How Infrared Thermometer Works: Non-Contact Thermometer

Do you know that anyone can check your temperature without the thermometer probe touching your body surface? Sounds interesting. Right? Yes, it’s possible. With Infrared Thermometer, body temperature can be checked from a distance. We will discuss how Infrared Thermometer works in this article.

COVID 19 has imposed many restrictions in our day-to-day life, and the infrared thermometer has become a very precious item. An infrared thermometer can check your body temperature without touching your body surface. That is why it is called a non-contact thermometer.

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With growing concerns for COVID 19, Infrared Thermometer is an essential item to check the temperature without the risk of getting infected.

Before we learn about how infrared thermometer works, we need to understand Infrared radiation and its works. Right? So let’s get into the basics of infrared radiation first, and then we will learn about the infrared thermometer.

What Is Infrared Radiation

Infrared Radiation ( IR), or simply call it ” Infrared” or “Infrared Light,” is the high wavelength electromagnetic radiation. If you don’t know about electromagnetic radiation, then I can say that those waves from the electromagnetic field spread across the atmosphere carrying radiant energy.

Electromagnetic radiations are categorized based on the wavelength. Shorter wavelength radiations can be hazardous like Gamma-ray, X-ray, Ultraviolet Ray, etc.

Longer wavelength electromagnetic radiations are not harmful. We are surrounded by longer wavelength electromagnetic radiations like a TV remote, Microwave, car key, etc.

The human eye can not see infrared radiation. Instead, humans can sense infrared radiation through heat. That is why infrared radiation is often called Heat Radiation.

Gamma-rayLess than .01 Nanometers
X ray.01-10 Nanometers
Ultraviolet10-400 Nanometers
Visible Light400-700 Nanometers
Infrared700 Nanometers -1 Millimeters
Microwave1 Millimeters – 1 Meter
Radio1 Meter- 100000 Kilometers

What Is Infrared Thermometer or IR Thermometer Or Non Contact Infrared Thermometer?

An infrared thermometer is a contactless thermometer that can detect the thermal radiation emitted by the human body or objects and convert that heat energy to electrical energy or signal. That signal is then mapped with the temperature range to display.

Since the thermometer probe does not touch the object, it is called a non-contact infrared thermometer or Contact Less Thermometer. It is often called a Laser Thermometer or temperature gun also.

Due to the different emissivity levels, an infrared thermometer can only give the temperature value in a range, or you can say that it gives an approximate value. But that value is very close to the actual value.

Key Components Of Infrared Thermometer

Although there are many small components in an infrared thermometer, but below are the key components.

Focal Lens

This lens absorbs the infrared radiation and pass it on the thermopile.


Thermopile is an electronic device that converts heat energy to electric energy or signal. Thermopile consists of many thermocouples connected in series and occasionally in parallel.


PCB Controller

An electronic circuit board gets the electrical signal from the thermopile and processes it to co-relate the electrical signal to a temperature range. This is the brain of the thermometer that does all the processing jobs with inputs from the thermopile.


The display gets the input for the temperature from the PCB controller and shows that on the LCD. The display is usually digital, but analog display thermometers are also available.

How Infrared Thermometer Works?

Like how light can be focused, absorbed, or reflected, infrared radiation can also be focused, absorbed, or reflected. An infrared thermometer uses a focal lens to absorb the infrared radiation from the human body or object and pass it on to an electronic detector called Thermopile.

infrared thermometer

For thermopile, the input is the heat energy. Thermopile has a series of thermocouples connected that convert heat energy to equivalent electrical power or electrical signal. Those electrical signals are then passed on to the Thermometer processor that evaluated the electrical signal and compared it with a proportionate temperature range. That temperature is then displayed on the LCD.

The working principle of the IR thermometer looks very completed, but in actuality, it takes a second to complete all those steps and display the temperature.

Application of Infrared Thermometer

An infrared thermometer can be used in any medical or engineering application where using a thermometer probe is not possible or not allowed.

  • Due to COVID 19 pandemic, infrared thermometers are used in hospitals to check body temperature without anybody’s surface contact.
  • To check temperature-controlled
  • food and drink.
  • To check the temperature of medicines.
  • To check the temperature of electronic devices.
  • To check the temperature of an object where the traditional thermometer probe can not reach like an internal electronics part.
  • To check product temperature during validation.

Advantages of Infrared Thermometer

Below are the key advantages that infrared thermometer has over mercury based traditional thermometer.

  • Temperature can be measured at a distance that is very good due to COVID 19 situation.
  • Temperature is very accurate compared to traditional thermometers.
  • Very fast and easy to use.
  • Some digital thermometer comes with storage as well. So you can check historical temperature data for analysis.

Disadvantages Of Infrared Thermometer

  • Way to costly compared to traditional thermometers
  • If you measure temperature in an environment where there are many objects emitting infrared radiations then the infrared thermometer may give incorrect temperature data. So a clean radiation-free environment is required.
  • Only external temperature can be measured.


That’s all I have in this article to brief about infrared thermometers and how it works. Infrared thermometers are now used everywhere due to the advantage of a contactless temperature check and a high level of accuracy. It is also becoming popular due to COVID 19 pandemic.

I tried to cover the basics of the Infrared Thermometer in this article. If you have any questions or queries, please do write to me in the comment section and I will be happy to reply.

Here is an excellent video to learn visually how Infrared Thermometer works.

You may also like to read: Difference between Microprocessor and Microcontroller

Frequently Asked Questions On Infrared Thermometer ( FAQ)

What Is Infrared Thermometer?

An infrared thermometer is an electronic device to measure temperature by converting the infrared radiation to heat energy and then the heat energy to an electrical signal.

Infrared Thermometer or Mercury based thermometer. Which is more accurate?

Infrared thermometers are more accurate if the temperature is taken in a clean environment


A 2004 batch Mechanical Engineering graduate From NIT, Agartala. Close to 16 years of experience in the field of consumer electronics and appliances domain as a Sr. Design Engineer and Team Leader in India and the United States. A GD&T practitioner, with expertise in Lean Manufacturing and Six Sigma. Crazy about exploring CAD-CAM tools and in his free time love to go for a ride with his champ, Rian.