Lecture 15 Temperature, distance, force transducers

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Lecture 15Temperature, distance, force
transducers
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Outline of todays class

• Review audio logy instruments
• EEG visit today
• Next week imaging lectures
• Following week special class at State
• Midterm up coming topics
• Review session State download ivote
• Homework review
• Student presentations
• Temperature Transducers

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Audio logy instruments

• Hearing test manual, automatic, Bekesy
• High Freq type
• Children audiometer
• Impedance meter
• Noise meters
• Hearing aids
• Cochlea implants
• Listening devices-stethoscope, low freq,
  frequency translators

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Temperature transducers

• Thermoelectric Thermocouple, thermopile
• Thermocapacitive change in capacitor
• Thermoresistive- Thermistors, platinum resistance
  thermometer
• Thermal expansion Glass thermometer, bimetal
  strip, quartz crystal
• Radiation- Thermopile, photo voltaic
• Thermochemical Liquid crystal
• Pyroelectric- polariztion/temp changes (lead
  zirconate-titanate materials)

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Factors in transducer selection
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RTR0(1a(T-T0))
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Sources of error

• 1st error source - RTR0(1ATAT2) non-linear
  approximation
• 2nd error source thermoelectric EMF at
  contacts- use AC bridge
• 3rd error source- self heating of resistive
  element

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Bridge circuit adjustments
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Resistance verse temperature in bead thermistors
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Simple method to linearize
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Bead thermistor
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(a) Seebeck effect (b) Pelitier effect
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Properties of Thermoelectric devices

• Require lots of current
• Heavy / slow
• Copper/Constantan
• Platinum/platinum rhodium
• Chromel / alumel (high sensitivity)
• Limited useful temperature range

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Thermocouple
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Radiation

• Planks law
• Radiation spectrum
• Sun spectrum why we see colors
• Color temperature of lights
• Is white or black cooler?
• Temperature of universe
• Big bang theory

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Radiation spectrum
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Frequency changing crystals
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Liquid crystals
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Other temperature devices

• Galileo jar
• Microwave oven
• Temp vs heat
• Convection / radiant heaters
• Human body temp regulation
• Cobbold text Transducers for biomedical
  measurement