Profibus123414

PROFIBUS

Process Field BusGroup: ➢ Nguyen Thanh Hoan ➢ Do Van Thach ➢ Mai Pham Khanh Cuong

OVERVIEWI. INTRODUCTION

II. PROFIBUS NETWORK

III.CLASSIFICATION

A. PROFIBUS DP

B. PRFIBUS PA

C. PRFIBUS FMS

IV.CONCLUSION

FIELDBUS AND PROFIBUS

▪ Fieldbus is a digital communication network providing two way communications for devices that are mounted in the field i.e. in the factory or plant being controlled or automated. ▪ PROFIBUS (PROcess Field BUS) is a well-proven, widely

accepted open fieldbus standard. ➢Initialized in 1987 by the German Ministry for Research and

Technological Development. ➢Now managed by an association of PROFIBUS

Manufacturers, Users and research institutions ➢More than 1100 members worldwide (Profibus International)

I. INTRODUCTION

A. PROFIBUS: FORMAL DEFINITION

❖ The PROFIBUS family is composed of three types of protocol, each of which is used for different tasks. All three protocols can communicate with each other in a complex system by means of a PROFIBUS network.

❖ The three types of protocols are: PROFIBUS FMS, DP, PA. Only the two protocol types DP and PA are important for process automation.

I. INTRODUCTION

DP

PAFMS

THE PROFIBUS FAMILY

❖ PROFIBUS FMS - Fieldbus Message Specification ➢FMS provided sophisticated multi-function communications

which was aimed at cell or controller level. FMS provides very sophisticated, flexible transmission of structured data.

➢ Unfortunately, FMS was quite complex and expensive to implement. Thus after a few years of experience a new simplified but improved specification was developed (PROFIBUS DP). FMS is no longer supported by PI. However, some manufacturers (e.g. Siemens) continue to provide FMS capability.

I. INTRODUCTION

❖ PROFIBUS DP - Decentralised Periphery ➢PROFIBUS DP was developed from the basic FMS

technology as a low cost, simple, high speed field-level communication.

➢The DP specification was very well thought out to meet the requirements of the automation and control industries.

➢PROFIBUS DP has now become the dominant technology used in factory automation and general control and monitoring systems.

I. INTRODUCTION

THE PROFIBUS FAMILY

❖ PROFIBUS PA - Process Automation ➢PROFIBUS PA was developed in the mid 1990’s specifically

for the process industry to replace 4-20mA transmission. 4-20mA transmission provides device power and data over a single cable (two cores).

➢PA similarly provides device power and data over a single cable. However, we must remember that PROFIBUS is a network, so PA provides power and data communications for many devices in one two-core cable.

I. INTRODUCTION

THE PROFIBUS FAMILY

Because of the two current versions (DP and PA), PROFIBUS is applicable to a wide range of applications and industries involving both manufacturing automation and process control: ➢High-speed, simple factory automation. ➢Drives and motor control. ➢Process control applications. ➢Operation in explosive environments (gas and oil etc.). ➢Functional safety systems (safeguarding and interlocking). ➢High-speed servos (machine tools and robotics).

I. INTRODUCTION

I. INTRODUCTION

I. INTRODUCTION

❖The DP suffix refers to "Decentralized Periphery", which is used to describe distributed I/O devices connected via a fast serial data link with a central controller. To contrast, a programmable logic controller (PLC) normally has its input/output channels arranged centrally. By introducing a network bus between the main controller (master) and its I/O channels (slaves), we have decentralized the I/O.

I. INTRODUCTION

B. COMMUNICATION

❖ProfiBus is based on universal international standards and oriented to the OSI (Open System Interconnection) reference model per international standard ISO 7498.

I. INTRODUCTION

B. COMMUNICATION

Layer 1 of this model is the physical layer and defines the physical transmission characteristics. Layer 2 is the data link layer and defines the bus access protocol. Layer 7 is the application layer and defines the application functions.

In this model, every layer handles precisely defined tasks.

ProfiBus DP uses only layers 1 & 2 of this model, plus the user interface. Layers 3 to 7 are not used.

LAYER 1 – THE PHYSICAL LAYER

❖The PROFIBUS physical layer has three different specifications. DP and FMS use RS485 wiring which is very widely used by other fieldbus and communication standards. DP (and FMS) can also use fibre-optic communication. PA uses a different standard, called Manchester Bus Powered (MBP) defined in IEC61158-2 which allows device power to be delivered over the bus cable.

I. INTRODUCTION

RS485 RS485 (also sometimes called H2) was d e v e l o p e d i n t h e 1 9 6 0 s b y Telecommunications Industry Association /Electronic Industries Alliance (TIA/EIA). R S 4 8 5 i s u s e d b y m a n y d i f f e r e n t communication and fieldbus systems to p rov ide s imple , robus t , h igh-speed communication over two-core shielded twisted pair cable. RS485 allows up to 32 stations or devices to be connected together on a single cable.


