Two-channeled measurement apparatus
The invention relates to a measurement apparatus for the determination of gas concentrations. The apparatus comprises two spectral channels, wherein the channels are separated by a single chopper wheel. The chopper wheel has several functions. On the transmitting side, it brings the light of the two light sources on the same measuring path, on the receiving side it associates the light to the associated receiver; it has its chopper function to use the lock-in technique; and it opens the possibility to implement an easy zero point correction.
1. A measurement apparatus having two spectral channels for the determination of gas concentrations comprising:
a first and a second light source ( 102 , 104 ; 302 , 304 ) which transmit light of different wavelength ranges into a measurement path ( 114 );
a receiver arrangement ( 124 ) which receives the light from the light sources ( 102 , 104 );
a chopper apparatus ( 110 ) which has two reflecting mirrors ( 134 ; 134 A) for one of the wavelength ranges and two cut-outs ( 136 ; 136 A) between the mirrors on the same part of a circle in the circumferential direction in order to alternately allow the light from the light sources to pass through and/or to deflect the light from the light sources ( 102 , 104 ) respectively in order to bring the light via the same optical path into the measurement path ( 114 ); and
an evaluation unit ( 140 ) for the evaluation of the received signals and for the determination of a gas concentration therefrom,
wherein the receiver arrangement ( 124 ) has a first and a second receiver ( 126 , 128 ; 326 , 328 ), with the first receiver ( 126 , 326 ) being associated with the first light source ( 102 ) and the second receiver ( 128 ; 328 ) being associated with the second light source ( 104 ) for the reception of the light of a corresponding wavelength range; and wherein the chopper apparatus ( 110 ) is also a part of the receiver arrangement ( 124 ) and the chopper apparatus ( 110 ) separates the light from the same optical path ( 112 ) following a passage along the measurement path ( 114 ) by deflection of light and/or by allowing the light to pass through and associates this with the corresponding receiver ( 126 or 128 respectively; 326 or 328 respectively) characterized in that the chopper apparatus ( 110 ) is designed as a single chopper wheel ( 130 ; 130 A) and the mirrors ( 134 ; 134 A) are formed as sectors of the chopper wheel ( 130 ; 130 A) and the reflexion surfaces of the mirrors are perpendicular to the rotation axis of the chopper wheel ( 130 ; 130 A).
2. The measurement apparatus in accordance with claim 1 , characterized in that the mirrors are made by vapor deposition of a reflexion surface on the chopper wheel.
3. The measurement apparatus in accordance with claim 1 , further comprising a retroreflector arranged behind the measurement path, wherein a transmission light path and a received light path are configured coaxial and a beam splitter separates the transmission light path from the reception light path.
4. The measurement apparatus in accordance with claim 1 , wherein one of the light sources transmits UV light and the other light source transmits IR light and wherein the respectively associated receiver is configured to receive the UV light and the IR light respectively.
5. The measurement apparatus in claim 1 , wherein the chopper wheel is configured point-symmetrically with respect to its axis of rotation.
6. The measurement apparatus in accordance claim 1 , wherein the mirrors and the cut-outs are arranged diametrically to each other.
7. The measurement apparatus in accordance with claim 1 , wherein the light sources each have an optical axis and the optical axes of the light sources are arranged perpendicular to one another.
8. The measurement apparatus in accordance with claim 1 , wherein the light of the first or second light source is used for zero point correction in those measuring phases in which measurement is done with light of the other light source, respectively.
9. The measurement apparatus in accordance with claim 1 , wherein a deflection mirror is provided with which the light of both wavelength ranges is deflected into the corresponding receivers while bypassing the measurement path.