Introduction to Fieldbus Lecture Number 7 Introduction to Fieldbus

In this session… In this session, you will learn about fieldbus systems and how they are applied to PLC systems.

Learning outcomes At the end of this session you should be able to: Discuss the technicalities of a fieldbus system Describe the function of a fieldbus system Understand basic fieldbus systems such as ASi and Profibus.

Introduction To Fieldbus By C Mayhew

Communications Concepts and Terms By C Mayhew

Communications Concepts Encoding Methods: Parallel Communication Cross Talk 1 1

Communications Concepts Encoding Methods: Serial Asynchronous Communication Stop 1 1 Start Separately Synchronised Clocks

Encoding Methods: Serial Synchronous Communication Communications Concepts Encoding Methods: Serial Synchronous Communication 1 1 Separate Clock Channel

Communications Concepts Encoding Methods: Manchester BiphaseL Encoding

Communications Concepts Encoding Methods: Baseband 1 1

Communications Concepts Encoding Methods: Carrierband 1 1 MODEM MODEM

Communications Concepts Signaling Methods: Differential 1 1 Noise Data High Data Low Subtraction of Differential Signal at the Receiver Negates Noise

Communications Concepts Connectivity: Point to Point Simplex Data Between Two Nodes in One Direction Only.

Communications Concepts Connectivity: Point to Point Duplex Data Between Two Nodes in Two Directions

Communications Concepts Connectivity: Multi Drop Multiple Access networks require some form of access method. Node 1 Node 2 Line Termination Media Node 3 Node 4 Node 5

Communications Concepts Access Methods: CSMA/CD If Node 1 wishes to send data to Node 3 It first ‘listens’ to the communication line to detect any data transmission. (Carrier Sense) All machines are capable of this. (Multiple Access) If two Nodes attempt to transmit simultaneously, the collision is detected and the two transmitting machines wait a random time until they try again.(Collision Detection) Node 3 Node 1 Node 2 Data can eventually be sent. This method is not deterministic.

Communications Concepts Access Methods: Token Passing Token Passing is a Deterministic access method. A digital signature called a Token is passed from one communicating device to the next in sequence. Only the device with the Token can send data. Node 3 Node 1 Node 2 Token

Communications Concepts Control: Master Slave Master Polls Slaves cyclically. Slave 1 Slave 2 Slave 2 Master

Communications Concepts Control: Peer to Peer All Nodes Have Equal Priority. Some Sort of Access Method is Required. Node 1 Node 2 Line Termination Media Node 3 Node 4 Node 5

Communications Concepts Some Terms Bit Rate, Baud Rate - Relates to the speed of the data RS232 - A simple Full Duplex, Single Ended, Point to Point protocol. Old but still used on devices in Industry RS422 - A Differential Point to Point protocol. Used in Industry due to its noise immunity. RS485 - A Differential Multi Drop protocol. Profibus and many other systems are based on this protocol.

Fieldbus Systems By C Mayhew

Fieldbus Ethernet, Profibus, ASi and Interbus The use of Fieldbus technologies greatly reduces the amount and cost of wiring individual devices. It enables I/O to be distributed around a machine or site. Connecting controlling devices facilitates information sharing between the devices and enables resources to be shared. Collection of production data is also more easily facilitated from interconnected devices. Many systems are promoted as Open Systems (OSI). This means that they are not manufacturer dependent. One of the main standards for Fieldbus Systems is IEC1158

Fieldbus Hierarchy There are various levels where Fieldbus can be employed: Process/Sensor Level Sensing and Measuring Devices Field Level PLC’s Robots, Drives Cell Level Workcell Areas There are also many Fieldbus and networking protocols, these include: Ethernet Profibus ASi Modbus Interbus Futurebus Foundation Fieldbus

Sensor/Actuator Level Fieldbus Hierarchy Higher Systems Internet Management Level Cell Level Field Level Sensor/Actuator Level

OSI Model The OSI (Open Systems Interconnection) Model is used to implement the system interconnection process. The interconnection problem is so complex it is broken down into seven areas or Layers. For example, the lower layer defines the requirements of the physical aspects of connection such as plugs, wires, signalling types etc.

