Case study, implemetation and examples of ProfiBus

                                       PROFIBUS

                                     

Introduction :

Profibus stands process field bus. it is mainly used in automation technology . Profibus is an industry-standard communications bus protocol used in process automation and sensor networks using programmable logic controllers. Profibus is a protocol for field bus communication in automation technology. Profibus links automation systems and controllers with decentralized field devices such as sensors, actuators, and encoders. Profibus networks exchange data using a single bus cable.

Profibus is a vendor-independent, open field bus standard for a wide range of applications in manufacturing and process automation. Vendor independence and openness are ensured by the international standards en 50170 and en 50254.profibus allows communication between devices Of different manufacturers without any special interface adjustment. Profibus can be used for Both high-speed time critical applications and complex communication tasks.

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 (Decentralised Peripherals) is used to operate sensors and actuators via a centralised 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 

Benefits:

Easy to use and universal

• PROFIBUS is based on standards and modularity. User benefits are ease of use and flexibility. The single communication protocol enables fully integated solutions of continuous as well as discrete and safety-related processes to run on the same bus.
  This eliminates the need for separate systems and allows hybrid automation.
• In process automation, the device profile ensures compatible device behavior on the bus enabling the user to choose any “profile device” of his choice.
• Diagnostic data display is sorted according to the NAMUR NE 107 standard:
  The operator can detect the status reliably and react appropriately.

Efficient and productive

• Efficient industrial processes require high machine and plant availability. The integrated redundancy of PROFIBUS is unreached  when it comes to uninterrupted operation.
• As important are the extensive diagnostic messages sent from bus, field devices and process to inform about the current status and to enable timely, status-based intervention.
  The result is higher availability combined with reduced maintenance costs.
• PROFIBUS is optimized for distributed I/O applications. Up to 126 I/O devices can be connected to a PROFIBUS DP cable. Since each I/O device can handle hundreds of connection points, this provides a very large number of connection possibilities for a single controller.

Proactive

• PROFIBUS enables proactive management over the life cycle of a plant. When more advanced device technology is to be deployed, plant operation must not be interrupted when installing the new devices. The solution: starting in profile for PA Devices version 3.02, new devices can temporarily adopt the functionality of predecessor versions. In  this  way plant operation is not interrupted, and the additional functions can be integrated during the next maintenance phase. The ability to take advantage of device innovations is assured, and the inventory of replacement devices is significantly reduced

Innovative

• PROFIBUS is known for its high degree of innovation: User requests are gathered and implemented rapidly. PA Profile 3.02 with its NAMUR-compliant diagnostics concept is an example.
• Other examples are the high-effective redundancy concepts and the proxy technology, enabling the user to PROFIBUS systems to the Ethernet level (PROFINET).
• Existing plants can be modernized and expanded at any time with PROFIBUS:
  HART technology is integrated easily, safety-related and drive tasks are solved with PROFIsafe and PROFIdrive, respectively.
• PROFIBUS supports advanced asset management strategies that allow plants and equipment to be better managed and maintained.

Implementing the communication protocol

A broad spectrum of base technology components and development tools (PROFIBUS ASICs, PROFIBUS stacks, bus monitors, test tools and commissioning tools) and services are available for implementation of the PROFIBUS protocol. Additionally, PI competence Center and many suppliers offer support in this regard. An overview of this is found in the product catalog from PI. When implementing a PROFIBUS interface, it must be considered that the device behavior is determined by the PROFIBUS protocol and the implemented application. For this reason, the entire field device is tested during a certification test along with an eventual pretesting of the used base technology. 

• Interface modules
  
  For small to medium quantities of devices, PROFIBUS interface modules are suitable which are available in a wide variety of versions on the market. They can be attached to the main PCB of the device as a supplementary module. They implement the full bus protocol and offer an easy-to-use user interface for each application.

• Protocol chips
  
  For larger quantities of devices, the use of protocol chips with or without additional microcontroller is the best solution with the following alternatives:
• Single chips, where all PROFIBUS protocol functions are integrated on the chip and which do not require a separate microcontroller (fig. 1, left). This is a hardware-only solution with a fixed functional scope. This solution using single chip ASICs is recommendable for basic IO devices. Only the components for the bus connection are required externally. 
• Chips, which implement smaller or larger portions of the protocol, are combined with an additional microcontroller and firmware offered for the chip (fig. 1, center) to provide the  full implementation of the PROFIBUS protocol. With this form of implementation, for instance, the essential layer-2 portions of the PROFIBUS protocol are implemented with a communication module.
• Protocol chips which already include a micro-controller in the communication module. In conjunction with firmware offered for the chip (fig. 1, right), the application communicates via an easy-to-use user interface. This soltion is used for highly time-critical applications, because the protocol chips with an integrated microcontroller already handles the entire PROFIBUS protocol autonomously and an externally-connected microcontroller can then be used entirely for the application.
  

Fig. 1:Different protocol chip solutions

Often the PROFIBUS chip and the supplemental protocol sofware (stack) come from different sources which increases the number of possible solutions and shows the the openness and multi-vendor capability of PROFIBUS. Pure software solutions can seldom be found on the market.

Case Study:

Project
It isn't often that an engineering team has the opportunity to build a new sugar refinery. In fact, the new refinery in Gramercy, LA is the first new one in the United States in 40 years. The refinery is a joint venture of agriculture company Cargill and the Louisiana Sugar Growers Association, involving a $220 million investment. 

Solution
Managers wanted PROFIBUS to be a key component in the new plants automation to achieve better process control, improved product quality and productivity, but - with PROFIBUS as new technology - they received many additional benefits including better energy efficiency, steam reduction, and a very smooth start up.
Siemens PCS 7 controllers formed the base platform along with redundant servers for the operator stations. Another server was dedicated to administrative tasks. PROFIBUS DP and PA constituted the control network with designers implementing fiber-optic ring to-pologies. Motor control was housed in three motor control centers that were delivered pre-wired with capability for the PROFIBUS ring in and out. The fiber ring helped during development and commissioning. Management did not wish to shut down processing so, when engineers commissioned a process, they simply unplugged the ring, plugged in the new process and re-made the ring connection.

Simocode Pro smart motor overload with PROFIBUS provided motor control, protection and key diagnostic, statistical and maintenance data. It also allowed remote configuration and eliminated the need for a controller to check initial rotation at commissioning. Managers reported that implementation of the entire refinery using this process "worked great!" 

Conclusion :
Besides many benefits in achieving better process control, better products quality, higher energy efficiency etc. PROFIBUS also helped significantly to perform installation and start up of the plant in a very smooth way.