What is CO2 Sensor : Working & Its Applications

Carbon dioxide gas or CO2 gas is odorless, colorless gas that can be formed throughout different processes like respiration, combustion & organic decomposition. So, measuring CO2 gas is significant in combustion processes monitoring, indoor air quality ecological CO2 gas emission levels, the lungs function in medical procedures, etc. So, carbon dioxide gas can be measured through NDIR (nondispersive infrared) technique otherwise electrochemical technology with better accuracy. These types of sensors are used in many industries like pharmaceutical, agri-food, beverage, refrigeration & brewing. So, this article discusses an overview of what is a carbon dioxide sensor or CO2 sensor and it’s working with applications.

What is a Carbon Dioxide Sensor?

CO2 sensor definition is, an instrument that is used to detect the CO2 gas content in the air or its surroundings is known as a carbon dioxide sensor. Once the instrument detects the CO2 gas content then it generates an alarm so that appropriate action can be taken by the people.

This type of sensor plays an essential role in making a good atmospheric situation for the public. The application areas of CO2 sensors mainly include different industries like carbonated beverage beer, coal, agricultural planting, agricultural breeding & the daily life of people.

Working Principle

The CO2 sensor working principle is similar to infrared hydrocarbon detectors. They generate an infrared light beam tuned to an exact frequency that is absorbed readily through CO2 molecules. The main difference between the CO2 sensor and IR hydrocarbon detector is the selection of IR wavelength & filter.

Since every CO2 molecule is absorbed by some of the infrared light, the quantity of absorption is proportional to the CO2 percentage available within the ambient air. These CO2 sensors utilize sapphire windows to guard the elements of the infrared transmitter & receiver from injury from any acidic gases that may be present in the ambient atmosphere.

Types of Co2 Sensor

The CO2 sensors are available in different types like Non-dispersive, Electrochemical, Semiconductor, and Catalytic combustion.

Electrochemical CO2 Sensor

This is one type of chemical sensor, used to change the carbon dioxide gas concentration into an electrical signal throughout an electrochemical reaction. Based on electrical signal detection, the type of electrochemical is separated into different types like current, capacitive & potential type.

Once the CO2 gas enters into the sensor, then it responds chemically to the sensor. When this reaction happens, the CO2 sensor will experience an electrical change.

So based on the particular type of sensor, the reaction can make the CO2 sensor receive an electrical current, modify an existing current or modify how well the sensor will carry a current. After that, this sensor will determine how much gas is used based on the change.

Catalytic Combustion CO2 Sensor

This type of co2 sensor is available with a catalyst-like basic element that utilizes the catalyst coating on the face of a particular type of resistor. The flammable gas at a particular temperature is burned catalytically on the surface like the carbon dioxide sensor principle. So, people call this CO2 sensor as a thermal combustion sensor. These sensors are improved and widely used in different industries like reliable sensors.

NDIR CO2 Sensor

The term “NDIR” stands for Non-Dispersive Infrared which uses specific light wavelengths to calculate the CO2 amount within the air. Every element on the Earth simply absorbs particular types of light.
Once air enters into the gas sensor, then it will turn on a set of light at one of the particular CO2 wavelengths, typically around 4 microns at one ending of the sensor.

The other face will hold a container that will calculate how much light makes it to the other face. When the light is turned ON, CO2 within the air will absorb the beams. So, the sum of light that makes it to another face of the CO2 sensor reduces. The sum of absorbed light mainly depends on how much CO2 is available. If there is more CO2, then more light will be absorbed.

Semiconductor CO2 Sensor

This sensor can be made with the oxidation-reduction reaction of the gas on the surface of the semiconductor to modify the value of resistance for the sensitive element. Once the semiconductor device gets heated to a particular level then it absorbs the gas molecules which contact the surface of the semiconductor. So these molecules are absorbed, they diffuse freely on the surface of semiconductors and lose their movement energy.

Some of the gas molecules will disappear & others leftover molecules will be decomposed thermally & absorbed by the semiconductor surface. Once the semiconductor work function is low as compared to the absorbed molecules, then these molecules will remove electrons from the semiconductor device and the semiconductor device surface provides a charge layer. If the semiconductor work function is higher than the absorbed energy molecules, then these molecules will discharge electrons toward the device to form positive ion absorption.

CO2 Sensor Circuit Diagram

This CO2 circuit diagram is used to measure carbon dioxide (CO2) & Total Volatile Organic Compounds (TVOC) within the air. In this interfacing, CCS811 is used as a digital gas sensor for detecting a wide range of TVOC & equivalent CO2 with metal oxide levels.

Previously, we have discussed the MQ135 gas sensor but the CCS811 gas sensor is capable of measuring the CO2 & TVOC levels in the air. So this is the best sensor to measure these two parameters and it also has some salient features like  small size, ultra-low power consumption, used in wearable’s & handheld devices to monitor air quality.

Here, we are designing a CCS811 Gas Sensor-based CO2 & TVOC Meter with Arduino Board. So, using the Library of CCS811 Arduino, code is written which is used to retrieve the TVOC and CO2 values and the values will be displayed on OLED display.

The required components of this interfacing mainly include any Arduino board like UNO R3, Nano, CO2 TVOC sensor, OLED, connecting wires, etc.

Pin Configuration

The pin configuration of the CCS811 GAS Sensor includes the following.

• Pin1 (VCC): This pin uses 3.3V to provide supply to the board.
• Pin2 (GND): This is a GND pin.
• Pin3 (SCL): This is the I2C clock pin pulled to VCC via a 10K resistor.
• Pin4 (SDA): This is the I2C data pin connected to VCC through a 10K resistor.
• Pin5 (WAKE): This is the wake-up pin for the CO2 sensor.
• Pin6 (INT): This is the interrupt o/p pin.
• Pin7(RST ): This is the reset pin.
• Pin8 (ADD): This is a single address select bit pin used to permit the alternate address to be chosen.

