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

GAS SENSORSGAS SENSORS

Prepared by:Prepared by:

Jiturvi ChokshiJiturvi ChokshiENPM-808BENPM-808B

Gas sensorsGas sensors

Introduction:Introduction:Sensor:Sensor:

A sensor is a technological device that A sensor is a technological device that detects / senses a signal, physical condition detects / senses a signal, physical condition and chemical compounds. and chemical compounds.

It is also defined as any device that converts It is also defined as any device that converts a signal from one form to another.a signal from one form to another.

Sensors are mostly electrical or electronic. Sensors are mostly electrical or electronic.


Introduction:Introduction:

Sensor:Sensor:

ApplicationsApplications AutomobilesAutomobilesMachinesMachinesRoboticsRoboticsIndustryIndustryMedicineMedicineAerospace etc. Aerospace etc.


Introduction:Introduction:Sensor:Sensor:

Examples of sensorsExamples of sensors ThermometerThermometerThermocoupleThermocouplePhototransistorPhototransistorPhoto resistorPhoto resistorMicrophoneMicrophoneSeismometerSeismometerHydrophone etc.Hydrophone etc.


Introduction:Introduction:Gas Sensor:Gas Sensor:

Gas sensor is a subclass of chemical Gas sensor is a subclass of chemical sensors.sensors.

Gas sensor measures the concentration of Gas sensor measures the concentration of gas in its vicinity. Gas sensor interacts with a gas in its vicinity. Gas sensor interacts with a gas to measure its concentration. gas to measure its concentration. Each gas Each gas has a unique breakdown voltage i.e. the has a unique breakdown voltage i.e. the electric field at which it is ionized. Sensor electric field at which it is ionized. Sensor identifies gases by measuring these voltages. identifies gases by measuring these voltages. The concentration of the gas can be The concentration of the gas can be determined by measuring the current determined by measuring the current discharge in the device. discharge in the device.


Applications of Gas Sensor:Applications of Gas Sensor:

Process control industriesProcess control industriesEnvironmental monitoringEnvironmental monitoringBoiler 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 safetyHome safetyGrading of agro-products like coffee and Grading of agro-products like coffee and spicesspices


Operating parameters:Operating parameters:

Operating temperatureOperating temperatureOperating humidityOperating humidity

Disadvantages:Disadvantages:

BulkyBulkyConsume lots of powerConsume lots of powerRequire “risky” high voltage to operate.Require “risky” high voltage to operate.


Gas sensing technologies:Gas sensing technologies:

Metal Oxide Based Gas SensorsMetal Oxide Based Gas Sensors Capacitance Based Gas SensorsCapacitance Based Gas Sensors Acoustic Wave Based Gas SensorsAcoustic Wave Based Gas Sensors Calorimetric Gas SensorsCalorimetric Gas Sensors Optical gas sensorsOptical gas sensors Electrochemical gas sensorsElectrochemical gas sensors


Gas sensing technologies:Gas sensing technologies:1.1. Metal Oxide Based Gas SensorsMetal Oxide Based Gas Sensors

Metal oxide sensors are also known as Metal oxide sensors are also known as chemiresistors. chemiresistors.

The detection principle of resistive sensors The detection principle of resistive sensors is based on is based on change of the resistancechange of the resistance of a of a thin film upon adsorption of the gas thin film upon adsorption of the gas molecules on the surface of a molecules on the surface of a semiconductor.semiconductor.

The gas-solid interactions affect the The gas-solid interactions affect the resistance of the film because of the resistance of the film because of the density of electronic species in the film. density of electronic species in the film.



2. Capacitance Based Gas Sensors2. Capacitance Based Gas Sensors They measure the They measure the change in dielectric change in dielectric

constantconstant of films between the electrodes of films between the electrodes as a function of the gas concentration. as a function of the gas concentration.

The capacitive sensor relies on inter-The capacitive sensor relies on inter-digitated electrode structures, which digitated electrode structures, which correspond to the two plates of a standard correspond to the two plates of a standard capacitor, to monitor changes of the capacitor, to monitor changes of the dielectric coefficient of the film.dielectric coefficient of the film.



2. Capacitance Based Gas Sensors (Contd.)2. Capacitance Based Gas Sensors (Contd.)

The simple theory behind it is if the The simple theory behind it is if the dielectric constant of the film is lower than dielectric constant of the film is lower than that of the analyte, the capacitance will that of the analyte, the capacitance will increase and vice versa.increase and vice versa.



3. Acoustic Wave Based Gas Sensors3. Acoustic Wave Based Gas Sensors

Sound based gas sensors are known as Sound based gas sensors are known as acoustic wave based gas sensors. acoustic wave based gas sensors.

