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Example Design – Milestone 1

Example Design – Milestone 1. Technical Research Sensor Technology Originally Prepared by: Prof. Shela Aboud Modified by: Prof. Bitar. Measurement System. Acoustic Biological Chemical Electrical Magnetic Mechanical Optical Radiant Thermal. LCD LEDs 7-segment dot-matrix alarm

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Example Design – Milestone 1

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  1. Example Design – Milestone 1 Technical Research Sensor TechnologyOriginally Prepared by: Prof. Shela AboudModified by:Prof. Bitar

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

  3. Input Sensor Technology • What types of sensors are needed on your project? • What sensor specifications do you need to consider?

  4. Sensor Selection Example Design: 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

  5. Types of Temperature Sensors • Thermoresistive RTD (resistive temperature detector) thermistor • Thermoelectric thermocouple • Semiconductor (IC’s) pn diode bipolar junction transistor • Optical infrared detector • Acoustic piezoelectric

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

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

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

  9. Optical Temperature Sensors • advantages: • thermally stable • waterproof • good in hostile environments • disadvantages: • limited temperature range

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

  11. Sensor Comparisons

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

  13. 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

  14. Selecting a NTC thermistor: glass probe

  15. 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

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

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

  18. Sensor Comparisons

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