Where Modbus Still Make Sense

when to use Modbus

I’d be willing to bet that if I tried to pawn off my old Betamax recorder on you, you’d have no use for it. Same thing for my mom’s typewriter, my brother’s iPod – and who would ever want my 45-pound cathode ray tube monitor. This stuff is so old that even the landfill is hesitant about taking them.

I’d understand if you would want to put Modbus in that category, but I think you’d be wrong. The reason you’d be wrong is that the application matters. If you want to communicate motor drive data – speed, energy, fault codes and more – Modbus isn’t the best choice. EtherNet/IP, PROFINET IO, EtherCAT and all the rest move complicated data like that quickly and easily. Especially since data like what you get from a Motor Drive has to end up in a Programmable Controller, and controllers from the Allen-Bradleys and Siemens of the world don’t easily interact with Modbus devices.

There are many applications, though, that makes sense for Modbus. I visited a milk processing facility recently, and they have a perfect Modbus processing facility. The state where they are located is very strict about regulating the sanitary, environmental and quality controls in the facility; hence they are highly regulated. The state has tests they want to run and data they want to be collected and archived. What’s interesting is how they want the data collected.

They collect room environmental data using ABB Circular Chart Recorders like the one in the attached picture. I hadn’t seen one of these in many years and didn’t think that they were used anymore. The local state government likes them because they still store all their environmental results on paper. Some of these systems have locks on them so that the state can be sure of the integrity of the results.

The units that aren’t locked can be replaced, and this is a perfect Modbus application. Here’s why. First, there are a ton of Modbus RTU and Modbus TCP temperature monitors available. The company can have their pick. Second, these types of sensors are extremely inexpensive and very reliable. Since they don’t support Ethernet, the part count is lower, the connector is less expensive and the processor doesn’t need a lot of bandwidth. Modbus is definitely a low-cost solution. And finally, Modbus is a slow response network. It can sometimes take 200ms or more to get a message across the network. In the slow world of temperature recording, that works just great.

Our new Historian product, that we’ll soon be announcing, is perfect for an application like this. We can collect data, save it in a local database and provide that data to a SQL database, ship it off using OPC UA or HTTP with JSON, or even deliver it in a CSV file.

That product will give our customers a great way to replace some of these old chart recorders that aren’t required by the state. If you’d like some preliminary information on our Historian product, give one of our application engineers a call at 800-249-1612.

Attention: Our office will be closed on Friday, July 3rd in observance of Independence Day. Normal business hours will resume on Monday, July 6th. Have a safe and happy holiday! Thank you.