FBus_97

Fieldbus

For central control

Contents

Why use Fieldbus A comparison Where to use Fieldbus Fieldbus types Serial communication Topology Nodes and I/O Communication Gateways Protocol

Valve Islands Remote input modules Fieldbus types

DeviceNet Interbus Profibus AS-I JETWay-R Sysmac Integrated PLC

Programming

Click the section to advance directly to it

Introduction

Messages

Introduction

Fieldbus is the generic term for serial communication systems used for control in the industrial work place

There are many specific Fieldbus systems providing a varied choice for the user. Here are just some of the logos you may have seen before

Introduction

Control is from a computer or a controller fitted with an interface for the appropriate bus system

Remote input and output device interface modules connect on a bus to the central controller

bus

PLC

bus interface

remote interfacemodules

Input devices

Standard switches and sensors wire to remote input interface modules

Includes, limit, push button, reed, level, pressure, proximity, temperature, also encoders and analogue devices

Bus specific sensors wire direct to the bus

Output devices

Standard output devices wire to remote output interface modules

Includes solenoid valves, relays, contactors, motors, lamps, message displays, alarms, servo actuators

Bus specific devices wire direct to the bus

A bus

A bus is the wiring or electrical conductors which carry the communication information

Serial communication needs only a pair of wires, a power line may be carried in the same cable

All remote devices are controlled from the bus

bus

PLC

Why use Fieldbus

For centralised control of remote input and output devices

To reduce the quantity of wiring To simplify cable routing Cost reduction Centralised diagnostics and monitoring

Benefits

Reduced cabling Reduced controller hardware ( requires no I/O ) Reduced assembly and installation time Reduced costs Better diagnostics Reduced machine downtime Increased productivity Simply made additions and modifications Increased flexibility

A comparison

Without serial communication: Each input and output device needs a separate cable

connecting it to the PLC The PLC must be fitted with input and output modules For applications with many I/O devices there can be

hundreds of wires that are bulky and expensive to install

plc

PLC

A comparison

With serial communication: There is reduced wiring The PLC needs no physical I/O modules Ideal for I/O that is widely distributed Ideal for large amounts of I/O

bus

PLC

Where to use Fieldbus

Machines with widely distributed I/O (input output) devices

Integrated process control

Assembly plant Manufacturing plant

consisting of many different machines

Monitoring and data collection systems

Applications include: Automotive assembly Paper making Printing Airport goods handling Chemical processing Food and drink packaging Energy production Security systems Water treatment Traffic control

Fieldbus types

There are many different Fieldbus systems operating in industry

Some have basic capabilities others are sophisticated

Some work over long distances others over shorter distances

Some are open systems allowing equipment designs from different manufacturers

Some are proprietary or closed systems consisting of only, one manufacturers products

Closed system

A proprietary or closed system is one developed by a single manufacturer

The system is designed around a specific group of the manufacturers products and their typical applications

Usually easy to use and program

The following are selected examples of closed systems

Sysmac (Omron) JETWay-R (Jetter) Pneubus (Norgren) Link Bus (Allen

Bradley) Melsec (Mitsubishi)

Open systems

An open system is available to different manufacturers

Controllers, and I/O devices from various manufacturers fitted with the same bus interface will be compatible and will communicate when fitted to the bus

The following are selected examples of open systems

Device-Net Interbus-S Profibus FMS Profibus DP AS-Interface

Open systems

Manufacturers that want to design control equipment with a built in interface for a particular open system, pay a fee to join the system club

The club provide the design specification and the right to manufacture

Many of the PLC manufacturers offer a range of interfaces to cover open systems as well as their own closed system.

