Abstract:
In accordance with one embodiment, energy savings is achieved in a cooktop by reducing the energy supplied to a burner when no cooking vessel is present. A sensor communicates the presence or absence of the cooking vessel to a controller. When the cooking vessel is present, the controller signals a valve by means of a digital-to-analog converter to allow energy to flow to burner unrestricted. When the cooking vessel is not present, the controller signals valve to restrict the flow of energy to burner.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefits of the earlier filed U.S. Provisional Application Ser. No. 60/959,559, filed 16 Jul. 2007 (16.07.2007) and the earlier filed U.S. Provisional Application Ser. No. 60/961,108, filed 19 Jul. 2007 (19.07.2007), which are incorporated by reference for all purposes into this specification. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to the field of cooktops and ranges (defined as an integrated cooktop and oven), and in particular a cooktop or range that includes an energy saving feature that reduces or removes the heat applied to a burner when the pan or other cooking vessel is removed from the burner. 
         [0004]    Cooking in an institutional or commercial setting is a very challenging and hectic enterprise. Chefs are typically racing to complete a variety of dishes simultaneously, which can lead them to take whatever shortcuts are practical. In this environment, it is common for a burner to be consuming energy while a pan is not in place. 
         [0005]    Commercial kitchens are near the top of the list of greatest energy usage per square foot in a commercial setting, and therefore offer some of the best opportunities for reducing the amount of energy consumed. The automation of the control of the gas, electricity, or other fuel as a function of the presence of a cooking vessel on a cooktop could yield significant energy savings. 
         [0006]    Most business owners are becoming increasingly aware of the need to conserve energy and other natural resources. Consumer sentiment and the regulatory climate demand that owners take every reasonable opportunity to preserve the environment. Additionally, many such owners have a strong personal interest in conservation. Therefore, products such as a cooktop that uses less energy have a strong and rapidly increasing market demand. 
         [0007]    The energy savings is multiplied in the case of a cooktop that uses less energy. Most commercial kitchens require substantial air conditioning capacity in order to maintain a reasonably comfortable environment for the kitchen staff. Reducing energy usage by the primary cooking equipment, such as the cooktops, provides a secondary benefit by reducing the required air conditioner tonnage. 
         [0008]    In addition, labor shortages are among the biggest issues encountered by operators of commercial kitchens. Innovations that improve the working conditions in a commercial kitchen would serve to increase the attractiveness of kitchen jobs. By using a cooktop that consumes less energy, owners will be able to provide a more comfortable environment for their employees without increasing their operating costs. 
         [0009]    2. Prior Art 
         [0010]    Previously, inventors have endeavored to sense the positioning of a cooking vessel on the burner of a cooktop. For instance, Smolenski, et al, in U.S. Pat. No. 6,350,971, issued in February 2002, sense lateral or rotational movement of a pan on a ceramic or glass cooktop in order to reduce the possibility of erroneously signaling a “boil-dry” condition. They also endeavor to reduce the power applied to a burner when a true “boil-dry” condition exists. However, they do not detect the presence or absence of a pan, nor do they decrease the power to the burner when the pan is absent in order to save energy. 
         [0011]    In a similar vein, Smith in U.S. Pat. No. 4,334,135, issued in June 1982, describes a method to detect the condition of a cooking vessel being placed off-center on a burner, but does not describe the advantages of the present invention. 
         [0012]    Others, including Scott in U.S. Pat. No. 5,977,523, issued in November 1999, and Gross, et al, in U.S. Pat. No. 5,491,423, issued in February 1996, describe means to detect the size of a pot placed on a glass ceramic cooktop so that the appropriate portion of a burner can be energized. This technique protects the portion of the cooktop not covered by the pot from excessive temperatures that can damage the surface of the cooktop. 
         [0013]    Some inventors have described the use of inductive sensors to detect the presence or absence of a pan on a burner, but have been forced by the difficulties inherent in this approach to limit the applicability to very convoluted and specific implementations. Inductive sensors have the additional weakness of only being effective with metal pans. 
