124 Programmable Logic Controllers: Hardware and Programming
Stop RPB
M1
L1 L2
GPB
M1 TSW
M1
W
Stop RPB
M2
Stop TSW
TSW
M2
TSW
Figure 6-29. Relay logic diagram.
(GPB) to turn on only motor #1. Both motors run until the normally
closed stop pushbutton is pressed.
If the temperature switch is open, motors will be in the jog mode.
This means that you must press and hold the pushbuttons in order to
run the motors.
Figure 6-30 displays the input/output connections of an Allen-
Bradley fixed SLC 500 PLC device. Table 6-6 illustrates the input/out-
put ports’ assignments.
Place the PLC in the offline mode and create the ladder logic dia-
gram displayed in Figure 6-31. Download the program into the PLC
and place the PLC in the run/online monitor mode.
Use the following steps to force some of the input instructions
ON and OFF. These steps will familiarize you with the use of the force
instruction.
1. Right-click input I:0/3 to open the shortcut menu. Click the
Force On
command to place the word ON below the input
instruction I:0/3. See Figure 6-32.
Click
Enable Force
and notice that the word ON under the input
instructions will change to red. The red ON is an indication that the
force instruction is enabled. You have just used the force instruction
to close the normally open input I:0/3. Therefore, the white light
turns on to indicate continuous run mode. See Figure 6-33.
Enable force:
Command that enables
the force conditions
of the input/output
instructions.