Abstract:
A signal generation system for flame ignition and sensing. The ignition signal generation is adaptive for improving flame ignition while eliminating excess energy usage. High voltage signals for flame sensing may also be provided. If more energy or speed is needed for ignition signal generation, then the flame sensing signal generation portion may be disabled to increase the amount of available energy. Adaptation for ignition signal generation may be guided by the results of flame sensing. The flame sensing voltage may be regulated based on the flame current strength. The flame current may be controlled within an optimum range to reduce rod contamination rate and yet provide reliable flame sensing when the rod contamination built up. The adaptation may be algorithmic-based with the facilitation of a microcontroller. The system may provide the high voltage signals from a low voltage power supply, such as that of 24 VAC.

Description:
BACKGROUND  
       [0001]     The invention pertains to ignition and sensing systems, and particularly to flame ignition and sensing systems. More particularly, the invention pertains to such systems having spark-type ignition.  
         [0002]     The present application is related to the following indicated patent applications: attorney docket no. 1161.1224101, entitled “Dynamic DC Biasing and Leakage Compensation”, U.S. application Ser. No. ______, filed ______; attorney docket no. 1161.1225101, entitled “Leakage Detection and Compensation System”; and attorney docket no. 1161.1227101, entitled “Flame Sensing System”, U.S. application Ser. No. ______, filed ______; which are incorporated herein by reference.  
       SUMMARY  
       [0003]     The invention is a flame sensing system having spark ignition. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0004]      FIG. 1  is a schematic of an adaptive spark ignition and flame sensing signal generation system; and  
         [0005]      FIG. 2  is a flow diagram of activity in the signal generation system;  
         [0006]      FIG. 3  is a flow diagram of a spark generation as it may be related to a burner;  
         [0007]      FIG. 4  is a graph of certain portions of  FIG. 3 ;  
         [0008]      FIG. 5  shows various flame thresholds for flame sensing;  
         [0009]      FIG. 6  is a flow diagram of an adaptive flame sensing approach; and  
         [0010]      FIG. 7  is a flow diagram of a more detailed adaptive flame sensing approach. 
     
    
     DESCRIPTION  
       [0011]     Relative to an automatic gas ignition system which uses sparking to ignite gas, the required spark energy and rate depend on various factors for successful ignition. Some of these factors may be application dependent or tied to environmental conditions such as humidity and temperature. A control of the system having an ability to adjust and adapt may easily overcome many of the things that adversely affect spark ignition. The system  10  of  FIG. 1  may be powered by, for example, a 24 volt AC source  51 . The 24 VAC may be connected to a full wave rectifier  12  with a capacitive filter  52  on the output to produce about 30 volts DC. Other configurations for providing electrical power to the system may be utilized. A high voltage may be needed for an ignition spark and a higher voltage yet may be needed for flame sensing.  
         [0012]     The present system may have the capability to generate the needed high voltages and closely monitor the amount of energy applied for a given spark and check for the presence of a flame after doing such. This capability may include increasing spark energy in difficult lighting conditions, decreasing spark energy where extra energy may be unnecessary since it would only cause additional noise emission. This capability may also include an increasing spark rate for situations where a trial for ignition time is short and high spark energy alone does not provide for successful ignition.  
         [0013]     The system  10  may also generate a voltage for sensing the presence of a flame after a spark attempt, thereby making it a very flexible system relative to input voltage requirements. The system may be able to control the flame sensing load by stopping an incorporated chopping circuit  59  when a quick charging of a spark capacitor  22  is necessary.  
         [0014]     The circuit of system  10  of  FIG. 1  shows circuits of both ignition and sensing. A voltage source  69  may include an AC source  51 , a rectifier  12  and a filter  52 . The AC source  51  outputting about 24 volts may be connected to the full-wave rectifier  12 . One phase of the AC source may be connected to the appliance ground  36 . The load filter capacitor  52  may be connected across the rectifier  12  output. An inductor  11  may have one end connected to about 30 volts DC from the full-wave rectifier  12 , and the other end connected to an anode of a fast recovery diode  47  with about a 30 k ohm resistor  48  in parallel with the diode as shown by network  46  which may dampen the possibility of inductor  11  oscillating with the parasitic capacitance of diode  47 . The cathode of the diode  47  may be connected to one end of a capacitor  13 , one end of a capacitor  14 , and a drain of a high voltage N-channel MOSFET  15 . Capacitor  13  may be about 10 nanofarads. Capacitor  14  may have a capacitance of about 10 nanofarads.  