         [0014]    For instance, Scott, in U.S. Pat. No. 5,900,174, issued in May 1999, describes a method using an inductive sensor placed in proximity to an electric burner that must track two separate decreases in signal in an attempt to distinguish between removal of a pot and a transition by the burner through its Curie temperature. 
         [0015]    Similarly, Turetta, et al, in U.S. Pat. No. 5,424,512, issued in June 1995, describe a method of detecting the presence of a pan, requiring that an inductive sensor be placed directly between the heating element and the surface of a glass ceramic cooktop. Unfortunately, few industrial environments are worse suited for the reliable deployment of an electronic sensor. 
         [0016]    Finally, Essig, et al, in U.S. Pat. No. 5,296,684, issued in March 1994, describe an attempt to overcome the weaknesses inherent in the use of inductive sensors by sensing the rate of change of the signal rather than the strength of the signal. 
       SUMMARY 
       [0017]    In accordance with one embodiment, energy savings is achieved in a cooktop or range by reducing the energy supplied to a burner when no cooking vessel is present. A sensor communicates the presence or absence of the cooking vessel to a controller. When the cooking vessel is present, the controller signals a valve to allow energy to flow to the burner unrestricted. When the cooking vessel is not present, the controller signals the valve to restrict the flow of energy to the burner. 
     
    
     
       DRAWINGS 
       Figures 
         [0018]      FIG. 1A  is a block diagram of the first embodiment. 
           [0019]      FIG. 1B  is a block diagram of an embodiment of the digital-to-analog buffer circuit required in the first embodiment. 
           [0020]      FIG. 2  is a perspective view of an embodiment of an electric field electrode. 
           [0021]      FIG. 3A  is a perspective view of an embodiment of an electric field electrode installed in a stove. 
           [0022]      FIG. 3B  is a cross-section view of the embodiment of  FIG. 3A . 
           [0023]      FIG. 4  is a flow chart of the software that controls the first embodiment. 
           [0024]      FIG. 5A  is a perspective view of an alternative embodiment for an electric field electrode. 
           [0025]      FIG. 5B  is a detailed view of the alternative embodiment of  FIG. 5A . 
           [0026]      FIG. 6  is a perspective view of a manual rotary gas valve driven by a motor. 
           [0027]      FIG. 7  is a perspective view of an optical detector installed in a stove. 
           [0028]      FIG. 8  is a perspective view of an ultrasonic detector installed in a stove. 
           [0029]      FIG. 9  is a perspective view of an alternative piping system that reduces the flow of gas when the energy saving mode is entered. 
           [0030]      FIG. 10  is a block diagram of an alternative embodiment that includes a keypad and display. 
       
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     FIGS.  1 - 4   
       [0031]    A block diagram of one embodiment of the energy saving cooktop system is illustrated in  FIG. 1A . A microcontroller  110  is connected to a digital-to-analog converter  112  and an electric field sensor  120 . The electric field sensor  120  comprises an electric field sensing integrated circuit  122 , an electric field electrode  128 , a signal connection  124 , and a shield connection  126 . Signal connection  124  is affixed to integrated circuit  122  and to electrode  128 . Shield connection  126  is affixed only to integrated circuit  122 . Electrode  128  is mounted in proximity to one burner of a cooktop (not shown in this figure). 
         [0032]    The digital-to-analog converter  112  connects the microcontroller  110  and an electronically controlled valve, also called a solenoid valve,  130 . Valve  130  comprises a gas inlet  132 , a gas outlet  134 , and a solenoid  136 . One of the electrical leads of solenoid  136  is connected to a standard direct current power supply (not shown). The other electrical lead of solenoid  136  is connected to digital-to-analog converter  112 . 
