Many people who aren’t familiar with electronics often struggle to differentiate between MQ-2, MQ-3, MQ-4, MQ-135 gas sensors. People have many doubts regarding which sensor to use and what is the difference between these, so from this blog, you will be clear about the difference between MQ-2, MQ-3, MQ-4, MQ-7 and MQ-135.
MQ-2 Flammable Gas and Smoke Sensor Module
The MQ2 gas sensor is one of the most widely utilized in the MQ sensor series. It's a Metal Oxide Semiconductor (MOS) type Gas Sensor, also known as Chemiresistors because the detection is dependent on a change in the sensing material's resistance when the gas comes into contact with it. Gas concentrations can be sensed using a simple voltage divider network.
Gases such as LPG, Alcohol, Propane, Hydrogen, CO, and even methane can be detected or measured using the MQ-2 Gas Sensor. The module version of this sensor has a Digital Pin, which allows it to work without a microcontroller, which is useful when you only want to detect one gas. When measuring the gas in ppm, the analog pin must be utilized. The analog pin is TTL controlled and operates at 5V, making it compatible with most microcontrollers.
MQ2 sensor operates on 5V DC and draws around 800mW power. It can detect Alcohol, Propane, LPG, Smoke, Hydrogen, Methane, and Carbon Monoxide concentrations anywhere from 200 ppm to 10000 ppm.
The internal structure of the MQ2 Gas Sensor
The sensor is actually protected by an Anti-explosion network, which is made up of two layers of tiny stainless steel mesh. Because we are monitoring combustible gases, it ensures that the heater element inside the sensor does not trigger an explosion. It also protects the sensor by filtering away suspended particles, allowing only gaseous constituents to pass through the chamber. The mesh is bound to the rest of the body via a copper-plated clamping ring.
The sensing element and six connecting legs that extend beyond the Bakelite base form the star-shaped structure. Two of the six leads (H) are in charge of heating the sensor element and are connected through a Nickel-Chromium coil, a well-known conductive alloy. Platinum Wires are used to connect the remaining four leads (A & B) that are responsible for output signals. These wires are attached to the sensing element's body and transmit minor changes in the current that passes through it.
The tubular sensor element is built of a ceramic based on Aluminum Oxide (AL2O3) with a Tin Dioxide covering (SnO2). The most important substance that is susceptible to combustion gases is tin dioxide. The ceramic substrate, on the other hand, only improves heating efficiency and guarantees that the sensor area is kept at a consistent working temperature.
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The sensor's analog output voltage varies in response to the amount of smoke/gas present in the environment. The output voltage increases as the gas concentration increases, while the output voltage decreases as the gas concentration decreases. You can modify the sensor's sensitivity by turning the potentiometer. It can be used to change the gas concentration at which the sensor detects it.
MQ-3 Alcohol Detector Gas Sensor Module
The MQ-3 module can detect alcohol, benzene, CH4, hexane, LPG, and CO. The MQ-3 gas sensor's sensitive substance is SnO2, which has lower conductivity in clean air. When the target alcohol gas is present, the sensor's conductivity increases in accordance with the increase in gas concentration. The MQ-3 sensor has a high sensitivity to alcohol and is resistant to fuel, smoke, and mist contamination. Based on the amount of alcohol in the system, this sensor produces an analog resistive output. When alcohol or gas is present, the sensor's conductivity increases along with the gas concentration.
There is the resistance across an A and B inside the sensor which varies on detection of alcohol. More the alcohol, the lower the resistance. the lesser the resistance, the more alcohol there is. A voltage divider is formed by the sensor and the load resistor, and the lower the sensor resistance, the greater the voltage reading. The LPG gas sensor operates at 5V DC and consumes about 800mW. It can detect Alcohol concentrations between 25ppm to 500 ppm
The internal structure of the MQ3 Alcohol Sensor
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MQ3 (LPG sensor) is a sensor that is driven by a heater that's why it's protected by an Anti-explosion network, which is made up of two layers of tiny stainless steel mesh. Because we are sensing flammable gas, it assures that the heater element inside the sensor does not trigger an explosion (alcohol).
