4-Wire P-NET Topology

4-WIRE P-NET is a wiring principle that enables a number of simple devices to be connected by means of a single cable, which provides both communication and a power supply to all of them.
4-WIRE P-NET is always installed as a bus topology and must be terminated at both ends by a PD 990 4-WIRE P-NET Conditioner connected as a termination.

Traditional P-NET devices can be connected to a 4-WIRE P-NET network by including a PD 990 4-WIRE P-NET Conditioner unit, wired as 4-WIRE conditioner. See example.

A 4-WIRE P-NET bus segment can have a maximum length of 600 metres and contain up to 125 devices.

The cable for 4-WIRE P-NET must be a shielded type with 2 twisted pairs. One twisted pair is used for the supply of power – “power pair”, and one twisted pair is used for communication – “communication pair”.

4-WIRE P-NET topics​

4-WIRE P-NET communication reference

4-WIRE P-NET is based on traditional RS485 with the additional special feature: the communication reference. In RS485, all devices must share a communication reference potential. In 4-WIRE P-NET this reference potential is derived from the supply voltage. This ensures that all devices refer to the same potential (with respect to ground), even if there is a voltage drop and voltage variations along the bus cable.

A traditional P-NET device can be included in a 4-WIRE P-NET system by using a PD 990 4-WIRE P-NET Conditioner to create the communication reference. For more details, please refer to: 4-WIRE P-NET connection to a traditional P-NET device.

In the M36 series, the BM 012 base module includes a communication reference circuit, which allows direct connection to 4-WIRE P-NET networks.