         [0033]    When in operation, the embodiment illustrated in  FIG. 1A  senses the presence or absence of a cooking vessel on the burner of a range or cooktop. Integrated circuit  122  drives a voltage waveform on signal connection  124 . The voltage waveform causes electrode  128  to generate a low level electric field. Integrated circuit  122  detects the variation in field loading caused by objects moving into and out of the electric field. The variation in field loading is due to a change in the total capacitance between the electrode and the circuit ground. As a result, the objects that are to be detected do not have to be metallic. Instead, they must be electrically conductive or must have a different dielectric constant than air. The inventor currently favors the use of Freescale Semiconductor&#39;s MC33941 e-field sensor device because it supports enough electrodes to control all the burners on most ranges. However, other integrated circuits can be easily substituted. 
         [0034]    Integrated circuit  122  generates a secondary signal that can be used when electrode  128  is located remotely, as would be the case in this application. The printed circuit board containing integrated circuit  122  usually will be mounted at least 25 centimeters away from any burner due to limitations on the upper operating temperature of typical integrated circuits. Conversely, electrode  128  should be located in close proximity to the burner to maximize the magnitude of the signal it generates when a pan is placed on the burner and removed from the burner. The secondary signal of integrated circuit  122  is joined to shield connection  126 . The secondary signal is a copy of the voltage waveform driven on signal connection  124 . The current flow between the signal connection  124  and shield connection  126  is proportional to the difference in voltage between them. Therefore, if shield connection  126  is maintained in close proximity to signal connection  124 , electrode  128  can be remotely located from integrated circuit  122  with minimal affect on the current flowing in signal connection  124 . 
         [0035]    Integrated circuit  122  measures the current flowing in signal connection  124  and converts the result to a DC voltage that is output on one of its pins. An analog-to-digital converter input of microcontroller  110  is connected to the DC voltage output pin of integrated circuit  122 . Thus, by performing sequential analog-to-digital conversions of the voltage, microcontroller  110  can generate a digital record of the electric field loading on electrode  128  versus time. 
         [0036]    When power is applied to the system, a calibration process is performed. Microcontroller  110  performs several analog-to-digital conversions of the DC voltage being output by integrated circuit  122 , averages the readings, and stores the result as a benchmark value. 
         [0037]    Initially, the burner controlled by the embodiment of  FIG. 1A  is enabled. That is, electronically controlled valve  130  is placed in its open position by de-energizing solenoid  136 . This allows the free flow of gas from gas inlet  132  to gas outlet  134 . The inventor currently favors the use of a normally open valve in this application, as a failure of the system would allow a burner to be used without the energy savings feature until repairs could be made. However, a normally closed valve can be used if desired. In this embodiment, the burner is disabled by energizing solenoid  136 , which causes the valve to close, thus preventing the flow of gas from gas inlet  132  to gas outlet  134 . 
         [0038]    Microcontroller  110  periodically performs an analog-to-digital conversion of the DC voltage being output by integrated circuit  122 . Minor variations in the resulting value can occur due to pans being moved on adjacent burners, food dropping onto electrode  128 , people moving through the electric field, and sundry other reasons. These minor variations are incorporated into the benchmark value. For example, if several readings are consistently slightly higher than the stored benchmark value, the benchmark value is adjusted upward. 
         [0039]    Conversely, if a larger change in sequential readings is detected, the state of the burner will be changed by microcontroller  110 . A large decrease in the result of the analog-to-digital reading while the burner is enabled indicates that a pan has been removed from the burner. When this happens, the burner is disabled. This is accomplished by microcontroller  110  by inverting the logical value of its pin that is connected to digital-to-analog converter  112 . 
         [0040]    Similarly, a large increase in the result of the analog-to-digital reading while the burner is disabled indicates that a pan has been placed on the burner. When this happens, the burner is enabled. This is accomplished by microcontroller  110  by inverting the logical value of its pin that is connected to digital-to-analog converter  112 . Note that a large increase in the reading can also happen when the burner is already enabled. This state can be reached if no pan is on the burner when the system is initially energized. The burner is initially enabled when power is applied to the system. If a pan is subsequently placed on the burner, a large increase in the analog-to-digital reading will be noted. However, this only results in an adjustment to the benchmark value. The burner remains enabled. 
