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GAS SENSORS Prepared by: Jiturvi Chokshi ENPM-808B.

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Presentation on theme: "GAS SENSORS Prepared by: Jiturvi Chokshi ENPM-808B."— Presentation transcript:

1 GAS SENSORS Prepared by: Jiturvi Chokshi ENPM-808B

2 Gas sensors Introduction:Sensor: A sensor is a technological device that detects / senses a signal, physical condition and chemical compounds. 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. It is also defined as any device that converts a signal from one form to another. Sensors are mostly electrical or electronic. Sensors are mostly electrical or electronic.

3 Gas sensors Introduction:Sensor:Applications Automobiles Automobiles Machines Machines Robotics Robotics Industry Industry Medicine Medicine Aerospace etc. Aerospace etc.

4 Gas sensors Introduction:Sensor: Examples of sensors Thermometer Thermometer Thermocouple Thermocouple Phototransistor Phototransistor Photo resistor Photo resistor Microphone Microphone Seismometer Seismometer Hydrophone etc. Hydrophone etc.

5 Gas sensors Introduction: Gas Sensor: Gas sensor is a subclass of chemical sensors. 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 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.

6 Gas sensors Applications of Gas Sensor: Process control industries Process control industries Environmental monitoring Environmental monitoring Boiler control Boiler control Fire detection Fire detection Alcohol breath tests Alcohol breath tests Detection of harmful gases in mines Detection of harmful gases in mines Home safety Home safety Grading of agro-products like coffee and spices Grading of agro-products like coffee and spices

7 Gas sensors Operating parameters: Operating temperature Operating temperature Operating humidity Operating humidityDisadvantages: Bulky Bulky Consume lots of power Consume lots of power Require risky high voltage to operate. Require risky high voltage to operate.

8 Gas sensors Gas sensing technologies: Metal Oxide Based Gas Sensors Metal Oxide Based Gas Sensors Capacitance Based Gas Sensors Capacitance Based Gas Sensors Acoustic Wave Based Gas Sensors Acoustic Wave Based Gas Sensors Calorimetric Gas Sensors Calorimetric Gas Sensors Optical gas sensors Optical gas sensors Electrochemical gas sensors Electrochemical gas sensors

9 Gas sensors Gas sensing technologies: 1.Metal Oxide Based Gas Sensors Metal oxide sensors are also known as chemiresistors. 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 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. The gas-solid interactions affect the resistance of the film because of the density of electronic species in the film.

10 Gas sensors Gas sensing technologies: 2. Capacitance Based Gas Sensors They measure the change in dielectric constant of films between the electrodes as a function of the gas concentration. 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. 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.

11 Gas sensors Gas sensing technologies: 2. Capacitance Based Gas Sensors (Contd.) The simple theory behind it is if the dielectric constant of the film is lower than that of the analyte, the capacitance will increase and vice versa. The simple theory behind it is if the dielectric constant of the film is lower than that of the analyte, the capacitance will increase and vice versa.

12 Gas sensors Gas sensing technologies: 3. Acoustic Wave Based Gas Sensors Sound based gas sensors are known as acoustic wave based gas sensors. Sound based gas sensors are known as acoustic wave based gas sensors. To launch the acoustic waves, this type of sensor use piezoelectric material either in the thin film form or in bulk form which has one or more transducers on its surface. To launch the acoustic waves, this type of sensor use piezoelectric material either in the thin film form or in bulk form which has one or more transducers on its surface.

13 Gas sensors Gas sensing technologies: 3. Acoustic Wave Based Gas Sensors (Contd.) Then type of acoustic wave generated and device resonant frequency has been determined. Then type of acoustic wave generated and device resonant frequency has been determined. Depending on that, it is possible to measure properties, processes, or chemical species in the gas phase, liquid phase, vacuum or thin solid films. Depending on that, it is possible to measure properties, processes, or chemical species in the gas phase, liquid phase, vacuum or thin solid films.

14 Gas sensors Gas sensing technologies: 4. Calorimetric Gas Sensors The principle of calorimetric gas sensors based on change in temperature at catalytic surfaces. The principle of calorimetric gas sensors based on change in temperature at catalytic surfaces. It consists of a surface of a film of a catalytically active metal (e.g. Platinum, Palladium or Rhodium). It consists of a surface of a film of a catalytically active metal (e.g. Platinum, Palladium or Rhodium). It burns combustible gases. Heat is generated due to the combustion. It burns combustible gases. Heat is generated due to the combustion. This heat is balanced by a reduction in the electrical heating power. Thus the power consumption indicates the concentration of gas. This heat is balanced by a reduction in the electrical heating power. Thus the power consumption indicates the concentration of gas.

15 Gas sensors Gas sensing technologies: 5. Optical gas sensors Following methods are used : Ellipsometry (Technique for the investigation of the dielectric properties) Ellipsometry (Technique for the investigation of the dielectric properties) Spectroscopy (luminescence, phosphorescence, fluorescence, Raman) Spectroscopy (luminescence, phosphorescence, fluorescence, Raman) Interferometry (white light Interferometry, modal Interferometry in optical waveguide structures) Interferometry (white light Interferometry, modal Interferometry in optical waveguide structures)

16 Gas sensors Gas sensing technologies: 5. Optical gas sensors (Contd.) In these sensors a desired quantity is determined by: Refractive index (Speed of the light) Refractive index (Speed of the light) Absorbance and Absorbance and Fluorescence properties (of the analyte molecules or a chemo-optical transducing element.) Fluorescence properties (of the analyte molecules or a chemo-optical transducing element.)

