Infrared radiation
All the materials that are a temperature over the zero absolute one (0 K, -273ºC) emit infrared energy. The energy emitted in the infrared band becomes an electrical signal by the detector (microbolometer), this signal becomes a black and white image in or color. The basic principle is described next.
The infrared radiation is a form of electromagnetic radiation like the radio waveses, the microwaves, ultra-violet rayses, gamma rays, the visible light, etc.... All these forms of radiation altogether give rise to the electromagnetic spectrum. It has in common that all of them emit electromagnetic waveform energy and they propagate at the speed of the light.
The infrared radiation defines like which µm has a wavelength between 0.78 and 1000 µm (microns). The infrared rays are subdivided based on the proximity of wavelength near, average or distant to the visible light like.
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| [Wavelenght in µm (microns)] |
The infrared cameras that are used in the industry work all in the average infrared band (they are those that detects the not cooled microbolometers calls).
The infrared cameras detect the invisible infrared radiation that they emit the objects and transforms it into an image within the visible phantom in which the scale of colors (or grays) reflects the different intensities.
The intensity of the infrared radiation is function of the temperature but not only of her, also influence the superficial characteristics of the object, the color and the type of material.
At first the infrared cameras give a value of temperature for each point, without considering that, for the same temperature, two materials can radiate infrared energy with very different intensities.
We see a very graphical example here, a metallic cup with a fervor that is to the same temperature, nevertheless the fervor and the metal of the cup emits infrared energy with very different intensities.
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| [Metallic Cup with sticky tape] | [View with infrared camera] |
It must to the different emisivity between the metal and the sticky tape.
Emisivity
The emisivity of an object is defined from the concept of black body. A black body is that that absorbs all the infrared radiation that receives, does not reflect or transmits therefore anything. The radiation emitted by a black body is function solely of the temperature.
The emisivity of an object for a temperature is defined as the quotient between the infrared energy emitted by the object and the emitted one by a black body.
The infrared cameras adopt as it generates a emisivity from 0.95 to 0,97. All the AMPERIS cameras adopt by defect a emisivity of 0.95, and also all allows to vary that value between 0.1 and 1. Of this form the different values from emisivity are not translated in readings different from temperature.
Infrared camera operation
Basically basic a infrared camera consists of:
- Lenses
- Filter
- Detector or microbolometer
- Circuit of processing of the image
- User interface (screen, video output, memory, etc...)
Today, less than 15 companies in the world they are able to make this type of cameras.
A concept very important to consider at the time of valuing an infrared camera is the space resolution then this concept defines until it distances are possible to be seen the objects.
Space resolution
The space resolution is the field of vision of the microsensors that comprise of the detector or microbolometer.
The space resolution defines as the relation between the size of the sensor and the distance between the lenses and the sensor. The more low it is the space distance the more resolution will be possible to be used the camera (or, for the same distance, small objects will be able to be visualized the more).
In the following graph the relation between the size of the objects and the distance to the camera is appraised:
