An Introduction to IR Sensor Systems

IR Camera

What is an IR sensor?

An infrared or IR sensor is an electrical device that measures and picks up infrared radiation in its surroundings. Infrared radiation is from the portion of the electromagnetic spectrum that extends from the red end to microwaves.  Infrared is invisible to the eye.

In the popular imagination, the most understood use of infrared sensing technology is in low light or night vision devices – or infrared remote controls for home entertainment systems. But the history of infrared and its uses (and usefulness) are much wider.

A brief history of the IR sensor

Infrared radiation (also sometimes abbreviated to IR) was first discovered in the year 1800 by British Astronomer William Herschel while he was studying the sun. Originally, he termed the phenomenon ‘calorific rays’ after the Latin word for heat ‘calor.’ The term infrared, meaning ‘below red’ (infrared falls below red on the spectrum of visible light), was not coined until later in the 19th century.

Infrared detection was first used in the Second World War as image intensifiers, based on work done by a Hungarian physicist in the 1930s named Kálmán Tihanyi. Development of this technology continued throughout the 20th century, with the technology moving into the commercial and industrial settings in the 1950s, but saw an explosion in popularity once solid-state infrared sensors were developed in the 1970s. Owing to their affordability and ruggedness compared to preceding technologies.

How do IR sensors work?

Infrared sensors work in a wide variety of forms dependent on the type. The following is the working principle of an infrared sensor:

IR or Infrared Imaging
  • Icon Objects that are warmer than their surroundings emit infrared light.
  • Icon When infrared radiation strikes an item, some of it is absorbed and others are reflected.
  • Icon The amount of infrared light emitted is related to the object's temperature.
  • Icon An infrared sensor detects the amount of infrared radiation emitted by an object.

Types of IR sensor

They can be divided into two broad categories:

Passive infrared sensors or PIR – these are sensors that do not emit any infrared radiation themselves but instead detect infrared radiation emitted by other objects. These types of sensors are used in applications such as motion sensing or temperature measurement. PIR sensors can be found in the home in the form of motion detectors for home security systems, the aforementioned remote controls, and smoke alarms to name a few. Thermographic cameras are also an example of a PIR sensor.

Active infrared sensors, or AIR - they emit infrared radiation themselves and detect that which is reflected at them, these are often used for applications such as detection and ranging. Night vision or security cameras are also an example of an AIR sensor..

In some cases, when used in conjunction with a passive infrared vision device, specially designed AIR devices can be used as a source of illumination in areas of low light. But we need not concern ourselves too much with this lattermost example, as they are not commonly used outside of military or law enforcement applications.

Beyond the two broad categories, there are subcategories of sensor all with slightly different use cases.

  • Thermopile sensors: detect the infrared radiation emitted by an object in order to measure the temperature of said object. They take advantage of the thermoelectric effect to measure temperature. These sensor systems are often utilized in industrial process control and medical devices.
  • Infrared spectroscopy sensors: These detect the absorption, transmission, and reflection of infrared radiation to identify and analyze the composition of materials. This type of sensor is frequently used in chemical analysis, environmental monitoring, and materials science.
  • Infrared imaging sensors: detect the intensity of infrared radiation emitted by objects and create an image based on the intensity distribution. They are used for thermal imaging, medical diagnosis, and low light/night vision devices. Bolometers: These sensors produce an electrical signal by measuring how a material's resistance changes when it is subjected to infrared light.

IR sensors - analog or digital?

The distinction between analog and digital IR sensors is different from the distinction between analog and digital media (a record vs a CD for example). Instead, an analog infrared sensor is a type of sensor that outputs a continuous signal that can take on any value within a certain range, whereas a digital IR sensor outputs a signal that can only take on a finite number of values e.g., one or zero, yes or no. An analog signal from an analog sensor can still be interpreted as ‘digital’ data.

Modern solid-state infrared sensors, particularly those used in large-scale industrial or commercial settings for measurement and analysis will collect the relevant data and output that data to a digital system. Either to a central control system such as Supervisory Control And Data Acquisition system (SCADA) or a Building Management System (BMS) in the case of networked sensor systems, or on a readout in the case of a single non-networked sensor.

Infrared (IR) sensor accuracy

Infrared sensors and infrared sensor systems have also become increasingly popular owing to their exceptional accuracy. For example, in the case of process control temperature measurement; when properly applied, maintained, and calibrated – an infrared sensor can provide measurements to within 0.5 degrees Celsius.

Infrared sensors can be contact or non-contact depending on the specific needs of the end user.

Contact IR sensors are typically used for temperature measurement of objects that operate or exist in temperature ranges too extreme for the use of a non-contact sensor. Contact sensors can be more accurate and more durable than their non-contact counterparts, but are more expensive and more difficult to use, additionally, unlike a non-contact sensor, if a contact sensor is improperly installed, they can cause damage to the very object they’re meant to be measuring.

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Infrared monitoring systems as continuous monitoring Solutions

An infrared monitoring system is a device that uses infrared technology to detect and monitor temperature changes. They are a valuable tool for the continuous monitoring of equipment and assets. Infrared monitoring systems are useful for monitoring security threats and identifying possible issues before they result in expensive failures. In industrial settings, this technology is frequently used to identify possible equipment issues like overheating or electrical shorts. Security applications for infrared surveillance systems include spotting burglars and keeping an eye on fires.

Monitoring systems that use infrared radiation operate by then detecting the energy that is emitted. The most common example is the IR sensor, used to detect infrared radiation and monitor an area or object. It works by detecting the infrared radiation that is emitted by an object. This radiation is then transformed into an electrical indication by the sensor. Then an alarm can be set off, an asset can be controlled, or data can be recorded using this signal. The amount of radiation emitted is directly related to the temperature of the item being measured. This suggests that an IR sensor or any other IR monitoring system can be used to create a temperature map of an area. Then, using this temperature map, potential trouble areas can be located.

Whether looking for a single sensor, or a system of sensors, it is imperative to do the proper research to understand exactly what kind of IR sensor is required for the task at hand. Not all are created equal, nor is there a one-size-fits-all solution to every problem that may require infrared sensing.

There are a multitude of options available to solve any number of problems. It is important to consider exactly what problem is being presented – and what kind of budget is available to solve that problem.

Benefits of infrared monitoring systems

There are numerous benefits for infrared sensors as an infrared monitoring system. The following are some of the most popular applications:



For detecting attackers, security systems utilize infrared sensors. They are also utilized in devices for detecting fires.



Infrared sensors are utilized in industrial settings like the manufacturing industry, oil and gas industry, and power generation industry to examine products, monitor equipment temperature, prevent fires/explosions, and detect leaks and hotspots in pipelines. This helps to prevent downtime and increase productivity.



Infrared sensors are utilized in a variety of medical procedures, including illness diagnosis, patient monitoring, and surgery.

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