Temperature Measurement: Types and Applications

Temperature measurement is one of the cornerstones of instrumentation and control systems in any industrial process. From chemical manufacturing to power generation, maintaining precise temperature control ensures product safety, efficiency, and quality. There are multiple temperature instrumentation technologies to suit the specific needs of different industries, each with unique operating principles, advantages, and limitations.

In this note, we will explore in detail the main types of temperature instrumentation, analyzing their measurement principles, characteristics, applications and selection criteria.

1. Instruments Based on Material Expansion

a. Liquid-in-Glass Thermometers

• Measuring Principle: Based on the thermal expansion of a liquid (usually mercury or alcohol) inside a calibrated glass tube.

• Advantages:

  • Economical and easy to use.

  • They do not require external energy.

• Disadvantages:

  • Limited to specific temperature ranges.

  • Fragility of glass and restrictions on the use of mercury.

• Uses:

  • Laboratories.

  • Environmental applications.

b. Bimetallic Thermometers

• Measuring Principle: Two metals with different expansion coefficients are joined together and deformed as the temperature changes.

• Advantages:

  • Robust and economical.

  • Suitable for mechanical applications.

• Disadvantages:

  • Lower accuracy compared to electronic sensors.

  • Limited to static applications.

• Uses:

  • Boilers.

  • Heating systems.

2. Resistivity-Based Sensors

a. Resistance thermometers (RTD)

• Measuring Principle: The electrical resistance of certain metals (such as platinum) varies with temperature.

• Advantages:

  • High precision and stability.

  • Wide temperature range (up to 600 °C).

• Disadvantages:

  • Expensive sensors compared to other types.

  • They require compensation circuits to correctly measure resistance.

• Uses:

  • Chemical and petrochemical plants.

  • Process control in food and beverages.

b. Thermistors

• Measuring Principle: Semiconductor components whose resistance changes significantly with temperature.

• Advantages:

  • Very high sensitivity for narrow temperature ranges.

  • Small and economical.

• Disadvantages:

  • Not suitable for high temperatures.

  • More fragile than RTDs.

• Uses:

  • HVAC systems.

  • Medical and electronic devices.

3. Thermoelectric Voltage Based Sensors

a. Thermocouples

• Measuring Principle: Two different metals generate a voltage proportional to the temperature difference between their ends (Seebeck effect).

• Advantages:

  • Wide temperature range (up to 2000 °C).

  • Quick response to temperature changes.

• Disadvantages:

  • Lower precision than RTDs.

  • They require frequent calibration.

• Uses:

  • Industrial ovens.

  • Internal combustion engines.

4. Instruments Based on Thermal Radiation

a. Optical Pyrometers

• Measurement Principle: They measure the radiation emitted by a hot object and convert it into a temperature reading.

• Advantages:

  • Without direct contact with the measured object.

  • Works in extreme and high temperature environments.

• Disadvantages:

  • Less accurate at low temperatures.

  • High initial costs.

• Uses:

  • Foundries and metallurgy.

  • Oven monitoring systems.

b. Thermal imaging cameras

• Measurement Principle: They use infrared sensors to map the thermal distribution of a surface.

• Advantages:

  • They generate detailed images of temperature distribution.

  • Ideal for non-intrusive inspections.

• Disadvantages:

  • They require specialized software for analysis.

  • High initial cost.

• Uses:

  • Predictive maintenance.

  • Thermal leak detection.

5. Solid State Electronic Sensors

a. Silicon Sensors

• Measuring Principle: Semiconductor devices that produce electrical signals proportional to temperature.

• Advantages:

  • Compact and economical.

  • Easy integration with electronic systems.

• Disadvantages:

  • Limited to moderate temperature ranges.

  • Sensitive to electromagnetic interference.

• Uses:

  • Portable electronic devices.

  • Automotive sensors.

6. Temperature Instruments Based on Gas Expansion

a. Gas Pressure Thermometers

• Measurement Principle: Based on the expansion of a gas inside a bulb, the pressure exerted is translated into a temperature reading.

• Advantages:

  • Accuracy over a wide temperature range.

  • Robust and reliable in industrial environments.

• Disadvantages:

  • Slower response than electronic sensors.

  • Limited by the nature of the gas used.

• Uses:

  • Chemical processes.

  • Laboratory applications.

Temperature Instrumentation Selection Criteria

Selecting the right temperature instrument depends on several key factors:

1. Temperature Range: The instrument must be able to operate in the expected range without loss of accuracy.

2. Environmental Conditions: Consider factors such as corrosion, vibrations, humidity and dust.

3. Required Accuracy: Depending on process tolerances.

4. Response Time: Important for dynamic or critical processes.

5. Fluid Compatibility: Materials resistant to the medium in contact.

6. Electronic Integration: Compatibility with existing control or monitoring systems.

   
   

Conclusion

Temperature instrumentation is a fundamental element in the control and safety of industrial processes. From simple thermometers to advanced thermal imaging cameras, each type of instrument offers a specific solution for a variety of applications. Understanding the operating principles, advantages and limitations of each technology is key to choosing the right instrument.

At Acciomate Engineering & Projects , we offer customized solutions for the implementation of temperature measurement systems, optimizing processes and guaranteeing efficiency and safety in your operations.