{"id":425,"date":"2018-11-30T04:32:04","date_gmt":"2018-11-30T04:32:04","guid":{"rendered":"http:\/\/msp04.epgpbooks.inflibnet.ac.in\/?post_type=chapter&p=425"},"modified":"2018-11-30T04:54:09","modified_gmt":"2018-11-30T04:54:09","slug":"transducers","status":"publish","type":"chapter","link":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/chapter\/transducers\/","title":{"rendered":"Transducers"},"content":{"raw":"
\r\n\r\n\u00a0 \u00a0 Transducers<\/strong>\r\n\r\n \r\n

While making measurements, the quantity to be measured, also called as Measurand, first of all comes in contact with the Detector. The measurand or the input signal is basically the Information which we require from the measurement system. This information can be present either in the form of a physical phenomenon or an electrical signal. This information is then sensed and translated into a suitable form for their recognition in the further stages of the system by the detector. Energy is required in order to detect and convert the input signal or information from one form to another. To reduce the loading effects, efforts are generally made to supply energy to the detector from the external sources so that no undue energy is being extracted from the input signal and the output of detector is faithful representation of the input.<\/p>\r\n \r\n

Broadly speaking, transducer is a device which receives energy in one form and transfers it into another convenient form or state. For example, the diaphragm produces displacement on application of pressure. Both pressure and displacement are both mechanical form of energy, still displacement is easier from the measurement point of view. Similarly, a thermocouple which is a junction of dissimilar metals generates electrical signals with a difference in temperature. Thus, it acts as converter of temperature difference or heat energy to electrical energy, which is easier for measurements. Thus, a thermocouple may be called as a temperature transducer.<\/p>\r\n \r\n

The sensors or the transducers may be electrical, mechanical, acoustic, optical, thermal, magnetic, nuclear, chemical or any of their combinations. Out of all these types, electrical signals are most preferred due to the following reasons:<\/p>\r\n\r\n

    \r\n \t
  1. Devices such as op-amps can be used to ensure a minimum loading of the system.<\/li>\r\n \t
  2. The electrical signal can be easily conditioned as required.<\/li>\r\n \t
  3. The measurements can be performed remotely and also multiple times.<\/li>\r\n \t
  4. Data-acquisition for the electrical signals is largely observer independent and can be controlled precisely using computers.<\/li>\r\n<\/ol>\r\n\u00a0 \u00a0 Classification of Transducers:<\/strong>\r\n\r\n \r\n\r\nElectrical transducers can be divided into two main categories:\r\n
      \r\n \t
    1. Active transducers<\/li>\r\n \t
    2. Passive transducers<\/li>\r\n<\/ol>\r\n\u00a0 \u00a0 1.\u00a0 <\/strong>Active transducers<\/strong>\r\n\r\n \r\n

      These are self-generating devices and do not require any external source of energy to be driven. Active transducers basically convert one form of energy to the other without requiring any external source for their excitation. These can be further divided into the following categories:<\/span><\/p>\r\n\r\n

        \r\n \t
      1. Thermoelectric transducers: these are based on the property of thermoelectricity generation. Devices such as <\/span>thermocouple, thermopile <\/span>and thermocouple gauge are based on this property for their application in the measurement of Temperature, radiation pyrometry or temperature of distant objects and low pressure respectively.<\/span><\/li>\r\n \t
      2. Piezoelectric transducers: These are based on the property of piezoelectricity generation. Devices such as piezoelectric transducers are based on this property for their application in the measurement of pressure.<\/li>\r\n \t
      3. Photovoltaic transducers: These are based on the property of photoelectricity generation. Devices such as photodiode in combination with a diaphragm are based on this property for their application in the measurement of pressure.<\/span><\/li>\r\n \t
      4. Electromagnetic transducers: These are based on the property of electricity generation by moving a coil in a magnetic field. Devices such as electromagnetic pick-up are based on this property for their application in the measurement of flow.<\/li>\r\n \t
      5. Galvanic transducers.<\/li>\r\n<\/ol>\r\n<\/div>\r\n
        \r\n\r\n\u00a0 \u00a0 2.\u00a0<\/strong>Passive Transducers:<\/strong>\r\n\r\n \r\n

        These transducers need to be excited from the external source of electrical energy for their working. The energy derived from the measured signal produces a change in the electrical state of the passive transducers which can further be assessed easily. Consider a photoresistor, it can be excited by an external cell and the voltage across it can be easily measured. When light of sufficient intensity is turned ON, the resistance of photoresistor changes, which ultimately alters the voltage across it. Depending upon the principle of operation, passive transducers can be further classified as follows:<\/p>\r\n\r\n

