Bài giảng Sensors and analytical devices - Part C: Some Basic Measurement Methods (Phần 2) - Nguyễn Công Phương

Nguyễn Công Phương Sensors and Analytical Devices Some Basic Measurement Methods, Temperature Measurement 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 Temperature Measurement 1. Introduction 2. Thermoelectric Effect Sensors (Thermocouples) 3. Varying Resistance Devices 4. Semiconductor Devices 5. Radiation Thermometers 6. Thermography (Thermal Imaging) 7. Thermal Expansion Methods 8. Quartz Thermometers 9. Fiber – Optic Temperature Sensors 10. Color Indicators 11. Change of State of Materials 12. Choice between Temperature Transducers sites.google.com/site/ncpdhbkhn 4 Introduction • Temperature measurement is very important in all aspects of life. • In engineering applications, it is the most commonly measured process variable. • Difficulty: any given temperature cannot be related to a fundamental standard of temperature. • 10 classes of instrument based on 10 principles: – Thermoelectric effect – Resistance change – Sensitivity of semiconductor device – Radiative heat emission – Thermography – Thermal expansion – Resonant frequency change – Sensitivity of fiber-optic devices – Color change – Change of state of materials sites.google.com/site/ncpdhbkhn 5 Temperature Measurement 1. Introduction 2. Thermoelectric Effect Sensors (Thermocouples) 3. Varying Resistance Devices 4. Semiconductor Devices 5. Radiation Thermometers 6. Thermography (Thermal Imaging) 7. Thermal Expansion Methods 8. Quartz Thermometers 9. Fiber – Optic Temperature Sensors 10. Color Indicators 11. Change of State of Materials 12. Choice between Temperature Transducers sites.google.com/site/ncpdhbkhn 6 Thermoelectric Effect Sensors (1)  E  Metal 1 Metal 2 2 3 n E a1 T  a 2 T  a 3 T ...  an T  a1 T Thermocouples sites.google.com/site/ncpdhbkhn 7 Thermoelectric Effect Sensors (2) E1 Th E2 E1 Th E3 E2 E4 E1 Th E3 E5 sites.google.com/site/ncpdhbkhn 8 Thermoelectric Effect Sensors (3) EEEEEE     Em m 1 2 3 4 5 E2 E4 E1 Th EEEEEE1 m  2  3  4  5 E3 E5 /How_Thermocouples_Work/?p=1 EE1  m sites.google.com/site/ncpdhbkhn 9 Thermoelectric Effect Sensors (4) • Chromel – constantan (type E) – Highest measurement sensitivity: 68 μV/oC – Inaccuracy: ±0.5% – Range: –200oC up to 900oC • Iron – constantan (type J) – Sensitivity: 55 μV/oC – Inaccuracy: ±0.75% – Range: –40oC up to 750oC • Copper – constantan (type T) – Sensitivity: 43 μV/oC – Inaccuracy: ±0.75% – Range: –200oC up to 350oC sites.google.com/site/ncpdhbkhn 10 Thermoelectric Effect Sensors (5) • Chromel – alumel (type K) – Highest measurement sensitivity: 41 μV/oC – Inaccuracy: ±0.75% – Range: –200oC up to 1300oC – Applications: 700oC up to 1200oC – Widely used, general – purpose • Nicrosil – nisil (type N) – Sensitivity: 39 μV/oC – Inaccuracy: ±0.75% – Range: up to 1300oC – Long – term stability & life • Nickel/molybdenum – nickel – cobalt – One wire made from a nickel – molybdenum alloy with 18% molybdenum & the other wire made from a nickel – cobalt alloy with 0.8% cobalt – Range: up to 1400oC – Rarely used except for special applications such as temperatuer measurement in vacuucm furnaces sites.google.com/site/ncpdhbkhn 11 Thermoelectric Effect Sensors (6) • Chromel – alumel (type K) – Sensitivity: 41 μV/oC – Inaccuracy: ±0.75% – Range: –200oC up to 1300oC – Applications: 700oC up to 1200oC – Widely used, general – purpose • Nicrosil – nisil (type N) – Sensitivity: 39 μV/oC – Inaccuracy: ±0.75% – Range: up to 1300oC – Long – term stability & life • Nickel/molybdenum – nickel – cobalt (type M) – One wire made from a nickel – molybdenum alloy with 18% molybdenum & the other wire made from a nickel – cobalt alloy with 0.8% cobalt – Range: up to 1400oC – Rarely used except for special applications such as temperatuer measurement in vacuucm furnaces sites.google.com/site/ncpdhbkhn 12 Thermoelectric Effect Sensors (7) • Platinum (type B) – One wire made from a platinum – rhodium alloy with 