300+ TOP Programmable Logic controllers Interview Questions [UPDATED]

1. What Are Different Components In Plc?

1. Input Interface
2. Memory Section
3. Central Processing Unit (CPU)
4. Programmable Language
5. Programming tool
6. An output Interface

2. Advantages Of Plcs Than Hard Wired Relay?

PLCs are highly reliable, easily programmable, Small and Inexpensive, PLCs can be designed with the communication capabilities so they can converse with the local or remote computer, They can sustain in robust environment less maintenance.

3. What Is The Programmable Language Used In Plc?

The general language program consists of Ladder Diagrams. Relay logic control scheme is represented in Ladder diagrams. Alternative languages uses Boolean representation of these control schemes as base of the computer representation.

4. What Does Central Processing Unit (cpu) Of Plc Consists?

CPU is the brain of the system and consists of Microprocessor: To carry out arithmetic and logical operations

Memory:
The area in the CPU in which the information is stored and retrieved

Power Supply:
The electrical supply that converts the ac voltage to various DC operating voltages.

5. What Is Scan In Plc ?

The sequential operation of the controller that goes through the ladder diagram from top to bottom of the ladder. In this process it updates all the outputs corresponding to the inputs. SCAN takes place from left to right of each rung. Usually SCAN time is in milliseconds and it is a continuous process.

6. What Is A Plc?

Programmable Logic Controllers are industrially hardened micro computers, designed to replac e electromechanical relays, used to control machines and processes.

7. What Are The Main Advantages Of Plc?

1.      Modular design
2.      Increased reliability
3.      Lower cost
4.      Compact size
5.      Ease of programming
6.      Rugged construction and designed to withstand vibrations, temperature, humidity and noise
7.      Ability to communicate with computer

8. What Is The Need Can Be Satisfied In Designing An Industrial Grade Lcu?

Flexibility of changing the control configuration Ability to use the controller without being a computer expert. Ability to bypass the controller in case it fails. So that the process still can be controlled manually. Ability of the LCU to communicate with other LCUs and other elements in system.

9. What Is Lcu?

Local control unit is the small collection of hard ware in the system that can do closed loop control. Local control unit interfaces directly to the process.

10. What Is The Significance Of Dcs?

DCS is used for interfacing and computing functions and also provides the means of communication between the other devices. It consists of local control unit, low level interface, high level interface, shared communication facility Etc.

11. What Is Scada? Give Any Four Editors Available In Scada Package?

Supervisory Control and Data Acquisition (SCADA) system is computerised hardware and software based project that provides a single integrated view of all control and information resources, enable engineers, supervisors, operators to view and interact with the working of an entire operation through graphical representation of their product process.

Four editors:

a. Inkscape SAGE – SCADA Animation Graphic Editor
b. Generic Logic
c. TRACE MODE
d. UCanCode

12. What Is Cimplicity?

CIMPLICITY is a SCADA package. It is based on a client server architecture consisting of servers and viewers. Servers are responsible for the collection and distribution of data. Viewers connect into servers and have full access to the collected data for viewing and control actions.

13. List The Potential Benefits Of Scada.?

a. Educed site visits and callouts
b. Predictive maintenance which allows proactive rather than reactive planning
c. The ability to view and adjust set points remotely
d. Reliability and robustness
e. Maximize productivity
f. Improve product quality
g. Reduce your operating and maintenance costs
h. Integrate with your business systems
i. Preserve your capital investment

14. Mention Some Of The Application Areas Of Scada?

Industrial process: chemical plants, power generation and distribution, Metallurgy etc and nuclear process: reactors, nuclear waste etc.

15. Define Scada.

Supervisory Control and Data Acquisition (SCADA) system is computerised hardware and software based project that provides a single integrated view of all control and information resources, enable engineers, supervisors, operators to view and interact with the working of an entire operation through graphical representation of their product process.

16. What Are The Major Areas Of Application Of Plc?

1.       Sequence control, timing, counting, and data calculation
2.       Batch or continuous process control
3.       Precise position/motion control
4.       Open loop or feedback control, process data acquisition and display

17. What Are The Advantages Of Plc Over Relays?

1.       They have to be hard-wired to perform a specific function
2.       No hard-wire requirement
3.       When the system requirement change, the relay wiring has to be changed or modified
4.       Can be easily changed or expanded through program
5.       Higher power consumption
6.       Lower power consumption

18. Explain The Functions Of Plc-input And Output Modules:

1. Input interface modules accept signals from the machine or process devices (120Vac) and convert them into signals (5Vdc) that can be used by the controller.
2. Output interface modules convert controller signals (5Vdc) in to external signals (120Vdc) used to control machine or process.

19. What Is Ladder Logicdiagram?

Ladder Logic Diagram is a symbolic language used in PLC. This diagram consist of series of symbols interconnected by lines to indicate the flow of current through the various devices. In ladder logic diagram the sides of the ladder forms the power sources and current flows through the various –logic input devices that form the rungs of the ladder.

20. Explain Advantages Of Plcs Than Hard Wired Relay?

PLCs are highly reliable, easily programmable, Small and Inexpensive, PLCs can be designed with the communication capabilities so they can converse with the local or remote computer, They can sustain in robust environment less maintenance.