Sensors & Transducers- Introduction & Types.pdf
- 1. Transducer circuitglobe.com/transducer.html Definition: The device which converts the one form of energy into another is known as the transducer. The process of conversion is known as transduction. The conversion is done by sensing and transducing the physical quantities like temperature, pressure, sound, etc. The electrical transducer converts the mechanical energy into an electric signal. The electrical signal may be voltage, current and frequency. The production of the signal depends on the resistive inductive and capacitive effects of the physical input. Needs of Transducer It is quite difficult to determine the exact magnitude of the physical forces like temperature, pressure, etc. But if the physical force is converted into an electrical signal, then their value is easily measured with the help of the meter. The transducers convert the physical forces into an electrical signal which can easily be handled and transmitted for measurement. The following are the advantages of converting the physical quantity into an electrical signal. 1. The attenuation and amplification of the electrical signals are very easy. 2. The electrical signal produces less friction error. 3. The small power is required for controlling the electrical systems. 4. The electrical signals are easily transmitted and processed for measurement. 5. The component used for measuring the electrical signal is very compact and accurate. 6. The electrical signals are used in telemetry. Parts of Transducer The transducer consists two important parts. 1. Sensing Element 2. Transduction Element 1/3
- 2. The transducer has many other parts like amplifiers, signal processing equipment, power supplies calibrating and reference sources, etc. 1. Sensing or Detector Element – It is the part of the transducers which give the response to the physical sensation. The response of the sensing element depends on the physical phenomenon. 2. Transduction Element – The transduction element converts the output of the sensing element into an electrical signal. This element is also called the secondary transducer. Factors Influencing the Choice of Transducer The choice of the transducers used for measuring the physical quantity depends on the following factors. 1. Operating Principle – The transducers are selected by their operating principles. The operating principle may be resistive, inductive, capacitive, optoelectronic, piezoelectric, etc. 2. Sensitivity – The sensitivity of the transducer is enough for inducing the detectable output. 3. Operating Range – The transducer must have wide operating ranges so that it does not break during the working. 4. Accuracy – The transducers gives accuracy after calibration. It has a small value for repeatability which is essentials for the industrial applications. 5. Cross Sensitivity – The transducers gives variable measured value for the different planes because of the sensitivity. Hence, for the accurate measurement, the cross sensitivity is essential. 6. Errors – The errors are avoided by taking the input output relations which is obtained by the transfer function. 7. Loading Effect – The transducers have high input impedance and low output impedance for avoiding the errors. 8. Environmental Compatibility – The transducers should be able to work in any specified environments like in a corrosive environment. It should be able to work under high pressure and shocks. 9. Insensitivity to Unwanted Signals – The transducer should be sensitive enough for ignoring the unwanted and high sensitive signals. 10. Usage and Ruggedness – The durability, size and weight of the transducer must be known before selecting it. 11. Stability and Reliability – The stability of the transducers should be high enough for the operation. And their reliability should be good in case of failure of the transducer. 12. Static characteristic – The transducer should have a high linearity and resolution, but it has low hysteresis. The transducer is always free from the load and temperature. 2/3
- 3. Applications of Transducer The following are the application of the transducers. 1. It is used for detecting the movement of muscles which is called acceleromyograph. 2. The transducer measures the load on the engines. 3. It is used as a sensor for knowing the engine knock. 4. The transducers measure the pressure of the gas and liquid by converting it into an electrical signal. 5. It converts the temperature of the devices into an electrical signal or mechanical work. 6. The transducer is used in the ultrasound machine. It receives the sound waves of the patient by emitting their sound waves and pass the signal to the CPU. 7. The transducer is used in the speaker for converting the electrical signal into acoustic sound. 8. It is used in the antenna for converting the electromagnetic waves into an electrical signal. The classifications of the transducers depend on the various factor like by transduction, the converting electrical signal from AC or DC, etc. 3/3
- 4. Types of Transducer circuitglobe.com/types-of-transducer.html The transducer changes the physical quantity into an electrical signal. It is an electronic device which has two main functions, i.e., sensing and transduction. It senses the physical quantity and then converts it into mechanical works or electrical signals. The transducer is of many types, and they can be classified by the following criteria. 1. By transduction used. 2. as a primary and secondary transducer 3. as a passive and active transducer 4. as analogue and digital transducer 5. as the transducer and inverse transducer The transducer receives the measurand and gives a proportional amount of output signal. The output signal is sent to the conditioning device where the signal is attenuated, filtered, and modulated. The input quantity is the non-electrical quantity, and the output electrical signal is in the form of the current, voltage or frequency. 1. Classification based on the Principle of Transduction The transducer is classified by the transduction medium. The transduction medium may be resistive, inductive or capacitive depends on the conversion process that how input transducer converts the input signal into resistance, inductance and capacitance respectively. 1/4