30% rhodium & the other wire made from a platinum – rhodium alloy with 6% rhodium – Sensitivity: 10 μV/oC – Range: 50oC up to 1800oC • Platinum (type R) – One wire made from pure platinum & the other wire made from a platinum – rhodium alloy with 13% rhodium – Sensitivity: 10 μV/oC – Inaccuracy: ±0.5% – Range: 0 up to 1700oC • Platinum (type S) – One wire made from pure platinum & the other wire made from a platinum – rhodium alloy with 10% rhodium – Sensitivity: 10 μV/oC – Inaccuracy: ±0.5% – Range: 0 up to 1750oC • Tungsten (type C) – One wire made from pure tungsten & the other wire made from a tungsten/rhenium alloy – Sensitivity: 20 μV/oC – Range: 0 up to 2300oC • Chromel – gold/iron – One wire made from chromel & the other wire made from a gold/iron alloy – Sensitivity: 15 μV/oK – Range: from 1.2oK – For very low temperature applications sites.google.com/site/ncpdhbkhn 13 Thermoelectric Effect Sensors (8) • Manufactured by connecting together two wires of different materials – Welding (the most common technique), or – Soldering, or – Twisting the wire ends together • Diameter – Between 0.4 & 2 mm (usually) – Some special case: 0.1 μm (for fast response time) sites.google.com/site/ncpdhbkhn 14 Temperature Measurement 1. Introduction 2. Thermoelectric Effect Sensors (Thermocouples) 3. Varying Resistance Devices 4. Semiconductor Devices 5. Radiation Thermometers 6. Thermography (Thermal Imaging) 7. Thermal Expansion Methods 8. Quartz Thermometers 9. Fiber – Optic Temperature Sensors 10. Color Indicators 11. Change of State of Materials 12. Choice between Temperature Transducers sites.google.com/site/ncpdhbkhn 15 Varying Resistance Devices • Rely on the physical principle of the variation of resistance with temperature. • 2 types: resistance thermometers & thermistors. sites.google.com/site/ncpdhbkhn 16 Varying Resistance Devices, Resistance Thermometers (1) • A.k.a. resistance temperature devices. • R = R0(1 + a1T + a2T2 + ... + anTn) • R ≈ R0(1 + a1T) • Platinum: – The most linear characteristic & the most commonly used. – Inaccuracy: ±1.2%. – Very expensive • Platinum thermometers are made in 3 forms: – A film deposited on a ceramic substrate. – A coil mounted inside a glass or ceramic probe. – A coil wound on a mandrel sites.google.com/site/ncpdhbkhn 17 Varying Resistance Devices, Resistance Thermometers (2) • The nominal resistance (platinum) at 0oC is typically 100 or 1000Ω. • Sensitivity (platinum): – 0.385Ω/oC (100Ω type) – 3.85Ω/oC (1000Ω type) • The working range: – Platinum: –270 to 1000oC – Copper: –200 to 260oC – Nickel: –200 to 430oC – tungsten: –270 to 1100oC sites.google.com/site/ncpdhbkhn 18 Varying Resistance Devices, Thermistors • Made from beads of semiconductor material prepared from oxides of the iron group of metals (chromium, cobalt, iron, manganese, & nickel). • Have a negative temperature coeficient, that is, resistance decreases as temperature increases:  (1/TT 1/0 ) R R0 e • Disadvantages: – Nonlinear – Low sensitivity • Advantages: – Low cost – Small size sites.google.com/site/ncpdhbkhn 19 Temperature Measurement 1. Introduction 2. Thermoelectric Effect Sensors (Thermocouples) 3. Varying Resistance Devices 4. Semiconductor Devices 5. Radiation Thermometers 6. Thermography (Thermal Imaging) 7. Thermal Expansion Methods 8. Quartz Thermometers 9. Fiber – Optic Temperature Sensors 10. Color Indicators 11. Change of State of Materials 12. Choice between Temperature Transducers sites.google.com/site/ncpdhbkhn 20 Semiconductor Devices • Consist of either diodes or integrated circuit transistors. • Advantage: inexpensive. • Disadvantage: require and external power supply to the sensor. sites.google.com/site/ncpdhbkhn 21 Semiconductor Devices, Diodes • The forward voltage across the device varies with temperature. • Output is in μA range. • Small size. • Good output linearity. • Inaccuracy: ±0.5%. • Silicon diodes: from –50 to 200oC. • Germanium diondes: from –270 to 40oC. sites.google.com/site/ncpdhbkhn 