Particle counter for measuring floating particles which can effectively reduce false counts
Inventors
Nakajima, Yasutaka • Matsuda, Tomonobu
Assignees
Publication Number
US-7755760-B2
Publication Date
2010-07-13
Expiration Date
2025-12-09
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Abstract
A particle counter for measuring the number of floating particles contained in a sample to determine the particle concentration therein includes: a memory section for storing a relational expression between the direct current level output from a photoelectric converter when no particles exist and the frequency of occurrence of false counts; and a subtraction section for determining the frequency of occurrence of the false counts corresponding to the direct current level output from the photoelectric converter at the time of commencement of measurement with reference to the relational expression stored in the memory section and subtracting a value based on the frequency of occurrence of the false counts from a discrete value after commencement of measurement.
Core Innovation
The invention is a particle counter for measuring the number of floating particles contained in a sample to determine the particle concentration therein. It includes a memory section for storing a relational expression between the direct current level output from a photoelectric converter when no particles exist and the frequency of occurrence of false counts, and a subtraction section for determining the frequency of occurrence of the false counts corresponding to the direct current level output at the time of measurement commencement. The subtraction section subtracts a value based on the frequency of occurrence of the false counts from a discrete value obtained after commencement of measurement.
The problem being solved is the occurrence of false counts in particle counters even when no particles of measurable size exist. These false counts are caused by noise generated from various sources such as laser beam sources, photoelectric converters, random voltage variations in circuits, and cosmic rays. Prior art reduces false counts from laser diode noise but cannot effectively reduce false counts from other factors.
The invention solves this problem by storing either a pre-calculated frequency of occurrence of false counts or a relational expression linking the direct current level output and occurrence frequency. The counting operation then subtracts values based on these stored data from the discrete particle counts over minimum time intervals during measurement to effectively reduce false counts from various factors in a relatively simple structure.
Claims Coverage
The patent includes four claims covering two independent inventive features related to a particle counter.
Subtraction of false counts based on pre-calculated occurrence frequency
A particle counter comprising a photoelectric converter, a memory section storing a frequency of occurrence of pre-calculated false counts, and a subtraction section which subtracts a value based on the stored false counts frequency from discrete values at minimum time intervals during measurement. The frequency of occurrence determines the reciprocal minimum time interval at which subtraction occurs successively.
Subtraction of false counts based on relational expression of direct current level and false counts frequency
A particle counter comprising a photoelectric converter, a memory section storing a relational expression between direct current level output when no particles exist and the frequency of occurrence of false counts, and a subtraction section which determines the frequency of occurrence of false counts from the direct current level at measurement start and subtracts a corresponding value from discrete counts at minimum reciprocal time intervals successively during measurement.
The claims cover particle counters that use stored data on false counts frequency—either a fixed pre-calculated value or a relational expression related to direct current output—to subtract false counts from measured discrete values at specified reciprocal time intervals, thereby improving measurement accuracy.
Stated Advantages
It is possible to control the influence of false counts within a certain range, resulting in a more precise discrete value.
The invention accounts for changes in use conditions by relating false counts frequency to the direct current level, increasing accuracy across different operation settings.
If no signals for increasing the discrete value occur within a time interval, the subtraction is carried over, preventing reduction of already displayed discrete values.
It improves usability by eliminating the need for users to manually subtract false counts from measurement results.
Documented Applications
Measuring the number of floating particles contained in a sample to determine the particle concentration therein using light scattering or light extinction methods.
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