Monday, April 15, 2024

Interview Questions For Plc Programmer

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Who Takes The Plc Test

PLC Programming Interview Questions – Building a 2 Button Motor Starter System Ladder Logic RSLogix

PLC tests are designed for applicants of various fields, including:

  • Computer Technicians
  • Commercial and Industrial Equipment Technicians
  • Electronics Engineering Technicians
  • Electrical and Electronics Repairers

In addition, PLC questions can appear on a variety of other tests, especially those dealing with maintenance, such as the Test or the MultiCrafTest.

What Is The Role Of Plc In Automation

PLC plays most important role in automation. All the monitoring as well as the control actions are taken by PLCs.

PLC Senses input via I / P modules, processes logic via CPU and memory, and provides output via output module.

Within a very short moment, it conducts accurate activities. Thats one of the reasons why PLC is commonly used in the industrial sector today.

Explain Types Of The Analog Input Signals

Typical analog input signals are 0 20 mA, 4 20 mA, 0 10 V or 0 5 V. The most commonly used analog input signal is 4 20 mA.

During the condition of fault or cable break,

  • If we use 4 20 mA, it returns 0 mA. This signals the PLC whether there is any fault.
  • If we use 0 20 mA, it also returns 0 mA which is the same as the input. The PLC cant detect the fault because the signal is the same as the input.

That is why 4 20 mA is preferred over 0 20 mA.

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Most Important Plc Interview Questions And Answers

Are you preparing for a PLC job? Do you want to test your PLC knowledge? Or do you want to learn more about PLC?

I am curating a list of PLC interview questions and answers based on my experience working in the PLC domain.

Whether if you are freshers or experienced, this list of interview questions will add value to your PLC knowledge.

Here you go.

What Is Role Of I/o Modules

Siemens PLC Interview Questions &  Answers

Electronic plug in units used for interfacing the i/p and o/p device in the machine or process to be controlled.

I/P module receives data from i/p devices and send it to processor. The O/P module receives data from processor and send it to output device .

  • Digital/Discrete :- Sends and Receives On/Off signal
  • Analog :- Sends and receives variable input or output signals

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What Is Master/slave Configuration

It is usually a single master device that talks with multiple slave devices . The master devices poll the slaves when they have the token. Slave devices only answer when asked a question. They are passive and the master can be said to be active. The slave devices just collect data and pass it to the master device when asked to do so.

Can You Tell Me About Your Favorite Programming Project

Learning about a persons favorite programming project can tell you what the applicant enjoys about work. You may find that the person values creative thinking used to solve complex issues, or you may discover that the interviewee prefers getting lost in repetitive lines of code.

What to look for in an answer:

  • Learn more about the applicants critical thinking skills
  • Whether the person will work well within the company
  • How the applicant approaches unknown problems


Early in college, I worked with a group of librarians to preserve letters written by Samuel Taylor Coleridge. They wanted to digitize each of the letters so students could access them online instead of coming to the library. We took high-quality images of the letters. I added XML tags to the images to make them easier to categorize and search. It was a fun interdisciplinary project that Im still proud of.

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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.
  • Driving Motors

How You Define Functional Block Programming

Top 13 Automation Engineer Interview Questions & Answers (Part 2 of 2)

Data flow is the prime principle behind an FBD. In these types of programs the values pass through feature blocks from the inputs to the outputs.

A FBD program is designed using function blocks that are bound together to describe the exchange of data. The connecting lines will have a type of data that must be compatible on both ends.

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What Are The Different Parts Of Automation

Ans: The various components of the PLC include:

Input/output modules: These are essentially the modules, which depend on the user-supplied input and output commands.

Power Supply: PLC can operate the DC current power supply.

CPU: Central Processing Unit is the brain of a computer that stores all commands and data.

Co-processor Modules: Actually, it is a set of microcomputers. It can do different programs. It can support PLC properly to function more efficiently.

Software: PLC needs software that stores and supplies all the commands and data to the PLC and Co-processors.

Peripheral Device: The monitor can be connected by the peripheral device.

What Is Grasp/slave Config

Ans: It is mostly an unmarried grasp tool that works with a couple of slave gadgets . The grasp gadgets ballot the slaves after instruction. Slave gadgets simplest solution while requested queries. They are ideal, the grasp may be stated for activation. The slave gadgets simply gather statistics and skip it to the grasping tool while requesting the same.

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How Exactly The Plc Cpu Works

PLC is a dedicated controller. It executes the user program again and again. It took very little time to execute this cycle once and this time is called scan time. This scan time is very less, usually in mS.