          \r\n \t
        1. Resistive transducers<\/li>\r\n \t
        2. Inductive transducers<\/li>\r\n \t
        3. Capacitive transducers<\/li>\r\n \t
        4. Magnetoresistace transducers<\/li>\r\n \t
        5. Photoconductive transducers<\/li>\r\n \t
        6. Thermoresistive transducers<\/li>\r\n \t
        7. Elastoresistive transducers<\/li>\r\n<\/ol>\r\n

          \u00a0 Transducer devices such as potentiometers, strain guage, pirani guage, hot-wire anemometer, platinum resistance thermometer, thermistor, photoconductive cell or light-dependent resistor (LDR) in combination with a diaphragm are a few examples of the devices which are based on the property of resistance variation.\u00a0These devices find application in the determination of displacement, small displacements useful in the measurement of strain, pressure, force or torque, to measure low pressure, flow, temperature, pressure etc.<\/span><\/p>\r\n \r\n

          Devices such as <\/span>linear variable differential transformer (LVDT), Synchro and eddy current gauge are based on the property of Inductance variation for their application in the measurement of displacement and angular displacement. Capacitance variation based devices such as Capacitor gauge and Dielectric gauge are used to measure displacement.<\/span><\/p>\r\n \r\n

          Electrical transducers have far more adaptability to the instrumentation than those of the transducers which generate <\/span>analogue output signals. Electrical transducers can be the first constituent element in a measurement system and hence are called as <\/span>primary<\/em> transducers. However, many times transducers are preceded by mechanical instruments in the measurement system. Such transducers are called as <\/span>Secondary<\/em> transducers. It should be noted that the precision of the data observed by a measurement depends mostly on the transducers as they are the sensing elements in the system.<\/span><\/p>\r\n\r\n<\/div>\r\n

          \r\n\r\n\u00a0 \u00a0 Analogue and Digital Transducers:<\/strong>\r\n\r\n \r\n

          Classification of the transducers can also be done on the basis of the type of output which can be either in the form of continuous signal as a function of time or as discrete steps.<\/p>\r\n \r\n

          Analogue Transducers: <\/strong>The transducers which convert the physical phenomenon into an analogue signal which is a continuous function of time. Examples of Analogue signals are LVDT, strain gauge, thermocouple or a thermistor.<\/p>\r\n \r\n

          Digital Transducers: <\/strong>These transducers convert the input physical phenomenon into an electrical output which is in the form of pulses. This transducer uses digital code marks to identify the position of a movable piece by a binary system of notation. The position is given out as a train of digital pulses.<\/p>\r\n \r\n\r\nElectrical Phenomena used in Transducers<\/strong>\r\n\r\n \r\n

          The transducers may be classified into different categories depending upon the principle employed by their transduction elements to convert the physical phenomenon (input) into output electrical signals. The different electrical phenomena employed in transduction elements of transducers are listed below. These phenomena may be combined with appropriate primary sensing elements (detectors) to produce a variety of transducers. ,<\/p>\r\n \r\n

          These phenomena are: 1. Resistive. 2. Inductive. 3. Capacitive. 4. Electromagnetic. 5. Piezoelectric. 6. Ionization. 7. Photoelectric or Photoemissive. 8. Photoconductive or Photoresistive. 9. Photovoltaic. IO. Potentiometric. 11. Thermoelectric or Thermovoltaic. 12. Electrokinetic.<\/p>\r\n \r\n\r\nMagnetic Effect based Transducers:<\/strong>\r\n\r\n \r\n

          Magnetic effect based sensors are gaining a lot of attention lately because of their diverse applications. For example, reluctance based transducers are based on Faraday effect and magnetoresistive transducers utilize Thomson effect. Transducers which are utilized in combination with piezoelectric elements for magnetometers\u00a0and potentiometers are based on the principle of Joule effect or Magnetostriction. Torque\/ force, displacement and level measurement are based on <\/span>Wiedemann effect. Magnetoelastic and magnetogalvanic sensors are based upon Villari and Hall effects respectively and SQUID magnetometers are based on Josephson effect.<\/span><\/p>\r\n \r\n

          Based on the principle of energy conversion, magnetic transducers can also be classified as active and passive transducers.<\/span><\/p>\r\n \r\n

