What Is String Data Type in PLC Programming?


Angela Bailey

The string data type is an essential component in PLC programming. It allows programmers to store and manipulate text-based information within their programs. In this article, we will explore what the string data type is, its characteristics, and how it can be used effectively in PLC programming.

What is a String Data Type?

A string is a sequence of characters, such as letters, numbers, or symbols. In PLC programming, the string data type is used to represent and manipulate textual information. It provides a way to store and process words, phrases, sentences, or any other form of text within a program.

Strings are typically enclosed in quotation marks (” “) to differentiate them from other data types. For example:

String name = "John Doe";

Characteristics of String Data Type

The string data type possesses several characteristics that make it unique:

  • Variable Length: Unlike other data types that have fixed lengths, strings can vary in length depending on the amount of text they contain. This flexibility allows programmers to handle different lengths of textual information efficiently.
  • Immutable: Strings are generally immutable, meaning they cannot be changed once they are assigned a value.

    Any modifications made to a string result in the creation of a new string object.

  • Concatenation: Concatenation refers to the process of combining two or more strings together. This operation is commonly used to create longer strings by joining smaller ones using the ‘+’ operator.

Using Strings in PLC Programming

The string data type finds applications in various scenarios in PLC programming:

Data Display and Communication

Strings are commonly used to display information on human-machine interfaces (HMIs) or operator panels. They allow for the dynamic presentation of data such as system status, alarms, or instructions.

Data Storage and Retrieval

Strings can also be used to store and retrieve data from databases or external files. This functionality enables PLCs to interact with other systems and exchange information effectively.

Data Manipulation

PLC programmers often need to manipulate strings by performing operations such as searching for specific patterns, extracting substrings, or replacing characters. These operations allow for advanced text processing capabilities within a PLC program.


The string data type is a powerful tool in PLC programming that allows for the handling of textual information. Its variable length, immutability, and concatenation capabilities make it an essential component for various applications such as data display, storage, retrieval, and manipulation. By leveraging the string data type effectively, programmers can create more versatile and robust PLC programs.

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