1. The term PLC stands for:
(A) Programmable Logic Controller
(B) Process Level Control
(C) Power Line Converter
(D) Programmable Load Circuit
2. A PLC is mainly used for:
(A) Automation of industrial processes
(B) Office data entry
(C) Power generation
(D) File storage
3. The brain of a PLC is the:
(A) CPU (Central Processing Unit)
(B) Power supply
(C) Input module
(D) Output module
4. The PLC scan cycle consists of:
(A) Input scan, program execution, and output update
(B) Program download only
(C) Data backup only
(D) Power-up and shutdown
5. The power supply module of a PLC provides:
(A) DC power to internal circuits and I/O modules
(B) Analog signals to sensors
(C) AC power to motors
(D) Voltage for external relays only
6. The input module of a PLC is used to:
(A) Receive signals from field devices such as switches and sensors
(B) Send signals to actuators
(C) Store the PLC program
(D) Supply power to the CPU
7. The output module of a PLC is used to:
(A) Send control signals to actuators or machines
(B) Read input from sensors
(C) Display data on the monitor
(D) Store ladder programs
8. The memory of a PLC is used to store:
(A) User program, data, and system information
(B) Power supply voltage
(C) Analog signals only
(D) External communication data only
9. The ladder diagram used in PLC programming is based on:
(A) Electrical relay logic
(B) Mechanical drawings
(C) Flowchart algorithms
(D) Mathematical models
10. A contact in a ladder diagram represents:
(A) A switch or sensor input condition
(B) An actuator output
(C) A power source
(D) A counter reset
11. The coil symbol in a ladder diagram represents:
(A) An output device to be energized
(B) An input sensor
(C) A memory address
(D) A timer reset
12. The scan time of a PLC is:
(A) The time taken to read inputs, execute logic, and update outputs
(B) The total execution time of the project
(C) The boot-up time
(D) The communication delay
13. PLCs operate primarily on:
(A) Digital signals
(B) Analog signals only
(C) Mechanical movement
(D) Pneumatic control
14. Analog inputs to a PLC can come from:
(A) Temperature sensors and pressure transducers
(B) Push buttons
(C) Limit switches
(D) Contact relays
15. Digital inputs to a PLC can come from:
(A) Switches and push buttons
(B) Potentiometers
(C) RTDs
(D) Thermocouples
16. The standard programming languages for PLCs are defined in:
(A) IEC 61131-3
(B) ISO 9001
(C) IEEE 1588
(D) ANSI 32-1
17. The most commonly used programming language in PLCs is:
(A) Ladder Diagram (LD)
(B) Structured Text (ST)
(C) Instruction List (IL)
(D) Sequential Function Chart (SFC)
18. The PLC output devices can include:
(A) Motors, relays, lamps, solenoid valves
(B) Switches and sensors
(C) Memory modules
(D) Temperature transmitters
19. The watchdog timer in a PLC is used to:
(A) Monitor and reset the system in case of program errors
(B) Control analog signals
(C) Synchronize communication
(D) Delay the scan cycle
20. PLC communication ports are used for:
(A) Uploading and downloading programs, and data exchange
(B) Power supply connection
(C) Analog signal conditioning
(D) Actuator control
21. The retentive memory in a PLC retains data:
(A) Even after power failure
(B) Only while power is ON
(C) Until program execution ends
(D) Only during scan time
22. The main advantage of using a PLC over relay logic is:
(A) Ease of reprogramming and flexibility
(B) Higher wiring complexity
(C) Increased size
(D) Slower response time
23. A timer in a PLC is used to:
(A) Provide time delays in operations
(B) Measure frequency
(C) Control voltage
(D) Store analog values
24. A counter in a PLC is used to:
(A) Count pulses or events
(B) Generate analog signals
(C) Measure voltage levels
(D) Reset program execution
25. The non-volatile memory in a PLC is used to:
(A) Store user programs permanently
(B) Execute logic temporarily
(C) Record runtime errors
(D) Save temporary variables
26. The real-time clock in a PLC is used to:
(A) Perform time-based operations and logging
(B) Measure frequency
(C) Control voltage
(D) Set scan time
27. A relay output module in a PLC is suitable for:
(A) AC and DC loads
(B) Only AC loads
(C) Only DC loads
(D) High-frequency switching
28. An optically isolated input in a PLC is used to:
(A) Protect the CPU from electrical noise and surges
(B) Increase speed of computation
(C) Convert analog signals
(D) Perform logical operations
29. The first PLC was developed by:
(A) Allen-Bradley
(B) Siemens
(C) Modicon (by Bedford Associates)
(D) Mitsubishi
30. The main advantages of PLCs are:
(A) Reliability, flexibility, and easy troubleshooting
(B) High maintenance cost
(C) Complex hardware
(D) Fixed programming logic