         [0041]    In this embodiment, the burner is either enabled or disabled, resulting in valve  130  being fully open or fully closed. Other embodiments are contemplated in which intermediate positions of valve  130  are possible. In those cases, the connection between microcontroller  110  and digital-to-analog converter  112  would consist of enough wires to represent each of the desired states. For instance, three wires could represent eight distinct valve positions. However, in this embodiment, a single wire suffices for the connection, and the digital-to-analog function of converter  112  is reduced to buffering the low voltage, low current output of microcontroller  110  into a high voltage, high current signal suitable for energizing solenoid  136 . 
         [0042]    Microcontroller  110  provides a means for controllably reacting to inputs from sensor  120  to modify the state of valve  130 . Any microcontroller with sufficient digital outputs and analog-to-digital inputs can be used for this function. 
         [0043]      FIG. 1B  illustrates one embodiment of the digital-to-analog buffering required between microcontroller  110  and valve  130 , namely an NPN Darlington transistor such as a Fairchild TIP120. Note, however, that any circuitry can be used that can translate the low voltage, low current output of microcontroller  110  into the high voltage, high current signal needed to energize solenoid  136 . Resistors R 1  and R 2 , transistors Q 1  and Q 2 , and diode D 1  are internal components of the TIP120 Darlington transistor. The external connections are base  114 , collector  116 , and emitter  118 . Base  114  is connected to microcontroller  110 , collector  116  is connected to solenoid  136 , and emitter  118  is connected to electrical ground. 
         [0044]    When microcontroller  110  outputs a logical 1, or positive voltage, to base B, transistors Q 1  and Q 2  turn on, connecting solenoid  136  to ground. Since the other lead of solenoid  136  is connected to a DC power supply (not shown), solenoid  136  is energized. When microcontroller  110  outputs a logical 0, or near zero voltage, to base B, transistors Q 1  and Q 2  turn off, disconnecting solenoid  136  from ground and de-energizing solenoid  136 . 
         [0045]      FIG. 2  illustrates one embodiment of electric field sensing electrode  128 . Electrode conductor  210  is mounted to electrode body  212  using a high temperature adhesive. A mica-based ceramic adhesive is preferred, but any adhesive that bonds ceramic and metal while withstanding high temperature can be used. In this embodiment, electrode conductor  210  is a disc of stainless steel. Any electrically conductive material that is resistant to mechanical shock, high temperature, and chemicals such as acids and solvents found in foodstuffs can be used. 
         [0046]    Electrode body  212  is a silica ceramic in this embodiment, although any material can be used that withstands high temperatures, thermal shock, and mechanical shock while being an electrical insulator. In this embodiment of electrode  128 , the center conductor of coaxial cable  220  serves as signal connection  124  first described in  FIG. 1 , and the shield conductor of coaxial cable  220  serves as shield connection  126  first described in  FIG. 1 . Signal connection  124  is electrically and mechanically connected to conductor  210 . In this embodiment, the connection is made by brazing. Alternatively, spot welding, or a machine screw and nut through the center of conductor  210 , or similar means can be used to affix signal connection  124 . Shield connection  126  is not electrically connected to electrode  128 . It is only electrically connected at its other end to integrated circuit  122 . 
         [0047]    In this embodiment, the upper portion of electrode body  212  has a circular cross-section to maximize the possible area of electrode conductor  210  when electrode  128  is installed in a stove with a round burner containing an opening in its center. Note, however, that other closed shapes might be useful in other circumstances. The lower portion of electrode body  212  has a rectangular cross-section. This lower portion also has two holes  214 A and  214 B to facilitate assembly to a bracket that will hold electrode  128  in the desired position inside the stove. Electrode body  212  contains a wiring channel  216  that runs from the surface upon which electrode conductor  210  is attached to the opposite end of electrode body  212 . Coaxial cable  220  is run through wiring channel  216 , exiting the bottom of electrode body  212 . 