          Joule effect or Magnetostriction:<\/strong><\/p>\r\n \r\n

          Magnetostriction refers to the property of materials (ferromagnetic) which expand or contract in the presence of magnetic fields. These materials have crystalline structure intrinsically which is divided <\/span>in several domains, each of which has a uniform magnetic polarization. In the presence of <\/span>external magnetic field, the domains become oriented with their axes almost parallel to each other. Also, the domain boundaries also get shifted and thus, a change in the dimension of material is observed.<\/span><\/p>\r\n \r\n

          Magnetostriction <\/span>coefficient, \u03bb refers to the fractional change in the length of the ferromagnetic material with the application of <\/span>magnetic field. The change in length can either be positive or negative i.e. the length can increase or decrease and the value of \u03bb is of the order of 10-5. There is a dissipation of energy in the form of sound which is related to the elastic strain energy associated with deformation. Vibrators, ultrasonic vibrations as sound waves or as ultrasonic waves in liquids utilize Magnetostriction effect.<\/span><\/p>\r\n \r\n

          Villari Effect: <\/strong>It is <\/span>reverse of Magnetostrictive effect, as it refers to the permanent change in the magnetic permeability of the material by generating stress in the Magnetostrictive material. Magnetostrictive displacement sensors and level sensors are based on the Villari effect.<\/span><\/p>\r\n \r\n

          Selection Criteria<\/strong><\/p>\r\n \r\n

          While selecting transducers for a measurement, <\/span>following parameters must be taken into account.<\/span><\/p>\r\n \r\n

          There are Fundamental Parameters which must be taken into account. These fundamental parameters can be classified as follows:<\/strong><\/p>\r\n\r\n<\/div>\r\n

          \r\n\r\n\u00a0 \u00a0 1. Selection of transducers will depend upon the Type of Measurand\r\n\r\n2.\u00a0Range of measurement will also decide the type of transducers to be used.\r\n\r\n3. Required precision during transducers selection will depend upon the following factors:\r\n\r\na. Allowable nonlinearity effects in the transducers\r\n\r\nb. Allowable dead-zone effects present in transducers\r\n\r\nc. Frequency-response of the transducers and\r\n\r\nd. Resolution of the transducers\r\n\r\n \r\n\r\nEnvironmental Parameters also play a significant role in <\/strong>transducers selection<\/span>: <\/strong>It includes consideration of<\/span>\r\n
            \r\n \t
          1. Ambient temperature for the measurements<\/span><\/li>\r\n \t
          2. Corrosive or non-corrosive atmosphere where measurements are to be carried out<\/span><\/li>\r\n \t
          3. Shock and vibration to be withstand during measurements<\/span><\/li>\r\n<\/ol>\r\n<\/div>\r\n
            \r\n

            \u00a0 \u00a0 Physical Conditions of the <\/strong>transducers and also the Measurand are very much important for the selection of transducers:<\/strong> These must also be taken care of:<\/p>\r\n\r\n

              \r\n \t
            1. Room or available space to mount the transducer is important<\/li>\r\n \t
            2. Whether the measurement is static or dynamic will also decide the type of transducers to be used.<\/li>\r\n \t
            3. How much energy can be extracted from the Measurand to do the measurement without loading is an important parameter for deciding the transducers.<\/li>\r\n<\/ol>\r\n\u00a0 \u00a0 Compatibility with the next stage:<\/strong>\r\n\r\n \r\n

              The transducer must be chosen properly so that it is compatible with the requirements of the next stage in the measurement system and the following points must be taken account of:<\/p>\r\n\r\n

                \r\n \t
              1. There should be Impedance matching of the transducers with the instruments to be used for measurements<\/li>\r\n \t
              2. There should be Excitation voltage matching with the next stage in the measurement system.<\/li>\r\n \t
              3. Also, there should be Sensitivity tolerance matching with the next stage in the measurement system.<\/li>\r\n<\/ol>\r\n

                \u00a0 Transducers in general can be prepared from a variety of materials but in order to have application in practical instrumentation, they must adapt the following requirements:<\/p>\r\n\r\n

                  \r\n \t
                1. They should have Ruggedness to withstand overload<\/li>\r\n \t
                2. There should be Linearity in their measurements.<\/li>\r\n \t
                3. The results should be Repeatable<\/li>\r\n \t
                4. The transducers must be Stable<\/li>\r\n \t
                5. The transducers must have Good dynamic response<\/span><\/li>\r\n \t
                6. The transducers must have Convenient instrumentation.<\/li>\r\n<\/ol>\r\n\u00a0 \u00a0 Smart Sensors<\/strong>\r\n\r\n \r\n

