Fieldbus control standard

More microprocessor-based process equipment, such as smart instruments and single-loop controllers, with digital communications capability are now becoming available and are used extensively in process plants. A fieldbus, which is a low-cost protocol, is necessary to perform efficient communication between the DCS and these devices. So-called mini-MAP architec ture was developed to satisfy process control and instrumentation requirements while incorporating existing ISA standards. It is intended to improve access time while... 

System installation in a permanent location may require a sample conditioning system featuring some degree of automation, such as automatic cleaning (the system illustrated above features such a system) and outlier sample collection and the need to interface to an existing control system process computer. The latter may require that the system operates with a standardized communications protocol, such as Modbus, for the chemical industry. Certain specialized industries use different protocols, such as the semiconductor industry, which uses SECS and SEC-11 protocols. A standardized approach designated the Universal Fieldbus is another method/protocol for process analyzers which is being supported by certain hardware manufacturers. 

The high-performance, all-digital, multidrop communication protocol for use in the process-control industry is known as fieldbus. Presently there are several regional and industry-based fieldbus standards including the French standard, FIP (NFC 4660x approved by UTE), the German standard, Profibus (DIN 19245 approved by DKE), and proprietary standards by DCS vendors. As of 1997, none of these fieldbus standards have been adopted by international standards organizations. 

ANSI/ISA-50. Fieldbus Standard for Use in Industrial Control Systems. Multiple part standard. ANSI/ISA. 

The electronic equipment and systems technology available for process control continues to evolve rapidly. Because of the pace of innovation, industry-wide standards have not been able to keep up consequently different manufacturers systems usually use proprietary technology and are often not fully compatible with each other. The implementation of the ISA SP50 Fieldbus standard is expected to substantially... 

Many control systems fail to integrate Fieldbus instruments properly and cannot support the required data structures at all levels in the system. The modern OCS must be able to communicate with the intelligent instruments using whatever physical medium and protocol that the standard dictates, and the structure of the OCS must be able to pass the secondary attributes of the instrument to wherever the relevant software resides. This must be achieved without disrupting the real-time communications of the system and without corrupting the data structure which both the instrument and the associated software understands. 

In the Fieldbus example, the Asset Management System converts the standard Fieldbus descriptor (in device descriptor language [DLL]) to a D-COM object. This is then passed to OCS where it is converted from D-COM into the OCS s own object model. This is so that the relevant parts of the Fieldbus device descriptor can be distributed to the various OCS nodes for display, trending, alarm purposes and so on. The OCS then uses its OMM to transfer the data to the OCS controller, where it is again converted to DLL format prior to sending across the Fieldbus link to the intelligent instrument. 

Where the OCS has a standard interface to a particular Fieldbus and the number of installations is such that this can be deemed as standard feature, there is little need for software module testing. This is true of any Fieldbus interface to any control system. In a traditional scenario, where data need to be transferred via the OCS to a maintenance application or a laboratory analysis package, the actual transfer of the data needs to be fully tested as a bespoke application. 

For safety instmmentation functions, fieldbus systems pass beta testing. (Prototype designed product tested at customer site for evaluation of the product.) Also, safe fieldbus systems are required to meet the lEC 61508 standard for functional safety systems for specified SIL so that suppliers can build their systems on the same. Also, protocols are subject to diird-party approval for safety applications. There are a number of fieldbus systems recognized in the world. Also, there are other system integration tools and protocols such OPC and HART, respectively. HART is a protocol, while OPC is a standard described in brief in Fig. IX/2.0.2-1. Now, initially each of them has their own ways and means to communications in intelligent way. There are some similarities in their network protocol but there was no common platform. These made it rather difficult to integrate various control systems, which is of tremendous demand not only from technological point of view but also from economical point of view. In 2003, major players in fieldbus systems joined hands and... 

Common BPCS and SIS are combined in the process control system, using common hardware (controller, fieldbus, I/O). However, standard and safety-related programs are executed in parallel and independent of each other. 

Safety-related controllers in conjunction with safety or fail safe I/O modules are used for critical and hazardous applications where an incident can result in danger to persons, and/or damage to plant and environment. These safety-related controllers can work with the safety-related distributed I/O system (may be with internal verification for input or output via safety switches as described in Clause 5.0.1—safe PLC approach), or directly with fail-safe transmitters cormected via the fieldbus. These controllers are supposed to detect faults both in the process and their own internal (self-diagnosis) to the system. It is the duty of the same to automatically set the plant to a safe state in the event of a fault. These controllers need to work in multitasking environment — may be in a mix of standard BPCS or safety-related applications, if integrated operation is permitted by the end-user. The programs of BPCS and SIS must be functionally separate, so that faults in BPCS applications have no effect on safety-related applications and vice versa. Special tasks with very short response times can also be implemented [14]. For safety applications controllers and I/O modules need to individually certified by third party and to comply SIL 2/SIL 3 (as the case may be — SIL 4 only for nuclear application) as per lEC 61508. For safety-related applications a few restrictions are followed such as ... 

Digital data communication systems have existed for nearly 40 years, ranging from straightforward serial communications represented by the RS 232 standard common on personal computer serial output ports, to more modern local area networks such as Ethernet. In recent years, much effort has been put into the development of fieldbus systems that allow controllers, sensors and actuators to be implemented in modular and distributed formats. Whereas the developments in fieldbus systems have been mainly targeted at the process industries, the devices are finding increasing application in the machinery sector. 

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