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

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

Sensor Selection Example Design: Beer Keg Tap Temperature Sensor  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) specific general  C ( C)  < 1degree accuracy  waterproof  durable  inexpensive  fast  low power <5 0 C C >7 0 C

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

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

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

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

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

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

Sensor comparisons ThermoresistorsSemiconductor Temperature IC RTDThermistor (NTC) Analog/Digital temperaturegood range costhigh costlower costinexpensive accuracymost preciseaccuratevery accurate durabilitysensitive to strain and shock ruggedsensitive to shock response timeslowfast powerproblems with self- heating lower powerlow power

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

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

Selecting a NTC thermistor: glass probe

NTC Thermistor: response time thermal time constant: initial ambient temperature electric power dissipation constant T a =25 0 C P= Watts  =0.70 mW/ 0 C t = 18 – 23 msec  =18 msec

NTC Thermistor: Sensitivity T ( 0 C)R T /R Temp Coeff = C

NTC Thermistor: Sensitivity T ( 0 C)R T /R 0 R T /R 0 minR T /R 0 max X=1% X=5% resistor tolerance R T =(R T /R T0 )R T0 +/- 0.02R T0

Sensor comparisons ThermoresistorsSemiconductor Temperature IC RTDThermistor (NTC)Analog temperaturegood range (-80 to C) good range costhigh costlower costinexpensive accuracymost preciseaccurate (+/- 0.02R T0 ) very accurate durabilitysensitive to strain and shock ruggedsensitive to shock response timeslowfast (18-23 msec) fast powerproblems with self- heating lower power (max 0.02 W) low power Other R=1k  -1M 

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?

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

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)

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

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)

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

what conversion measurement does it use?  Thermoelectric  Photoelectric  Photomagnetic  Thermoelastic  Electroelastic  Piezoelectric  Other

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

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 netwon: 2 points linear (zero point and armpit temperature of healthy englishman (point 12) water boils: point 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 degree 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!

Sensor 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 Sensor Acoustic Chemical Electrical Magnetic Mechanical Optical Radiant Thermal Electrical

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

Contact Temperature Sensor contact sensing….measurement is complete when no more thermal gradient between surface (beer) and sensor probe. dQ=aA(T1-T) dt Q=absorbed heat, a=thermal conductivity of sensor- beer interface A=heat transmitting surface area T=temperature sensor, specific heat c and mass m dQ=mcdT aA(T1-T) dt=mcdT T=T1-Ke-t/tT thermal time constant measurement after time constants tT=mc/a/A (short time constant) sensing element 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