22 Semiconductor Devices, Integrated Circuit Transistors • Produce an output proportional to the absolute temperature: – Current: 1μA/oK – Voltage: 10mV/oK • Very low cost. • Good output linearity. • Inaccuracy: ±3%. • Range: from –50 to 150oC. • Widely used in monitoring pipes & cables. sites.google.com/site/ncpdhbkhn 23 Temperature Measurement 1. Introduction 2. Thermoelectric Effect Sensors (Thermocouples) 3. Varying Resistance Devices 4. Semiconductor Devices 5. Radiation Thermometers 6. Thermography (Thermal Imaging) 7. Thermal Expansion Methods 8. Quartz Thermometers 9. Fiber – Optic Temperature Sensors 10. Color Indicators 11. Change of State of Materials 12. Choice between Temperature Transducers sites.google.com/site/ncpdhbkhn 24 Radiation Thermometers (1) • A.k.a. radiation pyrometers. • All objects emit electromagnetic radiation as a function of their temperature above absolute zero. • Radiation thermometers measure this radiation in order to calculate the temperature of the object. • The total rate of radiation emission per second is: E = KT4 sites.google.com/site/ncpdhbkhn 25 Radiation Thermometers (2) • Range: –100 to 10,000oC. • Inaccuracy: ±0.05%. • Versions: portable, battery – powered, hand-held. • Easy to use. • The important advantage: there is no contact between the hot body & the meter, hence: – The measured system is not disturbed. – No possibility of contamination (important in food, drug, etc). – Suitable for measuring high temperatures. – Capable of measuring moving bodies. • The use of radiation thermometers is complicated due to the absorption & scattering of the energy between the emitting body & the radiation detector – Absorption: by carbon dioxide, ozone, water vapor molecules. – Scattering: by atmospheric dust & water droplets. • Types: optical & radiation pyrometers. sites.google.com/site/ncpdhbkhn 26 Radiation Thermometers, Optical Pyrometer /temperature-measurement.html • To measure temperatures above 600oC (up to 10,000oC). • Contains a heated tungsten filement within its optical system. • The current in the filament is increased until its color is the same as the hot body (the filament disappears). • Temperature measurement is obtained in terms of the current flowing in the filament. • Can not be used in automatic systems because of the human eye. sites.google.com/site/ncpdhbkhn 27 Radiation Thermometers, Radiation Pyrometers Light from Detector hot body • A detector, not eye. • Range: from –100 to 3600oC. • Detector: a thermal detector, or a photon detector. • Thermal detectors: – Respond equally to all wavelengths in the frequency spectrum – Consist of resistaces thermometers & thermistors – Time constant: several miliseconds • Photon detectors: – Respond selectively to a particular band within the full spectrum – Consist of photoconductive or photovoltaic type – Time constant: a few microseconds sites.google.com/site/ncpdhbkhn 28 Temperature Measurement 1. Introduction 2. Thermoelectric Effect Sensors (Thermocouples) 3. Varying Resistance Devices 4. Semiconductor Devices 5. Radiation Thermometers 6. Thermography (Thermal Imaging) 7. Thermal Expansion Methods 8. Quartz Thermometers 9. Fiber – Optic Temperature Sensors 10. Color Indicators 11. Change of State of Materials 12. Choice between Temperature Transducers sites.google.com/site/ncpdhbkhn 29 Thermography Control unit Scanning Display radiation Processor unit detector • A.k.a. thermal imaging. • Scan an infrared radiation detector across an object. • The output is in the form of the temperature distribution. • Range: –20oC up to 1500oC. • Radiation detector: the same principles of operation as a radiation pyrometer. sites.google.com/site/ncpdhbkhn 30 Temperature Measurement 1. Introduction 2. Thermoelectric Effect Sensors (Thermocouples) 3. Varying Resistance Devices 4. Semiconductor Devices 5. Radiation Thermometers 6. Thermography (Thermal Imaging) 7. Thermal Expansion Methods a) Liquid-in-Glass Thermometers