Override BACnet Input Objects

By Matt

Have you ever had an outside air temperature sensor fail, causing a building’s automation to go nuts? Instead of overriding the entire building, why not just override the sensor? Usually with building automation systems you have to explicitly program this functionality. This is an area where BACnet shines: the protocol was designed by ASHRAE with servicing parts in mind! Override…

BACnet Object Types

By Matt

The BACnet standard supports at least 18 different BACnet objects. ASHRAE will add new object types from time to time, but it’s rare to see these exotic object types in the field. The common objects provide intuitive access to building automation features. There is a loop object for PID loops, a calendar object for holidays and special events, and a…

MS/TP Capture Tool now Included with Wireshark!

By Matt

Wireshark is a fantastic tool for network diagnostics. It’s been the best tool for BACnet/IP network troubleshooting for years. It’s even been able to dissect MS/TP traffic dumps if you knew how and had the right tools. Well, those tools come standard now! Check out the new Wireshark BACnet MS/TP capture tool, included in 2.4.4 (and possibly earlier): You’ll have…

What Is BACnet?

By Matt

The Basics – What is BACnet? BACnet is a popular building automation protocol used worldwide to enable communication between devices in commercial automation systems. Industrial automation has historically used other protocols such as OPC and Modbus. BACnet standardizes communication across vendors and simplifies the integration process. The name BACnet stands for building automation and control network. It was created by…

Overview of Commercial Automation Protocols

By Matt

In automation there are several communication protocols. Some are entirely proprietary and others are open. Despite the friendliness of the word, “open” isn’t always good news. Some of the older proprietary protocols are easy to integrate with off the shelf integration products. Two versions of the same protocol often look different. It’s a zoo out there, so here’s an overview…

Add a Remote Device Without a BBMD

By Matt

You may encounter a situation where you must add a device on a different network. You may have no control of the BBMD configuration or you may have no BBMDs available due to poor device support. In these situations, you may have to add a remote device without a BBMD. It’s a handy trick, but not an ideal long-term situation.…

BACnet Broadcast Distribution Table Example

By Matt

Setting up a BBMD-connected network is a manual and somewhat arcane process. The broadcast distribution table is a list of the BBMDs on the network. Each BBMD on each network should have the same broadcast distribution table. Here’s a quick example of a BACnet broadcast distribution table (BDT) that might help clear things up. The Setup With the above illustration…

Example BACnet Network Number & Instance Number Convention

By Matt

When I assign a BACnet instance number or BACnet network number, I never use the defaults provided by whatever product I’m using. A few moments of thought about some kind of standard for your site can save you a lot of time down the road when you want to expand your system to include more devices. You don’t know quite…

When and Why Do We Need an End of Line Termination?

By Matt

End of Line Termination Concept Most of the buses we use are specified with end of line termination in mind. In the field these terminations are not always present, especially in short runs. Do we need them? Here’s an analogy I like that illustrates why we need end of line terminations: a bus behaves like a rope held between two…

What is a BACnet Instance Number?

By Matt

A BACnet Instance Number Is a Globally-unique Address An often misunderstood and neglected topic is the BACnet instance number of a BACnet device. Neglecting to think about this number at installation might not bite you today, but it remains as technical debt that complicates future work. It’s a number that identifies a device uniquely on the entire interconnected BACnet network.…