Serial communication

Serial communication is simply information built up one element after the other such as writing letters to form words and words to form messages

Digital serial communication uses patterns of on and off states documented as 1 and 0

10011011100100010010000110001010111110101

Serial communication

There are many commonly known serial communication systems

Some work with digital signals others with modulated frequencies, these include:

Telephone Telex / Fax Internet Cable TV Radio / TV Satellite Telegraph Semaphore

Topology

“Bus Topology” refers to the allowable geometric construction of a bus,

Depending on the bus type these configurations are possible:

star line line with spurs ring line tree

Star topology

Multiple lines radiating from the master controller

Line topology

Single line running through all nodes

bus

Line with spurs topology

Line with T connections to one node each

bus

Ring topology

Line forming a complete loop back to the master controller

Each node repeats the message received

bus

Single cable ring topology

Modules connected with 5 core cable One pair is outward part of the bus the other is

the return part of the bus plus ground and screen

bus

Tree topology

Multiple branch and T construction

bus

Nodes and I/O

Each module on the bus has a unique address and is called a node

A node consists of one of the following:

a remote input module (single or multiple)

a remote output module (single or multiple)

a bus specific single component (in or out)

a bus specific group of components (in or out)

Nodes can be in any mix, position or sequence

PLC

Nodes and I/O

A single device remote module is dedicated to one input or output and is wired to an ordinary input or output device

A multiple device node is used to connect to a range of devices all belonging to that address

Some input and output devices are bus specific and have the node circuitry built in. They can be single devices or multiple device modules

PLC

Communication

A remote module sends and receives messages to and from the controller in a series of on (1) and off (0) states of the bus called bits

They are transmitted at hundreds of thousands of bits per second called the “Baud Rate”

All of the modules on a system work at the same baud rate and may be addressed and reply many times each second

Click the illustration to start and stop animation

Single master multi-slave

A single master multi-slave system relies totally on the master controller to initiate interaction with each node

This is usually carried out in sequence with each node addressed and replying in turn regardless of changes in the information

Any change of state of information will be transferred within one cycle


Multi-master multi-slave

A multi-master multi-slave system allows nodes and masters to send messages whenever they need to send

Anti-collision software prevents two or more nodes trying to send messages at the same time


Gateways

Sophisticated Fieldbus systems may link two or more Fieldbus types

A gateway converts one protocol to another to allow them to talk

A gateway / controller controls the local system with reporting and commands to and from a higher level Fieldbus

An example is Profibus linking to fast local AS-I subsections

PROFI BUS DP

AS-I

Gateway/Controller

Gateway/Controller

AS-I

PLC

Protocol

The protocol of a particular bus type is the set of rules that govern the structure and extent of messages and the order in which they can be issued

Messages Each Fieldbus type has a different protocol A simple message could be made up of these parts:

Start of message code / source address code / destination address code / instruction code / instruction data code / checksum / end of message code

0 11 0 0 0 0 0 1 0 0

start source dest instr data end

0 1 0 1 0 1 0 0 0 1 1 1 0 1 1 0 0 0 1 0 10 0 1 0

checksum

Speed A combination of baud rate, message length, number of nodes on the system,

and communication program will determine how often a slave node is polled by the master

Complex bus systems will have long message structures to contain the potentially complex messages. Simple messages will therefore be carried by more bits than they would on a simpler bus system

It is evident that a small simple bus system with a relatively low baud rate could be considerably faster than a large complex bus system with a high baud rate

Speed A change of state on the bus 0 to 1 or 1 to 0 will appear to be seen by all the

nodes on the bus at the same instant The duration of each bit is determined by the baud rate In theory with the following specification, all nodes can be individually addressed

and reply in about 4 milli seconds. (A baud rate of 500KBits/sec with a fixed 32 bit message length and 32 nodes on the bus)

In practice some of the input nodes will be reporting a change of state, this will involve the master controller in processing time before updating the output nodes

Programming The program within a master node (PLC or computer) can be considered

in two sections A front end program controlling the flow of bus messages in and out of

the serial port (programmed by the manufacturer or vendor)This is usually transparent to the user programmer who will not necessarily need knowledge of it