CO2 Sensor Circuit Diagram

The following CS811 Gas Sensor Interfacing with Arduino Board diagram is used to measure TVOC & CO2 levels in the air. The connections of this circuit are as follows.

First, connect the CCS811 gas sensor’s Vin and GND pins to 3.3V and GND Pin of the Arduino board
The required voltage to operate this sensor is 3.6 voltage.

Connect both the SDA and SCL pins of sensors to Arduino board’s A4 and A5 Pins respectively. The WAKE pin of the CCS811 sensor is connected to the GND pin of Arduino. If we leave the WAKE pin empty, the controller cannot read the Address of I2C.

The library of the CCS811 gas sensor is mainly used to interface the CCS811 gas sensor with the Arduino board. So, this Libray is simply written by both Sparkfun & Adafruit. So we can use any of the libraries by downloading them from the sites.

Here, the Adafruit library is used to retrieve the CO2 and TVOC values. Here, an additional OLED display is connected to the above circuit. And using the OLED library you can display the CO2 & TVOC value on OLED Display.

The circuit diagram of OLED Display with CCS811 Sensor & Arduino is shown below. Here the Arduino board & CCS811sensor connections will be the same. Connect the SDA & SCL pins of OLED Display to the Arduino’s A4 & A5 pins and connect the VCC pin to 3.3V and GND pin to GND.

The complete code of OLED display & CCS811 gas sensor interfacing with arduino board is given below.

#include “Adafruit_CCS811.h”
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128 // OLED display width, in pixels
#define SCREEN_HEIGHT 64 // OLED display height, in pixels
#define OLED_RESET -1 // Reset pin # (or -1 if sharing Arduino reset pin)
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

Adafruit_CCS811 ccs;

void setup()
{
Serial.begin(9600);
display.begin(SSD1306_SWITCHCAPVCC, 0x3C); //initialize with the I2C addr 0x3C (128×64)
delay(500);
display.clearDisplay();
display.setCursor(25, 15);
display.setTextSize(1);
display.setTextColor(WHITE);
display.println(“CCS811 Sensor”);
display.setCursor(25, 35);
display.setTextSize(1);
display.print(“Initializing”);
display.display();

Serial.println(“CCS811 test”);

if (!ccs.begin())
{
Serial.println(“Failed to start sensor! Please check your wiring.”);
while (1);
}

// Wait for the sensor to be ready
while (!ccs.available());
}

void loop()
{
if (ccs.available())
{
if (!ccs.readData())
{
Serial.print(“CO2: “);
Serial.print(ccs.geteCO2());
Serial.print(“ppm, TVOC: “);
Serial.println(ccs.getTVOC());

display.clearDisplay();
display.setTextSize(1);
display.setCursor(20, 0);
display.print(“Air Quality”);

display.setTextSize(2);
display.setCursor(0, 20);
display.print(“CO2:”);
display.print(ccs.geteCO2());
display.setTextSize(1);
display.print(” ppm”);

display.setTextSize(2);
display.setCursor(0, 45);
display.print(“TVOC:”);
display.print(ccs.getTVOC());
display.display();
}
else
{
Serial.println(“ERROR!”);
display.clearDisplay();
display.setTextSize(2);
display.setCursor(0, 5);
display.print(“ERROR!”);
while (1);
}
}
delay(1000);
}
Once the above code is uploaded, the OLED display will start to display the values of CO2 & TVOC. For testing purposes, we can introduce gas close to it.

Advantages

The co2 sensor benefits include the following.

• The advantages of semiconductor CO2 sensors are stable structure, quick response & environmental resistance is strong.
• The advantages of the NDIR CO2 sensor mainly include fast analysis speed, High sensitivity, long service life & good stability.
• The advantages of catalytic combustion CO2 sensor is quick response, precise measurement, and quick response.
• The advantages of electrochemical CO2 sensors mainly include, less cost, simple operation and measurement speed are fast.

Disadvantages

The co2 sensor disadvantages include the following.

• The disadvantages of electrochemical CO2 sensors mainly include,  accuracy may lose, easy to drift, short life, simple to aging, and accurate measurement is simply disturbed through other gases.
• The disadvantage of catalytic combustion CO2 sensors is the small selectable gas range.
• The disadvantages of the NDIR CO2 sensor mainly include; power consumption is high, the structure is complicated, and expensive.
• The disadvantages of semiconductor CO2 sensor is: it is simply affected by temperature, the reading will be affected by other substances within the air, etc.

CO2 Sensor Applications

The applications of a CO2 sensor include the following.

• Safety Industries.
• HVAC/ Indoor Air Quality Industries.
• University Research Applications.
• Life-Science & Medical Industries.
• Testing of Fire Suppression.
• Aerospace Industries.
• Transportation Industries.
• Industrial Applications.
• MAP (Modified Atmosphere Packaging).
• Agriculture Industries.
• Mining.
• Gasification.
• Indoor air quality.
• Biogas.
• HVAC.
• Landfill.
• Modified Atmosphere Packaging (MAP).
• Total Organic Carbon (TOC).
• Process Control.
• Controlled Environment Horticulture.
• Controlled Atmosphere Storage.

Thus, this is all about an overview of a carbon dioxide sensor or a CO2 sensor and its working with applications. There are many gas sensors available like MG811, LP8, ACD10, etc. Here is a question for you, what is an alcohol sensor?