Ventilation System Testing Using Modbus

Modbus is one of the oldest and most popular automation protocols in process automation, especially within the heating ventilation and air conditioning industry (HVAC), where most ventilation systems have a controller which can communicate via Modbus. Therefore, in this article we will look at how you can use Modbus when testing a ventilation system in your end-of-line test, capacity test or firmware test.

Kasper Kiis
By Kasper Kiis Jensen

A quick overview of Modbus. It was created in 1979 for PLC’s and is a common language for devices and equipment to communicate with each other based on a master / slave architecture. The master could be a PC, a PLC, or a controller in a ventilation system, while the slave could be a fan, a sensor, or some other device. The Modbus thereby make the master be able to control a range of slaves within the system either via RS232, RS485 or TCP/IP. If you want to learn more about Modbus itself, check out this video

A good example in home automation is the controller of a ventilation system turning on a fan controlled via Modbus when the temperature or humidity becomes too high.

You can utilize Modbus when testing ventilation systems as you can control fan speeds, bypass vents, and read sensor values directly from the ventilation system while testing. All these things are key when creating automated testing of ventilation systems as they give PC test software insights into what state the ventilation systems is in.

Testing Ventilation systems using Modbus

You can use Modbus for many different tests but here are 3 automated ventilation system tests where you can utilize Modbus communication.

End-of-line Test

When a ventilation system has been manufactured manufacturers usually perform an end-of-line test to ensure all sensors, fans and every other IO is correctly assembled and working as intended, because it is expensive to fix when first installed. 

Here Modbus is a great way to check every IO. If a temperature, humidity, or pressure sensor is not installed correctly you will get a wrong value or an error if the controller is smart. This can be read through the Modbus and in this way, you can check every sensor, fan, and vent. 

The alternative is a manual inspection where an operator checks every sensor and reads the value on the system or its PC program. This however requires a person which is slow and not scalable. 

Capacity Test

When researching and developing a new ventilation system multiple capacity tests are always performed to gauge the performance of the developed ventilation system. This in simple terms means checking the relationship between flow and pressure at multiple fan voltages. A single test can take a long time so automating it with Modbus can greatly reduce the time engineers have to use in testing. 

With test software you can control the ventilation system using Modbus while also controlling external vents and getting data from multiple sensors. This is necessary in order to measure the system performance in different scenarios at certain voltages.

Firmware Test

A ventilation system controller today can be a small computer with hundreds of features so each time a new firmware is developed manufactures need to ensure that the controller functions correctly testing inputs, outputs and how the controller behaves in certain conditions. 

So, a manual firmware test testcase could for example be manually heating up the temperature sensor to see if the fan starts spinning. This is very time consuming and seldom very accurate as you cannot test very many scenarios. With Modbus you can read the sensor and fan value directly in the controller and if this is coupled with some clever electronics to emulate the temperature sensor then you have a fully automated test, where you are able to test multiple temperatures quickly and accurately.

This way of testing is then setup for the next 100 testcases. So, firmware tests are a perfect way to utilize Modbus to ensure the controller behaves correctly.

How to connect a Modbus with you PC

Knowing what you can use Modbus for and how to do it are two different things. So, to help you get started here is a short introduction. You first need the datasheet, manual or instruction set where the Modbus protocol and addresses are listed. The primary two types of Modbus are RTU and TCP/IP.

Modbus RTU

When using Modbus RTU over e.g., RS485 you also need a USB to RS485 converter. For example a MOXA UPORT converter which you connect with you PC and the device. You then use either a Modbus software, a programming language, or Encidas test software SAFE to start communicating. If you want to learn in detail how to start communicating using Modbus RTU, I recommend reading our How to get started with Modbus RTU guide

Modbus TCP/IP

When using Modbus over TCP you do not need a converter you just need to connect your device to the same network as your PC. You can then again use either a Modbus software, a programming language or our Encidas test software SAFE to start communicating. If you want to learn in detail how to start communicating using Modbus TCP/IP I would recommend reading our reading our How to get started with Modbus TCP/IP guide.

I hope this post helped you get an idea on how you can utilize Modbus when testing you ventilation system and helped you getting started with Modbus on your own. Let me know how you fare, and you can always start a free trial with our software here to easily getting started with Modbus.

Heat Pump COP

Understand Heat Pump COP By Kasper Kiis Jensen Heat pump COP stands for Coefficient of Performance and is a ratio for the heating or cooling energy a heat pump can…

Ventilation System Testing using Modbus

Ventilation System Testing Using Modbus Modbus is one of the oldest and most popular automation protocols in process automation, especially within the heating ventilation and air conditioning industry (HVAC), where…

How to calculate octave band filters

How to Calculate Octave Band Filters Octave and fractional octave band filters are filters used in a huge amount of acoustic calculations. It is something every acoustician has some implementation…