P-NET in General -------------------------------------------------------------------------------- The P-NET Fieldbus is designed to connect distributed process components like process computers, intelligent sensors, actuators, I/O modules, field and central controllers, PLC’s etc., via a common two wire cable, as shown in fig. 1. This replaces traditional wiring, where a great many cables are involved. Process data (e.g. measurement values, valve signals) are transmitted digitally. P-NET is also used for data collection, for configuration of nodes/sensors, and for down-loading of programs.
Figure 1: P-NET Fieldbus with distributed process components. Apart from the usual measurement values and status data, the bus provides a bidirectional exchange of additional information concerning limit values, actuator positioning and feedback signals, fault signals and internal system data. P-NET can be used to download parameters and programs to modules, which then control the process. The use of intelligent P-NET sensors and actuators also offers much better diagnostic features than with traditional wiring. Further comparisons with conventional wiring, show that the incorporation of P-NET offers proved advantages when applied to industrial processes. The result is a simplification of planning and installation, a reduction in the amount and cost of cabling, a reduction in installation and maintenance costs, a reduction in installation errors, leading to a more straightforward future expansion of applications. Instant information about field device faults, and faults in the cable, can be detected automatically by the network protocol. P-NET applications are characterised by their low cost for a small system. The cost rises linearly with the size of a system. P-NET is as well suited for small plants, as for large plants having many controllers, sensors, and interface modules. In addition, any such system is always ready for any necessary expansion.