plc programming

PLC Programming Best Practices

As a fundamental component of any manufacturing automation solution, a Programmable Logic Controller (PLC) is a computer control system that monitors input devices and makes autonomous decisions based on a custom program to control and optimize output devices. Simply put, a PLC is the brain of any industrial automation platform. That’s why it’s crucial to follow a series of best practices to maximize productivity, ensure your automation solution works as intended, and make debugging easier. In this post, we’ll examine the core of these best practices, so your PLC can serve you for years to come.

Start with Documentation

Before you start coding a PLC, begin by creating a clear flowchart detailing precisely what the machine is supposed to do. Design a state machine sequential flowchart and list all inputs, outputs, parameters, and alarms.

Use a State Machine Program Structure

Also known as an event-driven architecture, a state machine program consists of a set of states and a case selector to determine which action the program transitions to next. State machine programming is also easy to maintain, document, and reuse.

Optimize Scan Cycles

Divide the PLC program into pages, beginning with a main page. To ensure your scan cycle is logical, ensure it reads inputs, executes a state machine, and writes outputs—in that order.

Centralize Outputs

Control all outputs in only one place in the program with direct output writing. Do not use, set, or reset outputs. If an output depends on multiple conditions, differentiate them with an OR/AND in the branch.

Structuring Reset Conditions

Always place reset conditions in a branch preceding the set condition. This prevents a fault from being discovered and then reset without the rest of the PLC noticing.

Never Use Loops

If you forget to close a loop, the program will loop forever without executing the rest of the PLC.

Add a Condition for a Division of Zero

Incorporate a condition for the division of zero into the code. Doing so prevents the PLC from going into a “division for zero” error and terminating program execution.

Limit Values

Be sure to put limits on values inserted from the operator in the configuration screen.

Understand Downloading

When talking about PLCs, downloading simply means sending data from a PC to the PLC.

Use Field Buses

Using field buses rather than discrete inputs and outputs to interact with external devices is safer and cheaper than using hard-wired digital inputs and outputs.

Print the Ladder Program in a PDF

Print the entire ladder program in a PDF for documentation in case you have to re-create it later.

Your PLC Programming Experts

If you need help programming a PLC at your facility, contact the experts at HEXA Engineers today. As a team of automation experts, we’ll work with you to optimize a PLC solution for your specific needs and project requirements.