Fieldbus Profibus, ASi and Interbus Profibus Profibus is a Fieldbus standard that has three protocols: Profibus PA (Process Automation) Sensor Level Profibus DP (Distributed Periphery) Field/Cell Level Profibus FMS (Fieldbus Message Specification) Cell Level Forerunner of DP The S7 314C-2 DP CPU has a Profibus DP interface that can be used to connect other CPU’s, Distributed I/O and any other equipment with a Profibus interface, such as Robot and drive Systems. The Profibus system can interconnect with other bus systems via Gateways. For example, the Siemens Link20E Module will Gateway from Profibus to ASi and also act as an ASi Master. Profibus is RS485 based and can currently run at speeds of up to 12 MBaud. Wireless (infrared) and Fibre Optic is also available. The bus currently supports over 100 Nodes and can be configure as a Master/Slave, Peer to Peer or Multi Master bus. Distance is limited to 2km (copper media). Access to the bus is via a deterministic Token Passing Sequence. Devices are connected via 9 pin D Type Fieldbus plugs with switchable terminating resistors. Nodes are configured via hardware, software or programmer depending on the type of node. The system is promoted as an Open System and uses layers 1,2 and 7 of the OSI model.

Fieldbus Profibus, ASi and Interbus Profibus Network Example Node 3 PLC Node 11 Node 20 Node 12 Inverter Node 25 Robot Node 10 HMI Node 5 Bus Gateway Other Network Profibus DP Media Node 8 PC Profibus PA Media DP/PA Coupler Node 30 Pressure Cell Node 35 Node 40

Fieldbus Profibus, ASi and Interbus ASi ASi (Actuator Sensor Interface) is a bus system that works at the sensor level. It is a Master/Slave MBP (Manchester Bus Powered) System, i.e. it has power and data on the same bus. The supply voltage is 24V@8A The current system can support up to 62 nodes and has analogue capability. The system employs a polling technique with 4 bit data frames and can access all 62 nodes in 10ms (31 nodes in 5ms). Nodes are generally 4 bit I/O but nodes with more I/O are available. The system is promoted as an Open System. Safety devices such as Safety Relays and Emergency Stop buttons can be used with the ASi Safe nodes. The Nodes connect to the unshielded, non terminated ASi cable via IDC connectors. The cable is self healing to IP67 when nodes are removed. The system will automatically number nodes when a new slave is added and will automatically give a replaced node the address of the old node when a slave is replaced after failure. Devices can be replaced while the system is energised (hot swapping). Distance is limited to 100m per segment. With repeaters 300m.

Fieldbus Profibus, ASi and Interbus ASi Network Example ASi Master Polls Slaves ASi PSU 24V@8A Slave 5 8 I/O Module Slave 8 Slave 2 4 Input Module Slave 1 Slave 6 8 I/O Module Asi Media Slave 7 Pneumatic Valve

Fieldbus Profibus, ASi and Interbus Interbus Interbus is RS422 based (differential signalling) and supports up to 512 devices. Topology is Ring. The Ring is required for the bus access method which relies on a deterministic Serial Ring Shift Register type action. Each device in the ring amplifies the signal and sends it on. Unlike many other bus system, the physical position of the node in the ring determines the device address. This is because of the Shift Register principle. The maximum distance is limited to 13km with no more than 400m between bus slaves. Transmission speed is currently 2MBaud. Because data frames do not need addresses, there is more room for data which makes the transmission system more efficient. Transmit and receive data can be sent simultaneously (Full Duplex).

