BACnet, KNX and LON are protocols for building automation that have been standardized in the European Community. LON has been approved as the Control Network Protocol (CNP). EN14908 Part 1 describes the protocol stack (ANSI/EIA-709) and provides information on how data is created and exchanged. Parts 2 and 3 define the transmission media, such as free-topology twisted pair, FT-10 and PL-10 power lines. Part 4 describes the communication method over IP (ANSI/EIA-852). Finally, Part 5 includes application guidelines for data exchange that comply with the LonMark functional specifications.
BACnet is based on client/server communication, including thirty types of objects, endowed with the necessary properties. Initially, the BACnet protocol developed from the upper level of automation and was associated with direct digital control technology (many data points, high performance). But increasingly, the BACnet protocol is used in automation and its components, in fact, not in such complex devices. BACnet protocol stacks are independent of hardware and can be used on any platform, providing significant performance.
The technical specification «Data Translation between LON and BACnet» was approved in 2005 as prCEN/TS15231 in committee CEN-TC-247 «Open Data Communication in Building Automation». This specification defines a mapping framework via gateways between network variables and BACnet objects. Each mapping of a BACnet object allows access to one network variable. The properties of the object include the information required for this purpose, such as the data address in the Object_Identifier. The data translation is implemented via the Present_Value property. In addition, the gateway generates typical BACnet information and converts it into Properties (e.g. Out_Of_Service). However, the consistency of the LonMark object is lost. And instead of event-based communication within LonWorks networks, data points are polled via the BACnet LON gateway. The gateway can only be configured after the LON network has been mapped and all addresses have been assigned.
Although communication is bidirectional, there is no provision for data conversion from BACnet to LON.
There is a clear lack of information and knowledge on the market today about the coexistence of LON and BACnet protocols. Data conversion enables synergies between the two protocols. This does not mean that one is better than the other or that one protocol has a future and the other does not. Rather, it is a matter of choice: how to correctly use open technologies and equipment in specifications. Understanding the methodology of open technologies for building automation is not yet widespread in the market and is mostly related to equipment manufacturers, designers and system integrators. Achieving greater results is the common goal of all three standards. Data conversion from LON to BACnet is precisely another very important practical step that contributes to achieving this goal.
The article was prepared using
materials from BACnet Europe Journal № 4,
04/06(BIG-EU). |
