Image Processing Reference
In-Depth Information
A data communication standard may be confined to physical characteristics, defining aspects like
the medium used or network topology. As a prime example for such a standard, EIA- is highly
popular for BA control networks. It provides the base for several open and seemingly countless
proprietary protocols.
While the protocol stack itself determines important characteristics (such as the available address
space or communication paradigms), standardized device profiles are equally essential for achieving
interoperability. For implementing devices and systems based on the standard, standard hardware
components and commissioning tools may be available. Other aspects of interest include which
kind of organization is responsible for development and maintenance of the standard and potential
compliance certification procedures.
In the following, a number of open data communication standards that are relevant in the field of
building automation are introduced. BACnet, LonWorks, and KNX have achieved considerable sig-
nificance in the worldwide market (in case of BACnet and LonWorks) or in the European market (in
the case of KNX) and are often chosen by both customers and system integrators for complete system
solutions. While no such discussion would be complete without mentioning them, a couple of other
standards, both established and new, further contribute to the picture and will be covered as well.
29.5.1 Plant Room and Field Level Subsystems
For communication with plant controllers and certain complex field devices (such as variable
frequency drives for fans and pumps in particular), fieldbus protocols which are well established in
factory and process automation (e.g., Interbus, CAN-based protocols such as Devicenet or
CANOpen, and Profibus DP) are occasionally used in building automation as well. However, they
are very seldom used system-wide. A Profibus FMS profile for building automation existed but, like
Profibus FMS at large, has fallen from use entirely.
Although of similar heritage, Modbus has gained comparably significant acceptance in BA. It is
also sometimes used at the room level. Designed by Modicon for their PLCs and published in ,
it is now maintained by the user and manufacturer association Modbus-IDA. Implementation of the
Modbus protocol is license-free, which makes it especially interesting for integration and interfacing
between BAS and other systems. Not limited to the HVAC domain, Modbus is also present in systems
and devices belonging to other building disciplines, such as alarm systems.
The Modbus application layer is basically confined to reading and writing of Boolean and -bit
integer register values using a simple request/response protocol. his yields a high degree of flexibility
in integration, but causes high engineering effort for coordinating the remaining required semantics.
Modbus supports serial communication using a simple master-slave protocol over EIA-. A total
of different slaves can be addressed. he typical data rate is . bps. A mode of transmission
over TCP/IP is also defined, in which every node can be both client and server.
Another example for an EIA--based protocol with a similar focus is Johnson Controls' Metasys
N, which, despite being owned by a single manufacturer, also provides a certain degree of openness.
Open standards have also emerged for communication with very specific classes of BA field
devices. The current prime example is DALI (Digital Addressable Lighting Interface), published as
an IEC standard [] and widely accepted for lighting applications. DALI allows control of up to
(dimmable) electronic ballasts for fluorescent lamps and intends to replace the traditional - V
interface.
ADALI
loop
can contain up to individually addressable devices. Additionally, each device can
be a member of possible groups. Devices can store lighting levels for power-on, system failure and
scene values, plus fading times. here are also immediate commands (without store functionality)
and commands for status feedback (such as lamp status). Assignment of addresses, group member-
ship and scene values is possible via the bus. Loops can be up to m long, with free topology.
The data rate is bps using a master-slave-based, asynchronous protocol. Since biphase coding
