Fault detection for a water level detection system of a washing machine appliance

Abstract

A washing machine appliance includes a sump for collecting wash fluid, a drain pump for discharging the wash fluid from the sump, and a water level detection system fluidly coupled to the sump. A controller is configured for monitoring the electric current drawn by the drain pump during a drain cycle and determining that the sump is empty based on a drop in the electric current. The controller then measures the sump pressure and determines that a fault condition exists with the water level detection system when the sump is empty and the sump pressure exceeds a predetermined pressure threshold, e.g., zero pressure corresponding to an empty sump.

What is claimed is: 
     
         1 . A washing machine appliance comprising:
 a sump for collecting wash fluid;   a supply valve for providing the wash fluid into the sump;   a drain pump for discharging the wash fluid from the sump;   a water level detection system comprising a pressure sensor fluidly coupled to the sump; and   a controller operably coupled to the supply valve, the drain pump, and the water level detection system, the controller being configured to:
 measure a sump pressure using the water level detection system; 
 operate the drain pump to drain the wash fluid from the sump during a drain cycle; 
 measure an electric current drawn by the drain pump during the drain cycle; 
 determine that the sump is empty based on the electric current drawn by the drain pump; and 
 determine that a fault condition exists with the water level detection system when the sump is empty and the sump pressure exceeds a predetermined pressure threshold. 
   
     
     
         2 . The washing machine appliance of  claim 1 , wherein determining that the sump is empty based on the electric current drawn by the drain pump comprises:
 determining a nominal electric current after initiation of the drain cycle; and   determining that the electric current drawn by the drain pump drops below the nominal electric current by a predetermined current drop percentage.   
     
     
         3 . The washing machine appliance of  claim 2 , wherein the predetermined current drop percentage is between about 5 percent and 50 percent. 
     
     
         4 . The washing machine appliance of  claim 1 , wherein determining that the sump is empty based on the electric current drawn by the drain pump comprises:
 determining a nominal electric current after initiation of the drain cycle; and   determining that the electric current drawn by the drain pump drops below the nominal electric current by a predetermined current drop threshold.   
     
     
         5 . The washing machine appliance of  claim 1 , wherein determining that the sump is empty based on the electric current drawn by the drain pump comprises:
 obtaining a moving average of the electric current drawn by the drain pump; and   determining that a slope of the moving average of the electric current falls below a predetermined slope.   
     
     
         6 . The washing machine appliance of  claim 1 , further comprising:
 a current sensor operably coupled to the drain pump, wherein the electric current drawn by the drain pump is measured at the drain pump using the current sensor.   
     
     
         7 . The washing machine appliance of  claim 1 , wherein the electric current drawn by the drain pump is approximated from a unit current drawn by the washing machine appliance. 
     
     
         8 . The washing machine appliance of  claim 1 , wherein the predetermined pressure threshold is zero or nominal pressure. 
     
     
         9 . The washing machine appliance of  claim 1 , wherein the predetermined pressure threshold corresponds to an empty sump. 
     
     
         10 . The washing machine appliance of  claim 1 , wherein the controller is further configured to:
 operate the supply valve to provide the wash fluid into the sump prior to the drain cycle.   
     
     
         11 . The washing machine appliance of  claim 1 , wherein the controller is further configured to:
 initiate a fault abatement process in response to determining that a fault condition exists with the water level detection system.   
     
     
         12 . The washing machine appliance of  claim 11 , wherein the fault abatement process comprises:
 providing a user indication of the fault condition.   
     
     
         13 . The washing machine appliance of  claim 11 , wherein the fault abatement process comprises:
 adjusting at least one operating parameter of the washing machine appliance.   
     
     
         14 . A method for operating a washing machine appliance, the washing machine appliance comprising a sump for collecting wash fluid, a drain pump for discharging the wash fluid from the sump, and a water level detection system fluidly coupled to the sump, the method comprising:
 measuring a sump pressure using the water level detection system;   operating the drain pump to drain the wash fluid from the sump during a drain cycle;   measuring an electric current drawn by the drain pump during the drain cycle;   determining that the sump is empty based on the electric current drawn by the drain pump; and   determining that a fault condition exists with the water level detection system when the sump is empty and the sump pressure exceeds a predetermined pressure threshold.   
     
     
         15 . The method of  claim 14 , wherein determining that the sump is empty based on the electric current drawn by the drain pump comprises:
 determining a nominal electric current after initiation of the drain cycle; and   determining that the electric current drawn by the drain pump drops below the nominal electric current by a predetermined current drop percentage.   
     
     
         16 . The method of  claim 15 , wherein the predetermined current drop percentage is between about 5 percent and 50 percent. 
     
     
         17 . The method of  claim 14 , wherein determining that the sump is empty based on the electric current drawn by the drain pump comprises:
 obtaining a moving average of the electric current drawn by the drain pump; and   determining that a slope of the moving average of the electric current falls below a predetermined slope.   
     
     
         18 . The method of  claim 14 , wherein the predetermined pressure threshold is zero or nominal pressure. 
     
     
         19 . The method of  claim 14 , wherein the controller is further configured to:
 initiate a fault abatement process in response to determining that a fault condition exists with the water level detection system.   
     
     
         20 . The method of  claim 19 , wherein the fault abatement process comprises:
 providing a user indication of the fault condition.