Thursday, July 21, 2011

PLC Interface CODAC Configurations

During incorporation, commissioning and sometimes during maintenance, it is normal that the engineers will desire to force some variables of the signal to a definite value, because the associated signal is not linked, missing, is not equipped or has failed. It is better to get this fact into account in the design of software, so that this “uneven” behavior will be prohibited. The goal is to keep away from dangerous “temporary-permanent” observes like forcing a signal with the PLC hardwired modifications, strapping of relays, hardcoded modifications, etc. This layer of the forcing must be developed and in particular:
• Some signals can’t be forced at any time as this could be destructive.
• The unit of control may not be able to achieve an operational state as long as variables signal are forced.
• Reducing this feature of forcing.
All permanent and runtime parameters will be provided by the CODAC configuration variables.
This interface attends to communications between the PLCs of a same manufacturing system I&C, for the case where a functional interface is needed. The protocol of Siemens to be used will be identified later in the document. There are 3 different cases from a conceptual point of view:
• A link of the master/slave where the master PLC is transferring the commands e.g. Boolean or numerical, to a slave PLC.
• A link of point-to-point where 2 PLCs are switching over states. This transmission of the state can be I/O of another PLC.
• A communication of multipoint where a PLC is issuing states to a group of PLCs. In an architecture of master/slave, the coordinator of master transfers orders to the slaves. A paradigm of communication must be defined for these orders. Every case will be implemented with the most suitable technology of Siemens.

The Monitoring of System
A job will be committed to the system monitoring of PLC: the following parameters will be examined:
• The operating mode, such as, RUN/STOP
• Memory:
- To load memory assigned within the range: 0..100%
- To work memory assigned within the range: 0..100%
- Retentive within the range: 0..100%
Scan cycles:
• Longest
• Shortest
• Average
• Standard deviation
- CPU Time including date and hour
- Configured
- Communication
- Connections accessible for max numbers
- The number of connections employed

- The status of board
- The raw value of every signal
Alive counter.

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