PROFIBUS Technology

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.

Read More:

https://us.profinet.com/documentation/system-description-profibus-technology-and-application/

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:

http://us.profinet.com/documentation/profibus-slide-set/

• Students receive a certificate for 5 Professional Development Hours (PDH) after completing the course
• The entire course is available online at no-cost
• Challenging quizzes help students test their understanding of the material
• The course includes educational content for end-users, OEMs, system integrators, manufacturers of automation devices, distributors, and students.

Take the course HERE.

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?

• 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

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:

https://us.profinet.com/documentation/system-description-profibus-technology-and-application/

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:

http://us.profinet.com/documentation/marketing-flyer-profibus-for-process-automation/

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.

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.

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.