Absolute zero
Absolute zero refers to the temperature of -273.15°C (0 Kelvin = -459.69°F). Absolute zero is an ideal state, in which all material’s atomic movement completely stopped. At this temperature, objects have no thermal energy.

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Absorptivity

Any object can absorb infrared radiation, and the direct result of infrared absorption is temperature rise. Objects with a higher temperature usually emit more energy than objects with a lower temperature. Infrared radiation an object absorbs is usually transformed into thermal energy of its own and gets re-emitted. Therefore, an object’s emissivity is linked to its absorptivity.

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Accuracy
It refers to how close the measured result is to the reference. Ex: if the actual temperature of an object surface is 100℃ , and the accuracy is ±2℃ , then the measured temperature would be 98℃ —102℃ .

Atmospheric windows
A range of wavelengths over which there is relatively little absorption of radiation by atmospheric gases is
called ‘atmospheric window’. The atmospheric window of the infrared band locates between 7~14μm, where the atmospheric transmittance is most stable. Therefore, thermal measurement on this window is particularly accurate.

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Blackbody Radiator

Black body radiator refers to objects that absorb all incident radiation and convert them into their energy to emit outwards, during which process there is no occurrence of either reflection or transmission. A blackbody’s emissivity ε= 1. A blackbody is an ideal object that does not exist in the real world. Blackbodies used for research and calibration are close approximations with emissivity close to 1 (usually greater than 0.95).

Color Palette
Color Palette determines how an image’s color is displayed. Based on different measurement assignments, the thermal imaging display uses different color contrast.

Color Isotherms
This function marks every point of the same temperature with the same color in a certain range. It aids real-time analysis.

Cold Spot and Hot Spot
The point with the highest temperature in a certain region is called a ‘hot spot’. Conversely, the point with the lowest temperature in a certain region is called a ‘cold spot’.

Conduction
Heat is always transferring from objects with higher temperatures to objects with lower temperatures. Conduction is the primary way of heat transfer in solids.

Convection
The process of transferring heat due to the movement of fluid is called convection and is usually caused by an
imbalance of temperature.

Celsius [℃ ]
Celsius is a temperature unit that is widely accepted globally. Under standard atmospheric pressure, water’s boiling temperature is defined 100℃ , and its melting point is defined 0℃ .

℃ = ( ℉ -32)/1.8 or ℃ = K–273.15

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Colored Body Radiator

A colored body radiator refers to materials whose emissivity changes based on wavelength and temperature difference. An object could have a few different emissivities. Most metals are colored body radiators. (Ex: Aluminum’s emissivity rises when heated).

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Condensation
It refers to the process of gas turning liquid. When an object’s surface temperature is lower than the ambient temperature, the moisture in the air will condense into water droplets on the surface.

Dew Point
When the temperature reaches a certain point, the unsaturated water vapor in the air will become 100%
saturated. The temperature point is called the dew point.

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Emissivity (ε)
Emissivity is a measure of how much radiation is emitted from the object, compared to that from a perfect blackbody of the same temperature. Emissivity is a physical property of a measured object, which determines by its surface characteristics, temperature, and wavelength.

Fahrenheit [ ℉ ]
Fahrenheit is a temperature unit that is widely accepted in North America.
℉ = (℃ x 1.8) + 32.

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Field of View (FOV)

Field of view refers to the vertical and horizontal angle objects project themselves in the thermal imager.

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Frame Rate

The unit for frame rate is ‘Hertz’. It refers to frequency image refreshes on the thermal imager. Ex: if a thermal imager’s refreshing rate is 30 Hz. It means the imager will update 30 complete thermal images in one second.

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Heat Transfer Coefficient
It reflects an object’s ability to convey heat by convection. Definition: when the temperature difference between fluid and solid surface is 1 k, the amount of energy been conveyed by convection of 1 unit area in a second.

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Infrared radiation
Infrared radiation is a form of electromagnetic radiation. Any object with a temperature above absolute zero emits infrared radiation.