         [0048]      FIG. 3A  illustrates a perspective view of one embodiment of electrode  128  mounted in a stove or cooktop upper surface  310 . A section of the stove upper surface  310  is depressed to form burner well  312 . Burner  314  is mounted within a hole in burner well  312 , and electrode  128  is mounted within a hole in burner  314 . 
         [0049]      FIG. 3B  illustrates a cross section view of one embodiment of electrode  128  mounted in a stove or cooktop upper surface  310 . Electrode  128  is held in place by mounting bracket  316  using standard machine screws (not shown) through holes in bracket  316  that mate with the mounting holes  214 A and  214 B in electrode body  212 . Bracket  316 , in turn, is connected to a cooktop structural member  318  by any convenient means such as machine screws, self-tapping metal screws, spot welding, or the like. 
         [0050]    Mounting bracket  316  is sized such that the electrode conductor  210  is situated slightly below the top of burner  310 . A distance of 1 to 1.5 centimeters is currently favored. The higher the placement of conductor  210 , the stronger the signal that is generated by the placement of a pan on burner  310 . However, higher placement also results in electrode  128  being required to withstand higher temperatures. 
         [0051]      FIG. 4  illustrates an embodiment of a software flowchart that controls the embodiment described in  FIG. 1  to accomplish the desired energy savings. The program starts at symbol  410 . 
         [0052]    Next, the hardware registers of microcontroller  110  are initialized as shown in block  412 . The port connected to sensor  120  is an analog-to-digital converter and is configured to perform single readings upon software command, as opposed to continuous conversions. The port connected to digital-to-analog converter  112  is configured as an output. A timer is configured to provide the source of an interrupt that will wake microcontroller  110  from a sleep state periodically. 
         [0053]    After the hardware is initialized, sensor  120  must be calibrated, as shown in block  414 . The DC voltage that is output by integrated circuit  122  is converted to a digital value by microcontroller  110 . After a suitable delay, presently defined to be on the order of 100 milliseconds, the conversion is repeated. This process of converting the DC voltage to a digital value, then waiting, should be repeated several times so that random electrical noise can be cancelled out. The average of the several readings is then used to calculate a lower threshold value for the system. The lower threshold is defined as the average of the several readings minus the system&#39;s delta value. 
         [0054]    The delta value is determined by characterizing the performance of the system as installed in the desired stove or cooktop. In a typical configuration, the difference in the result of the analog-to-digital conversion with and without a pan on the burner will be less than 20 units. Microcontroller  110  should first be programmed using a value of 20 for the delta value. If the placement and removal of a pan on the burner does not result in proper operation of the system, the delta value should be reduced to 19. This process should be repeated until the largest value that yields reliable operation of the system is found. This value is the system&#39;s delta value. 
         [0055]    Block  416  shows the burner being placed into its enabled state. This requires that a value be written to the port of microcontroller  110  that is connected to digital-to-analog converter  112 . The value written to the port should place valve  130  in its open position. This will allow gas to flow from gas inlet  132  to gas outlet  134 . Note that this means the burner will be energized when first turned on, whether a pan is in place or not. While this method has been chosen because it seems more intuitive, it will also be acceptable to have the burner start in a disabled mode. In that case, the burner will not start until a pan is placed on it. 
         [0056]    In block  418 , a new value is read by performing another analog-to-digital conversion of the DC value output by integrated circuit  122 . 
         [0057]    Block  420  illustrates the first decision point of the flowchart. The new value from the analog-to-digital conversion is compared to the lower threshold value. If it is greater than or equal to the threshold value, it is used to calculate a new threshold value, as shown in block  422 . The new threshold value is calculated by subtracting the system&#39;s delta value from the current reading. This process allows the system to adapt to changing conditions, such as pans being moved on adjacent burners. 