- 5. 2. Primary and Secondary Transducer Primary Transducer – The transducer consists the mechanical as well as the electrical devices. The mechanical devices of the transducer change the physical input quantities into a mechanical signal. This mechanical device is known as the primary transducers. Secondary Transducer – The secondary transducer converts the mechanical signal into an electrical signal. The magnitude of the output signal depends on the input mechanical signal. Example of Primary and Secondary Transducer Consider the Bourdon’s Tube shown in the figure below. The tube act as a primary transducer. It detects the pressure and converts it into a displacement from its free end. The displacement of the free ends moves the core of the linear variable displacement transformer. The movement of the core induces the output voltage which is directly proportional to the displacement of the tube free end. Thus, the two type of transduction occurs in the Bourdon’s tube. First, the pressure is converted into a displacement and then it is converted into the voltage by the help of the L.V.D.T. The Bourdon’s Tube is the primary transducer, and the L.V.D.T is called the secondary transducer. 3. Passive and Active Transducer The transducer is classified as the active and passive transducer. 2/4
- 6. Passive Transducer – The transducer which requires the power from an external supply source is known as the passive transducer. They are also known as the external power transducer. The capacitive, resistive and inductive transducers are the example of the passive transducer. Active Transducer – The transducer which does not require the external power source is known as the active transducer. Such type of transducer develops theirs owns voltage or current, hence known as a self-generating transducer. The output signal is obtained from the physical input quantity. The physical quantity like velocity, temperature, force and the intensity of light is induced with the help of the transducer. The piezoelectric crystal, photo-voltaic cell, tacho generator, thermocouples, photovoltaic cell are the examples of the active transducers. Examples – Consider the examples of a piezoelectric crystal. The crystal is sandwiched between the two metallic electrodes, and the entire sandwiched is fastened to the base. The mass is placed on the top of the sandwiched. The piezo crystal has the special property because of which when the force is applied to the crystal, they induce the voltage. The base provides the acceleration due to which the voltage is generated. The mass applies on the crystals induces an output voltage. The output voltage is proportional to the acceleration. The above mention transducer is known as the accelerometer which converts the acceleration into an electric voltage. This transducer does not require any auxiliary power source for the conversion of physical quantity into an electrical signal. 4. Analog and Digital Transducer The transducer can also be classified by their output signals. The output signal of the transducer may be continuous or discrete. Analog Transducer – The Analog transducer changes the input quantity into a continuous function. The strain gauge, L.V.D.T, thermocouple, thermistor are the examples of the analogue transducer. 3/4
- 7. Digital Transducer – These transducers convert an input quantity into a digital signal or in the form of the pulse. The digital signals work on high or low power. 5. Transducer and Inverse Transducer Transducer – The device which converts the non-electrical quantity into an electric quantity is known as the transducer. Inverse Transducer – The transducer which converts the electric quantity into a physical quantity, such type of transducers is known as the inverse transducer. The transducer has high electrical input and low non-electrical output. 4/4
- 8. Difference Between Active & Passive Transducer circuitglobe.com/difference-between-active-and-passive-transducer.html The most crucial difference between the active and passive transducer is that the active transducer does not use any external power source for producing the output, whereas the passive transducer requires the additional energy source for working. The other differences between active and passive transducer are explained below in the comparison chart. The physical forces like pressure, humidity, displacement etc. are difficult to measure. For measuring the physical quantities, the device is required, which converts the physical quantities into easy measurable energy. The conversion of physical forces or non-measurable energy into measurable energy can be done with the help of the transducer. Content: Active Vs Passive Transducer Comparison Chart Basis For Comparison Active Transducer Passive Transducer What is The transducer which generate the output in the form of voltage or current, without any external energy source is known as active transducer. The passive transducer means the transducer whose internal parameters like capacitance, resistance & inductance changes because of the input signal. Additional Energy Source Not Require Require Working Principle Draw energy from the measurand source. Take power from the external source which changes the physical properties of transducer. Design Simple Complicated Resolution Low High Output signal Produces from the signal to be measured. Output obtains by receiving the signal from the external power source. 1/4
