Temperature Sensor

12th Week

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THERMOCOUPLE

If we join two dissimilar metals at any temperature above absolute zero, there will be a potential difference between them which is a function of the temperature of the junction

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Resistance Temperature Detector (RTD)

RTDs rely on the predictable and repeatable phenomena of the electrical resistance of metals changing with temperature.

The most common metals used for temperature sensing are platinum, nickel, and copper.

Advantages: Stable, Accurate, and Linear. Disadvantages: Expensive, Current source required, Small DR, Self-

heating Platinum

𝑅𝑅 = 𝑅𝑅𝑜𝑜 1 + 𝛼𝛼1 𝑇𝑇 − 𝑇𝑇𝑜𝑜 + 𝛼𝛼2 𝑇𝑇 − 𝑇𝑇𝑜𝑜 2 + ⋯+ 𝛼𝛼𝑛𝑛 𝑇𝑇 − 𝑇𝑇𝑜𝑜 𝑛𝑛

𝛼𝛼1 = 3.9083 × 10−3/℃

𝛼𝛼2 = −5.775 × 10−7/℃2

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Resistance Temperature Detector (RTD)

The temperature characteristics of an RTD are specified as a single number (α), representing the average temperature coefficient over the 0 to 100°C temperature range as calculated by: Alpha: relative sensitivity

𝛼𝛼 =1𝑅𝑅𝑜𝑜

𝑅𝑅100 − 𝑅𝑅𝑜𝑜𝑇𝑇2 − 𝑇𝑇1

=1𝑅𝑅𝑜𝑜

𝑅𝑅100 − 𝑅𝑅𝑜𝑜100℃

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Thermistor

Thermal resistor or thermally sensitive resistor A semiconductor device having a resistance that changes rapidly

with an increase in temperature

Advantages: High output, fast response Disadvantages: non-linear, self-heating, limited temperature, current

source required Types of the thermistor

NTC(negative temperature coefficient) PTC(positive temperature coefficient) CTR(Critical temperature resistor)

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Thermistor: NTC

The temperature characteristics Ro: resistance at To B: material characteristic temperature (thermistor constant)

𝑅𝑅 = 𝑅𝑅𝑜𝑜 exp 𝐵𝐵1𝑇𝑇 −

1𝑇𝑇𝑜𝑜

𝐵𝐵 =1

1𝑇𝑇 −

1𝑇𝑇𝑜𝑜

ln𝑅𝑅𝑅𝑅𝑜𝑜

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TYPES OF TEMPERATURE SENSORS

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Temperature Sensing using RTD

RTD generates temperature-dependent output voltage with precision current source

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Temperature Sensing using RTD

Precision current source

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Temperature Sensing using RTD

Precision Temperature-Sensing With RTD Circuits

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Temperature Sensing using RTD

A 2nd order, low pass filter created with A4, R8, C8A, C8B, R9 and C9

A Bessel response and a bandwidth of 10 Hz R10 and R11 set a gain of 7.47 V/V

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SEMICONDUCTOR TEMPERATURE SENSORS

the relationship between a bipolar junction transistor's (BJT) base-emitter voltage to its collector current:

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CLASSIC BANDGAP TEMPERATURE SENSOR

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References

Handbook of modern sensors physics designs and application 4th ed., Jacob Fraden, Springer

microchip.com Analog.com Design of Analog CMOS Integrated Circuits, 2nd ed., Razavi,

McGraw-Hill College

Analog Integrated Circuit Design, 2nd ed., Tony Chan Carusone, David A. Johns, John Wiley & Sons

Analysis and Design of Analog Integrated Circuits, 5th ed., Paul R. Gray, Paul J. Hurst, Stehen H. Lewis, Robert G. Meyer, John Wiley & Sons

알기쉬운 최신 센서 기술(기초에서 응용까지), 복두출판사

센서전자공학, 동일출판사