Patent Publication Number: US-10314456-B2

Title: Dishwashing appliance and methods of operation

Description:
FIELD OF THE INVENTION 
     The present subject matter relates generally to dishwashing appliances, and more particularly to methods for controlling filling and draining of a wash fluid within dishwashing appliances. 
     BACKGROUND OF THE INVENTION 
     Dishwasher appliances or dishwashers generally include a tub that defines a wash chamber. Rack assemblies can be mounted within the wash chamber of the tub for receipt of articles for washing. Spray assemblies within the wash chamber can apply or direct wash fluid towards articles disposed within the rack assemblies in order to clean such articles. Multiple spray assemblies can be provided including e.g., a lower spray arm assembly mounted to the tub at a bottom of the wash chamber, a mid-level spray arm assembly mounted to one of the rack assemblies, and/or an upper spray assembly mounted to the tub at a top of the wash chamber. Other configurations may be used as well. 
     Conventional dishwashers have a water supply valve, such as a solenoid valve for filling the tub with water. An average or typical flow rate through a model water supply valve may be premeasured to provide a reference value for multiple assembled dishwashers. When those dishwashers operate to fill their respective tubs, water filling is controlled by time and the premeasured reference value of flow rate. Nonetheless, variations in individual water supply valves may occur, e.g., due to manufacturing tolerances and/or wear. The premeasured reference value may not exactly match the flow rate through the water supply valve of each assembled dishwasher. In order to accommodate variations in assembled water supply valves, dishwashers may be configured to open the water supply valve for longer than would otherwise be necessary. This may lead to an excessive amount of water (e.g., 0.1 gallon) being added for each filling or wash cycle. Moreover, it may lead to higher water consumption and operating costs for the dishwasher. 
     Conventional dishwashers may also have one or more drain pumps to remove water from the tub. Before assembly, one or more average or typical flow rates through a model drain pump may be premeasured to provide reference values for multiple assembled dishwashers. In turn, draining may be done by time based on the premeasured reference values of flow rates. However, variations in individual drain pumps may also occur, e.g., due to manufacturing tolerances and/or wear. In order to accommodate variations, dishwasher may be configured to operate a drain pump for longer than would otherwise be necessary. This may lead to an excessive drain pump operation, generating undesirable noise and costs. Moreover, it may complicate the dishwasher&#39;s ability to drain only a specific amount of water that might otherwise be used in later wash cycles or steps. 
     Accordingly, it would be advantageous to provide a dishwashing appliance that can accurately and consistently supply and/or drain a select amount of water. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In one aspect of the present disclosure, a method of controlling a dishwashing appliance is provided. The dishwashing appliance may define a vertical direction and include a tub, a base conductivity sensor mounted at a first level within the tub, and an elevated conductivity sensor mounted at a second level within the tub, the second level being higher along the vertical direction than the first level. The method may include initiating a flow of wash fluid into the tub, receiving a signal from the base conductivity sensor in response to wash fluid at the base conductivity sensor, receiving a signal from the elevated conductivity sensor in response to wash fluid at the elevated conductivity sensor, measuring a time period between the signal from the base conductivity sensor and the signal from the elevated conductivity sensor, determining a volumetric flow rate for the flow of wash fluid based on the measured time period, and adjusting the flow of wash fluid into the tub based on the determined volumetric flow rate. 
     In another aspect of the present disclosure, a method of controlling a dishwashing appliance is provided. The dishwashing appliance may define a vertical direction and include a tub, a base conductivity sensor mounted at a first level within the tub, and an elevated conductivity sensor mounted at a second level within the tub, the second level being higher along the vertical direction than the first level. The method may include initiating a drain flow of wash fluid from the tub, receiving a signal from the top conductivity sensor in response to a conductivity break at the top conductivity sensor when wash fluid falls below the upper level within the sump portion, receiving a signal from the middle conductivity sensor in response to a conductivity break at the middle conductivity sensor when wash fluid falls below the intermediate level within the sump portion, and adjusting the drain flow of wash fluid from the tub in response to the signal from the middle conductivity sensor. 
     In yet another aspect of the present disclosure, a dishwashing appliance is provided. The dishwashing appliance may define a vertical direction and include a tub, a sump, a fluid circulation assembly, and a fluid sensor assembly. The tub may define a wash chamber for receipt of articles for washing. The sump may be positioned at a bottom portion of the tub along the vertical direction. The sump including an internal wall defining a collection chamber. The fluid circulation assembly may provide a flow of wash fluid within the wash chamber. The fluid sensor assembly may be disposed within the sump. The fluid sensor assembly may include an isolated sensor enclosure defining a detection cavity in fluid communication with the collection chamber, a base conductivity sensor mounted at a first level within the isolate sensor enclosure, and an elevated conductivity sensor mounted at a second level within the isolated sensor enclosure, the second level being higher along the vertical direction than the first level. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures. 
