1. Department of Optical Engineering Zhejiang University Department of Optical Engineering Zhejiang University Advanced Sensor Technology Lecture 7 Jun. QIAN

2. Department of Optical Engineering Zhejiang University A Review of Lecture 6 Diaphragm deformation equations Diaphragm deformation equations Linear limit: Linear limit: center deflection < thickness center deflection < thickness Corrugated diaphragm ~10X thickness Corrugated diaphragm ~10X thickness Capacitive sensor or strain gauge Capacitive sensor or strain gauge Some silicon based example calculations carried out, Some silicon based example calculations carried out, An alternative technology: Kavlico sensor and learn as much as we can from the way it is designed, built, packaged, and priced. An alternative technology: Kavlico sensor and learn as much as we can from the way it is designed, built, packaged, and priced.

3. Department of Optical Engineering Zhejiang University Basic Intent Overview basic techniques for sensing temperature Overview basic techniques for sensing temperature Some techniques for the measurement of flow will be briefly highlighted Some techniques for the measurement of flow will be briefly highlighted

4. Department of Optical Engineering Zhejiang University Thermometers - traditional techniques There are a number of well- known historical technologies for the measurement of temperature. There are a number of well- known historical technologies for the measurement of temperature. mercury thermometer, in which a reservoir of mercury is sealed in a glass container under vacuum. mercury thermometer, in which a reservoir of mercury is sealed in a glass container under vacuum. When the reservoir is heated, the mercury expands, rising through a long thin column, upon which a graded ruler has been etched. When the reservoir is heated, the mercury expands, rising through a long thin column, upon which a graded ruler has been etched. What sort of sensitivity can be expected for such a system? What sort of sensitivity can be expected for such a system?

5. Department of Optical Engineering Zhejiang University Sensitivity and Resolution Concerns thermal expansion coefficient (CTE) of mercury ~ 30 PPM/K thermal expansion coefficient (CTE) of mercury ~ 30 PPM/K If we assume that dimensions of the container do not change appreciably If we assume that dimensions of the container do not change appreciably The thermal expansion coeffiecient of fused quartz is about 150x smaller than that of mercury, so this approximation is roughly valid. The thermal expansion coeffiecient of fused quartz is about 150x smaller than that of mercury, so this approximation is roughly valid. the mercury in the column expands linearly with temperature. the mercury in the column expands linearly with temperature. If we want 1 mm/K at room temperature, and we have a reservoir volume of 0.1 cm 3, we need a  660  m column: If we want 1 mm/K at room temperature, and we have a reservoir volume of 0.1 cm 3, we need a  660  m column: the sensitivity depends very strongly on the diameter of the column. the sensitivity depends very strongly on the diameter of the column.

6. Department of Optical Engineering Zhejiang University Other traditional techniques Bimetal Bimetal based on thermal expansion based on thermal expansion very popular even today. very popular even today. switches are fairly inexpensive, switches are fairly inexpensive, can operate reliably for many cycles, can operate reliably for many cycles, may still be the correct choice for temperature sensing applications. may still be the correct choice for temperature sensing applications. Shortcomings Shortcomings not accurate enough, not accurate enough, not allow operation over a broad temperature range. not allow operation over a broad temperature range.

7. Department of Optical Engineering Zhejiang University Other traditional techniques Thermocouple Thermocouple A metal wire ~ a vessel contains electrons A metal wire ~ a vessel contains electrons Heating one end of the wire: Heating one end of the wire: the effect of heat is to increase the average velocity of the electrons on the heated end of the wire the effect of heat is to increase the average velocity of the electrons on the heated end of the wire non-uniform distribution of electrons non-uniform distribution of electrons a voltage across two ends a voltage across two ends Difficulty in measuring the voltage using one wire Difficulty in measuring the voltage using one wire Heating the joints of two wires of different materials thermal couple Heating the joints of two wires of different materials thermal couple

8. Department of Optical Engineering Zhejiang University Thermocouple – good for high temp measurement The voltages generated by such effects are fairly small. The voltages generated by such effects are fairly small. K Type thermocouple: K Type thermocouple: - 1 0 0 ℃ ~ 1 3 0 0 ℃ - 1 0 0 ℃ ~ 1 3 0 0 ℃ J Type thermocouple: J Type thermocouple: - 1 0 0 ℃ ~ 7 6 0 ℃ - 1 0 0 ℃ ~ 7 6 0 ℃ A good thermocouple exhibits a voltage signal of only 10  V/Kelvin. A good thermocouple exhibits a voltage signal of only 10  V/Kelvin. accurate measurements of small temp changes require very well-designed electronics. accurate measurements of small temp changes require very well-designed electronics. For measurements which require accuracy of +/- 10 K, and need to be carried out at temperatures near 1000K, thermocouples are definitely the way to go. For measurements which require accuracy of +/- 10 K, and need to be carried out at temperatures near 1000K, thermocouples are definitely the way to go.

