8 Common PLC Programming Mistakes You Need To Avoid

Many automated systems rely on programmable logic controllers (PLCs) to keep operations running smoothly. These systems control everything from conveyor belts to robotic arms. While these powerful devices offer incredible flexibility and control, programming them incorrectly can lead to costly downtime, safety hazards, and operational inefficiencies.

Many small businesses and those new to automated systems experience issues with their PLC systems. That’s why Jaeckels Industrial is here with eight common PLC programming mistakes to avoid. Whether you’re new to automated systems or just looking to improve your current layout, these tips can save you from some costly errors and repairs.

1. Neglecting Proper Documentation Standards

One of the first things to set up with your PLC is a comprehensive documentation process. Neglecting this can lead to difficulties when troubleshooting issues or training new technicians on the system. A proper documentation system includes detailed comments within your code and clear, easy-to-understand naming conventions. You want to set up a simple system diagram that explains all the input and output relationships.

Avoid using generic labels like “Motor1” or “Timer7,” and instead make them as descriptive as possible. Consider labeling files and systems with names such as “PackageDelayTimer” or “ConveyorMotorWest.” These labels clarify the purpose of each component and help people new to the system determine the applications without trial and error.

2. Overlooking Input-Signal Conditioning

Almost every sensor or switch contains some form of electrical noise, voltage spike, or momentary interruption that can cause issues with your PLC’s behavior. It’s a good idea to connect field devices directly to your PLC inputs with these signal conditions in mind. Overlooking conditioning can lead to false readings and unpredictable system responses, which are especially problematic if you work with heavy machinery or electrical systems.

Proper signal conditioning involves filtering, isolation, and voltage level matching to ensure that clean, reliable signals reach the PLC. Debouncing circuits eliminate switch bounce from mechanical contacts, while optical isolators protect sensitive PLC inputs from voltage spikes.

3. Insufficient Error-Handling Implementation

PLC systems run smoothly in normal conditions but can fail in unexpected situations. Small businesses often overlook comprehensive error handling during initial programming, focusing primarily on normal operation sequences. It may seem like a good approach, but if there’s ever an issue with equipment malfunctions or sensor failures, the entire system may not know how to accommodate the error.

Effective error handling begins with identifying all possible failure modes within the automated system. Each sensor, actuator, and process step represents a potential failure point that requires monitoring and appropriate response procedures. Businesses should establish diagnostic routines in the program that can identify these problems as they arise instead of letting them result in shutdowns or other safety hazards.

4. Ignoring Scan-Time Optimization

Some of the most common PLC programming mistakes to avoid are those that cause extended scan times. Faulty programming can result in sluggish system response and timing issues that can derail automation. We recommend developing incremental programs and adding features that streamline overall system performance. Long scan times particularly affect applications requiring precise timing or high-speed operations.

Optimizing scan times requires understanding how different programming constructs affect execution speed. Complex mathematical calculations, extensive data manipulation, and inefficient loop structures consume significant processing time. You can move these time-intensive operations to interrupt routines or distribute calculations across multiple scan cycles to maintain consistent performance.

5. Inadequate Safety-System Integration

Safety systems require fundamentally different programming approaches than standard control functions, yet many small businesses treat them as routine programming tasks. This mistake can have serious consequences, as safety functions must operate independently from normal control logic and remain functional even when the primary system fails.

Hardwired safety circuits provide the highest levels of protection for critical functions such as emergency stops and safety interlocks. You want to establish circuits that work independently of the PLC program so you can’t override them with software commands. Integrating hardwired systems with PLC monitoring allows for comprehensive safety management while maintaining fail-safe operation.

6. Poor Memory-Management Practices

PLCs have finite memory resources, and inefficient programming can quickly exhaust available memory, leading to program upload failures or system instability. A common mistake is underestimating the memory requirements during an initial system design, which can tank capacity for future expansions or modifications.

Understanding different memory types helps optimize program storage and execution. Program memory stores the actual control logic, while data memory holds variable values and system status information. Efficient use of both memory types ensures reliable operation and provides room for system growth.

7. Neglecting Proper Grounding Techniques

A proper electrical grounding system is the foundation of your PLC operation, but it’s easy to overlook during installation. Poor grounding creates ground loops, allows electrical noise to corrupt signals, and can damage sensitive electronic components. These problems often manifest as intermittent faults that prove difficult to diagnose and resolve.

You want a single-point ground system that can eliminate ground loops and reduce erratic electrical behavior. Ensuring your system components go to a common grounding point eliminates a lot of potential issues. Separate grounding systems for distinct equipment types can create potential differences that interfere with normal operation.

8. Inadequate Testing and Validation Procedures

You should always conduct comprehensive testing on your PLC system throughout installation. Neglecting testing can lead to operational problems that you could have identified and repaired during development. Thorough testing requires systematic verification of all program functions under various operating conditions, including normal operation, fault conditions, and emergency scenarios.

You can perform many of these tests in a simulation, which allows you to verify that everything works without risking damage to your actual equipment. These tools can replicate various operating conditions and fault scenarios and identify programming errors before system deployment. Simulation testing is especially useful for determining safety-critical functions that you don’t want to test on expensive live equipment.

For reliable and efficient PLC and HMI programming that suits your operational needs, trust Jaeckels Industrial to deliver precision and expertise. Contact us today to discuss your project, and discover how we can optimize your automated systems for peak performance.