Optical apparatus and method for measuring the characteristics of materials by their fluorescence

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to an improved optical apparatus and method for measuring fluorescence in real time.
The design employs a new measurement principle wherein the field of illumination of the illuminative light is substantially contained within the field of view of the detector measuring the emitted fluorescence.
In a preferred form, the path followed by the illuminating light to the sample and the path followed by the emitted fluorescence to the detector are essentially coaxial in the overall sense.
This principle makes efficient use of the exciting light and makes the measurement sensitive to low concentrations of fluorophores since the field of view of the detector completely encompasses the fluorescence emitted within the field of illumination of the lamp.
This is not the case in some prior art instruments where a substantial angle exists between lamp and detector paths.
Since the principle is a special case of a surface detector, the measurement is more sensitive to highly light absorbant samples than procedures which measure fluorescence through a surface different than the surface used for illumination.
This principle permits the sensor to be assembled as a compact cylindrical probe which can be directly inserted in a process vessel through a variety of standard nozzles.
The cylindrical geometry of the probe facilitates the sealing of the probe to protect it externally from water (e.
g.
from tank washing, foam overs, accidental spills) or to allow the probe to contain a dry gas (e.
g.
to avoid water condensation within the probe).
This configuration avoids many of the problems normally associated with providing stable and representative samples in real time to prior art instruments which employ sample chambers.
The avoidance of a sample chamber also permits the optical path length to vary as a function of the light absorbing species in the sample as defined by total absorption.
This enhances the range and sensitivity of the probe over that obtainable at a single fixed path length