         FIG. 1  provides a front view of a dishwasher appliance according to an exemplary embodiment of the present disclosure. 
         FIG. 2  provides a side view of the exemplary dishwasher appliance of  FIG. 1 . 
         FIG. 3  provides a front perspective view an internal portion of the exemplary dishwasher appliance of  FIG. 2 , wherein a grate or coarse filter has been removed to reveal a recess in a sump portion of a wash chamber. 
         FIG. 4  provides an exploded view of a portion of the filter system of the exemplary dishwasher appliance of  FIG. 2 . 
         FIG. 5  provides a perspective view of a portion of the tub, including a magnified view of tub receptacle and conductivity sensors, according to an exemplary embodiment of the present disclosure. 
         FIG. 6  provides a magnified perspective view of a tub receptacle and conductivity sensors according to another exemplary embodiment of the present disclosure. 
         FIG. 7  provides a schematic side view of the exemplary tub receptacle and conductivity sensors of  FIG. 6 . 
         FIG. 8  provides a schematic side view of a tub receptacle and conductivity sensors according to an exemplary embodiment of the present disclosure. 
         FIG. 9  provides a schematic side view of a tub receptacle and conductivity sensors according to an exemplary embodiment of the present disclosure, wherein a wash fluid is at a lower first level. 
         FIG. 10  provides a schematic side view of a tub receptacle and conductivity sensors according to an exemplary embodiment of the present disclosure, wherein a wash fluid is at an intermediate second level. 
         FIG. 11  provides a schematic side view of a tub receptacle and conductivity sensors according to an exemplary embodiment of the present disclosure, wherein a wash fluid is at an upper third level. 
         FIG. 12  provides a flow chart of a method of operating a dishwashing appliance, according to an exemplary embodiment of the present disclosure. 
         FIG. 13  provides a flow chart of a method of operating a dishwashing appliance, according to an exemplary embodiment of the present disclosure. 
         FIG. 14  provides a flow chart of a method of operating a dishwashing appliance, according to an exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Generally, the present disclosure may provide a dishwasher appliance and method of operation that can accurately determine or predict the level of wash fluid within a tub portion of the dishwasher appliance. The dishwasher appliance may include multiple conductivity sensors that are mounted at different heights. As wash fluid fills (or is drained from) the tub, the time taken to reach two conductivity sensors may be used to estimate the current fill rate or drain rate. Certain conductivity sensors may additionally or alternatively serve to signal the drain appliance when filling/draining operations should be halted. 
       FIGS. 1 and 2  depict an exemplary domestic dishwasher appliance  100  that may be configured in accordance with aspects of the present disclosure. For the particular embodiment of  FIGS. 1 and 2 , the dishwasher appliance  100  includes a cabinet  102  having a tub  104  therein that defines a wash chamber  106 . The tub  104  includes a front opening (not shown) and a door  120  hinged at its bottom  122  for movement between a normally closed vertical position (shown in  FIGS. 1 and 2 ), wherein the wash chamber  106  is sealed shut for washing operations, and a horizontal open position for loading and unloading of articles from the dishwasher. Latch  123  is used to lock and unlock door  120  for access to wash chamber  106 . 
     Upper and lower guide rails  124 ,  126  are mounted on tub side walls  128  and accommodate roller-equipped rack assemblies  130  and  132 . In optional embodiments, each of the rack assemblies  130 ,  132  is fabricated into lattice structures including a plurality of elongated members  134  (for clarity of illustration, not all elongated members forming assemblies  130  and  132  are shown in  FIG. 2 ). Each rack  130 ,  132  is adapted for movement between an extended loading position (not shown), in which the rack is substantially positioned outside the wash chamber  106 , and a retracted position (shown in  FIGS. 1 and 2 ), in which the rack is located inside the wash chamber  106 . This rack movement is facilitated by rollers  135  and  139 , for example, mounted onto racks  130  and  132 , respectively. A silverware basket (not shown) may be removably attached to rack assembly  132  for placement of silverware, utensils, and the like that are otherwise too small to be accommodated by the racks  130 ,  132 . 
     The dishwasher appliance  100  further includes a lower spray-arm assembly  144  that is rotatably mounted within a lower region  146  of the wash chamber  106  and above a tub sump portion  142  so as to rotate in relatively close proximity to rack assembly  132 . In exemplary embodiments, such as the embodiment of  FIGS. 1 and 2 , one or more elevated spray assemblies  148 ,  150  are provided above the lower spray-arm assembly  144 . For instance, a mid-level spray-arm assembly  148  is located in an upper region of the wash chamber  106  and may be located in close proximity to upper rack  130 . Additionally or alternatively, an upper spray assembly  150  may be located above the upper rack  130 . 
