Corona current monitoring apparatus and circuitry for a.c. air ionizers

Abstract

Apparatus for measuring corona current in high voltage A.C. ionizers uses an electrical sensor adjacently spaced from at least one of the discharge electrodes and coupled to electronic circuitry for separating capacitive current from the corona current. In one mode, the capacitive current component is measured directly by a first sensor adjacently spaced from one discharge electrode whose corona current flow to such electrode is either obstructed or squelched entirely while a second sensor monitors total current. The signals from the two sensors are electrically subtracted when applied to opposing inputs of a differential amplifier to provide an output signal proportional to just corona current. In a second mode, a measure of corona current is again provided by electrically subtracting from a total current signal input to a differential amplifier a signal equal to the capacitive current component. However, while the total current signal in this case is again obtained by a single sensor adjacently spaced with respect to one electrode, the capacitive current signal is generated independently of a sensor through electronic circuitry coupled to the A.C. line voltage. In a third mode, a signal from a single sensor adjacently spaced from a single discharging electrode is applied to phase discriminator circuitry that passes only selected portions of the sensor-generated signal which contain equal positive and negative segments of the capacitive current component so that the average capacitive current signal thereof is equal to zero, whereby upon filtering the capacitive current signal will cancel out and leave remaining only that component proportional to corona current.