Apparatus and method for controlling the temperature of a furnace

Apparatus for controllably heating a furnace comprising:

• sensor means for providing a temperature signal indicative of the furnace temperature;
• heat source means responsive to a heat control signal for heating said furnace;
• and
• data processing means for providing the heat control signal, said data processing means being responsive to the temperature signal to determine the heating constants of the furnace from the heating characteristics of the furnace, the heating characteristics including at least the heat lag of the furnace defined as the difference between the time required for the furnace to reach the temperature at which a maximum heating rate is observed and the time necessary for a linearly heated furnace, having a heating rate equal to the observed maximum heating rate, to reach this same temperature, said data processing means being adapted to modulate the heat control signal in response to the determined heating constants to thereby control the temperature of the furnace.

A method for increasing the temperature of a furnace to a predetermined desired temperature without overshooting the desired temperature, said method comprising the steps of:

• (a) determining the heat lag of the furnace as a function of the system's response to a predetermined quantum of power input by using the input power to heat the furnace and determining the heat lag of the furnace defined as the difference between the time necessary for the furnace to reach the temperature at which the maximum heating rate is observed and the time necessary for a linearly heated furnace, having a heating rate equal to the observed maximum rate to reach this same temperature;
• (b) supplying a first predetermined quantum of power for heating the furnace until the determination is made, based on the determined heat lag, that power must be reduced in order to effectively reduce the rate of temperature increase of the furnace such that the furnace does not overshoot the desired temperature;
• and
• (c) using the determined heat lag to control the temperature increase of the furnace such that the furnace temperature increases to the desired temperature in an exponential manner.

Apparatus for preventing the transfer of power from a furnace power source to a furnace heat source upon the malfunction of the furnace control system, said apparatus comprising:

• first switch means coupled to receive power from said power source;
• second switch means coupled to receive power from said first switch means and responsive to a heat control signal for transferring power received from said first switch means to said heat source;
• power checker means for indicating when power is being received by said heat source;
• and
• data processing means responsive to a timed interrupt for providing the override signal and the heat control signal, said data processing means being responsive to said power checker means for determining when a control system malfunction has occurred and, upon making such determination, for interrupting the override signal, said first switch means being responsive to the override signal for transfering power received from said power source to said second switch means such that, upon interruption of the override signal, power is no longer applied to said second switch means.