System and method for heating element failure detection

Abstract

According to one aspect of the invention, a water heater is provided comprising an electric heating element circuit; a circuit coupled to the electric heating element circuit and configured to supply current to the electric heating element; a sensor coupled to the circuit and configured to detect a temperature associated with operation of the electric heating element circuit; and a controller coupled to the circuit. The controller is configured to perform a spike test on the operation of the electric heating element circuit by comparing a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold; identifying a negative spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is below the negative threshold indicating that the electric heating element circuit may have failed or failing operation caused by an open circuit; and identifying a positive spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is above the positive threshold indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit. The controller is also configured to perform a signature test on the operation of the electric heating element circuit by in response to identifying the negative spike, supplying or continuing to supply the current to the electric heating element for a first predetermined time period: terminating the supply of current after the first predetermined time period; and determining if a drop occurs in the temperature associated with the operation of the electric heating element circuit, indicating no failed or failing operation caused by an open circuit, or does not occur, confirming the failed or failing operation caused by the open circuit; and in response to identifying the positive spike terminating the supply of current to the electric heating element for a second predetermined time period; and determining during the second predetermined time period if an increase occurs in the temperature associated with the operation of the electric heating element circuit, confirming the failed or failing operation caused by the shorted circuit, or does not occur, indicating no failed or failing operation caused by the shorted circuit.

What is claimed is: 
     
         1 . A water heater comprising:
 an electric heating element circuit including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element;   a sensor coupled to the electric heating element circuit and configured to detect a temperature associated with operation of the electric heating element circuit; and   a controller coupled to the electric heating element circuit, the controller being configured to:
 perform a spike test on the operation of the electric heating element circuit by:
 comparing a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold; 
 identifying a negative spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is below the negative threshold indicating that the electric heating element circuit may have failed or failing operation caused by an open circuit or identifying a positive spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is above the positive threshold indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit; 
 
 perform a signature test on the operation of the electric heating element circuit by:
 in response to identifying the negative spike if identified:
 supplying or continuing to supply the current to the electric heating element for a first predetermined time period; 
 terminating the supply of current after the first predetermined time period; and 
 determining if a drop occurs in the temperature associated with the operation of the electric heating element circuit, indicating no failed or failing operation caused by an open circuit, or does not occur, confirming the failed or failing operation caused by the open circuit; or 
 
 in response to identifying the positive spike if identified:
 terminating the supply of current to the electric heating element for a second predetermined time period; and 
 determining during the second predetermined time period if an increase occurs in the temperature associated with the operation of the electric heating element circuit, confirming the failed or failing operation caused by the shorted circuit, or does not occur, indicating no failed or failing operation caused by the shorted circuit. 
 
 
   
     
     
         2 . The water heater of  claim 1 , wherein the electric heating element circuit comprises a thermally conductive circuit board. 
     
     
         3 . The water heater of  claim 2 , further comprising a plurality of electric heating elements and a plurality of electronic switches, each of the electric heating elements being electronically coupled to at least one of the electronic switches. 
     
     
         4 . The water heater of  claim 3 , wherein the temperature associated with the operation of the electric heating element circuit is at least one of a temperature of a thermal path for conducting heat through the thermally conductive circuit board, a temperature of at least one of the electronic switches, a temperature of electronic components of the water heater, or a temperature of electrical connections of the water heater. 
     
     
         5 . The water heater of  claim 3 , wherein one of the electric heating elements is mounted to an upper portion of a wall of a tank of the water heater, and another one of the electric heating elements is mounted to a lower portion of the wall of the tank. 
     
     
         6 . The water heater of  claim 3 , wherein the controller is electrically coupled to the sensor, the controller being configured to control at least one of the electronic switches based on signals received from the sensor. 
     
     
         7 . The water heater of  claim 6 , wherein the signals received by the controller from the sensor correspond to a sensed temperature of the circuit. 
     
     
         8 . The water heater of  claim 6 , wherein the signals received by the controller from the sensor correspond to a sensed temperature of at least one of the electronic switches. 
     
     
         9 . The water heater of  claim 3 , wherein the sensor is mounted to the thermally conductive circuit board and thermally coupled to at least one of the electronic switches, the sensor being configured to sense a temperature corresponding to a temperature of at least one of the electronic switches. 
     
     
         10 . The water heater of  claim 1 , wherein the negative spike corresponds to a temperature decrease within a fourth predetermined time period. 
     
     
         11 . The water heater of  claim 1 , wherein the positive spike corresponds to a temperature increase within a sixth predetermined time period. 
     
     
         12 . The water heater of  claim 1 , wherein at least one of the positive threshold or the negative threshold changes over time based on a dynamic value of a test signal reflecting the rate of change of the temperature associated with the operation of the electric heating element circuit. 
     
     
         13 . The water heater of  claim 12 , wherein the positive threshold is a dynamic positive threshold that changes based at least in part on the rate of change of the temperature associated with the operation of the electric heating element circuit. 
     
     
         14 . The water heater of  claim 1 , wherein the positive threshold is a dynamic positive threshold that changes over time based on a prediction methodology. 
     
