Method and apparatus for automatically controlling temperature in a furnace system

Abstract

A method and system for controlling the temperature in a furnace such as a continuous feed controlled atmosphere furnace includes an upstream thermocouple in a first area of the furnace, a second thermocouple in a second area of the furnace, and a heater control system. A sensed temperature from the upstream thermocouple is used to generate a control signal for a heater associated with the first area of the furnace. The sensed temperature from the first area of the furnace is further used to modify a set point that is compared to a sensed temperature from the second thermocouple. A control signal for a heater associated with the second area of the furnace is generated based upon the comparison of the modified set point to the sensed temperature from the second thermocouple.

1 . A continuous control atmosphere brazing furnace comprising: 
 a muffle having a first area and a second area;    a carrier operable to convey an item from the first area to the second area;    a first heating element operable to provide heat energy to the first area as a function of a first control signal;    a second heating element operable to provide heat energy to the second area as a function of a second control signal;    a first thermocouple operable to sense the temperature within the first area;    a second thermocouple operable to sense the temperature within the second area; and    a controller operably connected to the first heating element, the second heating element, the first thermocouple and the second thermocouple and programmed to 
 perform a first comparison of the sensed temperature from the first thermocouple with a first set point temperature,  
 generate the first control signal based upon the first comparison,  
 determine a current set point based upon the first comparison,  
 perform a second comparison of the sensed temperature from the second thermocouple with the current set point temperature, and  
 generate the second control signal based upon the second comparison.  
   
   
   
       2 . The continuous control atmosphere brazing furnace of  claim 1 , wherein the controller is further programmed to: 
 determine the current set point to be a low deviation current set point when the sensed temperature from the first thermocouple is less than the first set point by a first predetermined amount.    
   
   
       3 . The continuous control atmosphere brazing furnace of  claim 2 , wherein the controller is further programmed to: 
 determine the current set point to be a high deviation current set point when the sensed temperature from the first thermocouple is greater than the first set point by a second predetermined amount; and    determine the current set point to be a normal current set point when the sensed temperature from the first thermocouple is not determined to be less than the first set point by a first predetermined amount or greater than the first set point by a second predetermined amount.    
   
   
       4 . The continuous control atmosphere brazing furnace of  claim 2 , wherein the controller is programmed to: 
 perform the first comparison using a first proportional-integral-derivative function; and    perform the second comparison using a second proportional-integral-derivative function.    
   
   
       5 . The continuous control atmosphere brazing furnace of  claim 4 , further comprising: 
 a first silicon controlled rectifier located between the controller and the first heating element and operable to receive the first control signal and to provide power to the first heating element as a function of the first control signal; and    a second silicon controlled rectifier located between the controller and the second heating element and operable to receive the second control signal and to provide power to the second heating element as a function of the first control signal.    
   
   
       6 . The continuous control atmosphere brazing furnace of  claim 5 , further comprising: 
 an over-temperature probe located within an upper portion of the furnace and operable to generate a signal corresponding to a sensed over temperature condition within the muffle;    an over-temperature instrument operable to receive the signal from the first over-temperature probe and to interrupt power to the first and the second silicon controlled rectifiers when an over-temperature condition in the muffle is sensed.    
   
   
       7 . The continuous control atmosphere brazing furnace of  claim 1 , wherein: 
 the muffle comprises a third and a fourth area;    the carrier belt is further operable to convey an item from the third area to the fourth area;    the furnace further comprises 
 a third heating element operable to provide heat energy to the third area as a function of a third control signal,  
 a fourth heating element operable to provide heat energy to the fourth area as a function of a fourth control signal,  
 a third thermocouple operable to sense the temperature within the third area,  
 a fourth thermocouple operable to sense the temperature within the fourth area, and  
   the controller is further programmed to 
 perform a third comparison of the sensed temperature from the third thermocouple with a third set point temperature,  
 generate the third control signal based upon the third comparison, determine a second current set point based upon the third comparison,  
 perform a fourth comparison of the sensed temperature from the fourth thermocouple with the second current set point, and  
 generate the fourth control signal based upon the fourth comparison.  
   
   
   
       8 . The continuous control atmosphere brazing furnace of  claim 7 , wherein: 
 the muffle further comprises an upper portion, a lower portion, an inlet and an outlet downstream of the inlet;    the first area is about one third of the distance from the inlet to the outlet in the upper portion of the muffle;    the second area is about two thirds of the distance from the inlet to the outlet in the upper portion of the muffle;    the third area is about one third of the distance from the inlet to the outlet in the lower portion of the muffle; and    the fourth area is about two thirds of the distance from the inlet to the outlet in the lower portion of the muffle.    
   