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IR Detector

An infrared thermal imager’s detector can detect thermal radiation and transform it into an electrical signal. The minimum unit of a detector is called ‘pixel’.

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Kelvin [K]

Kelvin is a general temperature unit; an Object of 0 K temperature reaches absolute zero (-273.15°C).

273.15 K = 0℃ = 32 ℉。

K = ℃ + 273.15。

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Kirchhoff’s radiation law
Kirchhoff’s radiation law describes the relationship between an object’s emissivity and absorptivity of a certain wavelength: at thermal equilibrium, an object’s absorptivity of thermal radiation is equal to its emissivity at the same temperature.

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Lens
The lens determines the thermal imager’s range of field view. A wide-angle lens can measure the temperature distribution of a larger field, and a telephoto lens can observe finer detail in distance. Germanium, silicon, and zinc selenide are good materials for making camera lenses because they have high infrared transmittance.

Measurement Range
Measurement Range refers to the temperature range that a thermal imager can accurately measure and record. Outside of the measuring range, the device will neither be able to properly display the information nor guarantee the accuracy of the measurement.

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MFOV
The MFOV is the minimum pixel range in which a thermal detector can accurately measure temperature. There are two types: MFOV=1, and MFOV=3×3=9.

NETD
NETD stands for sensitivity (also known as Noise Equivalent Temperature Difference). It describes the minimal temperature difference the thermal imager can detect. The smaller the NETD, the more sensitive the thermal imager, and the image will be clearer.

Planck's Radiation Law
Planck’s radiation law indicates that energy emitted by a blackbody is dependent on the frequency of the radiation. E=hf, ‘h’ being the Planck’s constant and ‘f’ being the frequency of the radiation.

Radiation
Any object with a temperature higher than absolute zero is continuously radiating heat in the form of an electromagnetic wave. The capacity of emitting energy is called emissivity.

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Reflectance (ρ)

It refers to an object’s ability to reflect radiant energy. It depends on the material’s type, surface characteristics, temperature, and incident wavelength. Generally speaking, smooth and polished surfaces have larger reflectance.

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Relative humidity
It is the percentage of absolute humidity of air at a certain temperature, and saturated vapor pressure of water at the same temperature.

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Resolution
Resolution is a parameter for measuring the amount of data in an image. It refers to the number of pixels in a unit length.

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RTC

RTC stands for Reflected Temperature Compensation. Some objects have high reflectivity, which could induce false readings from reflecting thermal radiation of higher temperature objects nearby. In short, when the observed object has relatively low emissivity, and there are heat sources nearby, it’s a good idea to turn on RTC.

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Specular reflection

Specular reflection usually occurs on an object surface of high reflectivity or low emissivity. However, the occurrence of specular reflection does not guarantee high reflectivity.

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Stefan-Boltzmann-Law

The Stefan-Boltzmann law indicates the total power emitted by a blackbody is proportional to its temperature’s fourth power.

Wb=σ• e • T^4. s (sigma) = 5.67×10-8W/(m-2·K-4)

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Thermal Image

Thermal Image displays surface temperature distribution of an object. By receiving the object’s radiation energy, the thermal imager converts pixels’ temperature values into visible colors on the matrix coordinates. Each pixel represents a temperature measuring point on the object’s surface.

Thermal Imager
Thermal imager refers to devices that can detect radiations of infrared-band wavelength and convert the invisible infrared radiation into visible pictures. Thermal imagers are widely used for temperature measurement and infrared thermal imaging.

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Transmittance (τ)

It refers to a material’s ability to transmit radiation. It depends on the material’s type and thickness.

Uncooled Infrared Focal Plane Array (FPA)
In the earlier stage of development, FPA detectors require cryogenic cooling, and their sizes are massive; Nowadays, FPA detectors don’t necessarily require cooling and can take on high accuracy measurements. There are two types of FPA sensors: optical readout uncooled focal plane array and electrical readout uncooled focal plane array.

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Verification
Verification is a process, which compares the measurement result and the object’s standard value. Verification is not calibration; Verification records the deviation while calibration corrects the result.