---
title: "Transition Expressions"
id: "transition-expressions"
project: "MES User Manual"
url: "https://docs.sepasoft.com/articles/user-manual/transition-expressions"
updated: 2026-09-28T16:41:22Z
---
# Transition Expressions
**Sepasoft MES Module Suite**
## Transition Expressions
Transition Expressions can be used to determine logical flow within Batch Recipes. , e.g., to determine which branch of multiple branches the execution should follow after an Or\_Begin control.
The execution engine waits for the Transition expression to evaluate to True before execution continues.
Some examples:
| Waits for the step named Kettle to complete before continuing the execution.
 | Use Transitions to determine which branch of multiple branches the execution should follow after an **Or\_Begin** control.
Loop back if execute\_Count is less than or equal to '2'.
**Kettle.Execute\_Count <= 2**
* * *
Continue execution if Execute\_Count = '3'
**Kettle.Execute\_Count = 3**
**** |
| --- | --- |
Within Batch Recipes, add Transition after these elements:
* Phase
* And\_Begin
* And\_End
* Or\_Begin
* Or\_End
For information about when a transition is required, see [Batch Recipe Logic Validation](/articles/user-manual/batch-recipe-logic-validation).
A valid Transition Expression is one line of Python code referencing:
* Parameters: Batch Recipe (Procedure), Unit Procedure, Operation, Phase
* Ignition Tags
* Ignition Designer Project Scripts
|  | Auto Completion
Intellisense autocompletes the available options under and object. Navigate the autocomplete-**intellisense** using the keyboard: arrows and space bar. |
| --- | --- |
|  | In **MES 3.81.12 SP5**, **MES 4.83.1 SP5**, and later, a Transition expression can name a parameter on the current logic or step without a step or logic identifier:
Code
```
MyParam = True
```
Step and logic paths are still valid, and the leading / is optional:
Code
```
P2.Complete
/{}/P2.Complete
Procedure/P2.TargetTemp > 80
```
See [Referencing Parameters in Batch Recipes](/articles/user-manual/referencing-parameters-in-batch-recipes).
On a Unit Procedure or Operation template, a transition that refers to a parameter outside the template, such as a Procedure parameter, is not flagged when the template is validated. That reference is validated when the template is used in a recipe. |
| --- | --- |
### Valid Operands in Transition Expressions
**Operands in Transition Expressions**:
* operands
* fixed values
* tag path
* Recipe, Unit Procedure, Operation, Phase references up and down the batch recipe structure.
* script reference or one line of code: the return value returns and replaces the script reference before evaluating the expression.
| Valid operands | Expression including script and tag path |
| --- | --- |
| AND
OR
()
=
!=
>=
<=
>
<
IS NULL
IS NOT NULL
NOT | To call a tag from a Batch Transition use {tagValue:TagPath} descriptor
{TagValue:[Default]Tank 101/Level} >= 100.0 AND {Script:My Phase Complete}
P2.Operation IS NULL |
| **Expression including phase and procedure parameter** |
|  |
| **Expression including script reference** |
| To call a Batch Script from a Batch Transition, use {script:ScriptName} descriptor.
example: {script:My Phase Complete} |
**Sepasoft MES Module Suite**