Thermal Imaging: What is It and How it Works

Unlike infrared guns that average out temperature readings, thermal imagers instantly highlight temperature differences through vivid imagery, allowing users to detect hot spots with ease. 

Whether faced with great distances or extreme temperatures that surpass the capabilities of traditional thermocouples, thermal imaging rises to the challenge.

What is Thermal Imaging?

Thermal imaging is a technology that uses specialised equipment to identify and record images based on the infrared radiation emitted by an object. These images represent the heat patterns of objects, which are otherwise invisible to the human eye.

Key Concepts

Thermal imaging concepts are crucial for understanding how this works and to interpret the results obtained from thermal imaging equipment

Infrared Radiation 

Discovered by Sir William Herschel in 1800, infrared radiation is a form of electromagnetic radiation with wavelengths longer than visible light, and it is often referred to as heat waves. All objects with a temperature above absolute zero emit infrared radiation. The warmer an object is, the more infrared radiation it emits.

Electromagnetic Spectrum

Infrared waves are located on the electromagnetic spectrum between visible light and microwaves. The infrared spectrum is further divided into ranges, including Near-Infrared (NIR), Short-Wave Infrared (SWIR), Mid-Wave Infrared (MWIR), Long-Wave Infrared (LWIR), and Far-Infrared (FIR).

Thermal Imagers

Thermal imaging equipment detects and converts infrared wavelengths into visible images, producing thermograms which are graphic records of temperature variations. These imagers typically include a lens, a detector, and a display.

How Thermal Imagers Work 

The infrared energy from an object is focused by the lens onto an infrared detector, which sends information to sensor electronics for image processing. The electronics translate the data into a visible image, often displayed in colour or black and white, where variations in colour represent temperature differences.

Emissivity

Emissivity is the measure of how well an object radiates infrared energy, expressed as a value between 0 and 1. A theoretical black body has an emissivity of 1 and is a perfect emitter of heat energy. The emissivity of an object is affected by its shape, temperature, surface condition, and wavelength dependence.

Heat Transfer

Heat is transferred through conduction, convection, and radiation. Thermal imaging measures heat transferred by radiation, which does not require matter to move heat from one place to another. The rate of heat transfer is dependent on temperature differences, distance, and emissivity.

Detectors

Thermal imagers use detectors to measure infrared energy. The two most common types are resistive bolometers and pyroelectric sensors. Bolometers respond to the radiation being produced by an object, while pyroelectric sensors respond to changes in the radiation of an object. More advanced thermal imagers use cooled focal plane array (FPA) detectors or microbolometer detectors.

Applications of Thermal Imaging 

Thermal imaging has a wide range of applications across various industries, including:

Manufacturing

Thermal imaging is used for product development, quality control, equipment validation, and predictive maintenance. It can identify hot spots in electrical wiring and machinery, allowing for preventive measures.

Healthcare 

Medical thermography is used to measure thermal energy emitted from the body to identify inflammation or fever. It is also used for fever screening in airports during global health crises. However, it is not considered reliable as a primary diagnostic tool for conditions such as breast cancer.

Building Inspections

Thermal imaging cameras can detect temperature changes in buildings, indicating energy loss, moisture issues, or insulation problems.

Industrial Applications

Thermal imaging is a valuable diagnostic tool for industrial applications because it can identify anomalies that are usually invisible to the naked eye, allowing for corrective action before costly system failures occur. It is used to monitor electrical systems (high and low voltage), mechanical systems, pipework, refractory and petrochemical installations, and other equipment.

Types of Thermal Imaging Equipment

Thermal imaging equipment is used to detect and convert infrared wavelengths into visible images, producing thermograms and corresponding temperature measurements. 

This equipment generally includes a lens, a detector, and a display. There are four types of detectors that have been developed for thermal imaging equipment:

Mechanical Scanning Systems 

These were used in earlier thermal imaging cameras, using detectors that would scan an object to generate an image, but they required cooling agents to operate.

Pyroelectric Vidicon (PEV)

This type of detector uses a tube assembly with a germanium lens and a pyroelectric target, not requiring cooling.

Cooled Focal Plane Array (FPA)

These detectors use an array of light sensor pixels arranged on a focal plane, requiring cooling but providing high-resolution images.

Microbolometer

These detectors are an array of heat-detecting sensors and do not require cooling. They operate in the Long-Wave Infrared range.

Other Important Considerations

Several factors contribute to the beneficial use of thermal imaging, including its non-contact nature, its ability to detect thermal anomalies, and its capacity to provide both qualitative and quantitative data:

Night Vision

Thermal imaging is a type of night vision technology that can be used in dark environments, fog, smoke, dust, rain, or snow.

Image Enhancement

Image enhancement or low-light imaging uses small amounts of natural light to illuminate a dark environment. This is different from thermal imaging, which does not require any light.

Professional Certifications

Certified Thermographers are trained to operate thermal imaging equipment and are certified to perform infrared inspections. Certifications are issued in compliance with standards such as ASNT and ISO. There are three levels of certification: Level 1, Level 2, and Level 3, each with increasing levels of expertise.

Camera Resolution

High-resolution cameras provide better image quality and accuracy, with the most advanced models having a resolution of 640 x 480 pixels.

Thermal Sensitivity

The thermal sensitivity of a camera is a measure of how small a temperature difference the camera can detect. Better sensitivity means smaller temperature differences can be picked up and visualised.

Camera Features

Important camera features include the ability to manually set the span and level of the displayed images, a built-in digital camera, LED lights, Picture in Picture capabilities, and Thermal Fusion capabilities.

To Wrap Up

Overall, thermal imaging is a versatile technology with applications in various fields, providing valuable insights into thermal patterns and temperature variations. It is important to understand the technology, the equipment, and the potential limitations for the correct interpretation of the data.

If you're considering thermal imaging cameras in Malaysia, Inframatrix is a great place to start. Reach out to them for expert guidance.