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How to find the right CO2 sensor for your project?

Given the current circumstances (Corona virus, polluted air, ...), monitoring indoor air quality is strongly encouraged. CO2 meters are particularly suitable for controlling a ventilation system because they indicate whether there is sufficient fresh air in the room. Suddenly you can buy CO2 meters on every street corner. They are available in different price categories, sizes, types, etc. How do you select the right CO2 sensor for your project?
How to find the right CO2 sensor for your project?
In the infinite choice of CO2 sensors, how do you pick the most suitable one?
When purchasing/renting a CO2 meter, check whether it is of high quality and suitable for measuring in the space you want to install it. Other things you should pay attention to are: sensor type, measurement error, measuring range, calibration method, LED indicators, LED indication values, model and data logging.
In this article, we will take a closer look at some of these aspects.
NDIR sensor technology
It is advisable to choose a sensor that detects CO2 based on the NDIR principle. NDIR or non-dispersive infrared sensors contain an infrared (IR) lamp that directs waves of light through a tube filled with air towards an optical filter in front of an IR light detector. This detector measures the amount of IR light that passes through the optical filter. The difference between the amount of light radiated by the IR lamp and the amount of IR light received by the detector is measured. In this way the number of CO2 molecules in the air can be calculated.
The advantage of such NDIR CO2 sensors is their lengthy lifespan, the minimal to zero interference of other gases, low life-cycle cost and a precise and stable long-term operation. This is something Sentera Controls understood very well and therefore developed all its CO2-sensors based on the NDIR principle.
Calibration method
All carbon dioxide sensors need calibration. In case of the NDIR sensors, both the light source and the detector deteriorate over the years, resulting in slightly lower CO2 molecule counts. This is generally known as “drift” or measurement error. Depending on the application, calibration can be accomplished by calibrating the sensor to a known gas or using the automatic baseline calibration (ABC) method.
ABC calibration was developed to solve the difficulty of calibrating wall-mounted units for measuring occupancy or indoor air quality. Removing these units from the wall in order to calibrate them was expensive, required trained staff and was therefore often ignored.
The theory behind ABC self-calibration is that for IAQ use, at some point each day a room is unoccupied and the CO2 level will drop to outside ambient conditions of 400 ppm. All Sentera CO2-sensors make use of the ABC Logic® calibration method. When enabled, the sensor will typically reach its operational accuracy after 24 hours of continuous operation and will maintain its accuracy, given that it is at least four times in 21 days exposed to a reference level of 400 ppm. Depending on the installation environment, it is recommended to enable or disable this self-calibration technique.
Type of information provided
There are different types of CO2 measuring instruments, depending on how the measurement data is displayed, transmitted and/or archived. Some instruments combine different information options.
Direct display of the measured value on a screen - has the advantage of allowing easy immediate measurement and direct information to the people in the room.   
Data registration - the measured data is sent and archived remotely and can be consulted via an application on a smartphone, computer or website for example. This has the advantage that you can easily visualize and interpret the course of the CO2 values during a certain period and map the influence of certain interventions (e.g. opening extra windows or doors) to improve the rate of air exchange.
Additional visual (green, yellow, red LEDs) and/or audible (alarm) indicators show whether the measured data are still within range or if extra ventilation is needed.
The Sentera product range contains CO2 sensors that require 24 Volt supply voltage and versions that can directly be plugged in into a 230 VAC socket. All the CO2 room sensors have these LED indications visualising one of the measured values. Some of them are additionally equipped with an audible alarm. The sensors can be linked to an external screen showing the measured values. Data logging, remote control and monitoring is also possible by connecting the sensor and associated applications to Senteraweb, our own online HVAC platform. Both Sentera devices and registered non-Sentera devices can be connected to SenteraWeb.
Who is Sentera?

Sentera is one of the leading manufacturers of control solutions for HVAC and ventilation systems. Our mission is to make intelligent HVAC control solutions that are easy to use! We develop, manufacture and promote fan speed controllers, HVAC sensors, HVAC controllers and actuator powered dampers to control airflows and to monitor indoor air quality. Today, the Sentera group counts 8 companies and 150 employees based in 4 different locations. Headquarters and the central warehouse are located in Temse, Belgium. Sentera is a 100 % family owned group of companies. For more information, please contact Sentera!
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