Learn the process for troubleshooting a PLC program and fixing the errors, bugs, or malfunctions. Follow these 4 steps to identify, isolate, implement, and evaluate a solution.

Review the PLC program logic to identify potential areas where the problem may originate. This could involve examining ladder logic diagrams, function block diagrams, or other programming languages used in the PLC. Check input and output signals to ensure they are functioning as expected. Use diagnostic tools and monitoring software provided by the PLC manufacturer. Verify that sensors, actuators, and other hardware components are operating correctly.

After implementing the solution, monitor the system closely to verify that the problem has been resolved. Conduct functional tests to ensure that the PLC program is operating as intended and that all associated equipment is functioning properly.

What is the process for troubleshooting a PLC program?

A PLC program is a set of instructions that controls a physical process, such as a conveyor belt, a machine, or a robot. PLC stands for programmable logic controller, which is a device that executes the program and interacts with sensors and actuators. PLC programming is a skill that requires logical thinking, attention to detail, and knowledge of the process and the hardware. However, even the most experienced PLC programmers can encounter errors, bugs, or malfunctions in their programs. How can you troubleshoot a PLC program and fix the issues? Here are some steps to follow.

1 Identify the problem

The first step is to identify the problem that you are trying to solve. What is the expected behavior of the program and what is the actual behavior? Is the problem consistent or intermittent? Is it related to a specific input, output, or condition? Is it affecting the whole system or only a part of it? You can use various tools and methods to identify the problem, such as observing the process, reading the documentation, checking the status indicators, using the PLC software, or testing the hardware.

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Allun Seabourne

Purchasing at P & I Design Ltd
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The signal typically comes from a physical instrument. Ensure the unit is functioning as expected by discussing reported problem with the on-site engineer. Then start looking at the system. Have fault alarms activated? Check comms screen to ensure there are no network or hardware faults indicating. Then start reviewing the plc code against documentation. Has there been a change in the process or product which may have affected the approved conditions ?

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Shubham Shrivastav

Frontend Developer | React.js & Next.js Enthusiast | UI/UX Designer | Boosting Engagement |
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Gather information about the symptoms of the problem. This may include abnormal behavior of machinery or equipment controlled by the PLC, error messages, or alarms. Consult with operators, maintenance personnel, and any available documentation to understand the nature of the issue.

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Angadh Lambert

Business Strategist, Industrial Network Specialist @ Indu-Sol | Industrial Automation | AI explorer
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The first stage in resolving PLC problems involves determining whether the problem stems from hardware malfunction or communication breakdown. Employ tools such as Industrial network analyzers to make this distinction.

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2 Isolate the cause

The next step is to isolate the cause of the problem. This means narrowing down the possible factors that are affecting the program and eliminating the ones that are not relevant. You can use a systematic approach, such as dividing the program into smaller sections, testing each section individually, or using breakpoints and watchpoints to monitor the values of the variables. You can also use a trial-and-error approach, such as changing one parameter at a time, adding or removing components, or modifying the code. The goal is to find the root cause of the problem and not just a symptom.

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Shubham Shrivastav

Frontend Developer | React.js & Next.js Enthusiast | UI/UX Designer | Boosting Engagement |
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Review the PLC program logic to identify potential areas where the problem may originate. This could involve examining ladder logic diagrams, function block diagrams, or other programming languages used in the PLC. Check input and output signals to ensure they are functioning as expected. Use diagnostic tools and monitoring software provided by the PLC manufacturer. Verify that sensors, actuators, and other hardware components are operating correctly.

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3 Implement a solution

The third step is to implement a solution that fixes the problem and restores the normal operation of the program. Depending on the cause of the problem, the solution may involve changing the code, replacing the hardware, adjusting the settings, or updating the firmware. You should always backup your original program before making any changes and document your changes for future reference. You should also test your solution thoroughly and verify that it works as intended and does not create new problems.

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4 Evaluate the results

The final step is to evaluate the results of your solution and make sure that it solves the problem completely and permanently. You should monitor the performance of the program and the process over time and check for any signs of recurrence, side effects, or new issues. You should also measure the impact of your solution on the efficiency, quality, safety, and reliability of the process and compare it with the previous situation. You should also review your troubleshooting process and identify any lessons learned, best practices, or improvements that you can apply in the future.

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Shubham Shrivastav

Frontend Developer | React.js & Next.js Enthusiast | UI/UX Designer | Boosting Engagement |
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After implementing the solution, monitor the system closely to verify that the problem has been resolved. Conduct functional tests to ensure that the PLC program is operating as intended and that all associated equipment is functioning properly.

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5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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Pete Shilling

PLC Controls Engineer at Telsonic
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Something to consider when writing a program is having manual function screens for each station on your HMI. The screens could include buttons to switch outputs. Indicators to monitor the inputs. The ability to move motors etc. and fwd/back buttons to run the station through its complete sequence, step by step. This will not only enable you to test the machine in a controlled manner, when you start-up for the first time but will give an engineer the best chance to problem solve when the machine is in production.

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What is the process for troubleshooting a PLC program?

1

2

3

4

5

1 Identify the problem

2 Isolate the cause

3 Implement a solution

4 Evaluate the results

5 Here’s what else to consider

Programming

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What is the process for troubleshooting a PLC program?

1

2

3

4

5

1 Identify the problem

2 Isolate the cause

3 Implement a solution

4 Evaluate the results

5 Here’s what else to consider

Programming

Rate this article

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