Technical Research Sensor Technology Originally Prepared by: Prof. Shela Aboud Modified by: Prof. Bitar 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 Processing Output Transducer

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

Sensor Selection Example Design: 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  Thermoelectric thermocouple  Semiconductor (IC’s) pn diode bipolar junction transistor  Optical infrared detector  Acoustic piezoelectric

Thermoresistive sensors advantages: temperature range simple 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 rugged inexpensive fast depending on size disadvantages: error is larger than RTD or IC sensor some types are very sensitive to moisture

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

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

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 