
Red
pushbutton
1747-L20A
I:0
1
Temperat
switch
1747-L20A
I:0
3
Temperature
switch
I:0
3
I:0
0
Stop
1747-L20A
O:0
1
O:0
2
Temperature
switch
T
s
Figure 6-32. Temperature switch is forced on.