SOLUTION MANUAL PROGRAMMABLE LOGIC CONTROLLERS 4TH EDITION FRANK PETRUZELLA

SOLUTION MANUAL PROGRAMMABLE LOGIC CONTROLLERS 4TH EDITION FRANK PETRUZELLA

CHAPTER 9

Program Control Instructions

TEST 9 . 1

Choose the letter that best completes the statement. Answer

1. Which of the following PLC instructions would not be 1. c

classified as an override instruction?

1. a) master control reset
2. b) jump-to-subroutine
3. c) output energize
4. d) jump-to-label

2. The MCR instruction establishes a zone in the user 2. b

program in which all nonretentive outputs can be:

1. a) turned on simultaneously.
2. b) turned off simultaneously.
3. c) turned on in a defined sequence.
4. d) turned off in a defined sequence.

3-1. In the program of Figure 9-1, when the MCR instruction 3-1. b

is false, output(s) ____ will always be de-energized.

1. a) M, PL1 and SOL
2. b) M and PL1
3. c) PL1
4. d) SOL

3-2. Assume that the MCR instruction makes a false-to-true 3-2. a

transition. As a result:

1. a) all outputs will be controlled by the respective input conditions.
2. b) all nonretentive outputs will de-energize.
3. c) all retentive outputs will de-energize.
4. d) all nonretentive outputs will energize.

Figure 9-1 Program for question 3.

4-1. In the program in Figure 9-2, assume output SOL C is 4-1. b

energized at the time the MCR instruction makes a true-to-false transition. As a result, output SOL C will:

1. a) de-energize.
2. b) remain energized.
3. c) remain energized but still be controlled by inputs LS3 and LS4.
4. d) de-energize but still be controlled by inputs LS3 and LS4.

4-2. The fenced zone controlled by the MCR instruction is (are): 4-2. b

8. a) rungs No. 1 through No. 8.
9. b) rungs No. 3 through No. 6.
10. c) rungs No. 2 and No. 6.
11. d) rung No. 2.

4-3. Which of the following is the conditional instruction 4-3. c

that controls the MCR zone?

1. a) Stop
2. b) Start
3. c) Manual Automatic
4. d) Temperature Switch

4-4. The latch and unlatch instructions would be classified as: 4-4. a

1. a) retentive outputs.
2. b) nonretentive outputs.
3. c) condition instructions.
4. d) unconditional instructions.

4-5. Assume the alarm output is activated. This would require the: 4-5. a

1. a) temperature switch input to be true.
2. b) Manual Automatic input to be true.
3. c) LS4 input to be true.
4. d) both a and b.

Figure 9-2 Program for question 4.

5. The main advantage to the jump-to-label instruction is that: 5. d
6. a) any number of rungs may be programmed between the jump and label rungs.
7. b) it allows you to use one set of condition instructions to control multiple outputs.
8. c) it allows you to use one set of condition instructions to control multiple inputs.
9. d) it has the ability to reduce the processor scan time.

6. The label (LBL) instruction is: 6. d
7. a) always logically true.
8. b) has the same address as the jump instruction with which it is used.
9. c) is used to identify the ladder rung that is the target destination of the JMP instruction.
10. d) all of these.

7. Which of the following instructions would most likely be 7. b

programmed outside the jumped area of a program?

1. a) Latch and unlatch instructions
2. b) Timer and counter instructions
3. c) Immediate inputs and outputs
4. d) Forced inputs and outputs

8-1. In the program of Figure 9-3, which output is not 8-1. a

affected by the jump instruction?

1. a) M
2. b) SOL 1
3. c) SOL 2
4. d) PL2

8-2. Rungs 5, 6, and 7 are not scanned by the processor 8-2. d

when rung ____ has logic continuity.

1. a) 1
2. b) 2
3. c) 3
4. d) 4

8-3. When the jump-to-label instruction is exe­cuted, 8-3. d

the outputs of the jumped rungs:

1. a) are all energized.
2. b) are all de-energized.
3. c) are all immediately updated.
4. d) remain in their last state.

Figure 9-3 Program for question 8.

9. The jump-to-subroutine instruction can save a great 9. c

deal of duplicate programming in cases:

1. a) that require the programming of several timers.
2. b) that require the programming of several counters.
3. c) where a machine has a portion of its cycle that must be repeated several times during one machine cycle.
4. d) all of these.

