GAS SENSORS Prepared by: Jiturvi Chokshi ENPM-808B

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GAS SENSORSPrepared byJiturvi
ChokshiENPM-808B
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Gas sensors

• 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.

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Gas sensors

• Introduction
• Sensor
• Applications
• Automobiles
• Machines
• Robotics
• Industry
• Medicine
• Aerospace etc.

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Gas sensors

• Introduction
• Sensor
• Examples of sensors
• Thermometer
• Thermocouple
• Phototransistor
• Photo resistor
• Microphone
• Seismometer
• Hydrophone etc.

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Gas sensors

• Introduction
• 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.

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Gas sensors

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

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Gas sensors

• Operating parameters
• Operating temperature
• Operating humidity
• Disadvantages
• Bulky
• Consume lots of power
• Require risky high voltage to operate.

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Gas sensors

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

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Gas sensors

• Gas sensing technologies
• 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.

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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.
• 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.

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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.

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Gas sensors

• Gas sensing technologies
• 3. 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.

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

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Gas sensors

• Gas sensing technologies
• 4. Calorimetric Gas Sensors
• 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 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.

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Gas sensors

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

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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)
• Absorbance and
• Fluorescence properties (of the analyte molecules
  or a chemo-optical transducing element.)

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Gas sensors

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

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Gas sensors

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

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

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Gas sensors

• Discussion on some gas sensors
• Carbon monoxide (CO) gas sensor
• Carbon dioxide (CO2) gas sensor
• Hydrogen gas sensor

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Gas sensors

• 1. 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.

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Gas sensors

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

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Gas sensors

• 2. 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.

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Gas sensors

• 2. Carbon dioxide (CO2) gas sensor (Contd.)
• Infrared radiation which is not being absorbed by
  CO2 produces heat so the temperature will
  increase.
• The infrared detector measures the temperature.
• A voltage is produced due to the temperature
  increase in the infrared sensor.
• We can read amplified voltage into the data
  logger.

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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.
• Types of hydrogen gas sensor
• Optical fiber hydrogen sensors
• Nanoparticle-based hydrogen microsensors
• Diode based sensor

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Gas sensors

• 3. Hydrogen gas sensor (Contd.)
• Development
• There is a recent progress in developing MEMS
  (Micro-Electro-Mechanical Systems) based H2 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 H2 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.

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Gas sensors

• LITERATURE CITED
• http//scholar.google.com/scholar?hlenlrqgas
  sensor
• http//en.wikipedia.org/wiki/Gas_sensor
• http//en.wikipedia.org/wiki/Hydrogen_microsensor
• http//vernier.com/probes/co2-bta.html
• http//sensors-transducers.globalspec.com/LearnMor
  e/Sensors_Transducers_Detectors/Gas_Sensing/Gas_Se
  nsors
• http//etd.ncsi.iisc.ernet.in/handle/2005/281
• Proceeding of the 2000 Hydrogen Program Review,
  NREL/CP-570-28890
• http//www.gasdetection.com/TECH/sensorprinciple2.
  htm
• http//physicsworld.com/cws/article/news/17869