All the inputs and outputs status must be stored in the memory section of the PLC. The memory section also stores complex information like mathematical calculation answer, scaling of analog inputs, and outputs other complex information.

There are mainly three steps to control the process in the PLC,

  • Monitors the input status
  • Updates the output status according to use logic.
  • What Is The Use Of Scripts In Intouch

    PLC Interview Questions and Answers

    Is a way of writing logic in InTouch. InTouch has its own instructions and way of writing program.

    • Application : Linked to the entire application. Window : Linked to a specific window.
    • Key : Linked to a specific key or key combination on the keyboard. Condition : Linked to a discrete tagname or expression.
    • Data Change : Linked to a tagname and/or tagname.field only.

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    What Is The On Do Away With/ Off Do Away With A Stopwatch

    Ans: An ON-do away with energizing timer output guidance each offers time-now no longer on time-movement or measures the length for which some event occurs. Once the rung continues, the timer begins counting time-based absolutely genuinely truly periods and counts down until the amassed time equals the preset time.

    An OFF-do away with energizing timer output guidance offers time-now no longer on-time movement. If the control line rung does now no longer have continuity, the timer begins counting time-based absolutely genuinely truly periods until the amassed time price equals the predefined values.

    Plc Programmer Job Description Template

    We are looking to hire a skilled PLC programmer to design and install controller system software for our clients. You will be traveling to clients’ locations, analyzing system requirements, writing and installing custom programmable logic code, testing system efficiency, and providing operational support.

    To ensure success as a PLC programmer, you should have excellent knowledge of machine mechanics, a logical approach, and the ability to work with minimal supervision. A skilled PLC programmer should be able to easily identify and design a robust program fit for any mechanical or electrical purpose.

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    Plcs Advantages Or Benefits

    Higher Reliability:

    Once the program written and tested it can be easily downloaded into other PLCâs memory. It requires lesser and simpler wiring compared to conventional hard wired circuits employed.

    Hence reliability of the system increases significantly with PLCs.

    More Flexibility:

    It is easier to create a new program module or change an existing program in PLC compared to hard wired circuitry system. These software program modules can be changed whenever required.

    User can modify the programs in the field and if required, security can be enhanced by hardware interlocks such as key locks and software features such as passwords

    Lower Cost:

    PLCs were originally designed to replace relay control logic which is not economical and complex especially for large control circuits.

    With PLCs the cost savings have been so significant that the relay control becomes uneconomical except for some power applications.

    Generally if the application consists of more than half a dozen control relays, PLCs are least expensive to install

    Communication Capability:

    Communication capability of PLC with the other controllers and computers in the system is one of the main advantages compared to relay control circuit.

    Functions such as Supervisory control, data acquisition from the field, monitoring devices and process parameters associated with the field and downloading and uploading of programs can be easily possible with the PLC compared to hardwired circuits

    Faster Response:

    What Are Reed Relays

    Allen Bradley PLC Programming Interview Questions | Building a Retentive Timer Using TON Instruction

    Ans: These relays are designed with the aid of using coils wounded round a reed transfer. The reed transfer of the relay acts as an armature, and it’s far a tumbler tube or pill full of an inert fuel line inside which overlapping reeds are hermetically sealed.

    The overlapping ends of a reed encompass contacts in order that enter, and output terminals may be related to them. When the energy is provided to the coils, a magnetic subject is produced. These fields motivate reeds to be drawn together thereby, their contacts make a closed route thru the relay.

    Also, at some stage in the de-energizing technique of the coil, reeds are separated aside with the aid of using the pulling pressure of the spring connected to them.

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    What Is The Difference Between Plc And Your Personal Computer

    The architecture of a PLCs CPU is essentially the same as that of a general-purpose computer however, they are differentiated by some important characteristics. Firstly, unlike machines, PLCs are explicitly designed to survive the harsh industrial conditions

    A well-designed PLC can be mounted in an environment with significant amounts of electrical noise, electromagnetic interference, mechanical vibration and humidity-free of condensation

    What Are The Sinking And Sourcing In Plc

    Sinking and Sourcing are very important concepts related to PLC.

    Sinking Input and Sinking Output

    Sinking means internally connected with the common . An input or output card wired internally to common is typically regarded as a sinking input or sinking output card.

    Sourcing Input and Sourcing Output

    Sourcing means internally connected with the source . An input or output card connected directly to power, its typically called as sourcing input or sourcing output card.

    Read more about Sinking Vs Sourcing Concepts in PLC.

