Friday, July 22, 2011

CODAC Interface in PLC Core Application

The core application of PLC will calculate the configuration variables of CODAC and the inputs of hardware and produce the outputs in order to achieve the requested of configuration. The changeable of state report the effective state of the process. The major principle is that it is always probable to have a simple comparison in CODAC between the configuration or state of the process that was asked for and the actual state. Mutual data are state variables generated by other plant systems and transferred by core system of CODAC. Crosswise wired connects between plant systems are strictly not allowed. Information transmission of between plant systems will employ the mutual data link.

The CODAC interface main function is to run the communication PLC side with CODAC, which is built up in an EPICS environment. The communication CODAC side is controlled by a specific driver in the PSH. This communication decays in 4 categories, as represented:
• Simple commands
• Configuration variables
• Collaborative data
• State variables
In 2 the link “8” demonstrates another use of these variables: offer configuration to the I/O interface of hardware. Mostly, it will give parameters conversion from physical to engineering units, inhibits and forcing values, it will also influence the mode of simulation. The variables of state are used to transfer the process state:
• Straight from the I/O interface of hardware. This direct link is needed as the core applications of CODAC use these variables without involve computing in the core application of PLC. It is significant to note that these variables are in units of engineering, and they can also can be simulated or forced.
• From the calculated variables issued by the core application of PLC.
• From the monitoring of system.

Simple controls are variables command to “TRUE” during one cycle in the PLC. These simple commands are utilized in the cases where it is not essential to remember the action related to this command, as is the case for variables of configuration.

The data collaboration is state variables transferred between plant system I&Cs. A strong necessity of the PCDH is that no oblique physical link is permitted between plant system I&Cs. Any such link has to be in the form software of a link between 2 PLCs from the 2 different plant system I&Cs. This mutual data will be state variables with the “Collaborative Data” specific classification.


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