Particle sizes and liquid samples can be measured by passing the liquid stream to be measured through a beam of light, preferably a laser beam, and measuring the characteristics of the light scattered from the sample or the unscattered portion of the beam through which the sample has passed. U.S. patent application Ser. No. 144,225, filed Jan. 15, 1988 and invented by Kenneth Paul Von Bargen discloses such a system for measuring particle sizes in liquid streams. The system of the above mentioned patent application and most other prior art systems for measuring particle size require that a small number of particles, e.g., one at a time, pass through the laser beam. Thus, when the particle density in the sample is too great, there is a need to dilute the sample before making the particle size measurements.
In particle size measuring applications, there is a need to know the relative numbers of particles in different size ranges. The absolute numbers of the particles in each size range in the sample in many applications is not important. An automatic dilution system has been proposed to take advantage of this latter fact. This system automatically dilutes the sample by continuously introducing diluent into a mixing chamber containing the sample to be measured while the mixture of the diluent and sample in the mixing chamber is allowed to continuously flow from the mixing chamber. With such an arrangement, the mixture in the mixing chamber will continuously become more diluted. When the mixture has become sufficiently diluted, the particle size measurements are made. With this technique, the degree of dilution of the original sample is not known, but, theoretically, the relative counts of particles in each size range will give an accurate indication of the relative number of particles in each size range in the original sample.
As a practical matter, the automatic dilution system of the above described proposal may not give an accurate count of particles in each size range, because in this system the mixing carried out in the mixing chamber was simply that which occurred as a result of the diluent stream flowing into the mixing chamber. The inflow of the diluent result in a whirlpool flow pattern which tends to cause the particles of different sizes to segregate. As a result, the outflow from the mixing chamber may fail to contain a distribution of particle sizes corresponding to their distribution in the original sample, and the system of the proposal may fail to give accurate counts of the relative particle sizes.