     The lower and mid-level spray-arm assemblies  144 ,  148  and the upper spray assembly  150  are part of a fluid circulation assembly  152  for circulating a wash fluid, such as water and/or dishwasher fluid, in the tub  104 . In turn, fluid circulation assembly  152  may provide a flow of wash fluid within the wash chamber  106 . For instance, fluid circulation assembly  154  includes a water inlet hose  172  in fluid communication with the wash chamber  106  (e.g., through bottom wall and/or sidewall of tub  104 ) to supply water thereto, as generally recognized in the art. The sump portion  142  may thus be filled with water through a fill port  175  that outlets into wash chamber  106 . A water supply valve  174  may be provided to control water to the wash chamber  106 . Water supply valve  174  may have a hot water inlet  176  that receives hot water from an external source, such as a hot water heater and a cold water input  178  that receives cold water from an external source. It should be understood that the term “water supply” is used herein to encompass any manner or combination of valves, lines or tubing, housing, and the like, and may simply comprise a conventional hot or cold water connection. 
     The fluid circulation assembly  152  also includes a recirculation pump  154  positioned in a machinery compartment  140  located below the tub sump portion  142  (i.e., below a bottom wall) of the tub  104 , as generally recognized in the art. The recirculation pump  154  receives fluid from sump  142  to provide a flow to assembly  152 , or optionally, a switching valve or diverter (not shown) may be used to select flow. A heating element  170  can be used to provide heat during, e.g., a drying cycle. 
     Each spray-arm assembly  144 ,  148  includes an arrangement of discharge ports or orifices for directing washing fluid received from the recirculation pump  154  onto dishes or other articles located in rack assemblies  130  and  132 . The arrangement of the discharge ports in spray-arm assemblies  144 ,  148  provides a rotational force by virtue of washing fluid flowing through the discharge ports. The resultant rotation of the spray-arm assemblies  144 ,  148  and the operation of the spray assembly  150  using fluid from the recirculation pump  154  provides coverage of dishes and other dishwasher contents with a washing spray. Other configurations of spray assemblies may be used as well. 
     In some embodiments, the dishwasher appliance  100  is further equipped with a controller  137  to regulate operation of the dishwasher appliance  100 . The controller  137  may include one or more memory devices and one or more microprocessors, such as general or special purpose microprocessors operable to execute programming instructions or micro-control code associated with a cleaning cycle. The memory may represent random access memory such as DRAM or read only memory such as ROM or FLASH. In one embodiment, the processor executes programming instructions stored in memory. For certain embodiments, the instructions include a software package configured to operate appliance  100  and, e.g., execute the exemplary methods  1200 ,  1300 , and/or  1400  described below with reference to  FIGS. 12 through 14 . The memory may be a separate component from the processor or may be included onboard within the processor. Alternatively, controller  137  may be constructed without using a microprocessor, e.g., using a combination of discrete analog and/or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, and the like) to perform control functionality instead of relying upon software. 
     The controller  137  may be positioned in a variety of locations throughout dishwasher appliance  100 . In the illustrated embodiment, the controller  137  may be located within a control panel area  121  of door  120  as shown in  FIGS. 1 and 2 . In some such embodiments, input/output (“I/O”) signals may be routed between the control system and various operational components of dishwasher appliance  100  along one or more wiring harnesses that may be routed through the bottom  122  of door  120 . Optionally, the controller  137  includes a user interface panel/controls  136  through which a user may select various operational features and modes and monitor progress of the dishwasher appliance  100 . In exemplary embodiments, the user interface  136  may represent a general purpose I/O (“GPIO”) device or functional block. For instance, the user interface  136  may include input components, such as one or more of a variety of electrical, mechanical, or electro-mechanical input devices including rotary dials, push buttons, and touch pads. The user interface  136  may include a display component, such as a digital or analog display device designed to provide operational feedback to a user. The user interface  136  may be in communication with the controller  137  via one or more signal lines or shared communication busses. 
     It should be appreciated that the invention is not limited to any particular style, model, or configuration of dishwasher. The exemplary embodiment depicted in  FIGS. 1 and 2  is for illustrative purposes only. For example, different locations may be provided for user interface  136 , different configurations may be provided for racks  130 ,  132 , and other differences may be applied as well. 
     Referring now to  FIGS. 2 , through  4 , an exemplary filtering system  200  is provided. As shown, in exemplary embodiments, filtering system  200  is located in the sump portion  142  and provides filtered fluid to the pump inlet  162 . Generally, filtering system  200  removes soiled particles from the fluid that is recirculated through the wash chamber  106  during operation of dishwasher appliance  100 . In exemplary embodiments, filtering system  200  includes both a first filter  202  (also referred to as a “coarse filter”) and a second filter  204  (also referred to as a “fine filter”). 
