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Profibus Technology

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.

PROFIBUS Definition

PROFIBUS links controllers and control systems with sensors and actuators on the field level (field devices) and also enables simultaneous consistent data exchange with superordinate systems. PROFIBUS is the fieldbus-based automation standard of PROFIBUS & PROFINET International (PI). PI has also developed the PROFINET Ethernet-based automation standard and launched it successfully on the market. PROFIBUS and…

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PROFIBUS links controllers and control systems with sensors and actuators on the field level (field devices) and also enables simultaneous consistent data exchange with superordinate systems. PROFIBUS is the fieldbus-based automation standard of PROFIBUS & PROFINET International (PI). PI has also developed the PROFINET Ethernet-based automation standard and launched it successfully on the market. PROFIBUS and PROFINET use identical device profiles, thereby creating investment security and investment protection for the users and manufacturers of these technologies. Both systems cover the fields of production and process automation and therefore also enable mixed (hybrid) applications, which are often seen in the pharmaceutical, food and beverage industries.

PROFIBUS consistency is based on the standardized “PROFIBUS DP” communication protocol, which supports a variety of applications in factory automation and process automation as well as motion control and safety-related tasks. This integration makes planning, installation, and service easier.

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System Description: PROFIBUS Technology and Application

 

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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…

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  •  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 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
  • 2013- over 50 million PROFIBUS devices installed
  • 2014- the PNO celebrates 25 years since its foundation
  • 2017- 11.5 million PROFIBUS devices in process automation systems
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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 through 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…

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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 through 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, making commissioning 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 for general management and maintenance.

A huge number of vendor companies have developed PROFIBUS capable devices for discrete and process automation, therefore system integrators have many choices. This multi-vendor environment has lead to security and flexibility of supply. It also encourages healthy competition amongst vendors, leading to favorable pricing 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(ie. integrated Functional Safety and 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

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

More on PROFIBUS Here:

PROFIBUS Slide Set

 

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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…

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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.

Analog system: one-way communication

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.

Fieldbus system: two-way digital communication

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 downtime.

Learn more about fieldbuses and their value with this white paper: Why use a Fieldbus?

Why Use a Fieldbus?

 

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ISO/OSI Model

The design of the technology modules with PROFIBUS is oriented toward the ISO/OSI  7-layer model. The communication process between two nodes is distributed over seven layers, from Layer 1 (Physical Layer) to Layer 7 (Application Layer). PROFIBUS uses layers 1, 2 and 7. Layer 1 defines the physical transmission. With PROFIBUS, there are copper-wire versions…

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The design of the technology modules with PROFIBUS is oriented toward the ISO/OSI  7-layer model. The communication process between two nodes is distributed over seven layers, from Layer 1 (Physical Layer) to Layer 7 (Application Layer). PROFIBUS uses layers 1, 2 and 7.

  • Layer 1 defines the physical transmission. With PROFIBUS, there are copper-wire versions (RS485 and MBP) and optical and wireless transmission.
  • Layer 2 defines the description of the bus access method, including data security. With PROFIBUS, this is the master-slave method in conjunction with the token method.
  • Layer 7 forms the interface to the application and thus represents the link between the application and communication. With PROFIBUS, the communication protocol PROFIBUS DP is used here.
  • The actual application process lies above layer 7 and is not part of the OSI model.

ISO OSI Model and PROFIBUS

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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…

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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 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.

PROFIBUS cyclic and acyclic communication

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 overview read the PROFIBUS System Description:

System Description: PROFIBUS Technology and Application

 

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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…

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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.

    High Power Trunk to supply Zone 1

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 installed controllers, if one fails then another takes over seamlessly
  • Media Redundancy – A ring topology is formed, then 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.

More on PROFIBUS PA Here:

Marketing Flyer: PROFIBUS and PROFINET for Process Automation

 

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Transmission Technologies

PROFIBUS offers flexibility in terms of transmission technology: copper-wire versions (RS485 and MBP) and optical and wireless transmission. RS485: The easy-to-use and cost-effective RS485 transmission technology is preferred for use with tasks that require a high transmission speed, but which do not require explosion protection. It is widely used in the production industry and is also…

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PROFIBUS offers flexibility in terms of transmission technology: copper-wire versions (RS485 and MBP) and optical and wireless transmission.

RS485: The easy-to-use and cost-effective RS485 transmission technology is preferred for use with tasks that require a high transmission speed, but which do not require explosion protection. It is widely used in the production industry and is also found in parts of the process industry. In compliance with certain values, the use of the RS485 interface with its high transmission rates is also possible in intrinsically-safe areas (RS485-IS).

MBP: Manchester Coded Bus Powered (MBP) transmission technology implements the simultaneous supply of power to the connected field devices and communication of the data over a single cable. This enables wiring overhead to be significantly reduced, meets requirements for much simpler and safer installation and boasts all the benefits of digital transmission down to the field device. MBP was specifically developed to meet the demands of process automation and is standardized in IEC 61158-2.