b) Bimetallic Thermometer c) Pressure Thermometers 8. Quartz Thermometers 9. Fiber – Optic Temperature Sensors 10. Color Indicators 11. Change of State of Materials 12. Choice between Temperature Transducers sites.google.com/site/ncpdhbkhn 31 Liquid-in-Glass Thermometers • A well – known temperature – measuring instrument used in a wide range of applications. • The fluid is normally either mercury or colored alcohol, contained within a bulb & capillary tube. • As the temperature rises, the fluid expands along the capillary tube & the level is read. • Range: –200 to 1000oC. • Inaccuracy: ±0.15%. sites.google.com/site/ncpdhbkhn 32 Bimetallic Thermometer • Based on the fact that if two strips of different metals are bonded together, any temperature change will cause the strip to bend. • In the bimetallic thermostat, it is used as a switch. • If the magnitude of bending is measured, it is a thermometer. • Range: –75 to 1500oC. • Inaccuracy: ±0.5%. bimetallic_strip.html sites.google.com/site/ncpdhbkhn 33 Pressure Thermometers • Consist of a stainless-steel bulb containing a liquid or gas. Bourdon • Temperature rises will cause the fluid’s tube pressure increases (not its volume, because the fluid is constrained). • The change in pressure of the fluid is measured by a suitable pressure transducer (such as the Bourdon tube). • Range: –250 up to 2000oC. • Inaccuracy: ±0.5%. ogpe.com/newsimages/ Pressure_type_thermo • A particulary long time constant. meter_2_glossary-1.gif sites.google.com/site/ncpdhbkhn 34 Temperature Measurement 1. Introduction 2. Thermoelectric Effect Sensors (Thermocouples) 3. Varying Resistance Devices 4. Semiconductor Devices 5. Radiation Thermometers 6. Thermography (Thermal Imaging) 7. Thermal Expansion Methods 8. Quartz Thermometers 9. Fiber – Optic Temperature Sensors 10. Color Indicators 11. Change of State of Materials 12. Choice between Temperature Transducers sites.google.com/site/ncpdhbkhn 35 Quartz Thermometers • Make use of the principle that the resonant frequency of a material such as quartz is a function of temperature. • Temperature changes are translated into frequency change. • Measurement of the oscillator frequency allows the measured temperature to be calculated. • Have a very linear output characteristic. • Range: –40 up to 230oC. • Inaccuracy: ±0.1%. • Resolution: 0.0003oC!!! • Very expensive. sites.google.com/site/ncpdhbkhn 36 Temperature Measurement 1. Introduction 2. Thermoelectric Effect Sensors (Thermocouples) 3. Varying Resistance Devices 4. Semiconductor Devices 5. Radiation Thermometers 6. Thermography (Thermal Imaging) 7. Thermal Expansion Methods 8. Quartz Thermometers 9. Fiber – Optic Temperature Sensors 10. Color Indicators 11. Change of State of Materials 12. Choice between Temperature Transducers sites.google.com/site/ncpdhbkhn 37 Fiber – Optic Temperature Sensors • Fiber – optic can be used as either intrinsic or extrinsic temperature sensors. • Range: 250 up to 3000oC. • Inaccuracy: ±1.0%. • Applications: – Measuring temperatures in hard-to-reach locations. – Very high measurement accuracy is required. sites.google.com/site/ncpdhbkhn 38 Temperature Measurement 1. Introduction 2. Thermoelectric Effect Sensors (Thermocouples) 3. Varying Resistance Devices 4. Semiconductor Devices 5. Radiation Thermometers 6. Thermography (Thermal Imaging) 7. Thermal Expansion Methods 8. Quartz Thermometers 9. Fiber – Optic Temperature Sensors 10. Color Indicators 11. Change of State of Materials 12. Choice between Temperature Transducers sites.google.com/site/ncpdhbkhn 39 Color Indicators • The color of various substances & objects changes as a function of temperature. • One use of this is in the optical pyrometer (discussed). • The other main use is in special color indicators, widely used in industry to determine whether objects placed in furnaces have reached the required temperature. • Such color indicators consist of special paints or crayons that are applied to an object before it