I. INTRODUCTION

❖ Fibre optic (FO) DP (and FMS) can also use fibre-optic communication where optical (light) signals pass down plastic or glass fibre-optic cable. Fibre optic transmission gives high speed, interference free communication with electrical isolation between devices. ❖ MBP (H1) Manchester Bus Powered (MBP) transmission is used by PA (also sometimes called H2). MBP transmission uses shielded twisted pair wire allowing up to 32 stations per segment. However, MBP uses different cable to RS485. Using the wrong cable is one of the common problems in PROFIBUS systems causing communications to fail, or even worse, intermittent or spurious faults. MBP wiring provides power supply and data over the same cable.

I. INTRODUCTION


❖ Layer 2 – The data link layer The layer 2 protocol is called the Fieldbus Data Link (FDL) layer. This is common to all versions of PROFIBUS and is the reason that they can all run together within a network. ❖ Layer 7 – The application layer Layers 3 to 6 are not used in any fieldbus system. These layers are provided for much more complex and flexible systems like IT networks and the internet etc. Layer 7, the Application Layer, defines the functions, services and message contents for PROFIBUS communications.

I. INTRODUCTION

I. INTRODUCTION

Functionality of the PROFIBUS DP version with key features

I. INTRODUCTION

Each RS485 segment is best laid out as a “linear bus”, where the cable daisy-chains from device to device.

I. INTRODUCTION

ADDRESSING

❖ Within a network, every PROFIBUS device or station is given an address through which communication is directed. There are 128 different addresses provided (numbered 0 to 127). However, address 127 is reserved for broadcast messages and so cannot be used for a device. Address 126 is also reserved for devices whose address is set over the bus. The remaining 126 addresses (0 to 125) are available for PROFIBUS devices.

The standard PROFIBUS DP data rates are: 9.6 kbit/s 1.5 Mbit/s 19.2 kbit/s 3.0 Mbit/s 93.75 kbit/s 6.0 Mbit/s 187.5 kbit/s 12.0 Mbit/s 500.0 kbit/s

Some DP devices from Siemens also use 45.45 kbit/s. However this is a non-standard bit rate. Most modern DP slaves support all the data rates and further will automatically detect and adjust to the network speed. Very occasionally the data rate needs to be set using switches on the device.

PROFIBUS PA is quite different in that it always runs at a fixed rate of 31.25 kbit/s. Note that this is not one of the DP rates, so PA always runs at a different speed to DP.


❖ The Profibus network is built on a master/slave communication principle. A central controller, the fieldbus master, cyclically reads information from the field devices, the fieldbus slaves, and writes the output values to them.

❖ In addition to cyclic services, Profibus provides acyclic services that permit modification of devices parameters during operation. This enables configuration of modern field devices, which contain many parameters and variables in addition to the measured and manipulated values.



❖ ProfiBus DP defines two classes of masters. A class 1 master handles the normal communication or exchange of data with the slaves assigned to it. A class 2 master is a special device primarily used for commissioning slaves and for diagnostic purposes. Some masters may support both class 1 and class 2 functionality.

❖ Master-to-master communication is normally not permitted in Profibus, except in order to grant bus access rights to another master via the exchange of a token. However, master-to-master communication between two mono-master systems can be facilitated using a DP-DP gateway. Note that the exchange of bus access rights via this "token ring" only applies between masters on the bus.


❖ Because ProfiBus uses a cyclic (periodic) polling mechanism between masters and slaves, it is also deterministic. That is, the behavior of a ProfiBus system can be reliably predicted over time. In fact, ProfiBus was designed to guarantee a deterministic response. To contrast, CAN and Ethernet are event-driven bus systems and consequently form non-deterministic systems.

PROFIBUS NETWORK OPERATION

Single Class-1 master in cyclic communication


TOKEN PASSING

Two masters share the token so that each can enter cyclic data exchange with its slaves


PLC PROGRAMMING ❖Instead a PROFIBUS master chip communicates the IO data from a shared

area of the PLC memory to the salve devices that are attached to the network.

PLC with PROFIBUS Class-1 master functionality


SYSTEM CONFIGURATION

GSD files

In order to facilitate device configuration all PROFIBUS equipment suppliers provide s t a n d a r d “ G e n e r a l S t a t i o n Description” or GSD files. These GSD files can be read by the configuration tool to provide detailed information on the devices being used on the network. GSD files make integration of devices from different vendors in a bus system simple.



