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Scripts → Tutorial | Concept | How-to Guide | Reference

Creating Script Expressions

1. Navigate to Scripts → Expressions
2. Select insert row (first blank row)
3. Configure:
   • Object: Target tag to receive result
   • Expression: VB.NET statement or calculation
   • Execution: Trigger method
   • Domain: Server (default) or Client

Configuration Properties

Execution Modes

Expression Syntax

Key Syntax Rules

<ac:structured-macro ac:name="info"> ac:rich-text-body Automatic Conversions: The platform automatically converts C#-style operators to VB.NET:

• == becomes =
• No semicolon needed at the end
• No @ prefix needed for tags (unlike Script Tasks) </ac:rich-text-body> </ac:structured-macro>

Direct Tag Access

vbnet

' No @ symbol needed in expressions
Tag.Temperature * 1.8 + 32  ' Convert C to F
Tag.Output = Tag.Input1 + Tag.Input2

Calling Script Classes

vbnet

' Call methods from Script Classes
Script.Class.Calculations.GetAverage(Tag.Value1, Tag.Value2)
Script.Class.DataProcessor.Validate(Tag.RawData)

Arithmetic Operations

vbnet

' Standard .NET operators
(Tag.Flow * Tag.Density) / 1000
Math.Round(Tag.Value, 2)
Math.Max(Tag.Limit, Tag.Current)

Conditional Evaluation Methods

IIF Method (Immediate If)

Evaluates all parameters regardless of condition:

vbnet

IIF(Tag.Status = 1, "Running", "Stopped")
' Both "Running" and "Stopped" are evaluated

IIF(Tag.Level > 80, Script.Class.Alerts.High(), Script.Class.Alerts.Normal())
' WARNING: Both High() and Normal() methods execute!

TIF Method (True If) - Recommended

Evaluates only the selected branch:

vbnet

TIF(Tag.Status = 1, "Running", "Stopped")
' Only evaluates the matching result

TIF(Tag.Level > 80, Script.Class.Alerts.High(), Script.Class.Alerts.Normal())
' Only executes High() OR Normal(), not both

<ac:structured-macro ac:name="warning"> ac:rich-text-body Important: Use TIF instead of IIF when calling methods to avoid unnecessary execution. </ac:rich-text-body> </ac:structured-macro>

Threading and Performance

Multi-Threading

• Each expression executes in thread pool
• Hundreds/thousands of expressions don't block each other
• Automatic thread management
• No manual synchronization needed

Compilation

• Automatic compilation before runtime
• Manual verification available via button
• All expressions compile together
• No need to compile after each change

Domain Execution

<ac:structured-macro ac:name="info"> ac:rich-text-body Default Setting: Client-side expressions are disabled by default for web compatibility. Enable in Solution → Settings if needed. </ac:rich-text-body> </ac:structured-macro>

Server Domain (Default)

• Executes on server (TServer.exe)
• Global scope
• Typical use: Calculations, business logic

Client Domain

• Executes on each client
• Local scope
• Only for WPF clients (not web)
• Typical use: UI calculations, local formatting

Examples

Simple Calculations

vbnet

' Temperature conversion
Tag.TempF = Tag.TempC * 1.8 + 32

' Percentage calculation
Tag.Efficiency = (Tag.Actual / Tag.Target) * 100

' Conditional assignment
Tag.Status = TIF(Tag.Value > 100, 2, 1)

Time-Based Operations

vbnet

' Reset counter at midnight
Tag.DailyCount = 0  ' Execution: TriggerOrTimeOfDay, Time: 00:00

' Calculate hourly average
Tag.HourlyAvg = Script.Class.Statistics.GetHourlyAverage()

Complex Logic via Classes

vbnet

' Call complex processing in Script Class
Script.Class.Production.CalculateOEE()

' Conditional processing
TIF(Tag.AlarmActive, Script.Class.Alerts.Send(), 0)

Best Practices

•  Use for simple logic - Complex code belongs in Script Tasks or Classes

•  Prefer TIF over IIF - Avoid unnecessary method execution

•  Group related expressions - Use Label field for organization

•  Monitor performance - Many OnChange expressions can impact performance

•  Test with Verify - Use button to check syntax before runtime

•  Consider execution mode - Choose appropriate trigger method

•  Document purpose - Use Label field to explain expression

Troubleshooting

Expression not executing:

• Check BuildStatus for compilation errors
• Verify DisableCondition is not active
• Confirm Domain matches deployment
• Check trigger tag is changing

Performance issues:

• Review OnChange expressions for high-frequency tags
• Consider time-based instead of change-based
• Move complex logic to Script Classes
• Check for IIF with method calls

Compilation errors:

• Click Verify button to see errors
• Check VB.NET syntax (not C#)
• Verify referenced tags exist
• Ensure Script Classes are compiled

Unexpected results:

• Remember IIF evaluates all branches
• Check automatic operator conversion
• Verify tag data types match
• Test with simpler expression first

Claude can make mistakes.
Please double-check responses.

Research

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