String OperationsIntermediateIEC 61131-3

CONCAT (String Concatenation)

Joins two or more strings into a single combined string.

The CONCAT function joins two or more strings together into a single string. It is the primary string-building operation in IEC 61131-3, used for constructing display messages, log entries, communication frames, and formatted output. CONCAT appends the second string to the end of the first string and returns the combined result.

Parameters

Inputs

Name	Type	Description
IN1	STRING	First string
IN2	STRING	Second string to append

Outputs

Name	Type	Description
OUT	STRING	Concatenated result (IN1 + IN2)

Structured Text Example

// Build alarm message
Alarm_Msg := CONCAT('ALARM: ', Alarm_Description);

// Build log entry with multiple parts
Log_Entry := CONCAT(CONCAT(Date_Str, ' - '), Event_Description);

// Build communication frame
Telegram := CONCAT(CONCAT(Header, Data_Payload), Checksum_Str);

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Platform-Specific Implementation

Siemens (TIA Portal)

Use CONCAT instruction in TIA Portal. Max string length is 254 characters.

Allen-Bradley (Studio 5000)

Use CONCAT instruction in Studio 5000. STRING data type max 82 characters default.

CODESYS

Use CONCAT() function in ST. String length depends on declaration.

Common Applications

Alarm message construction
Log entry formatting
Communication frame building
HMI display text
Report generation

Frequently Asked Questions

What is CONCAT (String Concatenation) in PLC programming?

Joins two or more strings into a single combined string. The CONCAT function joins two or more strings together into a single string. It is the primary string-building operation in IEC 61131-3, used for constructing display messages, log entries, communication frames, and formatted output.

What are common applications of CONCAT (String Concatenation)?

CONCAT (String Concatenation) is commonly used for: Alarm message construction, Log entry formatting, Communication frame building, HMI display text, Report generation.

How do I use CONCAT (String Concatenation) in different PLC platforms?

Siemens: Use CONCAT instruction in TIA Portal. Max string length is 254 characters. Allen-Bradley: Use CONCAT instruction in Studio 5000. STRING data type max 82 characters default. CODESYS: Use CONCAT() function in ST. String length depends on declaration.