Abstract: Apparatus and method for detecting and correcting for evaporation from recirculated unused ink drops in an ink jet printer. The specific gravity of the recirculating ink is compared with that of a standard by measuring the time of fall of heavy floats through reservoirs of circulated and uncirculated fluid. A significant difference in fall times is compensated by the replenishment of fluid in the recirculating ink supply.

Abstract: Vacuum cleaned high voltage deflection electrode apparatus may be utilized in conjunction with further deflection electrode means to establish an electrostatic deflection field for ink jet. The high voltage electrode includes a pair of parallel planar fine screens interposed between two rows of ink jet stream paths and has a vacuum between the screens. Two separate rows of ink jet orifices may cause two rows of ink jet streams to be formed which pass through two corresponding rows of charging electrodes to selectively charge the drops upon breakoff. The drops pass on opposite sides of the high voltage electrode through the deflection field which deflects the charged drops and not the uncharged drop for selectively impacting a gutter or for recording. Significant ink mist may be generated and may come into proximity to the high voltage electrode which is then drawn through the screens by the vacuum to prevent mist accumulation on the electrode.