• Home
• Function/Function Block Reference
• Safety-Related Recipe Handling Function Blocks
• Use Cases, Signal Sequence Diagrams & Application Examples
• Use case: Reading safety-related threshold values from a recipe file

Use case: Reading safety-related threshold values from a recipe file

The safety-related application of a boiler is intended to prevent a certain pressure from being exceeded at a certain temperature. The application is operated several times in different plants, each with different media in the boiler.

In a safety application executed by a Safety PLC, an instance of the SF_RecipeWrite FB is used to write the limit values for pressure and temperature (according to the risk analysis performed) into a recipe file.

The writing operation is repeated several times with the different limit values. The resulting recipe file is saved in each case and the respective DataSetCRCs and FileCRC (output by the SF_RecipeWrite FB) are noted.

In the safety-related application of the boiler, the recipe file with the limit values for pressure and temperature is read from the flash memory using an instance of the SF_RecipeRead FB when the safety-related application program is started. Now, when commissioning the boiler application, the consistent limit values for a specific boiler medium can be loaded from the recipe file. When reading the data, the validation of the DataSetCRCs and FileCRC should be activated. For this purpose the inputs CheckFileCRC and DataSetCRC must be set to SAFETRUE at the SF_RecipeRead FB and the user must specify the checksums at the corresponding inputs.