9. Department of Optical Engineering Zhejiang University Resistance Thermometry Platinum wires are commonly used for resistance thermometry. Platinum wires are commonly used for resistance thermometry. though expensive, it is favored for these applications for several very good reasons: though expensive, it is favored for these applications for several very good reasons: reasonably large temperature coefficient, reasonably large temperature coefficient, not affected by most chemicals, mechanically stable not affected by most chemicals, mechanically stable withstand very high temperatures, withstand very high temperatures, few other metals offer such a favorable collection of long-term stability performance advantages. few other metals offer such a favorable collection of long-term stability performance advantages. For narrower temperature ranges, what can we use? For narrower temperature ranges, what can we use?

10. Department of Optical Engineering Zhejiang University Thermistors and the Steinhart-Hart Equation NTC thermister NTC thermister depositing a small quantity of semi- conductor paste on to closely spaced parallel platinum alloy wires depositing a small quantity of semi- conductor paste on to closely spaced parallel platinum alloy wires sintered at a high temperature at which time the material forms a tight bond between the two wires. sintered at a high temperature at which time the material forms a tight bond between the two wires. Steinhart-Hart equation for thermistors Steinhart-Hart equation for thermistors

11. Department of Optical Engineering Zhejiang University Glossary of terms - Thermister Zero-Power Resistance (Ro): Zero-Power Resistance (Ro): The dc resistance value of a thermistor at a specified temperature with negligible electrical power to avoid self heating. The dc resistance value of a thermistor at a specified temperature with negligible electrical power to avoid self heating. Zero Power Temperature Coefficient of Resistance (Alpha): Zero Power Temperature Coefficient of Resistance (Alpha): The ratio at a specified temperature(T), of the rate of change of zero power resistance with temperature to the zero power resistance The ratio at a specified temperature(T), of the rate of change of zero power resistance with temperature to the zero power resistance Resistance Temperature Characteristic: Resistance Temperature Characteristic: The relationship between the zero power resistance of a thermistor and its body temperature. The relationship between the zero power resistance of a thermistor and its body temperature. Temperature-Wattage Characteristic: Temperature-Wattage Characteristic: The relationship at a specified ambient temperature between the thermistor temperature and the applied steady state wattage. The relationship at a specified ambient temperature between the thermistor temperature and the applied steady state wattage.

12. Department of Optical Engineering Zhejiang University Products by some manufacturers

13. Department of Optical Engineering Zhejiang University Resolution Limit Resolution limitation imposed by noise Resolution limitation imposed by noise R1: thermister, R2: load resistor R1: thermister, R2: load resistor if RL>>R1 if RL>>R1 If the temp of R1 changes by 1 K, the resistance changes by  R1, the voltage changes by  (V in R 1 /R L ). the resistance changes by  R1, the voltage changes by  (V in R 1 /R L ).Noise:

14. Department of Optical Engineering Zhejiang University Improve the Resolution by reducing by reducing the temperature, the temperature, the bandwidth, and the bandwidth, and the load resistor, the load resistor, by increasing by increasing the temperature coefficient the temperature coefficient the bias voltage, Vin. the bias voltage, Vin. Of all of these parameters, it may be easiest to increase the bias voltage. Of all of these parameters, it may be easiest to increase the bias voltage.

15. Department of Optical Engineering Zhejiang University Self-heating Problem The bias causes power to be dissipated in the sense resistor. The bias causes power to be dissipated in the sense resistor. assume that the sense resistor is attached to the object of interest with a finite thermal conductance G. assume that the sense resistor is attached to the object of interest with a finite thermal conductance G. There will be a temperature difference between the sense resistor and the object of interest given by : There will be a temperature difference between the sense resistor and the object of interest given by : Thermal conductance between the core of the thermistors and the surface are generally of order 10 -2 to 1 W/K Thermal conductance between the core of the thermistors and the surface are generally of order 10 -2 to 1 W/K power dissipation 1mW  T=10 -3 - 0.1degree C power dissipation 1mW  T=10 -3 - 0.1degree C Self-heating will can cause substantial errors. Self-heating will can cause substantial errors.

16. Department of Optical Engineering Zhejiang University Measurement of changing temperature with contact temp sensors A thermometer is attached to an object with a thermal conductance of G (W/K). Assume that A thermometer is attached to an object with a thermal conductance of G (W/K). Assume that The thermometer has a heat capacity C (J/K). The thermometer has a heat capacity C (J/K). some power, P, is being applied to the thermometer (bias currents) some power, P, is being applied to the thermometer (bias currents) From energy balance, the energy into the thermometer equals the change in energy of the thermometer: From energy balance, the energy into the thermometer equals the change in energy of the thermometer:

17. Department of Optical Engineering Zhejiang University Measurement of changing temperature with contact temp sensors A finite temperature offset due to A finite temperature offset due to bias power (P/G), bias power (P/G), oscillation amplitude which varies with frequency. oscillation amplitude which varies with frequency. At low frequency, Ts 2  To 2, At low frequency, Ts 2  To 2, At higher frequencies, the thermal time constant associated with the heat capacity of the thermometer can cause a reduce oscillation and a phase lag. At higher frequencies, the thermal time constant associated with the heat capacity of the thermometer can cause a reduce oscillation and a phase lag. These issues are important to keep in mind for measurements of time-varying temperatures. These issues are important to keep in mind for measurements of time-varying temperatures.

