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Example Design – Milestone 1

This document outlines the essential aspects of sensor technology, focusing on various types of sensors, their specifications, and selection criteria for specific projects. It covers acoustic, biological, chemical, electrical, magnetic, mechanical, optical, and thermal sensors, detailing their advantages and disadvantages. The guide also discusses input/output requirements, environmental conditions, accuracy, sensitivity, and other critical factors that influence the choice of sensors. Insight into temperature sensor types, such as thermoresistive, thermoelectric, and semiconductor sensors, is provided, along with their key characteristics.

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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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