How to Troubleshoot Common PLC Problems

Programmable Logic Controllers (PLCs) have become indispensable to industrial automation and control systems. They form the operational hub that keeps your automated equipment running correctly, managing all the different machines and processes under their control. 

Although they're known to be rugged and robust, PLCs aren't immune to the occasional malfunction or just general wear and tear. Like all electronic devices, they suffer from joint problems like: 

• Electrical failures

• Software glitches

• Component deterioration

• Operator error

• External interference

• Environmental influences

PLC systems are integral to most industrial operations, so a failure can be disastrous to production. If you're encountering difficulties with your automated equipment, here are some ideas for troubleshooting common PLC problems. 

Identifying PLC Systems Failure

Electrical Issues

Electrical failures can be caused by short circuits, voltage fluctuations or power surges. Your PLC's internal components will suffer damage after such events, with subsequent malfunctions. To help mitigate these risks, make sure you have surge protection and conduct regular electrical maintenance.

Software Glitches

PLCs rely on their software programs to carry out the various control tasks. System failures can arise from programming errors or issues like software incompatibilities or corruption. To avoid these problems, ensure your programs are regularly updated and you're diligent in your programming practices.

Component Deterioration

PLCs are subject to regular wear and tear on their mechanical components, like connectors, cooling systems and fans. When these parts deteriorate, you can suffer electrical issues, overheating and poor performance. Ensure that a regular repair and maintenance programme for your PLC is instigated when worn-out components can be identified and replaced. 

Operator Error

PLC failures can be caused by human error. People may not know how to use the system and mishandle it. They might accidentally modify a program or input incorrect data. You can reduce the risk here with adequate training and stringently controlled access. Also, make sure to back up your PLC data regularly.

External Interference

A PLC's operation may also be disrupted by external factors. Nearby electrical sources or equipment may cause radio frequency interference (RFI) or electromagnetic interference (EMI). To protect your PLC against them, make sure your PLC is adequately grounded, shielded and isolated from external interferences.

Environmental Influences

Many PLCs are designed to cope with harsh industrial environments. They may have to resist contamination from dirt, dust, humidity, extreme temperatures, and corrosive substances. Even rugged PLCs will eventually suffer, requiring regular repair and maintenance to minimise their impact. Routine cleaning and protection are also essential to ensure your PLC continues running well.

Signs Of A PLC's Impending Failure

You might be able to prevent a PLC failure if you recognise the symptoms and take steps to deal with problems promptly and efficiently. Some common signs to look out for are:

• Issues with I/O modules or field devices: signs may include actuators not responding as expected, malfunctioning sensors or erratic readings.

• Electrical noise and interference affecting ground integrity: indications include voltage fluctuations, unpredictable behaviour and erratic readings.

• Compromised power supply: you may be unable to power up, and the system may become unstable, causing intermittent failures or even a complete shutdown.

• Network communication issues: telltale signs include dropped connections, network communication errors, or missing data.

• Overheating: this is a classic symptom of impending PLC failure. Excessive heat will damage components, having a noticeable effect on overall performance and lifespan.

• Conflict or incompatibility with other control system components: your PLC might begin to operate erratically, demonstrating unpredictable behaviour, system errors or crashes.

• Corrupted memory: symptoms of PLC memory corruption include data loss, program errors or system crashes, resulting in unreliable operation and unpredictable outcomes.

How To Troubleshoot Common PLC Problems

Once you know the most common faults you might find in your PLC systems, you can begin to troubleshoot them. Here's how:

1. Check PLC Indicators

Your PLC control module will likely feature a status indicator, giving valuable information about its activities and conditions. Check these indicators carefully for any fault messages or error codes. You'll find the correct interpretation of the codes and messages in the manufacturer's documentation. This should help you identify the problem's source to initiate repairs quickly.

2. Ground Loops

This is a common factor in PLC failures, causing interference and electrical noise. You must verify your system's ground integrity to troubleshoot this issue. Ensure every component is grounded correctly and no unintended ground paths exist. You may have to isolate more sensitive components to minimise ground loop effects or use isolation transformers.

3. Inputs

A PLC with unresponsive sensors or erratic readings may have faulty input components. To prevent PLC failure, check all input devices, such as switches and sensors, to be sure they're wired correctly and functioning as expected. Use a multimeter to test and help troubleshoot these devices.

4. Outputs

If you get imperfect or no response from output devices like relays or actuators, your PLC may have faulty outputs. Examine them carefully for loose connections, damaged wiring or other faults. You should also troubleshoot for errors in the program logic that controls these outputs.

5. The CPU

This is the PLC's operational core. Any problems here can lead to issues throughout the whole system. Check the CPU carefully for damaged components, loose connections or overheating. Consult a professional PLC service provider if your CPU has a problem. A specialist repair and maintenance team can carry out thorough diagnostics and take any required remedial action.

Taking Care Of Your PLC

We've seen several ways to diagnose and troubleshoot common PLC problems. You can help reduce the risk of failures by initiating a regular cleaning and maintenance schedule. Check key indicators frequently and take sensible steps to keep your PLC in an environment protected from external contamination and interference.