Patent ID: 7961325

Claim:
An arrangement for determining a concentration of at least one substance in a fluid, the arrangement comprising: a light source coupled to a pulse generating means, so that the light source generates primary light pulses within at least one wavelength interval comprising at least one predetermined wavelength that is absorbed differently in the fluid depending on the concentration of said substance; a light pulse splitter coupled with an input terminal to the light source, said light pulse splitter to split the primary light pulses into at least one secondary light pulse comprising the at least one predetermined wavelength, said secondary light pulse(s) are separated in time as well as wavelength; means for transmitting said secondary light pulse(s) via an output terminal of the light pulse splitter through the fluid; a detector to detect the intensity of the secondary light pulse(s) of the at least one predetermined wavelength which have been at least partly absorbed in the fluid; a reference light pulse generating device coupled between the output terminal of the light pulse splitter and the detector to generate at least one reference intensity that bypasses the fluid without passing through a reference sample, the at least one reference intensity comprising the at least one predetermined wavelength, and having a delay in time relative to the at least one secondary light pulse; and a comparator connected to the detector to compare the intensity of the secondary light pulse(s) with the at least one reference intensity comprising the at least one predetermined wavelength to thereby determine the concentration of said at least one substance in the fluid.