Abstract:
A burner shutoff for a burner, the burner shutoff including a solenoid moveable between an open position permitting fuel supply to the burner and a closed position cutting off fuel supply to the burner. The burner shutoff including a thermocouple in communication with the solenoid, wherein the thermocouple producing a voltage output signal when heated by the burner for maintaining the solenoid in the open position. The burner including a safety timer for selectively generating and communicating a reverse polarity voltage signal to the solenoid such that the voltage signal received by the solenoid is altered sufficiently to move the solenoid to the closed position, thereby shutting off the burner.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to a safety automatic shut off device for gas burners.  
       BACKGROUND OF THE INVENTION  
       [0002]     Heaters often utilize gas fired burners which normally operate with propane fuel, however can also have other sources of fuel, including but not limited to natural gas, butane and heating oil. Most portable heaters having gas fired burners are fitted with a safety thermocouple which communicates electrically with a solenoid valve in order to detect a flame out condition. The thermocouple mounted proximate the flame or heat source develops a millivolt signal which in turn is communicated back to the solenoid valve. The millivolt signal maintains the solenoid valve in the open position. When a flame out condition occurs, the thermocouple cools downs and the millivolt signal decreases which in turn closes off the solenoid valve once the signal from the thermocouple has dropped to a certain predetermined level.  
         [0003]     Small heaters having gas fired burners are often used in very small enclosed spaces and under the right conditions, the gas fired burners may deplete the amount of oxygen within the enclosed space and under certain conditions may give off carbon monoxide which can be hazardous to the occupant of the enclosed space.  
         [0004]     Therefore it is desirable to have a safety device and/or a safety feature which will prevent or minimize the possibility of oxygen depletion within small enclosed spaces and/or the development of carbon monoxide in order to prevent hazardous conditions from forming within small enclosed spaces in which the heaters are located. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]     The embodiments now be described by way of example only with reference to the following diagrams in which:  
         [0006]      FIG. 1  is a schematic diagram of the burner shut off as shown deployed with a heater.  
         [0007]      FIG. 2  is a schematic wiring diagram of the burner shut off showing details of the wiring of the safety timer. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0008]     The present embodiment of burner shut off is shown generally as  100  in  FIGS. 1 and 2 . In  FIG. 1 , burner shut off  100  is shown deployed together with a heater  102 . In one example heater  102  is a portable space heater of the type having a high intensity ceramic type gas burner. Burner shut off  100  may also be applicable to other heaters.  
         [0009]     Burner shut off  100  includes safety timer  202  which includes circuit board  214  having the following major components, namely a timer  204 , a micro processor  206 , a power storage device  208  and a power supply preferably a battery  212 .  
         [0010]     The burner shut off  100  further includes a thermocouple  220  having thermocouple wires  222  in electrical communication with solenoid valve  230  which also has a manual push button  232 .  
         [0011]     Safety timer  202  is in electrical communication with thermocouple wires  222  via timer wires  216 .  
         [0012]     Typical heater  102  includes a gas supply  110 , burner  116  producing a flame  118 .  
         [0013]     Certain components of heater  102  are not shown for simplicity sake for example, the mixing of air with gas supply  110  is not shown and also the ignition source for lighting flame  118  is also not shown. The components of heater  102  which interact with burner shut off  100  are generally shown namely burner  116  having flame  118  as well as solenoid valve  230 .  
         [0000]     In Use  
         [0014]     Heater  102  is started in the manner generally known in the art namely, manual push button  232  of solenoid valve  230  is manually depressed in order to allow gas supply  110  to flow freely to burner  116 . Not shown, gas is mixed in appropriate proportions with air in order to produce a combustible mixture of fuel and air which can be ignited at the end of burner  116  to produce flame  118 . An ignition source not shown is used to ignite the combustible fuel mixture at the end of burner  116  to produce flame  118 . Once flame  118  has been initiated, it heats thermocouple  220  and the heating of thermocouple  220  creates a millivolt output normally in the range between 0.007 to 0.020 volts (7 to 20 millivolts) and this potential produced by thermocouple  220  is electrically communicated back to solenoid  230 . The millivolt out of thermocouple  220  is enough to hold the solenoid valve  230  in the open position allowing gas supply  110  to flow freely to burner  116 .  
         [0015]     A person skilled in the art will recognize that once thermocouple  220  has been heated to the normal operating temperature by flame  118 , enough millivolts and/or current are produced by thermocouple  220  to hold solenoid valve  230  in the open position, and therefore manual push button  232  can be released and the valve  230  is retained in the open position to ensure continuous firing of burner  116 .  
         [0016]     Thermocouple  220  is there to ensure that should for some reason flame  118  be extinguished, thermocouple  220  will naturally cool down and therefore the millivolts produced by thermocouple  220  will decrease to a point where the current produced by thermocouple  220  can no longer hold solenoid valve  230  in the open position and therefore, gas supply  110  will be shut off. A person skilled in the art will recognize this as a normal safety feature that is found on many commercially available portable space heaters for safety purposes to ensure that the gas supply  110  is cut off should there be an interruption or an extinguishment of flame  118 .  
         [0017]     A person skilled in the art will recognize that the electromotive force or the voltage output of thermocouple  220  is extremely low, normally in the range of 7 to 20 millivolts and once the voltage falls below about 5 millivolts the solenoid valve  230  will normally trip to the closed position.  
