Do you want to learn how thermal camera work?
Infrared cameras are fantastic devices that can 'see' the surface temperature of a room or object.
In this guide, I will go over...
- Sensor arrays in thermal cameras
- So-called thermal blindness
- The visual representation of thermal cameras (thermogram)
Let's get started with this guide!
Thermal cameras are great devices to 'see' things that are invisible to normal human vision.
Police officers in helicopters use thermal cameras to catch criminals at night. Thermal cameras are important tools for firefighters because it allows them to see hot areas through smoke, darkness, and heat resistant building materials.
And in my profession, home inspectors use thermal cameras to find water leaks, missing insulation, and electrical hot spots.
How Does An Infrared Camera Work?
Thermal cameras work by converting infrared radiation or heat signatures into electrical signals, and then into a visual image known as a thermogram.
The specific temperature sensors (sometimes millions) in thermal imagers are known as microbolometers. And the camera turns these temperature readings at physical points into a visual representation.
Warmer temperatures are represented by the reddish orange color range. And cooler temperatures are represented by the bluish purple color territory.
Focal Plane Arrays
The total sensor used in thermal cameras (composed of individual microbolometers) are known as a focal plane arrays. The array has a fixed pixel dimension, such as 640 x 480, which will give your camera over 300,000 individual pixels.
Each pixel acts as a temperature sensing device, so that is a lot of temperature data points. This is equivalent to having 300k+ individual laser thermometers!
So the bigger focal plane array, the more detailed thermogram you will get, but it will also make the thermal camera more expensive.
Read Also: How To Interpret Thermal Images?
Do Thermal Cameras Detect Heat?
Thermal imagers can detect heat that is emitted in the form of electromagnetic waves which is invisible to humans. This wavelength of energy is known as infrared radiation.
When an object heats up, the molecules increase in vibration and they bounce off of each other.
This increased energy activity of molecules (which we feel as heat) releases photons from the material, and this photonic release is known as electromagnetic radiation.
It is this invisible radiation which is detected by the camera, which corresponds to a particular temperature. The hotter an object becomes, the more radiation will be released, and the higher the frequency of the radiation. All objects above absolute zero release infrared radiation.
Can Thermal Cameras See Through Walls?
A common misconception of thermal cameras is that it gives you some type of x-ray vision.
Thermal imaging cameras cannot see through walls, they can only see the surface temperature of a room or object. But of course, the surface temperature can give you information about what is going on 'inside' a wall.
If I use a thermal camera to discover a water leak in the corner of a basement, then you can be almost certain that the water leak is entirely within the wall, and not just the surface. When I find a water leak, I always confirm the discovery with a moisture meter, and I never rely completely on my thermal camera.
What Is Thermal Blindness?
Thermal blindness is a phenomenon that home inspectors frequently encounter with thermal imaging cameras. One of the most common thing inspectors look for is water leaks.
However, during the course of the day, all of the home's materials (wood, drywall, carpet) become the same temperature. And when we use our thermal camera, everything is the same color, which we call thermal blindness. So in order to actually find things, such as water leaks or missing insulation, we need to change the environmental temperature.
The easiest way to do this is to raise or lower the HVAC thermostat by around ten degrees, which increases the Delta T or change in temperature. And since water is always the last thing to change temperature, there will be a significant temperature difference that will show up in the camera.
When inspectors use thermal cameras outside, such as on a roof inspection, the best time to do this is right after the sun rises or sets. We use the sun the same way as lowering or raising the HVAC temperature.
The roof surface will cool down after the sun sets, but the water will be very slow to change temperature, and therefor it will stick out as red or orange on a thermal camera.
Thermal cameras act pretty much the same way as infrared thermometers, except that they have significantly more sensors. And then these temperature sensors are converted into a visual image that can be seen as humans.
If you want a bird's eye view of a room or an object, and see possibly millions of temperature data points, then thermal cameras are the way to do it.
Thermal cameras have large sensors known as focal plane arrays, which converts temperature data into a visual image. The hotter areas of a room will be reddish orange on a thermal camera. And the cooler areas will be bluish purple.