This chapter explains how to use the MQ-131 sensor. You will learn its features, operating principles, specifications, connection pin arrangement, output values, and connect Arduino and the sensor together to measure the air around you easily using the library.
Contents
MQ-131 Ozone Gas Sensor
We travel to companies, schools, and academies, and we also do outdoor activities such as camping, picnics, swimming, and traveling to spend time with our family, friends, and lovers. We are always exposed to air pollutants in places we are not aware of.
Most of the human-made air pollutants exist within 1-2 km of the ground. Ozone is not discharged directly into the atmosphere, but it is a secondary pollutant that is created by photochemical reactions of primary air pollutants such as nitrogen oxides (NOx), hydrocarbons (HC), methane (CH₄), and carbon monoxide (CO). In fact, nitrogen oxides (NOx) and volatile organic compounds (VOCs) are the biggest causes of ozone. Nitrogen oxides are collectively referred to as nitrogen monoxide (NO) and nitrogen dioxide (NO₂), and are emitted in the process of burning fossil fuels such as coal and petroleum.
Some of the generated ozone (surface ozone) reacts secondarily with another pollutant in the atmosphere, causing photochemical smog. Photochemical smog is a phenomenon that creates a yellowish-brown fog, which limits visibility and irritates the respiratory tract and eyes. The government sets air quality standards and manages as air pollutants, and it refers to ozone that affects human health as the tropospheric ozone.
Cities known for photochemical smog are Los Angeles and Tokyo. In the summer of 1955, the Los Angeles city had an abnormally high temperature exceeding 38℃, and an ozone concentration of 0.05ppm lasted for one week. During this time, a number of people developed asthma and bronchitis. The number of deaths for the elderly aged 65 and over increased more than four times. In 1970, in Tokyo's photochemical smog, over ten thousand citizens complained of damages over three months.
Effects on the human body
Ozone is typically in the troposphere (about 10 km above the ground), but it has a strong oxidizing power and is beneficial to humans when it is in an appropriate amount (sterilization, deodorization, etc.). However, if the concentration of ozone generated on the earth's surface rises above a certain level, repeated exposure adversely affects the human body.
For example, chest pain, cough, nausea, neck irritation, digestion, etc., bronchitis, heart disease, emphysema and asthma exacerbation, decreased lung capacity, decreased pulse and blood pressure, and dizziness may occur.
Severe cases can cause lung damage, and exposure to the eyes can cause inflammation. In particular, if children with weak immunity and the elderly are exposed to ozone for a long time, they may complain of shortness of breath and dizziness, and may cause asthma and chronic diseases of the respiratory system.
MQ-131 Sensor?
The MQ-131 sensor measures ozone. Ozone sensors are divided into two types: a gas phase ozone sensor that measures ozone leaking in the air, and a dissolved ozone sensor that measures ozone dissolved in water.
[Winsen homepage]
[MQ-131 sensor configuration]
According to the MQ-131 sensor data sheet, the sensor consists of a pair of platinum (Pt) coils, with a gold (Au) electrode and an electrode line made of of metal oxide semiconductors. It is composed of metal oxide (SnO2), a semiconductor material surrounding the coil. The heater is made of a Ni-Cr alloy.
[MQ-131 sensor measurement principle]
The semiconductor sensor measures the change in electrical conductivity due to adsorption of ozone (O3) gas on the surface of a metal oxide semiconductor (SnO2).
When oxygen in the atmosphere is adsorbed on the surface of SnO2 grains, an electron depletion layer is formed on the surface, thereby forming a potential barrier between the grains. When a gas such as ozone (O3) is introduced, the concentration of oxygen adsorbed on the surface decreases, and accordingly, the thickness of the hypo-depletion layer decreases, thereby lowering the potential barrier and reducing the overall resistance. At this time, the value obtained by dividing the changed resistance value by the original resistance value appears as a gas sensitivity. In other words, when ozone gas is present, the conductivity of the sensor decreases as the ozone gas concentration increases. The change in gas sensitivity according to the SnO2 grain size was reported by Kyushu University and shows that the gas sensitivity increases rapidly as the grain size decreases.
The circuit diagram of a MQ-131 ozone gas sensor module includes a BAOTER 3296 potentiometer and an LM393 comparator.
[MQ-131 sensor specifications]
According to the data sheet of the MQ-131 sensor, the sensor is divided into a low concentration sensor and a high concentration sensor. The low concentration sensor measures 10~1000ppb, and the high concentration sensor measures 10~1000ppm. The input voltage is 5v, and the preheating time required is over 48 hours. The output voltage of the low concentration sensor is ≥1.0v (in 200 ppb) in a standard test environment.
[MQ-131 sensor output value]
The sensitivity characteristic curve of the MQ-131 sensor is as follows.
• This is a graph of the gas concentration versus Rs/R0 in ppb.
• The y-axis is the resistance ratio (Rs / R0) of the sensor.
• The x-axis is the value of the low concentration of ozone gas. The low concentration range is 10 to 1000 ppb.
• Rs is the resistance of the sensor in the target gas and R0 is the resistance in clean air.
Typical temperature/humidity characteristics of the MQ-131 sensor.
In addition, the MQ131 sensor has a variable resistor, which is a BAOTER 3296 trimmer potentiometer. It can control the sensitivity of the sensor during digital output.
Purchasing the MQ-131 sensor
As follows, the [MQ-131] sensor used in the book [Arduino Sensors for Everyone] can be purchased at Ali Express, Amazon.
Software Coding
Run the example file in Steamedu123_Sensor-master > examples.