                  Transducers or ordinary sensors help in sensing or controlling the process parameters such as temperature, pressure, strain, flow, pH etc. Smart sensors provide functions beyond all these.<\/p>\r\n\r\n

                    \r\n \t
                  1. A smart sensor acquires the data from the instruments.<\/li>\r\n \t
                  2. Conditioning of the signals is also done by the smart sensors.<\/li>\r\n \t
                  3. Smart sensors convert the measurement into the attribute\u2019s units and<\/li>\r\n \t
                  4. Also, smart sensors transmit the data to a network by wireless method or through wire line.<\/span><\/li>\r\n<\/ol>\r\n<\/div>\r\n
                    \r\n

                    \u00a0 \u00a0The smart sensors also possess built-in digital interface that provides a communication channel with the network control. A functional smart sensor system consists of two main components namely,<\/p>\r\n\r\n

                      \r\n \t
                    1. Transmitter interface module (TIM) which contains physical transducers and data acquisition system and<\/li>\r\n \t
                    2. Network capable application processor (NCAP) where control and data correction take place.<\/span><\/li>\r\n<\/ol>\r\nTIM performs the following functions:\r\n
                        \r\n \t
                      1. Analogue signal conditioning<\/li>\r\n \t
                      2. Triggering<\/li>\r\n \t
                      3. Analogue to digital conversion<\/span><\/li>\r\n \t
                      4. Command processing<\/li>\r\n \t
                      5. TEDS storage and<\/li>\r\n \t
                      6. Data transfer and communication<\/li>\r\n<\/ol>\r\nThe NCAP functions are:\r\n
                          \r\n \t
                        1. Message encoding and decoding<\/li>\r\n \t
                        2. Detection and control of TIMs.<\/li>\r\n \t
                        3. Correction and interpretation of TEDS data and<\/li>\r\n \t
                        4. Message routing and interface control.<\/li>\r\n<\/ol>\r\n<\/div>\r\n\u00a0 \u00a0 Questionnaire<\/strong>\r\n
                            \r\n \t
                          1. Transducers are devices which receive energy in one form and convert it into another. (True\/ False)<\/li>\r\n \t
                          2. Conditioning of signals is not possible by smart sensors. (True\/ False)<\/li>\r\n \t
                          3. The broad categories in which transducers can be divided are ______________________.<\/li>\r\n \t
                          4. Which of the following is not a passive transducer:<\/li>\r\n<\/ol>\r\n(a) Magnetoresistace transducers\r\n\r\n(b) Photoconductive transducers\r\n\r\n(c) Thermoresistive transducers\r\n\r\n(d) Photovoltaic transducers\r\n
                              \r\n \t
                            1. The transducer must be chosen properly so that<\/li>\r\n<\/ol>\r\n

                              \u00a0 (a) There should be Impedance matching of the transducers with the instruments to be used for measurements<\/p>\r\n

                              (b) There should be Excitation voltage matching with the next stage in the measurement system.<\/p>\r\n

                              (c) Also, there should be Sensitivity tolerance matching with the next stage in the measurement system.<\/p>\r\n

                              (d) All the above.<\/p>\r\n \r\n\r\nReferences:<\/strong>\r\n

                                \r\n \t
                              1. Electronic Measurements and Instrumentation by Bernard M. Oliver and John M. Cage.<\/li>\r\n \t
                              2. Measurement and Instrumentation Principles by Alan S. Morris.<\/li>\r\n \t
                              3. Instrumentation and Measurement in Electrical Engineering by Roman Malaric.<\/li>\r\n \t
                              4. Measurement and Instrumentation Systems by William Bolton.<\/li>\r\n \t
                              5. Engineering Measurements and Instrumentation by Leslie Frank Adams.<\/li>\r\n \t
                              6. Electrical Measurements and Instrumentation by U. A. Bakshi.<\/li>\r\n \t
                              7. Introduction to Measurements and Instrumentation by Arun K Ghosh.<\/li>\r\n<\/ol>","rendered":"
                                \n