PICK-UP IN FIELDBUS CABLESII. PROFIBUS NETWORK

Pick-up reduction

Earthed shielding can reduce electrostatic pick-up

Twisted pair cable can reduce electromagnetic pick-up

II. PROFIBUS NETWORKPICK-UP IN FIELDBUS CABLES

Solid steel trunking with a lid.


PROFIBUS RS485 and MBP transmission are both balanced to improve noise rejection.

PROFIBUS RS485 transmission


Active termination used in PROFIBUS RS485 wiring


▪ Specification by 13 industrial firms and 5 university institutes ▪ 1988 German DIN Standard 19245 ▪ 1996 European Fieldbus Standard EN 50170 ▪ 2000 International Standard IEC 61158




TOPOLOGY

❖ PROFIBUS uses the bus topology. In this topology, a central line, or bus, is wired throughout the system. Devices are attached to this central bus. One bus eliminates the need for a full-length line going from the central controller to each individual device.

❖ In the past, each PROFIBUS device had to connect directly to the central bus. Technological advancements, however, have made it possible for a new “two-wire” system. In this topology, the PROFIBUS central bus can connect to a ProfiNet Ethernet system. In this way, multiple PROFIBUS busses can connect to each other.


A. PROFIBUS DP (DECENTRALIZED PERIPHERY)

▪ Profibus DP is responsible for communication between the Controller level of a process automation system (PLC) and the decentralized periphery in the field, also intrinsic safety (RS485-IS) via DP-Ex barriers into hazardous area. ▪One feature of PROFIBUS DP is its high speed of transmission

up to 12 Mbit/s.

III. CLASSIFICATION

❖The second type of PROFIBUS is more universal. Called PROFIBUS DP, for Decentralized Periphery, this new protocol is much simpler and faster. PROFIBUS DP is used in the overwhelming majority of PROFIBUS application profiles in use today. Application profiles allow users to combine their requirements for a specific solution, and they will be discussed in more detail shortly.

❖PROFIBUS DP has, itself, three separate versions. Each version, from DP-V0 to DP-V1 and DP-V2, provides newer, more complicated features.

A. PROFIBUS DP (DECENTRALIZED PERIPHERY)

III. CLASSIFICATION

B. PROFIBUS PA (PROCESS AUTOMATION)❖ PROFIBUS PA is a protocol designed for Process Automation.

In actuality, PROFIBUS PA is a type of PROFIBUS DP Application profile. PROFIBUS PA standardizes the process of transmitting measured data. It does hold a very important unique characteristic, though. PROFIBUS PA was designed specifically for use in hazardous environments.

❖ Profibus PA comply with IEC 1158-2 standard (synchronous). This media, along with the PA application profile supports power over the bus. In explosive environments, though, that power can lead to sparks that induce explosions. To handle this, PROFIBUS PA can be used with Manchester Bus Powered technology (MBP).

III. CLASSIFICATION

A key feature of the technology IEC 61158 -2

Network structure Bus, Start and Tree

Cable Shielded, twisted pair cable

Communication Distance 1900m

Speed 31.25 Kbps

Number of connected nodes

Max127 nodes/network

B. PROFIBUS PA (PROCESS AUTOMATION)III. CLASSIFICATION

SIGNAL CONVERTERS❖ Signal is converted from RS-485 transmission systems

Profibus DP (NRZ code) to IEC 1158-2 (Manchester synchronous code) for Profibus PA by the "DP / PA couple" or "DP / PA link "

➢DP/PA Coupler ➢DP/PA Link


DP/PA COUPLER

❖ DP / PA couple has two modes: ➢ Not fire resistant mode can be

powered to 31 devices. ➢ Fire resistant mode power

supply for 10 devices

III. CLASSIFICATION

❖Coupler convert data from asynchronous (11 bits/character) to synchronization (8 bits/character), transfer rate from 45.45 kbit/s to 31.35 kbit/s.

❖ DP / PA does not need to configure and can not be detected by the station, power devices, current limit (fire protection function).

DP/PA LINK

❖ It includes 5 DP / PA coupler (type Fire resistant) or 5 DP / PA category (not Fire resistant) is connected via a Profibus-DP module to the station.

❖ Module slave station is at a higher level Profibus-DP (12 Mbits / s maximum) and a PA master for the subordinate lines.

III. CLASSIFICATION

❖ PROFIBUS PA uses Manchester Bus Powered (MBP) transmission at the physical layer.

❖ The different transmission technology means that a “DP/PA coupler” is required to connect PA to a DP network

❖ MBP transmission was specifically designed for the process industries, to replace 4-20mA technology, where power is supplied to the device over the communication cable. A separate power supply is not necessary. However, there is a fundamental difference between PROFIBUS PA and 4-20mA devices: PA uses MBP transmission, which is digital (operating at 31.25 kbit/s), whereas 4-20mA devices transmit an analogue signal which represents the scaled process value as the current varies from 4mA to 20mA.

