Page 116 - Programmable Logic Controllers, Fifth Edition

7. Assuming the hardwired circuit drawn in
Figure 5-60 is to be implemented using a PLC L1 PB1 CR1 L2
program, identify LS1
a. All input field devices
b. All output field devices CR1 PL1
c. All devices that could be programmed using inter-
nal relay instructions SS1
8. What instruction would you select for each of the PS1 CR1 SOL A
following discrete input field devices to accomplish
the desired task? (State the reason for your answer.) CR2
a. Turn on a light when a conveyor motor is running
in reverse. The input field device is a set of con-
tacts on the conveyor start relay that close when LS2 LS3 CR2 SOL B
the motor is running forward and open when it is
running in reverse. PB2
b. When a pushbutton is pressed, it operates a so- PB3 CR2 SOL C
lenoid. The input field device is a normally open
pushbutton.
c. Stop a motor from running when a pushbutton LS4 CR3 CR3
is pressed. The input field device is a normally
closed pushbutton. PL2
d. When a limit switch is closed, it triggers an instruc-
tion ON. The input field device is a limit switch
that stores a 1 in a data table bit when closed.
9. Write the ladder logic program needed to implement Figure 5-60 Hardwired circuit for Problem 7.
each of the following (assume inputs A, B, and C are
all normally open toggle switches):
a. When input A is closed, turn ON and hold ON c. When input A is closed or open, turn ON
outputs X and Y until A opens. output Y.
b. When input A is closed and either input B or C is d. When input A is closed, turn ON output X and
open, turn ON output Y; otherwise, it should be OFF. turn OFF output Y.

Basics of PLC Programming Chapter 5 97

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