An apparatus for controlling droplets allows the phase difference between a calibration signal and its signature signal on a detector to be minimized, or the amplitude of the signature signal to be maximized, by adjusting the droplet charging means of the device, or the droplet generation means, and the signals on either. The apparatus converts a stream of fluid into a stream of droplets under the influence of a droplet stimulation signal imposed onto the droplet generating means. Droplets are subsequently signal-wise charged under the influence of a droplet charging signal imposed on the droplet charging means. The charged droplets are then deflected. The calibration signal is imposed onto the stream of droplets. The calibration signal has characteristics that do not appreciably affect the trajectory of the stream of droplets, thereby ensuring that the placement accuracy of the individual droplets is a maintained. The calibration signal further has a signal phase that is independent of the droplet charging signal. A charge detection means is used to extract a charge detection signal from the at least a part of the droplets. The charge detection signal is filtered to extract a signature signal of the calibration signal. The phase control system then varies at least one of the droplet generation means, droplet stimulation signal, droplet charging means and droplet charging signal until the phase between the signature signal and the calibration signal is minimized. A plurality of streams of droplets may be controlled by the method of the invention.

 
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