The Pyrolaser®, Pyrofiber® & Optitherm® III instruments use a patented laser based infrared technology to determine a targets True Emissivity Correct Temperature (Te). Pyrolaser®, Pyrofiber® & Optitherm® III accomplishes this by automatically measuring the target diffuse reflectivity at the same location, temperature and wavelength as the radiance measurement to determine the precise target temperature.
Pyrolaser®, Pyrofiber® & Optitherm® III incorporates the passive characteristics of conventional infrared pyrometers along with an active reflectometer technique to determine the target emissivity. A low-powered pulsed GaAS laser is fired at the target measuring zone via a dedicated optical path (Laser Channel) and both the laser return signal and infrared signal are detected via a secondary optical path (Radiance Channel); the laser signal being (AC) on top of the (DC) target signal. Having monitored the laser outgoing energy and knowing the geometry involved (including target distance), Pyrolaser®, Pyrofiber® & Optitherm® III can determine the reflectivity and thus the emissivity of the target measuring zone. The wave band of the collected target radiance is limited to a narrow (10-50nm) band centered in the laser wavelength typically 865nm, 905nm or 1550nm depending on the specific instrument or application.
The emissivity is measured by firing a pulsed laser of monitored output energy (Lo) to the target and measuring the reflected laser energy (Lr). Assuming that no energy is transmitted through the target (opaque material) the impinging energy (Lo) must either be absorbed or reflected. The unknown absorbed energy (La) can be calculated from the two measured quantities outgoing energy (Lo) and reflected energy (Lr):
La = Lo - L
Absorptivity (a) and reflectivity ( r ) of the target are the normalized values of this equation:
a = La/Lo = 1-Lr/Lo = 1-r
Since absorptivity (a) and emissivity (e) are equal, as discussed earlier, the target emissivity (e) is known as soon as the absorptivity (a) is known.
e = a = 1 - r
Above consideration is only true for the total hemispherical integral of the reflected energy( r ). As the instruments optical sensor path captures only a small solid angle from the total hemisphere it must be guaranteed that the target has a Lambertian surface reflecting homogeneously into a hemisphere. Small specular portions are acceptable as long as it avoids the specular reflected energy from hitting the receiving channel. The provided optics guarantees this if mounted with its axis perpendicular to the target surface.
The temperature is measured by collecting the radiance in a narrow band (10-50nm) at the same wavelength (865nm, 905nm or 1550nm depending on the specific instrument) where emissivity is measured with the laser. In a first step the measured radiance Qm is corrected with measured emissivity e to a black body radiance Qb:
Qb = Qm /e
Using this black body radiance, the Pyrofiber® then calculates according to Plancks radiance law for the true temperature (T) of the target.
C1 is a calibration constant depending on the efficiency of the optics and electronics.
h = Plancks constant = 6.625*10E-34 Wss
c = velocity of light = 2.998*10E+8 m/s
k = Boltzmanns constant = 1.380*10E-23 Ws/K
l = Pyrofiber® Wavelength = 865*10E-9 m
In case of irradiance being present the black body radiance Qb is calculated by taking this extraneous radiance Qx according to the measured reflectivity (r) into account to:
Qb = ( Qm-r*Qx) / (1-r)
Once the radiance is corrected to black body radiance all temperature calculations use the same above temperature formula.
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