Abstract:
An ignitor spark indicator  100  is described that monitors RF signals within a flame rod  25  located near a spark rod  23 . The signal from the flame rod  25  is processed to provide a waveform that indicates when electrical arcing is occurring. The indication when arcing is occurring is also provided to flame-detecting equipment. The flame-proving device  60  only operates when the arcing is not produced so that the flame-detecting device  60  does not confuse the arcing with a flame reducing the false positive determinations.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a system for more accurately indicating if a spark and a flame are being produced in a fuel ignitor. 
     BACKGROUND 
     In typical gas and light oil-fueled utility burners, the gas/oil is ignited from a pilot flame on an ignitor. The ignitor must start this pilot flame. Therefore, it creates a spark from a spark rod connected to a high voltage transformer. The transformer provides high voltage electrical power (about 8 kV) to the spark rod that is adjacent to a grounded metal housing. The electrical power causes an arc (spark) to be produced between the spark rod and housing (ground). This arc occurs for a predefined time (typically 10 seconds) when the ignitor is first turned on. In prior art devices there are no external verifications that arcing is actually occurring. 
     The ignitor also has a flame rod located near a small fuel source, the spark rod and the housing. The spark rod creates arcing that lights the fuel from the small fuel source creating the pilot flame. The pilot flame spans the area between the flame rod and the housing. Since fire conducts electricity, this causes current to flow from the flame rod to the housing through the flame. 
     This current is monitored by an externally mounted electronic device. The electronic device and flame rod are referred to as a flame-proving device. The flame-proving device analyzes the flow of current from the flame rod to the housing to determine the presence of a pilot flame. 
     The arc from the high voltage transformer sometimes interferes with the ignitor flame-proving device, causing it to falsely indicate flame while the arc is on. 
     When an ignitor will not correctly light a pilot flame, the technician diagnosing the problem will usually remove the ignitor from the boiler and activate it without fuel to visually determine if an arc is being produced. This takes time and effort. 
     Currently, there is a need for a device that automatically determines if an ignitor is producing arcing and more accurately determines if a pilot flame is being produced. 
     SUMMARY OF THE INVENTION 
     The present invention may be embodied as an ignitor diagnostic device  100  for detecting the presence of arcing between an energized spark rod  23  and a housing  11 . It employs a flame rod  25  for sensing an electromagnetic (EM) signal radiated by the spark rod  23  when energized. 
     A sensing device  50  is coupled to the flame rod  25  and receives the EM signal from the flame rod  25  and processing the EM signal to create a spark indication signal. 
     A user interface  90  adapted to provide output to a user. 
     A logic unit  60  is coupled to the user interface  90 . The logic unit  60  is adapted to receive the spark indication signal from the sensing device  50 , determine if arcing is occurring based upon the strength of the spark indication signal. The logic unit  60  provides this information to the user interface  90  to cause an output to be displayed to the user. 
     The spark indication signal is comprised by a plurality of periodic lobes separated by low voltage timer periods, and the logic unit  60  monitors the low voltage time periods in the spark indication signal and measures the spacing between lobes to indicate ‘health’ of the spark producing equipment. 
     The present invention may also be embodied as an ignitor diagnostic device  100  for more accurately determining if a pilot flame is present. 
     It includes a flame rod  25  for sensing an electromagnetic (EM) signal radiated by the spark rod  23  when the spark rod  23  is energized, 
     a sensing device  50  coupled to the flame rod  25  for receiving the EM signal from the flame rod  25  and processing the EM signal to create a spark indication signal; 
     a logic unit  60  adapted to receive the spark indication signal from the sensing device  50 , determine if arcing is occurring based upon the strength of the spark indication signal and provide a logic signal indicating when arcing is occurring; and 
     a flame-proving device  70  coupled to the logic unit  60  adapted to receive the logic signal from the logic unit  60  and only test for a pilot flame when the logic signal indicates that no arcing is occurring. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide a system that accurately determines if an ignitor is producing a spark. 
     It is another object of the present invention to indicate to a flame detector that an arc is currently being produced. 
     It is another object of the present invention to aid a flame detector in more accurately determining if there is currently a pilot flame burning. 
     It is another object of the present invention to indicate when there are problems with the spark apparatus. 
     It is another object of the present invention to predict failures of the spark apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawings in which: 
         FIG. 1  is a perspective view of a pipe ignitor compatible with the present invention with its housing removed. 
         FIG. 2  is a perspective view from a different angle of a pipe ignitor compatible with the present invention with its housing removed. 
         FIG. 3  is a partially cut-away diagram of a pipe ignitor compatible with the present invention. 
         FIG. 4  is a schematic block diagram of the general elements for one embodiment of a circuit according to the present invention for processing a signal received from the flame rod. 
