Field Buses ( Smart transmitter, Rack Bus, Mod Bus, Profi Bus, FIP Bus)

We are discussing field buses only with respect to PLC industrial Automation.

Field buses are specially designed to link sensors and actuators at the process level with the system intelligence i.e. Distributed control system (DCS), Programmable logical controller (PLC) etc so that information can flow into plant information center. It has several advantages over hardware installation as given below:

1.       By directional and closed wiring

2.       Simple cabling and cross wiring

3.       Easy expandability

4.       Reduction of cost and maintenance

5.       Higher safety with through self monitoring

6.       Higher resolution of process values

Factory Automation

It implies higher transmission rate, short reaction time and bus length upto 300 m.

Process Control

It implies average cycle time of 100m/sec, Bus length up to 1500m and supply of field instruments with power over the bus cables.

There are many types of field buses in Industrial automation. Some of them are given below:

1.    Smart transmitter: It operates as standard 4-20 mA with super impose digital signal which are able to transport measurement and configure data.

2.   Rack Bus : It is serial character oriented bus develop link intelligence transmitter to external network via Gateway. It operates as a fixed master slave principle where as master is the Gateway. Special module that provide the link to external network act as slave.

3. Mod Bus : It is transmission protocol for process control system in context to other buses. There is no transmission medium is defined.

It defines a digital communication network to have one master and one or more slave devices. Either a single or multi-drop network is possible. All message transactions are initiated by MASTER. Eurotherm instruments communicate using the MODBUS RTU binary protocol.

Note: Details description will be provided in next blog about MODBUS.

4.  Profi Bus:

 It specify layer 1, 2 and 7 in accordance to OSI model. It aim to provide a higher performance communication system and inexpensive equipments.

5. Field info protocol Bus :

 It specifies both protocol and interface. It aims to provide very fast transmission rate and strictly define scanning intervals.

It offers the user freedom in the design of the system architecture and eliminates all of the connections between functional organization of automation process and its physical implementation.