         [0058]    As shown in block  424 , microcontroller  110  then enters a low power sleep state for a short time, on the order of 100 milliseconds. When it is awakened from the sleep state by an internally generated timer interrupt, it jumps back to block  418 . 
         [0059]    If the new value in block  420  is less than the lower threshold value, a sequence is started that may result in the burner being disabled. In this case, the new value indicates that the pan has been lifted from the burner. However, this may be due to normal cooking techniques such as sautéing or flipping the contents of the pan. Therefore, the burner is not disabled yet. 
         [0060]    Block  426  shows that the system waits a predefined period of time. This lag time should be a compromise between premature triggering and reduced energy savings. A value in the range of one to 1.5 seconds is currently favored. 
         [0061]    Block  428  illustrates that the next action is to retrieve a new value from integrated circuit  122  by converting the DC voltage present on its output to a digital value. 
         [0062]    Block  430  shows the second decision point. If the new value is greater than or equal to the lower threshold value, the burner will remain enabled and block  432  will be executed next. If the new value is less than the lower threshold, block  434  is executed next. 
         [0063]    In block  432 , a new lower threshold is calculated by subtracting the system&#39;s delta value from the reading taken in block  428 . Then, the system jumps to block  424  and goes to sleep. 
         [0064]    If control passes from block  430  to block  434 , microcontroller  110  disables the burner by writing a value to digital-to-analog converter  112  that energizes solenoid  136  of valve  130 . This causes valve  130  to close, preventing gas from flowing between valve inlet  132  and valve outlet  134 . 
         [0065]    After the burner is disabled, block  436  serves to calculate an upper threshold value by adding the latest value read from sensor  120  in block  428  to the system delta value. 
         [0066]    In block  438 , the system enters a sleep mode for an interval equal to that of block  424 . After that time has elapsed, an internally generated timer interrupt awakens the system. 
         [0067]    In block  440 , a new value is read from sensor  120  by performing an analog-to-digital conversion of the DC voltage output by integrated circuit  122 . 
         [0068]    In block  442 , the new value is compared to the upper threshold value. If the new value is less than or equal to the upper threshold, block  444  uses the new value to calculate a new upper threshold by adding the new value to the system delta value. The system then jumps to block  438 . 
         [0069]    If the new value from block  440  is greater than the upper threshold value, the system jumps to block  446 . In block  446 , a new lower threshold value is calculated by subtracting the system delta value from the new value from block  440 . From block  446 , the system jumps back to block  416 , where the burner is enabled again. 
       Other Embodiments 
     FIGS.  5 - 10   
       [0070]      FIG. 5A  illustrates a perspective view of an alternative embodiment for electrode  128 . For burners such as burner  510  that do not have a hole in their center, electrode  128  could not be properly placed. In this case, an electrode  520  could be fitted around the outside of burner  510 . Electrode  520  can be affixed to burner well  212  using a high temperature adhesive or mechanical fasteners. 
         [0071]      FIG. 5B  illustrates the details of the alternative embodiment of the electric field sensing electrode. As was the case with electrode  128 , signal connection  124  of coaxial cable  220  is affixed to electrode conductor  524 . Coaxial cable  220  is passed through wiring channel  526 , which is a hole in electrode body  522 . 
         [0072]      FIG. 6  illustrates an alternative embodiment for controlling the flow of gas when entering or leaving the energy saving mode. A manually controlled valve  620  comprises a valve body  622 , a valve stem  624 , a gas inlet  132 , and a gas outlet  134 . Motor  630  comprises shaft  632  and body  634 . Shaft  632  of motor  630  is connected to valve stem  624  using coupler  640 . When valve stem  624  is rotated clockwise to its full extent, the flow of gas between gas inlet  132  and gas outlet  134  is enabled. When valve stem  624  is rotated counterclockwise to its full extent, the flow of gas between gas inlet  132  and gas outlet  134  is disabled. 
