What Is Infrared Thermometer?

Devices that can measure the temperature of objects remotely and quickly without any contact are called infrared thermometers. Infrared thermometers collect infrared light emitted from objects and estimate their temperature based on the amount of energy. These devices are frequently used in industrial applications as well as preferred by home users.

What Is Infrared Thermometer?
28.11.2022
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Devices that can measure the temperature of objects remotely and quickly without any contact are called infrared thermometers. These devices are frequently used in industrial applications as well as preferred by home users.

Every object that is not at absolute zero temperature (-273.15 °C) has atoms moving inside. The speed of movement of these atoms is directly related to the temperature of the object. The higher the temperature, the faster the molecules move. Moving molecules emit energy in the form of infrared radiation.

Infrared thermometers collect infrared light emitted from objects and estimate their temperature based on the amount of energy. The measurement result is shown on the screen within seconds.

Infrared thermometers are often used to detect overheated equipment, inspect electrical circuits, find the source of the fault, and test heating and cooling systems.

The infrared thermometer is directed towards the object whose temperature is to be measured and the measurement is made by pressing the button on it. Incorrect and misleading measurements can be taken when infrared thermometers are not used correctly. Measuring distance and surface gloss are extremely important for accurate results.

Each infrared thermometer has a D:S (Distance to spot) ratio, which indicates the relationship between the measuring distance and the diameter of the measured area. For example, a thermometer with a D:S ratio of 12:1 will measure an area of ​​2.5 cm diameter when held 30 cm from the target. It measures the temperature of an area with a diameter of 7.5 cm when held 90 cm from the target, and 12.5 cm when held at a distance of 150 cm.

The farther the thermometer is held from the point to be measured, the larger the area is measured. If the area to be measured is a small place and the thermometer is held too far, the areas outside the area to be measured will also be included in the measurement.

The D:S ratio of infrared thermometers available in the market ranges from 1:1 to 50:1. The higher this ratio, the higher the price of thermometers.

Most handheld infrared thermometers have a laser pointer. The red laser dot indicates the center of the measured area. Infrared thermometers are supposed to measure only the area illuminated by laser light, but this light is only a guide.

Infrared thermometers work by measuring infrared rays emitted by objects. Infrared thermometers can measure the temperature of many kinds of objects with high accuracy. However, some problems arise with glossy and reflective surfaces. The decisive factor here is the emissivity.

The emissivity is a number between 0 and 1. 0 is not emitter, 1 is considered perfect emitter. Glossy surfaces have lower emissivity than matte surfaces. For example, the emissivity of bright copper is 0.01, bright aluminum is 0.05, galvanized steel is 0.28, white paper is 0.9, glass is 0.92, rubber is 0.93, and water is 0.98.

The emissivity of many infrared thermometers commonly used in the market is fixed at 0.95. In such thermometers, it is possible to take measurements closer to reality by sticking black electrical tape (emissivity is approximately 0.95) on glossy surfaces.

In some advanced thermometers it is possible to change the emissivity. The emissivity setting can be selected as high (0.95) on wood, concrete, plaster and paint, medium (0.7) on rusted or dull metals, and low (0.3) on shiny metals.

The emissivity of the human body is in the range of 0.95-0.98. The measurement accuracy of industrial devices is ± 1 °C or ± 2 °C. Therefore, it cannot be used in sensitive measurements such as the human body. Infrared body and forehead thermometers, on the other hand, can measure in a much lower temperature range (35 °C – 42 °C), with higher accuracy (± 0.2 °C).

Emre Yılmaz, the founder of Lighting Portal, graduated from Atılım University Department of Electrical and Electronics Engineering in 2013, and since then has been involved in the management and product development activities of state-supported projects in the lighting industry. He completed his master's degree at Gazi University Industrial Design Engineering Department and continues his education in the doctorate program of the same department.
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