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sensors:temperature [2018/06/05 23:20] admin [Media] |
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- | ====== Temperature ====== | ||
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- | ===== Summary ===== | ||
- | ==== Introduction ==== | ||
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- | There are four main contact temperature-sensing devices available, divided in three families: thermocouples (self-generating sensors), resistance temperature detectors and thermistors (resistive sensors), and temperature-transducing ICs (PN or Semiconductive). These sensors translate the temperature into a reference voltage, resistance or current, which is then measured and processed and a numerical temperature value is computed. | ||
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- | ==== Types of temperature sensor ==== | ||
- | === Thermocouples === | ||
- | Thermocouples are a physically simple sensor, though how they function is more complex. | ||
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- | The hot junction is the sensing element, and the cold junction is kept at a constant reference temperature. | ||
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- | {{: | ||
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- | Fraden (1997) defines three laws for proper connection of thermoelectric materials : | ||
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- | Law No.1 (A) - A thermoelectric current can not be established in a homogeneous circuit by heat alone. (LAW OF HOMOGENEOUS CIRCUITS) | ||
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- | Law No.2 (B) - The algebraic sum of the thermoelectric forces in a circuit composed of any number and combination of dissimilar materials is zero if all junctions are at a uniform temperature. | ||
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- | Law No.3 (C) - If two junctions at temperature T1 and T2 produce Seebeck voltage V2, and temperatures T2 and T3 produce voltage V1, then temperatures T1 and T3 will produce V3 = V1 + V2. (LAW OF INTERMEDIATE TEMPERATURES) | ||
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- | {{: | ||
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- | The theory behind the thermocouple and thermoelectric effect is based upon the atomic structure of the alloys and is beyond the scope of this report. | ||
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- | {{: | ||
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- | The Seebeck EMF produced by a thermocouple is of such small scale that the voltage must be amplified and processed by a specialized thermocouple input module. | ||
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- | Thermocouples are calibrated with a cold junction temperature of 0°C. However, two problems arise when connecting thermocouples to their input device: | ||
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- | === Resistance temperature detectors (RTDs) | ||
- | The same year Seebeck discovered the principle behind the thermocouple (1822), Humphrey Davy announced that the resistivity of metals were highly influenced by temperature. | ||
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- | {{: | ||
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- | RTDs function on the principle that as the sensing element is heated, the resistance of the metal wire increases proportionally. | ||
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- | RTDs are calibrated to exhibit a resistance of 100 Ω at 0°C. Their resistance at other temperatures depends on the value of the mean slope of the metal’s resistance-temperature plot, known as the //constant alpha// | ||
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- | === Thermistors | ||
- | Thermistors, | ||
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- | {{: | ||
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- | Comprised of a metal oxide ceramic semiconductor sensing element, thermistors are notorious for their non-linearity, | ||
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- | === Temperature-transducer ICs === | ||
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- | Semiconductor temperature sensors are produced in the form of ICs. Their design results from the fact that semiconductor diodes have temperature-sensitive voltage vs. current characteristics. | ||
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- | The use of IC temperature sensors is limited to applications where the temperature is within a –55° to 150°C range. The measurement range of IC temperature sensors may be small compared to that of thermocouples and RTDs, but they have several advantages: they are small, accurate, and inexpensive. | ||
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- | Temperature sensing ICs are available either in analog form, which output a voltage or current which is proportional to the temperature, | ||
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- | === Projects That Use Temperature Sensors === | ||
- | The [[http:// | ||
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- | [[https:// | ||
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- | ==== Comparison of temperature sensor types ==== | ||
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- | The following table offers a comparison of the different characteristics of the various temperature sensor types. | ||
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- | ^Characteristic | ||
- | ^Active Material | ||
- | ^Changing Parameter | ||
- | ^Temperature Range |-200°C to 500°C | ||
- | ^Sensitivity | ||
- | ^Accuracy | ||
- | ^Linearity | ||
- | ^Response Time |2-5 s |1-2 s |2-5 s | | ||
- | ^Stability | ||
- | ^Base Value |100 Ω to 2 kΩ |1 kΩ to 1 MΩ |< 10 mV |Various | ||
- | ^Noise Susceptibility | ||
- | ^Drift | ||
- | ^Special Requirements | ||
- | ^Device Cost |$60 - $215 |$10 - $350 |$20 - $235 |$5 - $50 | | ||
- | ^Relative System Cost |Moderate | ||
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- | ===== Devices | ||
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- | <box 100% round blue|**Analog Devices AD592AN**> | ||
- | <box 30% round red right|Sources> | ||
- | [[http:// | ||
- | </ | ||
- | Description: | ||
- | Datasheet: {{http:// | ||
- | Resources: | ||
- | Notes: Changes output current proportional to absolute temperature.\\ | ||
- | Variants: AD592CN, AD592BN\\ | ||
- | </ | ||
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- | <box 100% round blue|**BC Components BC1566KR**> | ||
- | <box 30% round red right|Sources> | ||
- | [[http:// | ||
- | </ | ||
- | Description: | ||
- | Datasheet: {{http:// | ||
- | Resources: | ||
- | Notes:\\ | ||
- | Variants: BC1560DKR, BC1561DKR\\ | ||
- | </ | ||
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- | <box 100% round blue|**Omega F3105**> | ||
- | <box 30% round red right|Sources> | ||
- | [[http:// | ||
- | </ | ||
- | Description: | ||
- | Datasheet: [[http:// | ||
- | Resources: | ||
- | Notes: Temperature Range -50 to 600°C\\ | ||
- | Variants: W2100, W2200\\ | ||
- | </ | ||
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- | ===== Media ===== | ||
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- | [[http:// | ||
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- | ===== External Links & References ===== | ||
- | * Hollinger, Avrum, 2002. {{: | ||
- | * Awtrey, Dan (Dallas Semiconductor), | ||
- | * Ogden Manufacturing, | ||
- | * O' | ||
- | * Omega Engineering, | ||
- | * [[http:// | ||
- | * Lecture Series on Industrial Instrumentation by Prof.Alok Barua, Department of Electrical Engineering, | ||
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- | {{tag> | ||
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