In the MBP-IS version, this transmission technology is especially suitable for use in hazardous areas and is therefore widely used in applications of the chemical, oil and gas industries. Explosion protection is implemented via limiting power in the incoming bus supply or more frequently in the installation components in the field.

PROFIBUS Fiber Optic Cable Specifications

Optical Transmission: There are fieldbus usage conditions 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 supported PROFIBUS fiber optic cable types are shown in the table below. The implementation of a fiber optic cable network in the simplest case involves the use of electro-optical converters which are connected to the field device with the RS485 interface and the fiber optic cable on the other side.

Wireless: PROFIBUS can transmit messages wirelessly but often requires proprietary radios from the same manufacturer at both ends.

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Topology

RS485: If RS485 transmission technology is used, all PROFIBUS field devices are typically connected in a line structure with up to 32 nodes (master and slaves) in one segment. The beginning and end of each segment are provided with active bus termination, which must be supplied with power continuously. The bus terminations are usually implemented…

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RS485: If RS485 transmission technology is used, all PROFIBUS field devices are typically connected in a line structure with up to 32 nodes (master and slaves) in one segment. The beginning and end of each segment are provided with active bus termination, which must be supplied with power continuously. The bus terminations are usually implemented as optionally activatable in the devices or plugs. If there are more than 32 nodes or the network span is being extended, repeaters must be used to link the networks.

MBP: If MBP transmission technology is used, basically any topology is permissible. Linear and tree structures and combinations of both are thus possible. In practice, the “trunk & spur topology” has established itself as the de-facto standard, as it is especially clear and well-laid-out. Thanks to the technically-mature installation technologies available on the market, it also exhibits a high degree of robustness. The overall length of a segment may not exceed 1,900 m. Also, the maximum length for a spur in intrinsically-safe applications is 60 m.

Coupling RS485 and MBP Transmission Technology: The MBP transmission technology is typically limited to certain subsegments of a system, e.g. a group of field devices in a hazardous area. The connection of such subsegments to the RS485 segment is carried out using segment couplers or links.

  • Segment couplers are transparent from the standpoint of the bus protocol, the devices of the MBP segment are directly visible on the DP side and the segment coupler itself does not require configuration.
  • Links, on the other hand, are intelligent and map all devices connected in the MBP segment as a single slave in the RS485 segment. The link needs to be configured and restricts the total amount of data that can be transferred to and from the connected devices to 244 bytes. The cyclical data from the PA devices is compressed into a single DP telegram on the DP side and must be reselected by the DP master. The faster DP segment enables a number of PA segments to be integrated into a single DP network via segment couplers or links.
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Profiles

PROFIBUS Application Profiles are vendor-independent specifications implemented into PROFIBUS devices to enable the uniform behavior of devices from different manufacturers. The basic functions and services of the nodes must match to ensure smooth interaction between the bus nodes. They have to “speak the same language” and use the same concepts and data formats. This applies…

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PROFIBUS Application Profiles are vendor-independent specifications implemented into PROFIBUS devices to enable the uniform behavior of devices from different manufacturers. The basic functions and services of the nodes must match to ensure smooth interaction between the bus nodes. 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
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Quality Assurance and Certification

For PROFIBUS devices of different types and manufacturers to be able to perform different tasks in the automation process correctly, they must exchange information over the bus without errors. A prerequisite for this is a standard-compliant implementation of the communication protocols and application profiles by the device manufacturer. To ensure that this demand is met,…

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For PROFIBUS devices of different types and manufacturers to be able to perform different tasks in the automation process correctly, they must exchange information over the bus without errors. A prerequisite for this is a standard-compliant implementation of the communication protocols and application profiles by the device manufacturer. To ensure that this demand is met, PI established a quality-assurance procedure where certificates are granted for test-passing devices. Certification, assures users that PROFIBUS field devices from different manufacturers are capable of error-free operation when used together. For this purpose, the field devices are tested in practical applications in accredited independent test laboratories.

The test procedure, which is the same for all test laboratories, has several steps:

  • A GSD/EDD check ensures that the device description files comply with the specifications.
  • During the hardware test, the electrical properties of the PROFIBUS interface on the test subject are tested for compliance with the specifications.
  • The function test addresses the bus access protocol, transmission protocol and the functions of the test subject.
  • The conformity test is the focal point of testing. It verifies that protocol implementation is in line with the standard. The test primarily covers the state machine, behavior in case of errors, addressability, diagnostic data, and mixed operation.
  • During the interoperability test, the interplay between the test device and the PROFIBUS devices from other manufacturers is tested in a multi-vendor system.
  • The profile test is carried out to determine whether the test devices work together smoothly during operation. The profile test is carried out for the PROFIdrive, PA device, and PROFIsafe profiles. The test determines whether the profile functions were implemented in accordance with the specifications.

Once a field device has passed all the tests, the manufacturer can request a certificate from PI. Each certified device includes a certification number as a reference. The certificate has a validity of 3 years and can be extended by a manufacturer declaration or after new testing. The addresses of the test laboratories can be obtained from the PI website.

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