1. About the field control bus
Fieldbus is a computer local area network in the field of automatic control. It is applied in the production site to realize two-way, serial, and multi-node digital communication between microcomputer measurement and control equipment. It is an open, digital, and multi-point communication underlying control network.
Fieldbus has a high measurement and control capability index
· Thanks to the microcomputerization of the instrument;
· Thanks to the communication function of the device
Technical characteristics of fieldbus
1. Adopt intelligent field equipment to realize complete decentralized control;
2. Using digital signals instead of analog signals can realize the transmission of multiple signals on a pair of cables;
3. Openness;
4. Interoperability and interoperability;
5. Intelligent and functional autonomy of field equipment;
6. Highly decentralized system structure;
7. It can adapt to the harsh on-site environment.
Advantages of Fieldbus
· Save hardware quantity and investment;
· Save installation costs;
· Save maintenance costs;
· Users have a high degree of initiative in system integration;
· Improve system accuracy and reliability.
The Role of Field Control Bus in Building Networks
The field control bus is the communication network of the field control level of the building automation system, and it is the basis for realizing data sharing and communication between the underlying control devices. The field control bus technology improves the reliability of the system, shortens the response time, and reduces the computing load of the upper computer, which is the guarantee for the performance improvement of the entire control system.
2. About the LON bus
1. The basic concept of LON bus
LON: The full name is Local Operating Networks, that is, local operating network. Launched by Echelon Corporation of the United States, it is one of the most popular field buses at present.
LonWorks: It is a complete set of development platform developed by Echelon Company to support the design of LON bus.
LonTalk: It is an open communication protocol used in LonWorks, and its biggest feature is the full support for the ISO/OSI seven-layer reference model.
LonMark: It is a LonWorks user standardization organization that has nothing to do with Echelon. LonWorks products designed according to the LonMark design specification can be easily integrated.
2. Neuron chip
The neuron chip (neuron chip) is the core of LonWorks technology. It is not only the communication processor of the LON bus, but also can be used as a general-purpose processor for acquisition and control. In fact, all network operations in LonWorks technology are carried out through it. Completed.
A neuron chip has three unit processors. One for link layer control (MAC processor); one for network layer control (network processor); the other for user applications (application processor). In addition, it also includes 11 I/O ports, so that the network and control functions can be completed on one neuron chip.
3. Composition of LonWorks technology
· LonWorks nodes and routers
· LonTalk protocol
· LonWorks Transceiver
· LonWorks network and node development tools
4. LonWorks node
LonWorks nodes include: application CPU, I/O processing unit, communication processor, transceiver and power supply
The composition form of the two nodes of LonWorks:
1) Control node with neuron chip as the core: a neuron chip almost contains most of the functional modules of a field node - application CPU, I/O processing unit, communication processor, therefore, a neuron chip plus The transceiver can constitute a typical field control node.
2) Control nodes using MIP (Host Base) structure: For some complex controls, neuron chips can be used as communication coprocessors, and advanced host resources can be used to complete complex measurement and control functions, thereby improving the computing and control capabilities of nodes.
5. The role of routing equipment in LonWorks technology
It is precisely because of the use of routing equipment that the LON bus breaks through the limitations of traditional field buses—it is not limited by communication media, communication distance, and communication speed. In LonWorks technology, routing equipment includes the following types: repeaters, bridges, routers.
6. Basic elements of LonWorks control network
· Lon Network Server - LNS
· NSS network service server
· NSI web server interface
· LCA Object Server
· LCA data server
· Workstation communication interface (PCLTA, SLTA, etc.; LonMaker)
· Communication channel
· router
· Subnet
· Node
7. LonWorks technical features include
1) The functions of network and control can be completed on one neuron chip.
2) Support multiple communication media (twisted pair, power line, optical fiber, wireless, etc.), and their interconnection.
3) LonTalk supports the ISO/OSI seven-layer reference model and provides a network operating system solidified in the neuron chip.
4) Provide users with a complete development platform, including on-site debugging tool LonBuilder, protocol analysis tool, network development language Nenron C, etc.
5) Since it supports object-oriented programming (network variable NV), it is easy to realize network interoperability.
