Profibus
Encyclopedia
Automation
Automation is the use of control systems and information technologies to reduce the need for human work in the production of goods and services. In the scope of industrialization, automation is a step beyond mechanization...
technology and was first promoted in 1989 by BMBF (German department of education and research). It should not be confused with the PROFINET standard for Industrial Ethernet
Industrial Ethernet
Industrial Ethernet refers to the use of the Ethernet family of computer network technologies in an industrial environment, for automation and process control. A number of techniques are used to adapt Ethernet for the needs of industrial processes, which require real time behavior...
.
Origin
The history of PROFIBUS goes back to a publicly promoted plan for an association started in Germany in 1987 and for which 21 companies and institutes devised a master project plan called "field bus". The goal was to implement and spread the use of a bit-serialBit-serial
In digital logic applications, bit-serial architectures send data one bit at a time, along a single wire, in contrast to bit-parallel architectures, in which data values are sent all bits at once along a group of wires....
field bus based on the basic requirements of the field device interfaces. For this purpose, member companies agreed to support a common technical concept for production (i.e discrete or factory automation
Automation
Automation is the use of control systems and information technologies to reduce the need for human work in the production of goods and services. In the scope of industrialization, automation is a step beyond mechanization...
) and process automation. First, the complex communication protocol Profibus FMS (Field bus Message Specification), which was tailored for demanding communication tasks, was specified. Subsequently in 1993, the specification for the simpler and thus considerably faster protocol PROFIBUS DP (Decentralized Peripherals) was completed. Profibus FMS is used for (non deterministic) communication of data between Profibus Masters. Profibus DP is a protocol made for (deterministic) communication between Profibus masters and their remote I/O slaves.
There are two variations of PROFIBUS in use today; the most commonly used PROFIBUS DP, and the lesser used, application specific, PROFIBUS PA:
- PROFIBUS DP (Decentralized Peripherals) is used to operate sensors and actuators via a centralized controller in production (factory) automation applications. The many standard diagnostic options, in particular, are focused on here.
- PROFIBUS PA (Process Automation) is used to monitor measuring equipment via a process control system in process automation applications. This variant is designed for use in explosion/hazardous areas (Ex-zone 0 and 1). The Physical Layer (i.e. the cable) conforms to IEC 61158-2, which allows power to be delivered over the bus to field instruments, while limiting current flows so that explosive conditions are not created, even if a malfunction occurs. The number of devices attached to a PA segment is limited by this feature. PA has a data transmission rate of 31.25 kbit/s. However, PA uses the same protocol as DP, and can be linked to a DP network using a coupler device. The much faster DP acts as a backbone network for transmitting process signals to the controller. This means that DP and PA can work tightly together, especially in hybrid applications where process and factory automation networks operate side by side.
In excess of 30 million PROFIBUS nodes were installed by the end of 2009. 5 million of these are in the process industries.
Technology
PROFIBUS Protocol (OSI reference model)
| OSI-Layer | PROFIBUS | ||||
|---|---|---|---|---|---|
| 7 | Application | DPV0 | DPV1 | DPV2 | Management |
| 6 | Presentation | -- | |||
| 5 | Session | ||||
| 4 | Transport | ||||
| 3 | Network | ||||
| 2 | Data Link | FDL | |||
| 1 | Physical | EIA-485 | Optical | MBP | |
Application layer
To utilize these functions, various service levels of the DP protocol were defined:- DP-V0 for cyclic exchange of data and diagnosis
- DP-V1 for acyclic and cyclic data exchange and alarm handling
- DP-V2 for isochronousIsochronousIsochronous : From Greek iso, equal + chronos, time. It literally means regularly, or at equal time intervals. In general English language, it refers to something that occurs at a regular interval, of the same duration; as opposed to synchronous which refers to more than one thing happening at the...
mode and data exchange broadcast (slave-to-slave communication)
Security layer
The security layer FDL (Field bus Data Link) works with a hybrid access method that combines token passingToken passing
In telecommunication, token passing is a channel access method where a signal called a token is passed between nodes that authorizes the node to communicate. The most well-known examples are token ring and ARCNET....
with a master-slave method. In a PROFIBUS DP network, the controllers or process control systems are the masters and the sensors and actuators are the slaves.
Various telegram types are used. They can be differentiated by their start delimiter (SD):
No data:
SD1 = 0x10
| SD1 | DA | SA | FC | FCS | ED |
Variable length data:
SD2 = 0x68
| SD2 | LE | LEr | SD2 | DA | SA | FC | DSAP | SSAP | PDU | FCS | ED |
Fixed length data:
SD3 = 0xA2
| SD3 | DA | SA | FC | PDU | FCS | ED |
Token:
SD4 = 0xDC
| SD4 | DA | SA | ED |
Brief acknowledgement:
SC = 0xE5
| SC |
SD: Start Delimiter
LE: Length of protocol data unit, (incl. DA,SA,FC,DSAP,SSAP)
LEr: Repetition of protocol data unit, (Hamming distance = 4)
FC: Function Code
DA: Destination Address
SA: Source Address
DSAP: Destination Service Access Point
Service Access Point
A Service Access Point is an identifying label for network endpoints used in Open Systems Interconnection networking.When using the OSI Network Layer , the base for constructing an address for a network element is an NSAP address, similar in concept to an IP address...