/*
@401 MQ-131 Ozone gas sensor
*/
#include <C401_Steam_Air_MQ131_O3.h> // Internal library header file
#define AoutPIN A1
#define TEMP 24 // °C
#define HUMI 40 // %
SteamMQ131 mq131(AoutPIN); // Instance, pin number
void setup() {
Serial.begin(115200); // Start serial communication at a speed of 115200bps.
mq131.begin(); // (1) Initialize the sensor.
}
void loop() {
mq131.read(TEMP, HUMI); // (2) Measure the value of the sensor.
mq131.display(); // (3) Output the sensor value.
delay(6000); // Wait for 6 second.
}
MQ-131 Arduino sensor operation check
When the hardware connection and software coding are completed, you can check the operation screen as follows.
------------------------------------------------------
Development environment: WINDOWS 10
Arduino IDE: 1.8.13
------------------------------------------------------
01 library copy
You can easily check the operation by using the library.
The libraries \Steamedu123_Sensor-master folder is copied to the folder below.
* This folder is created automatically after installing Arduino C:\Users\s\Documents\Arduino\libraries
02 *. ino file execution
-Connect Arduino and PC
-Run Arduino IDE
-Menu → Tools → Board: Check Arduino UNO
-Menu → Sketch → Check/Compile
03 Check compilation
Select Sketch>OK/Compile (CTRL+R) to compile.
04 Arduino Uno upload
When the compilation is completed without any problems, select Sketch>Upload (CTRL+U) to upload the compiled file.
05 Operation check
You can check the operation as follows.
Wrap-up
You can connect Arduino and [MQ-131] sensor and practice the sensor easily with simple coding.
In this section, we investigated the influence of ozone on the human body, the reference concentration, the measurement range of the simple measuring instruments, and the sensors used in the measuring instruments, We also measured ozone directly using the MQ131 ozone gas sensor and Arduino.
Ozone exists everywhere. If the outdoor ozone level is high, and it is 'bad' or 'very bad', you should refrain from outdoor activities and do indoor activities as much as possible. In addition, ozone is mainly generated outdoors, but indoor ozone levels may rise when there are electronic products that are introduced into the room due to the movement of air or ozone generated indoors.
Sterilization, deodorization, and decolorization are possible by using the strong oxidizing power of ozone. Therefore, it is used not only in daily life, but also in various indoor spaces such as water purification plants and hospitals. Some of the devices that generate ozone in daily life include home appliances such as air purifiers, ozone sterilization and washing machines, and office equipment such as photocopiers and laser printers. Ozone has a characteristic fishy odor that can be recognized. However, the moment the smell is detected, you already have been exposed to ozone above a certain concentration. If you have been exposed for a long time, you can become accustomed to the smell and may not be recognized.
According to the indoor air quality recommendation standard (related to Article 4) of the Indoor Air Quality Management Act Enforcement Regulations, indoor ozone for multi-use facilities is 0.06 ppm or less, and indoor parking lot is 0.08 ppm or less.
The MQ131 low ozone concentration sensor described in this section can be used not only outdoors but also indoors to measure ozone. When using a product that generates ozone or uses ozone indoors for a long time, periodic indoor ventilation is required to allow fresh air to enter the room if there are no fine dust or ozone warning. If ventilation is difficult while using an ozone generating device, it is recommended to provide natural ventilation for at least 30 minutes after use.
References
References for [MQ-131sensor] used in the book [Arduino for Sensors Everyone] are as follows.
[1] Air Korea Real-time Atmosphere Information, http://www.airkorea.or.kr/index
[2] Air Korea Air Quality Standards (Overseas), https://bit.ly/3oSpuj2
[3] Winsen Datasheet, https://bit.ly/3p0hI72
[4] ATI 00-1008 Datasheet, https://bit.ly/2XQO7Ri
[5] AliExpress MQ-131, https://aliexpi.com/JwxI
[6] SR-G04 Ozone Sensor, https://bit.ly/2M0lChy
[7] ATI Ozone Sensor 0-2 ppm (00-1008), https://bit.ly/3p6SeF7
[8] Winsen homepage ozone sensor, https://bit.ly/3p6S94h
[9] mq131-(low-concentration)-ver1_3-manual, "Technical Parameters", p3
[10] mq131-(low-concentration)-ver1_3-manual, "Description of Sensor Characters", p4
[11] Air Korea, https://bit.ly/2KsKRZs
Purchasing a book
[Arduino Sensors for Everyone] The book is available for purchase on Google Book and Apple Books.
In this book, you will learn how to use the PMS7003, GP2Y1010AU0F, PPD42NS, SDS011 Fine Dust Sensor, DHT22 temperature/humidity sensor, MH-Z19B carbon dioxide sensor, ZE08-CH2O formaldehyde sensor, CCS811 total volatile organic compound (TVOC) sensor , GDK101 radiation (gamma ray) sensor, MQ-131 ozone (O3) sensor, MQ-7 carbon monoxide sensor, MICS-4514 nitrogen dioxide sensor, MICS-6814 ammonia sensor, DGS-SO2 sulfur dioxide (SO2) sensor, BME280 atmospheric pressure sensor, GUVA-S12SD ultraviolet (UV) sensor, MD0550 airflow sensor, and QS-FS01 wind speed sensor.
Arduino Sensors for Everyone, 저자: Ronnie Kim - Google Play 도서
Arduino Sensors for Everyone - 저자가 Ronnie Kim인 eBook입니다. PC, Android, iOS 기기에서 Google Play 북 앱을 사용해 이 책을 읽어 보세요. 책을 다운로드하여 오프라인으로 읽거나 Arduino Sensors for Everyone을(를)
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