                                \u00a0 \u00a0 Transducers<\/strong><\/p>\n

                                 <\/p>\n

                                While making measurements, the quantity to be measured, also called as Measurand, first of all comes in contact with the Detector. The measurand or the input signal is basically the Information which we require from the measurement system. This information can be present either in the form of a physical phenomenon or an electrical signal. This information is then sensed and translated into a suitable form for their recognition in the further stages of the system by the detector. Energy is required in order to detect and convert the input signal or information from one form to another. To reduce the loading effects, efforts are generally made to supply energy to the detector from the external sources so that no undue energy is being extracted from the input signal and the output of detector is faithful representation of the input.<\/p>\n

                                 <\/p>\n

                                Broadly speaking, transducer is a device which receives energy in one form and transfers it into another convenient form or state. For example, the diaphragm produces displacement on application of pressure. Both pressure and displacement are both mechanical form of energy, still displacement is easier from the measurement point of view. Similarly, a thermocouple which is a junction of dissimilar metals generates electrical signals with a difference in temperature. Thus, it acts as converter of temperature difference or heat energy to electrical energy, which is easier for measurements. Thus, a thermocouple may be called as a temperature transducer.<\/p>\n

                                 <\/p>\n

                                The sensors or the transducers may be electrical, mechanical, acoustic, optical, thermal, magnetic, nuclear, chemical or any of their combinations. Out of all these types, electrical signals are most preferred due to the following reasons:<\/p>\n

                                  \n
                                1. Devices such as op-amps can be used to ensure a minimum loading of the system.<\/li>\n
                                2. The electrical signal can be easily conditioned as required.<\/li>\n
                                3. The measurements can be performed remotely and also multiple times.<\/li>\n
                                4. Data-acquisition for the electrical signals is largely observer independent and can be controlled precisely using computers.<\/li>\n<\/ol>\n

                                  \u00a0 \u00a0 Classification of Transducers:<\/strong><\/p>\n

                                   <\/p>\n

                                  Electrical transducers can be divided into two main categories:<\/p>\n

                                    \n
                                  1. Active transducers<\/li>\n
                                  2. Passive transducers<\/li>\n<\/ol>\n

                                    \u00a0 \u00a0 1.\u00a0 <\/strong>Active transducers<\/strong><\/p>\n

                                     <\/p>\n

                                    These are self-generating devices and do not require any external source of energy to be driven. Active transducers basically convert one form of energy to the other without requiring any external source for their excitation. These can be further divided into the following categories:<\/span><\/p>\n

                                      \n
                                    1. Thermoelectric transducers: these are based on the property of thermoelectricity generation. Devices such as <\/span>thermocouple, thermopile <\/span>and thermocouple gauge are based on this property for their application in the measurement of Temperature, radiation pyrometry or temperature of distant objects and low pressure respectively.<\/span><\/li>\n
                                    2. Piezoelectric transducers: These are based on the property of piezoelectricity generation. Devices such as piezoelectric transducers are based on this property for their application in the measurement of pressure.<\/li>\n
                                    3. Photovoltaic transducers: These are based on the property of photoelectricity generation. Devices such as photodiode in combination with a diaphragm are based on this property for their application in the measurement of pressure.<\/span><\/li>\n
                                    4. Electromagnetic transducers: These are based on the property of electricity generation by moving a coil in a magnetic field. Devices such as electromagnetic pick-up are based on this property for their application in the measurement of flow.<\/li>\n
                                    5. Galvanic transducers.<\/li>\n<\/ol>\n<\/div>\n
                                      \n

                                      \u00a0 \u00a0 2.\u00a0<\/strong>Passive Transducers:<\/strong><\/p>\n

                                       <\/p>\n

                                      These transducers need to be excited from the external source of electrical energy for their working. The energy derived from the measured signal produces a change in the electrical state of the passive transducers which can further be assessed easily. Consider a photoresistor, it can be excited by an external cell and the voltage across it can be easily measured. When light of sufficient intensity is turned ON, the resistance of photoresistor changes, which ultimately alters the voltage across it. Depending upon the principle of operation, passive transducers can be further classified as follows:<\/p>\n

                                        \n
                                      1. Resistive transducers<\/li>\n
                                      2. Inductive transducers<\/li>\n
                                      3. Capacitive transducers<\/li>\n
                                      4. Magnetoresistace transducers<\/li>\n
                                      5. Photoconductive transducers<\/li>\n
                                      6. Thermoresistive transducers<\/li>\n
                                      7. Elastoresistive transducers<\/li>\n<\/ol>\n

