MQ-2 Gas Sensor Module

Introduction

The gas sensitive material used in the MQ-2 gas sensor is SnO2, a low electrically conductive material in clean air. When there is combustible gas in the surrounding air, the electrical conductivity of the sensor will increase with the higher intensity of the combustible gas. Here, we can convert the changing electrical conductivity into output signal by building a simple circuit.

Main Features

Detected Gas: Combustible Gas, Smoke

Detection Intensity: 300～10000ppm(Combustible Gas)

Working Voltage: 5.0V±0.1V AC or DC

Preheating Time: ≥2 minutes

Introduction of the Pins

VCC: 5V Working Voltage

GND: Ground.

D0: Output Interface of Digital Switch (0 and 1).

A0: Analog Output Interface

Working Principle

After wiring VCC and GND, the Power LED of the module lights up. Before your using, the power supply preheats for at least 2 minutes. It is normal for the sensor to generate heat slightly, because there is heating wire inside. But it is abnormal that the sensor becomes overheating. When there is no impact of the sensible gas or the gas concentration is not more than the preset threshold, the digital interface D0 outputs high level and the voltage of the analog interface A0 is around 0V. When the gas concentration is beyond the threshold, the digital interface D0 outputs low level and the digital indicator light is on. And the output voltage of the analog interface A0 increases with the raising of the gas concentration,A0 Output: 0.1-0.3V (relatively non-polluted).

With the gas concentration being higher, the voltage can reach up to 4V. Rotate the knob of the potentiometer clockwise, you can get the sensing range of the gas concentration wider (only for the sensitivity of the TTL output). The digital output D0 can drive the relay module directly, which can form a gas switch. The digital output D0 can also drive the positive buzzer module and this module can be used to make up a gas alarm. The analog output A0 can be connected to AD module and get the approximate values of the ambient gas concentration via AD conversion.

For Arduino

Using Steps

Step 1: Connect the circuit.

Step 2: Copy the following codes and paste them in Arduino.

///Arduino Sample Code

void setup()

{

Serial.begin(9600); //Set serial baud rate to 9600 bps

}

void loop()

{

int val;

val=analogRead(0);//Read Gas value from analog 0

Serial.println(val,DEC);//Print the value to serial port

delay(100);

}

The codes above are used to acquire the signal of the gas sensor via the analog interface 0 and to output the signals into the computer via serial port. To observe the consequence, we can use serial port monitor.

Due to the internal structure of the gas sensor, the measurement can only begin after one minute's preheating. During preheating, you can easily feel the hot of the probe. When the preheat is finished, the data are around 120 (only for reference, the value can be variable with the changing of the circumstance). According to the parameter of the probe, in the clean air, the data value might be less than 310.

///Arduino Sample Code

void setup()

{

Serial.begin(9600); //Set serial baud rate to 9600 bps

}

void loop()

{

int val;

val=analogRead(0);//Read Gas value from analog 0

Serial.println(val,DEC);//Print the value to serial port

delay(100);

}

A gas detector is a device that detects the presence of gases in an area, often as part of a safety system. A gas detector can sound an alarm to operators in the area where the leak is occurring, giving them the opportunity to leave. This type of device is important because there are many gases that can be harmful to organic life, such as humans or animals.

Gas detectors can be used to detect combustible, flammable and toxic gases, and oxygen depletion. This type of device is used widely in industry and can be found in locations, such as on oil rigs, to monitor manufacturing processes and emerging technologies such as photovoltaic. They may be used in firefighting.

Gas leak detection is the process of identifying potentially hazardous gas leaks by sensors. Additionally a visual identification can be done using a thermal camera These sensors usually employ an audible alarm to alert people when a dangerous gas has been detected. Exposure to toxic gases can also occur in operations such as painting, fumigation, fuel filling, construction, excavation of contaminated soils, landfill operations, entering confined spaces, etc. Common sensors include combustible gas sensors, photoionization detectors, infrared point sensors, ultrasonic sensors, electrochemical gas sensors, and metal-oxide-semiconductor sensors (MOS sensors). More recently, infrared imaging sensors have come into use. All of these sensors are used for a wide range of applications and can be found in industrial plants, refineries, pharmaceutical manufacturing, fumigation facilities, paper pulp mills, aircraft and shipbuilding facilities, hazmat operations, waste-water treatment facilities, vehicles, indoor air quality testing and homes.