3. About the BACnet protocol
· B ACnet : Building automation control network data communication protocol (ie: A Date Communication Protocol for Building Automation and Control Networks, referred to as "BACnet protocol")
· Developed by the Standard Project Committee 135P (Stand Project Committee: SPC135P) organized by the American Society of Heating, Air Conditioning and Refrigeration Engineers (ASHRAE) over eight and a half years.
· The protocol is designed for heating, ventilation, air conditioning, and refrigeration control equipment, and also provides a basic principle for the integration of other building control systems (such as lighting, security, fire protection, etc.).
1. The background of the BACnet protocol
With the development of information technology and the entire information industry, the building automation system (BAS) is moving towards the direction of integration, intelligence and networking.
The field bus only defines the field control level network of the building automation system, and the standardization process of the building automation system network is not satisfied with the openness and standardization of the field control level network, but further pursues the standardization of the overall communication solution.
For a long time, the different proprietary protocols of many manufacturers have hindered the development of BAS systems. A system that is not open and interoperable brings inconvenience to the operation, maintenance and upgrading of the system. Therefore, users expect that products from different manufacturers can use the same standard communication language to achieve interoperability and openness.
Affected by the energy crisis in the 1970s, in the building automation system, the air conditioning and heating and cooling system (HVAC&R) was the first to realize the importance of open standards.
In 1987, a roundtable conference on "standardized energy management system protocol" composed of experts in the field of building automation was held in New York, USA. The meeting decided to formulate a standard building automation network data communication protocol funded by ASHRAE.
2. Basic goals of BACnet
By defining the standard communication protocol of the workstation-level communication network, the proprietary gateways between workstations of different manufacturers are eliminated, and products of different manufacturers and functions are integrated in one system, and the interoperability of equipment from various manufacturers is realized, so as to realize the whole building Standardization and openness of the control system.
3. BACnet development process
♦1987.1 ASHRAE initiated the establishment of the SPC135p Committee-Standard Project Committee 135p
♦1991.8 The first draft standard for public review
♦1994.3 The second public review draft standard
♦1995.3 The third public review draft standard
♦1995.6 officially became the ASHRAE standard
♦1995.12 Approved as American National Standard and officially named as ANSI/ASHRAE 135-1995 standard
♦2002.1 Officially released the new version of ANSI/ASHRAE 135-2001 standard
♦2003.1.18 became the official standard ISO16484-5 of ISO
4. Organization of BACnet
BMA --- BACnet Manufacturers Association
A non-profit academic organization dedicated to promoting the opening of building control systems, promoting the successful application of BACnet in building control systems through interoperability experiments, teaching media and rewarding activities.
BTL --- BACnet Test Lab
Responsible for testing whether the products meet the requirements of BTL based on ASHRAE standards, only products that meet BTL requirements can enter the BTL list, and release products that meet BACnet standards to the industry.
A related standard of BACnet -- "ASHRAE 135.1P BACnet Conformance Test Method" is authorized by this institution.
5. Basic principles of BACnet
BACnet is a data communication protocol standard applied in the field of building automation, which is jointly reached by a number of building automation system product suppliers.
The BACnet protocol provides a method for building automation systems to achieve interoperability, expounds in detail the functions of the building automation network system, and clarifies how the system components share data, what functions can be used, information formats, communication media, etc. rule.
6. BACnet's building equipment representation method -- "object"
·The object is the modeling and abstract description of the building automation equipment.
·BACnet object is a collection of different properties (Property), which is essentially a data structure composed of data items.
·The attribute of the object is the reflection of the external characteristics shown in the interoperability process of the building automation equipment.
7. BACnet standard objects
The standard object is the most commonly used object defined by BACnet, and it is the basic element that represents the specific building automation equipment.
The actual specific building automation equipment can be "mapped" as a combination of different BACnet standard object instances.
BACnet defined 18 standard objects in the first official version in 1995.
8. BACnet standard object types and application examples
9. BACnet architecture diagram
10. BACnet application layer service "Service"
· In the building automation network environment, "object" is an abstract interoperable interface, and the interoperability between building equipment can be regarded as the information exchange between BACnet objects.
· The access to the BACnet object must define the "command" or "message" of the operation, and this "command" or "message" is defined as "service".
