Abstract: A microphone is provided for converting the impact force of a moving charged droplet into a corresponding electrical signal. A vertical support member supports a diaphragm in the path of the moving droplet. The diaphragm flexes or vibrates in response to a group of impinging droplets. A bimorph piezo-electric element is in contact with the diaphragm to move therewith and is fixedly secured at its opposite end to an adjacent housing member. The bimorph generates an electrical signal in response to bending stresses created when the bimorph is bent.

Abstract: An ink jet printer has a printing head which contains at least one cavity with a discharge orifice therein for dispersing droplets of ink onto a medium for printing thereon. Means are disclosed herein for maintaining the temperature of the ink in the cavity at a preselected value prior to dispersement from the discharge orifice. Preferably, the ink is heated by an electrical heating rod mounted in the printing head adjacent to the cavity. Means are also provided for sensing the temperature of the ink in the cavity. The heating rod is selectively energized to maintain the ink at the preselected temperature by means of a feedback control circuit coupled with the sensing means.