     In some embodiments, the first filter  202  is constructed as a grate having openings  218  for filtering fluid received from wash chamber  106 . The sump portion  142  includes a recessed portion  216  over which the first filter  202  is removably received. In one exemplary embodiment, the first filter  202  operates as a coarse filter having media openings  218  in the range of about 0.030 inches to about 0.060 inches. The recessed portion  216  may define a filtered volume wherein debris or particles have been filtered by the first filter  202  and/or the second filter  204 . As shown, pump inlet  162  is defined within recessed portion  216 . A recirculation conduit  156  may be disposed in fluid communication with the pump inlet  162  and the recirculation pump  154 . During certain operations, wash fluid may selectively flow through pump inlet  162  and recirculation conduit  156  before being motivated, e.g., by the recirculation pump  154 , to one or more of lower spray arm assembly  144 , mid-level spray-arm assembly  148 , or upper spray assembly  150 . 
     The second filter  204  may be non-removable or can be provided as a removable cartridge positioned in a tub receptacle  212  formed in sump portion  142 . Specifically, the second filter  204  may be removably positioned within a collection chamber  232  defined by tub receptacle  212 . The second filter  204  may be generally shaped to complement tub receptacle  212 . For instance, the second filter  204  may include a cylindrical wall  226  that complements a generally cylindrical shape of tub receptacle  212 . Alternatively, tub receptacle  212  may have a suitable non-cylindrical shape to receive the second filter  204  and direct fluid to the drain outlet  210  through cylindrical wall  226 . 
     Cylindrical wall  226  may be formed from one or more fine filter media. Some such embodiments may include filter media, e.g., screen or mesh, having pore or hole sizes in the range of about 50 microns to about 600 microns. As illustrated, cylindrical wall  226  may define an internal chamber  224 . A top portion  214  of fine filter positioned above internal chamber  224  may define one or more openings  228  permitting fluid to flow into internal chamber  224  without passing through the first filter  202  or the fine filter media of cylindrical wall  226 . Top portion  214  may include a handle that allows a user to grasp and remove the second filter  204  for replacement or cleaning. An opening  222  defined through the first filter  202  allows for positioning of the second filter  204  into receptacle  212 . 
     Between openings  228  and drain pump  208 , internal chamber  224  defines an unfiltered volume. An exit conduit  209  may be positioned downstream from drain pump  208  in fluid communication with internal chamber  224 . As illustrated, exit conduit  209  may extend to a drain outlet  210 . During certain operations, debris or particles may pass through openings  228  and into internal chamber  224 . When drain pump  208  is activated, fluid and/or particles within internal chamber  224  may be directed through exit conduit  209  and drain outlet  210 , flowing wash fluid to an area outside of appliance  100 , e.g., an ambient area. 
     Based on the shape of the sump portion  142  ( FIG. 2 ), during certain operations, e.g., washing or cleaning cycles, fluid flows down along a primary flow direction, e.g., in fluid series from the wash chamber  106  to the recessed portion  216 , for filtration in the filtering system  200 . After the fluid is filtered by passing through the first filter  202  or the second filter  204  the filtered fluid is fed to the inlet  162  of the recirculation pump  154  for return to the wash chamber  106  by way of fluid circulation assembly  152 . Optionally, one or more sensors, e.g., turbidity sensors, may be disposed within fluid circulation assembly  152 , e.g., at pump inlet  162 , for monitoring a condition of recirculated fluid during operations. After being sprayed onto articles in the dishwasher appliance  100  using one or more of the spray elements  144 ,  148 , and  150 , the fluid eventually flows to sump portion  142  and is filtered again. Although a separate recirculation pump  154  and drain pump  208  are described herein, it is understood that other suitable pump configurations, e.g., using only a single pump for both recirculation and draining, may be provided. 
     Turning to  FIGS. 5 through 11 , receptacle  212  of the sump portion  142  includes an internal wall  230  defining a collection chamber  232  into which wash fluid may collect. Internal wall  230  may, for instance, define a generally cylindrical or frusto-conical collection chamber  232  above drain outlet  210  in fluid communication with fluid circulation assembly  152  ( FIG. 2 ). Internal wall  230  may generally extend about a sump axis SA defined thereby. Second filter  204  may further extend about the sump axis SA, e.g., at the cylindrical wall  226 , when mounted within sump portion  142 . In turn, cylindrical wall  226  is positioned radially inward (i.e., closer to sump axis SA along a radial direction R) from internal wall  230 . 
     A fluid sensor assembly  240  is disposed within the sump portion  142  to detect the amount of wash fluid that is and/or will be contained in the sump portion  142 . In certain embodiments, a plurality of conductivity sensors  242 ,  244 ,  246  is mounted within receptacle  212 . At least a portion of each conductivity sensor  242 ,  244 ,  246  may be contained within sump portion  142 . Specifically, at least a portion of each conductivity sensor  242 ,  244 ,  246  may be in fluid communication with collection chamber  232 . Each conductivity sensor  242 ,  244 ,  246  may further be operably connected (e.g., electrically coupled) to controller  137  to communicate therewith. For instance, conductivity sensors  242 ,  244 ,  246  may be operably connected to controller  137  via one or more suitable transmission paths, such as that defined by wire or wireless communications band. Controller  137  and/or conductivity sensors  242 ,  244 ,  246  may thus send and/or receive one or more signals therebetween. 