                                        \u00a0 Transducer devices such as potentiometers, strain guage, pirani guage, hot-wire anemometer, platinum resistance thermometer, thermistor, photoconductive cell or light-dependent resistor (LDR) in combination with a diaphragm are a few examples of the devices which are based on the property of resistance variation.\u00a0These devices find application in the determination of displacement, small displacements useful in the measurement of strain, pressure, force or torque, to measure low pressure, flow, temperature, pressure etc.<\/span><\/p>\n

                                         <\/p>\n

                                        Devices such as <\/span>linear variable differential transformer (LVDT), Synchro and eddy current gauge are based on the property of Inductance variation for their application in the measurement of displacement and angular displacement. Capacitance variation based devices such as Capacitor gauge and Dielectric gauge are used to measure displacement.<\/span><\/p>\n

                                         <\/p>\n

                                        Electrical transducers have far more adaptability to the instrumentation than those of the transducers which generate <\/span>analogue output signals. Electrical transducers can be the first constituent element in a measurement system and hence are called as <\/span>primary<\/em> transducers. However, many times transducers are preceded by mechanical instruments in the measurement system. Such transducers are called as <\/span>Secondary<\/em> transducers. It should be noted that the precision of the data observed by a measurement depends mostly on the transducers as they are the sensing elements in the system.<\/span><\/p>\n<\/div>\n

                                        \n

                                        \u00a0 \u00a0 Analogue and Digital Transducers:<\/strong><\/p>\n

                                         <\/p>\n

                                        Classification of the transducers can also be done on the basis of the type of output which can be either in the form of continuous signal as a function of time or as discrete steps.<\/p>\n

                                         <\/p>\n

                                        Analogue Transducers: <\/strong>The transducers which convert the physical phenomenon into an analogue signal which is a continuous function of time. Examples of Analogue signals are LVDT, strain gauge, thermocouple or a thermistor.<\/p>\n

                                         <\/p>\n

                                        Digital Transducers: <\/strong>These transducers convert the input physical phenomenon into an electrical output which is in the form of pulses. This transducer uses digital code marks to identify the position of a movable piece by a binary system of notation. The position is given out as a train of digital pulses.<\/p>\n

                                         <\/p>\n

                                        Electrical Phenomena used in Transducers<\/strong><\/p>\n

                                         <\/p>\n

                                        The transducers may be classified into different categories depending upon the principle employed by their transduction elements to convert the physical phenomenon (input) into output electrical signals. The different electrical phenomena employed in transduction elements of transducers are listed below. These phenomena may be combined with appropriate primary sensing elements (detectors) to produce a variety of transducers. ,<\/p>\n

                                         <\/p>\n

                                        These phenomena are: 1. Resistive. 2. Inductive. 3. Capacitive. 4. Electromagnetic. 5. Piezoelectric. 6. Ionization. 7. Photoelectric or Photoemissive. 8. Photoconductive or Photoresistive. 9. Photovoltaic. IO. Potentiometric. 11. Thermoelectric or Thermovoltaic. 12. Electrokinetic.<\/p>\n

                                         <\/p>\n

                                        Magnetic Effect based Transducers:<\/strong><\/p>\n

                                         <\/p>\n

                                        Magnetic effect based sensors are gaining a lot of attention lately because of their diverse applications. For example, reluctance based transducers are based on Faraday effect and magnetoresistive transducers utilize Thomson effect. Transducers which are utilized in combination with piezoelectric elements for magnetometers\u00a0and potentiometers are based on the principle of Joule effect or Magnetostriction. Torque\/ force, displacement and level measurement are based on <\/span>Wiedemann effect. Magnetoelastic and magnetogalvanic sensors are based upon Villari and Hall effects respectively and SQUID magnetometers are based on Josephson effect.<\/span><\/p>\n

                                         <\/p>\n

                                        Based on the principle of energy conversion, magnetic transducers can also be classified as active and passive transducers.<\/span><\/p>\n

                                         <\/p>\n

                                        Joule effect or Magnetostriction:<\/strong><\/p>\n

                                         <\/p>\n

                                        Magnetostriction refers to the property of materials (ferromagnetic) which expand or contract in the presence of magnetic fields. These materials have crystalline structure intrinsically which is divided <\/span>in several domains, each of which has a uniform magnetic polarization. In the presence of <\/span>external magnetic field, the domains become oriented with their axes almost parallel to each other. Also, the domain boundaries also get shifted and thus, a change in the dimension of material is observed.<\/span><\/p>\n

