Device and method for determining the composition of a mixture of fluids

1. A device for determining the composition of a mixture of fluids that along a pipe, which comprises:

a radiation source for illuminating the mixture with radiation;

a detector for detecting radiation that has been attenuated by the mixture;

a device for monitoring the flow rate of fluid along the pipe and outputting a signal indicative of the flow rate:

wherein it includes a device for adjusting the intensity of radiation emitted by the radiation source in response to the signal indicative of the flow rate so that the intensity of the radiation source is reduced if the flow rate reduces.

2. A device according to claim 1 wherein said radiation source is a broadband NIR source synthesised from solid state devices.

3. A device according to claim 1 , wherein the radiation source is a broadband radiation source that is operable to emit radiation over the entire range of absorption bands of the fluids.

4. A device according to claim 1 , wherein it includes a digital mirror device for modulating radiation from the radiation source.

5. A device according to claim 1 , wherein said radiation source has a range of wavelengths that extends over a predefined absorption band of each one of said fluids and over at least one predefined reference band outside, but adjacent to, each and every one of said absorption bands,

and wherein it comprises a separating device configured for separating the radiation that has been attenuated by the mixture before said radiation reaches said detector, and wherein said separating device comprises:

a first radiation divider configured for separating said radiation into different wavelength bands, each one of which extending over the absorption band of a corresponding one of said fluids and over at least one of said reference bands adjacent to said absorption band;

a second radiation divider configured for receiving from said first radiation divider the radiation corresponding to each one of said different wavelength bands and for further separating it into a wavelength band corresponding to the respective said absorption band and a wavelength band corresponding to the respective at least one of said reference bands.

6. A device as claimed in claim 5 , wherein the separating device comprises a dichroic beam splitter and/or a rugate notch filter.

7. A device as claimed in claim 6 , wherein said first radiation divider includes a plurality of dichroic beam splitters to split the radiation into a plurality of wavelength bands, and said second radiation divider includes a rugate notch filter configured for splitting the radiation in each wavelength band into an absorption band and a reference band having a wavelength range adjacent to the absorption band.

8. A device as claimed in claim 7 , wherein it is arranged so that radiation impinges on the dichroic beam splitters and/or rugate notch filters at an angle of incidence of not more than 20°.

9. A device as claimed in claim 5 , wherein it is operable to multiplex radiation from a plurality of narrowband radiation sources to generate the radiation, and the detector is operable to demultiplex the detected radiation.

10. A method of determining the composition of a mixture of fluids that ow along a pipe, comprising the steps of:

illuminating the mixture with radiation from a radiation source;

detecting radiation that has been attenuated by the mixture;

monitoring the flow rate of fluid along the pipe;

wherein it further comprises the step of adjusting the intensity of radiation emitted by the radiation source in response to the flow rate determined so that the intensity of the radiation source is reduced if the flow rate reduces.

11. A method as claimed in claim 10 , wherein said radiation is emitted from a radiation source having a range of wavelengths that extends over an absorption band of each one of said fluids and over at least one reference band outside, but adjacent to, each one of said absorption bands, and wherein it further comprises the steps of:

separating the radiation that has been attenuated by the mixture into different wavelength bands, each one of which extending over the absorption band of a corresponding one of said fluids and over at least one of said reference bands adjacent to said absorption band;

further separating the radiation corresponding to each one of said different wavelength bands into a wavelength band corresponding to the respective said absorption band and a wavelength band corresponding to the respective at least one of said reference bands;

said separation steps being performed before said step of detecting the radiation.

12. A method as claimed in claim 11 , wherein said step of separating the radiation comprises separating the radiation into two of said reference bands located adjacent and on opposite sides of the absorption band of one of the fluids.

13. A method as claimed in claim 12 , wherein said two reference bands are located substantially symmetrically on either side of said absorption band.

14. A method as claimed in claim 12 , wherein it includes the step of interpolating the level of absorption of the radiation in said two reference bands in order to generate a baseline for the corresponding absorption band.

15. A method as claimed in claim 10 , wherein the mixture comprises water and hydrocarbons.