- 9. Examples Tachogenerator, Thermocouple, Photovoltaic cell etc. Thermistor, Differential transformer, Photomultiplier tube, Photovoltaic cell. Basis For Comparison Active Transducer Passive Transducer Definition of Active Transducer The transducer whose output is obtained in the form of voltage or current without any additional auxiliary source is known as the active transducer. It works on the principle of conversion of energy from one form to another. The active transducer is also known as the self-generating transducer because they self-develop their electrical output signal. The energy requires for generating the output signals are obtained from the physical quantity which is to be measured. Example: The Piezo electrical crystal is the example of the natural active transducer. The crystal has the property of producing the output voltage when the external force applied to them. The piezoelectric crystal is placed between the two metallic electrodes. When the force applied to the crystal, the voltage induces across it. Definition of Passive Transducer In passive transducer, the output is obtained by changing the physical properties (resistance, inductance, and capacitance) of the material. In other words, the passive transducer takes power from the external energy source for transduction. The word transduction means conversion of energy from one form to another. 2/4
- 10. Example: The linear potentiometer is the examples of the passive transducer. It is used for measuring the displacement. The POT requires the external power source e for work. It measures the linear displacement x . Consider the L is the length of the potentiometer. R is their total internal resistance and x is their input displacement. The output voltage is calculated by the formula shown below. Key Differences between Active and Passive Transducer The transducer which gives the electrical output (in the form of voltage and current) without any external energy source is known as the active transducer. The transducer whose physical properties varies because of the input or measurand signal is known as the passive transducer. The active transducer does not require any additional source while the passive transducer requires the additional energy source. Active transducer draws energy from the measurand source and gives the electrical output while in passive transducer the transduction can be done by changing the physical property of the material. The design of active transducer is simple as compared to the passive transducer. The resolution of an active transducer is low while that of the passive transducer is high. Note: The term resolution means the variation occurs in the input of the transducer causes the change in their output. i i i i 3/4
- 11. The active transducer produces the output signal of very low amplitude. Thus, their output signal needs to be amplified. Whereas, the amplification is not required in the output signal of the passive transducer. In the active transducer, the output electrical signal is obtained from the measurand signal. Whereas in passive transducer the output signal is obtained by taking power from the external energy source. Conclusion The active and passive transducer both converts the physical forces into easy measurable energy. The active transducer converts the energy without taking the auxiliary energy supply. And in the passive transducer, the external power source is required for energy conversion. 4/4
- 12. Difference Between Transducer & Inverse Transducer circuitglobe.com/difference-between-transducer-and-inverse-transducer.html One of the major difference between the transducer and the inverse transducer is that the transducer changes the non-electrical quantity into an electrical quantity while the inverse transducer changes the electrical quantity into the non-electrical quantity. The other differences between the transducer and inverse transducer are shown below in the comparison chart. The control action of the physical quantities like flow, rate, position, speed, temperature, pressure etc. depends on the measurement of the physical quantities. In simple words, the control action of the physical quantity is possible only when these quantities are correctly measured. For measuring the physical quantities, it is essential to convert it into an electrical signal, and this can be done with the help of the transducer. For example, in servomechanism, the position of the shaft is controlled by measuring the exact position of the shaft. Content: Transducer Vs Inverse-Transducer Comparison Chart Basis For Comparison Transducer Inverse Transducer Definition The transducer converts the non-electrical quantity into an electrical quantity. The inverse transducer converts the electrical quantity into the non- electrical quantity. Input Non-electrical quantity Electrical quantity Output Electrical quantity Non-electrical quantity Examples Photoconductive transducer, Thermocouple, Pressure gauge, strain gauge Piezoelectric Transducer, current carrying conductor placed in an magnetic field. Definition of Transducer The transducer is a type of device that converts the physical quantities like pressure, brightness, displacement into an electrical quantity. The process of conversion of quantities is known as the transduction. 1/3
- 13. Examples: The thermocouple converts the temperature into the small voltage. And the LVDT is used for measuring the displacement. Definition of Inverse Transducer The inverse transducer is the transducer which converts the electrical quantity into a non-electrical quantity. In other words, the transducer is a kind of actuator which has an electrical input and the non-electrical output. Examples: The analogue ammeter and the voltmeter convert the current into a displacement. The oscilloscope is used for converting the electrical signal into a physical displacement. Key Differences Between Transducer and Inverse Transducer 1. The transducer transforms the non-electrical quantity into the electrical quantity. Whereas, the inverse transducer changes the electrical quantity into the non- electrical quantities. 2. The input of the transducer is the non-electrical quantity. Whereas, the input of the inverse transducer is the electrical quantity. 3. The output of the transducer is the electrical quantity while the output of the inverse transducer is always the non-electrical quantity. 2/3
- 14. 4. The photoconductive cell, thermocouple, pressure gauge are the examples of the non-electrical quantities. The piezoelectrical transducer, current carrying conductor placed in a magnetic field are the examples of the inverse transducer. Conclusion The transducer changes the physical quantity into an electrical quantity. Whereas, the inverse transducer changes the electrical quantity into the physical quantity. 3/3