P-NET in General 　　　　--------------------------------------------------------------------------------　　　　The P-NET Fieldbus is designed to co ect distributed proce  components like proce  computers, intelligent se ors, 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. 　　　　Proce  data (e.g. measurement values, valve signals) are tra mitted digitally. P-NET is also used for data collection, for configuration of nodes/se ors, and for down-loading of programs. 　　　　  　　　　 　　　　Figure 1: P-NET Fieldbus with distributed proce  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 proce . The use of intelligent P-NET se ors and actuators also offers much better diagnostic features than with traditional wiring. 　　　　Further compariso  with conventional wiring, show that the incorporation of P-NET offers proved advantages when a lied to industrial proce es. 　　　　The result is a simplification of pla ing and i tallation, a reduction in the amount and cost of cabling, a reduction in i tallation and maintenance costs, a reduction in i tallation errors, leading to a more straightforward future expa ion of a licatio . I tant information about field device faults, and faults in the cable, can be detected automatically by the network protocol. 　　　　P-NET a licatio  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, se ors, and interface modules. In addition, any such system is always ready for any nece ary expa ion.