         FIG. 5  is an illustration of a waveform monitored at test point “A” of the circuit of  FIG. 4 . 
         FIG. 6  is an illustration of a waveform monitored at test point “B” of the circuit of  FIG. 4 . 
         FIG. 7  is an illustration of a waveform monitored at test point “C” of the circuit of  FIG. 4 . 
         FIG. 8  is an enlargement of a portion of the waveform shown in  FIG. 7 . 
         FIG. 9  is a cross sectional, elevational view of a side ignitor compatible with the present invention as it would appear installed within a boiler. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a perspective view of a pipe ignitor  10  compatible with the present invention with its housing removed. 
       FIG. 2  is a perspective view from a different angle of a pipe ignitor  10  compatible with the present invention with its housing removed. 
       FIG. 3  is a partially cut-away diagram of a pipe ignitor  10  compatible with the present invention. 
     The following description is made with reference to  FIGS. 1 ,  2  and  3 . Pipe ignitor  10  has an elongated housing  11  having an internal end  13  passing inside of a combustion chamber of a boiler and an external end  12  extending outside of the combustion chamber. 
     The external end  12  has a spark rod cable  33  and a flame rod cable  35  extending out to external equipment. Internally, the spark rod cable  33  connects to an electrically conductive spark rod  23 . Spark rod  23  extends from the spark rod cable  33  to the internal end  13 . It extends parallel to, but does not come in contact with, the outer housing  11 . The outer housing  11  is electrically connected to ground. There is a predetermined gap between spark rod  23  and outer housing  11 . 
     High voltage electric power source  3  provides electric power, preferably in the form of alternating current, through the spark rod cable  33  and to the spark rod  23 . This causes pulsating arcing between the spark rod  23  and the internal end  13  of housing  11 . This arcing produces high frequency electro-magnetic radiation and induces current flow in nearby conductors. 
     A flame rod  25  is enclosed within the outer housing  11  and extends to the internal end  13  of the pipe ignitor  10 . It is positioned between the fuel tube  40  and the end of spark rod  23 . This allows the flame rod  25  to be immersed in a pilot flame when the pilot flame is burning. 
     Flame rod  25  is connected to a flame rod cable  35  that connects ultimately to a flame-proving device that detects the presence of a pilot flame. 
     Referring now also to  FIG. 4 , one type of flame-proving device  70  measures electrical current passing through a flame. Flame-proving device  70  applies a voltage difference between the flame rod  25  and the housing (ground). Since the pilot flame (fire) conducts electricity, the pilot flame between the fuel tube  40  and the housing  11  creates a circuit allowing current to flow from the flame rod through the pilot flame and to the housing  11 . This is typically about 30 volts. This current is measured by the flame-proving device  70 . The presence of electrical current flow indicates that a pilot flame is present. Conversely, the absence of current flow indicates that a pilot flame is not present. 
     The present inventors discovered that the flame rod  25  could act as an antenna as well as functioning to provide current through the pilot flame. It was also determined that the arcing produced by the spark rod  23  creates high frequency RF ‘splatter’ radiation that was being sensed by the flame rod  25 . The characteristic AC pulsing is sensed by the flame rod  25 . Therefore, it was determined that the signal sensed by the flame rod  25  can be monitored to indicate when the spark rod  23  is creating arcing. This signal also indicates that a spark is being produced. This information may also be used to determine when the spark rod and associated power source are not functioning properly. It also may be used to cause the flame-proving device to sense the flame only when no arcing is being produced, and therefore detect the flame more accurately. 
     The theory of the present invention is to monitor electrical signals sensed by the flame rod  25 , filter out the DC and low frequencies in the sensed signal, rectify the signals, filter out the high frequencies and digitize the signal. This leaves a low frequency envelope signal that is twice the frequency of the AC current used (100 Hz. or 120 Hz.). When this signal is detected, the spark rod  23  is arcing. 
     The arcing of the spark rod  23  creates current that may be mistaken by the flame-proving device  70  as originating from a flame and incorrectly indicates that a flame is present when it is not. This is a false positive. Therefore, the sensing device  50  of the present invention must communicate with the flame-proving device  70  to indicate when arcing is occurring. 
     The flame-proving device  60  must then test for a flame only when the spark rod is not operating to detect if there is a flame. 
     This eliminates the interference and false-positives that occur due to the inadvertent detection of arcing and confusing the arcing with the presence of a pilot flame. This results in a more accurate flame-proving device. 