                                         <\/p>\n

                                        Magnetostriction <\/span>coefficient, \u03bb refers to the fractional change in the length of the ferromagnetic material with the application of <\/span>magnetic field. The change in length can either be positive or negative i.e. the length can increase or decrease and the value of \u03bb is of the order of 10-5. There is a dissipation of energy in the form of sound which is related to the elastic strain energy associated with deformation. Vibrators, ultrasonic vibrations as sound waves or as ultrasonic waves in liquids utilize Magnetostriction effect.<\/span><\/p>\n

                                         <\/p>\n

                                        Villari Effect: <\/strong>It is <\/span>reverse of Magnetostrictive effect, as it refers to the permanent change in the magnetic permeability of the material by generating stress in the Magnetostrictive material. Magnetostrictive displacement sensors and level sensors are based on the Villari effect.<\/span><\/p>\n

                                         <\/p>\n

                                        Selection Criteria<\/strong><\/p>\n

                                         <\/p>\n

                                        While selecting transducers for a measurement, <\/span>following parameters must be taken into account.<\/span><\/p>\n

                                         <\/p>\n

                                        There are Fundamental Parameters which must be taken into account. These fundamental parameters can be classified as follows:<\/strong><\/p>\n<\/div>\n

                                        \n

                                        \u00a0 \u00a0 1. Selection of transducers will depend upon the Type of Measurand<\/p>\n

                                        2.\u00a0Range of measurement will also decide the type of transducers to be used.<\/p>\n

                                        3. Required precision during transducers selection will depend upon the following factors:<\/p>\n

                                        a. Allowable nonlinearity effects in the transducers<\/p>\n

                                        b. Allowable dead-zone effects present in transducers<\/p>\n

                                        c. Frequency-response of the transducers and<\/p>\n

                                        d. Resolution of the transducers<\/p>\n

                                         <\/p>\n

                                        Environmental Parameters also play a significant role in <\/strong>transducers selection<\/span>: <\/strong>It includes consideration of<\/span><\/p>\n

                                          \n
                                        1. Ambient temperature for the measurements<\/span><\/li>\n
                                        2. Corrosive or non-corrosive atmosphere where measurements are to be carried out<\/span><\/li>\n
                                        3. Shock and vibration to be withstand during measurements<\/span><\/li>\n<\/ol>\n<\/div>\n
                                          \n

                                          \u00a0 \u00a0 Physical Conditions of the <\/strong>transducers and also the Measurand are very much important for the selection of transducers:<\/strong> These must also be taken care of:<\/p>\n

                                            \n
                                          1. Room or available space to mount the transducer is important<\/li>\n
                                          2. Whether the measurement is static or dynamic will also decide the type of transducers to be used.<\/li>\n
                                          3. How much energy can be extracted from the Measurand to do the measurement without loading is an important parameter for deciding the transducers.<\/li>\n<\/ol>\n

                                            \u00a0 \u00a0 Compatibility with the next stage:<\/strong><\/p>\n

                                             <\/p>\n

                                            The transducer must be chosen properly so that it is compatible with the requirements of the next stage in the measurement system and the following points must be taken account of:<\/p>\n

                                              \n
                                            1. There should be Impedance matching of the transducers with the instruments to be used for measurements<\/li>\n
                                            2. There should be Excitation voltage matching with the next stage in the measurement system.<\/li>\n
                                            3. Also, there should be Sensitivity tolerance matching with the next stage in the measurement system.<\/li>\n<\/ol>\n

                                              \u00a0 Transducers in general can be prepared from a variety of materials but in order to have application in practical instrumentation, they must adapt the following requirements:<\/p>\n

                                                \n
                                              1. They should have Ruggedness to withstand overload<\/li>\n
                                              2. There should be Linearity in their measurements.<\/li>\n
                                              3. The results should be Repeatable<\/li>\n
                                              4. The transducers must be Stable<\/li>\n
                                              5. The transducers must have Good dynamic response<\/span><\/li>\n
                                              6. The transducers must have Convenient instrumentation.<\/li>\n<\/ol>\n

                                                \u00a0 \u00a0 Smart Sensors<\/strong><\/p>\n

                                                 <\/p>\n

                                                Transducers or ordinary sensors help in sensing or controlling the process parameters such as temperature, pressure, strain, flow, pH etc. Smart sensors provide functions beyond all these.<\/p>\n

