PROFIBUS

PROFIBUS, fieldbus for networks in industrial automation.

PROFIBUS is the worldwide standard when it comes to networks in industrial automation. With a majority share of the fieldbus market, it has grown to become the unequivocal leader in this industry.
Via a single cable, PROFIBUS links controllers or control systems with decentralized field devices (sensors and actuators) on the field level and also enables consistent data exchange with higher ranking communication systems. The consistency of PROFIBUS is enabled by utilizing a single, standardized, application-independent communication protocol which supports fieldbus solutions both in factory and process automation as well as in motion control and safety-related tasks.

History

•  1987 – the German Federal Ministry for Research and Technology requests a collaboration project called “Field Bus”. 13 companies and 5 universities jointly develop an open field bus under the name PROFIBUS, for PROcess-FIeld-BUS
• 1989 – the PROFIBUS Nutzerorganisation (PNO) is established in Germany as the first user organization
• 1992 – Switzerland establishes the second (counting PNO) Regional PROFIBUS Association (RPA), with the motto “develop globally, support locally”
• 1993 – PROFIBUS DP (Decentralized Periphery) is released and its use for discrete I/O begins
• 1994 – here in the USA, the PROFIBUS Trade Organization (PTO) is formed
• 1995 – All RPAs are pooled under the newly formed international umbrella organization PROFIBUS International (PI)
• 1996 – PROFIBUS PA (Process Automation) is created for process instruments and all all related scope of applications
• 1997 – 1 million PROFIBUS devices installed
• 1999 – PROFIBUS DP is adopted as an international standard under IEC 61158
• 2000 – the first PI Competence Center (PICC) is established
• 2001 – the PROFIsafe common application profile is specified to allow for safety over logic, leveraging the establishment of PROFIBUS
• 2003 – 10 million PROFIBUS devices installed
• 2006 – the PI name is updated to include PROFINET: PI – PROFIBUS and PROFINET International
• 2009 – 30 million PROFIBUS devices installed

Value Proposition

Part of the value proposition of PROFIBUS is its ability to cut costs and improve operations across the life-cycle of a plant, from design right though ongoing maintenance and even revamps. It does this in many ways: at the engineering stage it simplifies plant design, eliminates hard wiring and requires less hardware, leading to faster commissioning and lowered costs. It supports better diagnostics, so commissioning is much faster. PROFIBUS also helps achieve better productivity and higher product quality through the delivery of better and more timely data to operations and management staff. In addition, it supports advanced asset management strategies that allow plants and equipment to be better managed and maintained.

A huge number of vendor companies have developed PROFIBUS capable devices for discrete and process automation, so system integrators have massive choice. Not only does this lead to security and flexibility of supply, it also means healthy competition amongst vendors, leading to pricing that is highly favorable to end users.

The success of PROFIBUS is underpinned by the global technical and administrative network of PI, which has carefully guided its development to ensure end users’ needs continue to be met. The applications coverage  has been continuously extended to include new and relevant functionality such as integrated Functional Safety and advanced Motion Control. Users have made substantial investments in training, tools, inventories, and plants. In short, the value proposition of PROFIBUS has become commandingly high. That’s why PROFIBUS is the most successful fieldbus in history.

10 reasons for choosing PROFIBUS

• Preferred fieldbus for most end users and used in the largest number of applications worldwide
• Openness and interoperability, allowing changes/updates at low cost
• Protocol optimized for factory and process control using standardized interfaces, and therefore ideal for hybrid applications too
• Less hardware needed, which means less costs and space leading to lowered installation and life-cycle costs
• Easy migration to PROFINET
• Easy and consistent integration of functional safety and motion control for factory and process automation
• Flexible media redundancy to ensure maximized up-time
• Stringently managed technology development, including test and certification processes
• Supported by PI, the world’s largest fieldbus organization
• Huge vendor and product choice

Fieldbuses in General

Stepping from analog to digital communication means a major paradigm shift.

