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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

1. Use for simple logic - Complex code belongs in Script Tasks or Classes
2. Prefer TIF over IIF - Avoid unnecessary method execution
3. Group related expressions - Use Label field for organization
4. Monitor performance - Many OnChange expressions can impact performance
5. Test with Verify - Use button to check syntax before runtime
6. Consider execution mode - Choose appropriate trigger method
7. 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.

Configurating Script Expressions

Besides the table in Script / Expressions, you can use expressions in several other places using the syntax described here to determine a value or configure a condition. The following is a list of recommendations when using expressions:

• Our platform implements automated replacements, such as "==" to "=". The syntax of an expression is close to a C# statement but without a need to add the semicolon “;” at the end. Therefore, VB.NET and C# programmers can use the expression fields seamlessly.
• You do not need to put an "@" before tag names in expressions. Instead, insert the "@" in the code editor to differentiate your Tags from .NET variables. However, expressions do not have local .NET variables, so you use the solution object directly.
• Use the standard operands described in the .NET documentation for arithmetic operands.
  

Evaluation methods

The platform has two methods for single-line evaluation, they are as follows:

 The IIF method, which currently is used only with VB.Net, has three parameters: IIF (A, B, C) the first being a condition. This method will return B if condition A is true and C if the condition is false. For example:

IIF (tag.A = 1, "True", "False")

The code above will return the string True  if the value of the tag.A  is 1, or False  if tag.A  has a different value.
In this .NET method, all three parameters are evaluated regardless of the condition. For instance, given the following code:

IIF (tag.A = 1, script.class.client.Func1(), script.class.client.Func2())

The TIF method should be used when you want to execute only the function according to the value. For example, given the following code:

TIF (tag.A = 1, script.class.client.Func1(), script.class.client.Func2())

For more complex calculations, you can call a class that you create on the Classes tab. See Configuring Classes earlier in this chapter.

Adding Script Expressions

• Go to Scripts → Expressions.

• Select an expression, or select the insert row (first blank row) to create a new expression.

• Enter or select information, as needed.

Script Expressions Configuration Properties

Field

Description

Object

Select an existing tag or object.

Expression

Enter the expression. The expression can be a basic mathematical expression, a class, or a conditional expression.

Domain

Select where the expression executes:

• Client: expression executes on each client system. These are expressions that apply locally (on the user's computer). For example, report generation.

• Server: expression executes on the server system. These are expressions that apply across the application, that is, globally.

Execution

Select when the expression executes:

• OnChange: the expression executes when the value of any tag in the expression changes.

• TriggerOrTimeInterval: the expression executes when the trigger event occurs or when the interval set in the period elapses.

• ChangeOrStartup: the expression executes when the value of any tag in the expression changes or at startup.

• TriggerOrTimeOfDay: The expression executes when a trigger event occurs or on a specific time of day

Trigger

Enter or select the tag or object that triggers the expression execution. The expression executes when the value of the object changes.

DisableCondition

Enter or select the tag or object that disables the expression execution.

Time

Specify the time when the expression runs. 

Label

Set a label to the specified class.

BuildMessages

Return the message status after the expression runs

BuildStatus

Read-only. Set after you click Verify.

• Green check mark: expression runs without errors.

• Red X: expression has errors.

BuildErrors

Read-only. Displays any errors encountered during the last build.

Managing External References

If you need references to your own assemblies, you can use Scripts References (Reference).

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