It also protects the sensor by filtering away suspended particles, allowing only gaseous constituents to pass through the chamber.
The module includes a potentiometer for altering the digital output's sensitivity (DO). You can use it to fix a threshold, so that the module outputs LOW if the alcohol concentration exceeds the threshold value, otherwise HIGH.
MQ-4 Methane Gas Sensor Module
The MQ-4 module can detect Methane, CNG Gas. The MQ3 alcohol sensor operates at 5V DC and consumes about 750mW. It can detect methane, Natural gas concentrations anywhere from 300 to 10000 ppm. A crust made of plastic and stainless steel net holds the sensor, which is made up of a micro AL2O3 ceramic tube, a Tin Dioxide (SnO2) sensitive layer, a measuring electrode, and a heater. The heater creates the ideal working environment for sensitive components. The wrapped MQ-4 has six pins, four of which are used to fetch signals and two of which provide heating current.
MQ-135 Air Quality and Hazardous Gas Sensor Module
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The MQ-135 is a sensor that measures air quality or pollution. It can detect a variety of chemical contents in the air and adjust the voltage at the output pin accordingly, based on the chemical concentration in the air. It can detect things like alcohol, benzene, smoke, NH3, butane, and propane, among other things. If any of the mentioned chemical concentrations rises, the sensor converts the chemical concentration in the air to a voltage range that Arduino or any microcontroller can process. It is impossible to determine what chemical concentrations rose in the air.
This sensor may be the correct solution for you if you need a sensor to detect or measure common air quality gases including CO2, smoke, NH3, NOx, alcohol, or benzene.
As a gas-leakage detector, the MQ-135 gas sensor uses SnO2, which has a higher resistance in clean air. The resistance of the gas sensor falls in tandem with the increase in harmful gases.
MQ-7 Carbon Monoxide Gas Sensor Module
MQ-7 is a sensor that detects CO levels in the air. CO levels ranging from 10 to 500 parts per million can be detected with the MQ-7. The sensitivity of this sensor is excellent, and the response time is quick. The sensor's output is an analog resistance. The sensor may be used in temperatures ranging from -10 to 50°C and uses less than 150 milliamps at 5 volts. The board's preset allows you to easily alter the threshold level for digital output. Microcontrollers, Arduino, and other devices can readily interface with the MQ-7 sensor module. The sensor can detect a variety of CO-containing gases and is a low-cost module that can be used in a variety of applications. With the help of a potentiometer, we can easily adjust the sensitivity of MQ-7.
PINOUT OF MQ SERIES SENSORS
Pin Description
- VCC: This pin powers the module, typically the operating voltage is +5V
- GND: Used to connect the module to system ground
- Digital Out (DO): You can also use this sensor to get digital output from this pin, by setting a threshold value using the potentiometer
- Digital Out (DO): You can also use this sensor to get digital output from this pin, by setting a threshold value using the potentiometer
HOW DOES MQ SENSORS WORK?
It is simple to detect a gas with a MQ sensor. To accomplish this, you can use either the digital or analog pin. Simply supply 5V to the module, and you should see the power LED glow. If no gas is detected, the output LED will remain off, indicating that the digital output pin is at 0V. Remember that you must leave these sensors on for a period of time to allow them to pre-heat before you can use them. Introduce the sensor to the gas you want to detect, and the output LED and digital pin should both go high; if not, adjust the potentiometer until the output goes high. Increase sensitivity by turning the screw clockwise, or decrease sensitivity by turning the screw anticlockwise. When your sensor is exposed to this gas at this concentration, the digital pin will go high (5V), otherwise it will remain low (0V). You can also achieve the same result by using the analogue pin. Using a microcontroller, read the analog values (0-5V), which will be directly proportional to the gas concentration detected by the sensor.