Foundations May 2016

Page 9


Passenger and equipment safety on the Barrakka Lift in Malta is controlled with wind speed and light sensors incorporated into the elevator system. If there is a high wind event the lift will slow down or stop to ensure passenger comfort and safety. The system will also turn on elevator lighting after dark or during weather events. Other applications include automated monitoring of membrane roofs in agricultural and other systems, fountain controls, awning control systems, and more. With BACnet there are many opportunities for managing the relationship between the outdoor environment and building systems that can improve energy efficiency, occupant comfort, and safety. ABOUT THE AUTHOR Andrew White is the President of Comptus. The company works closely with a wide range of customers from large automation product manufacturers, to engineering firms, government and municipal agencies, contractors, distributors and end users. Comptus products are deployed on all seven continents and in addition to the building automation industry are used in environmental research, renewable energy, fountain and other markets.

BACnet and Numbers By Bennet Levine

R&D Manager, Contemporary Controls


ACnet can be a little confusing when it comes to its numbers. There are MS/TP MAC address numbers, BACnet/IP IP address numbers, device instance numbers, network numbers, etc.

In some cases these numbers must be unique. In some cases these numbers should be the same. Here we will outline the rules for some of the more obscure BACnet numbers and why BACnet has these requirements. I think most people understand IP address numbers. IP addresses and their rules are fairly well understood and there are many sources to explain these rules. MS/TP MAC addresses are also fairly simple; addresses range from 0 to 127 (for master devices) and must be unique on the MS/TP network. However if you have multiple MS/TP networks, which are not directly connected, each network can use the same set of MAC addresses, for example MS/TP network 1 can have MACs 0, 1, 2, and 3. On MS/TP network 2 you can also have MACs 0, 1, 2, and 3 (see figure 1). This is not an issue as the two networks will also have a network number to help distinguish the full identity of the device. For example on network 1 we have MAC 0. To talk to this device you would talk to network 1/MAC 0. To talk to MAC 0 on network 2 you would use network 2/MAC 0.

Figure 1: Two MS/TP networks connected to one head-end through two BACnet routers

Device instances are another set of numbers which can seem a little superfluous as each device has its own network address such as a MAC address or IP address, etc. However, the device instance is used as a way to uniquely identify


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