Types

Gas detectors can be classified according to the operation mechanism (semiconductors,[4] oxidation, catalytic, photoionization, infrared, etc.). Gas detectors come packaged into two main form factors: portable devices and fixed gas detectors.

Portable detectors are used to monitor the atmosphere around personnel and are either hand-held or worn on clothing or on a belt/harness. These gas detectors are usually battery operated. They transmit warnings via audible and visible signals, such as alarms and flashing lights, when dangerous levels of gas vapors are detected.

Fixed type gas detectors may be used for detection of one or more gas types. Fixed type detectors are generally mounted near the process area of a plant or control room, or an area to be protected, such as a residential bedroom. Generally, industrial sensors are installed on fixed type mild steel structures and a cable connects the detectors to a SCADA system for continuous monitoring. A tripping interlock can be activated for an emergency situation.

Electrochemical

Main article: Electrochemical gas sensor

Electrochemical gas detectors work by allowing gases to diffuse through a porous membrane to an electrode where it is either chemically oxidized or reduced. The amount of current produced is determined by how much of the gas is oxidized at the electrode,[5] indicating the concentration of the gas. Manufactures can customize electrochemical gas detectors by changing the porous barrier to allow for the detection of a certain gas concentration range. Also, since the diffusion barrier is a physical/mechanical barrier, the detector tended to be more stable and reliable over the sensor's duration and thus required less maintenance than other early detector technologies.

However, the sensors are subject to corrosive elements or chemical contamination and may last only 1–2 years before a replacement is required.[6] Electrochemical gas detectors are used in a wide variety of environments such as refineries, gas turbines, chemical plants, underground gas storage facilities, and more.

Catalytic bead (pellistor)

Catalytic bead sensors are commonly used to measure combustible gases that present an explosion hazard when concentrations are between the lower explosion limit (LEL) and upper explosion limit (UEL). Active and reference beads containing platinum wire coils are situated on opposite arms of a Wheatstone bridge circuit and electrically heated, up to a few hundred degrees C. The active bead contains a catalyst that allows combustible compounds to oxidize, thereby heating the bead even further and changing its electrical resistance. The resulting voltage difference between the active and passive beads is proportional to the concentration of all combustible gases and vapors present. The sampled gas enters the sensor through a sintered metal frit, which provides a barrier to prevent an explosion when the instrument is carried into an atmosphere containing combustible gases.

Pellistors measure essentially all combustible gases, but they are more sensitive to smaller molecules that diffuse through the sinter more quickly. The measureable concentration ranges are typically from a few hundred ppm to a few volume percent. Such sensors are inexpensive and robust, but require a minimum of a few percent oxygen in the atmosphere to be tested and they can be poisoned or inhibited by compounds such as silicones, mineral acids, chlorinated organic compounds, and sulfur compounds.

#define MQ2pin (0)

float sensorValue; //variable to store sensor value

void setup()

{

Serial.begin(9600); // sets the serial port to 9600

Serial.println("Gas sensor warming up!");

delay(20000); // allow the MQ-6 to warm up

}

void loop()

{

sensorValue = analogRead(MQ2pin); // read analog input pin 0

Serial.print("Sensor Value: ");

Serial.print(sensorValue);

if(sensorValue > 300)

{

Serial.print(" | Smoke detected!");

}

Serial.println("");

delay(2000); // wait 2s for next reading

}

The output on the serial monitor looks like:

Code Explanation:

The sketch starts by defining Arduino pin to which analog pin of MQ2 gas sensor is connected. A variable called sensorValue is also defined to store sensor value.