Most people have heard of fieldbus. However, not everyone understands it, such as why fieldbus has so many applications in daily life. This article aims to enhance understanding of fieldbus by introducing the advantages of fieldbus control systems and two important considerations for its application. If you are interested in fieldbus-related content, please continue reading.
I. Advantages of Fieldbus Control Systems
Fieldbus is an open digital communication technology developed in response to the development of intelligent field instruments. Its initial purpose was to replace one-to-one I/O connections with digital communication, extending digital communication networks to industrial process sites. According to the definitions of IEC and ISA, fieldbus is a digital, bidirectional, multi-branch communication network that connects intelligent field devices and automation systems. Its key characteristic is its ability to support bidirectional, multi-node, bus-based, fully digital communication.
With the development of fieldbus technology and the integration of intelligent instrument control (instrument calibration, control configuration, diagnostics, alarms, and recording), this open factory-level control network has constructed a new generation of network-integrated fully distributed computer control systems, namely the Fieldbus Control System (FCS). As a new generation control system, FCS adopts open and standardized communication technology, breaking through the limitations of DCS using dedicated communication networks; at the same time, it further transforms the "centralized" system structure in DCS, forming a fully distributed system architecture, and completely decentralizing control functions to the field.
1. Saves on hardware quantity and investment.
Because the intelligent devices distributed at the front end of the equipment in the fieldbus system can directly perform a variety of sensing, control, alarm and calculation functions, the number of transmitters can be reduced. There is no need for separate controllers, computing units, etc., nor for the signal conditioning, conversion and isolation technology and other functional units of the DCS system and their complex wiring. An industrial control PC can also be used as an operator station, thus saving a lot of hardware investment. Due to the reduction of control equipment, the floor space of the control room can also be reduced.
2. Saves on installation costs.
Wiring in a fieldbus system is very simple. Since multiple devices can typically be connected to a single twisted pair or cable, the amount of cables, terminals, cable trays, and conduits used is greatly reduced, as is the workload for wiring design and connector calibration. When adding field control devices, there is no need to install new cables; they can be connected to existing cables nearby, saving investment and reducing design and installation work. According to calculations from typical pilot projects, installation costs can be reduced by more than 60%.
3. Save on maintenance costs.
Because the field control equipment has self-diagnostic and simple fault handling capabilities, and transmits relevant diagnostic and maintenance information to the control room via digital communication, users can query the operation, diagnostic, and maintenance information of all equipment to analyze the cause of faults early and quickly resolve them. This shortens maintenance downtime, and the simplified system structure and wiring also reduce maintenance workload.
4. Users have a high degree of initiative in system integration.
Users can freely choose equipment from different manufacturers to integrate their systems. This avoids being "limited" by choosing a particular brand, and prevents them from being at a loss due to incompatible protocols and interfaces during system integration. It puts the initiative entirely in the hands of the user during the system integration process.
5. Improved the accuracy and reliability of the system.
Due to the intelligence and digitization of fieldbus devices, compared to analog signals, it fundamentally improves the accuracy of measurement and control and reduces transmission errors. Simultaneously, the simplified system structure, reduced equipment and wiring, and enhanced internal functionality of field instruments reduce signal round-trip transmission and improve system reliability. Furthermore, its standardized equipment and modular functions offer advantages such as simple design and ease of reconfiguration.
II. Precautions for Fieldbus Applications
1. High maintenance costs
If a traditional DCS system is replaced with a DCS system equipped with fieldbus technology, all field devices need to be replaced to adapt to the fieldbus requirements. The increased regulatory functions of these intelligent field devices will also increase their cost. Similarly, replacing even a single instrument during maintenance will incur significant expenses. To reduce these costs, it's essential to choose reputable manufacturers and use their equipment. If the equipment has good performance and strong environmental adaptability, it can also reduce production costs and improve equipment operating performance.
2. The protection design of the unit should be given priority consideration.
In power plants, the most important aspect of thermal control is the rigorous design of thermal protection. This is to prevent false trips while ensuring that the protection does not fail to trip. This requires a two-out-of-three requirement in the I/O cards and equipment of the control system. For example, in the design of the steam drum water level transmitter and the furnace negative pressure, the three devices in the field must be connected to three different I/O cards on the DCS. These three different I/O cards belong to different control stations, so that the protection will not trip due to the failure of a single device, I/O card, or control station.
Fieldbus should be given special consideration in this regard, because fieldbus deployment requires us to change this design, otherwise it will increase costs. For example, local devices need to complete the 2-out-of-3 function locally, and the signals need to reach the three control cabinets separately with three local buses. This undoubtedly increases the workload and costs. Only in this way can the field design requirements be met.
The above is the content related to "fieldbus" brought to you by the editor. Through this article, we hope that you will have a certain understanding of the advantages of fieldbus control systems and the precautions for fieldbus application.