   
       9 . The continuous control atmosphere brazing furnace of  claim 7 , further comprising: 
 a first silicon controlled rectifier located between the controller and the first heating element and operable to receive the first control signal and to provide power to the first heating element as a function of the first control signal;    a second silicon controlled rectifier located between the controller and the second heating element and operable to receive the second control signal and to provide power to the second heating element as a function of the first control signal;    a third silicon controlled rectifier located between the controller and the third heating element and operable to receive the first control signal and to provide power to the third heating element as a function of the third control signal; and    a fourth silicon controlled rectifier located between the controller and the fourth heating element and operable to receive the fourth control signal and to provide power to the fourth heating element as a function of the fourth control signal.    
   
   
       10 . The continuous control atmosphere brazing furnace of  claim 7 , wherein: 
 the muffle comprises a first zone and a second zone, the second zone located downstream of the first zone;    the first and second areas are located within the first zone; and    the third and fourth areas are located within the second zone.    
   
   
       11 . A furnace system comprising: 
 a furnace with a first area and a second area;    a first thermocouple operable to sense the temperature within the first area and to generate a signal indicative of the sensed temperature;    a second thermocouple operable to sense the temperature within the second area and to generate a signal indicative of the sensed temperature;    a first heating element with a variable heat output located proximate the first area and operable to affect the temperature within the first area;    a second heating element with a variable heat output located proximate the second area and operable to affect the temperature within the second area;    a controller, operable to receive the signal from the first thermocouple and the signal from the second thermocouple and programmed to 
 compare the signal from the first thermocouple to a first set point, and  
 modify a second set point based on the comparison of the signal from the first thermocouple to the first set point, wherein the first set point is used in determining the amount of heat to be provided to the first area and the second set point is used in determining the amount of heat to be provided to the second area.  
   
   
   
       12 . The furnace system of  claim 11 , further comprising: 
 an over-temperature probe located within an upper portion of the furnace and operable to sense an over-temperature condition in the upper portion of the furnace;    an over-temperature instrument operably connected to the first over-temperature probe and operable to disable the first heating element and the second heating element when an over-temperature condition is sensed in the upper portion of the furnace.    
   
   
       13 . The furnace system of  claim 11 , wherein the controller is programmed to: 
 compare the signal from the first thermocouple to the first set point using a first proportional-integral-derivative function;    generate a first control signal based upon the comparison by the first proportional-integral-derivative function;    compare the signal from the second thermocouple to the modified second set point using a second proportional-integral-derivative function; and    generate a second control signal based upon the comparison by the second proportional-integral-derivative function.    
   
   
       14 . A method of controlling temperature within a furnace comprising: 
 defining a first temperature set point for a first area in a furnace;    obtaining a first signal indicative of the temperature in the first area of the furnace;    comparing the first signal to the first temperature set point;    controlling the temperature in the first area based upon the comparison of the first signal to the first temperature set point;    defining a second temperature set point for a second area in the furnace;    defining a third temperature set point for the second area in the furnace selecting one of the second temperature set point or the third temperature set point based upon the comparison of the first signal to the first temperature set point;    obtaining a second signal indicative of the temperature in the second area of the furnace;    comparing the second signal to the selected temperature set point; and    controlling the temperature in the second area based upon the comparison of the second signal to the selected temperature set point.    
   
   
       15 . The method of  claim 14 , wherein: 
 the step of comparing the first signal to the first temperature set point comprises determining when the first signal indicates that the temperature in the first area is lower than the first temperature set point by an amount greater than about a first deviation value;    the step of defining a third temperature set point comprises defining the third temperature set point to be value greater than the second temperature set point; and    the step of selecting comprises selecting the third temperature set point when it is determined that the first signal indicates that the temperature in the first area is lower than the first temperature set point by an amount greater than about the first deviation value and selecting the second temperature set point when it is determined that the first signal indicates that the temperature in the first area is not lower than the first temperature set point by an amount greater than about the first deviation value.    
   
