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Temperature Sensors

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A summary of temperature sensors

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Temperature Sensors

  1. 1. Temperature Sensors Scandium σ
  2. 2. Temperature Sensors Thermometers Resistance Temperature Detectors Thermocouples
  3. 3. Factors that determine which Temperature Sensor to use <ul><li>Type of temperature sensor to be used in a particular application is dependent on several factors </li></ul><ul><li>Cost </li></ul><ul><li>Space Constraints </li></ul><ul><li>Durability </li></ul><ul><li>Accuracy of Temperature Sensor </li></ul><ul><li>Range of Temperature Sensor </li></ul><ul><li>Sensitivity of Temperature Sensor </li></ul><ul><li>High voltage/ Low voltage </li></ul>
  4. 4. Thermometer <ul><li>The first thermometers were called thermoscopes (thermometers without a scale). </li></ul><ul><li>Mercury or Alcohol Thermometers (most common LIGs), are filled with a chemical that expands and contracts when heated or cooled, allowing for a direct correlation between the length of the liquid column and the temperature of the material being measured </li></ul><ul><li>Advantages and Disadvantages </li></ul><ul><li>Simplest and cheapest form of temperature sensor, its accuracy is limited to the calibration marks along the tube length </li></ul><ul><li>Simply a visual sensor, without electrical control, making it difficult to use in a process controls apparatus </li></ul>
  5. 5. Resistance Temperature Detectors: Advantages/Disadvantages <ul><li>Advantages </li></ul><ul><li>Stable output for long period of time </li></ul><ul><li>Ease of calibration and accurate readings over relatively narrow temperature spans </li></ul><ul><li>High Accuracy and Precision </li></ul><ul><li>Disadvantages </li></ul><ul><li>Smaller overall temperature range compared to thermocouples </li></ul><ul><li>[-200 C – 800 ° C] </li></ul><ul><li>Higher initial cost </li></ul><ul><li>Less rugged in high vibration environments </li></ul>
  6. 6. Thermocouples <ul><li>Definition: </li></ul><ul><li>A thermocouple is a resistance thermometer that measures temperature. It consists of two different types of metals, joined together at one end. When the junction of the two metals is heated or cooled, a voltage is created that can be correlated back to the temperature. </li></ul><ul><li>Thermocouples are very often used in industry. The following criteria are used in selecting a thermocouple: </li></ul><ul><li>Temperature range </li></ul><ul><li>Chemical resistance of the thermocouple or sheath material </li></ul><ul><li>Abrasion and vibration resistance </li></ul><ul><li>Installation requirements (may need to be compatible with existing equipment; existing holes may determine probe diameter) </li></ul>
  7. 7. Thermocouple: Typical Application <ul><li>A typical application: </li></ul><ul><li>Tube and shell heat exchanger is used to heat solvent ( tube side) with steam (shell side) </li></ul><ul><li>Steam supply is controlled manually </li></ul><ul><li>Thermocouple was placed in a thermo weld, which was then installed in the drop leg of the pipe on the tube outlet side. </li></ul>Shell and Tube Exchanger
  8. 8. Temperature Sensors Thermometers Resistance Temperature Detectors Thermocouples

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