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.

An ion current is produced between two spatially separated electrodes by creating a corona discharge about one of these electrodes and causing ions to flow to the other electrode. Aerosols introduced into the region between the two electrodes interact with the flowing ions causing a resultant decrease in ion current. A decrease in ion current is sensed to indicate the presence of aerosols. A reflecting member reflects aerosols towards the electrodes causing a relatively lengthy interaction between the aerosols and the ion current.

An ion current is produced between two spatially separated electrodes by creating a corona discharge about one of these electrodes and causing ions to flow to the other electrode. Aerosols introduced into the region between the two electrodes interact with the flowing ions causing a resultant decrease in ion current. A decrease in ion current is sensed to indicate the presence of aerosols.

A container is positioned on an electrically insulated support and pierced by a spring actuated piercing device while a stream of gas flows adjacent the support.

Smoke is detected by a surface ionization effect on a heated wire filament disposed opposite a negative ion collector electrode. Current flow between the wire and the electrode increases in the presence of smoke. The increase is probably attributable to surface ionization of smoke particles on the heated wire.