18. Department of Optical Engineering Zhejiang University Flow Sensors There are three basic approaches to the measurement of flow There are three basic approaches to the measurement of flow thermal effects to measure fluid motion. thermal effects to measure fluid motion. In general, this approach uses a heat source to deposit heat into the fluid, and a thermometer to measure the temperature of the fluid. If the heat source is upstream of the sensor, flow increases heat transport and causes the sensor temperature to increase. In general, this approach uses a heat source to deposit heat into the fluid, and a thermometer to measure the temperature of the fluid. If the heat source is upstream of the sensor, flow increases heat transport and causes the sensor temperature to increase. Another possible arrangement is to heat a thermistor with a fixed power, and measure its temperature. In this case, fluid flow acts to cool the thermometer. Another possible arrangement is to heat a thermistor with a fixed power, and measure its temperature. In this case, fluid flow acts to cool the thermometer.

19. Department of Optical Engineering Zhejiang University A Commercial Product

20. Department of Optical Engineering Zhejiang University Flow Sensors A slightly more complicated approach relies on Bernoulli's Equation, which is : A slightly more complicated approach relies on Bernoulli's Equation, which is : This principle is applied by measuring pressure at a pair of points in a fluid. This principle is applied by measuring pressure at a pair of points in a fluid. When water flows through a pipe with a varying diameter, the total flow rate in each region is a constant, therefore, changes in tube diameter are compensated for by changes in fluid velocity. When water flows through a pipe with a varying diameter, the total flow rate in each region is a constant, therefore, changes in tube diameter are compensated for by changes in fluid velocity. By measuring the pressure in regions with different diameter, it is possible to measure fluid velocity. By measuring the pressure in regions with different diameter, it is possible to measure fluid velocity. Only work if the flow is not turbulent Only work if the flow is not turbulent Optical+ Microfluidics

21. Department of Optical Engineering Zhejiang University An Example: Pressure Difference Based Flowmeter Measure the pressure difference between the wide and narrow regions Measure the pressure difference between the wide and narrow regions Pressure drop techniques only work if the flow is not turbulent (dissipative). Pressure drop techniques only work if the flow is not turbulent (dissipative). Modern MFC (mass flow controller) Modern MFC (mass flow controller)

22. Department of Optical Engineering Zhejiang University Doppler effect based flow sensor The last technique for flow measurement is based on measurement of Doppler effects in sound transport. The last technique for flow measurement is based on measurement of Doppler effects in sound transport. Since sound is carried by pressure waves in a medium (the fluid), its transport laterally across a channel is affected by the motion of the fluid. Since sound is carried by pressure waves in a medium (the fluid), its transport laterally across a channel is affected by the motion of the fluid. It is possible to measure the change in sound frequency due to fluid motion (direct Doppler effect, or listen for changes in the travel time from transmitter to receiver. It is possible to measure the change in sound frequency due to fluid motion (direct Doppler effect, or listen for changes in the travel time from transmitter to receiver. High sensitivity techniques generally measure frequency shifts, since excellent accuracy may be obtained by use of analog or digital signal processing techniques to measure small frequency shifts. High sensitivity techniques generally measure frequency shifts, since excellent accuracy may be obtained by use of analog or digital signal processing techniques to measure small frequency shifts.

23. Department of Optical Engineering Zhejiang University Doppler effect based flow sensor

24. Department of Optical Engineering Zhejiang University How to use Doppler effect? Wave source: Wave source: Ultrasound Ultrasound Freq>= hundreds of KHz Freq>= hundreds of KHz Microwave Microwave 24.125 GHz, less than 1mW/cm2 24.125 GHz, less than 1mW/cm2 Required reflection media Required reflection media Fine particles Fine particles Bubbles Bubbles Flow Rate Range: 0.08 to 12.2 m/sec Pipe Size: Any pipe ID from 12.7 mm to 4.5 m Accuracy: ±2% of full scale. Requires solids or bubbles minimum size of 100 microns, minimum concentration 75 ppm. Repeatability: ±0.1%, Linearity ±0.5% of full scale

25. Department of Optical Engineering Zhejiang University Flow Sensor: Review Flow may be measured by Flow may be measured by thermal, thermal, Bernoulli, Bernoulli, Doppler techniques. Doppler techniques. Thermal techniques are generally least accurate and least expensive, Thermal techniques are generally least accurate and least expensive, Bernoulli techniques can work well, but are accurate only for non-turbulent flow, Bernoulli techniques can work well, but are accurate only for non-turbulent flow, Doppler techniques are potentially most accurate, but are also generally most expensive. Doppler techniques are potentially most accurate, but are also generally most expensive.

26. Department of Optical Engineering Zhejiang University Temperature Sensors: Review Temperature Sensors Temperature Sensors Bimetal sensor/switch Bimetal sensor/switch Thermocouple Thermocouple Thermistor Thermistor Solid-state Solid-state Issues associated with applications Issues associated with applications Self-heating Self-heating Thermal response Thermal response Noise limited resolution Noise limited resolution Linearity Linearity