Fieldbus Profibus, ASi and Interbus Interbus Slave 1 1010 Slave 2 1011 Slave 3 0011 Slave 4 1111 Slave 5 1110 Slave 6 0001 Slave 7 1001 Slaves Data 1001 0001 1110 1111 0011 1011 1010 Overhead Data Clocked Around Slave 1 Slave 2 Slave 3 Slave 4 Slave 5 Slave 6 Slave 7 10101

Ethernet Ethernet is a fast bus system compared to most other bus systems. Speeds of 10MBit, 100Mbit and 1GBit are common. Its addressing system is more complicated than node addresses on many other bus systems, addresses being arrange in Octets. The communication protocol is TCP/IP (Transport Communication Protocol/Internet Protocol). The addressing format is commonly called IP addressing. The IP Address has two parts: The IP Address The Net Mask The IP Address is assigned to a device. The Net Mask defines which part of the IP address is for the node and which part is for the network. In order to understand this we have to remember that many networks can be interconnected and each network must have an address, as well as the individual node on the network. DHCP (Dynamic Host Configuration Protocol) or equivalent protocols can be used to assign IP addresses. This means that addresses may be assigned automatically as nodes are attached. Alternatively addresses may be fixed. Access protocol is by non deterministic CSMA/CD (Carrier Sense Multiple Access/Collision Detection).

Ethernet Net Mask Example Machine IP Address Gives theoretical 16581376 network addresses with 256 node addresses on each network. IP = 19.194.162.82 IP = 19.194.162.83 Ethernet Media 19.194.162 Net Mask = 255.255.255.0 Node 82 on network 19.194.162 Ethernet Media 19.183.165 IP = 19.183.165.82 Net Mask = 255.255.255.0 IP = 19.183.165.87 Node 82 on network 19.183.165 Router

Mapping Fieldbus I/O Must be ‘Mapped’ to PLC I/O ASi Master Slave 10 4 Input Module Slave 20 8 I/O Module Slave 15 Fieldbus Devices Fieldbus Master has a list of all active nodes and maps them to PLC I/O. Profibus Node 3 PLC Control Devices PLC communication setup has Node 4 (Gateway) as a connected device. GSD (General Station Description) files are used to set up device parameters in Connection Manager. Profibus Node 4 Gateway I:7.0, I7.1, I7.2, I7.3 Q7.0, Q7.1, Q7.2, Q7.3 Node 15 I:10.4, I10.5, I10.6, I10.7 Q10.4, Q10.5, Q10.6, Q10.7 Node 20 I5.4, I5.5, I5.6, I5.7 Node 10 PLC I/O Address Node Address Node Mapping The mapping may be pre defined or by software.

Mapping Example: ASi

What PLC I/O address would be used for Slave 12? Mapping Example: ASi What PLC I/O address would be used for Slave 12? I/Q 6.4, 6.5, 6.6, 6.7

Full System Example ASi Media Profibus Media Ethernet Media Internet Profibus Node 5 Bus Gateway ASi Media ASi Master Slave 1 Slave 2 Slave 3 Slave 4 Profibus Media Profibus Node 10 HMI Profibus Node 12 Inverter Profibus Node 3 PLC Profibus Node 11 Profibus Node 2 PC PC Station running SCADA software IP = 19.194.162.82 Net Mask = 255.255.255.0 PC PLC Ethernet IP = 19.194.162.90 Ethernet Media IP = 19.194.162.83 Internet Internet Gateway

Test Your Knowledge Proximity sensors are at which level in the Fieldbus Hierarchy?: Sensor/Actuator level The ISO model has seven levels. To what does level 1 refer to?: Physical connections such as plugs and wiring. The Profibus DP protocol supports devices such as?: PLC, PC, Robots The ASi protocol supports devices such as?: I/O blocks, Pneumatic valves The Ethernet protocol is a fast bus with speeds up to?: 1GBit A Gateway is a device that can interconnect?: Two totally different communication systems

Summary You should now have a basic understanding of fieldbus systems and how they apply to PLC systems.