On the weak School】 【building automation system structure --- Power By 【China】 weak home network..

<br> Abstract: This paper analyzes the basic model building automation, component, control structure and classification, and introduces direct digital control (DDC) of the development process and the status of DDC building automation system in the way of introduction and configuration .evaluation, building automation system (BAS) as a necessary component of intelligent buildings, more and more widely appreciated, for the building automation system function and composition of most of the industry is very clear, but go into the development process from the building automation and why .using such a model might not be all of them have been carefully analyzed. .Building automation system and other control systems, automatic control system to follow the principle: the "decentralized control, centralized management, independent work," not for the building automation system, this comprehensive discussion, but in accordance with the principle of automatic control system for a few key issues .step of the deep. .1. The level of building automation systems Most of the building automation system is the use of three-tier structure. .The first layer is the central control management, and central monitoring and management by computer system software and associated communications equipment components. .It should be noted that most building automation software is divided into two parts upper. .Part is set and programming software, and more prepared for the firms themselves; another part of the monitoring software, often referred to as SCADA. .Some is used in building automation manufacturers developed their own SCADA, some using common SCADA. .Generally targeted special SCADA, simple, but relatively simple function, processing capacity and weak secondary development, compatibility is not strong, difficult to upgrade. .As an independent software products, general industry and construction have SCADA in a large number of applications. .Mature, stable, powerful, fast track, you can always replace, but the price is relatively high. .Building Automation System field of the second layer is the direct digital control (DDC). .The third layer is the on-site sensors, transmitters and actuators. .Some building automation system uses a two-tier structure, both the first and second floors will be combined. .This form prevalent in the field bus network using token ring structure, central monitoring and management computer and the DDC is the same as the node processing, information transfer is just a transit station. .Using this model the reliability of data transmission is relatively high, mainly because you can two-way transmission, communications line on the circuit can be re-routed, it is redundancy. .But the biggest problem is the communication efficiency is low, slow, especially true for large systems. .There is also a two-layer structure is not DDC model, the following will be introduced. .In the process of development of building automation is also the structure of the system, there have been four in the first layer of the central management and DDC control adds a layer between the gateway layer. .This is due to the field bus communication protocol is not perfect, DDC can not point to point communication between the (Peer To Peer), must transit through the gateway. .In theory, the way in which the most dangerous part of the gateway, any communication must be done through it, so if there are problems caused by system failures may cause a significant loss. .Therefore, the majority of IPC gateways or embedded systems to manufacturing, to improve reliability, so the current structure becomes less and less. .2. Building automation system control mode control mode is the most building automation system changes, with the development of science and technology building automation system control models have been improved gradually from a centralized control system into the distributed control system, but the process is also .are experiencing different stages, one by one in the following analysis: whether the initial industrial automation or building automation are based on centralized control approach, mainly because of time restrictions on computer and communications technology, the controller is difficult to miniaturization, mutual .there are technical difficulties in communications and collaboration, so the controller can only use a large, all the sensors, transmitters and other input signals, all received the central controller, the output control signals sent from the controller. .Can see that this model is very flexible routing heavy workload, long lines, signal loss and interference than the larger, part of the primary control system. .With the development of computer technology, SBC or the single chip computing capacity has been significantly improved, DDC Direct Digital Controller can do is relatively small. .As processing power increased, DDC and the host computer's communication capabilities have greatly improved, there is a relatively large DDC by the composition of the control system, which we call semi-decentralized control system. .This system has a certain dispersion, construction, management and control more convenient, but the size of the controller and the controlled equipment or do not match the demand, in most cases is still the next one controller to control multiple devices, cabling, or the amount of .larger configuration is more difficult, very difficult to achieve direct control, is still not an ideal control mode. .Is currently used more widely distributed in the building control systems, controllers and controlled devices according to the control points need functional requirements and different controllers of different sizes, so that device configuration is more reasonable. .The best configuration of which is: a device used to control a DDC controller, or a group of related functions of the device by a management and DDC control (such as: chillers, cooling water pumps, chilled water pumps and cooling .towers and other equipment with a set of interrelated functions.) .Such a model the main control functions can be done independently on the DDC, fast response, high reliability, with little or rely on the network does not rely on complete control. .As a result of one to one control, the controller can be placed next to the controlled device, the smaller the amount of wiring, commissioning and maintenance are relatively easy. .But so far, most types of DDC building automation manufacturers are not more difficult to do one to one control. .But the pursuit of this effect is a lot of design institutes and engineering company's goal, and sometimes this will waste some of DDC monitoring points. .Because it both for the future implementation of the project management process or the owners have a significant benefit in the long run this is a good control mode. .It should be noted there is a phenomenon in the country is extensive use in the control system expansion modules. .For a controlled device is concerned, if the DDC is not enough capacity, appropriate to increase the expansion board.