WinCC VB Scripting Fundamentals

• Use Option Explicit and declare every variable.
• Keep object-event scripts short and move repeated logic into reusable procedures.
• Treat every HMI write as an operator request; PLC interlocks remain authoritative.

1. What Is WinCC VBScript?

VBScript is a lightweight scripting language available in classic SIMATIC WinCC for custom Runtime behavior. It can connect an object event to tag operations, calculations, navigation, text handling, logging or approved external interfaces when standard dynamics are not sufficient.

2. Where WinCC VBS Actions Run

The configured trigger determines frequency. Do not place slow file, database or network operations in fast cyclic actions or frequently evaluated object properties.

3. VBScript Syntax Fundamentals

Option Explicit

Dim tagName
Dim currentValue

tagName = "Demo_Temperature"
currentValue = 0

If currentValue >= 80 Then
    HMIRuntime.Trace "Temperature is high: " & CStr(currentValue)
End If

VBScript is case-insensitive, uses Dim for variables, & for safe string concatenation and block statements such as If ... Then ... End If. Option Explicit makes misspelled variable names fail early instead of silently creating a new variable.

4. Read a WinCC Tag with HMIRuntime

Dim temperatureTag
Dim temperatureValue

Set temperatureTag = HMIRuntime.Tags("Demo_Temperature")
temperatureTag.Read
temperatureValue = temperatureTag.Value

HMIRuntime.Trace "Demo_Temperature = " & CStr(temperatureValue)
Set temperatureTag = Nothing

Read updates the tag object before its Value is used. Test with an internal tag first. For an external PLC tag, also verify connection state, tag quality, data type and acquisition settings.

5. Write a WinCC Tag Safely

Dim commandTag
Dim requestedValue

requestedValue = 1

If requestedValue = 0 Or requestedValue = 1 Then
    Set commandTag = HMIRuntime.Tags("Demo_StartCommand")
    commandTag.Write requestedValue
    Set commandTag = Nothing
Else
    HMIRuntime.Trace "Rejected invalid command value"
End If

Validate values before writing and use an internal tag or approved simulation tag during training. A production command should be accepted or rejected by PLC-side mode, permissive and interlock logic. User Administration should also restrict the HMI action to the correct operator role.

6. Build Reusable Subs and Functions

Sub TraceTagValue(ByVal tagName)
    Dim tagObject
    Set tagObject = HMIRuntime.Tags(tagName)
    tagObject.Read
    HMIRuntime.Trace tagName & " = " & CStr(tagObject.Value)
    Set tagObject = Nothing
End Sub

Function IsBinaryValue(ByVal value)
    IsBinaryValue = (value = 0 Or value = 1)
End Function

Use a Sub for an action and a Function when a value must be returned. Pass inputs with ByVal unless the procedure intentionally needs to change the caller variable.

7. Handle Runtime Errors and Always Clean Up

On Error Resume Next

Dim processTag
Set processTag = HMIRuntime.Tags("Demo_Temperature")
processTag.Read

If Err.Number <> 0 Then
    HMIRuntime.Trace "Read failed: " & CStr(Err.Number) & _
        " - " & Err.Description
    Err.Clear
End If

Set processTag = Nothing
On Error GoTo 0

On Error Resume Next must be paired with immediate Err.Number checks. A broad error-suppression block can hide bad tag names and failed external operations. Restore normal handling with On Error GoTo 0.

8. Complete WinCC VBScript Practice Program

Option Explicit

Sub Main()
    Const SOURCE_TAG = "Demo_Temperature"
    Const STATUS_TAG = "Demo_StatusText"

    Dim sourceTag
    Dim statusTag
    Dim processValue
    Dim statusText

    On Error Resume Next

    Set sourceTag = HMIRuntime.Tags(SOURCE_TAG)
    sourceTag.Read

    If Err.Number <> 0 Then
        HMIRuntime.Trace "Cannot read " & SOURCE_TAG & ": " & Err.Description
        Err.Clear
        Set sourceTag = Nothing
        Exit Sub
    End If

    processValue = CDbl(sourceTag.Value)

    If processValue >= 80 Then
        statusText = "HIGH"
    ElseIf processValue >= 50 Then
        statusText = "NORMAL"
    Else
        statusText = "LOW"
    End If

    Set statusTag = HMIRuntime.Tags(STATUS_TAG)
    statusTag.Write statusText

    If Err.Number <> 0 Then
        HMIRuntime.Trace "Cannot write " & STATUS_TAG & ": " & Err.Description
        Err.Clear
    Else
        HMIRuntime.Trace SOURCE_TAG & "=" & CStr(processValue) & _
            ", status=" & statusText
    End If

    Set statusTag = Nothing
    Set sourceTag = Nothing
    On Error GoTo 0
End Sub

Create the two internal tags before testing. Adjust their names only in the constants so spelling remains consistent throughout the script.

9. Performance, Security and Maintainability Rules

• Prefer standard WinCC dynamics when they solve the requirement without code.
• Use descriptive tag, procedure and constant names.
• Avoid blocking dialogs and slow external calls in cyclic or picture-property actions.
• Do not hard-code passwords or unrestricted database credentials.
• Trace meaningful failures without flooding diagnostics every cycle.
• Test the action under the same Runtime account and station role used in production.
• Keep a versioned project backup and document the event that calls each script.

10. Common WinCC VBScript Errors