A typical human nose contains 400 different types of scent receptors, allowing us to detect approximately 1 trillion different odours. However, many of us are unable to identify the type or concentration of gas present in our atmosphere. This is where sensors come in; there are many different types of sensors for measuring different parameters, and a gas sensor comes in handy in applications where we need to detect changes in the concentration of toxic gasses to keep the system safe and avoid/caution any unexpected threats.
There are various gas sensors available to detect gasses such as oxygen, carbon dioxide, nitrogen, and methane. They are also commonly found in devices used to detect harmful gas leaks, monitor air quality in industries and offices, and so on.
What is a Gas sensor?
A gas sensor is a device that detects the presence or concentration of gasses in the surrounding environment. The sensor generates a corresponding potential difference based on the concentration of the gas by changing the resistance of the material inside the sensor, which can be measured as output voltage. The type and concentration of the gas can be estimated using this voltage value.
The type of gas that the sensor can detect is determined by the sensing material used inside the sensor. These sensors are typically available as modules with comparators, as shown above. These comparators can be configured for a specific threshold value of gas concentration. When the gas concentration exceeds this level, the digital pin goes high. The analogue pin can be used to measure gas concentration.
List of some MQ series gas sensors:
The gas sensors are divided into different series depending on the gas or application. These are
MQ-2 Gas Sensor
The MQ-2 Gas Sensor module is useful for detecting gas leaks (home and industry). It can detect H2, LPG, CH4, CO, alcohol, smoke, or propane. Because of its high sensitivity and quick response time, measurements can be taken as soon as possible. The potentiometer can be used to adjust the sensitivity of the sensor.
MQ-3 Gas Sensor
The MQ-3 Gas Sensor module is useful for detecting gas leaks (in home and industry). It can detect Alcohol, Benzine, CH4, Hexane, LPG, and CO. Measurements can be taken as soon as possible due to their high sensitivity and quick response time. The potentiometer can be used to adjust the MQ-3 Gas sensor’s sensitivity.
MQ-4 Gas Sensor
The MQ-4 Gas Sensor is a fast and reliable natural gas sensor with high sensitivity to natural gas and methane, as well as good sensitivity to propane and butane. This natural gas sensor has a long life and is inexpensive, making it popular for detecting gas leaks.
MQ-5 Gas Sensor
The MQ-5 Gas Sensor module is useful for detecting gas leaks (in home and industry). It is appropriate for detecting H2, LPG, CH4, CO, and alcohol. Measurements can be taken as soon as possible due to its high sensitivity and quick response time. The potentiometer can be used to adjust the sensor’s sensitivity.
MQ-6 Gas Sensor
The MQ-6 Gas sensor is an easy-to-use liquefied petroleum gas (LPG) sensor that can detect LPG concentrations in the air (mostly propane and butane). The MQ-6 can detect gas concentrations ranging from 200 to 10000ppm.
This sensor has a high sensitivity and a quick response time. The sensor’s output is an analogue resistance. The drive circuit is very simple; all you need to do is supply 5V to the heater coil, add a load resistance, and connect the output to an ADC.
MQ-7 Gas Sensor
The MQ-7 Gas sensor module is used to determine CO, which is clean air with lower conductivity. It detects CO when the temperature is low and uses a cycle of high and low temperatures to do so (heated by 1.5V). The conductivity of the sensor increases as the gas concentration increases. When the high temperature (heated by 5.0V) is reached, it cleans the other gasses that have been adsorbed at low temperatures.
MQ-8 Gas Sensor
MQ-8 Gas Sensor for determining the amount of hydrogen (H2) in the air. This sensor is capable of measuring concentrations ranging from 100 to 10,000 ppm. Heater drive and measurement circuits are simple to implement. This sensor is built for long life and consistent output. MQ-8 Hydrogen Gas Sensor is ideal for detecting gas leaks in a Gas Leakage Circuit.
MQ-9 Gas Sensor
The MQ-9 Gas Sensor is extremely sensitive to carbon monoxide, methane, and propane. SnO2, which has lower conductivity in clean air, is the sensor that can be used to detect various gasses containing the MQ-9 gas sensor. It detects CO when the temperature is low by cycling between high and low temperatures (heated by 1.5V). The conductivity of the sensor increases as the gas concentration increases. When the temperature rises (heated by 5.0V), it detects Methane, Propane, combustible gas, and other gasses and cleans them as they are adsorbed at low temperatures. MQ-9 is commonly used in domestic gas leakage detectors, industrial gas detectors, portable gas detectors, and so on.
MQ-131 Gas Sensor
The MQ-131 gas sensor’s sensitive material is SnO2, which has a lower conductivity in clean air. When Ozone gas is present. The conductivity of the sensor increases as the gas concentration increases. The MQ131 gas sensor has a high sensitivity to Ozone and is also sensitive to CL2, NO2, and other gasses.
MQ-135 Gas Sensor
The MQ-135 Gas sensor is capable of detecting a variety of gasses such as NH3, NOx, alcohol, benzene, smoke, and CO2. Excellent for use in the office or factory. The MQ135 gas sensor is highly sensitive to ammonia, sulphide, and benzene steam, as well as smoke and other harmful gasses. It is inexpensive and ideal for air quality monitoring applications.
MQ-136 Gas Sensor
The MQ-136 Gas Sensor can monitor hydrogen sulphide gas concentrations. When the target hydrogen sulphide gas is present, the conductivity of the sensor increases, as does the concentration of the gas. The MQ136 gas sensor has a high sensitivity to hydrogen sulphide and a low sensitivity to other flammable gases. It is inexpensive and suitable for a wide range of applications.
MQ-137 Gas Sensor
The MQ-137 Gas sensor detects and measures gases such as ammonia (NH3) and carbon monoxide (CO). The module version of this sensor includes a Digital Pin, which allows it to operate without a microcontroller, which is useful when only trying to detect one gas. When measuring the gas in ppm, the analogue pin must be used. The analogue pin is also TTL driven and operates on 5V, making it compatible with most common microcontrollers.
MQ-138 Gas Sensor
The MQ-138 gas sensor’s sensitive material is SnO2, which has a lower conductivity in clean air. When the target Organic Steam is present, the sensor’s conductivity increases along with the gas concentration.
The MQ138 gas sensor is extremely sensitive to Toluene, Acetone, Ethanol, and Formaldehyde, as well as other organic steam. The sensor could be used to detect various organic steams; it is inexpensive and suitable for a variety of applications.
MQ-214 Gas Sensor
The MQ-214 gas sensor, after detecting the levels of methane in the air, displays its reading as an analogue voltage. These gas sensors are capable of detecting gases in high concentrations. Detectable concentrations: 500–10,000 parts per million for LPG and propane, 1000–20,000 for methane, and 500–10,000 for hydrogen.
WHAT IS 1PPM EQUAL?
When measuring gasses such as carbon dioxide, oxygen, or methane, the quantity of gas by volume in the air is referred to as concentration. Depending on the chemical being tested, 1 ppm can mean a variety of things. Milligrams per kilogram (mg/kg), microliters per litre (ml/L), and micrograms per litre (g/L) are the preferred units for expressing ppm. an improved illustration
The ratio of one gas to another is expressed in parts per million (abbreviated as ppm). For example, if methane is measured at one part per million, one molecule is methane and the other molecules are other gasses in the atmosphere.
ppm = 1/10,00,000 = 0.0001%
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