BTL Mark: Resolve interoperability issues & increase buyer confidence
KYZ, 4-20mA, AI, DO, Modbus, BACNet, LONWORKS, SMTP client, Web server, DHCP, HTTP, FTP, CSV, XML, XSL, 10BaseT, RS-485, TCP/IP, ODBC…….
Confused by this alphabet salad?
This series of articles will explain gateway features and provide a basic understanding of what is important in the "alphabet salad" above.
Part 1: How Are They Used to Provide Real Savings
Part 2: Connecting a Gateway to the Software Application
Web enabled gateway capabilities and benefits, as well as the communications and software that is required to provide value when implementing a gateway-based system will be clarified.
What is a gateway?
Although a basic description is, "A device that allows you to access building information and transfer the information to another device or system", this description falls far short of the capabilities of modern gateways.
Modern gateways include a variety of features in order to fulfill the basic description above. Although the features should serve the functionality required by the gateway, often gateways are rich with unnecessary features as a result of the underlying components that are used. Although a rich feature set is attractive, identifying the feature benefits and the associated costs in performance and implementation can be challenging.
Understanding how gateways work and how they interact with other parts of a solution enables avoiding the pitfalls and completing a gateway project that meets your specific requirements. These articles will help you understand gateways so that you can identify the benefits they can bring to you.
Connecting to buildings
According to the simple definition above, one of the two functions of a gateway is to connect to devices that provide information about the building operation. How this is done falls into the categories of connecting to sensors or to DDC/BAS/EMS systems. (DDC - Direct Digital Control, BAS - Building Automation System, EMS - Energy Management System)
In addition to inputs, some gateways also provide outputs that can be used to control building devices or act as inputs to the DDC/BAS/EMS system.
Connecting to sensors includes using gateway pulse inputs to count pulses from pulse enabled meters, and using analog inputs to connect to sensors such as flow meters and temperature sensors. Serial connections are used to connect to intelligent devices such as smart meters, controllers and flow computers. Serial connections use RS-485 for multipoint networks or RS-232 for direct point-to-point connections. Protocols such as MODBUS are used "on top of" these serial connections. (A "protocol" describes how the devices speak to one another as well as the meaning of the individual data that is communicated.)
DDC/BAS/EMS system connections can be divided into non-proprietary protocols such as LONWORKS, BACNet and OPC, and proprietary protocols such as those by Johnson Controls, Novar Controls etc. In general, proprietary protocols are used only by a single manufacturer and in many cases; the details of the protocol are not available. The actual physical connections depend on the protocol and can range from RS-485, RS-232, and Ethernet 10BaseT to special purpose hardware that implements a particular communications network.
Non-proprietary protocols are becoming popular in modern DDC/BAS/EMS systems, and in some cases such as BACNet, where the protocol supports Internet communications, a gateway may not be needed.
The majority of installed systems use proprietary communications protocols. In these cases, gateways perform a valuable service in connecting legacy systems to server-based applications and to equipment from multiple manufacturers thereby preserving the investment in the legacy system.
In order to connect to proprietary systems, gateway manufacturers implement communications drivers with, but often without, the cooperation of the original equipment manufacturer. This can result in partial protocol implementations that can limit the types of data available and the equipment models that are supported. In selecting a gateway for this purpose, the protocol feature set required, and equipment models supported, should be clearly established.
In terms of the amount of information available, communication protocol based systems can provide enormous amounts of information over a few wires as compared to individual sensors that require wiring and an input or output for each signal.
The other device or system
In our simple definition above, the second function is to transfer the building information to another device or system, and sometimes in addition, provide information to the building device or system.
What are these "other devices and systems"?
In some cases, gateways are used to translate between DDC/BAS/EMS systems that cannot communicate directly due to hardware incompatibility or in most cases due to the lack of a common communications protocol.
Today, the most common use of gateways is to communicate building information to remote server applications by making use of prevalent, low cost Web and Internet Technologies. This brings significant benefits in allowing centralized management of remote sites and making integrated information available to all levels in an organization, at costs that are a fraction of the cost of DDC/BAS/EMS operator stations.
Examples of server applications include:
Remote operations management
Operations and energy reporting
Billing and sub metering
Measurement and verification
Gateway communication with servers or software applications
As the computers that run applications are typically not located at the gateway, some sort of communications infrastructure is required. In implementing a gateway system, careful attention is required in choosing the means of communication. Although some communications options are almost free of ongoing costs, other options can incur significant monthly and capital costs. These costs can swamp the expected savings, or in some wireless applications, data packet based pricing can severely limit the amount of information transferred, making the gateway only effective as part of an alarm reporting solution.
To minimize communications costs, understanding the information transfer requirements and available infrastructure is required.
Information transfer requirements are defined by answering these questions:
How much and how often do you need information from the gateways?
Continuously or periodically? If periodically, how often?
Are there particular times when information is required? Is event-based information required, for instance when an alarm occurs?
Where can the gateways and servers be located? Will users outside corporate firewalls require access?
The available infrastructure can sometimes provide no cost or low cost communications, especially if the Internet is used.
Questions to ask about available infrastructure:
Is there a corporate network, and if so, are there connection points available at the planned server and gateway locations?
Are there limitations on network use?
Are there times where bandwidth is unavailable?
Are static (fixed) IP addresses available or is only dynamic (DHCP) IP addressing available?
Is there a cost in using the network, and if so, how is it priced?
Are there restrictions on the TCP/IP ports and protocols that may be used?
If there is no corporate network, do the sites have an Internet connection via Broadband or DSL?
Is there an existing telephone line that can be shared?
Answers to the above questions can have a direct bearing on the equipment selected as well as on the usefulness of the system and the expected savings. Typical answers and their ramifications will be explored in the next article of this series.
BostonBase Inc specializes in products and solutions that are designed to provide information and control systems, which provide energy and operations savings by taking advantage of modern low cost web technology and communications.
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