fieldbus system

8/8/2019 Fieldbus System

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SEMINAR ON

BY

PRADNYA GHAWALKAR



Protocol

A Protocol is a set of rules which is used by computers to communicate with each other across

a network.

The rules that work together are grouped called as µProtocol Suite¶.

Most protocols in the communications or networking, are layered together into protocol stacks.

The Protocol Stack denotes a specific combination of protocols that work together.

The classic seven-layer reference model is the OSI model, which is used for conceptualizing

protocol stacks.

Examples of automation protocols :

1. Foundation Fieldbus

2. Profibus

3. CIP (Common Industrial Protocol)

4. CAN (Controller Area Network)



Fieldbus System

A serial bus system designed for industrial real-time data communication is called µFieldbus¶.

Fieldbus System is :

1. Open, digital, bi-directional communication network

2. Used among field measurement and control devices and automation/display systems

3. It replaces the traditional point-to-point connections



A complex automated industrial system consists of :

Human Machine Interface (HMI)

Programmable Logic Controllers (PLCs)

Fieldbus System



TRADITIONALLY WIRED S YSTEM

The IO connections involve long runs of cable from the control room to the plant.

To reduce cabling effort, multi-corecables can be used.

These require junction boxes,

marshalling racks to route the signals tothe correct location.

Hence, each IO channel will have manyconnections.

Such wiring is :

1. Expensive to install

2. Complex to maintain

3. Fault-finding can be difficult



S YSTEM WITH THE FIELDBUS

Fieldbus is designed for communicationbetween industrial controllers and thefield-mounted sensors and actuators.

It replaces the point-to-point wiring.

Provides capability of µremote deviceconfiguration¶.

The digital or analog IO modules aremounted in the field.

The data is communicated to the remoteIO module via the fieldbus cable.



Foundation Fieldbus H1

Foundation Fieldbus H1 is one of the Foundation Fieldbus protocol versions.

Utilizes either twisted pair, or fiber media to communicate.

Requires only one communication point to communicate with up to 32 nodes.

Supports for Intrinsically Safe Wiring with 4-6 devices per segment.

Supports interoperability between transmitters and actuators from different suppliers.

It works at the speed of 31.25 kbit/s.

There is another level of protocol called HSE (for High-Speed Ethernet), catering tolevel 2 automation hierarchy.



Foundation Fieldbus HSE

The technology is designed for device, subsystem and enterprise integration.

High Speed Ethernet (HSE) runs at 100 Mbit/s.

Supports complex logic functions, such as those performed by PLCs.

Enhances access to H1 fieldbus technology via linking devices.

Provides the same benefits as H1, but at the subsystem integration level.

Supports interoperability between disparate controllers and gateways.



7-layer OSI model

OSI medel is a description for layeredcommunications and computer network protocoldesign.

It divides network architecture into seven layers

A layer is a collection of conceptually similar functions.

A layer provide services to the layer above itand receives service from the layer below it.



OSI model for Fieldbus System1. Application layer provide the services that are required by specific applications.

2. Presentation layer allows the interoperability among different equipments.

3. Session layer is concerned with execution of remote actions.

4. Transport layer is responsible for the end-to-end communication control.

5. Network layer is concerned with logical addressing.

6. Datalink layer is responsible for the physical addressing.

7. Physical layer offers media, signal and binary transmission.



Network Topology1. Point-to-Point Topology :

This topology consists of a network having onlytwo devices.

The network could be :

a) In a field (e.g. a transmitter and valve, with no

connection beyond the two)

b) A field device connected to a host system(doing control or monitoring).

It is not an economic design .

. pur Topology :

It consists of fieldbus devices connected to amulti-drop bus segment through a length of cable

called a pur .

It is technically acceptable but not a good

economic choice.

It should be used in new installations that have alow density of devices in an area.



3. Tree Topology ( Chicken Foot ) :

It consists of a single fieldbus segment connectedto a common junction box to form a network.

Used at the end of a home run cable.

Used for reuse of existing wiring.

It should be used for the following situations:

Retrofit installations.High density of fieldbus devices in a particular area.

High Speed Ethernet is being used.

4. Combination Topology :

It is the combination of tree topology and spur topology.

Preferred for designs using bricks with tray cable.

Spurs are permitted to extend only from trunk lines

and not from other spur lines.



5. Daisy Chain Topology :

It consists of a network/segment that is routed

from device to device, and is connected at the

terminals of the fieldbus device.

This topology should not be used because :

a) It is unacceptable for maintenance

purposes.

b) Devices cannot be added or removed from

a network during operation.



Foundation fieldbus Wiring

Cable should be as follows :

Suitable for the electrical area classification.

Suitable for outdoor use in cable trays.

Twisted pair wire is used than a pair of parallel wires to reduce external noise.

A shield over the twisted pair further reduces noise susceptibility.

Cables shall have thermoplastic elastomer (TPE) flame-retardant insulation.

Cable jacket shall be of flame-retardant polyvinyl chloride (PVC).

Distance Constraints :

The maximum allowed length of a fieldbus segment is 1900 meters (6232 ft.)

Total Segment Length = Trunk + All Spurs



Fieldbus System Vs 4-20 mA System

4-20 mA system enables :

OPEN, interoperable and interchangeable

Broad range of equipment

Unidirectional : Limited information transmitted

Point-to-point wiring

Foundation Fieldbus System enables :

Increased capabilities (due to full digital communication)

Reduced wiring

Increased selection of suppliers (due to interoperability)

Reduced control room loading (control on wire)



Advantages of Fieldbus System

Significant reduction in wiring

Cost of installing field equipment in a fieldbus system is less

The simpler system design enables :

a) Fewer system drawings for designing fieldbus system

b) Less complex and faster bus systems

c) Increased flexibilityd) Less maintenance

e) Long term reliability



Operators can easily see all of the devices and interact between the individual devices.

Online diagnostics on individual field devices enables enhanced debugging and maintenance

of the system.

Two-way communication is possible.

The user will only be required to have a limited knowledge of the management services.

It enables multi-sensor application.

Chemical Reactor



Disadvantages of Fieldbus System

The price of fieldbus components is higher.

Slightly longer reaction times with fieldbus, depending on the system.

Device manufacturers have to offer different versions of their devices due to thenumber of different (incompatible) fieldbus standards.

This can add to the cost of the devices and to the difficulty of device selection andavailability.

One or more fieldbus standards may predominate in future and others maybecome obsolete.

This increases the investment risk when implementing fieldbus.



Future Trends

There is new technology called the "X-by-wire".

It replaces all the mechanical linkages in thevehicles with digital links.

It wire all these links into one network protocolthat entirely runs the vehicle.

There is one more new protocol : Flex Ray

It try to resolve problems while designing thenew X-by-wire automobiles using the old CANprotocol.

It provides :

a) Better fuel economy

b) Better vehicle performance in adverse

conditions

c) Safety features such as collision warning and

automatic collision avoidance systems

fieldbus system

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