Patent ID: 7929135

Claim:
A method of detecting a size of particles in a liquid by irradiating a tube channel having translucency with coherent light such that the light traverses a flow direction of a liquid flowing in the tube channel, and detecting diffraction fringes that appear due to the particles included in the liquid by a light detection portion, a first light detection portion and a second light detection portion being provided as the light detection portion, and the second light detection portion being provided so as to be separated from the first light detection portion by a predetermined distance farther downstream along the flow direction of the liquid than the first light detection portion, and the method comprising the steps of: measuring, for each diffraction fringe detected in a predetermined time period by the first light detection portion and the second light detection portion, a peak time difference T 2 that is a difference between times at which peak values appear in a detection signal from the first light detection portion and the second light detection portion, and an area SQ based on the waveform of the detection signal; and detecting a size of the particles included in the liquid based on the peak time differences T 2 and the areas SQ that were measured.