         [0015]     A microcontroller  16  may have an output  18  connected to a gate of FET  15 . Output  18  may be about a 31 kHz switching square wave signal to FET  15 . Output  18  may be of other frequencies. Microcontroller  1   6  may have a ground line connected to terminal  17 . A source of FET  15  may be connected to a ground terminal  17 . The other end of capacitor  13  may be connected to a cathode of a diode  19  and an anode of a diode  21 . The other end of capacitor  14  may be connected to the cathode of diode  23  and an anode of diode  28 . The anode of diode  19  may be connected to the ground terminal  17 . The cathode of diode  21  may be connected to one end of capacitor  22 , the anode of diode  23 , a terminal  24  of a primary winding of a step-up transformer  25 , and a cathode of diode  26 . Capacitor  22  may have a value of about one microfarad. The step-up transformer  25  may have a primary-to-secondary winding turn ratio of about 200. The anode of diode  26  may be connected to a terminal  27  of the primary winding of the transformer  25 . The other end of capacitor  22  may be connected to the ground terminal  17 . Inductor  11 , FET  15 , capacitor  13 , diodes  19  and  21 , and capacitor  22  may constitute a boost DC-DC step-up converter  49 . Converter  49  may provide about a 150 volt potential at a node  53 .  
         [0016]     An SCR  29  may have an anode connected to terminal  27  of transformer  25  and a cathode connected to the ground terminal  17 . Microcontroller  16  may have an output  31  connected to a gate of SCR  29  via a resistor  32 .  
         [0017]     A terminal  33  of a secondary winding of transformer  25  may be connected to a spark rod assembly  34 . A terminal  35  of the secondary winding of transformer  25  may be connected to a spark rod ground  36 . The spark rod assembly  34  may be connected to the rod ground  36 .  
         [0018]     The cathode of diode  28  may be connected to one end of a capacitor  37 . The other end of capacitor  37  may be connected to the ground terminal  17 . The cathode of diode  28  may also be connected to one end of a resistor  38  and to a collector of an NPN transistor  39 . The other end of resistor  38  may be connected to a base of transistor  39 , a cathode of diode  41 , and a collector of an NPN transistor  42 . The emitter of transistor  42  may be connected to the ground terminal  17 . Microcontroller  1   6  may have an output  43  connected via a resistor  58  to a base of transistor  42 . The emitter of transistor  39  may be connected to an anode of diode  41  and to one end of a capacitor  44 . The other end of capacitor  44  may be an output  63  of system  10  connected to a flame sensing rod  45 . Block  68  may be a resistor and diode network used to represent the flame.  
         [0019]     System  10  may have an algorithm embedded in the microcontroller  16  with A/D (analog-to-digital converter) input and PWM (pulse width modulation) output capability. The microcontroller may use the PWM channel output  18  to control the high voltage MOSFET  15  such that, during the MOSFET on-time, energy may be built up in the inductor  11  in the form of a current. When the MOSFET is switched off, the energy may cause a significant voltage rise on the drain of MOSFET  15 , thus dumping energy through capacitors  13  and  14 , respectively, into capacitors  22  and  37 . The process may repeat while the output capacitors are charged to a desired level. While the charging is taking place, the microcontroller  16  may monitor the voltage on capacitor  22  at node  53  via an analog-to-digital converter (ADC)  57  connection, and a simple voltage divider or other means (not shown), and control the charging rate and the voltage on the capacitors by varying the duty cycle of FET  15 . Also, controller  1   6  may determine when to turn on SCR  29  based on the potential on node  53 . The spark energy may be proportional to the square of the voltage on capacitor  22 .  
         [0020]     Once a trial for ignition is initiated, the microcontroller  16  may trigger the SCR  29  which dumps energy from capacitor  22  through the primary winding of the spark coil or transformer  25  thereby causing a high voltage to appear across the secondary winding of transformer  25  to provide a spark on the spark rod  34 . The microcontroller  16  may then use a signal on line  65  from the flame sensing circuit  64  to determine if a flame is present or not, and then to adjust the spark energy accordingly with a rate control signal via line  31  to the gate of SCR  29  via resistor  32 , and a magnitude control signal via line  18  to FET  15 . Sensing circuit  64  may be connected to output  63  and ground  17 . Also, a signal on line  43  may go to transistor  42  via resistor  58  to shut down the chopper circuit  59  to save energy in the circuit  49  for the spark ignition network or circuit  56 .  
