Method for detection of solid particles in fluid and particle sensor

Abstract

A method for detecting the solid particles contained in a fluid, by the use of a particle sensor having a flow path of a fluid, having a fluid inlet and a fluid outlet, and a sensor element provided in the flow path, which comprises (a) a vibrating section having such a mass that is sensitive to the collision of solid particles contained in the fluid, with the vibrating section and (b) a detecting section for detecting the vibration of the vibrating section caused by the collision and converting the vibration to electric signals. The method includes steps of: passing a fluid to be examined, through the particle sensor, selectively detecting, from the electric signals outputted from the particle sensor, an electric signal portion having particular frequencies ranging from 1/50 to 10 times the primary resonance frequency of the sensor element, measuring the maximum amplitude of the electric signal portion, comparing the maximum amplitude measured above, with a given value predetermined with the particle sensor based on (1) the maximum amplitude of a portion of the electric signals caused by the collision of solid particles contained in a fluid, having the above particular frequencies and (2) the maximum amplitude of a portion of the electric signals caused by the turbulent flow of the same fluid containing no solid particles, having the above particular frequencies, and judging, depending upon the result of the above comparison, whether or not the electric signals outputted from the particle sensor with the fluid to be examined have been caused by the collision of solid particles with the particle sensor.