10-1. In the program of Figure 9-4, when the examine on 10-1. d

sensor instruction is true, the processor:

1. a) turns on all outputs in the subroutine area.
2. b) turns off all outputs in the subroutine area.
3. c) stops executing the subroutine.
4. d) starts executing the subroutine.

10-2. When the processor scan reaches the RET instruction, 10-2. d

it will return the processor to the:

1. a) start of the program.
2. b) end of the program.
3. c) rung above the JSR instruction.
4. d) rung below the JSR instruction.

Figure 9-4 Program for question 10.

11. The immediate input and output instructions provide a way of: 11. c
12. a) ending the program immediately.
13. b) restarting the program immediately.
14. c) temporarily interrupting the program scan to allow selected bits in the data table to be updated.
15. d) temporarily interrupting the program scan to reset all bits in the data table to zero.

12. Immediate instructions should be used only when: 12. c
13. a) a program must be halted immediately.
14. b) a program must be restarted immediately.
15. c) the updating of an input or output is critical to your operation.
16. d) the resetting of all bits in the data table is critical to your operation

13. Immediate instructions are most useful when programmed: 13. c
14. a) immediately after the I/O scan has occurred.
15. b) immediately prior to the I/O scan.
16. c) at the middle or toward the end of the program.
17. d) near the beginning of the program.

14. The use of immediate instructions: 14. a
15. a) increases the total scan time of the program.
16. b) decreases the total scan time of the program.
17. c) increases the number of rungs that can be programmed.
18. d) decreases the number of rungs that can be programmed.

15. The forcing function of a PLC allows the user to turn 15. c

an external input or output on or off:

1. a) according to the forced program.
2. b) according to the main program.
3. c) from the keyboard regardless of its actual status.
4. d) all of these.
5. Forcing functions are often used: 16. d
6. a) to continue a machine process until a faulty field device can

be repaired.

1. b) for testing purposes during an initial start-up.
2. c) for troubleshooting purposes.
3. d) all of these.

17-1. In the program of Figure 9-5, the actual status of 17-1. b

input 1:1/3 is ____ but the forced status is ____ .

1. a) false …true
2. b) true …false
3. c) false …false
4. d) true …true

17-2. The output of 0:2/5 would be ____ and the output 17-2. c

of 0:2/6 would be ____ .

1. a) false … true
2. b) true … false
3. c) false … false
4. d) true … true

Figure 9-5 Program for question 17.

18-1.In the program of Figure 9-6, the actual status of 18-1. a

output address 0:2/5 is ____, but the forced status is ____ .

1. a) false … true
2. b) true … false
3. c) false … false
4. d) true … true

18-2. The status of examine on instruction 0:2/5 would 18-2. c

be ____ and the status of output 0:2/6 would be ____ .

1. a) false …true
2. b) true …false
3. c) false …false
4. d) true …true

Figure 9-6 Program for question 18.

19. Forcing functions should not be used: 19. d
20. a) with retentive outputs.
21. b) with nonretentive outputs.
22. c) with immediate I/O instructions.
23. d) without consideration for any potential unsafe effects.

20. PLC emergency stop circuits should be: 20. a
21. a) hardwired outside the controller program.
22. b) programmed as part of the master control reset instruction.
23. c) programmed as part of the zone control last state instruction.
24. d) programmed as an immediate input instruction.

21-1. In the diagram of Figure 9-7, power to the processor 21-1. c

module is controlled by the:

1. a) master control relay.
2. b) start/stop buttons.
3. c) main disconnect switch.
4. d) all of the above.

21-2. Power to the input and output module is controlled by the: 21-2. d

1. a) master control relay.
2. b) start/stop buttons.
3. c) main disconnect switch.
4. d) all of the above.

21-3. The transformer is used to: 21-3. a

1. a) isolate the controller from the main power lines.
2. b) step up the main power line voltage.
3. c) provide the low-voltage do operating voltage for the controller.
4. d) all of the above.

21-4. Assume the processor comes equipped with a 21-4. c

normally closed fault relay contact output designed to open when a processor malfunction is detected. This contact would be:

1. a) programmed as part of the master control reset instruction.
2. b) programmed as part of the zone control last state instruction.
3. c) hardwired in series with the emergency stop button.
4. d) hardwired in parallel with the emergency stop button.

