2. SENSORS PRINCIPLES AND APPLICATION BY Dr GOVIND SINGH Dy.Manager (Chemical)

3. Introduction Introduction of electronics in daily life, increasing tendency for automation of industrial systems and of course complex sensing approach of living systems have directed the world class scientists to design a technology for dealing these requirements named as Sensors. These sensors provide direct information about the chemical composition of environmental component. The sensor consists of a chemically selective layer and physico-chemical transducer which are used for the measurement of the phenomena and answering the obvious requirements in the area of environmental protection, process control, food technology, medical engineering and pollution control studies.

4. Types of Sensors Chemical Electromagnetic Ionizing radiation Mechanical Optical Thermal Pressure

5. CATEGORIES OF THE CHEMICAL SENSORS: Thermal Sensors: Heat is a general property of any chemical reaction. As such it should be an ideal physical parameter to be used for sensing. Enzymatic reactions are chemically selective heat generators. The course of reaction of chemically selective layer and species of interest, leads to the generation of thermal sensor for the measurement of temperature change. The sensors, which use such transduction mode, are referred as thermal sensors.

6. Mass Sensors: Mass sensors involve the detection of mass change as a result of the interaction of chemically selective catalytic layer with the chemical composition of the environment. These mass sensors are based on piezoelectric bulk oscillators or surface acoustic wave

7. Optical Sensors: Optical mode of transduction is most suitable for the utilization in the construction of sensors. In optical sensors, optrode detection of reflected light is carried out based on the interaction of immobilized chemical selective layer with an analyte at the trace level using optical fiber via adsorption, fluorescence, reflectance and refractive index.

8. Electrochemical Sensor: The electrochemical sensor constitutes a major category of the sensor technology where the mode of transduction for chemical sensing is based on the electrochemical processes. Potentiometry, amperometry and conductometry are well known electrochemical processes, which involve the measurement of potential, current and conductance of the cell. On the basis of the modes of transduction, the electrochemical sensors are categorized as amperometric sensors, conductometric sensors and potentiometric sensors.

9. Amperometric Sensors In amperometric sensor a constant potential is applied between the working electrode (chemically modified electrode) and reference electrode. This applied potential result in electron transfer reaction to take place, as a result of which net current flows within the cell. The magnitude of this net current is directly related to the concentration of analyte.

10. Conductometric Sensors: Sensors in this group rely on changes of electric conductivity of a film or a bulk material, whose conductivity is affected by the analyte presence. Zinc oxide or tin oxide, doped with platinum microcrystals, was useful for determining traces of hydrogen in liquid hydrocarbons. Aqueous ozone can be measured by an In thin-film semiconductor ozone gas sensor. Polymer benzo-15-crown-5 complexes as sensor materials, were used to detect benzene in air and ethanol and dichloromethane in water.

11. Potentiometric Sensors: Potentio- metric sensors measure the potential difference between the transducing electrode and reference electrode. The catalytically sensitive membranes are the source of the generating potential which is proportional to the logarithm of analyte concentrations. Potentiometric measurements are made under the condition of zero current flow, as the flow of current tends to disturb the equilibrium at the sample membrane interface. Ion selective, gas selective, glass electrodes are mainly used in combinative of catalytic membrane for the construction of the potentiometric sensors

12. How we can develop a sensor. ?

13. The photograph of electrode body for the electropolymerization and subsequently development of electrochemical sensors, (a) Vertical view (b) Frontal view.

14. The photograph of the whole experimental set-up showing Solatron Electrochemical Interface connected to a PC through the serial port and one compartment cell consisting of working (Platinum disc), Ag/AgCl reference and platinum foil auxiliary electrodes.

15. The photograph of the whole experimental set-up showing Keithley multi-meter (model 2000) connected to a PC through the serial port in one compartment cell consisting of platinum disc working, Ag/AgCl reference and platinum foil auxiliary electrodes.

16. Typical potentiometric response of electrode on the addition of varying concentrations of acetic acid

17. Typical potentiometric response of electrode on the addition of varying concentrations of NH4OH

18. The plot of potentiometric response of tetraphenyl borate (TPB) anion doped polyaniline modified electrode pH at 25 0 C using 1 mM HCl for pH 3.0, 0.5 M Tris-acetate buffer pH 4.5, 0.5 M phosphate buffer for pH 6 to 8, 0.5 M borate buffer for pH 9.0.

19. Typical potentiometric response of urea biosensor on the addition of increasing concentrations of urea

20. The calibration curve for urea analysis using polyaniline based urea biosensor in 1 mM Tris-HCl buffer (pH 7.0)

23. Properties of a good sensor Sensitivity Selectivity Reproducibility Stability

24. Microphones are acoustic sensors A thin membrane in the microphone vibrates in response to sound waves Uses of Sensors

25. Breath analyzers are chemical sensors Any alcohol in the user’s breath undergoes an oxidation reaction An electrical current is produced and analyzed by the sensor Uses of Sensors

26. Metal detectors are electromagnetic sensors. Detect change in magnetic field due to induced current in metal brought through the device Uses of Sensors

27. Thermometers are thermal sensors Material inside the bulb has a physical change in response to change in temperature

28. Artificial liquid system - electronic tongue Sensor responses ComputerSensor array Pattern recognition Taste cell Nerve cell Taste compounds Electric responses Brain Taste reception Biological taste system Electronic Tongue Uses of Sensors

29. Applications of sensors Acoustic, sound, vibration Geophone Hydrophone Lace SensorLace Sensor a guitar pickup Microphone Seismometer Accelerometer

30. Chemical Carbon dioxide sensor Carbon monoxide detector Catalytic bead sensor Electrochemical gas sensor Electronic nose Hydrogen sensor Hydrogen sulfide sensor Ion-selective electrode Nondispersive infrared sensor Microwave chemistry sensor Nitrogen oxide sensor Optode Oxygen sensor pH glass electrode

31. Environment, weather, moisture, humidity Gas detector Hook gauge evaporimeter Hygrometer Leaf sensor Pyranometer Pyrgeometer Psychrometer Rain gauge Rain sensor Seismometers Snow gauge Soil moisture sensor Stream gauge Tide gauge

32. Flow, fluid velocity Air flow meter Anemometer Flow sensor Gas meter Mass flow sensor Water meter

33. Ionising radiation, subatomic particles Bubble chamber Cloud chamber Geiger counter Neutron detection Particle detector Scintillation counter Scintillator Wire chamber

34. Thermal, heat, temperature Bolometer Calorimeter Exhaust gas temperature gauge Gardon gauge Heat flux sensor Infrared thermometer Microbolometer Microwave radiometer Net radiometer Resistance temperature detector Resistance thermometer Silicon bandgap temperature sensor Temperature gauge Thermistor Thermocouple Thermometer

35. Thanking You