GRAIN COUNTER

PURPOSE:To count an impurity grain floating in a fluid irrespective of the degree of vacuum by radiating a light beam to a transparent tubular body, receiving the light beam from the tubular body by a collimator lens having a focus in an irradiation area in the tubular body and projecting it to a counting detector. CONSTITUTION:A light beam from a light source 13a is converted to the center axis of a transparent tubular body 11 by a condensing lens 13b. If an impurity grain, etc. exist in an optical path, the irradiation light is scattered. A part of its scattered light is received by a collimator lens 14a, and projected to a counting detector 14b. In such a state, the counting detector 14b counts the incident light beams and executes an operation, and the density of the number of the impurity grain in gas and its size are displayed on a display part 14c.