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Infrared Temperature Sensors

Image shows someone taking their temperature using an infrared temperature sensor.

Infrared temperature sensors measure temperature using infrared light. They are used to measure temperature in applications that require utmost accuracy.
Infrared temperature sensors are typically integrated into thermometers and are used to measure the surface temperature of objects, for instance, a baby’s head.
In this post, we’ll cover the basics of infrared temperature sensors. We’ll also discuss how they are used in different applications then we’ll walk you through the steps you need to take to pick the right infrared temperature sensor for your needs.


What are Infrared Sensors?

Infrared sensors, also known as IR sensors, are devices that detect and measure infrared radiation of surfaces in their range. They then convert the infrared energy into an electrical signal.
Infrared sensors work on the principle that all objects emit infrared radiation (Planck’s Law) and that the emitted infrared energy is proportional to the object’s temperature (Stephen Boltzmann Law). Infrared radiation is not visible to the human eye, though you can feel the energy in heat form.


What Types of Infrared Sensors are there?


Infrared sensors can be classified as either active or passive infrared sensors. Active infrared sensors can emit and detect radiation, while passive infrared sensors can only detect radiation.
Active infrared sensors have both a light-emitting diode (LED) or laser diode that emits radiation and a photodiode (PD) or phototransistor that receives and detects infrared radiation.
Passive infrared sensors, on the other hand, rely on outer objects to emit infrared radiation. They then receive and detect the radiation. Examples of passive infrared sensors include thermocouples and pyro-electric detectors.


How Do Infrared Sensors Work?


For infrared sensors to work, they require the following elements:

  • IR source – The IR source can be the infrared sensor or an object within range.
  • Transmission medium – It can be optical fibres, air or a vacuum.
  • IR receiver or detector – The IR receivers detects radiation from the IR source and converts it to an output signal.
  • Signal processing – The output signal from the IR source is displayed in a gauge or measuring device. In most cases, the output signal relayed by the IR receiver is small. An amplifier can be used to intensify it.

The IR source emits radiation and transmits it to the IR receiver through the transmission medium. The IR receiver then detects the radiation and processes it to an output signal equivalent to its intensity. The output signal is then amplified and displayed on a gauge.


What are the Different Types of Applications where Infrared Sensors can be Used?

We’ve all come across infrared sensors in our everyday life, for instance, when using the TV remote control or during a security scan at the airport. Below are a few industries where infrared sensors come in handy.

Infrared Imaging


A classic example of infrared imaging is night vision devices. These devices emit infrared radiation to detect an object that is not visible at night.

Industrial Application

Infrared sensors are used in industries to measure and control variables like temperature, pressure, motion and speed.


In the Medical World


The medical industry uses infrared thermometers to measure body temperature without direct contact.

How to Choose an Infrared Sensor?


When selecting an infrared sensor, you need to consider the:

  • Distance to Spot (D:S) ratio


The further an object is from the infrared sensor, the more inaccurate the reading. When measuring surfaces that are far away, use an infrared sensor with a high D:S ratio, for instance, 60:1 instead of 12:1.

  • Emissivity


Emissivity can be defined as how accurately or efficiently a surface emits radiation. Shiny objects, for instance, have a low emissivity. The temperature reading of a shiny object might not be as accurate as of that of a matt surface. When measuring a shiny object, choose a sensor with a variable emissivity setting.

  • Temperature Range

Infrared thermometers have different temperature ranges. For instance, a Mica lens infrared thermometer is ideal for measuring high temperatures, while a No-lens infrared thermometer is good for cold temperatures. It is important to properly research different sensors when choosing the best temperature sensors for your specific needs.


Other factors that you should consider are:

  • Response speed
  • Design
  • Warranty
  • Ability to record