To launch the acoustic waves, this type of To launch the acoustic waves, this type of sensor use piezoelectric material either in sensor use piezoelectric material either in the thin film form or in bulk form which has the thin film form or in bulk form which has one or more transducers on its surface. one or more transducers on its surface.


Gas sensing technologies:Gas sensing technologies:3. Acoustic Wave Based Gas Sensors (Contd.)3. Acoustic Wave Based Gas Sensors (Contd.)

Then Then type of acoustic wavetype of acoustic wave generated and generated and device device resonant frequencyresonant frequency has been has been determined. determined.

Depending on that, it is possible to measure Depending on that, it is possible to measure properties, processes, or chemical species in properties, processes, or chemical species in the gas phase, liquid phase, vacuum or thin the gas phase, liquid phase, vacuum or thin solid films. solid films.


Gas sensing technologies:Gas sensing technologies:4. Calorimetric Gas Sensors4. Calorimetric Gas Sensors

The principle of calorimetric gas sensors The principle of calorimetric gas sensors based on change in temperature at based on change in temperature at catalytic surfaces. catalytic surfaces.

It consists of a surface of a film of a It consists of a surface of a film of a catalytically active metal (e.g. Platinum, catalytically active metal (e.g. Platinum, Palladium or Rhodium) . Palladium or Rhodium) .

It burns combustible gases. Heat is It burns combustible gases. Heat is generated due to the combustion. generated due to the combustion.

This heat is balanced by a reduction in the This heat is balanced by a reduction in the electrical heating power. Thus the electrical heating power. Thus the power power consumption indicates the concentration of consumption indicates the concentration of gas. gas.


Gas sensing technologies:Gas sensing technologies:5. Optical gas sensors5. Optical gas sensors

Following methods are used :Following methods are used :

Ellipsometry (Technique for the Ellipsometry (Technique for the investigation of the dielectric properties)investigation of the dielectric properties)

Spectroscopy (luminescence, Spectroscopy (luminescence, phosphorescence, fluorescence, Raman)phosphorescence, fluorescence, Raman)

Interferometry (white light Interferometry, Interferometry (white light Interferometry, modal Interferometry in optical waveguide modal Interferometry in optical waveguide structures)structures)


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

In these sensors a desired quantity is In these sensors a desired quantity is determined by:determined by:

Refractive index (Speed of the light)Refractive index (Speed of the light) Absorbance andAbsorbance and Fluorescence properties (of the analyte Fluorescence properties (of the analyte

molecules or a chemo-optical transducing molecules or a chemo-optical transducing element.)element.)



5. Optical gas sensors (Contd.)5. Optical gas sensors (Contd.)


Gas sensing technologies:Gas sensing technologies:6. Electrochemical gas sensors6. Electrochemical gas sensors

It consists of: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 Anode is responsible for oxidization process and cathode is responsible for process and cathode is responsible for reduction process. reduction process.

As a result, current is created.As a result, current is created. Positive ions flow to the cathode and the Positive ions flow to the cathode and the

negative ions flow to the anode. negative ions flow to the anode.


Gas sensing technologies:Gas sensing technologies:6. Electrochemical gas sensors (Contd.)6. Electrochemical gas sensors (Contd.)

We can find reducible gases (such as We can find reducible gases (such as oxygen, nitrogen oxides and chlorine) at oxygen, nitrogen oxides and chlorine) at the cathode and oxidizable gases (carbon the cathode and oxidizable gases (carbon monoxide, nitrogen dioxide, and hydrogen monoxide, nitrogen dioxide, and hydrogen sulfide) at the anode. sulfide) at the anode.

The output is directly proportional to the The output is directly proportional to the concentration or partial pressure of the concentration or partial pressure of the gaseous species. gaseous species.


Discussion on some gas sensors:Discussion on some gas sensors:

Carbon monoxide (CO) gas sensorCarbon monoxide (CO) gas sensor Carbon dioxide (COCarbon dioxide (CO22) gas sensor) gas sensor

Hydrogen gas sensorHydrogen gas sensor


1. Carbon monoxide gas sensor1. Carbon monoxide gas sensor It can either be battery-operated or AC It can either be battery-operated or AC

powered. powered. Mostly the sensor will not sound an alarm Mostly the sensor will not sound an alarm

at lower concentrations (e.g. 100 ppm). at lower concentrations (e.g. 100 ppm). The alarm will sound within a few minutes The alarm will sound within a few minutes at 400 ppm. So the function is specific to at 400 ppm. So the function is specific to concentration-time. Figure shows simple concentration-time. Figure shows simple carbon monoxide sensor.carbon monoxide sensor.


