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Worked example of LCF Blocks

Communications watchdog and deadband controller

The diagram below illustrates a simple but important application for Local Control Function blocks:

COMMO EXAMPLE FLOW DIAGRAM


The designer has been asked to implement a local deadband controller, residing in the firmware of the duTec Remote I/O controller, to take over whenever a watchdog timer timeout indicates that communications from the host may have failed. In the normal mode, the host decides, based on the input thermocouple reading and its own control logic, whether a process heater should be on or off. If, however, a timeout occurs, indicating that the host has not scanned the value for a specified time, the duTec controller is to take over, based on a simple deadband control point.

To see how this scheme, and others, can be implemented through the duTec LCF program generator, you can examine them through the duTec demonstration program DEMOLCF.EXE. This worked example appears as the file COMMO.LCF when you download and install the demonstration program. (Return to lcfread.htm  for instructions on downloading the demonstration software.)


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