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    Which Of The Following Statements Is Correct

    a) Ladder logic is a PLC graphical programming technique introduced in the last 10 years.

    b) A ladder logic program is hard to analyze because it is totally different when compared with the equivalent relay logic solution.

    c) The number of ladder logic virtual relays and input and output instructions is limited only by memory size.

    d) The number of contacts for a mechanical relay is limited to number of coils on the relay.

    Explain Plc Operation With Controlling Motor As Example:

    PLC Interview Questions and Answers

    With reference to the picture:

    PLCs consist of input or point modules, a central processing unit , and output or point modules. An input accepts a variety of digital or analog signals from different field devices and converts them to a logic signal which the CPU can use. The Processor makes decisions and executes control instructions in memory based on the instructions for the program.

    Output modules transform CPU control instructions into a digital or analog signal which can be used to control different field devices . Use a programming tool to enter the directions you want. These instructions specify what a given input will be achieved by the PLC. These instructions specify what a given input will be achieved by the PLC.

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    Explain 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.

    What Is Redundancy

    The capacity to switch from primary equipment to standby equipment automatically without affecting the process under control.

    Redundancy means provision for standby module. In case of failure of one module is running process, the standby module takes over.

    Hot redundancy means the changeover of control from active processor to standby processor in less than 1 scan time

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    What Is A Relay

    Ans: Relays are used to isolate one voltage degree from another. A PLC can be used to manipulate the operation of a medium-voltage motor, possibly 2,300V or 4,160V. A relay is used to energize the starter, which, in turn, switches the motor voltage at the same time as the PLC controls the relay.

    Wired to offer a manage sequence, relays will also be used for easy management schemes in which a PLC might show uneconomical.

    Which Of The Following Statements About Rll Is Not True

    Ace Your PLC Programming Interview

    a) NO contact symbol has two parallel lines to indicate an open contact.

    b) RLL stands for Relay Ladder Logic.

    c) NC contact symbol has the same two parallel lines with a line across them to indicate closed contacts.

    d) The right power rail is positive or the high side of the source, and the left power rail is the power return or ground.

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    What Are The Types Of I/os

    Local â These are the I/Os placed in the PLC main rack containing CPU. These I/Os are connected to CPU through backplane.

    Distributed/Remote â These are the I/O placed at remote location from the main rack containing the CPU.

    These I/Oâs are to be connected on communication bus like control net, device net or FIP I/O.

    What Do You Know About Instruction List

    • Instruction List is a textual language of low level which has a similar structure to a basic machine assembler.
    • The IEC has developed IL by reviewing the many low level languages offered by PLC manufacturers.
    • The IEC has built IL by evaluating the many low level languages provided by PLC manufacturers.

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    + Plc Interview Questions

    Are you a fresher and searching for a job in the field of Automation, Instrumentation, Electrical? Then this article might be helpful for you to crack some of the interview questions related to PLC.

    We are listing here some of the most popular and most asked interview questions of PLC based on our working experience in the field of Instrumentation.

    No matter what if you are a fresher or experienced, this list will help you to add more value to your PLC knowledge.

    So further not waste more time and Lets explore the list.

    Below Find A List Of Significant Plc Interview Questions You Need To Be Ready To Answer

  • What steps would you take to troubleshoot a Programmable Logic Controller?

  • Describe the experience you have in testing and commissioning of PLC systems and what are some important pre-start-up procedures and checks one should follow?

  • Why do we need a fail-safe system in PLCs? What are some of the fundamental safety considerations that should be considered for the hardwiring of PLC systems?

  • Describe two PLC projects that you have worked on that you consider as major accomplishments and why?

  • How many PLC brands have you worked with and what are they?

  • What are the different PLC programming languages listed under IEC 61131-3 standard you have experience working with?

  • Describe the role of PLC in Industrial Automation?

  • How many years of programming and troubleshooting experience do you have with PLC hardware, and programming software, preferably in an industrial automation environment.

  • Which PLC emulation and simulation software have you used to write PLC programs?

  • How does a PLC communicate with field devices such as sensors, actuators, DCS, SCADA or other PLCs? What are some of the common communication protocols used by PLC systems?

  • Being prepared for an interview is an important step in landing a job. Not only do you need to do your homework and research the company you need to be ready to handle key interview questions. By planning and being prepared you’ll feel more confident, relaxed, making for a more successful interview, and helping you get the job.

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    What Is An Hmi

    HMI is a Human Machine Interface designed for industrial use. HMI systems can be called a window of a process. This window can be on a monitor or on special tools such as operator panels. An HMI system has connected an industrys hardware and software components so that the HMI can exchange user-system information.

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