12-06-2012, 02:11 PM
SEMINAR ON CHEMICAL SENSORS-GAS SENSORS
[attachment=24193]
Introduction:
Sensor:
A sensor is a technological device that detects / senses a signal, physical condition and chemical compounds.
It is also defined as any device that converts a signal from one form to another.
Sensors are mostly electrical or electronic.
Gas Sensor:
Gas sensor is a subclass of chemical sensors.
Gas sensor measures the concentration of gas in its vicinity. Gas sensor interacts with a gas to measure its concentration. Each gas has a unique breakdown voltage i.e. the electric field at which it is ionized. Sensor identifies gases by measuring these voltages. The concentration of the gas can be determined by measuring the current discharge in the device.
Gas sensing technologies:
1)Metal Oxide Based Gas Sensors
Metal oxide sensors are also known as chemiresistors.
The detection principle of resistive sensors is based on change of the resistance of a thin film upon adsorption of the gas molecules on the surface of a semiconductor.
The gas-solid interactions affect the resistance of the film because of the density of electronic species in the film.
2)Capacitance Based Gas Sensors
They measure the change in dielectric constant of films between the electrodes as a function of the gas concentration.
The capacitive sensor relies on inter-digitated electrode structures, which correspond to the two plates of a standard capacitor, to monitor changes of the dielectric coefficient of the film.
Carbon monoxide gas sensor
It can either be battery-operated or AC powered.
Mostly the sensor will not sound an alarm at lower concentrations (e.g. 100 ppm). The alarm will sound within a few minutes at 400 ppm. So the function is specific to concentration-time. Figure shows simple carbon monoxide sensor.
Carbon dioxide (CO2) gas sensor
CO2 absorbs infrared light therefore CO2 sensor consists of a tube containing an infrared source at one end and an infrared detector at the other end.
The infrared detector detects the infrared light which is not absorbed by CO2 between source and detector.
Hydrogen gas sensor
Mostly palladium is used to detect hydrogen because palladium selectively absorbs hydrogen gas and forms the chemical palladium hydride.
Types of hydrogen gas sensor:
Optical fiber hydrogen sensors
Nanoparticle-based hydrogen microsensors
Diode based sensor.
[attachment=24193]
Introduction:
Sensor:
A sensor is a technological device that detects / senses a signal, physical condition and chemical compounds.
It is also defined as any device that converts a signal from one form to another.
Sensors are mostly electrical or electronic.
Gas Sensor:
Gas sensor is a subclass of chemical sensors.
Gas sensor measures the concentration of gas in its vicinity. Gas sensor interacts with a gas to measure its concentration. Each gas has a unique breakdown voltage i.e. the electric field at which it is ionized. Sensor identifies gases by measuring these voltages. The concentration of the gas can be determined by measuring the current discharge in the device.
Gas sensing technologies:
1)Metal Oxide Based Gas Sensors
Metal oxide sensors are also known as chemiresistors.
The detection principle of resistive sensors is based on change of the resistance of a thin film upon adsorption of the gas molecules on the surface of a semiconductor.
The gas-solid interactions affect the resistance of the film because of the density of electronic species in the film.
2)Capacitance Based Gas Sensors
They measure the change in dielectric constant of films between the electrodes as a function of the gas concentration.
The capacitive sensor relies on inter-digitated electrode structures, which correspond to the two plates of a standard capacitor, to monitor changes of the dielectric coefficient of the film.
Carbon monoxide gas sensor
It can either be battery-operated or AC powered.
Mostly the sensor will not sound an alarm at lower concentrations (e.g. 100 ppm). The alarm will sound within a few minutes at 400 ppm. So the function is specific to concentration-time. Figure shows simple carbon monoxide sensor.
Carbon dioxide (CO2) gas sensor
CO2 absorbs infrared light therefore CO2 sensor consists of a tube containing an infrared source at one end and an infrared detector at the other end.
The infrared detector detects the infrared light which is not absorbed by CO2 between source and detector.
Hydrogen gas sensor
Mostly palladium is used to detect hydrogen because palladium selectively absorbs hydrogen gas and forms the chemical palladium hydride.
Types of hydrogen gas sensor:
Optical fiber hydrogen sensors
Nanoparticle-based hydrogen microsensors
Diode based sensor.