ABNORMALITY DETECTING CIRCUIT FOR IONIZATION MEASURING INSTRUMENTS AND IONIZATION MEASURING INSTRUMENTS

PROBLEM TO BE SOLVED: To capture the state of a needle electrode as varying pulses of applied current of a high-voltage stabilized current source, and to realize abnormality detecting circuit to detect the needle electrode abnormal exceeding the threshold. SOLUTION: A needle electrode 2 produces corona discharge with a high voltage applied from a high-voltage stabilized current source 5. The current applied to the needle electrode 2 is converted into voltage with a current detecting resistor 6. Variation of the converted voltage is given as pulse output with signal amplifying circuit and differentiating circuit at a current detecting portion 7, and counted with a pulse counter circuit 8 at a fixed time interval. A counting comparison circuit 9 compares the counted value and with a setting dial 10 for threshold to regard the current variation abnormal and gives fault signal for the needle electrode when exceeding the value of the set dial 10. Maintenance of cleaning or replacement for the needle electrode becomes easier because the fault signal is given when a current variation of the needle electrode exceeds the threshold and maintenance of the needle electrode with the fault signal.