ABB M4M Network Analyser

OVERVIEW

The M4M network analyser includes versions with the Profibus DP-V0 communication protocol (M4M 20 Profibus and M4M 30 Profibus).

1.1 Profibus

Profibus stands for Process Field Bus.

Profibus is a fieldbus according to IEC 61158/EN 50170. which is mainly used in industrial automation and process areas.

Profibus is a single-master-multi-slave communication network; it is an open, reliable and powerful fieldbus system.

It is characterised by its fast response time, its complete definition according to international standards and its ability to connect devices from different manufacturers (if all devices comply with the same standard).

Profibus also reduces wiring between network nodes, as it requires only one communication cable.

Profibus communication technology is based on a master-slave architecture:

- Every Profibus system requires at least one master (e.g. PC or PLC).

- Up to 127 devices (master + slave) can be connected to a single system.

- Profibus systems can be ‘multi-masters’; in this case, a ‘token’ structure is used in which only one master can communicate on the network at a time.

The M4M Profibus (M4M 20 Profibus and M4M 30 Profibus) type instruments are slave devices that implement the Profibus DP-V0 protocol.

The DP slave is a peripheral device that acquires input information and sends data to the central master.

According to the IEC 61158/EN 50170 standard, Profibus DP (decentralised periphery) is typically used to connect decentralised peripheral devices with fast response times.

The standard specifies node distances of up to 300 metres with bit rates ranging from 9.6 kbps to 12 Mbps, using standard cables and maintaining maximum operating speed.

Transmission method

The transmission method for Profibus DP is the RS485 interface (according to the EIA standard) using shielded twisted-pair cables.

The simple RS485 twisted-pair transmission method is ideally suited for linear/tree networks with high transmission speeds.

The Profibus must always be terminated with two terminals. As shown in the figure below, either terminal must consist of three resistors;

The terminals must be fed with a voltage of 0 to 5 volts DC, otherwise their resistance is not equal to the characteristic impedance of the cable.

With this structure, the voltage on the bus is fixed when there are no active devices.

Profibus network characteristics

The Profibus network extension by means of signal segmentation and regeneration is limited to a maximum of 32 nodes/partners (master/slave) per segment;

On the other hand, the entire network can have up to 126 nodes/partners. If you need to increase the length of the bus or use more than 32 stations, you must use repeaters.

Any repeater is a ‘load’ on the bus. Each new segment introduced must be terminated at both ends of the segment, the maximum length of which depends on the baud rate; however, standard procedure is to connect up to 30 loads per segment.