TEST 1 . 1 - without the prior written consent of McGraw-Hil...

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CHAPTER 1

Programmable Logic Controllers (PLCs): An Overview

TEST 1 . 1

Choose the letter that best completes the statement. Answer

1. PLCs were originally designed as replacements for: 1. b

• microcomputers. c) analog controllers.
• relay control panels. d) digital controllers.
• Basically, the function of a PLC is to: 2. d
• amplify various weak signal sources.
• control a high voltage output with a low voltage input.
• control the speed of motors.
• make logical decisions and control outputs based on them.
• Modifying relay-type process control circuits usually involves 3. a

changing the:

• circuit wiring.
• input circuit modules.
• output circuit modules.
• circuit operating voltage levels. 1 / 4

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• Which of the following is not an advantage that PLCs 4. c

offer over the conventional relay-type of control system?

a) Smaller size c) Higher current capacity

b) Less expensive d) More reliable

• The main difference between a PLC and relay control system 5. d

is that:

• different types of input devices are used.
• different types of output devices are used.
• different input and output voltage levels are used.
• one uses hardwired relay control logic and the other uses programmed

instructions.

• The central processing unit: 6. a
• looks at the inputs, makes the decisions based on the program,

and sets the outputs.

• looks at the outputs, makes the decisions based on the program, and sets

the inputs.

• serves only to store the program in memory.
• serves only to supply power to the backplane. 2 / 4

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• PLC proprietary architecture 7. d
• is the opposite to open architecture .
• makes it more difficult to connect to devices made by other

PLC manufacturers.

• does not allow programs to be interchanged between different PLC

manufacturers.

• all of these.

8. The output interface module connects to: 8. b

• sensing devices such as switches or pushbuttons.
• load devices such as lamps or solenoids.
• a programming device such as a computer.
• all of the above.

9. Field or real-worlddevices refer to: 9.d

• input devices only.
• output devices only.
• load devices only.
• all devices that are physically wired to the PLC.
• The power required to operate the logic circuits 10 c

of the processor unit is typically:

• low voltage ac. c) low voltage dc.
• high voltage ac. d) high voltage dc. 3 / 4

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11. The control plan stored in the PLC is called: 11. a

• a program. c) FORTRAN.
• a Boolean ladder. d) a microprocessor.

12. The programming device: 12. d

• is used to enter the program into the memory of the processor.
• is commonly a personal computer.
• can be a hand-held device.
• all of the above.

13. The programming device must be connected to the controller: 13. d

• at all times. c) when monitoring a program.
• when entering a program. d) both b and c.
• The symbol in a ladder logic diagram: 14. a
• can be thought of as a normally open contact.
• represents a capacitor.
• is always at logic 0.
• is always at logic 1.
• The symbol in a ladder logic diagram 15. b

represents a:

• set of normally closed contacts.
• virtual relay coil.
• seal-in contact.
• field input sensing device.
• / 4