     In some embodiments, the conductivity sensors  242 ,  244 ,  246  are provided at various discrete levels or positions along the vertical direction V. These various levels include a lower or first level  252  as well as one or more elevated levels  254 ,  256  that are higher along the vertical direction V than the lower or first level  252 . In certain embodiments, a base conductivity sensor  242  is mounted at the lower or first level  252 , while an elevated conductivity sensor  244  or  246  is mounted at a level  254  or  256  above the first level  252 . In optional embodiments, at least one discrete conductivity sensor is provided at each of three different levels  252 ,  254 ,  256 . For instance, base conductivity sensor  242  is mounted at the lower or first level  252 , a middle or elevated conductivity sensor  244  is mounted at an intermediate or second level  254 , and a top or additional elevated conductivity sensor  246  is mounted at an upper or third level  256  that is higher than both the first level  252  and second level  254 . Optionally, one or more conductivity sensors  242 ,  244 ,  246  may include a pair of parallel sensors  242 A,  242 B. For instance, base conductivity sensor  242  includes a paired first sensor  242 A and a paired second sensor  242 B, each being mounted at parallel positions along the first level  252 . Each parallel sensor of the pair  242 A,  242 B may be spaced apart (e.g., circumferentially about the sump axis SA) at a predetermined distance such that water contacts each at the same vertical fluid level but does not bridge respective electrodes of the parallel sensors  242 A,  242 B. 
     Fluid sensor assembly  240  further provides a sensor enclosure  260  that covers or extends over one or more of conductivity sensors  242 ,  244 ,  246 . In some such embodiments, sensor enclosure  260  defines a detection cavity  262  in fluid communication with collection chamber  232 . For instance, sensor enclosure  260  may include opposing sidewalls  264  and a rear wall  266  that extending radially outward from internal wall  230  of the sump portion  142 . Together, sidewalls  264  and rear wall  266  may define detection cavity  262 . 
     A leveling partition  268  may be positioned radially outward from collection chamber  232 , e.g., between collection chamber  232  and detection cavity  262 . Leveling partition  268  may form a solid barrier spanning at least a portion of opposing sidewalls  264 . Wash fluid may thus be prevented or restricted from passing directly through the leveling partition. In some embodiments, sensor enclosure  260  defines a bottom channel  270 , e.g., beneath partition and/or between opposing sidewalls  264 . Bottom channel  270  may be defined below base conductivity sensor  242  in fluid communication between collection chamber  232  and detection cavity  262 . 
     A vent aperture  272  may further be defined above bottom channel  270 . For instance, vent aperture  272  may extend above leveling partition  268 , e.g., between opposing sidewalls  264 . Moreover, vent aperture  272  may be defined at a position above the uppermost conductivity sensor, e.g., top conductivity sensor  246 . Vent aperture  272  may be defined in fluid communication between a portion of the sump  142  and detection cavity  262 . 
     As the volume or height of wash fluid within sump portion  142  rises and/or falls, the level of wash fluid within detection cavity  262  will similarly rise and/or fall. In other words, the level of wash fluid within collection chamber  232  may be substantially the same as the level of wash fluid within detection cavity  262 . However, the level of wash fluid within detection cavity  262  may be advantageously isolated from turbulence, e.g., caused by the swirling of water, that would otherwise affect the height of wash fluid within sump portion  142  and complicate the detection of a fluid level. 
     As noted above, a plurality of conductivity sensors  242 ,  244 ,  246  may be provided at various levels  252 ,  254 ,  256 . In some embodiments, the conductivity sensors  242 ,  244 ,  246  are mutually connected to detect variations in conductivity across fluid sensor assembly  240 . A change in conduction, e.g., such as that causes by wash fluid spanning the distance between two or more of conductivity sensors  242 ,  244 ,  246 , may cause an electrical conduction circuit to be completed. In turn, completion of the circuit may generate a signal indicating detection of a specific level of wash fluid at a given moment. For instance, completion of the circuit between the pair of parallel sensors  242 A,  242 B of base conductivity sensor  242  may indicate detection of wash fluid at the first level  252 ; completion of the circuit between base conductivity sensor  242  and middle conductivity sensor  244  may indicate detection of wash fluid at the second level  254 ; and completion of the circuit between base conductivity sensor  242  and top conductivity sensor  246  may indicate detection of wash fluid at the third level  256   
     As described above, each conductivity sensor  242 ,  244 ,  246  may be connected to the controller  137 . Optionally, the controller  137  can receive a unique signal in response to the completion or break of each conduction circuit. In some embodiments, controller  137  is configured to determine a volumetric flow rate for wash fluid based on one or more received signals from the plurality of conductivity sensors  242 ,  244 ,  246 . 
