Intelligent P-NET Modules

Typical P-NET slave modules give the system integrator more than just Input / Output functions. They very often contain additional process oriented functions varying from simple limit switch monitoring, to PID regulator or program channels, allowing the system integrator to configure local control loops or specify process steps.

Figure 5: An intelligent P-NET module in a chemical plant.

The diagram in fig. 5 shows how a standard P-NET I/O-module can handle the temperature control, and the loading and unloading of products for a heating vessel within a chemical plant.

In this example, the internal process functions of the module take care of temperature and level regulation, and the control of filling. Only the set points for temperature and level are required from a P-NET master.

Another example of a slave module could be a weight transmitter, where the analogue signal from a load cell is continuously converted, scaled and stored, within the memory of the slave. When a request is received from a master, the slave immediately responds with the latest stored result. Error checking is also continuously performed within the slave, and the master is notified if any error has occurred, by a code in the response message, when the slave is requested.