17 Gas sensors Gas sensing technologies: 5. Optical gas sensors (Contd.)

18 Gas sensors Gas sensing technologies: 6. Electrochemical gas sensors It consists of: Chemical reactants (electrolytes or gels) Chemical reactants (electrolytes or gels) Two terminals (an anode and a cathode) Two terminals (an anode and a cathode) Anode is responsible for oxidization process and cathode is responsible for reduction process. Anode is responsible for oxidization process and cathode is responsible for reduction process. As a result, current is created. As a result, current is created. Positive ions flow to the cathode and the negative ions flow to the anode. Positive ions flow to the cathode and the negative ions flow to the anode.

19 Gas sensors Gas sensing technologies: 6. Electrochemical gas sensors (Contd.) We can find reducible gases (such as oxygen, nitrogen oxides and chlorine) at the cathode and oxidizable gases (carbon monoxide, nitrogen dioxide, and hydrogen sulfide) at the anode. We can find reducible gases (such as oxygen, nitrogen oxides and chlorine) at the cathode and oxidizable gases (carbon monoxide, nitrogen dioxide, and hydrogen sulfide) at the anode. The output is directly proportional to the concentration or partial pressure of the gaseous species. The output is directly proportional to the concentration or partial pressure of the gaseous species.

20 Gas sensors Discussion on some gas sensors: Carbon monoxide (CO) gas sensor Carbon monoxide (CO) gas sensor Carbon dioxide (CO 2 ) gas sensor Carbon dioxide (CO 2 ) gas sensor Hydrogen gas sensor Hydrogen gas sensor

21 Gas sensors 1. Carbon monoxide gas sensor It can either be battery-operated or AC powered. 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. 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.

22 Gas sensors 1. Carbon monoxide gas sensor (Contd.) Carbon monoxide sensor can be of different types such as: Semiconductor sensor Semiconductor sensor Electrochemical sensor Electrochemical sensor Digital sensor Digital sensor Biomimetic sensor (chem-optical or gel cell sensor) Biomimetic sensor (chem-optical or gel cell sensor)

23 Gas sensors 2. Carbon dioxide (CO 2 ) gas sensor CO 2 absorbs infrared light therefore CO 2 sensor consists of a tube containing an infrared source at one end and an infrared detector at the other end. CO 2 absorbs infrared light therefore CO 2 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 CO 2 between source and detector. The infrared detector detects the infrared light which is not absorbed by CO 2 between source and detector.

24 Gas sensors 2. Carbon dioxide (CO 2 ) gas sensor (Contd.) Infrared radiation which is not being absorbed by CO 2 produces heat so the temperature will increase. Infrared radiation which is not being absorbed by CO 2 produces heat so the temperature will increase. The infrared detector measures the temperature. The infrared detector measures the temperature. A voltage is produced due to the temperature increase in the infrared sensor. A voltage is produced due to the temperature increase in the infrared sensor. We can read amplified voltage into the data logger. We can read amplified voltage into the data logger.

25 Gas sensors 3. Hydrogen gas sensor Mostly palladium is used to detect hydrogen because palladium selectively absorbs hydrogen gas and forms the chemical palladium hydride. 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 Optical fiber hydrogen sensors Nanoparticle-based hydrogen microsensors Nanoparticle-based hydrogen microsensors Diode based sensor Diode based sensor

26 Gas sensors 3. Hydrogen gas sensor (Contd.) Development: There is a recent progress in developing MEMS (Micro-Electro-Mechanical Systems) based H 2 gas sensors. These sensors couple novel thin films as the active layer with a MEMS structure known as a Micro-Hotplate. This coupling results in a H 2 gas sensor that has several unique advantages in terms of speed, sensitivity, stability and amenability to large scale manufacture. Preliminary results are extremely encouraging and suggest that this technology has substantial potential for meeting the sensing requirements of a hydrogen based energy economy. There is a recent progress in developing MEMS (Micro-Electro-Mechanical Systems) based H 2 gas sensors. These sensors couple novel thin films as the active layer with a MEMS structure known as a Micro-Hotplate. This coupling results in a H 2 gas sensor that has several unique advantages in terms of speed, sensitivity, stability and amenability to large scale manufacture. Preliminary results are extremely encouraging and suggest that this technology has substantial potential for meeting the sensing requirements of a hydrogen based energy economy.

27 Gas sensors LITERATURE CITED: 1.http://scholar.google.com/scholar?hl=en&lr=&q=ga s+sensor 2.http://en.wikipedia.org/wiki/Gas_sensor 3.http://en.wikipedia.org/wiki/Hydrogen_microsensor 4.http://vernier.com/probes/co2-bta.html 5.http://sensors- transducers.globalspec.com/LearnMore/Sensors_T ransducers_Detectors/Gas_Sensing/Gas_Sensors 6.http://etd.ncsi.iisc.ernet.in/handle/2005/281 7.Proceeding of the 2000 Hydrogen Program Review, NREL/CP http://www.gasdetection.com/TECH/sensorprincipl e2.htm 9.http://physicsworld.com/cws/article/news/17869


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