Patent ID: 8226199

Claim:
A jet break-off length measurement apparatus for a continuous liquid drop emission system comprising: a liquid drop emitter containing a positively pressurized liquid in flow communication with the at least one nozzle for emitting a continuous stream of liquid; resistive heater apparatus configured to transfer pulses of thermal energy to the liquid in flow communication with the at least one nozzle sufficient to cause the break-off of the at least one continuous stream of liquid into a stream of drops of predetermined volumes, and wherein said break-off occurs at a break-off length from the nozzle; charging apparatus configured to inductively charge at least one drop of the stream of drops of predetermined volumes; sensing apparatus configured to detect the stream of drops of predetermined volumes; and control apparatus configured to determine a characteristic of the stream of drops of predetermined volumes that is related to the break-off length, wherein at least one drop of the stream of drops of predetermined volumes is an inductively charged drop having an electrical charge after break-off from the continuous stream and a predetermined flight trajectory; and the sensing apparatus comprises an electrical charge sensor that is responsive to the electrical charge on the inductively charged drop, wherein the charging apparatus comprises a charge electrode held in close proximity to the at least one continuous stream of liquid and having a length along the stream of liquid, L c , wherein the drops of predetermined volume are separated by a nominal inter drop-spacing in flight, λ 0 , and L c <2 λ 0 .