21-5. When replacing modules or working on equipment 21-5. d

controlled by the PLC installation, the safest way to proceed is to:

1. a) de-energize the MCR coil.
2. b) block open the emergency stop switch.
3. c) remove the fuse from the circuit.
4. d) pull and lock the disconnect switch.

Figure 9-7 Program for question 21.

22-1. In the program in Figure 9-8, the use of the starter 22-1. d

auxiliary contact instead of a programmed contact:

1. a) is more costly.
2. b) is safer.
3. c) provides positive feedback about the exact status of the motor.
4. d) all of these.

22-2 Assume that the stop button was changed to a normally 22-2. a

open contact type. As a result, the program could be made to operate as before by changing the instruction at address:

1. a) stop to examine if open.
2. b) start to examine if open
3. c) starter auxiliary contact to examine if open.
4. d) both a and c.

22-3. Assume that the NC stop button is replaced with an 22-3. d

NO stop button and that the program is changed so it operates as before. Should the field wire connected to one end of the stop button break off:

1. a) the motor would stop automatically.
2. b) pressing the stop button would stop the motor.
3. c) pressing both the start and stop buttons would stop the motor.
4. d) none of these.

Figure 9-8 Program for question 22.

23. A jump instruction is similar to a(n): 23. c
24. a) MCR command.
25. b) ZCL command.
26. c) skip command.
27. d) JSR command.

24. A JSR instruction: 24. a
25. a) tells the processor to jump from the main program to a subroutine area or file.
26. b) tells the process to execute the fault routine.
27. c) latches outputs when energized.
28. d) latches outputs when de-energized.

25. The MCR instruction: 25. d
26. a) is an output instruction.
27. b) is used in pairs.
28. c) is used to disable or enable a zone within a ladder program.
29. d) all of these.

26. The ____ is the target for the jump instruction. 26. a
27. a) LBL
28. b) TND
29. c) IOT
30. d) RET

27. The ____ instruction will return the scan to your 27. d

main program at the completion of the subroutine.

1. a) LBL
2. b) IIN
3. c) TND
4. d) RET

28. The ____ instruction stops the processor from 28. c

scanning the rest of the program.

1. a) LBL
2. b) IOT
3. c) TND
4. d) STI

29. The MCR instruction can be used to control: 29. d
30. a) entire sections of a program.
31. b) entire rungs of a program.
32. c) selected elements within a rung of a program.
33. d) both a and b

30. The JMP and LABEL instructions allow a processor to: 30. c
31. a) return to the beginning of a program.
32. b) take a shorted route to the end of the program.
33. c) skips sections of the program, reducing scan time.
34. d) create a fault condition.

31. The JSR instruction requires that a: 31. a
32. a) separate file be created
33. b) separate processor be used
34. c) separate power supply be used
35. d) all of these

CHAPTER 9

Program Control Instructions

TEST 9 . 2

Place the answers to the following questions in the

answer column at the right. Answer

1. Master control reset (MCR) and jump (JMP) 1. override

are often referred to as ____ instructions.

2. The MCR instruction can only be programmed 2. False

to control an entire circuit. (True or False)

3. When the MCR instruction is ____ , all rung 3. True

outputs below the MCR will be controlled by their respective input conditions.

4. If the MCR output is turned off or de-energized, 4. de-energized

all nonretentive rungs below the MCR will be ____ .

5. ____ instructions should not normally be placed 5. Retentive

within an MCR zone because they will remain in their last active state when the instruction goes false.

6. When programming an MCR instruction to control 6. False

a fenced zone, an MCR rung with no conditional inputs is placed at the beginning of the zone and an MCR rung with conditional inputs is placed at the end of the zone. (True or False)

7. The master control instruction is used as a 7. False

substitute for a hardwired emergency stop switch. (True or False)

8. The jump (JMP) instruction is used to jump over 8. True

certain program instructions if certain conditions exist. (True or False)

9. The advantage of the JMP instruction is the ability 9. scan time

to reduce the processor ____ .

10. In a jump-to-label program, the ____ instruction 10. Label

is used to identify the ladder rung that is the target destination of the jump instruction.