SSAP: Source Service Access Point
Service Access Point
A Service Access Point is an identifying label for network endpoints used in Open Systems Interconnection networking.When using the OSI Network Layer , the base for constructing an address for a network element is an NSAP address, similar in concept to an IP address...
| SAP (Decimal) | SERVICE |
|---|---|
| Default 0 | Cyclical Data Exchange (Write_Read_Data) |
| 54 | Master-to-Master SAP (M-M Communication) |
| 55 | Change Station Address (Set_Slave_Add) |
| 56 | Read Inputs (Rd_Inp) |
| 57 | Read Outputs (Rd_Outp) |
| 58 | Control Commands to a DP Slave (Global_Control) |
| 59 | Read Configuration Data (Get_Cfg) |
| 60 | Read Diagnostic Data (Slave_Diagnosis) |
| 61 | Send Parameterization Data (Set_Prm) |
| 62 | Check Configuration Data (Chk_Cfg) |
Note: SAP55 is optional and may be disabled if the slave doesn't provide non-volatile storage memory for the station address.
PDU: Protocol Data Unit (protocol data)
FCS: Frame Checking Sequence
ED: End Delimiter (= 0x16 !)
The FCS is calculated by simply adding up the bytes within the specified length. An overflow is ignored here. Each byte is saved with an even parity and transferred asynchronously with a start and stop bit.
There may not be a pause between a stop bit and the following start bit when the bytes of a telegram are transmitted. The master signals the start of a new telegram with a SYN pause of at least 33 bits (logical "1" = bus idle).
Bit-transmission layer
Three different methods are specified for the bit-transmission layer:- With electrical transmission pursuant to EIA-485, twisted pair cables with impedances of 150 ohmOhmThe ohm is the SI unit of electrical resistance, named after German physicist Georg Simon Ohm.- Definition :The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere,...
s are used in a bus topology. Bit rates from 9.6 kbit/s to 12 Mbit/s can be used. The cable length between two repeaterRepeaterA repeater is an electronic device that receives asignal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.-Description:...
s is limited from 100 to 1200 m, depending on the bit rate used. This transmission method is primarily used with PROFIBUS DP. - With optical transmission via fiber optics, star-, bus- and ring-topologies are used. The distance between the repeaters can be up to 15 km. The ring topology can also be executed redundantly.
- With MBP (Manchester Bus Powered) transmission technology, data and field bus power are fed through the same cable. The power can be reduced in such a way that use in explosion-hazardous environments is possible. The bus topology can be up to 1900 m long and permits branching to field devices (max. 60 m branches). The bit rate here is a fixed 31.25 kbit/s. This technology was specially established for use in process automation for PROFIBUS PA.
For data transfer via sliding contacts for mobile devices or optical or radio data transmission in open spaces, products from various manufacturers can be obtained, however they do not conform to any standard.
Profiles
Profiles are pre-defined configurations of the functions and features available from PROFIBUS for use in specific devices or applications. They are specified by PI working groups and published by PI. Profiles are important for openness, interoperability and interchangeability, so that the end user can be sure that similar equipments from different vendors perform in a standardised way. User choice also encourages competition that drives vendors towards enhanced performance and lower costs.There are PROFIBUS profiles for Encoders, Laboratory instruments, Intelligent Pumps, Robots and Numerically Controlled machines, for example. Profiles also exist for applications such as using HART and wireless with PROFIBUS, and process automation devices via PROFIBUS PA. Other profiles have been specified for Motion Control (PROFIdrive) and Functional Safety (PROFIsafe
PROFIsafe
PROFIsafe is the first open functional safety communication technology for distributed automation systems worldwide. Its specification for PROFIBUS DP and PROFIBUS PA was published first back in spring 1999. It incorporates the knowledge of more than 25 renowned safety companies...
).
Standardization
PROFIBUS was defined in 1991/1993 in DIN 19245, was then included in EN 50170 in 1996 and, since 1999, established in IEC 61158/IEC 61784.Organization
The PROFIBUS Nutzerorganisation e.V. (PROFIBUS User Organization, or PNO) was created in 1989. This group was composed mainly of manufacturers and users from Europe. In 1992, the first regional PROFIBUS organization was founded (PROFIBUS Schweiz in Switzerland). In the following years, additional Regional PROFIBUS & PROFINET Associations (RPAs) were added.In 1995, all the RPAs joined together under the international umbrella association PROFIBUS & PROFINET International (PI). Today, PROFIBUS is represented by 25 RPAs around the world (including PNO) with over 1400 members, including most if not all major automation vendors and service suppliers, along with many end users.
See also
- FieldbusFieldbusFieldbus is the name of a family of industrial computer network protocols used for real-time distributed control, now standardized as IEC 61158....
- List of automation protocols