         [0018]     A person skilled in the art will also recognize that due to the small millivolt output of thermocouple  220 , the electrical connections between thermocouple  220  and solenoid valve  230  are extremely sensitive, particularly to any contact resistance which may inhibit the flow of current between thermocouple  220  and solenoid valve  230  along thermocouple wires  222 . Therefore, any mechanical contact which is introduced between thermocouple  220  and solenoid valve  230  may be undesirable in that it may introduce an unwanted contact resistance and falsely close solenoid valve  230  when in fact, flame  118  has not been extinguished.  
         [0019]     Therefore in one embodiment a burner shut off  100  is contemplated which will allow solenoid valve  230  to shut gas supply  110  without introducing any mechanical contact resistance of additional switches or contacts along thermocouple wires  222 . In other words thermocouple wires  222  are continuous and free of intervening contacts between thermocouple  220  and solenoid valve  230  in order to ensure the most reliable operation of heater  102 . This continuous aspect of thermocouple wires  222  means there are no mechanical contacts introduced between thermocouple  220  and solenoid  230  other than to accomplish connection between thermocouple  222  and solenoid  230 . The connection between the timer wires  216  and thermocouple wires  222  does not introduce a mechanical contact and therefore no additional contact resistance along thermocouple wires  222 . The timer wires  216  are connected to the thermocouple wires using a contact less connection  219 . The contact less connection can be in any location provided a connection is made to the solenoid  230 . In another embodiment it is contemplated that contacts may be used provided the contact resistance does not falsely close solenoid valve  230 .  
         [0020]     One embodiment includes a safety timer  202  which consists of a circuit board  214  having thereon a timer  204  which is electronic in nature and furthermore includes a micro processor  206 , and further includes a power storage device  208  and has a power supply which could be a battery  212 . Circuit board  214  further includes a reset button  210  which is a manual push button or other type of button and/or switch device which upon pushing of the reset button  210  initiates the timer cycle which may for example be a preselected programmed amount of time through processor  206  and timer  204 .  
         [0021]     For example, heater  102  is ignited and lit in the conventional manner as described above by manually depressing manual push button  232  igniting flame  118 , wherein thermocouple  220  is brought up to temperature and the solenoid valve  230  is held open by thermocouple  220  even after the release of manual push button  232 . At this point in time, heater  102  will continue to operate until there is an interruption in the signals between thermocouple  220  and solenoid valve  230 .  
         [0022]     Initiating the current between thermocouple  220  and solenoid valve  230 , acts to initiate the timer  204  of safety timer  202  which provides for a preset amount of time before an event is triggered by circuit board  214 . So for example, by initiating firing of burner  116 , namely flame  118 , the heater  102  will operate for example for a period of 10 minutes as predetermined by microprocessor  206  and timer  204  after which time safety timer  202  will create a reverse bias electromotive force (millivolt signal) along timer wires  216  which effectively counteracts the millivolt output developed by thermocouple  220 . In other words a voltage signal or electromotive force of about 20 millivolts (0.020 volts) will be created across thermocouple wires  212  in reverse polarity to the natural millivolt output of thermocouple  220 , therefore the applied voltage at solenoid  230  will in effect be reduced to zero or very close to zero.  
         [0023]     If in the above example, the operator presses reset button  210  prior to the expiry of the 10 minutes allotted by timer  204 , timer  204  together with microprocessor  206  is reset to allow for an additional 10 minutes before an event is again triggered by safety timer  202 .  
         [0024]     Upon expiration of the next 10 minutes, safety timer  202  will automatically create a millivolt signal across timer wires  216  which counteract the millivolt signal created by thermocouple  220 , therefore reducing the voltage seen by solenoid valve  230  effectively to zero, thereby causing gas supply  110  to be shut off.  
         [0025]     Therefore, heater  102  is allowed to operate for a maximum time of 10 minutes unless resent button  210  is depressed prior to the expiration of the preset time of 10 minutes.  
         [0026]     Should a heater  102  be used in a confined space, and the occupant for example become unconscious and unable to press reset button  210 , heater  102  will automatically be shut down by safety timer  202 , extinguishing flame  118  and shutting off gas supply  110 .  
         [0027]     If for some reason there is failure of the power supply, namely battery  212  to circuit board  214 , safety timer  202  will detect this condition and there will be enough residual power stored within power storage  208  to be able to send enough electromotive force across timer wires  216  to counteract the millivolt output generated by thermocouple  220  and therefore shut down heater  102 . The power storage  208  could be a capacitor or inductor or a combination of electrical components which are capable of storing enough residual power to produce the reverse polarity voltage signal to close solenoid valve  230 .  
         [0028]     The cycle time of timer  204  is preselected depending upon the application and can vary any where from a few seconds to many hours. It normally is a pre-programmed amount of time however could also be a selected value.  
         [0029]     A person skilled in the art will immediately recognize that the advantages of having an electrical connection between thermocouple wires  212  and timer wires  216  which eliminates mechanical switch contacts used to break the connection between thermocouple  220  and solenoid valve  230 . In one embodiment the electrical connection between thermocouple  220  and solenoid valve  230 , namely thermocouple wires  222  are not mechanically broken to effect shut off. The shut off of solenoid valve  230  is accomplished by permanent electrical connections between timer wire  216  and thermocouple wires  222  by applying a reverse bias voltage to thermocouple wires  222 .  
         [0030]     In addition, the safety timer  202  can operate very easily with a portable battery power of for example three volts or less creating a safety timer not depending on 110 volt AC line current.  
         [0031]     Additionally, this safety timer shut off device provides for a low cost method of efficiently shutting down heater  102  and a completely self contained apparatus not requiring any sources of external power other than the self contained battery  212 .  
         [0032]     It should be apparent to persons skilled in the arts that various modifications and adaptation of this structure described above are possible without departure from the spirit of the invention the scope of which defined in the appended claims.