11. The label address must match that of the jump 11. True

instruction with which it is used. (True or False)

12. The JMP instruction does not contribute to 12. False

logic continuity and, for all practical purposes, is always logically true. (True or False)

13. The jump-to-subroutine instruction is used 13. repeated

where a machine has a portion of its cycle that must be ____ several times during one machine cycle.

14. When the program scan reaches an immediate 14. updated

I/O instruction, the scan is interrupted and the bits of the

addressed word are ____ .

15. The immediate I/O instruction is used with 15. cirtical

____ I/O devices that require updating in advance of the I/O scan.

16. The immediate I/O instruction is most useful if 16. False

the instruction associated with the device is at the beginning of the program. (True or False)

17. The use of the immediate I/O instruction increases 17. scan time

the total ____ of the program.

18. The forcing capability of a PLC allows the user 18. state

to turn an external I/O on or off regardless of the ____ of the device.

19. Random forcing of given inputs or outputs 19. True

can cause equipment damage. (True or False)

20. Emergency stop circuits should be ____ outside 20. hardwired

of the controller program so that, in the event of total controller failure, independent and rapid shutdown means are available.

21. A main ____ is installed on the incoming power 21. disconnect switch

lines as a means of removing power from the entire PLC system.

22. Power to the PLC input and output devices 22. Master Control Relay

are usually controlled by means of a hardwired ____ circuit.

23. The master control relay instruction can be used as a 23. False

substitute for a disconnect switch. (True or False)

24. The use of a motor starter seal-in contact in 24. Positive

place of a programmed contact provides ____ feedback about the exact status of the motor.

25. The safest way to wire a stop button to a PLC 25a. NC

system is to use a (a) ____ contact programmed 25b. ON

to examine for an (b) ____ condition.

26. The label instruction has a logical true condition. 26. True

(True or False)

27. Jumping to a subroutine does not cause any 27. True

rungs of the main program to be skipped over. (True or False)

28. The jump instruction allows a section of a 28. True

program to be jumped when a production fault occurs. (True or False)

29. It is not possible to jump backward in 29. False

the program. (True or False)

30. Nesting subroutines allow you to direct program 30a. main

flow from the (a) ____ program to a subroutine and 30b. subroutine

then to another (b) ____ .

31. Nested subroutines make complex programming 31. True

easier. (True or False)

32. Forcing outputs affects only the addressed 32. True

output terminal. (True or False)

33. Programming the selectable timed interrupt is 33. time

done when a section of program needs to be executed

on a ____ basis rather than on an event basis.

34. The fault routine allows for an orderly shutdown 34. True

in case of a fault. (True or False)

35. The temporary end instruction, when true, 35. stops

____ the program scan.

36. A latch instruction will automatically unlatch 36. False

if it is contained within a de-energized MCR zone. (True or False)

37. The MCR instruction is not a replacement for a 37. True

hardwired master control relay that provides emergency stop. (True or False)

38. When programming MCR instructions, the first rung 38. unconditional

has a conditional MCR output instruction and the last rung is an

____ MCR rung.

39. When an MCR zone goes false, off-delay timers 39. True

within the zone will automatically activate and begin their off delay cycle.

(True or False)

40. Each JMP instruction must have a LBL instruction. 40. True

(True or False)

41. You must de-energize the JMP instruction to 41. False

activate it. (True or False)

42. You must energize the MCR instruction to 42. False

activate it. (True or False)

Programming Assignments

For Chapter 9

This section will require you to simulate several program control applications. The instructions used are intended to be generic in nature and, as such, will require some conversion for the particular PLC model you are using. The use of a prewired PLC input/output control panel is recommended to simulate the operation of these circuits.

1. Construct a simulated program for the MCR program of Figure 9-9 using any available addresses, switches, and lights on your PLC control panel. After constructing your program on paper, enter the program into the PLC. Demonstrate that when the MCR instruction is de-energized, all nonretentive outputs de-energize and all retentive outputs remain in their last state.

Figure 9-9 Program for assignment 1.

To be completed by the student.

2. Construct a simulated program for the MCR fenced zone program of Figure 9-10. After constructing your program on paper, enter it into the PLC. Demonstrate how the rungs between the two MCR instructions are controlled.

Figure 9-10 Program for assignment 2.

To be completed by the student.

3. Construct a simulated program for the jump-to-label program of Figure 9-11. After constructing your program on paper, enter it into the PLC. Demonstrate how the jump-to-label operation is executed.

