Technical Research Sensor Technology

1. Example Design – Milestone 1 Technical Research Sensor Technology ECE 2799 D04

2. Measurement System Acoustic Biological Chemical Electrical Magnetic Mechanical Optical Radiant Thermal LCD LEDs 7-segment dot-matrix alarm etc… Input Sensor Modifier Output Transducer Power Supply

3. Sensor Selection Example Design: Beer Keg Tap Temperature Sensor specific general • Environmental Conditions • Input/Output Range • Linearity • Offset • Operating Life • Output Format • Overload Characteristics • Repeatability/Hysteresis • Resolution/Accuracy • Sensitivity/Selectivity • Size/Cost/Weight • Speed of Response • Stability (long and short term) • 5 - 7 0C (4 - 8 0C) • < 1degree accuracy • waterproof • durable • inexpensive • fast • low power >70C 5-70C <50C

4. Types of temperature sensors • Thermoresistive RTD (resistive temperature detector) thermistor (thermometer + resistor) • Thermoelectric thermocouple • Semiconductor (IC’s) pn diode bipolar junction transistor • Optical phosphorescent signal • Acoustic piezoelectric

5. Thermoresistive sensors NTC/PTC Thermistor RTD (PTC) • advantages: • temperature range • simplicity of interface circuits • sensitivity • long term stability • inexpensive • disadvantages • not rugged • self-heating • advantages • temperature range • sensitivity • inexpensive • disadvantages: • PTC less sensitive • nonlinear • self-heating

6. Thermoelectric sensor thermocouples • advantages: • temperature range • very ruggedness • inexpensive • fast depending on size • disadvantages: • error is larger than RTD or IC sensor • some types are very sensitive to moister

7. Semiconductor IC sensors • advantages: • temperature range • highly linear • small • accurate • easy to interface • disadvantages: • sensitive to shock

8. Optical temperature sensors • advantages: • thermally stable • waterproof • good in hostile environments • disadvantages: • expensive • impractical (too big, complicated, etc.) Richard Box fluorescent tubes under high tension wires outside of Bristol England

9. Acoustic Temperature sensors • advantages: • thermally stable • waterproof • good in hostile environments • disadvantages: • expensive • complicated circuitry T ultrasound dry air

10. Sensor comparisons

11. NTC Thermistor Negative Temperature Coefficient example material constant zero-power resistance at temp T

12. Types of NTC Thermistors • Metallized surface contact • slow response times • high power dissipations • low cost • Bead type • fast response times • high stability/reliability • low power dissipation • more costly • bare beads • no environmental protection. • glass coated beads • not rugged • glass probes • easy to handle, durable, stable • glass rods • good for mounting on circuit boards www.thermometrics.com

13. Selecting a NTC thermistor: glass probe

14. NTC Thermistor: response time thermal time constant: t=18 msec initial ambient temperature Ta=25 0C electric power P= 0.020 Watts t = 18 – 23 msec dissipation constant d=0.70 mW/0C

15. NTC Thermistor: Sensitivity Temp Coeff =-3.7 %/C @ 5 C

16. NTC Thermistor: Sensitivity X=1% resistor tolerance X=5% RT=(RT/RT0)RT0+/- 0.02RT0

17. Sensor comparisons

18. Sensor Classification • what does it measure? • what are its specifications? • what physical phenomenon is it sensitive to? • what material is it fabricated from? • what conversion measurement does it use? • what are its field of application?

19. what does it measure (stimulus)? Wave amplitude, phase, polarization Spectrum Wave velocity Other • Acoustic • Biological • Chemical • Electrical • Magnetic • Mechanical (pressure) • Optical • Radiant • Thermal Magnitude Difference Rate of change Other Wave amplitude, phase, polarization Spectrum Wave velocity Refraction index Reflectivity, absorption Other

20. what are its specifications? • Environmental Conditions • Cost • Input/Output Range • Linearity • Offset • Operating Life • Output Format • Overload Characteristics • Repeatability/Hysteresis • Resolution/Accuracy • Sensitivity/Selectivity • Size/Weight • Speed of Response • Stability (long and short term)

21. what are its specifications? • Environmental Conditions • Cost • Input/Output Range • Linearity • Offset • Operating Life • Output Format • Overload Characteristics • Repeatability/Hysteresis • Resolution/Accuracy • Sensitivity/Selectivity • Size/Weight • Speed of Response • Stability (long and short term) temperature acceleration vibration shock ambient pressure moisture corrosive materials electromagnetic fields

22. what are its specifications? • Environmental Conditions • Cost • Input/Output Range • Linearity • Offset • Operating Life • Output Format • Overload Characteristics • Repeatability/Hysteresis • Resolution/Accuracy • Sensitivity/Selectivity • Size/Weight • Speed of Response • Stability (long and short term)

23. what physical phenomenon is it sensitive to? • Biological • Chemical • Electric, Magnetic or EM wave • Heat • Mechanical displacement or wave • Radioactivity, radiation • Other

24. what conversion measurement does it use? • Thermoelectric • Photoelectric • Photomagnetic • Thermoelastic • Electroelastic • Piezoelectric • Other

25. What are its field of application? • Agriculture • Civil Engineering • Energy, Power • Health, Medicine • Manufacturing • Military • Scientific Measurements • Transportation, automotive • Recreation, toys • Space • Other

26. Temperature Scale temperature scales 1664 Hooke: zero scale at freezing point of distilled water (zero point) 1694 Renaldi: 2 points linear (melting point ice and boiling point water) divide by 12 1701 netwon: 2 points linear (zero point and armpit temperature of healthy englishman (point 12) water boils: point 34 1706 Fahrenheit: zero point mixture of water, ice, salt…..96 degrees (found in the blood of a healthy man)…ice melts 32, boils 212degrees 1742 celsius: ice melts 0 and water boils at 100 kelvin…..triple point…at 273.16degree kelvin, at 4.58 mm Hg pressue..water vapor, liquid and ice can coexist. (approximately 0 degrees C)….linear, zero point is temp where kinetic energy of all moving particle is zero….absolute zero…not possilbe!

27. Sensor Acoustic Chemical Electrical Magnetic Mechanical Optical Radiant Thermal Sensor Electrical Advantages of electrical measurement systems • many microelectronic circuits already exist (applications: amplification, filtering, modulation) • many options for information display or recording • electrical signal is well suited for transmission

28. Temperature Measurement conduction, convection, radiation sensor type: contact sensor or thermal radiation sensor?

29. Contact Temperature Sensor sensing element contact sensing….measurement is complete when no more thermal gradient between surface (beer) and sensor probe. 1.sensing element: low specific heat, high thermal conductivity, strong and predictable temp sensitivity. 2.contacts: interface between sensing element and electrical circuit….low thermal conductivity, low electrical resistance (sometimes used to support sensor) 3. protective element: physically protects sening element from environment: low thermal resistance, high elctrical isolation properties……impermeable to moisture or other factes that spuriously affect sensing element Q=absorbed heat, a=thermal conductivity of sensor-beer interface A=heat transmitting surface area T=temperature dQ=aA(T1-T) dt sensor, specific heat c and mass m dQ=mcdT aA(T1-T) dt=mcdT tT=mc/a/A T=T1-Ke-t/tT thermal time constant measurement after 5 -10 time constants (short time constant)