Scripts Expressions(Reference) provide lightweight, event-driven automation for simple calculations and method calls, ideal for scenarios with many triggers but straightforward logic. A Script Expression is single-line statements that:
- Execute on events or schedules without creating full tasks
- Run in multi-threaded environment for optimal performance
- Automatically detect tag changes in the expression
- Support both arithmetic operations and Script Class calls
Use Expressions when you need many simple automations that would otherwise require numerous one-line tasks. The parse of the expression is VB.NET syntax, but it automatically converts and accepts C# syntax also.
In this page:
Creating Script Expressions
- Navigate to Scripts → Expressions
- Select insert row (first blank row)
- Configure:
- Object: Target tag to receive result
- Expression: VB.NET statement or calculation
- Execution: Trigger method
- Domain: Server (default) or Client
Configuration Properties
| Property | Description |
|---|---|
| Object | Tag or object that receives the expression result |
| Expression | VB.NET statement (arithmetic, conditional, or method call) |
| Domain | Server (global) or Client (local) execution |
| Execution | When expression runs (see Execution Modes) |
| Trigger | Tag/object that triggers execution (optional) |
| DisableCondition | Tag/object that disables execution when true |
| Time | Specific time for time-based execution |
| Label | User-defined label for organization |
| BuildStatus | ? Green = Success, ? Red = Errors |
| BuildErrors | Compilation error details |
| BuildMessages | Status messages after verification |
Execution Modes
| Mode | Description | Use Case |
|---|---|---|
| OnChange | Runs when any tag in expression changes | Real-time calculations |
| TriggerOrTimeInterval | Runs on trigger change OR time interval | Periodic updates with override |
| ChangeOrStartup | Runs on tag change OR at startup | Initialize and maintain values |
| TriggerOrTimeOfDay | Runs on trigger OR specific time | Scheduled operations with manual trigger |
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.Input2Calling 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