Alcohol Sensor | What is an Alcohol Sensor? | MQ3 Alcohol Sensor working and applications

 Alcohol Sensor

What is an Alcohol Sensor?

An alcohol sensor detects the attentiveness of alcohol gas in the air and an analog voltage is an output reading. The sensor can activate at temperatures ranging from -10 to 50° C with a power supply is less than 150 Ma to 5V. The sensing range is from 0.04 mg/L to 4 mg/L, which is suitable for breathalyzers.

MQ3 Alcohol Sensor

MQ3 is one of the most commonly used sensors in the MQ sensor series. It is a Metal Oxide Semiconductor (MOS) type of sensor. Metal oxide sensors are also known as Chemiresistors, because sensing is based on the change of resistance of the sensing material when exposed to alcohol. So by placing it in a simple voltage divider network, alcohol concentrations can be detected.

MQ3 alcohol sensor works on 5V DC and draws around 800mW. It can detect Alcohol concentrations anywhere from 25 to 500 ppm.

Complete Specifications

• Operating voltage : 5V
• Load resistance : 200 KΩ 
• Heater resistance : 33Ω ± 5%
• Heating consumption : <800mw
• Sensing Resistance : 1 MΩ – 8 MΩConcentration Scope :- 25 – 500 ppmPreheat Time : Over 24 hour
• Power requirements: 5 VDC @ ~165 mA (heater on) / ~60 mA (heater off)
• Current Consumption: 150mA
• DO output: TTL digital 0 and 1 ( 0.1 and 5V)
• AO output: 0.1- 0.3 V (relative to pollution), the maximum concentration of a voltage of about 4V
• Detecting Concentration: 0.05-10mg/L Alcohol
• Interface: 1 TTL compatible input (HSW), 1 TTL compatible output (ALR)
• Heater consumption: less than 750mW
• Operating temperature: 14 to 122 °F (-10 to 50°C)
• Load resistance: 200kΩ
• Sensitivity S: Rs(in air)/Rs(0.4mg/L Alcohol)≥5
• Sensing Resistance Rs: 2KΩ-20KΩ(in 0.4mg/l alcohol)
• Dimensions: 32 x 22 x 16 mm

Features of MQ-3 Alcohol Sensor

• Sensor Type - Semiconductor
• Easy SIP header interface
• Compatible with most of the microcontrollers
• Low-power standby mode
• Requires heater voltage
• Good sensitivity to alcohol gas
• Fast response and High sensitivity  
• Long life and low cost
• Requires simple Drive circuit

MQ3 Alcohol Sensor Module Pinout

VCC 

• supplies power for the module. You can connect it to 5V output from your Arduino.

GND 

• is the Ground Pin and needs to be connected to GND pin on the Arduino.

D0 (Digital Out)

• You can also use this sensor to get digital output from this pin, by setting a threshold value using the potentiometer
• provides a digital representation of the presence of alcohol.

A0 (Analog Out)

• This pin outputs 0-5V analog voltage based on the intensity of the gas
• provides analog output voltage in proportional to the concentration of alcohol.

For MQ-3 Sensor

H -Pins

• Out of the two H pins, one pin is connected to supply and the other to ground

A-Pins

• The A pins and B pins are interchangeable. These pins will be tied to Supply voltage.

B-Pins

• A pins and B pins are interchangeable. One pin will act as output while the other will be pulled to ground.

Internal structure of MQ3 Alcohol Sensor

MQ3 is a heater-driven sensor. That’s why it is enclosed in two layers of fine stainless steel mesh called an Anti-explosion network. It ensures that heater element inside the sensor will not cause an explosion, as we are sensing flammable gas (alcohol).

It also provides protection for the sensor and filters out suspended particles so that only gaseous elements are able to pass inside the chamber.

This is what the sensor looks like when outer mesh is removed. The star-shaped structure is formed by the sensing element and six connecting legs that extend beyond the Bakelite base. Out of six, two leads (H) are responsible for heating the sensing element and are connected via a Nickel-Chromium coil ( a well known conductive alloy).

The remaining four leads (A & B) responsible for output signals are connected using Platinum Wires. These wires are connected to the body of the sensing element and convey small changes in the current that passes through the sensing element.

The tubular sensing element is made up of Aluminum Oxide (AL2O3) based ceramic and has a coating of Tin Dioxide (SnO2). The Tin Dioxide is the most important material being sensitive towards alcohol. However, the ceramic substrate only increases the heating efficiency and ensures that the sensor area is continuously heated to the working temperature.

So, to summarize, the Nickel-Chromium coil and Aluminum Oxide based ceramic forms a Heating System; while Platinum wires and coating of Tin Dioxide forms a Sensing System.

How MQ3 Alcohol Sensor Works?

When SnO2 semiconductor layer is heated at high temperature, oxygen is adsorbed on the surface. In clean air, electrons from the conduction band in tin dioxide are attracted to oxygen molecules. This form an electron depletion layer just below the surface of SnO2 particles and forms a potential barrier. As a result, the SnO2 film becomes highly resistive and prevents electric current flow.

In the presence of alcohol, however, the surface density of adsorbed oxygen decreases as it reacts with the alcohols; which lowers the potential barrier. Electrons are then released into the tin dioxide, allowing current to flow freely through the sensor.

Alternative MQ-3 Gas Sensors

Sensor Name and Gas to measure

• MQ-2 : Methane, Butane, LPG, Smoke
• MQ-3 : Alcohol, Ethanol, Smoke
• MQ-4 : Methane, CNG Gas
• MQ-5 : Natural gas, LPG
• MQ-6 : LPG, butane
• MQ-7 : Carbon Monoxide
• MQ-8 : Hydrogen Gas
• MQ-9 : Carbon Monoxide, flammable gasses
• MQ131 : Ozone
• MQ135 : Air Quality
• MQ136 : Hydrogen Sulphide gas
• MQ137 : Ammonia
• MQ138 : Benzene, Toluene, Alcohol, Propane, Formaldehyde gas, Hydrogen
• MQ214 : Methane, Natural Gas
• MQ216 : Natural gas, Coal Gas
• MQ303A : Alcohol, Ethanol, smoke
• MQ306A : LPG, butane
• MQ307A : Carbon Monoxide
• MQ309A :Carbon Monoxide, flammable gas

Applications of MQ-3 Gas Sensor

• Gas level over-limit alarm
• Breathalyser
• Portable alcohol detector
• Stand-alone/background sensing device
• Environmental monitoring equipment