   
       16 . The method of  claim 14 , wherein: 
 the step of comparing the first signal to the first temperature set point comprises determining when the first signal indicates that the temperature in the first area is higher than the first temperature set point by an amount greater than about a second deviation value;    the step of defining a third temperature set point comprises defining the third temperature set point to be a value greater than the second temperature set point; and    the step of selecting comprises selecting the second temperature set point when it is determined that the first signal indicates that the temperature in the first area is higher than the first temperature set point by an amount greater than about the second deviation value and selecting the third temperature set point when it is determined that the first signal indicates that the temperature in the first area is not higher than the first temperature set point by an amount greater than about the first deviation value.    
   
   
       17 . The method of  claim 14 , further comprising the step of defining a fourth temperature set point for the second area in the furnace to be a value less than the second temperature set point, wherein: 
 the step of comparing the first signal to the first temperature set point comprises 1) determining when the first signal indicates that the temperature in the first area is higher than the first temperature set point by an amount greater than about a third deviation value and 2) determining when the first signal indicates that the temperature in the first area is lower than the first temperature set point by an amount greater than about a fourth deviation value;    the step of defining a third temperature set point comprises defining the third temperature set point at a temperature greater than the second temperature set point; and    the step of selecting comprises 1) selecting the fourth temperature set point when it is determined that the first signal indicates that the temperature in the first area is higher than the first temperature set point by an amount greater than about the third deviation value, 2) selecting the third temperature set point when it is determined that the first signal indicates that the temperature in the first area is lower than the first temperature set point by an amount greater than about the fourth deviation value, and 3) selecting the second temperature set point when it is determined that the first signal indicates that the temperature in the first area is (a) greater than the remainder of the first temperature set point minus the fourth deviation value, and (b) less than the sum of the first temperature set point and the third deviation value.    
   
   
       18 . The method of  claim 17 , further comprising after the step of selecting the third temperature set point: 
 maintaining the third temperature set point as the selected temperature set point until it is determined that the first signal indicates that the temperature in the first area is greater than the remainder of the first temperature set point minus the fourth deviation value by a fifth deviation value.    
   
   
       19 . The method of  claim 14 , wherein: 
 the step of obtaining a first signal indicative of the temperature in the first area of the furnace comprises obtaining the first signal when an item on a conveyer belt is within the first area; and    the step of controlling the temperature in the second area based upon the comparison of the second signal to the selected temperature set point comprises controlling the temperature in the second area to be at about the selected temperature set point at about the time that the item present in the first area at the time the first signal indicative of the temperature in the first area of the furnace was obtained is conveyed into the second area.    
   
   
       20 . The method of  claim 14 , further comprising 
 defining a fifth temperature set point for a third area in a furnace;    obtaining a third signal indicative of the temperature in the third area of the furnace;    comparing the third signal to the fifth temperature set point;    controlling the temperature in the third area based upon the comparison of the third signal to the fifth temperature set point;    defining a sixth temperature set point for a fourth area in the furnace;    defining a seventh temperature set point for the fourth area in the furnace selecting one of the sixth temperature set point or the seventh temperature set point as a second selected temperature set point based upon the comparison of the third signal to the fifth temperature set point;    obtaining a fourth signal indicative of the temperature in the fourth area of the furnace;    comparing the fourth signal to the second selected temperature set point; and    controlling the temperature in the fourth area based upon the comparison of the fourth signal to the second selected temperature set point.    
   
   
       21 . A method of controlling temperature within a conveyer type furnace comprising: 
 defining a first temperature set point for a first area in a furnace;    obtaining a first signal indicative of the temperature in the first area of the furnace;    comparing the first signal to the first temperature set point;    controlling the temperature in the first area based upon the comparison of the first signal to the first temperature set point;    defining a second temperature set point for a second area in the furnace;    determining if the first signal indicates a temperature greater than the first temperature set point by a first deviation value;    decreasing the second temperature set point if the first signal indicates a temperature greater than the first temperature set point by the first deviation value;    obtaining a second signal indicative of the temperature in the second area of the furnace;    comparing the second signal to the decreased second temperature set point; and    controlling the temperature in the second area based upon the comparison of the second signal to the decreased second temperature set point.    
   
   
       22 . The method of  claim 21 , further comprising: 
 determining if the first signal indicates a temperature less than the first temperature set point by a second deviation value;    increasing the second temperature set point if the first signal indicates a temperature less than the first temperature set point by the second deviation value;    comparing the second signal to the increased second temperature set point; and    controlling the temperature in the second area based upon the comparison of the second signal to the increased second temperature set point.