Method for automatically setting the correct phase of the charge pulses

Abstract

In order to initiate the charging of droplets at a specific point in time with respect to the formation of those droplets in an electrostatic flow sorting system, the charge phase of the system of the present invention is continuously and automatically adjusted by droplet break point monitoring. The charge phase is therefore flow rate and fluid velocity independent. The break point is monitored by a light source which is focused onto the jet stream at the droplet formation break point, or close to it, and the modulation of light caused by the scatter induced by the sheath stream portion as it passes the focused beam of light is detected via the use of a suitable electro-optical detector. From the output of the electro-optical detector, after appropriate signal conditioning, an electrical wave form is obtained which shape depends upon the shape of the fluid column passing the focus beam. Using this conditioned detector output, the charge pulse phase is automatically controlled to occur at a set point in time with respect to a transition point on the waveform thus obtained. Additionally, in order to compensate for large flow rate variations, the focused beam detector can be automatically repositioned to track with the breakpoint. The correct phase of the charge pulse will accordingly continue to be derived from the breakpoint electrical waveform. Alternatively, by monitoring the jet stream at points above or below the breakpoint, the phase adjustment is possible, however, somewhat fluid velocity dependent.