A user program defining the operation of the plant by calling outputs and reading inputs in a similar way as if the I/O were individually wired

Typical scan

A PLC complete with a Fieldbus interface will usually implement both the front end and user program on each scan as follows:

Read the status of the remote inputs and write them to the PLC’s input memory

Process the user program

Write to the remote outputs the status of the PLC’s output memory

Read Inputs (front end program)

Process logic (user program)

Writes Outputs(front end program)

Configuration (front end)

A new system needs to be set up using the supplied configuration software

Addresses of the input and output nodes are allocated to addresses on the PLC’s I/O memory map

The front end program will automatically transfer data to and from the I/O memory and input and output nodes

Node PLC I/O Memory

0102030405 ¦

16 bits 10000 to 1001516 bits 10100 to 10115 8 bits 10200 to 1000732 bits 10300 to 10415 4 bits 10500 to 10503 ¦

The quantity of bits per node will depend on the number of devices required at that point

The maximum quantity depend on the bus type

Configuration (front end)

The bit pattern in word 121 is the reported on/off state of 16 inputs of a node e.g. node 11

The bit pattern in word 124 is the required on/off state of the 16 outputs of a node e.g. node 14

These two words are an image of the I/O state of 2 nodes

On every scan of the bus word 121 is received from node 11 and word 124 is sent to node 14

120

121

122

123

124

125

126

127

128

BitsWords15 13 11 09 07 05 03 01

0002040608101214

Section of memory map from a PLC running a Fieldbus system

0 1 1 0 1 0 1 0 0 1 1 0 01 1 0

1 0 0 0 0 0 0 0 1 1 0 1 10 0 1

Programming (user program)

In a user program for the PLC, outputs for node 14 are written to word 124 and inputs from node 11 are read from word 121

This replaces writing to bits that are the PLC’s own inputs and outputs

The I/O for other nodes are contained in other words which are also received and sent on each scan of the bus

120

121

122

123

124

125

126

127

128

BitsWords15 13 11 09 07 05 03 01

0002040608101214


0 1 1 0 1 0 1 0 0 1 1 0 01 1 0

1 0 0 0 0 0 0 0 1 1 0 1 10 0 1


The inputs 0,2,4,6,7,15 of node 11 are ON the others are OFF

The outputs 1,3,5,6,9,11,13,14 of node 14 are ON the others are OFF

The program will respond to the changing state of the input images and update the output images accordingly

BitsWords


120

121

122

123

124

125

126

127

128

15 13 11 09 07 05 03 010002040608101214

0 1 1 0 1 0 1 0 0 1 1 0 01 1 0

1 0 0 0 0 0 0 0 1 1 0 1 10 0 1


The I/O image bit numbers are shown on the respective hardware

The ladder diagram calls these numbers to inspect inputs and drive outputs

120

121

122

123

124

125

15 13 11 09 07 05 03 010002040608101214

0 0 0 0 0 0 0 0 0 0 0 0 00 0 0

0 0 0 0 0 0 0 0 0 0 0 0 01 1 0

12100 1210212101 12103

12400eb1

12401

12402

12403

eb2

eb3

eb4

12101 12100 12103 12102

12400 12401 12402 12403

eb = enable bit from another part of the program

Valve Islands

A Fieldbus valve island is a bus specific multiple output node

It is fitted with a bus interface of whatever type the system is running i.e. Device Net, Profibus, Interbus-S etc.

An island can be constructed with the required number of valves up to a maximum of 16

Connections for power, and bus

POWER

RUNNING

ANYBUSREMOTE VALVE DRIVER

Remote input modules

A remote input module is a bus specific multiple input node

It is fitted with a bus interface of whatever type the system is running i.e. Device Net, Profibus, Interbus-S etc.