     As an example, when wash fluid is supplied to wash chamber  106 , controller  137  may measure a time period between the moment a signal is received from base conductivity sensor  242  (e.g., when the conduction circuit is completed at base conductivity sensor  242 ) and the moment a signal is received from one of the elevated conductivity sensors  244 ,  246 , (e.g., when the conduction circuit is completed between base conductivity sensor  242  and elevated conductivity sensor  244  or  246 ). As an additional or alternative example, when wash fluid is being drained from wash chamber  106 , e.g., through drain outlet  210  via pump(s)  152 ,  208  ( FIG. 2 ), the controller  137  may measure a time period between the moment a signal is received from top conductivity sensor  246  (e.g., when the conduction circuit between top conductivity sensor  246  and base conductivity sensor  242  is broken) and the moment a signal is received from middle conductivity sensor  244  (e.g., when the conduction circuit between top conductivity sensor  246  and base conductivity sensor  242  is broken). Each level  252 ,  254 ,  256  of sensors  242 ,  244 ,  246  may correspond to a known fluid volume (e.g., of collection chamber  232 ), so the measured time period may be used to determine the change in fluid volume over time, i.e., the volumetric flow rate. 
     In some embodiments, controller  137  is further configured to adjust or change an operational setting according to received signals. As an example, controller  137  may initiate a valve closure, e.g., at water supply valve  174  ( FIG. 3 ), in response to receiving a signal from one or more of the conductivity sensors  242 ,  244 ,  246 . Optionally, controller  137  may initiate closing of supply valve  174  to terminate the flow of wash fluid therethrough once a signal has been received from the top conductivity sensor  246 . As an additional or alternative example, controller  137  may deactivate pump(s)  152 ,  208  ( FIG. 2 ) to halt or terminate draining in response to receiving a signal, e.g., indicating a break in conductivity, from one or more of the conductivity sensors  242 ,  244 ,  246 . Optionally, controller  137  may deactivate pump(s)  152 ,  208  in response to receiving a signal from base conductivity sensor  242  (e.g., when the conduction circuit between the pair of parallel sensors  242 A,  242 B is broken). 
     In additional or alternative embodiments, the controller  137  is configured to adjust or change an operational setting based specifically on the determined volumetric flow rate. For instance, a fill point or target point for when a desired wash fluid volume will be reached may be calculated. The controller  137  may adjust (e.g., increase or decrease) the flow of wash fluid to/from the wash chamber  106  according to the fill point and/or target point. Optionally, the controller  137  may permit filling or draining to occur only up until the fill point or target point is met. 
     Turning now to  FIGS. 12 through 14 , various methods  1200 ,  1300 , and  1400  for operating a dishwashing appliance are illustrated. Methods  1200 ,  1300 , and  1400  may be used to operate any suitable dishwashing appliance. As an example, some or all of methods  1200 ,  1300 , and  1400  may be used to operate dishwashing appliance  100  ( FIG. 1 ). The controller  137  ( FIG. 2 ) may be programmed to implement some or all of methods  1200 ,  1300 , and  1400 . 
     Turning specifically to  FIG. 12 , method  1200  may include, at  1210 , initiating a flow of wash fluid into a tub, e.g., within a wash chamber, of the dishwashing appliance. In some embodiments, water is supplied to the wash chamber through a water supply valve, as described above. For instance, the water supply valve may be opened to permit the flow of water into tub, including a sump portion. 
     At  1220 , the method  1200  may include receiving a signal from a base conductivity sensor in response to wash fluid at the base conductivity sensor. The signal may indicate detection of a wash fluid at a base conductivity sensor. As described above, the base conductivity sensor may include two parallel sensors. Wash fluid within the sump at the level of the base conductivity sensor may form an electrical circuit connecting the two parallel sensors. In turn,  1220  may include detecting conductivity between the two parallel sensors e.g., continuity of the circuit between the two parallel circuits. 
     At  1230 , the method  1200  may include receiving a signal from an elevated conductivity sensor in response to wash fluid at the elevated conductivity sensor. The signal may indicate detection wash fluid at the elevated conductivity sensor. Wash fluid spanning the vertical distance between the base conductivity sensor and the elevated conductivity sensor may form an expanded electrical circuit. In other words, a circuit connecting the base conductivity sensor and the elevated conductivity sensor. In some embodiments,  1230  includes detecting conductivity between the base conductivity sensor and the elevated conductivity sensor, e.g., continuity of the expanded circuit between the base conductivity sensor and the elevated conductivity sensor. 