1. Carbon monoxide gas sensor (Contd.)1. Carbon monoxide gas sensor (Contd.)

Carbon monoxide Carbon monoxide sensor can be of sensor can be of different types such as: different types such as:

Semiconductor sensorSemiconductor sensor Electrochemical sensorElectrochemical sensor Digital sensorDigital sensor Biomimetic sensor (chem-optical or gel cell Biomimetic sensor (chem-optical or gel cell

sensor)sensor)


2. Carbon dioxide (CO2. Carbon dioxide (CO22) gas sensor) gas sensor

COCO22 absorbs infrared light therefore absorbs infrared light therefore COCO22

sensor consists of a tube containing an sensor consists of a tube containing an infrared source at one end and an infrared infrared source at one end and an infrared detector at the other end. detector at the other end.

The infrared detector detects the infrared The infrared detector detects the infrared light which is not absorbed by light which is not absorbed by COCO22

between source and detector.between source and detector.


2. Carbon dioxide (CO2. Carbon dioxide (CO22) gas sensor ) gas sensor (Contd.)(Contd.)

Infrared radiation which is not being Infrared radiation which is not being absorbed by absorbed by COCO22 produces heat so the produces heat so the temperature will increase. temperature will increase.

The infrared detector measures the The infrared detector measures the temperature. temperature.

A voltage is produced due to the A voltage is produced due to the temperature increase in the infrared temperature increase in the infrared sensor. sensor.

We can read amplified voltage into the We can read amplified voltage into the data logger. data logger.


3. Hydrogen gas sensor3. Hydrogen gas sensor

Mostly palladium is used to detect hydrogen Mostly palladium is used to detect hydrogen because palladium selectively absorbs because palladium selectively absorbs hydrogen gas and forms the chemical hydrogen gas and forms the chemical palladium hydride. palladium hydride.

Types of hyTypes of hydrogen gas sensor:drogen gas sensor:

Optical fiber hydrogen sensorsOptical fiber hydrogen sensors Nanoparticle-based hydrogen microsensorsNanoparticle-based hydrogen microsensors Diode based sensorDiode based sensor


33. Hydrogen gas sensor . Hydrogen gas sensor (Contd.)(Contd.)Development: Development: There is a There is a recent progress in developing recent progress in developing

MEMS (Micro-Electro-Mechanical MEMS (Micro-Electro-Mechanical Systems) based HSystems) based H22 gas sensors. These gas sensors. These sensors couple novel thin films as the sensors couple novel thin films as the active layer with a MEMS structure known active layer with a MEMS structure known as a as a Micro-HotplateMicro-Hotplate. This coupling results . This coupling results in a Hin a H22 gas sensor that has several unique gas sensor that has several unique advantages in terms of speed, sensitivity, advantages in terms of speed, sensitivity, stability and amenability to large scale stability and amenability to large scale manufacture. Preliminary results are manufacture. Preliminary results are extremely encouraging and suggest that extremely encouraging and suggest that this technology has substantial potential for this technology has substantial potential for meeting the sensing requirements of a meeting the sensing requirements of a hydrogen based energy economy.hydrogen based energy economy.


LITERATURE CITED:LITERATURE CITED:

1.1. http://scholar.google.com/scholar?http://scholar.google.com/scholar?hl=en&lr=&q=gas+sensorhl=en&lr=&q=gas+sensor

2.2. http://en.wikipedia.org/wiki/Gas_sensorhttp://en.wikipedia.org/wiki/Gas_sensor3.3. http://en.wikipedia.org/wiki/Hydrogen_microsensorhttp://en.wikipedia.org/wiki/Hydrogen_microsensor4.4. http://vernier.com/probes/co2-bta.htmlhttp://vernier.com/probes/co2-bta.html5.5. http://sensors-transducers.globalspec.com/http://sensors-transducers.globalspec.com/

LearnMore/Sensors_Transducers_Detectors/LearnMore/Sensors_Transducers_Detectors/Gas_Sensing/Gas_SensorsGas_Sensing/Gas_Sensors

6.6. http://etd.ncsi.iisc.ernet.in/handle/2005/281http://etd.ncsi.iisc.ernet.in/handle/2005/2817.7. Proceeding of the 2000 Hydrogen Program Review, Proceeding of the 2000 Hydrogen Program Review,

NREL/CP-570-28890NREL/CP-570-288908.8. http://www.gasdetection.com/TECH/http://www.gasdetection.com/TECH/

sensorprinciple2.htmsensorprinciple2.htm9.9. http://physicsworld.com/cws/article/news/17869http://physicsworld.com/cws/article/news/17869

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

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