       FIG. 4  shows a schematic block diagram of the general elements for one embodiment of a sensing device  50  according to the present invention for sensing when arcing is occurring. The signal from the flame rod  25  is received through the flame rod cable  35  and provided to a high pass filter  51 . High pass filter  51  employs a capacitor C 1  and resistor R 1  connected to ground that will block lower frequencies in the signal caused by flame impingement on the flame rod  25 . High pass filter  51  passes the higher frequency signal due to the arcing radiation “splatter”. One such signal is that shown in  FIG. 5 . 
     The filtered signal passes through a rectifier D 1  that rectifies the signal to flip the negative lobes to make them all positive. This signal is shown in  FIG. 6 . 
     The rectified signal is provided to a low pass filter  55 . Low pass filter  55  in this embodiment employs a resistor R 2  and capacitor C 2  that block the high frequency arcing signal to produce an envelope signal. The envelope signal has a frequency that is twice the frequency produced by the AC power supply. The signal is shown in  FIG. 7 . 
     An analog to digital converter  57  receives the analog envelope signal and digitizes it to create a set of digital samples approximating the analog envelope signal of  FIG. 7 . This may be in the form of a series of measured amplitude values, or a block or table of such data. 
     A logic unit  60  senses the digitized signal provided by the ND converter  55 . Logic unit  60  may be a standalone device with its own microprocessor or be part of a calculation device  80  that has a microprocessor that runs several different programs and performs several different functions. One embodiment compares the amplitude of the digitized signal with a minimum amplitude, such as a 2  of  FIGS. 7 and 8 . 
     Logic unit  60  then monitors the digitized signal to identify if the signal is at periodic peaks that exceed the threshold with a regular frequency. This frequency should be double the frequency of the signal provided by the spark power supply ( 3  of  FIGS. 1 ,  2 ) to the spark rods ( 23  of  FIGS. 1 ,  2 ). If so, arcing is being produced. If not, then no arcing is being produced. 
     Logic unit  60  receives the signal from the sensing device  50  and calculates information that there is, or is not, arcing being produced. This information is provided from the logic unit  60  to the flame-proving device  70 . Flame-proving device  70  is modified in this embodiment to operate when the output of the logic unit  60  indicates that no arcing is being produced. It is not allowed to operate when the logic unit  60  indicates that arcing is being performed. 
     In an alternative embodiment, the flame-proving device  70  is allowed to operate at all times, but readings indicating that there is a flame present while logic unit  60  indicates that arcing is being performed are ignored. 
       FIG. 5  is an illustration of a waveform monitored at test point “A” of the circuit of  FIG. 4 . Here the high frequency signal has an envelope with a frequency that follows the AC input frequency. 
       FIG. 6  is an illustration of a waveform monitored at test point “B” of the circuit of  FIG. 4 . Here the signal of  FIG. 5  has been rectified, flipping the signal lobes to the positive side. 
       FIG. 7  is an illustration of a waveform monitored at test point “C” of the circuit of  FIG. 4 . Here the resultant signal is only the envelope of the rectified AC input frequency. The high frequency signal due to the arcing has been filtered out. 
       FIG. 8  is an enlargement of a portion of the waveform shown in  FIG. 7 . 
     This is a time vs. amplitude plot of the envelope of the rectified waveform. As the waveform envelope reduces amplitude (input voltage), it reaches a point at time t 1  that the curve drops to zero amplitude. 
     Similarly, as voltage is provided by the power source  3  to the spark rod  23  during the period from time=t 2  to time just before t 3 , there is no measurable amplitude response. It is only at time=t 3  that arcing begins and increases its amplitude rapidly until it follows the normal waveform envelope. 
     It has been determined that the health of the power source  3 , spark rod  23 , the spark rod cable  33  and the remainder of the connections between these units can be determined by the distances between t 1  and t 3 . 
     The probability of failure may be determined not only by these distances, but by how these distances change over time. 
     Referring now to  FIGS. 4 and 8 , optionally, logic unit  60  measures the amplitudes and times shown in  FIG. 8 . It then compares these measurements to predetermined thresholds or optimum measurements to determine health of the system. Based on the deviations from the thresholds, one can determine how ‘healthy’ the system is. 
     Also, if the logic unit  60  is capable of storing historic data, the change over time can be determined and a prediction may be made as to when the system will fail. This can be very useful in the maintenance and repair of these ignitors. 
       FIG. 9  shows a variation of the pipe ignitor  10 . This is a side ignitor. All of the parts have the same function as those with the same reference numbers that have been previously described. Housing  21  is different since this is intended to be mounted in the sidewall of a boiler. Also, spark plug  24  is employed instead of a spark rod  23 . This is due to the different geometry that makes it difficult to be close to the housing. Therefore, spark plug  24  has both a positive and negative electrode spaced by a gap to create a spark similar to spark plugs in an average automobile. 
     It should be emphasized that the above-described embodiments of the present invention, particularly any “preferred” embodiments, are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiment(s) of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention.