Patent ID: 8017928

Claim:
A fluorometer for detecting the level of fluorescent material in a body of water, the fluorometer comprising: an excitation system including an excitation source for producing excitation light capable of causing fluorescence in fluorescent material; and a detection system for detecting said fluorescence, wherein said excitation system comprises an excitation source comprising one or more light emitting diodes (LEDs), the excitation system further comprising means to cause said excitation light to form, in use, a generally conical divergent beam projecting from the fluorometer, said beam causing means comprising at least one collimating lens, said excitation system further including means for modulating said beam with a modulating signal having a modulating frequency, and wherein said detection system comprises means for receiving light and for converting said received light into a corresponding electrical signal, and at least one lens arranged to direct said received light onto said light receiving and converting means, wherein said at least one lens of the detection system is arranged to provide a generally conical convergent detection volume for the detection system, said generally conical detection volume converging in a direction towards said fluorometer and at least partially overlapping with said generally conical divergent beam and wherein said detection system further includes means for detecting, in the electrical signal produced by said light receiving and converting means, a signal component of substantially the same frequency as said modulation frequency, said detecting means including means for performing spectral analysis of said electrical signal and means for determining the value of a spectral component of said electrical signal corresponding to said modulation frequency, wherein said detection system is arranged to determine the level of fluorescent material present in said body of water depending on said value of said spectral component, such that the fluorometer is capable of detecting fluorescent material located remotely from the fluorometer in said body of water.