How to Write SCADA Scripts: Basic Syntax and Examples

To write SCADA scripts, use the scripting language provided by your SCADA system, typically based on VBScript, Python, or proprietary syntax. Scripts automate tasks like data logging, alarms, and control by using commands to read/write tags and handle events.

Syntax

SCADA scripts usually follow a simple structure to interact with system tags and events. Common parts include:

• Tag Access: Read or write values using tag names.
• Control Structures: Use If, For, and While for logic.
• Event Handlers: Scripts run on events like tag changes or timers.
• Functions: Define reusable code blocks.

Each SCADA platform may have slight syntax differences but generally follow these patterns.

vbscript

If Tag("PumpStatus") = 1 Then
    Tag("ValveOpen") = 1
Else
    Tag("ValveOpen") = 0
End If

Example

This example script turns on a valve when a pump is running and logs the action. It runs whenever the pump status tag changes.

vbscript

Sub OnPumpStatusChange()
    If Tag("PumpStatus") = 1 Then
        Tag("ValveOpen") = 1
        LogEvent "Valve opened because pump started"
    Else
        Tag("ValveOpen") = 0
        LogEvent "Valve closed because pump stopped"
    End If
End Sub

Output

When PumpStatus changes to 1:
ValveOpen tag set to 1
Event logged: Valve opened because pump started

When PumpStatus changes to 0:
ValveOpen tag set to 0
Event logged: Valve closed because pump stopped

Common Pitfalls

Common mistakes when writing SCADA scripts include:

• Using incorrect tag names causing script failures.
• Not handling all possible tag values, leading to unexpected behavior.
• Writing scripts that run too frequently, causing performance issues.
• Ignoring event triggers and writing scripts that never execute.

Always test scripts in a safe environment before deploying.

vbscript

'' Wrong: Missing else branch
If Tag("PumpStatus") = 1 Then
    Tag("ValveOpen") = 1
End If

'' Right: Complete if-else
If Tag("PumpStatus") = 1 Then
    Tag("ValveOpen") = 1
Else
    Tag("ValveOpen") = 0
End If

Quick Reference

Command	Description
Tag("TagName")	Access or set the value of a tag named TagName
If ... Then ... Else ... End If	Conditional logic to control flow
Sub SubName()	Define a script function or event handler
LogEvent "message"	Write a message to the SCADA event log
For ... Next	Loop through a block of code multiple times

Key Takeaways

Use your SCADA system's scripting language to read and write tag values for automation.

Write scripts triggered by events like tag changes to react in real time.

Always include complete conditional branches to avoid unexpected states.

Test scripts carefully to prevent performance issues or control errors.

Refer to your SCADA platform's documentation for exact syntax and functions.