To improve the accuracy and efficiency of temperature measurement, selecting the most suitable thermometer is crucial. There are various temperature measurement devices, each with unique characteristics and advantages. Choosing the right device enables more precise measurements, facilitating efficient energy and quality management. This chapter explains the types of representative temperature measurement devices and how to select them.

2.1 Types of Thermometers

Thermometers are broadly classified into contact and non-contact types:
Contact-type thermometers: Measure temperature by directly touching the object (e.g., thermistors, thermocouples, resistance temperature detectors).
Non-contact-type thermometers: Utilize infrared radiation to measure surface temperature (e.g., radiation thermometers, thermal imaging cameras).

The characteristics of each type are introduced below.

2.1.1 Contact-Type Thermometers

Thermistors

A thermistor is a semiconductor element whose electrical resistance changes with temperature. The term combines “Thermal” (heat) and “Resistor” (resistance). Thermistors use metal oxides such as nickel oxide or manganese oxide, and temperature variations alter electron movement inside, changing electrical resistance. This allows temperature measurement as an electrical signal.
Characteristics: High accuracy, fast response time.
Temperature range: -50℃ to +300℃ (High temperature type 500℃)
Applications: Temperature control in home appliances, automobiles, medical devices, and precision equipment.
Considerations: Self-heating may increase temperature, causing measurement errors.

Thermocouples

Thermocouples measure temperature using the voltage generated (Seebeck effect) when two different metals are joined, creating a temperature difference at the junction.
Characteristics: Wide temperature range compatibility, high durability, suitable for measuring small objects.
Temperature range:
K-type thermocouple: -200°C to +1200°C (general use).
R-type/S-type thermocouple: Up to +1600°C (for high-temperature applications).
Applications: From factory automation and process control to automotive, aerospace, military, energy, metal manufacturing, medical, and many other industries.
Considerations: Prolonged use can degrade materials or cause oxidation, leading to increased measurement errors.

Resistance Temperature Detectors (RTDs)

RTDs utilize metals (such as platinum) whose electrical resistance changes with temperature. They provide highly accurate and stable temperature measurements and are widely used in industrial and research applications.
Characteristics: High accuracy (±(0.15+0.002|t|)°C/class A), excellent stability, suitable for long-term use.
Temperature range: -196°C to +600°C (for general platinum RTDs).
Applications: Precision temperature control in semiconductor manufacturing, chemical plants, and food processing
Considerations: Larger in size compared to thermistors or thermocouples, slightly slower response to temperature changes.

2.1.2 Non-Contact-Type Thermometers

Non-contact thermometers measure infrared radiation emitted from an object’s surface to determine its temperature.

Radiation Thermometers

Radiation thermometers utilize infrared radiation to measure surface temperature.
Characteristics: Non-contact measurement, suitable for high-temperature or hazardous objects.
Temperature range: -50°C to +3000°C (depending on the model).
Applications: Steel and glass manufacturing, food processing, medical applications, HVAC (heating, ventilation, air conditioning).
Considerations: Surface color and material affect emissivity; incorrect emissivity settings can result in measurement errors.

 

 

 

 

 

 

Thermal Imaging Cameras

Like radiation thermometers, thermal imaging cameras use infrared radiation but can visualize temperature distribution as an image.
Characteristics: Enables visualization of temperature inconsistencies, capable of measuring large areas simultaneously.
Applications: Equipment inspection, detecting abnormal heat generation, thermal insulation diagnostics in buildings.
Considerations: Surface color and material affect emissivity; incorrect emissivity settings can result in measurement errors.

2.2 How to Choose a Thermometer

2.2.1 Temperature Range of the Object to Be Measured

When selecting a thermometer, considering the target temperature range is essential.
Low temperature (-50°C to 300°C): Thermistors, RTDs, thermocouples.
Medium temperature (-200°C to 1200°C): High-temperature thermistors (500°C), Pt100 RTDs (600°C), K-type thermocouples (1200°C).
High temperature (above 1200°C): R-type/S-type thermocouples, radiation thermometers.

2.2.2 Accuracy and Stability

For high-accuracy requirements: RTDs and high-precision thermistors.
For environments with temperature fluctuations: Thermocouples and thermistors with fast response times are suitable.

2.2.3 Measurement Environment

Harsh environments (high temperature, vibration, shock resistance): Thermocouples.
Remote or high-temperature non-contact measurements: Radiation thermometers, thermal imaging cameras.
Limited spaces: Thermistors, thermocouples.

2.3 Summary

Temperature measurement results vary significantly depending on the equipment used, so selecting the most suitable device for the intended application is crucial.

Choosing the right thermometer enhances efficiency and accuracy in temperature management, contributing to improved product quality and energy management. Use the characteristics and selection methods introduced in this chapter to choose the optimal thermometer for your needs.