JPS5587952A - Particle counter - Google Patents

Abstract

PURPOSE: To eliminate the fluctuation of a base line and enable accurate counting, by providing a variable time constant differentiation circuit between a particle detector and a threshold circuit and changing a time constant depending on the rising or falling of an input signal.

CONSTITUTION: A signal detected by a particle detector 4 is changed into an electric signal by a detection circuit 6. The electric signal is applied to a counter circuit 12 through a variable time constant differentiation circuit 8 and a threshold circuit 10 having threshold values corresponding to an upper and a lower limit values. The variable time constant differentiation circuit 8 has a time constant switching circuit 26. A signal entered into a buffer amplifier 28 is applied to a differentiation circuit 16 after amplification. A positive and a negative signals corresponding to the rising and falling of the signal applied to the circuit 26 are produced by comparison circuit 30, 32 succeeding to the circuit 26. The positive and the negative signals are applied to an RS flip-flop 34. The time constant of the time constant switching circuit is changed to be small at the rising of the signal but large at the falling of the signal. This results in always flattening the base line of the output of the variable constant differentiation circuit 8.

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