Programmable Logic Controller multiple choice questions

 Programmable Logic Controller

1. The acronym PLC stands for
a) Pressure Load Control
b) Programmable Logic Controller
c) Pneumatic Logic Capstan
d) PID Loop Controller
Answer: Programmable Logic Controller
2. In PLC programming, a retentive function is one that
a) Defaults to the “on” state
b) Is not reset after a power cycle
c) Defaults to the “off” state
d) Cannot be edited or deleted
Answer: Is not reset after a power cycle
3. A good application for a timed interrupt in a PLC program would be
a) A communications function block
b) A PID function block
c) A math function block
d) A motor start/stop rung

Answer: A PID function block

4. In a PLC, the scan time refers to the amount of time in which 
a) the technician enters the program
b) timers and counters are indexed by
c) one “rung” of ladder logic takes to complete
d) the entire program takes to execute
Answer: the entire program takes to execute
5. The difference between online and offline PLC programming is
a) whether the PLC is running or stopped
b) whether the programming PC has internet connectivity
c) the type of programming cable used
d) where the edited program resides
Answer: where the edited program resides
6. Ladder logic programming consists primarily of
a) Virtual relay contacts and coils
b) Logic gate symbols with connecting lines
c) Function blocks with connecting lines
d) Text-based code
Answer: Virtual relay contacts and coils
7. An OR function implemented in ladder logic uses
a) Normally-closed contacts in series
b) Normally-open contacts in series
c) A single normally-closed contact
d) Normally-open contacts in parallel
Answer: Normally-open contacts in parallel
8. What is the largest integer number that a PLC counter function can reach if it uses a 16 bit register?
a) 32,768
b) 65,535
c) 65,536
d) 65,537
Answer: 65,535
9. The part that monitors the inputs and makes decisions in a PLC is the CPU.
a) True
b) False
Answer: True
10. In a PLC “I” is used for output and “Q” is used for input
a) True
b) False
Answer: False
11. To increase the number of inputs and outputs of the PLC, one can use expansion modules.
a) True
b) False
Answer: True
12. An example of discrete (digital) control is
a) Varying the volume of a music system
b) Turning a lamp ON or OFF
c) Varying the brightness of a lamp
d) Controlling the speed of a fan
Answer: Turning a lamp ON or OFF
13. The _____ is moved toward the relay electromagnet when the relay is on.
a) Armature
b) Coil
c) NO contact
d) NC contact
Answer: Armature
14. Which of the following RLL applications is not normally performed in early automation systems?
a) On/off control of field devices
b) Logical control of discrete devices
c) On/off control of motor starters
d) Proportional control of field devices
Answer: Proportional control of field devices
15. When a relay is NOT energized
a) There is an electrical path through the NO contacts
b) There is an electrical path through the NC contacts
c) Neither the NO or the NC contacts have an electrical path
d) Both the NO and the NC contacts have an electrical path
Answer: There is an electrical path through the NC contacts
16. Which of the following cannot be an input that is given to the PLC?
a) Manual switches
b) Relays 
c) Sensors
d) None of the above
Answer: None of the above
17. In a current sinking DC input module _____
a) The current flows out of the input field device
b) Requires that a AC sources be used with mechanical switches
c) The current flows out of the input module
d) Currents can flow in either direction at the input module
Answer: The current flows out of the input field device
18. How is the speed of operation of conventional relay system as compared to digital controllers?
a) very slow
b) very fast
c) same
d) almost similar
Answer: very slow
19. What one item in the input module circuit above should be changed to make it correct.
a) The battery polarity
b) Input module should be sinking
c) Field device should be sinking
d) Current flow direction
Answer: Input module should be sinking
20. The type of memory which is fast and temporarily stores the data which are immediately required for use is called as______.
a) HDD
b) ROM
c) RAM
d) SSD
Answer: RAM
21. PLC can be _____ in plant to change the sequence of operation.
a) only programmed
b) only reprogrammed
c) programmed and reprogrammed
d) able to give a set point
Answer: programmed and reprogrammed
22. The capability of convention relay systems for complex operations is ____ that of the PLCs .
a) poor than
b) excellent than
c) as good as
d) unpredictable as
Answer: poor than
23. How is the noise immunity of PLCs to electrical noises as compared to that of conventional relay controllers?
a) poor
b) excellent
c) as good as noise immunity of conventional relay controllers
d) unpredictable
Answer: poor
24. _____ of PLCs can be done in very little time.
a) Programming
b) Installation
c) Commissioning
d) All of the above
Answer: All of the above
25. When _____ contacts are actuated, they disrupt the power supply through them.
a) normally open type
b) normally closed type
c) both a. and b.
d) none of the above
Answer: normally closed type
26. The PLC is used in _______.
a) machine tools
b) automated assembly equipment
c) moulding and extrusion machines
d) all of the above
Answer: all of the above
27. Current flows into the _____
a) Input terminal of a sinking DC input module
b) Input terminal of a sinking output field device
c) Output terminal of a sinking input field device
d) All of the above
Answer: All of the above