         [0073]      FIG. 7  illustrates an alternative embodiment of a sensor to detect the presence or absence of a pan on a cooktop. An optical detector  710  is mounted below a burner  314 . Optical detector  710  comprises an emitter  712  and a detector  714 . Emitter  712  radiates electromagnetic energy in the visible or infrared spectrum when energized. If a pan  716  is present on burner  314 , the electromagnetic energy will be reflected back in the direction of detector  714 . Therefore, activation of detector  714  by incident electromagnetic energy signals the presence of pan  716  on burner  314 . 
         [0074]    If optical detector  710  operates in the visible spectrum, measures must be taken to filter out ambient light to avoid false triggering of detector  714 . For example, emitter  712  can be pulsed off and on. Then, the output of detector  714  can be processed using a high pass filter to eliminate the effects of ambient light hitting detector  714 . The observation of pulses of light by detector  714  that are coincident in time with the emission of pulses of light by emitter  712  indicate that a pan  716  is present on burner  314 . 
         [0075]    If optical detector  710  operates in the infrared spectrum, ambient emissions are not a problem if optical detector  710  is properly placed in relation to burner  314 . Detector  714  should be situated such that it is not triggered by infrared emissions from burner  314 . Considerations include the characteristics of detector  714  with respect to the allowable angle of incident infrared energy that will trigger it, the vertical distance between detector  714  and burner  314 , and the horizontal distance between detector  714  and burner  314 . If desired, detector  714  can be screened from ambient energy by placing a shield  718  in front of it. Note that ambient emissions from pan  716  will not cause a malfunction of the system. Whether detector  714  is sensing reflected infrared energy from emitter  712  or infrared energy emitted from a hot pan  716 , the activation of detector  714  will correctly indicate that a pan  716  is on burner  314 . 
         [0076]      FIG. 8  illustrates yet another alternative embodiment of a sensor to detect the presence or absence of a pan on a cooktop. An ultrasonic range finder  810  is mounted below a burner  314 . Range finder  810  comprises an ultrasonic emitter  812  and an ultrasonic detector  814 . Emitter  812  outputs pulses of ultrasonic energy. If a pan  716  is present on burner  314 , the ultrasonic energy is reflected into detector  814 . Therefore, activation of detector  814  by incident ultrasonic energy signals the presence of pan  716  on burner  314 . Range finder  810  should be positioned so that reflections from the burner  314  do not cause false triggering of detector  814 . 
         [0077]      FIG. 9  illustrates an embodiment of a gas piping system that results in the gas flow being reduced, but not completely blocked, when the system enters the energy saving mode. Many chefs prefer to keep the grates of their cooktops hot, to facilitate a quick turnaround time when an order is received in the kitchen. In this embodiment, the reduction of the gas flow in energy savings mode represents a compromise between this quick turn requirement and the desire to save the maximum possible amount of energy. 
         [0078]    In this embodiment, gas inlet  132  is connected to a Y connector  912 . One output of Y connector  912  is coupled to electronically controlled valve  918  using metal tubing  914 . The other output of Y connector  912  is coupled to flow restrictor  920  via metal tubing  916 . Valve  918  and flow restrictor  920  are coupled to a second Y connector  926  using metal tubing  922  and  924 . The output of Y connector  926  is affixed to gas outlet  134 . 
         [0079]    The characteristics of flow restrictor  920  are specified so as to result in the desired energy output of burner  314  when the system is in the energy saving mode. In this mode, valve  918  is closed, so the energy output of burner  314  is completely determined by the rate of gas movement through flow restrictor  920 . When the system is not in energy saving mode, valve  918  is opened, and the energy output of burner  314  is determined by the sum of the flows through valve  918  and restrictor  920 . 
         [0080]      FIG. 10  illustrates the block diagram of an additional embodiment. A keypad  1010  and a display  1030  have been connected to microcontroller  110 . Keypad  1010  can be used to enter configuration information into the energy saving system. Display  1030  provides visual feedback that the desired information has been entered correctly. 