Up to 16 inputs can be connected

Connections for power, and bus

POWER

ANYBUSREMOTE INPUT DRIVER

RUNNING

Fieldbus Types

Fieldbus types

Valve islands and remote input modules are available for these Fieldbus types

Click the system titles for further details

Open systems

Device-Net Interbus-S Profibus DP and FMS AS-I Proprietary systems Sysmac (Omron) JETWay-R (Jetter) Pneubus (Norgren) Integrated PLC

DeviceNet

Fieldbus Type

DeviceNet

Originally developed as CAN in 1980 for the automobile industry to reduce wiring looms

Message set for industrial control defined by Allen-Bradley to give the basis of DeviceNet

An open system administered by ODVA (Open Device Vendors Association)

Multi-master multi-slave configuration Masters can access the bus at any time to request or

issue data Slaves can access the bus to reply to a master Non-destructive anti collision

control prevents lost data

DeviceNet

Protocol: DeviceNet (CAN)

Norgren remote input module: max. 16 inputs

Norgren remote output driver: max. 16 outputs

Topology: Line (May contain spurs (10ft each maximum)

Configuration: Multi- masters, multi-slaves

Communication (CAN standard)

Max. Baud rate500 kBits/sec

Cable length at max. Baud rate 100m

Nodes per installation:64

Max I/O per node 32 (2048 I/O total)

Cable: twisted pair, with screen and 24V.d.c. power line

End of DeviceNet

InterBus-S

Fieldbus Type

InterBus-S

A ring system with both the forward and return data lines contained in one cable running through each node. This gives the appearance of a line

Uses point to point transmission so each node is a repeater. This allows up to 400m between each device and an overall distance of 13 km

A secondary ring bus (local bus) can be branched from any point using a bus terminal module giving the installation a tree like structure

InterBus-S

Protocol: InterBus-S Norgren remote input

module: max. 16 inputs Norgren remote output

driver: max. 16 outputs Topology: Ring (Line) Configuration: Single

master, multi-slaves Communication RS 485

(422)


Cable length at max. Baud rate 400m between modules, maximum 13 km

Nodes per installation:master + 64 (128 possible)

max. I/O per node 16, can be extended with extra circuitry

Cable: 2 x twisted pair, with screen and ground

End of InterBus-S

PROFIBUS ( Process Field Bus)

Fieldbus Type

PROFIBUS

PROFIBUS FMS (Fieldbus Message Specification)

The original version of this bus system. Can be slow for use with simple I/O systems (solenoid valves and sensors) due to long message structure

PROFIBUS DP (Decentral Periphery)Connects to a wide range of devices. Fast baud rate and shorter message structure than FMS

PROFIBUS PA (Process Automation)The same as DP but with an IS (intrinsically safe) hardware specification

PROFIBUS FMS

Protocol: PROFIBUS FMS Norgren remote input


driver: max. 16 outputs Topology: line Configuration: multi-

master, multi-slave Communication RS 485


Cable length at max. Baud rate 200m (1000m with repeater)

Nodes per installation:126 including masters

Cable: twisted pair with screen

PROFIBUS DP

Protocol: PROFIBUS DP Norgren remote input


driver: max. 16 outputs Topology: line Configuration: multi-

master (3 max), multi- slave

Communication RS 485

Max. Baud rate12 MBits/sec

Cable length at max. Baud rate 200m (1000m with repeater)

Nodes per installation:3 masters + 121 slaves with repeaters

Max I/O per node 256 Cable: twisted pair with

screen

End of PROFIBUS

AS-Interface (Actuator Sensor Interface)

Fieldbus type

AS-I (Actuator Sensor Interface)

An open system designed primarily for binary input/output devices (switches and solenoids) and low cost per node installation

Can also connect to and remotely configure intelligent sensors

Stand alone system or sub-system through a gateway to higher level Fieldbuses

Simple attachment of nodes to profile flat yellow insulation displacement cable (IDC). Connection pins pierce the insulation as the node is snapped on and screwed into place (protection to IP65)

High immunity to noise and interference

AS-I (Actuator Sensor Interface)

