Abstract: A system and method for continuously producing and maintaining a predetermined proportionate mixture of two fluids, such as water and foam concentrate, in accordance with conductivity measurements of the fluids and the mixture. A set point is established which is representative of the conductivity of the predetermined proportionate mixture, by way of continuously measuring the conductivity of each fluid and feeding data to a microprocessor which calculates the conductivity of the desired proportionate mixture. The conductivity of the mixture is measured and compared with the set point by conductivity probes and a microprocessor. A control valve is continuously adjusted to maintain the predetermined proportionate mixture in response to control signals from the microprocessor in accordance with the comparisons of the conductivity values.

Abstract: An improved apparatus and method for monitoring the characteristics of materials by their fluorescence are described. A unique design is employed in which common fields of view are provided for the optical paths for the illuminating light and the emitted fluorescence. In a preferred form they are coaxial. This permits the apparatus to be contained within a probe which may be inserted directly in a vessel containing the material to be analyzed. The device is specifically designed to withstand sterilization with steam, to operate aseptically within biological processes, and to maintain a high stability and sensitivity over extended periods of time.