Fast-acting spark-over detector

Claim 1

A spark-over detector for detection of spark-overs in an electrostatic precipitator, said detector comprising: a pulse circuit, a current sensor, said sensor providing a current-representing voltage signal proportional with the current in said pulse circuit; a first differentiation unit receiving said current-representing voltage signal, to differentiate said voltage signal and to provide a first output signal; a second differentiation unit receiving said first output signal from said first differentiation unit, to differentiate said first output signal and provide a second output signal; a first level-detecting circuit providing a third output signal when said second output signal is above a preset level; and AND-gate, said AND-gate having a first and second inputs, said first input receiving said third output signal; a second level-detecting circuit providing a fourth output signal as long as said current-representing voltage is above a preset level; and a timing circuit receiving said fourth output signal and transmit a fifth signal to said second input of said AND-gate throughout a period starting at a first preset time after said fourth output signal has been received from said second level-detecting circuit and ending at a second preset time after said fourth signal has been received or after said fourth signal has ceased; the said AND-gate outputting a signal when there are simultaneous signals on its said first and second inputs, thereby to indicate that a spark-over is developing.