Lecture 7:
PLC: Review Questions
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Question 1
There are three machines, each with its own start and
stop buttons. Any two machines may run at one time
(also, any one may run by itself). Each start button is to
have a latch circuit. Construct a PLC program with
appropriate interlocking for this problem.
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Question 2
There are 3 part conveyor lines (1,2,3) feeding a main
conveyor. Each of the three conveyor lines has its own
counter. Design a ladder logic program to obtain the
total counts of parts on the main conveyor.
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Question 3
Write a ladder logic program that will cause a light to
come on if a PLC UP counter value is less than or equal
10 or more than or equal 30.
Hint: you may use LE (less than or equal) and GE
(greater than or equal ) functions available in ladder
diagram.
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Question 4
Develop the ladder logic that will turn on a pump using
a start switch. The pump should run for 5 min or 10
minutes depending on the state of another switch A. If
A is on at the time of starting the pump, it should run
for 5 min. otherwise it should run for 10 min.
Hint: you may use the MOVE function to store or
assign values to the variables in memory.
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Question 5
In an automated system for sorting good work pieces
from defected ones, two sensors are available. One of
them is activated each time a work piece enters the
system (%I0.0.2). The other is activated each time a
defected work piece is rejected from the system
(%I0.0.3). It is desired to start a conveyor belt (%Q0.2.0)
with “Start” push button (%I0.0.0) and stop it once
eight good pieces have passed the test or once “Stop”
push button (%I0.0.1) is pressed. Each time a defected
work piece passes the system, a flipper (%Q0.2.1) must
be activated for 4 sec to reject the work piece.
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Question 6
Write a ladder program to count up 5 counts and then
reset and at the same time (i.e. after reaching the 5th
counter) turn a light on for 5 seconds.
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