     At  1240 , the method  1200  may include measuring a time period between the signal from the base conductivity sensor and the signal from the elevated conductivity sensor, e.g., measuring the time period between  1220  and  1230 . For instance, a timer may be started once wash fluid is detected at the base conductivity sensor. The timer may be subsequently stopped once wash fluid is detected at the elevated conductivity sensor. The measured time may be the recorded time period between the moment the timer was started and the moment the timer was stopped, which generally corresponds to the time taken for wash fluid to rise from the base conductivity sensor to the elevated conductivity sensor. 
     At  1250 , the method  1200  may include determining a volumetric flow rate for the flow of wash fluid based on the measured time period. The appliance may include predetermined information regarding the volume of the sump portion of the dishwashing appliance. For instance, a controller may store a predetermined volume of the dishwashing appliance for the sump portion that is below the level at which the base conductivity sensor is mounted. The controller may also store predetermined volumes for the sump portions that are below each of the elevated conductivity sensor and the additional conductivity sensor. The determined volumetric flow rate may be calculated as the total volume that is filled over the measured time period. 
     At  1260 , the method  1200  may include adjusting the flow of wash fluid into the tub based on the determined volumetric flow rate. For instance, a baseline volumetric flow rate may be included with the appliance (e.g., stored within controller) for comparison to the determined volumetric flow rate. In some embodiments, if the baseline volumetric flow rate is below the desired volumetric flow rate, the time during which water supply valve remains open may be increased. If the determined volumetric flow rate is above the baseline volumetric flow rate, the time during which water supply valve remains open may be decreased. In additional or alternative embodiments, if the baseline volumetric flow rate is below the desired volumetric flow rate, the opening of water supply valve may be increased. If the determined volumetric flow rate is above the baseline volumetric flow rate, the opening of water supply valve may be decreased. The flow of wash fluid into the tub may be halted or terminated. Optionally,  1260  may include terminating, e.g., immediately terminating, the flow of wash fluid in response to receiving a signal from an additional elevated conductivity sensor indicating wash fluid. 
     In certain embodiments, the method  1200  further includes calculating a fill time for when a desired wash fluid volume will be reached within the tub based on the determined volumetric flow rate. For example, the fill time may be a future time or period of time at which the desired wash fluid volume will be reached if the determined volumetric flow rate remains constant. Flow of wash fluid into the tub may be terminated at the expiration of the target point. Advantageously, over-filling of the sump portion may thus be prevented. 
     In further optional embodiments, the method  1200  includes receiving a signal from an additional elevated conductivity sensor in response to wash fluid at the additional elevated conductivity sensor, as described above. The method  1200  may include measuring a new time period between the signal from the elevated conductivity sensor and the signal from the additional elevated conductivity sensor, as described above. Based on the new time period, the method  1200  may include determining a revised volumetric flow rate for the flow of wash fluid. Subsequently, the method  1200  may provide for adjusting the flow of wash fluid into the tub based on the revised volumetric flow rate. 
     Turning specifically to  FIG. 13 , method  1300  may include, at  1310 , initiating a drain flow of wash fluid from the tub. In some embodiments, wash fluid is drained from the wash chamber through one or more pumps, as described above. For instance, a pump may be activated to force the flow of wash fluid through and from the sump portion. 
     At  1320 , the method  1300  may include receiving a signal from the top conductivity sensor in response to a conductivity break at the top conductivity sensor when wash fluid falls below an upper level within the sump portion. As described above, a circuit may be initially formed by the wash fluid extending from the top conductivity sensor to the base conductivity sensor. When the wash fluid falls below the top conductivity sensor, i.e., below the upper level at which the top conductivity sensor is mounted, the circuit between the top conductivity sensor and the base conductivity sensor will be broken. The controller may be configured to detect such a break in conductivity, e.g., the moment at which the conductivity between the top circuit and the base circuit no longer exists. Although the circuit between the top conductivity sensor and the base conductivity sensor is broken, the circuit between the middle conductivity sensor and the base conductivity sensor may be detected. 
     At  1330 , the method  1300  may include receiving a signal from a middle conductivity sensor in response to a conductivity break at the middle conductivity sensor when wash fluid falls below an intermediate level within the sump portion. When the wash fluid falls below the middle conductivity sensor, i.e., below the intermediate level at which the top conductivity sensor is mounted, the circuit between the middle conductivity sensor and the base conductivity sensor will be broken. The controller may be configured to detect such a break in conductivity, e.g., the moment at which the conductivity between the middle circuit and the base circuit no longer exists. Although the circuit between the middle conductivity sensor and the base conductivity sensor is broken, the circuit at the base conductivity sensor may be detected, e.g., the circuit between two parallel sensors. 