B. PROFIBUS PA (PROCESS AUTOMATION)

III. CLASSIFICATION

❖MBP transmission uses changing current to transmit the data transmission over two wires. A fixed transmission speed of 31.25 kbit/s is used and a special “Manchester encoded” synchronous protocol is used. Manchester encoding simply means that the individual bits are transmitted as transitions rather than simply logic levels. MBP transmission allows device power and data to be combined on one pair of wires.

❖The average current does not change from the basic current since the ±9mA modulation always comes in pairs which on average cancel out.

B. PROFIBUS PA (PROCESS AUTOMATION)

III. CLASSIFICATION

❖ MBP transmission Up to 32 PA devices can be connected to a MBP segment (the coupler and up to 31 PA slaves). The coupler supplies the basic current to all the connected PA devices and also translates between the RS484 signals and the MBP signals.


PA and DP integrated into one network

III. CLASSIFICATION

❖The initial version of PROFIBUS was PROFIBUS FMS, Fieldbus Message Specification. PROFIBUS FMS was designed to communicate between Programmable Controllers and PCs, sending complex information between them.

❖Unfortunately, being the initial effort of PROFIBUS designers, the FMS technology was not as flexible as needed. This protocol was not appropriate for less complex messages or communication on a wider, more complicated network. New types of PROFIBUS would satisfy those needs. PROFIBUS FMS is still in use today, though the vast majority of users find newer solutions to be more appropriate.

C. PROFIBUS FMS (FIELDBUS MESSAGE SPECIFICATION)

III. CLASSIFICATION

❖ PROFIBUS FMS (Fieldbus Message Specification), which was tailored to demanding communication tasks. A further step in 1993 saw completion of the specification for the more simply configured and faster PROFIBUS DP protocol (Decentralized Periphery). This protocol is now available in three functionally scaleable versions DP-V0, DP-V1 and DP-V2.

III. CLASSIFICATIONC. PROFIBUS FMS (FIELDBUS MESSAGE SPECIFICATION)

Profibus-FMS – Application layer

C. PROFIBUS FMSIII. CLASSIFICATION

❖The FMS Communication Profile is designed for communication at cell level. At this level, programmable controllers (PLCs and PCs) communicate primarily with each other. In this application area a high degree of functionality is more important than fast system reaction times.

❖The communication model of Profibus-FMS is based on the definition of a Virtual Field Device. This is the part of a device that is reachable by the communication system.

❖The PROFIBUS-FMS communication model permits distributed application processes to be unified into a common process by using communication relationships.

III. CLASSIFICATIONC. PROFIBUS FMS

❖ All accessible values, variables are listed in a so called object dictionary, which itself can be read out over the bus.

➢ The object dictionary holds index, name, type of each variable. ➢ That portion of an application process in a field device which

can be reached via communication is called a virtual field device (VFD).

➢ All communication objects of an FMS device are entered in the object dictionary (OD). The object dictionary contains description, structure and data type, as well as the relationship between the internal device addresses of the communication objects and their designation on the bus (index/name).

III. CLASSIFICATION

C. PROFIBUS FMS

Virtual Field Device (VFD) with object dictionary (OD)

III. CLASSIFICATION

❖ The FMS application layer consists of the following parts: ➢ The Fieldbus Message Specification (FMS) . ➢ The Lower Layer Interface (LLI)

III. CLASSIFICATION

C. PROFIBUS FMS

THE BENEFITS OF PROFIBUS

✓ Large installed base and well known technology outside of US ✓ All digital communication for process data and auxiliary data ✓ Communications speeds PA=31.24 Kbits/sec, DP up to 12

Mbits/sec and ethernet speeds with Profinet. ✓ Auxiliary data is broadcast. ✓ More flexible wiring and faster commissioning ✓ Multivariable Access

IV. CONLUSION

✓ Fast and Easy access to contained parameters ✓ Status Value coming with every Process Value in the same

scan ✓ In addition to Status Value more Diagnostics information is

pushed instead of polled ✓ Alarm Values from the Device ✓ PROFIBUS Diagnostics ✓ No analog conversion in device

THE BENEFITS OF PROFIBUS

IV. CONLUSION

Quality Assurance ▪The PROFIBUS User Organization has created a conformance

testing program to ensure devices meet high standards. In this program, a device is sent to an independent laboratory for testing. The device then undergoes a comprehensive series of tests, including Hardware, Conformity, and Function tests, among others. The test results are documented ▪When a device passes all tests, its manufacturer can apply for

a conformance certificate. The certificate is valid for three years and can be renewed with further testing.

IV. CONLUSION

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