How Does Thermal Imaging Camera Work?

Heat rays (also called infrared radiation) are invisible, long-wave, electromagnetic waves. In general, we distinguish between “visible” and “invisible” electromagnetic waves. Invisible electromagnetic waves (infrared, radio waves, X-rays) are located in a very narrow wavelength range and therefore are not perceived by the human eye. Visible electromagnetic waves such as light can be perceived by the human eye and operate in a smaller wavelength range. 
Invisible electromagnetic signals are from a specific wavelength range also able to penetrate dense sub measures such as smoke. The significant advantage of a thermal imager or heat rays is that it can be used both during the day and at night. Even in the apartment, when a standard commercial lamp is in use, the light would not distort the measurement result.

In addition to the wavelength range, heat radiation to light have another difference: it is actively emitted by each body whose temperature is above 0 Kelvin (-273.15 ° C). 
On the other hand, in the visible range (e.,g. light), the bodies themselves do not emit rays but only reflect them. Only at higher temperatures, starting from a few hundred degrees, do these bodies also begin to radiate in the visible area.

For us, humans’ heat radiation is invisible. Although we cannot see the radiant heat, we can feel it in the form of heat, heat, or cold. So there is something “measurable.” This is where the thermal imager comes into play: It visualizes the heat radiation visually. 
For this purpose, the infrared radiation is collected and converted into an image using electrical impulses.

Technology

When using a thermal imager, a total of four properties play an essential role:

• Absorption means that the body absorbs infrared radiation.
• Reflection means that the body reflects infrared radiation.
• The transmission means that the heat radiates through the body.
• Emission is the surface texture. It indicates how the body radiates the infrared radiation. Smooth surfaces such as glass reflect heat radiation. Water and concrete, on the other hand, are impermeable to heat emission.

The construction of a thermal imaging camera

Overall, the development of a thermal imaging camera consists of four essential components:

Lens

The lenses of a thermal imaging camera usually consist of monocrystalline semiconductor materials. However, there are also exceptions, such as the use in the fire department: Here, the lens is mostly made of germanium. 
Germanium, in contrast to glass, ultimately transmits the infrared radiation (transmission).

Detector

The detector is located directly behind the lens. He is responsible for receiving the incoming infrared radiation and converting it into electrical signals. The translated messages are then forwarded to the control board.

Electronics

By electronics is meant the control board, which receives the electrical signals of the detector. It processes these signals to pass them on to the display of the thermal imager.

Display

The display is responsible for displaying the heat or infrared image. It receives all the necessary information from the control board. Here, the user ultimately sees the infrared image.

Detectors functionality

We distinguish between cooled and uncooled detectors. The difference lies in the size and function of the sensors. 
While cooling systems have the power to have higher image quality, in return, they are also more significant than the uncooled detectors. 
By contrast, uncooled detectors are small, handy, and cheaper than cooling systems, but they also have a lower image quality.

Most detectors work on the principle of ” changing the resistance.” The “change of resistance” is a way to measure the temperature of infrared radiation. 
As soon as radiant heat hits the detector, resistance, current, and voltage inevitably change. The sensor makes use of this and measures the temperature of the incoming radiation by this information. 
The preset emission factor is compared with the change in resistance (temperature change at the detector) and thus outputs the temperature at the measuring point.

The temperature measurement is not always 100% accurate. This is because the emission factor scatters material between 0.012 and 0.98. An emissivity of Exact one is only used for the theoretical consideration. He is also known as ” Black Spotlight ” or ” Planckian Spotlight.” The reason for this is that no materials with an emissivity of 1 are known, which can absorb infrared radiation.

NETD value

Significant for the thermal imaging camera, Functionality is the NETD value. The NETD value describes the ” temperature sensitivity,”i.e., the smallest temperature difference that can be detected by the detector. 
For example, if the temperature difference between two adjacent objects is 10 ° C, the detector may depend on the NETD value, pass the same temperature to the control board. 
So it can happen then that the two objects, in the end, have the same temperature on display, although it is not that way. 
Accordingly, when measuring accurately, the NETD value must be as low as possible.