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How Does Thermal Imaging Camera Work?

We have often seen the photographs in which there is a mess of yellow and red colors. These photos are taken with the aid of thermography. It is also known as thermal imaging. Thermal imaging is a highly useful method of detecting heat, objects, storms, and diseases. It is also used for security purposes at the front doors of the homes and important buildings. Many people have a question in mind that how does thermal imaging work. A thermal imaging camera works on the principle of detecting the infrared radiation in the form of heat and then converting it into an image. In this article, I will discuss the thermal imaging camera’s working principle in detail. Let us start our discussion:

Thermal Imaging – What it actually is?

Almost every object radiates off heat from itself. Thermal imaging allows us to see the objects on the base of detecting the radiation coming off from the objects. In a frame, a thermal imaging camera records the temperature and then assign a shade of color to the recorded temperature. It can easily distinguish the heat radiation coming off from the object as compared to the surrounding objects. The warmer temperatures are shaded in red, orange, or yellow by a thermal camera while colder temperatures are shaded in blue, purple, or green. Police helicopters use greyscale for shading of a suspect. Greyscale is not used most often but it is used for some special purposes including the detection of a suspect.

Working Principle of a Thermal Imaging Camera

Infrared light emits from every object at different levels and a thermal imaging camera recognizes and captures those levels. The infrared light is usually invisible for a human eye but it can be felt if the intensity is good enough. Heat is transferred in the form of infrared rays and every object emits some infrared rays all the time due to the transfer of heat. For example, if you hold your hands over some hot coals on a grill, the heat is transferred to your hands in the form of tons of infrared radiation. Sun emits the energy in the form of ultraviolet, infrared, and visible light. Half of the energy comes from the sun in the form of visible light while the other half comes in the form of ultraviolet and infrared rays.

Hotter objects produce more infrared radiation as compared to the cold objects. Thermal cameras can easily capture those radiations and convert them into an image. A night vision camera works on the principle of capturing the visible light while a thermal imaging camera works on the principle of capturing infrared radiation. Many people think that the working of both cameras is the same but it is quite different.

Microbolometers are used inside a thermal imaging camera and each pixel has one microbolometer. Microbolometers are measuring devices that capture infrared radiation. They record temperature and assign an appropriate color to the pixel.

Working principle of Microbolometer

The resolution power of a thermal imaging camera is quite low as compared to other displays like modern TVs, etc. 640×180 is the maximum resolution of a very good thermal imaging camera. If you compare a thermal imaging camera with a night vision camera then you will come to know that a thermal imaging camera captures longer wavelengths of infrared rays while a night-vision camera captures shorter wavelengths.

The lens of a thermal imaging camera focuses the infrared energy onto the microbolometers that detect the temperature. Microbolometers create a pattern on the base of infrared energy focused on them, this pattern is known as a thermogram. The thermogram is converted to the electrical signals for the creation of an image. The electrical signals are then passed through a signal-processing unit, a circuit board, and some dedicated chips. The chips translate the electrical signals into data for display. The combination of the signals coming for the detectors is displayed on a screen. We can then see the object and interpret it.

Types of Thermal Imaging Cameras

There are two types of thermal imaging cameras on the base of their working principle. Thermal imaging devices have the ability to scan the images at a rate of 30 times/second. They can detect the temperature in the range of -4 degrees Fahrenheit to 3600 degrees Fahrenheit or -20 degrees Celsius to 2000 degrees Celsius. Most of the thermal imaging cameras can detect the temperature change of approximately 0.4 degrees Fahrenheit or 0.4 degrees Celsius. Here are two common types of thermal imaging cameras:

1. Uncooled Cameras

It is the most common, quiet, and battery built-in type of thermal imaging cameras. An uncooled camera contains a unit of infrared detectors that operate at room temperature. The best thing about these cameras is that they activate immediately.

2. Cryogenically Cooled Cameras

These are expensive but most effective thermal imaging cameras. They are more susceptible to damage from their rugged use. These cameras contain a container in which the infrared detectors are sealed. The container cools the elements for keeping them below 32 degrees Fahrenheit or 0 degrees Celsius. There are several advantages of these cameras as compared to the uncooled cameras including:

  • Cryogenically Cooled Cameras provide incredible resolution
  • These cameras have huge sensitivity. The sensitivity is achieved due to the cooling down of the elements
  • These cameras can detect a temperature change of about 0.2 Fahrenheit or 0.1 degree Celsius
  • These cameras can detect if a person has a gun or not from 300 meters or 1000 feet away
  • Thermal imaging cameras are more useful in the near-absolute darkness as compared to the night vision cameras.
Difference between cooled & uncooled thermal detectors

Where are the Thermal Imaging Cameras used?

Thermal imaging is a process of detecting the objects in the darkness or invisible places. These cameras have a huge range of usability in our life. In daily life, these cameras are not used most often but they can be used for some special purposes. Here are the places or scenarios when you can use a thermal imaging camera:

Building: A thermal camera can detect the moisture and energy efficiency inside a domestic or commercial building.

Electrical: A thermal camera can detect the overheating electrical components and systems immediately.

Firefighting: A thermal imaging camera can make us able to see through smoke-filled areas for the detection of fire parts which are still hot.

Industrial: The industrial thermal imaging cameras can help in the maintenance and regulation of the temperature.

Law Enforcement: A thermal imaging camera can make us able to see through the darkness, foliage, and other conditions for the detection of criminals.

Mechanical: A thermal imager can help to detect the issues in the machines due to the heat.

Veterinary: The non-invasive thermal imaging cameras are helpful for testing the animals. They help in the detection of Arthritis and other problems.

Wildlife: A thermal imaging camera helps in tracking and following the wildlife animals in almost every weather and outdoor condition.

A thermal imaging camera is helpful in our life as it makes us able to see which is invisible with naked eyes. It works on a simple and effective mechanism of detecting the infrared rays coming out from the objects and capturing them to be shown on a display. There are several elements that are used for the detection of infrared radiation. The detected temperatures are then converted into electrical signals. These signals are processed through a signal-processing unit that converts these signals into the data. The data is displayed on a screen and we can easily see the image. Uncooled and cryogenically cooled cameras are two types of thermal imaging cameras. The detecting elements are cooled for keeping them below zero degrees Celsius. The resolution of the sensitivity of the cryogenically cooled thermal cameras is better than the uncooled thermal imaging cameras. Thermal imaging cameras are used in the field of building, firefighting, veterinary, wildlife, electrical, mechanical, industrial, and law enforcement.  

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