Topology: Tree Configuration: single

master, multi-slave Communication:

Manchester II coded data with sin2 data pulsing for high immunity to RFI

Baud rate167 kBits/sec

Cable length 100m (total tree structure)can be extended with repeaters

Nodes per installation:master + 31 slaves

Max I/O per node 4 in + 4 out (124 max. per system)

Cable: parallel pair no screen in flat insulation displacement cable (yellow) or round cable and connectors

Power: On bus cable up to 8A usually for inputs only plus power cable in black for outputs

Input output Modules

Connection pins pierce the insulation as the node is clipped on (protection to IP65)

4 Way modules2 inputs and 2 outputs4 inputs4 outputs

8 Way modules4 inputs and 4 outputs









AS-I Power Supplies

Power for the AS-I modules and input devices is placed on the yellow communications cable

Power for 24 V output devices is supplied on the additional black cable

AS-I range of units to suit 115/230V a.c. and 24V d.c. source. 85W and 180W

24V d.c. range to suit 115/230V a.c. source. 2.5A, 5A and 10A

AS-I Power Supplyfor the yellow

cable

24 V d.c.Power Supplyfor the black

cable

AS-I Controllers

These Gateway controllers can function in three ways

A stand alone AS-I controller

Active gateway controlling the local AS-I system but with a link to a higher level bus (relieves traffic on the higher bus)

A passive gateway acting only as a translator for the higher level bus (more traffic on the higher bus)

DeviceNet

ProfiBus DP

AS-I System

Power supply 24V d.c. on the black cable for output devices

Power supply 30V d.c. on yellow cable for AS-I modules and inputs

Controller giving bus signals on yellow cable

4 Outputs module 4 Inputs module 2 Inputs / 2 Outputs

module AS-I Valve Island

End of AS-Interface

Sysmac

Proprietary Fieldbus Type (Omron)

Sysmac (Omron)

A proprietary system for use with Omron PLC’s as the master controller

Uses Omron manufactured node electronics Suitable for local moderate sized systems Simple to set up and program Norgren valve islands fitted with integral Omron

interface module Norgren remote input modules fitted with

integral Omron interface module

Sysmac (Omron)

Protocol: SYSMAC Norgren remote input


driver: max. 16 outputs Topology: Line Configuration: Single


Max. Baud rate187,5 kBits/sec


Nodes per installation:master + 32

Cable: twisted pair, with screen

End of Sysmac

JETWay-R

Fieldbus Type

JETWay-R

A proprietary system for use with a Jetter PLC as the master controller

Suitable for medium sized systems Simple to set up and program using descriptive

language sequential statements Software supplied at no extra cost with a PLC Norgren valve islands and remote input modules

fitted with integral Jetter interface cards

JETWay-R

Protocol: JETWay-R Norgren remote input




Max. Baud rate115.2 kBits/sec


Nodes per installation:master + 97

Cable: twisted pair, with screen

End of JETWay-R

Pneu Bus

Fieldbus Type

Pneubus

Protocol: PneuNet V.4.0 Norgren remote input




Max. Baud rate19.2 kBits/sec


Nodes per installation:master + 31 slaves

max. I/O 190 outputs, 190 inputs

Cable: twisted pair with screen

End of Pneu Bus

Integrated PLC and Valve Island

Stand alone or bus master


For Nugget 30, 40, 120 and MIDI*STAR Valve Islands

Integrated Jetter Mikro PLC Up to 16 attached valves Inputs 16 Built in JETWay-R Fieldbus interface Can be used as a Fieldbus master to control up

to 62 slaves or as a stand alone valve controller Easy programming using descriptive text

statements


POWER

RUNNING

Choice of valve islands Optional remote outputs for valves or devices not part of

the valve island ( 8 maximum ) 16 Local inputs IP 65 protection ( no enclosure required )

Inputs

Valve Island

Remote outputs

Display unit port

JETWay-R communications port

End of Integrated PLC

End

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