What is Thermal Imaging? How a Thermal Image is Captured

Thermal imaging, Fundamentals

What is Thermal Imaging?

Thermal imaging is a sophisticated and non-invasive technique that utilizes infrared technology to detect heat emissions from various objects. This process converts the infrared energy, which is invisible to the human eye, into a visible light display. The infrared (IR) energy, or thermal energy, is emitted by all objects above absolute zero temperature, and the variations in these emissions form the basis of thermal imaging.

In industrial settings, thermal imaging is a crucial component of preventive maintenance strategies. By enabling the detection of abnormal heat patterns, such as those caused by overloads or impending equipment failures, thermal imaging can significantly enhance operational efficiency and safety.
Thermal imaging is a powerful, versatile, and proactive technology that has found indispensable applications in various industries. By providing a clear picture of thermal anomalies, it helps in early detection of potential problems, maximizing operational efficiency, safety, and cost savings.

What is a Thermal Image?

A thermal image, or thermogram, is the visual output produced by thermal imaging processes. Thermal images are captured using a specialized device, often referred to as a thermal camera or infrared camera. A thermal image is distinctly different from a traditional photograph. While a conventional photograph captures visible light reflected from objects, a thermal image represents varying levels of infrared radiation emitted by the objects.

The interpretation of a thermal image is facilitated by a color palette, where each color represents a specific range of temperatures. For instance, shades of blue often indicate cooler temperatures, while shades of red signify hotter areas. Thus, a thermal image provides a detailed temperature map of the surveyed area, highlighting hotspots and potential anomalies that may need further investigation.

What Does a Thermal Imaging Device Detect?

A thermal imaging device, such as a thermal imager or infrared imager, detects the infrared radiation or heat emitted by objects. Based on these detections, it creates a 'thermal profile' or heat map of the area in focus.
Thermal imagers can detect:
  • Overheating and circuit overload issues in electrical and mechanical systems.
  • Building inefficiencies such as heat loss due to poor insulation, air leaks in HVAC systems, and water leaks within structures.
  • Detection of pests or rodents within concealed areas and identification of trespassers in security applications.
  • Human or animal presence in search and rescue operations and hot spot detection in forest fire management.
  • Identification of structural defects in construction and engineering.
  • Detection of health issues in medical and veterinary applications, and thermal pattern analysis in geological and environmental studies.
Industrial Inspections
In the context of industrial inspections, a thermal imaging camera is a valuable tool for detecting overheated components, insulation failures, and other potential problems that may not be visible to the naked eye. Thermal imagers can identify hot spots in electrical inspections, highlighting areas at risk of overheating or fire.
Building Maintenance
In building maintenance, thermal imaging devices are used for detecting heat losses due to poor insulation or air leaks, thereby identifying opportunities for improving energy efficiency. They also find applications in detecting water leaks within walls or beneath floors.

For security applications, thermal cameras can detect the presence of intruders in low light or adverse weather conditions by picking up their heat signatures.
In essence, a thermal imaging device can detect and visualize heat anomalies that could indicate a range of potential issues, from equipment malfunctions to security threats. By doing so, it plays an invaluable role in preventive maintenance, proactive troubleshooting, and efficient resource management.

Thermal imagers should not be confused with infrared thermometers, but Fluke does bridge the gap between infrared thermometers and thermal imagers.

How Does Thermal Imaging Work? (The Short Answer)

Thermal imaging operates on a simple yet effective principle: all objects emit infrared energy as a function of their temperature. This form of energy, invisible to the human eye, can be detected and translated into a visual image by a thermal imaging system. Here's a step-by-step look at the process:
  1. The thermal camera, equipped with an infrared detector, captures the infrared radiation emitted from all objects in its field of view.
  2. The captured radiation data is then processed by the camera's built-in software. An optical system focused infrared energy to a sensor array, or detector chip, with thousands of pixels in a grid.
  3. The software translates the data into an image, known as a thermal image or thermogram, representing the temperature variations of the scene.
  4. Each temperature value is assigned a different color. Typically, warmer areas are represented in red, and cooler areas are shown in blue. A matrix of colors corresponding to temperatures is sent to the camera display as a picture.
  5. Leading thermal and infrared cameras from manufacturers like Fluke give you the power to then edit, transfer, store, and analyze your thermal images.

What is an Infrared Thermal Imaging Camera?

An infrared thermal imaging camera, often referred to as a thermal camera or an infrared camera, is a device that creates an image using infrared radiation.

Unlike conventional cameras that create pictures using visible light, thermal cameras operate in the long-wavelength infrared spectrum, which extends up to 14,000 nanometers.

A thermal camera works by detecting the heat emitted by objects and converting it into an electronic signal. This signal is then processed to produce a thermal image on a video monitor. The camera can also perform temperature calculations, making it a versatile tool for any application that requires accurate temperature readings. From diagnosing electrical issues to identifying insulation gaps in buildings, infrared thermal imaging cameras are invaluable in many professional fields. Handheld thermal cameras are the most popular variety, but there are also devices like stationary infrared scanners.