     In optional embodiments, the method  1300  may further include measuring a time period between  1310  and  1320 . For instance, a timer may be started once a circuit between the top conductivity sensor and the base sensor is broken. The timer may be subsequently stopped once a circuit between the middle conductivity sensor and the base conductivity sensor is broken. The measured time may be the recorded time period between the moment the timer was started and the moment the timer was stopped, which generally corresponds to the time taken for wash fluid to fall from the top conductivity sensor to the middle conductivity sensor. 
     Further embodiments of the method  1300  may include determining a volumetric flow rate for the drain flow of wash fluid based on the measured time period. The dishwashing appliance may include predetermined information regarding the volume of the sump portion of the dishwashing appliance. For instance, a controller may store a predetermined volume of the dishwashing appliance for the sump portion that is below the level at which the base conductivity sensor is mounted. The controller may also store predetermined volumes for the sump portions that are below each of the elevated conductivity sensor and the additional conductivity sensor. The determined volumetric flow rate may be calculated as the volume that is drained over the measured time period. 
     At  1340 , the method  1300  may include adjusting the drain flow of wash fluid from the tub in response to the signal from the middle conductivity sensor, e.g.,  1330 . For instance,  1340  may include deactivating a pump to stop draining wash fluid at the moment the circuit between the middle conductivity sensor and the base conductivity sensor is broken. Additionally or alternatively,  1340  may include changing an operational speed of the pump such that the rate of drain flow is increased or decreased. 
     In some embodiments, the method  1300  includes adjusting the drain flow of the dishwashing appliance according to the determined volumetric flow rate. The method  1300  may include calculating a target point for when a desired wash fluid volume will be reached within the tub, e.g., at the sump portion, based on the determined volumetric flow rate. For instance, the target point may be an estimated time period at which the wash fluid will be substantially drained from the tub. Alternatively, the target point may be an estimated time period at which only a select amount of wash fluid remains within the tub. Adjusting the drain flow may include deactivating the pump according to the target point, e.g., at the moment at which the estimated time period expires. 
     Additionally or alternatively, adjusting the drain flow of method  1300  may include deactivating the pump when no water is detected in the sump portion of the tub. In other words, when an absence of water is detected within the sump portion of the tub. The pump may be deactivated after a predetermined time period once a signal is received from the base sensor. For instance, once a circuit at the base sensor is broken. Alternatively, the pump may be deactivated immediately once a signal is received from the base sensor. Optionally, detecting an absence of water may override or supersede deactivation based on the target point. 
     Turning specifically to  FIG. 14 , method  1400  may provide a discrete cleaning cycle to be performed. Optionally, the method  1400  may be initiated, for example, in response to received input signal provided by a user at the user interface of an appliance. 
     At  1410 , the method  1400  may include initiating a water flow into the wash chamber of a dishwashing appliance. A water supply valve may be opened and wash fluid may begin filling a tub, e.g., in a sump portion of the dishwasher appliance. Once a certain volume of wash fluid fills the tub, continuity (e.g., a continuous circuit) may be detected at a base conductivity sensor a between a pair of parallel sensors, as described above. 
     At  1420 , the method  1400  may include determining a fill rate. Optionally,  1420  may occur in response to  1410  being completed. At  1420 , a timer may be started. Once a certain increased volume of wash fluid fills the tub, continuity (e.g., a continuous circuit) may be detected between the base conductivity sensor and a middle conductivity sensor. The timer may be stopped in response to continuity between all three conductivity sensors. A fill rate may be calculated based on the time measured, e.g., volume filled over the time measured. 
     At  1430 , the method  1400  may include directing a required fill volume of wash fluid to the wash chamber based on the determined fill rate. Optionally, the required fill volume may be calculated as a function of time and the determined fill rate. Wash fluid may be steadily supplied to tub, e.g., through water supply valve, until the required fill volume is reached. Once the required fill volume is reached, the water supply valve may be closed. 
     At  1440 , the method  1400  may include initiating a wash operation. The wash operation may start washing dishes within the tub and continue until it is determined that washing is complete. Once washing is determined to be complete,  1440  may include starting or activating a drain pump. 
     At  1450 , the method  1400  may include determining a drain rate. A continuous circuit may be detected between a top conductivity sensor and the base conductivity sensor, as described above. Once the continuity or continuous circuit is broken at the top conductivity sensor, the timer may be started to measure a drain time. The timer may be subsequently stopped once the continuity or continuous circuit is broken at the middle conductivity sensor. A drain rate may be calculated for the volume of water drained between the top and middle conductivity sensors over the drain time measured by the timer. 
     At  1460 , the method  1400  may include draining a required volume of wash fluid (e.g., the remaining volume of wash fluid) from the sump. Optionally, the required drain volume may be calculated as a function of time and the determined drain rate. Wash fluid may be steadily removed from tub, e.g., through drain pump, until the required drain volume is reached. Once the required fill volume is reached, draining may be terminated. The drain pump may be stopped or deactivated. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.