     
         15 . The water heater of  claim 14 , wherein the dynamic positive threshold is calculated using derivative methods to predict low and high raw temperature values in test signals. 
     
     
         16 . The water heater of  claim 15 , wherein the dynamic positive threshold is calculated using at least one of mean values of the test signals and standard deviations from the test signals. 
     
     
         17 . The water heater of  claim 14 , wherein the dynamic positive threshold is calculated by at least one of adding additional percentages to a calculated intermediary positive dynamic threshold value or limiting a minimum value of the positive dynamic threshold value to a predetermined amount. 
     
     
         18 . The water heater of  claim 1 , wherein during the signature test and in response to the negative spike, the controller is further configured to determine if another negative spike occurs within a third predetermined time period, indicating a false positive result from the spike test and no failed or failing operation caused by the open circuit. 
     
     
         19 . A water heater comprising:
 an electric heating element circuit including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element;   a sensor coupled to the electric heating element circuit and configured to detect a rate of change of circuit temperature associated with operation of the electric heating element circuit; and   a controller coupled to the electric heating element circuit, the controller being configured to:
 perform a spike test on the operation of the electric heating element circuit by:
 comparing a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold; and 
 identifying a negative spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is below the negative threshold indicating that the electric heating element circuit may have failed or failing operation caused by an open circuit: or identifying a positive spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is above the positive threshold indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit. 
 
   
     
     
         20 . The water heater of  claim 19 , wherein the sensor is a lower temperature sensor positioned to sense a temperature associated with a lower portion of a wall of a tank of the water heater, the water heater further comprising an upper temperature sensor positioned to sense a temperature associated with an upper portion of the wall of the tank. 
     
     
         21 . The water heater of  claim 20 , wherein at least one of the lower temperature sensor and the upper temperature sensor comprises a thermistor. 
     
     
         22 . The water heater of  claim 19 , further comprising a plurality of electric heating elements and a plurality of electronic switches, each of the electric heating elements being electronically coupled to at least one of the electronic switches. 
     
     
         23 . The water heater of  claim 22 , wherein at least one of the plurality of electronic switches comprises a TRIAC. 
     
     
         24 . The water heater of  claim 22 , wherein the sensor is a dual-purpose temperature sensor thermally coupled to a wall of a tank of the water heater to sense a temperature corresponding to a temperature of the wall of the tank and relating to a temperature of water stored in the tank, and thermally coupled to at least one of the plurality of electronic switches to sense a temperature corresponding to a temperature of the at least one of the plurality of electronic switches. 
     
     
         25 . The water heater of  claim 19 , the sensor comprising a tank wall temperature sensor thermally coupled to a wall of a tank of the water heater, and configured to sense a temperature of the wall of the tank. 
     
     
         26 . The water heater of  claim 19 , wherein the positive threshold is a dynamic positive threshold that changes over time based on a prediction methodology. 
     
     
         27 . The water heater of  claim 26 , wherein the dynamic positive threshold is calculated using derivative methods to predict low and high raw temperature values in test signals. 
     
     
         28 . The water heater of  claim 27 , wherein the dynamic positive threshold is calculated using at least one of mean values of the test signals and standard deviations from the test signals. 
     
     
         29 . The water heater of  claim 26 , wherein the dynamic positive threshold is calculated by at least one of adding additional percentages to a calculated intermediary positive dynamic threshold value or limiting a minimum value of the positive dynamic threshold value to a predetermined amount. 
     
     
         30 . A water heater comprising:
 an electric heating element circuit including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element;   a sensor coupled to the electric heating element circuit and configured to detect a temperature associated with operation of the electric heating element circuit; and   a controller coupled to the electric heating element circuit, the controller being configured to:
 detect whether the electric heating element circuit may have failed or failing operation caused by an open circuit; 
 detect whether the electric heating element circuit may have failed or failing operation caused by a shorted circuit; 
 perform a signature test on the operation of the electric heating element circuit by:
 in response to detecting that the electric heating element circuit may have failed or failing operation caused by an open circuit:
 supplying or continuing to supply the current to the electric heating element for a first predetermined time period; 
 terminating the supply of current after the first predetermined time period; and 
 determining if a drop occurs in the temperature associated with the operation of the electric heating element circuit, indicating no failed or failing operation caused by an open circuit, or does not occur, confirming the failed or failing operation caused by the open circuit; or 
 
 in response to detecting that the electric heating element circuit may have failed or failing operation caused by a shorted circuit:
 terminating the supply of current to the electric heating element for a second predetermined time period; and 
 determining during the second predetermined time period if an increase occurs in the temperature associated with the operation of the electric heating element circuit, confirming the failed or failing operation caused by the shorted circuit, or does not occur, indicating no failed or failing operation caused by the shorted circuit. 
 
 
   
     
     
         31 . The water heater of  claim 30 , wherein the controller is further configured to perform a spike test to detect whether the electric heating element circuit may have failed or failing operation caused by an open circuit or a shorted circuit, by:
 comparing a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold.   
     