                                                  \n
                                                1. A smart sensor acquires the data from the instruments.<\/li>\n
                                                2. Conditioning of the signals is also done by the smart sensors.<\/li>\n
                                                3. Smart sensors convert the measurement into the attribute\u2019s units and<\/li>\n
                                                4. Also, smart sensors transmit the data to a network by wireless method or through wire line.<\/span><\/li>\n<\/ol>\n<\/div>\n
                                                  \n

                                                  \u00a0 \u00a0The smart sensors also possess built-in digital interface that provides a communication channel with the network control. A functional smart sensor system consists of two main components namely,<\/p>\n

                                                    \n
                                                  1. Transmitter interface module (TIM) which contains physical transducers and data acquisition system and<\/li>\n
                                                  2. Network capable application processor (NCAP) where control and data correction take place.<\/span><\/li>\n<\/ol>\n

                                                    TIM performs the following functions:<\/p>\n

                                                      \n
                                                    1. Analogue signal conditioning<\/li>\n
                                                    2. Triggering<\/li>\n
                                                    3. Analogue to digital conversion<\/span><\/li>\n
                                                    4. Command processing<\/li>\n
                                                    5. TEDS storage and<\/li>\n
                                                    6. Data transfer and communication<\/li>\n<\/ol>\n

                                                      The NCAP functions are:<\/p>\n

                                                        \n
                                                      1. Message encoding and decoding<\/li>\n
                                                      2. Detection and control of TIMs.<\/li>\n
                                                      3. Correction and interpretation of TEDS data and<\/li>\n
                                                      4. Message routing and interface control.<\/li>\n<\/ol>\n<\/div>\n

                                                        \u00a0 \u00a0 Questionnaire<\/strong><\/p>\n

                                                          \n
                                                        1. Transducers are devices which receive energy in one form and convert it into another. (True\/ False)<\/li>\n
                                                        2. Conditioning of signals is not possible by smart sensors. (True\/ False)<\/li>\n
                                                        3. The broad categories in which transducers can be divided are ______________________.<\/li>\n
                                                        4. Which of the following is not a passive transducer:<\/li>\n<\/ol>\n

                                                          (a) Magnetoresistace transducers<\/p>\n

                                                          (b) Photoconductive transducers<\/p>\n

                                                          (c) Thermoresistive transducers<\/p>\n

                                                          (d) Photovoltaic transducers<\/p>\n

                                                            \n
                                                          1. The transducer must be chosen properly so that<\/li>\n<\/ol>\n

                                                            \u00a0 (a) There should be Impedance matching of the transducers with the instruments to be used for measurements<\/p>\n

                                                            (b) There should be Excitation voltage matching with the next stage in the measurement system.<\/p>\n

                                                            (c) Also, there should be Sensitivity tolerance matching with the next stage in the measurement system.<\/p>\n

                                                            (d) All the above.<\/p>\n

                                                             <\/p>\n

                                                            References:<\/strong><\/p>\n

                                                              \n
                                                            1. Electronic Measurements and Instrumentation by Bernard M. Oliver and John M. Cage.<\/li>\n
                                                            2. Measurement and Instrumentation Principles by Alan S. Morris.<\/li>\n
                                                            3. Instrumentation and Measurement in Electrical Engineering by Roman Malaric.<\/li>\n
                                                            4. Measurement and Instrumentation Systems by William Bolton.<\/li>\n
                                                            5. Engineering Measurements and Instrumentation by Leslie Frank Adams.<\/li>\n
                                                            6. Electrical Measurements and Instrumentation by U. A. Bakshi.<\/li>\n
                                                            7. Introduction to Measurements and Instrumentation by Arun K Ghosh.<\/li>\n<\/ol>\n","protected":false},"author":3,"menu_order":24,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":["prof-vinay-gupta"],"pb_section_license":""},"chapter-type":[],"contributor":[58],"license":[],"class_list":["post-425","chapter","type-chapter","status-publish","hentry","contributor-prof-vinay-gupta"],"part":3,"_links":{"self":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/pressbooks\/v2\/chapters\/425","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/wp\/v2\/users\/3"}],"version-history":[{"count":4,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/pressbooks\/v2\/chapters\/425\/revisions"}],"predecessor-version":[{"id":429,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/pressbooks\/v2\/chapters\/425\/revisions\/429"}],"part":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/pressbooks\/v2\/parts\/3"}],"metadata":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/pressbooks\/v2\/chapters\/425\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/wp\/v2\/media?parent=425"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/pressbooks\/v2\/chapter-type?post=425"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/wp\/v2\/contributor?post=425"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp04\/wp-json\/wp\/v2\/license?post=425"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}