Figure 9-11 Program for assignment 3.

To be completed by the student.

4. The jump-to-label program of figure 9-12 is described in the text. Prepare an I/O connection diagram and ladder logic program that will simulate its operation. Use addresses that apply to your PLC installation. Enter the program into the PLC and verify its operation.

Figure 9-12 Program for assignment 4.

To be completed by the student.

5. Construct a simulated program for the jump-to-subroutine program in Fig. 9-12. After constructing your program on paper, enter it into the PLC. Demonstrate how the jump-to­-subroutine operation is executed.

Figure 9-13 Program for assignment 5.

To be completed by the student.

6. The flashing pilot light subroutine program of figure 9-14 is described in the text. Prepare an I/O connection diagram and ladder logic program that will simulate its operation. Use addresses that apply to your PLC installation. Enter the program into the PLC and verify its operation.

Figure 9-14 Program for assignment 6.

To be completed by the student.

7. Enter the forcing program of Figure 9-15 into the PLC and demonstrate how each of the following is executed: (a) forcing the switch on; (b) forcing the switch off; (c) forcing PL1 on; and (d) forcing PL1 off.

Figure 9-15 Program for assignment 7.

To be completed by the student.

8. Enter the simulated start/stop pushbutton program of Figure 9-16 in the

PLC.

• Demonstrate how an open in the stop pushbutton circuit will fail to de-energize the output.
• Replace the normally open stop pushbutton with a normally closed type and modify the program so that the circuit operates properly. Demonstrate how an open in the stop pushbutton circuit of this program will automatically de-energize the output

Figure 9-16 Program for assignment 8.

To be completed by the student.

9. Construct a simulated program for the MCR program of Figure 9-17. Enter the program into the PLC. Operate the program according to the following sequence:
10. a) Close switches 1, 2, 3, 4, and 6 and allow timer T4:2 to time out. What

lights are on?

1. b) Open switch 1. What light is on now? Why did lights 1 and 2 go off?
2. c) Open switch 4 and close switch 5. Did light 1 go off? Why or why not?
3. d) What happened to the two timers when you disabled the MCR zone?
4. e) What happened to the two timers when you re-enabled the MCR zone?

Figure 9-17 Program for assignment 9.

To be completed by the student.

10. Construct a simulated program for the ladder logic program of

Figure 9-18. Enter the program into the PLC. Operate the program to force specified inputs and outputs according to the following sequence:

1. a) Turn switches 1 and 2 off and switch 3 on.
2. b) Force off switch 3. Use the data monitor to observe the status of the corresponding bit for switch 3 in the input image table file. Close switch 3 and observe the status of the bit. How does forcing inputs manipulate the input image table file bits? Disable the force and exit from the data monitor to the ladder logic screen.
3. c) With all switches turned off, force on pilot light 2. Use the data monitor to observe the status of the corresponding bit for pilot light 2 in the output image table file. How does forcing outputs manipulate the output image table file bits?

Figure 9-18 Program for assignment 10.

To be completed by the student.

11. Construct the example of the subroutine instruction (SBR) and the return instruction (RET) program shown in Figure 9-19. The purpose of the program is to find the average value of N7:5 and N7:20 and store the result in N7:30. This is accomplished by passing parameters to the subroutine and doing the math in the subroutine, and then returning the answer to the main program through the RET instruction. The operation of the program can be summarized as follows.

• When S1 is closed, the data from the input parameter, N7:5, is copied into the first input parameter in the SBR instruction, N7:50.
• The data from the second input parameter, N7:20, is copied into the second input parameter in the SBR, N7:51.
• In the subroutine, N7:50 and N7:51 are then added together, with the result stored in N7:52.
• The value in N7:52 is then divided by 2, which gives the average of N7:50 and N7:51, with the result stored in N7:53.
• The RET instruction then returns the average value through the return parameter, N7:53, to N7:30 in the JSR instruction in the first rung in the main program.

Prove the operation by using the data monitor to insert values for N7:5 and N7:20 and verifying that the average value is contained in N7:30.

Figure 9-19 Program for assignment 11.

To be completed by the student.

12. Design a program that uses the temporary end (TND) instruction described in the text. Demonstrate how this instruction can be used to progressively debug the program.