Structured Text

Structured Text (ST) is a high-level, text-based programming language used for programming Programmable Logic Controllers (PLCs). It is part of the IEC 61131-3 standard, which defines programming languages for PLCs. Structured Text is designed to handle complex mathematical operations and algorithms, resembling traditional programming languages like Pascal and Ada in its syntax and structure. It allows for the use of variables, control flow statements such as loops and conditionals, and functions, providing a powerful tool for developing sophisticated control algorithms. The language’s ability to perform intricate calculations and logical evaluations makes it especially suitable for applications requiring precision and complex data manipulation.

Common Applications

Industrial Automation

Structured Text is frequently used in industrial automation to program PLCs that control machinery, manufacturing processes, and production lines. Its high-level capabilities allow for the implementation of advanced control logic and data processing.

Complex Mathematical Computations

Due to its powerful mathematical and logical capabilities, Structured Text is ideal for applications requiring complex calculations, such as process control, motion control, and data analysis.

Process Control

In process industries, Structured Text is used to create sophisticated control routines that manage variables such as temperature, pressure, and flow rates, ensuring optimal operation and efficiency.

Safety Considerations

Code Readability and Maintenance

Structured Text, while powerful, can become complex and difficult to read if not well-documented and structured. This can lead to errors in the code, which might affect the safety and reliability of the PLC-controlled systems.

Compliance with Safety Standards

When programming safety-critical applications, it is crucial to follow industry-specific safety standards and guidelines to ensure that the system behaves predictably and safely under all operating conditions.

Related Terms or Concepts

IEC 61131-3

The international standard for programmable controller programming languages, which includes Structured Text as one of the five languages defined for PLC programming.

Ladder Logic

Another PLC programming language that is graphical and commonly used for simpler, less complex applications. It is often compared to Structured Text due to its widespread use in the industry.

Function Block Diagram (FBD)

A graphical programming language for PLCs that uses blocks to represent functions and data flows, often used alongside Structured Text in complex control systems.

Pascal and Ada

High-level programming languages that Structured Text draws similarities from in terms of syntax and structure, known for their strong typing and structured programming features.