Lecture Sensors and analytical devices: Sensor technologies - Nguyễn Công Phương

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The main contents of this chapter include all of the following: Capacitive sensors, resistive sensors, magnetic sensors, hall – effect sensors, piezoelectric transducers, strain gauges, piezoresistive sensors, optical sensors, ultrasonic transducers, nuclear sensors, microsensors.

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Nội dung Text: Lecture Sensors and analytical devices: Sensor technologies - Nguyễn Công Phương

Nguyễn Công Phương Sensors and Analytical Devices Some Basic Measurement Methods, Sensors Technologies
Contents A. Introduction B. Sensors Characteristics C. Some Basic Measurement Methods D. Measurement Systems sites.google.com/site/ncpdhbkhn 2
Some Basic Measurement Methods I. Sensor Technologies II. Temperature Measurement III. Pressure Measurement IV.Flow Measurement V. Level Measurement VI.Mass, Force, and Torque Measurement VII.Translational Motion, Vibration, and Shock Measurement VIII.Rotational Motion Transducers sites.google.com/site/ncpdhbkhn 3
Sensor Technologies 1. Capacitive Sensors 2. Resistive Sensors 3. Magnetic Sensors 4. Hall – Effect Sensors 5. Piezoelectric Transducers 6. Strain Gauges 7. Piezoresistive Sensors 8. Optical Sensors 9. Ultrasonic Transducers 10. Nuclear Sensors 11. Microsensors sites.google.com/site/ncpdhbkhn 4
Capacitive Sensors S C   r 0 d S d • d is variable, or • εr is variable, or • S is variable. sites.google.com/site/ncpdhbkhn 5
Resistive Sensors • They rely on variation of the resistance of a material when the measured variable is applied to it. • This principle is applied most commonly in temperature measurement using resistance thermometers or thermistors. • It is also used in displacement measurement using strain gauges or piezoresistive sensors. • Some moisture meters work on the resistance – variation principle. sites.google.com/site/ncpdhbkhn 6
Sensor Technologies 1. Capacitive Sensors 2. Resistive Sensors 3. Magnetic Sensors a) Inductive Sensors b) Variable Reluctance Sensors c) Eddy Current Sensors 4. Hall – Effect Sensors 5. Piezoelectric Transducers 6. Strain Gauges 7. Piezoresistive Sensors 8. Optical Sensors 9. Ultrasonic Transducers 10. Nuclear Sensors 11. Microsensors sites.google.com/site/ncpdhbkhn 7
Inductive Sensors i V I 2 fL( d ) + – v V  L( d )  2 fI  d  f (V , I , f ) Displacement d • To measure translational & rotational displacement. sites.google.com/site/ncpdhbkhn 8
Variable Reluctance Sensors  d ( ) v dt    f (V ) N • To measure rotational V velocities. S sites.google.com/site/ncpdhbkhn 9
Eddy Current Sensors Thin metal sheet Sensor • To measure the displacement sites.google.com/site/ncpdhbkhn 10
Sensor Technologies 1. Capacitive Sensors 2. Resistive Sensors 3. Magnetic Sensors 4. Hall – Effect Sensors 5. Piezoelectric Transducers 6. Strain Gauges 7. Piezoresistive Sensors 8. Optical Sensors 9. Ultrasonic Transducers 10. Nuclear Sensors 11. Microsensors sites.google.com/site/ncpdhbkhn 11
Hall – Effect Sensors Current I V  KIB Output voltage V + – V B KI Applied magnetic field B • Basically to measure the magnitude of a magnetic field. • Can be a proximity sensor • Used in computer keyboard push buttons sites.google.com/site/ncpdhbkhn 12
Piezoelectric Transducers (1) kFd V A http://www.ask.com/wiki/Piezoelectricity • V: the induced voltage (its polarity depends on whether the material is compressed or stretched) • k: the piezoelectric constant • F: the applied force • d: the thickness of the material • A: the area of the material • They produce an output voltage when a forcce is applied to them, • Or being applied a voltage, they produce an output force. sites.google.com/site/ncpdhbkhn 13
Piezoelectric Transducers (2) • Used frequently as ultrasonic transmitters & receivers. – Transmitters: application of a sinusoidal voltage at a frequency in the ultrasound range causes sinusoidal variations in the thickness of the material & results in a sound wave being emitted at the chosen frequency. – Receivers: sinusoidal amplitude variations in the ultrasound wave received are translated into sinusoidal changes in the amplitude of the force applied to the piezoelectric transducer. • Also used as displacement transducers (particularly as part of devices measuring acceleration, force, & pressure). sites.google.com/site/ncpdhbkhn 14
Sensor Technologies 1. Capacitive Sensors 2. Resistive Sensors 3. Magnetic Sensors 4. Hall – Effect Sensors 5. Piezoelectric Transducers 6. Strain Gauges 7. Piezoresistive Sensors 8. Optical Sensors 9. Ultrasonic Transducers 10. Nuclear Sensors 11. Microsensors sites.google.com/site/ncpdhbkhn 15
Strain Gauges • Experience a change in resistance when they are stretched or strained. • Able to detect very small displacement, usually 0 – 50μm. • Manufactured to various nominal values of resistance, e.g. 120, 350, & 1000Ω. • The typical maximum change of resistance in a 120-Ω device would be 5Ω at maximum deflection. sites.google.com/site/ncpdhbkhn 16
Piezoresistive Sensors • Made from semiconductor material in which a p-type region has been diffused into an n-type base. • Its resistance varies greatly when the sensor is compressed or stretched. • Used in semiconductor – diaphragm pressure sensors & in semiconductor accelorometers. sites.google.com/site/ncpdhbkhn 17
Sensor Technologies 1. Capacitive Sensors 2. Resistive Sensors 3. Magnetic Sensors 4. Hall – Effect Sensors 5. Piezoelectric Transducers 6. Strain Gauges 7. Piezoresistive Sensors 8. Optical Sensors a) Air Path b) Fiber Optic 9. Ultrasonic Transducers 10. Nuclear Sensors 11. Microsensors sites.google.com/site/ncpdhbkhn 18
Optical Sensors Light Light source detector • Based on transmission of light between a light source & a light detector. • The path can be air or fiber – optic. • They give immunity to electromagnetically induced noise. sites.google.com/site/ncpdhbkhn 19
Optical Sensors (Air Path) Light Light source detector • Light sources: tungsten – filement lamps, laser diodes, light – emitting diodes (LED). • Visible light is rather easy to be interfered with sun & other sources, so infrared laser diodes & LED are preferred. • Light detectors: photoconductors, photovoltaic devices, photodiodes, phototransistor. sites.google.com/site/ncpdhbkhn 20