Yet Still Gives Modbus Its Due

The Rolling Stones or the Beatles? Mac computer or PC? Ford or Chevy? No matter the topic or industry, it seems there’s always a “who’s better” competition.

When it comes to industrial and commercial facilities automation communication protocols, the comparison is often “BACnet or Modbus: Which is better?”

Definition of BACnet and Modbus

Before igniting a debate or launching into a comparison, let’s start by talking about what BACnet and Modbus are – and are not.

At their core, BACnet and Modbus are the names of two open protocols.

BACnet stands for building automation and control (BAC) networks. It was developed and is maintained by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) and published in 1995. Designed for cross-communication, it enables devices to “talk” with one another.

Modbus® is an older protocol that was introduced in 1979 by Schneider Electric, then known as Modicon. Modbus is a forerunner of programmable logic controllers (PLCs).

Primary Way BACnet and Modbus Are Similar – and Different

Both BACnet and Modbus are open, interoperability/communication protocols, which means they are:

• Standard
• Independent of any manufacturer
• Support information sharing
• Work among a wide variety systems, such as controllers, sensors, devices, and interfaces, as well as a range of vendor, including Allen-Bradley and Siemens.

Although there are many differences between these protocols, the main differentiator is in how they’re used and how they respond. BACnet networks can be discovered very easily by a device. In addition, when a simple “who is” message is sent on to the network, all BACnet discovered devices respond with what they (the devices) are and what data points are available.

Modbus delivers a single data point and nothing else. Because it is such a basic response due to the lack of overhead data, the response is very quick. Modbus developer Schneider Electric explains that Modbus is rooted in a “master/slave principle … the master sends a request and the addressed slave sends back a response.”¹  In other words, think of it as “one and done” for each request.

6 Ways BACnet Is Better Than Modbus

While it’s true that Modbus currently has a very large installation base, in this case, bigger doesn’t not mean better. Yes, Modbus came before BACnet, making it an “OG” or original protocol.

However, Modbus has changed very little in comparison to BACnet in the 40+ years since its launch. Originally designed for industrial applications, Modbus has spread to other applications, including building automation. Unlike BACnet, however, it has yet to keep pace with digital advancements and modern-day connectivity.

Here are six essential ways BACnet outperforms Modbus in an ever-connected world.

1. Intelligent

BACnet provides lots of metadata, ranging from trends, configurations, input and output, data values, schedule information, alarms, and event logs. Modbus, on the other hand, provides only a single data set.

Here’s an example of how BACnet differs from Modbus with respect to polling for a temperature reading:

Modbus will answer with the exact temperature, say, 70ºF, and nothing else.

BACnet, on the other hand, will answer with the temperature, the device location, when the software update is due, and much more – plenty of relevant metadata to help you make important decisions.

2. Plays Well With Others

BACnet’s widespread interoperability capabilities means it can be applied to pretty much any type of available system and across thousands of devices from a wide variety of vendors. BACnet was intentionally designed for true interoperability, meaning that every object and every property – no matter what it is – is accessed exactly the same.

BACnet is highly compatible with routers with BBMD, automatically retrieving information from one subnet to another. Modbus, however, requires manual IT intervention to set up network routers.

3. Assured Conformance

BACnet uses testing authorities, namely BTL – BACnet Test Laboratories, to ensure that what you want to support is tested and works with BACnet. While Modbus does have a certification process, the majority of installations have not gone through it. That means Modbus is “self-certified.”

With BACnet, you can be sure that 99.99% of the time, your protocol is certified and signed off on. In addition, BACnet has plug fests in which suppliers can test their products with other suppliers.

4. Network Commissioning

System integrators find it very easy to commission BACnet networks due to the discovery of devices and their objects list (points list). This makes BACnet a lot quicker when connecting data points to graphics and automation systems.

5. Multiple Applications

BACnet supports all types of organizations and systems, ranging from HVAC to lighting to access, fire, security, and more. BACnet International is constantly releasing new BACnet objects to keep up with vertical markets such as Life Safety, which ensures that the data has relevant meaning and priority on networks.

6. Future-Proof Investment

BACnet is continually being enhanced and extended. Recently, ASHRAE introduced a new proposal for best practice secure communication. BACnet Secure Connect, or BACnet/SC, helps create secure connections between devices, the cloud, and within facilities.

BACnet/SC is designed to ensure network and information security and infrastructure integrity. It provides a secure means so that every device is authenticated and authorized to use the network.

MSA FieldServer BACnet

Although Modbus is known for fast implementation, BACnet is fast-becoming the go-to solution for users and suppliers in Building Automation. In fact, upwards of 64% of all users and suppliers are adopting it – and that percentage is growing.²

For those looking to adopt or switch to BACnet, the MSA FieldServer BACnet IoT gateway lets you connect and create a smarter facility. Plus, it deploys rapidly – in just an hour.

So, whether you’re working with HVAC units, boilers, chillers, lighting systems, fire panels, or something else as part of a connected system, MSA BACnet gateways are a powerful solution. MSA BACnet gateways let you get the data you need to monitor and control equipment, and make informed decisions about your systems so you can save thousands on energy costs.

Contact your local MSA representative using the form below to learn more about BACnet for your systems, including:

• Heating
• Cooling
• Fire, Life & Safety
• Energy Management
• Lighting Control
• Security

¹ https://www.se.com/us/en/product-range/574-modbus/#overview

² BACnet International, “BACnet Adoption Market Research Report,” April 2018.