In control systems that do not rely on a fieldbus, there is a clear divide between the devices and the controls; the tasks of each are separated. Only analog values (measured data) are transferred between devices and controllers, and this communication is one-way. From a personnel perspective this typically meant that an instrumentation technologist was responsible for the field devices, and a control engineer scales the (4-20mA) analog values coming into the control system accordingly.

In a fieldbus system, the instruments are an integral part of the system, and the control engineer has full control over field devices. From the engineer’s point of view, there is now no distinction between the instruments and the control system. It is an integrated whole. Having the instruments as part of the control system is a major paradigm shift as it gives the instrument a role that in the past had been reserved for the control system. Conversely, the instrument technologist needs access to the control system for set up and monitoring of the instruments. The communication is no longer analog, but digital; no longer one-way, but two-way. And with this shift, we now have a network, and different topologies are possible.

Benefits of using a digital fieldbus (PROFIBUS)

• Plant Asset Management – Information from process instruments and sensors and actuators are available in the controller.
• Engineering and Documentation – Engineering is simpler, and the documentation is far less complicated as hundreds of separate wires are reduced to just a single cable.
• Installation – With less hardware, installation is easier and faster.
• Commissioning – Devices can sequentially be brought online, one by one, with start-up initiated from a central location.
• Process Variables – The diagnostic information and status bytes available tell the user if they can trust the process variable or not.
• Manufacturing Flexibility – As demand shifts, changes in manufacturing can be implemented rapidly.
• Maintenance and Operations – With the powerful diagnostics of a fieldbus come improved availability and reduced down-time.

Discrete Automation

Discrete -or Factory Automation- is typically characterized by faster processes than process applications. Here we use PROFIBUS DP (Decentralized Periphery). The most prevalent medium for PROFIBUS transmission is over copper wire, and for this the easy-to-use and cost-effective RS-485 transmission technology is used. We are able to transport 244 bytes of data from 9600 bit/s up to 12 Mbit/s. This range of speeds can accommodate nearly every application. There are some instances under which wired transmission technology reaches its limits, for example in an environment with heavy interference or when bridging long distances. In these cases, optical transmission via fiber-optic cables is available.

The communication basis for PROFIBUS lies in the cyclic data exchange between PLCs (masters) and devices (slaves). A cycle will consist of a master sending outputs to, and receiving inputs from all of it’s devices, and then repeating the cycle. This also includes device-, module-, and channel-specific diagnostics (e.g. wire break, short circuit, etc.) for quick fault localization. All field devices have the same priority, and every device is scanned every cycle. “DP-V0″ is the base protocol for cyclic I/O and diagnostics.

This is further extended in “DP-V1″ which allows for the acyclic exchange of data between PCs or PLCs and slave devices. This also includes the on-demand access of device parameters, and the setting of alarm limits. Finally, the “DP-V2″ extension provides the capability for slave-to-slave communication in a broadcast Publisher/Subscriber fashion. DP-V2 applications include motion control and other high speed requirements.

For a deeper look into the protocol, it is highly recommended that you consult the PROFIBUS System Description.

Process Automation

Process Automation environments, while typically requiring slower procedures, might also be characterized by explosive or hazardous environments. In such applications, we use PROFIBUS PA as opposed to PROFIBUS DP. Similarly we can use copper wiring or fiber-optic cabling. In the case of the former, instead of RS-485 the physical layer is MBP (Manchester Encoded Bus Powered). It is important to note that even though a different physical layer is employed, PROFIBUS PA is the exact same protocol as PROFIBUS DP. MBP only transmits at one speed: 31.25 kbit/s, which is plenty for process applications. A significant departure however is that power and data are transported via the same cable. As such there are rules regarding network topology that must be followed.

