Patent ID: 6529796
Filing Date: 2003-03-04
Classification: B29C,G05B,G05D

Abstract:
An apparatus comprising:(a) multiple zones, each zone having at least one heater and at least one temperature sensor outputting a temperature indicating signal; (b) a power source providing power to the heaters; and (c) a controller for controlling the temperature of at least some of the zones, the controller comprising: (i) a data-receiving processor for receiving the temperature indicating signal from each temperature sensor, computing RMS values corresponding to measured heater currents and computing the average of the temperature indicating signals; (ii) a power driver comprising respective on/off switches for controlling power to each heater, respective current sensors for measuring the heater currents in each heater, and a zero crossing detector for triggering the on/off switch; and (iii) a separate control processor for receiving data from the data-receiving processor, storing a selected range for the temperature in each zone, performing a PID calculation of the amount of power required to maintain the temperature of each zone within a selected range based on the values computed by the data-receiving processor, and for controlling the amount of power provided to the heaters in response to the data received from the data-receiving processor, the separate control processor comprising a zero crossing interrupter interposed between the zero crossing detector and the on/off switches to provide only complete AC cycles to the heaters; whereby each zone is maintained within the selected range of operating temperatures.