The gas sensor is a device that detects the concentration level of gases that are present in the atmosphere depending on the level of concentration the sensor observes the potential difference and this changes the resistance of the material inside the sensor. The output voltage gives the types of gas and also the concentration level of gas. These gas sensors are classified into different types depending on the type of sensing element present in it.
Gas sensor: Pin out
- Vcc (+5V)which powers the module
- Ground which connects the system to ground
- Digital out by setting threshold value we get the digital output by using a potential meter
- Analog out based on the intensity of gas .its gives output between 0 to 5V
Working of gas sensor
The gas sensor detects gases depends on the chemiresister to conduct current. Generally, chemiresistor is Tin Dioxide (SnO2) which is an n-type semiconductor that has free electrons. The atmosphere contains more oxygen than combustible gases. The oxygen particles attract the free electrons present in SnO2 which pushes them to the surface of the SnO2. Since there are no free electrons available then the output current will be zero.
When the sensor is placed in the toxic or combustible gases atmosphere, this reducing gas reacts with the adsorbed oxygen particles and breaks the chemical bond between oxygen and free electrons so it will release the free electrons. As the free electrons are back to their initial position they can now conduct current, this conduction will be proportional to the number of free electrons available in SnO2, if the gas is extremely toxic more free electrons will be available.
Various types of gas sensors
Electrochemical gas sensors
It is typically used to measure the concentration of target gas within an external circuit. It measures toxic gases in very low concentrations and can detect a wide range of gases.
Catalytic bead sensors
Catalytic bead sensors are typically used to measure combustible gases that come with an explosive hazard. Catalytic bead sensors are Simple and low-cost technology. It
Measures flammability of gases
Infrared Gas Sensor
It is used when there is no oxygen present or in situations where we measure high carbon dioxide concentration. It uses physical techniques only for sensing And There are no unseen failure modes. It can also be used in inert atmospheres.
Thermal Conductivity Gas Sensor
Thermal conductivity sensors are devices that quantify gases such as methane, helium, and hydrogen with percentage volume ranging from 0 to 100% and with varying thermal conductivities corresponding to a reference gas such as air. It has simple construction and robust along it is easy to operate in the absence of oxygen.
Surface Acoustic Wave Gas Sensor
Surface Acoustic Wave Gas Sensor is an Acoustic Wave propagating along the surface of a solid material. It can detect nerve and blister agents. It is used in wireless applications.
Applications of gas sensors
- Gas sensor used to monitor the concentration of the toxic gases in industries.
- It is used in households to detect an emergency incident.
- It also used at hotels to avoid customers from smoking as well as in detecting fire
- Used in air quality check at offices.
- Used air conditioners to monitor the CO2 levels.
- Used to check the concentration of gases in mines.
