HOMEWORK HW4
EE436 – Programmable Logic Controllers
Date: 27/03/2017, Due date: 03/04/2017
1. Assume that a thermocouple is connected to an analog input module. Explain how the
temperature of the thermocouple is communicated to the processor.
2. Study the data transfer counter program of figure 1 and answer the following questions:
a. What determines the preset value of the counter?
b. Outline the steps to follow to operate the program so that the PL1 output is energized
after 25 off-to-on transitions of the count PB input.
Figure 1: Ladder program for question 2
3. Write a program to perform the following:
a. Turn on pilot light 1 (PL1) if the thumbwheel switch value is less than 9.
b. Turn on pilot light 2 (PL2) if the thumbwheel switch value is equal to 3.
c. Turn on pilot light 3 (PL3) if the thumbwheel switch value is greater than 4.
d. Turn on pilot light 4 (PL4) if the thumbwheel switch value is less than or equal to 7.
e. Turn on pilot light 5 (PL5) if the thumbwheel switch value is greater than or equal to 5.
4. Write a program for the following: The temperature reading from a thermocouple is to be
read and stored in a memory location every 4 minutes for 5 hours. The temperature reading
is brought in continuously and stored in address N7:150. File #7:200 is to contain the data
from the last full 5-hour period.
5. Answer each of the following with reference to the overfill alarm program shown in figure 2
a. Assume that the vessel is filling and has reached the 300-lb point. State the status of
each of the logic rungs (true or false) at this point.
b. Assume that the vessel is filling and has reached the 480-lb point. State the value of the
number stored in each of the following words at this point:
i. I:012
ii. N7:1
c. Assume that the vessel is filled to a weight of 502 lb. State the status of each of the logic
rungs (true or false) for this condition.
d. Assume that the vessel is filled to a weight of 510 lb. State the value of the number
stored in each of the following words for this condition:
i. I:012
ii.
N7:1
e. With the vessel filled to a weight of 510 lb, state the status of each of the logic rungs
(true or false).
Figure 2: Program sequence of problem 5
6. A main conveyor has two conveyors, A and B, feeding it. Feeder conveyor A puts six packs of
canned soda on the main conveyor. Feeder conveyor B puts eight-packs of canned soda on
the main conveyor. Both feeder conveyors have counters that count the number of packs
leaving them. Construct a PLC program to give a total can count on the main conveyor.