is placed in a furnace. • At a certain temperature, a chemical reaction takes place & a permanent color change occurs in the paint or crayon. sites.google.com/site/ncpdhbkhn 40 Temperature Measurement 1. Introduction 2. Thermoelectric Effect Sensors (Thermocouples) 3. Varying Resistance Devices 4. Semiconductor Devices 5. Radiation Thermometers 6. Thermography (Thermal Imaging) 7. Thermal Expansion Methods 8. Quartz Thermometers 9. Fiber – Optic Temperature Sensors 10. Color Indicators 11. Change of State of Materials 12. Choice between Temperature Transducers sites.google.com/site/ncpdhbkhn 41 Change of State of Materials • Seger cones or pyrometric cones. • Used commonly in the ceramics industry. • Consist of a fused oxide & glass material that is formed into a cone shape. File:Segerkegel.jpg • The tip of the cone softens & bends over when a particular temperature is reached. • Range: 600 up to 2000oC. interpreting_orton_cones_193.html sites.google.com/site/ncpdhbkhn 42 Temperature Measurement 1. Introduction 2. Thermoelectric Effect Sensors (Thermocouples) 3. Varying Resistance Devices 4. Semiconductor Devices 5. Radiation Thermometers 6. Thermography (Thermal Imaging) 7. Thermal Expansion Methods 8. Quartz Thermometers 9. Fiber – Optic Temperature Sensors 10. Color Indicators 11. Change of State of Materials 12. Choice between Temperature Transducers sites.google.com/site/ncpdhbkhn 43 Choice between Temperature Transducers (1) • Depends substantially on whether the medium to be measured is a solid or a fluid. – Solid: • It is essential that good contact is made between the body & the transducers (unless a radiation thermometer) •  thermocouples, resistance thermometers, thermistors, semiconductor devices, & color indicators – Fluid: any • The most commonly used device in industry for temperature measurement is the base metal thermocoupe. – Relatively inexpensive – Inaccuracy: ±0.5% – Range: –250 to 1200oC – Low-level output voltage  prone to noise  unsuitable for measuring small temperature differences. sites.google.com/site/ncpdhbkhn 44 Choice between Temperature Transducers (2) • Resistance thermometers – Also commonly used – Range: –270 to 650oC (smaller than thermocouples) – Inaccuracy: ±0.5% – More stable (compared to thermocouples) & can measure small temperature differences • Thermistors – Also commonly used – Small & inexpensive – Fast output response to temperature changes – Good measurement sensitivity – Range is quite limited sites.google.com/site/ncpdhbkhn 45 Choice between Temperature Transducers (3) • Semiconductors devices – Have a better linearity than thermocouples & resistance thermometers – A similar level of accuracy – Integrated circuit transistor sensors: particularly inexpensive, but poor accuracy & limited range – Diode sensors: much more accurated, wider range, more expensive • Radiation thermometers – Major importance: noncontacat, noninvasive mode of measurement – Expensive – Able to measure fast temperature transients of duration as small as 10μs sites.google.com/site/ncpdhbkhn 46 Choice between Temperature Transducers (4) • Thermal expansion – Used mainly as temperature-indicating devices rather than as components within automatic control systems – The bimetallic thermometer is more rugged than liquid-in-glass types but less accurate • Fiber-optic devices – More expensive than most other forms of temperature sensors – A means of measuring temperature in very inaccessible locations – Up to 3600oC sites.google.com/site/ncpdhbkhn 47 Choice between Temperature Transducers (5) • Quartz thermometer – Very high resolution – Expensive (the complex electronics required to analyze the frequency-change form of output) – Limited range, low inaccurac • Color indicators – Used widely to determine when objects in furnaces have reached the required temperature – Work well if the rate of rise of temperature of the object in the furnace is relatively slow – Inexpensive sites.google.com/site/ncpdhbkhn 48