How does Infrared Thermometer Work?

Infrared (IR) thermometers also known as contactless or non contact thermometers that are widely used to measure surface or body temperature from a distance using infrared radiations.

With the current Covid situation, use of non-contact IR thermometers to measure body temperature has increased drastically. In this article we will discuss how infrared thermometer works? their advantages, limitations and applications. Click this link to know various types of temperature sensors and their applications.

How Infrared Thermometers Work?

Infrared thermometer works or measure a body / surface temperature by detecting infrared radiations coming from that body or surface. Therefore to understand the working of an infrared thermometer, firstly we need to understand what are infrared radiations?

What are Infrared Radiations?

Infrared Radiation are types of electromagnetic radiations or heat that are generated due to temperature difference between a body or surface and atmosphere.

All hot bodies emit IR radiations that can even travel in vacuum. The amount of IR radiation emitted by a body depends on its temperature and it’s emissivity. Where emissivity is a property of a material that measures a body efficiency to emit thermal radiations.

Only a part of IR radiations is visible to human eyes. Because IR radiations have wavelengths in the range of 700 nm to 1 mm that is larger than the visible light. Click this link!! to know in detail about emissivity and black body concept.

Working of Infrared Thermometer

As shown in the below image IR Thermometers works and measure a body or surface temperature in following steps:

Step-1: Focus the energy coming from a body or surface in the form of infrared rays on to a sensor known as thermopile.

Step-2: Thermopile absorbs IR radiations and converts the radiations into heat.

Step-3: The generated heat is converted into the electrical signal that is sent to the thermometer processor.

Step-4: In the processor, electrical signal is analyzed and its value is mapped with stored values to calculate object or a body temperature.

This image shows the Working of Infrared Thermometer
Working of Infrared Thermometer

To determine a body temperature IR thermometers compare the IR radiations emitted by the object (whose temperature is unknown) and a reference point. This is done to ensure environmental temperature has a minimal impact on thermometer reading.

Applications of Infrared Thermometer?

IR thermometers have following applications in healthcare and engineering fields.

  • Infrared thermometers are a good alternative to measure temperature in conditions where temperature probes can not be used.
  • Used to check body temperature.
  • Check food or drink temperature during cooking or serving.
  • During product validation, engineers use an IR thermometer to check product temperature.
  • Check goods temperature during transportation.
  • During covid epidemic, Various agencies are using IR thermometers to monitor body temperature and control the spread of covid-19.

Advantages and Disadvantages of IR Thermometer?

Compared to traditional probe type or mercury thermometers, infrared thermometers has the following advantages:

  • IR Thermometers are very fast. Depending on thermometer quality. You can get reading even in less than 1 second.
  • Contact less temperature measurements are possible.
  • Digital IR thermometers come with memory options as well.
  • Easy to use.

Compared to traditional probe type or mercury thermometers, infrared thermometers has the following disadvantages:

  • IR Thermometers are more costly compared to conventional thermometers.
  • For a low cost Infrared thermometer, temperature measurement accuracy is a concern.
  • Clean environment is required for temperature measurements.

Commonly asked questions on Infrared Thermometer?

It depends on the quality of the thermometer. Clinical grade infrared thermometers are available in accuracy range of ±0.3º. ASTM E 1965-98 has defined the Standard Specification for Infrared Thermometers for intermittent determination of patient temperature.

Yes, IR thermometers can be used to measure a surface or skin temperature. But thermometers designed to measure a surface or body temperature can not be used to measure skin temperature. In other words to measure skin temperature accurately, you require FDA approved IR thermometers for medical use.

Infrared thermometers don’t emit any radiations to measure temperature. They are sensing devices. For more safety

  • You can turn off the laser attached with the thermometer.
  • Use only clinically approved thermometers
  • Best practices for temperature measurement shall be followed.

For more details, contact your doctor.

To sum up Infrared thermometers are one of the best way for contactless temperature measurement. It is also available at reasonable prices. 

We will keep updating this article on how infrared thermometers work. Write your suggestions and questions on the Working of Infrared Thermometers in the comment box.

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