PLC Interview Questions
- Aarush Shukla
- 02nd Jun, 2022
- 1059 Followers
PLC Interview Questions
This is an era of technology and everyone relies on technology. Technology has changed mankind a lot. Technology has the immense effect on mankind. It has basically given birth to new mankind in which men just have to design certain tools or devices for their work and then command them to work accordingly
One such device, which has the immense effect and is based on logical technology in the field of different industries, is PLC. PLC is abbreviated form of Programmable Logic Controller or Programmable Controller. It is a type of computer.
But it is not an ordinary computer; it is a digital computer which has been designed especially for industries which deal with the manufacture of assembly lines for video games, automobile devices etc. and for designing certain devices which are used to manufacture robots and has easy programming and diagnosis.
For the first time, they were developed and used by an automobile industry in order to provide flexible, simple and easily programmable controls which could replace the hard and complex computers, sequencers and timers.
Read Common PLC Interview Questions
Plc Interview Questions
1) What is PLC?
2) What are different components Of PLC?
- Input/output Modules: These are basically the modules, which depend on the input and the output commands given by the user.
- Power Supply: As the name suggest; power supply is the work of supplying power to be specific supplying DC current, which operates the PLC.
- Central Processing Unit (CPU As it is CPU, it will work as brain of the computer and will supply and store all the commands and the data given to the computer.
- Co-processor Modules: These are set of different microcomputers, which can do different programmes. Their main aim is the function PLC more properly and appropriately.
- Software: As the name suggests, software is the pioneer of PLC which stores and supplies all the commands and data to the PLC and Co-processors.
- Peripheral Device : The peripheral device works for inputting data and other equipment which are needed to the monitor.
3) What are various applications of PLC?
- Driving Motors
- Light Lamps
- Button Switches
- Traffic Signals
- Water Draining Pumps
- Photo Sensors.
Since all of these have hard and complex machines to convert electric energy in mechanical energy, the hard machines are now replaced by the PLCs.
4) Who are leading suppliers of PLC?
- Allen Bradley
- Texas Instrument
- General Electric
5) What is redundancy in PLC?
6) What is an HMI in PLC?
The HMI is the Human Machine Interface. It basically allows the operators to interface or communicate with the system that they are overseeing. The HMI provides a pictorial overview of the status of the mechanical system as well as its operation’s direct control. The graphical screens of the HMI can be so programmed as to allow the operator to view all-important statuses as well as control information. The HMIs make use of pictures, sounds, icons and solid colors in order to visually exemplify the various operating conditions. Many HMIs even deploy the advanced touch screen technology to improve the user’s interaction with the elements displayed on-screen.
7) What is SCAN in PLC?
8) List the advantages of PLC over Relays?
The advantages of PLC over Relays are:
- Small size.
- Easy expandability.
- Simple programming.
- Economical in long term.
- High reliability.
- Ability to the interface.
9) Explain scan cycle of PLC?
The scan cycle is the cycle in which the PLC gathers the inputs, runs the PLC program, and updates the outputs. It basically checks on the hardware and software for faults, also called a self-test.
10) What is role of I/O modules in PLC?
I/O modules are used to provide I/O signal in the form of simple on and off instructions in PLC, such that an input module detects the status of input signals such as push-buttons, switches, temperature sensors, etc whereas an output module controls devices such as relays, motor starters, lights, etc.
11) What is LD in PLC?
LD stands for ladder diagram and is also known as Ladder logic. LD is a graphical programming language used to program a PLC in order to express the logical operations with symbolic notation.
12) What is MCR in PLC?
MCR stands for Master Control Reset. MCR is a type of instruction that is used in pairs to create zones that clear all set outputs within that zone or turns off all the non-retentive outputs in the zone.
13) How Do Fixed PLCs differ from modular PLCs?
On the other hand, modular PLCs have different independent systems and components and they have numerous I/O systems and they can be repaired easily.
14) Which programmable languages are used in PLCs?
The programming languages used in PLCs are:
- Instruction List Programming
- Structured Text Programming
- Functional Block Programming
- Ladder Logic Programming
- Sequential Functional Chart
15) Differentiate between PLCs and DCS.
- PLCs were invented much earlier than DCS.
- PLCs are used for electrochemical processors while DCS are used for Pneumatic/Single Loop Controls.
- PLCs have generally fixed scan time while the scan time for DCS is adjustable.
- PLCs are used for discrete controls and DCS are used for regulatory controls.
16) Differentiate between PLCs are Relays
- PLCs are much cheaper compared to relays.
- The PLCs are more efficient compared to relays.
- They are used more.
- PLCs can be repaired easily but it is hard to repair Relays.
17) Which PLC ranges are available in Rockwell?
- Micrologix 1000, 1200 and 1500 Series
- SLC: SLC 5/01, 5/02, 5/03.
- Pico: Non modular small PLCs
- Control Logix Flex Logic and Soft PLC.
18) What is the RS LINX software used for?
19) How are PLCs more advantageous than hard-wired Relay?
20) Which one would you prefer: 4-20 ma or 0-20 ma? Explain your answer.
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