Frozen carbonated beverage apparatus and method and control system

Abstract

The present invention concerns improvements in the electronic control of frozen carbonated beverage machines and improvements in electric defrost heaters used therein. A control scheme is shown that provides for accurately determining the viscosity of a semi-frozen beverage as a function of the torque of a drive motor used in the harvesting and mixing thereof. The torque is first calculated based upon the current and voltage to the motor and the phase difference there between. The torque is adjusted to compensate for motor efficiency after which the net torque value is converted to a viscosity scale. The viscosity scale has a zero value relating to the net torque experienced by the motor when the beverage is known to be completely liquid. Viscosity is maintained within a narrow range based upon pre-defined three level low, medium and high viscosity sets, and wherein compressor short-cycling is eliminated. Recalibration control is shown for reestablishing a new viscosity zero value to allow for changes in the net torque at the beverage known liquid point that can result from machine wear, inaccurate initial calibration and the like. A safety defrost control is shown for reducing potential hazards associated with the use of electric defrost heaters. Improved electrical defrost heaters are shown that allow for easy removal and replacement thereof.