Patent ID: 7671984

Claim:
A spectrometric measuring head with recalibration means, the measuring head comprising: a housing which is provided with a window to an external measurement location; arranged in said housing are an illumination source, a spectrometer arrangement and at least two standards for internal recalibration; said standards adapted to being swiveled into the beam path to an internal measurement location of the measuring head selectively; a processor for acquiring and processing measured values and an interface to a bus system, also being arranged in the housing; and a controlling and evaluating unit which recalibrates the spectral measuring head by using: a) intensity values for internal standards measured at the internal measurement location; and b) intensity values for at least two additional external standards measured at the external measurement location; wherein one of the two internal standards is a light internal standard, and the other of the two internal standards is a dark internal standard; wherein one of the two external standards is a light external standard, and the other of the two internal standards is a dark external standard; and wherein a reflectance R p ′ (at the start) and the corrected reflectance R p ′(t) (after recalibration) of the measurement sample is calculated from the following formulas: R p ′ = D 4 - D 3 D 1 = R p - R se R we - R se ; and R p ′ ⁡ ( t ) = D 4 ⁡ ( t ) * q ⁡ ( t ) - D 3 D 1 = R p - R se R we - R se ; where: R f is the reflectance of the window: R we is the reflectance of the external light standard; R se is the reflectance of the external dark standard; R wi is the reflectance of the internal light standard; R si is the reflectance of the internal dark standard; and R p is the reflectance of a measurement sample; where the quotient q(t) is calculated by the following formula: q ( t )= D 2 /D 2 ( t )= I e /I e ( t )= I i /I i ( t ); where D 1 to D 4 are calculated by the following formulas: D 1 =I we −I se =I e ·[1− R f ] 2 ·( R we −R se ); D 2 =I wi −I si =I i ·( R wi −R si ); D 3 =I se −I si =I e ·( R f +R se ·[1 −R f ] 2 )− I i ·R si ; and D 4 =I p −I si =I e ·( R f +R p ·[1 −R f ] 2 )− I i ·R si ; where: I e is the measurement intensity at the external measurement location; I i is the measurement intensity at the internal measurement location; and I d is the measurement intensity of a dark signal; and where I we , I se , I wi , I si , and I p are calculated by the following formulas: I we =I e ·( R f +R we ·[1 −R f ] 2 )+i I d ; I se =I e ·( R f +R se ·[1 −R f ] 2 )+ I d ; I wi =I i ·R wi +I d ; I si =I i ·R si +I d ; and I p =I e ·( R f +R p ·[1 −R f ] 2 )+ I d .