When operating PROFIBUS PA in hazardous areas, there are two concepts used to ensure that a sparking condition does not occur:

• The FISCO (Fieldbus Intrinsically Safe COncept) model makes it easy to plan, install and expand PROFIBUS PA networks. This model is based on the specification that a communication network is intrinsically safe and does not require complex calculations for validating intrinsic safety if the relevant components (field devices, cables, segment couplers, and bus terminations) conform to a set of limit values for voltage/current/output/inductivity/capacitance. Intrinsic safety is guaranteed on a network segment if all components are certified as per FISCO. It is characterized, however, by a considerably low input power into a segment and therefore shorter cable lengths and fewer devices per segment.
• The High-Power Trunk concept relies on the separation in the different zones of explosive and hazardous environments. In less stringent hazardous zones (where only increased safety is required), a trunk cable is laid. It is assumed no ‘hot’ maintenance will be required on the trunk line. Off of this (‘spurs’), field devices are connected that lie in areas where intrinsic safety is required. Proof of intrinsic safety therefore only involves the field barrier and the device(s). This ‘Trunk and Spur’ concept is very popular as it leverages the topology options available with MBP physics.

For applications which demand high system availability, such as is common in continuous processes, redundant systems are generally used. This can mean:

• Master Redundancy – Two controllers are used, such that if one fails the other takes over seamlessly
• Media Redundancy – A ring topology is formed, such that if one segment is broken the topology is automatically converted to a line configuration.
• Both – Often times both methods are employed; for example, a dual-master ring network.

The best starting point for more information is the PROFIBUS for Process document. Further information can be found in the PROFIBUS Slide Set.

Profiles

PROFIBUS Application Profiles are vendor-independent specifications implemented into PROFIBUS devices to enable uniform behavior of devices from different manufacturers. To ensure smooth interaction between the bus nodes of an automation solution, the basic functions and services of the nodes must match. They have to “speak the same language” and use the same concepts and data formats. This applies both for communication and for device functions and industry sector solutions. This uniformity is achieved through the use of “profiles” relating to device families or special industry sector solutions. These profiles specify features which “profile devices” must exhibit as a mandatory requirement. These can be cross-device-class features, such as safety-relevant behavior (Common Application Profiles) or device-class-specific features (Specific Application Profiles). Application Profiles are specified and maintained by PI Working Groups.

Profile Name	Profile Content
Specific Application Profiles
Dosing / Weighing	Describes the use of dosing and weighing systems on PROFIBUS
Encoder	Describes the connection of linear, angular, and rotary encoders with single-turn and multi-turn resolution
Fluid Power	Describes the control of hydraulic drives via PROFIBUS (cooperation with VDMA)
HART on PROFIBUS	Defines the integration of HART devices in PROFIBUS systems
Ident Systems	Describes the communication between identification devices (barcode reader, transponder, etc.)
Lab Devices	Specifies the properties of laboratory automation devices on PROFIBUS
Liquid Pumps	Defines the use of liquid pumps on PROFIBUS (cooperation with VDMA)
Low Voltage Switchgear	Defines data exchange for low-voltage switchgear (switch disconnector, motor starter, etc.)
PA Devices	Specifies the properties of process automation devices
PROFIdrive	Describes the device behavior and access behavior to data for variable speed electric drives
Remote I/O	Defines the interchangeability of remote I/O devices in process automation
SEMI	Describes the properties of semiconductor manufacturing devices (SEMI standard)
Common Application Profiles
Identification & Maintenance	Specifies a concept for identification of PROFIBUS devices and Internet access to device-specific information
iPar-Server	Defines the saving of additional i-parameters in the controller and the read-back of i-parameters after a device replacement
PROFIsafe	Defines safe communication of safety-related devices (emergency STOP button, photoelectric array, etc.) with safety controllers via PROFIBUS
Redundancy	Specifies the mechanism for field devices with redundant communication behavior
Time Stamp	Defines the precisely timed assignment of certain events and actions by time stamping

And also download some useful datas:

• PROFINET
• PROFIBUS_system_description
• PROFINET  
• pi_white_paper_profinet_it