Abstract: A particle counter includes a detector that receives, using a light receiving element, interference light between scattered light and reference light, generates a detection signal corresponding to the interference light, and amplifies the detection signal using an amplifier; a counting unit that performs counting of the particle, based on the detection signal in a measurement period for measuring particle; and an optical path length variable unit that causes the optical path length of at least one of a first optical path and a second optical path to be changed at a predetermined rate, wherein the predetermined rate is set based on a flow velocity of the fluid so as to slow a change in a phase difference between the scattered light and the reference light and to make the frequency of the detection signal lower by changing the optical path length.

Abstract: A particle counter provided with: a detector configured to receive interference light by scattered light and reference light with a light receiving element, and generate a detection signal corresponding to the interference light; a filter configured to perform, with respect to the detection signal generated by the detector, a filtering process for passing a frequency component corresponding to an intensity change of the interference light; a determination unit configured to determine, from a peak level of the detection signal before filtering and a peak level of the detection signal after filtering, whether the detection signal is due to a particle; and a counting unit configured to perform, if it is determined by the determination unit that the detection signal is due to the particle, particle counting based on the detection signal after filtering.

Abstract: A particle counter includes a detector that receives, using a light receiving element, interference light between scattered light and reference light, generates a detection signal corresponding to the interference light, and amplifies the detection signal using an amplifier; a counting unit that performs counting of the particle, based on the detection signal in a measurement period for measuring particle; and an optical path length variable unit that causes the optical path length of at least one of a first optical path and a second optical path to be changed at a predetermined rate, wherein the predetermined rate is set based on a flow velocity of the fluid so as to slow a change in a phase difference between the scattered light and the reference light and to make the frequency of the detection signal lower by changing the optical path length.

Abstract: A particle counter provided with: a detector configured to receive interference light by scattered light and reference light with a light receiving element, and generate a detection signal corresponding to the interference light; a filter configured to perform, with respect to the detection signal generated by the detector, a filtering process for passing a frequency component corresponding to an intensity change of the interference light; a determination unit configured to determine, from a peak level of the detection signal before filtering and a peak level of the detection signal after filtering, whether the detection signal is due to a particle; and a counting unit configured to perform, if it is determined by the determination unit that the detection signal is due to the particle, particle counting based on the detection signal after filtering.

Abstract: Provided is a particle counter including: a light source; a light superimposition unit configured to superimpose light beams; an irradiation optical system configured to irradiate a fluid in a flow passage with one of a plurality of light beams from the light source; a detection optical system configured to make a part of scattered light beams by a particle in the fluid enter the light superimposition unit; a reference optical system configured to split another one of the plurality of light beams into a plurality of reference light beams and makes the reference light beams enter the light superimposition unit; and a counting unit configured to count the particles on the basis of detection signals corresponding to an interference light beam received by a light receiver. The interference light beam is generated by interference between the scattered light beam and one of the reference light beams at the light superimposition unit, and is received by the light receiver corresponding to the reference light beam.

Abstract: Provided is a particle counter including: a light source; a light superimposition unit configured to superimpose light beams; an irradiation optical system configured to irradiate a fluid in a flow passage with one of a plurality of light beams from the light source; a detection optical system configured to make a part of scattered light beams by a particle in the fluid enter the light superimposition unit; a reference optical system configured to split another one of the plurality of light beams into a plurality of reference light beams and makes the reference light beams enter the light superimposition unit; and a counting unit configured to count the particles on the basis of detection signals corresponding to an interference light beam received by a light receiver. The interference light beam is generated by interference between the scattered light beam and one of the reference light beams at the light superimposition unit, and is received by the light receiver corresponding to the reference light beam.