Thermal Imaging: How Thermal Cameras Work

The human eye is a rather capable optical organ but also one that can’t see certain waves including infrared waves. Invisible to the naked eye, infrared waves can be detected with a thermal camera. Just like sewer inspection cameras, thermal cameras let you see something you otherwise can’t.

As part of the electromagnetic spectrum, thermal energy is detected thanks to a sensor that’s made especially for it which means a thermal camera can’t detect visible light. This is why thermal cameras are made with a much lower resolution since they need to be able to detect larger wavelengths than that of visible light.

Types of Thermal Cameras

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Handheld

Similar to how there are regular point-and-shoot cameras, there are point-and-shoot thermal cameras too. These types of heat imaging devices are easy to use and offer the best detection in the quickest way possible but only for certain applications. Handheld thermal imaging cameras can be used to locate leaks in a system with compressed air, inspect electrical and mechanical issues and for monitoring purposes.

Fixed

A fixed thermal camera is one that you can use to continuously monitor the state of a system or hotspots in a large area. You don’t have it as easy when it comes to carrying it, as it’s rather bulky and has a mount that suggests you should place it somewhere and leave it. However, because of its static nature, a fixed IR thermal camera comes with features that are not present on handheld devices. This includes setting alarms, built-in analytics tools as well as streaming capabilities.

Cooled

While cooled devices are more complex, bulkier and more expensive than fixed ones, they are also more capable. When it comes to detecting even the faintest of infrared signals, cooled cameras are the best at it as well as when it comes to long-range detection. That’s because the cryogenic cooling mechanism increases sensitivity and image quality and the same goes for frame rates which makes the device suitable for real-time monitoring.

Non-Cooled

A non-cooled heat imaging device is the same as a cooled one except it comes without the cryogenic mechanism. Unlike a cooled camera, a non-cooled one can be both a handheld or fixed unit, but it’s not as capable. However, non-cooled cameras are more fairly priced and have lower power consumption.

Short-Wavelength

When it comes to the way a heat camera detects infrared light you have three options and short-wavelength cameras are one of them. SWIR cameras offer the best spatial resolution and they can see through materials such as plastic and glass making them ideal for the inspection of solar cells. Their downsides are that they cost quite a bit and are quite limited when compared to MWIR and LWIR.

Mid-Wavelength

MWIR thermal cameras have solid spatial and temperature resolution while being able to detect gas leaks, especially in high-temperature environments. Mid-wavelength cameras operate in a spectral region between 3µm and 5µm which also makes them susceptible to atmospheric interference and much more expensive than LWIR cameras.

Long-Wavelength

Long-wavelength IR cameras are able to detect thermal radiation higher than 5µm which means they can provide better penetration through dust and fog. LWIR cameras are ideal for general use as they offer good temperature resolution across a wider range of applications. But it’s because of that, they also have quite limited capabilities when it comes to more demanding conditions such as high-temperature environments.

What to Look for

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Resolution

Talking about resolution, the higher it is the more pixels there are and thus the more detail you get to see. But the nature of a thermal imaging device doesn’t allow for high numbers here as the most common resolution ranges from as low as 80 x 60 pixels to as high as 1280 x 1024 pixels. Although the latter might seem like a high resolution, in comparison to regular cameras, it isn’t. Remember though, lower resolution results in another advantage which is faster image processing.

Range

The temperature range of thermal imaging cameras refers to the highest and lowest temperature levels they can detect in the image you take. A device with a wider temperature range makes for a more versatile model but also one that can be used for more generic applications. If you’re going to use an IR thermal device for more specific tasks, a smaller temperature range will suit it better.

Lens

Just like a regular camera, a thermal one can use different types of lenses such as a macro, wide angle, telephoto and a standard lens. The type of lens you need depends on what you want to use the camera for as not every single one will perform well in most cases unless, that is, you go for one with a standard lens.

Focus

Having a selection of different focus mechanisms helps make for a more versatile thermal imaging device too. For instance, autofocus helps keep the focus of the lens on the target while manual focus lets you choose what you want the camera to focus on. Laser-assisted autofocus is able to automatically focus on a subject more precisely.