         [0081]    Keypad  1010  is a matrix keypad connected to microcontroller  110 . The rows of keypad  1010  are connected to port pins  1012 ,  1014 ,  1016 , and  1018  of microcontroller  110  that are configured as inputs with internal pullup resistors. The columns of keypad  1010  are connected to port pins  1020 ,  1022 , and  1024  of microcontroller  110  that are configured as outputs. 
         [0082]    Microcontroller  110  drives each of the port pins  1020 ,  1022 , and  1024  low in turn, while keeping the other two in a high impedance condition. If any of the input pins  1012 ,  1014 ,  1016 , and  1018  read as a low voltage, this indicates that a particular key of keypad  1010  has been depressed. The depressed key is at the intersection of the column of keypad  1010  that is currently driven low by microcontroller  110  and the row of keypad  1010  that is connected to the input pin that is providing the low voltage input to microcontroller  110 . 
         [0083]    Display  1030  is an LCD display with an integral serial communication port known in the electronics industry as an Inter-Integrated Circuit or I2C port. It is connected to the I2C port of microcontroller  110  using a three-wire bus. 
         [0084]    Keypad  1010  can be used to enter a desired lag time in seconds between the removal of a pan from burner  314  and the reduction of gas flow to burner  314 . The desired time is indicated by pressing the corresponding keys on keypad  1010 , confirming that the correct number of seconds is shown on display  1030 , and pressing the “#” key on keypad  1010 . 
         [0085]    Keypad  1010  can also be used to enter the maximum time in seconds that a pan can be off burner  314  before replacing the pan will not re-enable burner  314 . The desired time is entered using keypad  1010  followed by the “*” key. This mode of operation is included for added safety. If significant time had passed since the pan was removed, the chef might not notice that burner  314  automatically came on when the pan was placed on burner  314 , creating a fire hazard. If this situation occurs, the burner can be re-enabled by pressing any key on keypad  1010 . 
       CONCLUSIONS, RAMIFICATIONS, AND SCOPE OF INVENTION 
       [0086]    The descriptions of the previous embodiments demonstrate several methods that can provide the desired effect of the present invention, namely the capability to reduce the energy usage of a cooktop. 
         [0087]    In the context of this invention, the term valve can refer to a device that modulates the flow of a flammable gas or electricity. In the case of electricity, the valve would be an electronic valve such as a transistor, triac, thyristor, semiconductor-controlled rectifier, Darlington pair, insulated gate bipolar transistor, or similar apparatus that modulates the flow of electricity, or an electromechanical device such as a relay. 
         [0088]    Other means of sensing the presence of a pan could be used. By way of example, a strain gauge or other method of detecting the weight of the pan on the burner could be employed. By way of further example, a camera could be mounted in proximity to the burner and pattern-matching software could determine whether a pan was present on the burner. Alternately, the burner&#39;s grate could be divided into two segments that were electrically isolated from each other, allowing a conductive pan to complete a circuit to signal its presence. Other examples include the use of a laser range finder, a radar range finder, or an ultraviolet sensor. 
         [0089]    While a programmable microcontroller has been described in the embodiments, other means of monitoring the state of the cooktop sensors and modifying the state of the valves could be utilized. Programmable microprocessors, field programmable gate arrays, application-specific integrated circuits, digital signal processors, programmable logic devices, and complex programmable logic devices comprise alternatives that could be selected in lieu of the microcontroller. 
         [0090]    While one embodiment describes the use of a motor to activate a manual valve, other means of generating electromotive force could be substituted within the scope of the present invention. By way of example, solenoids, piezoelectric transducers, or muscle wires could be used to modulate the flow of gas through a manual valve. 
         [0091]    While the above descriptions contain many specificities, these should not be construed as limitations on the scope of the invention, but rather as an exemplification of several embodiments thereof. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.