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What You Need To Know About Infrared Thermometers

Updated: Jan 22, 2021


Non-contact thermometers infer the temperature of the measured body through the measurement of the infrared radiation that is emitted from the body. There are various advantages of using them over the old liquid-in-glass versions, making non-contact thermometers infinitely better suited to all manner of uses across a broad range of 21st century industries and applications. Most non-contact thermometers are based on thermopile as the infrared detector that converts thermal energy into electrical energy (voltage output). The electrical potential output of the thermopiles is then correlated to the temperature of the measured body. This correlation is done in the factory calibration and the accuracy of such thermometers is very much a function of the system design as well as the calibration procedure carried out.

Infrared thermometers are described as a perfect device for performing quick spot checks of hot and cold holding stations and buffet lines in restaurants. They are also helpful in a home kitchen. The temperature of soups, sauces and other liquids can be checked with an infrared thermometer, along with temperature detection in living beings. Beyond consumer usage, these cameras are also well suited for industrial applications that demand accurate temperature control of the process with moving parts or where contact-based temperature measurements are difficult or impossible.

What is an infrared thermometer and how accurate they are?

An infrared thermometer is a device that is used to measure temperature by converting the absorbed thermal radiation from the measured body to an electrical potential and then correlating it to the temperature of the measured body. They are also sometimes mistakenly referred to as laser thermometers (because a laser is used to help aim the thermometer). By capturing the amount of infrared energy emitted by the object and adjusting for its emissivity and the ambient temperature, the object's temperature can often be determined within a certain range of its actual temperature. Infrared thermometers belong to a category of devices known as "thermal radiation thermometers".

Research has established that when used correctly, infrared or non-contact thermometers are even as accurate as oral or rectal thermometers. In the present global scenario when many establishments now require temperature checks, these hand-held thermometers are proving to be safe, quick and accurate when used correctly.

How does an infrared thermometer work?

Infrared thermometer uses a sensor that may consist of a lens to focus the infrared (IR) energy on to a detector. This detector then converts the energy to an electrical signal that is displayed in units of temperature after being compensated for ambient temperature variation. This permits temperature measurement from a distance without contact with the object to be measured. Contactless infrared thermometer is useful for measuring temperature under circumstances where thermocouples or other probe-type sensors cannot be used.

Is it safe for people to use - especially newborn and elderly and pregnant women? Why?

While infrared thermometers measure infrared radiation, they do not emit any infrared radiation themselves. In fact, they measure the infrared radiation from the person being measured. All objects, including human from newborn to elderly, emit infrared radiation (any object will emit infrared radiation if it is above absolute zero, or -273°C). Due to the non-contact nature of the thermometers, they may be safer than traditional contact thermometers. Non-contact thermometers that are meant for human body temperature measurements are safe for use, including infants, elderly and pregnant women. However, industrial non-contact thermometers, which typically come with a laser pointer for guidance, should not be used to avoid risk of eye injury (even though these are typically Class 1 lasers which are rated eye safe). Moreover, industrial non-contact thermometers are meant to measure over a wider temperature range and will not provide the accuracy required for human body temperature measurements

What do terms like accuracy and repeatability mean in non-contact thermometers?

On the onset, the terms like accuracy & repeatability might seem to mean the same. However, there is actually a distinct difference between the terms, making it important to understand what each one means and its relation to the other.


The accuracy of a medical instrument is based on the difference of a measured value compared to its actual (true) value. Since no measurement is 100% accurate, an element of inconsistency and inaccuracy needs to be accounted for, that is why the accuracy figures are quoted with ‘±’. Ultimately, accuracy measures how close you come to the correct result. The accuracy improves when instruments or tools are calibrated properly.


Repeatability allows one to measure how close a particular result or set of data is in comparison to the same measurements, made with the same device or instrument, under the exact same circumstances. In other words, the measurement procedure, observer, device or instrument, testing conditions and location would all need to be exactly the same and testing needs to be conducted over a short space of time. All devices will have a natural variation between measurements. This is a direct result of inherent noise present in the system. It is highly desirable to have a thermometer with highly repeatable measurements.

How does software affect accuracy?

The output from the thermopile in the infrared thermometer is an electrical potential that has to be correlated to a temperature. This is done through the firmware (software of the hardware) in the thermometer and the calibration procedure in factory. The output of the thermopile is affected by the ambient temperature and thus, this has to be properly accounted, calibrated and compensated for. This is done through proper system design, calibration procedure, and firmware codes and algorithm that can adequately account for changes in the ambient temperatures.

It is suggested to have a software architecture which allows a simple validation of internal measuring instrument calculations. The well-built digital thermometer is the one that is able to bring out all its internal calculation functions to the communication interface, so the end-user can compare the results of the internal measuring instrument calculation with reference results. That’s why it is important to have well-built software that gathers data and reflects reading accurately.

Usage of Infrared Thermometers

One of the most common uses of the infrared thermometer is to read temperature from a particular spot on a surface of the wall, ventilation, automobile, or food item. Now due to COVID-19 pandemic, they are commonly seen at various establishments to measure human temperature as well.

Interested to find out more about infrared thermometers/non-contact thermometers? Read “Common Questions about Infrared Thermometers”.

T-SMART is introducing state of the art Thermopile 2.0 with responsivity of 2 orders of magnitude higher than the current generation of thermopiles. The company is focused on taking thermal detection technology to an elevated level, using sensing integration algorithms, for a cognitive understanding through thoughts, experience and senses. Thermopile 2.0 will allow for more accurate and repeatable non-contact thermometers. Click here to learn more about Thermopile 2.0.

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