We know that a field bus must meet certain special features, such as flexibility, resistance to electromagnetic interference, ease of installation, maintenance and programming. Its main advantages over the conventional technique of wiring to a central control are:
- Easy and fewer cables.
- Short routes to critics like analog signals.
- Easy installation.
- Easy to implement changes.
- Ease of expansion.
- Ease of maintenance.
- Reduction of interfaces and terminals.
- Lower cost per mounting supplies (gutters, pipes, conduit, etc.)..
- High speed signal processing.
- High reliability of operation.
Current efforts are focused on automation of complex troubleshooting and this usually means greater use of user programs, lower reaction times and processing: an increasing number of inputs and outputs. Cost comparison studies have shown that the installation of a fieldbus system can represent savings of up to 35% over a centralized system.
Different field buses in a distributed control
When considering the implementation of a distributed systems solution must distinguish the following possibilities:
- DECENTRALIZED CONTROL
This name is a direct connection to I / O modules, signal inputs and outputs close to the process or machine control. The stations I / O are connected via the fieldbus system of central control.
"Instead of wiring voluinitioso select decentralized control."
In designing an automated installation, the modules or cards I / O automata are usually placed in the center. This requires that each field device, such as sensors, transmitters, measurement and actuators connected via cable 2 or 4 wire to entry or departure for him in those modules or cards.
This form of wiring can become very large and little clear. Also, would generally be mounted mechanical support structures such as ducts, conduits, etc.. On the other hand, electromagnetic interference seriously affect the reliability of the installation and long distances to save these solutions are economically viable conventional wiring.
In addition, the automation system is very expensive to maintain and drive to any extension or modification.
Therefore, to geographically dispersed facilities and a flexible structure, the ideal solution is the system of decentralized periphery.
Figure 3.3 Replacement of the bundle of cables (eg ASI).
- DISTRIBUTED CONTROL
Distributed control is called the allocation of tasks to multiple controllers (eg PLC) smaller installed at strategic locations in the plant. Instead of installing a central controller for high capacity, small drivers are nterconectados system via a fieldbus.
This solution has the following advantages:
Programming easier with smaller programs.
A more reliable basis of the structure of the system.
Easy to extend or modify the system.
Increased availability of information in the system due to the presence of autonomous controllers.
Very short reaction times, independent of the bus operation times.
... And what are the advantages of decentralized control?
Advantages of Distributed Control
- Reduced wiring costs.
- Reduce costs by decreasing the mounting hardware.
- Reduced maintenance costs.
- Calibration and remote diagnostics.
- Interoperability.
- Direct interface with open systems.
- High speed data processing,
- Behavior similar to that of centralized systems.
- Improvements in the quality of the final product.
- Ability to communicate at all levels of the plant.
... Now what considerations must take to integrate dispositíwos a fieldbus?
Well, this will answer the following article. Until next time.
