How do Infrared Thermal Imaging Thermometers Work?

Handheld infrared thermal imaging thermometers can be used to measure temperature in a variety of industrial and clinical settings. These non-contact temperature measurement devices work well in situations where objects are fragile and dangerously close, or where other types of thermometers are impractical.

Infrared thermometers use the concept of infrared radiation to determine the surface temperature of an object, without any physical contact. Let's find out what infrared radiation is to better understand how infrared thermometers work.

Every object that is not at absolute zero temperature has atoms moving through it. The speed of this movement is directly related to its temperature. The higher the temperature, the faster the molecules move. These moving molecules emit energy in the form of infrared radiation.

The wavelength of this radiation is longer than that of visible light. Therefore, we cannot see it with the naked eye. But if the object gets too hot, the radiation can jump into the visible spectrum. Hot metals that glow red or even white are an example of this.

While we may not be able to see infrared radiation, we can still perceive it as heat. The heat we feel from sunlight, a radiator, or a fire are all examples of infrared radiation. It is this heat that infrared thermometers detect to measure the temperature of an object.

Similar to visible light, infrared light can also be focused, reflected, or absorbed. Infrared thermal imaging thermometers use a lens to focus infrared light from an object onto a detector called a thermopile.

The thermopile is nothing but thermocouples connected in series or parallel. When infrared radiation falls on the surface of the thermopile, it is absorbed and converted into heat. The voltage output is proportional to the incident infrared energy. The detector uses this output to determine the temperature, which is displayed on the screen.

While the whole process may sound complicated, infrared thermal imaging thermometers take just seconds to record the temperature and display it in the units you want.

The most critical aspect of any thermometer is its accuracy. For thermal imaging thermometers, the accuracy depends on its distance-to-spot ratio (D/S ratio). This ratio represents the maximum distance a thermometer can assess the specific surface area. 

For example, if you need to measure the surface temperature of a 4-inch area with an IR thermometer with a D/S ratio of 8:1, the maximum distance from which the temperature can be recorded accurately is 32 inches (8:1 x 4). This means that with a larger ratio, you can measure the temperature from a greater distance. However, the surface area also increases with distance.

Emissivity shows how much-infrared energy a thermometer can emit at one time. An infrared thermometer with an emissivity near 1.00 can read more material than an infrared thermometer with a lower emissivity value. Choose a thermometer with an adjustable emissivity level to adjust the infrared energy emitted and compensate for the energy reflected by the material to account for temperature measurements.

The temperature range of an infrared thermal imaging thermometer affects what you can do with it. You may want an infrared thermal imaging thermometer with a wide temperature range to record various processes at different temperatures. Conversely, infrared thermometers with a narrower temperature range are better where higher resolution is required to ensure proper temperature control for a particular process.

Reading speed is the time it takes for a thermometer to provide an accurate reading after initiating the thermometer reading process. This factor is essential when measuring the temperature of a moving object or when the object is heating up rapidly.

Industrial infrared thermometers must have a robust design. Lensless and Fresnel lens thermometers are durable due to their polymer construction, which keeps them safe. However, rugged mica lens thermometers require a more durable housing and carrying case implemented in their design to prevent lens breakage.

The backlit screen makes reading the thermometer easier even in adverse lighting conditions.

Warranty is a must for thermometers, as they are fragile and can even be defective. Lensless and Fresnel's thermometers are less expensive than mica lens thermometers, which can be a considerable investment. If you're buying any expensive thermometer, buy one that comes with a manufacturer's warranty.

Using an infrared thermometer is essential when reading surface temperatures that are too dangerous and nearly impossible to reach. With a complex inner working process, these thermometers provide quick results and are easy to use. However, before choosing an infrared thermometer, try to figure out the temperature range and your application. Also, make sure to use the device correctly in the correct location for accurate results.

The above describes the working principle of infrared thermal imaging thermometers and the factors to be considered when choosing an infrared thermal imaging thermometer. If you are planning to purchase a thermal imaging camera, please contact us.

JAVOL provides thermal imaging cameras and infrared imaging solutions, relying on multi-spectral high-sensitivity photoelectric sensor chips based on advanced compound semiconductor materials, using deep learning AI algorithms as the engine, integrating low-light night vision technology, infrared thermal imaging technology, short-wave infrared technology, and multiple Spectral fusion technology, our company designs, develops and manufactures advanced imaging products and system solutions, which are widely used in machine vision, autonomous driving, drone payloads, high-end manufacturing and medical diagnosis.