Temperature achievement controller

A temperature achievement controller for controlling the temperature of a device which is heated by a heating unit in accordance with a predetermined temperature versus time curve, said controller comprising:

• temperature sensing means for producing an achieved temperature signal which corresponds to an achieved temperature of the device;
• generating means for generating a desired temperature signal which varies with time in accordance with said predetermined temperature versus time curve;
• initiating means responsive to said achieved temperature signal for causing said generating means to commence generating said desired temperature signal when said achieved temperature reaches a predetermined value;
• error detecting means for producing an error signal proportional to the difference between said achieved temperature signal and said desired temperature signal;
• differentiating means for generating a first signal proportional to the derivative with respect to time of said error signal;
• integrating means for generating a second signal proportional to the integral with respect to time of said error signal;
• proportioning means for generating a third signal proportional to said error signal;
• and
• summing means for generating a control signal which comprises the sum of said first, second and third signals;
• duty cycle modulating means for switching power supplied to the heating unit on and off with the ratio of the power on time period to the power off time period being proportional to said control signal;
• whereby when said achieved temperature is less than said desired temperature, said power on/power off time ratio increases and when said achieved temperature is greater than said desired temperature said ratio decreases thereby maintaining said achieved temperature substantially at said desired temperature level.