Patent ID: 7249828

Claim:
A method for controlling charging of droplets, the method comprising: a. generating a stream of droplets; b. applying a droplet charging signal to the stream of droplets, the droplet charging signal having a droplet charging signal amplitude, a droplet charging signal phase and a droplet charging signal frequency, thereby creating a population of charged droplets in the stream of droplets; c. imposing a calibration signal on the stream of droplets, the calibration signal having a calibration signal frequency, a calibration signal amplitude and a calibration signal phase, the calibration signal phase being independent of the droplet charging signal; d. deflecting for charge detection at least a sub-population of charged droplets from among the population of charged droplets; e. obtaining, from the sub-population of charged droplets, a signature signal of the calibration signal, the signature signal having a signature signal frequency, a signature signal amplitude and a signature signal phase, the signature signal frequency being equal to the calibration signal frequency; and f. maximizing the charge on the population of charged droplets based on the difference between the signature signal phase and the calibration signal phase.