PLC Programming Questions

Question 1

What does an “output module” in a PLC do?
a) Reads sensor inputs
b) Controls external devices
c) Executes the ladder logic program
d) Monitors voltage levels

Answer 1

b) Controls external devices

Question 2

Which PLC component stores the user program?
a) RAM
b) ROM
c) EEPROM
d) CPU

Answer 2

c) EEPROM

Question 3

What is the primary function of ladder logic in PLC programming?
a) Create mechanical diagrams
b) Simplify troubleshooting of hydraulic systems
c) Program control sequences using graphical symbols
d) Test the electrical resistance of components

Answer 3

c) Program control sequences using graphical symbols

Question 4

What does a “normally open” (NO) contact in a PLC mean?
a) The contact is always closed
b) The contact closes when energized
c) The contact opens when energized
d) The contact is always open

Answer 4

b) The contact closes when energized

Question 5

What is a “scan cycle” in a PLC?
a) The process of running a program continuously
b) A one-time program execution
c) A diagnostic check of hardware
d) A test for ladder logic errors

Answer 5

a) The process of running a program continuously

Question 6

Which programming language is commonly used for PLCs?
a) Assembly
b) Ladder logic
c) Python
d) Java

Answer 6

b) Ladder logic

Question 7

What is the purpose of an HMI in a PLC system?
a) To control motors
b) To interface with the operator
c) To store the PLC program
d) To measure current

Answer 7

b) To interface with the operator

Question 8

What does the term “real-time” mean in PLC systems?
a) Program execution is delayed
b) Program execution happens instantly
c) Program execution happens as events occur
d) Program execution happens in parallel

Answer 8

c) Program execution happens as events occur

Question 9

What is the purpose of a rung in ladder logic programming?
a) To create a visual diagram
b) To represent a single logical operation
c) To interface with sensors
d) To display the scan time

Answer 9

b) To represent a single logical operation

Question 10

PLCs were originally designed as replacements for:
a) Microcomputers
b) Relay control panels
c) Analog controllers
d) Digital controllers

Answer 10

b) Relay control panels

Question 11

The primary function of a PLC is to:
a) Amplify various weak signal sources
b) Control a high voltage output with a low voltage input
c) Control the speed of motors
d) Make logical decisions and control outputs based on them

Answer 11

d) Make logical decisions and control outputs based on them

Question 12

Modifying relay-type process control circuits usually involves changing the:
a) Circuit wiring
b) Input circuit modules
c) Output circuit modules
d) Circuit operating voltage levels

Answer 12

a) Circuit wiring

Question 13

Which of the following is not an advantage that PLCs offer over conventional relay-type control systems?
a) Smaller size
b) Less expensive
c) Higher current capacity
d) More reliable

Answer 13

c) Higher current capacity

Question 14

The main difference between a PLC and a relay control system is that:
a) Different types of input devices are used
b) Different types of output devices are used
c) Different input and output voltage levels are used
d) One uses hardwired relay control logic and the other uses programmed instructions

Answer 14

d) One uses hardwired relay control logic and the other uses programmed instructions

Question 15

Which type of connector is most commonly used for Ethernet networking?
a) RJ11
b) RJ45
c) DB9
d) SC

Answer 15

b) RJ45

Question 16

Which of the following connectors is typically used for coaxial cable?
a) F-Type
b) USB Type-B
c) RJ45
d) LC

Answer 16

a) F-Type

Question 17

Which connector is used in legacy systems for serial communication?
a) DB9
b) RJ45
c) USB Type-C
d) SC

Answer 17

a) DB9

Question 18

Which connector type is often used for RS485 communication in industrial PLC systems?
a) Phoenix Terminal Blocks
b) RJ45
c) SC
d) USB Type-A

Answer 18

a) Phoenix Terminal Blocks

Question 19

When programming a PLC remotely over a network, which connector is typically used?
a) USB Type-B
b) HDMI
c) RJ45
d) DB9

Answer 19

c) RJ45

Question 20

What does it indicate if a PLC’s fault light is on?
a) The power supply is disconnected
b) The CPU has detected an error in the program or hardware
c) All inputs and outputs are functioning correctly
d) The PLC is running normally

Answer 20

b) The CPU has detected an error in the program or hardware

Question 21

Which type of PLC I/O module is used for connecting sensors like temperature probes?
a) Digital Input Module
b) Analog Input Module
c) Output Module
d) Communication Module

Answer 21

b) Analog Input Module