· Through "service", BACnet device can read/write the data of another device, or command another device to perform certain operations.
11. BACnet application layer service
BACnet defined 35 "services" in the first official version in 1995, divided into 6 functional groups:
(1) Object Access Services group (Object Access Services);
(2) Remote Device Management Services group (Remote Device Management Services);
(3) File Access Services group (File Access Services);
(4) Safety Services group (Safety Services);
(5) Alarm and Event Services Group (Alarm and Event Services);
(6) Virtual Terminal Services group (Virtual Terminal Services).
12. BACnet network layer
The BACnet network layer is located above a variety of LAN technologies, and its function is to shield the differences of different LANs and provide a unified "view" to the application layer.
The interconnection devices of the BACnet network layer include BACnet routers and semi-routers, whose function is to connect the BACnet network to form a BACnet interconnection network.
13. BACnet LAN
· The role of the BACnet LAN is to transmit BACnet service data units.
· The BACnet standard defines four local area networks and one remote connection technology based on cost performance.
14. BACnet supports multiple data link layer protocols
15. Summary of BACnet standard
In summary, the BACnet standard can be summarized as the following equation:
BACnet standard = object model + application layer service + network layer + various local area networks
16. Features of BACnet
· Dedicated to building automation network
· Completely open, advanced technology
Accepted as a standard by many standard organizations, with extensive authority
· Does not depend on existing LAN or WAN technology, has good interconnection characteristics
· Good scalability
· Good scalability
4. KNX bus standard
· EIB (European installation bus), as the first open standard specially applied in the fields of electrical installation, house automation and security systems, has been used in functional buildings such as venue lighting, smart home, and large-scale electrical control at home and abroad in recent years great success. But the promotion of EIB as a standard in general civil construction, HVAC and security technology has not been successful.
· The KNX bus standard is based on the EIB standard and is formed by combining the configuration mechanism and physical media of the other two famous European bus standards BatiBUS and EHS.
1. KNX structure model
2. The relationship between KNX and LON, BACnet, Ethernet
5. Gateway technology
·From the perspective of general communication principles, a gateway, also known as an Internet connector or a protocol converter, is the primary means to realize the interconnection of different protocol networks.
·In the building automation system, we collectively refer to all interconnected devices or standards that implement different protocol systems as gateways (bottom device gateways, management integration gateways, etc.).
6. OPC Standard
· OPC is the abbreviation of OLE for Process Control in English, which means object embedding technology in process control, and is an industrial technical specification and standard.
The OPC standard is developed by developers on the basis of Windows' Object Linking and Embedding (OLE, Object Linking and Embedding), Component Object Model (COM, Component Object Model), and Distributed Component Object Model (DCOM, Distributed Component Object Model) technologies And got it.
OPC provides a convenient solution to system integration problems. In this solution, including OPC server and OPC client. The OPC server generally does not know its clients, and the OPC client connects or disconnects the link with the OPC server as needed. The role of OPC is to provide a unified and standard interface specification for the server/client link. According to this unified specification, each server/client can form a link mode as shown in figure (b). A plug-and-play simple and standardized link relationship is formed between each client/server. Compared with the situation in (a), it is obviously simplified a lot.
1. OPC mode link indication
2. The role of OPC
· Hardware manufacturers only need to write a set of drivers to meet the needs of different users.
· Application developers only need to write an interface to connect different devices.
· Software developers do not need to repeatedly write a large number of device drivers.
· Engineers have more choices in equipment selection.
3. C/S structure and B/S structure
C/S (Client/Server) is the client/server structure. In this structure, the client needs to install dedicated client software.
B/S (Browser/Server) is the browser/server structure. This structure is a new type of structure produced with the rise of Internet technology, and it is an improvement of the C/S structure.
4. Comparison of C/S and B/S structures
Service range: C/S is suitable for small LAN, B/S is suitable for Intranet or Internet.
Client: C/S needs to install client software, B/S does not.
Security: C/S is strong, B/S is weak.
Program structure: C/S is relatively closed, and B/S is open.
Software reusability: C/S is poor, B/S is strong.
System maintenance: C/S is difficult, B/S is simple.