How Infrared Cameras Work (The Long Answer)

All objects emit infrared energy, known as a heat signature. An infrared camera (also known as a thermal imager) detects and measures the infrared energy of objects. The camera converts that infrared data into an electronic image that shows the apparent surface temperature of the object being measured.

An infrared camera contains an optical system that focuses infrared energy onto a special detector chip (sensor array) that contains thousands of detector pixels arranged in a grid.

Each pixel in the sensor array reacts to the infrared energy focused on it and produces an electronic signal. The camera processor takes the signal from each pixel and applies a mathematical calculation to it to create a color map of the apparent temperature of the object. Each temperature value is assigned a different color. The resulting matrix of colors is sent to memory and to the camera’s display as a temperature picture (thermal image) of that object.

Many infrared cameras also include a visible light camera that automatically captures a standard digital image with each pull of the trigger. By blending these images it is easier to correlate problem areas in your infrared image with the actual equipment or area you are inspecting.

IR-Fusion® technology (exclusive to Fluke) combines a visible light image with an infrared thermal image with pixel-for-pixel alignment. You can vary the intensity of the visible light image and the infrared image to more clearly see the problem in the infrared image or locate it within the visible light image. This technique is essential for applications ranging from building inspection to moisture investigations.

Beyond basic thermal imaging capabilities, you can find infrared cameras with a wide range of additional features that automate functions, allow voice annotations, enhance resolution, record and stream video of the images, and support analysis and reporting.

Types of Thermal Imagers

Thermal imagers fall into two main categories: cooled and uncooled.
  • Cooled thermal imagers are high-performance devices that operate within a vacuum-sealed case and are cryogenically cooled. This cooling enhances their sensitivity, allowing them to detect temperature differences as tiny as 0.02°C. While these imagers offer superior performance, they are expensive and typically reserved for specialized applications like scientific research and military operations.
  • Uncooled thermal imagers, on the other hand, operate at ambient temperature and are significantly more affordable than their cooled counterparts. They are engineered to detect temperature differences as small as 0.2°C and are robust enough for everyday use. From routine industrial inspections to security surveillance, uncooled thermal imagers are the go-to choice for a wide variety of applications.

What is Thermal Imaging Used For?

Thermal imaging, a technology that translates thermal energy (heat) into visible light, is used to analyze a particular object or scene. Using a thermal camera or infrared camera, this technique captures the temperature profile of an area, displaying it as a thermal image, which is essentially a heat map.

The applications of thermal imaging are vast and diverse. In the industrial sector, thermal imaging cameras are used for preventive maintenance. By detecting overheating in machinery or electrical circuits, these cameras can help prevent costly equipment failures and enhance safety.

In the building industry, thermal imaging is used to detect heat loss, poor insulation, and water leaks, making it a vital tool in energy audits and building inspections. In the medical field, thermal imaging cameras can detect changes in body temperature, aiding in the early detection of conditions like breast cancer.

Thermal imaging also plays an essential role in security and surveillance. A thermal imager or infrared imager can detect heat signatures, making it possible to identify people or animals in low light or dark conditions.

Follow this thermal imaging inspection checklist to learn the fundamentals of thermal inspection.

What is Thermography? Thermal Energy, Emissivity, Passive vs. Active

Thermography, often associated with thermal imaging, is a technique that uses infrared technology to detect and visualize variations in temperature. This method relies on the principle that all objects emit thermal energy, which can be captured and represented as a thermal image.

Thermal energy refers to the infrared radiation emitted by objects based on their temperature. The amount of this energy that an object emits is determined by its emissivity, which varies according to the material's properties.
Thermography can be classified as either passive or active. Passive thermography involves observing an object's naturally emitted thermal energy. It's commonly used in applications like surveillance or monitoring electrical systems. Active thermography, on the other hand, involves applying a heat source to the object being inspected. This method is particularly useful in detecting subsurface defects in materials.

Choosing the Best Thermal Camera or Thermal Imager

Selecting the right thermal camera or thermal imager depends largely on your specific needs and applications. Here are a few factors to consider:

Resolution: Higher resolution cameras provide clearer, more detailed thermal images. A thermal imaging camera with a high resolution can detect small temperature differences, making it ideal for tasks that require a high level of accuracy.

Sensitivity: The sensitivity of a thermal camera is its ability to detect minimal differences in temperature. If you need to capture subtle thermal variations, choose a camera with high thermal sensitivity.

Field of View (FOV): The FOV determines the area that the thermal camera can capture at any given time. A wide FOV is beneficial for scanning large areas quickly, while a narrow FOV is better suited for focusing on small, specific areas.

Functionality: Consider what additional features might be useful, such as the ability to record video, capture multiple images simultaneously, or connect to other devices for data sharing.

By understanding these key concepts and factors, you can make an informed decision when choosing a thermal camera or infrared imager for your thermal imaging needs. Whether for industrial inspections, building diagnostics, or research purposes, the right thermal imaging tool can offer invaluable insights and contribute significantly to your operational efficiency.
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