Method And Device For Measuring The Concentration Of Substances In Gaseous Or Fluid Media Through Optical Spectroscopy Using Broadband Light Sources

Abstract

The invention relates to a method and to a device for using partially non-stabilized broadband light sources to accurately measure partially broadband-absorbing substances using referencing measuring cells. In order to create a low-cost, high-resolution, and at the same time fast spectrographic device for measuring concentrations of substances in fluid or gaseous media that is also suitable for harsh environments, the light radiated by the broadband light sources ( 1 ) through light guiding optical systems is fed through the measuring section of the self-referencing measuring cell ( 20, 30, 40 ) or only partially through a measuring cell ( 10 ) to a measurement detector (photoreceptor 11 ) and partially through a reference path (optical waveguide 8 ) to a reference detector (photoreceptor 15 ), and a mode coupler ( 5, 9, 14 ) is associated with each optical waveguide ( 2, 4, 7, 8 ) in order to homogenize the radiation characteristic of the broadband light sources ( 1 ), which varies over time and space.

1 . A method for determining the concentration of substance(s) in gaseous or fluid media using optical absorption spectroscopy with broadband light sources, wherein the light of an optical fibre-coupled broadband light source is guided by way of an optical wave guide and a mode mixer after the light source directly via an optical path to a free path-absorption measurement cell, is partially absorbed therein and guided via an optical wave guide and mode mixer after the measurement cell to a measurement detector, and that the influences of the emission characteristics of the broadband light source are referenced via a reference detector which is connected via an optical wave guide coupler, a mode mixer and an optical wave guide directly to the optical fibre-coupled broadband light source, wherein the measurement detector and the reference detector may be the same. 
     
     
         2 . The method of  claim 1 , wherein for referencing the light source and/or for determination of the concentration of further substances several spectral different broadband optical fibre coupled light sources are added to the optical path via mode mixer and optical wave guide coupler, and the emission of the light sources are separated from each other at the detector and reference unit. 
     
     
         3 . The method of  claim 1 , wherein a part or the whole optical wave guide outside the measurement cell is realized via free path optics. 
     
     
         4 . The method of  claim 1 , wherein instead of a reference detector a self referencing measurement cell is used, where the path length of the interaction between the irradiated light and the measuring media is varied and thus a reference signal is generated, whereby disturbances within the emission characteristics can be suppressed. 
     
     
         5 . A device for determining the substance concentration in gaseous or fluid media via optical absorption spectroscopy with broadband light sources according to the method of  claim 1 , wherein the light of an optical fibre-coupled broadband light source ( 1 ) is guided by way of optical wave guide ( 2 ) and mode mixer ( 3 ) after the light source directly via an optical path with mode mixer ( 5 ) and optical wave guide ( 6 ) into the free path absorption measurement cell ( 7 ), it is partly absorbed therein, and is guided by way of an optical wave guide ( 9 ) and mode mixer ( 10 ) after the measurement cell ( 7 ) to a measurement detector ( 11 ), and that the influences of the emission characteristics of the broadband light source ( 1 ) are compensated via a reference detector ( 13 ) which is connected via an optical wave guide coupler ( 4 ), mode mixer ( 14 ) and optical wave guide ( 12 ) to the optical fibre-coupled broadband light source ( 1 ), wherein the measurement detector ( 11 ) and the reference detector ( 13 ) may be the same. 
     
     
         6 . The device of  claim 5 , wherein for referencing the light source and/or for determining the concentration of further substances several spectrally different broadband optical fibre coupled light sources ( 1 A,  1 B, . . . ) are added to the optical path via mode mixer and optical wave guide ( 19 ), and the emissions from the light sources are separated from each other at the detector unit and reference unit. 
     
     
         7 . The device of  claim 5 , wherein a part or the whole optical wave guide outside the measurement cell ( 7 ) is realized in free path optics. 
     
     
         8 . The device of  claim 5 , wherein instead of the reference detector a self referencing measurement cell ( 16 ) is installed, wherein the path length of the interaction ( 17 ) between the irradiated light and the media to be measured is varied and thus a reference signal is generated, whereby disturbances within the emission characteristics can be suppressed. 
     
     
         9 . The device of  claim 8 , wherein the self referencing measurement cell is realized as an inclining or rotating glass plate ( 33 ), whereby the interaction path length of the measurement media is varied. 
     
     
         10 . The device of  claim 8 , wherein at the end of the measurement cell a concave mirror is implemented as reflector. 
     
     
         11 . The device of  claim 8 , wherein the light coupled into the self referencing measurement cell ( 40 ) is partly reflected by a half mirror ( 42 ) to a full mirror ( 46 ), and an additional rotor propelled by the flow of the media and located within the optical path between the half and the full mirror ( 42  and  46 , respectively) temporarily interrupts the reflection of the full mirror ( 46 ), and thereby the interaction path length and thus the measurement signal for referencing is varied. 
     
     
         12 . The device of  claim 8 , wherein the strength of the interaction is varied via the pressure, and the pressure is detected via a sensor ( 18 ) or defined by way of an actuator.