     
         32 . The water heater of  claim 31 , wherein the controller is configured to detect whether the electric heating element circuit may have failed or failing operation caused by an open circuit by:
 comparing the rate of change of the temperature associated with the operation of the electric heating element circuit to the negative threshold; and   identifying a negative spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is below the negative threshold indicating that the electric heating element circuit may have failed or failing operation caused by an open circuit.   
     
     
         33 . The water heater of  claim 31 , wherein the controller is configured to detect whether the electric heating element circuit may have failed or failing operation caused by a shorted circuit by:
 comparing the rate of change of the temperature associated with the operation of the electric heating element circuit to the positive threshold; and   identifying a positive spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is above the positive threshold indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit.   
     
     
         34 . The water heater of  claim 33 , wherein the positive threshold is a dynamic positive threshold that changes over time based on a prediction methodology. 
     
     
         35 . The water heater of  claim 34 , wherein the dynamic positive threshold is calculated using derivative methods to predict low and high raw temperature values in test signals. 
     
     
         36 . The water heater of  claim 35 , wherein the dynamic positive threshold is calculated using at least one of mean values of the test signals and standard deviations from the test signals. 
     
     
         37 . The water heater of  claim 35 , wherein the dynamic positive threshold is calculated by at least one of adding additional percentages to a calculated intermediary positive dynamic threshold value or limiting a minimum value of the positive dynamic threshold value to a predetermined amount. 
     
     
         38 . A water heater comprising:
 an electric heating element circuit including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element;   a sensor coupled to the electric heating element circuit and configured to detect a temperature associated with operation of the electric heating element circuit; and   a controller coupled to the electric heating element circuit, the controller being configured to:
 compare a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold; 
 detect a positive spike or a negative spike in the rate of change of the temperature associated with the operation of the electric heating element circuit, indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit or an open circuit, respectively; 
 if a negative spike is detected, terminate the supply of current to the electric heating element after a first predetermined time period; 
 if a positive spike is detected, immediately terminate the supply of current to the electric heating element for a second predetermined time period; and 
 confirm failed or failing operation of the electric heating element circuit if a temperature increase occurs during the second predetermined time period or if a temperature drop occurs during a third predetermined time period after the first predetermined time period. 
   
     
     
         39 . A water heater comprising:
 an electric heating element circuit including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element;   a sensor coupled to the electric heating element circuit and configured to detect a temperature associated with operation of the electric heating element circuit; and   a controller coupled to the electric heating element circuit, the controller being configured to:
 perform a spike test on the operation of the electric heating element circuit by:
 comparing a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold; 
 identifying a negative spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is below the negative threshold indicating that the electric heating element circuit may have failed or failing operation caused by an open circuit; 
 identifying a positive spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is above the positive threshold indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit; 
 
 perform a signature test on the operation of the electric heating element circuit by:
 in response to identifying the negative spike if identified:
 supplying or continuing to supply the current to the electric heating element for a first predetermined time period; 
 terminating the supply of current after the first predetermined time period; and 
 determining if a drop occurs in the temperature associated with the operation of the electric heating element circuit, indicating no failed or failing operation caused by an open circuit, or does not occur, confirming the failed or failing operation caused by the open circuit; 
 
 in response to identifying the positive spike if identified:
 terminating the supply of current to the electric heating element for a second predetermined time period; and 
 determining during the second predetermined time period if an increase occurs in the temperature associated with the operation of the electric heating element circuit, confirming the failed or failing operation caused by the shorted circuit, or does not occur, indicating no failed or failing operation caused by the shorted circuit. 
 
 
   
     
     
         40 . A method for detecting failed or failing operation in a water heater, the method comprising:
 performing a spike test on the operation of an electric heating element circuit, including an electric heating element and interconnection circuitry coupled to the electric heating element and configured to supply current to the electric heating element, by:
 comparing a rate of change of the temperature associated with the operation of the electric heating element circuit to a positive threshold and a negative threshold; 
 identifying a negative spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is below the negative threshold indicating that the electric heating element circuit may have failed or failing operation caused by an open circuit; 
 identifying a positive spike when the rate of change of the temperature associated with the operation of the electric heating element circuit is above the positive threshold indicating that the electric heating element circuit may have failed or failing operation caused by a shorted circuit; 
   performing a signature test on the operation of the electric heating element circuit by:
 in response to identifying the negative spike if identified:
 supplying or continuing to supply the current to the electric heating element for a first predetermined time period; 
 terminating the supply of current after the first predetermined time period; and 
 determining if a drop occurs in the temperature associated with the operation of the electric heating element circuit, indicating no failed or failing operation caused by an open circuit, or does not occur, confirming the failed or failing operation caused by the open circuit; 
 
 in response to identifying the positive spike if identified;
 terminating the supply of current to the electric heating element for a second predetermined time period; and 
 determining during the second predetermined time period if an increase occurs in the temperature associated with the operation of the electric heating element circuit, confirming the failed or failing operation caused by the shorted circuit, or does not occur, indicating no failed or failing operation caused by the shorted circuit.