         [0021]     Capacitor  13  may provide DC isolation for the spark circuit from the input voltage source  69 . Without DC current blocking capacitor  13 , once SCR  29  is triggered, SCR  29  could keep conducting and inductor  11  may be burned or ruined.  
         [0022]     Capacitor  14 , diode  23 , diode  28  and capacitor  37  may form a voltage doubler  54 . The voltage on capacitor  37  may be made roughly twice as high (e.g., about 300 volts) as the voltage on capacitor  22 . About 150 volts may be across capacitors  14  and  22 . With the diodes  23  and  28  in place, the voltage charges on capacitors  14  and  37  may be sustained and prevented from flowing back off the capacitors to nodes  53  and  55 , respectively. An added advantage of the circuit  54  is that the voltage rating of FET  15  may not have to be as high as the voltage needed on capacitor  37 . Thus, it is possible to use a low cost MOSFET as the FET  15 . However, one may leave out the voltage multiplier or doubler circuit  54  and take a voltage directly from the voltage step-up circuit  49  and even if a higher rated switch or FET  15  is needed. Voltage adjustment on either of the voltage circuits may be effected by loading the output.  
         [0023]     Transformer  25 , diode  26 , SCR  29  and gate resistor  32  may constitute a switching step-up voltage circuit  56  for providing sufficient voltage for spark ignition of gas at the spark rod  34 . SCR  29  may be turned on to discharge a charge on the capacitor  22  through the primary winding of the transformer  25  to ground. At that time a high voltage pulse (about 12k to 17k volts) may appear on the secondary winding of transformer  25  and go to spark rod  34 . Diode  26  may prevent a significant reverse current (i.e., from terminal  27  to terminal  24 ) appearing across the primary winding of the transformer  25 . SCR  29  may be turned off when the current going through it goes to zero. The charging and switching cycle may be repeated. A periodic pulse from the controller  16  may go to the gate of SCR  29  to turn it on to achieve appropriate spark timing.  
         [0024]     To perform flame sensing with system  10 , the microcontroller  16  may chop the high voltage on node  61  from capacitor  37  for an output signal to the flame detector  45  with a square wave signal on line  43  via a base input resistor  58  to transistor  42  of a chopping or chopper circuit  59 . The chopper circuit  59  may additionally consist of the transistor  39 , resistor  38 , diode  41  and DC blocking capacitor  44  at output  63 . The output  63  may be connected to the flame detector  45 . The signal  43  from microcontroller  16  may have a frequency of about 2.4 kHz. This frequency may range between 50 Hz and 200 kHz. When the signal  43  is positive, transistor  42  may be turned on to conduct some current from node  61  via resistor  38 . That may provide a close to zero voltage on the base of transistor  39  effectively shutting it off and thereby reducing the signal at node  62  to nearly zero except for a diode drop or so. When the signal on line  43  is about zero or less, the transistor  42  may shut off and effectively reduce the amount of current, flowing from node  61  to ground  17  via transistor  42 , to nearly zero. Then the voltage drop across resistor  38  may be negligible and a positive voltage may appear on the base of transistor  39  relative to its emitter. This positive voltage may turn on transistor  39  thereby resulting in a high voltage at node  62  nearly the same as the voltage on node  61 . The waveform at node  62  may be a square wave with peaks at about 300 volts to about a diode drop above zero. At the output node  63 , because of capacitor  44 , the waveform may be symmetrical about zero volts with plus and minus 150 volt square peaks with a little droop down and up, respectively, with the degree of droop depending on the value of the capacitor  44  and an amount of flame sensor impedance. The signal frequency at the output  63  may be the same as the frequency of the signal input to the base of the transistor  42 . The output signal may go to flame rod  45  for flame rectification.  
         [0025]     The microcontroller  16  may monitor the amount of energy applied to a given spark and check for the presence of a flame via node  53  and line  65 , respectively. Information about the spark energy and flame presence may enable the microcontroller  16  to increase or decrease spark energy via control on lines  18 ,  31  and  43  for difficult or easy lighting conditions. The spark rate may be increased by microcontroller  16  when room for ignition time is short and high spark energy does not solve an ignition difficulty. The chopper circuit  59  for flame sensing may be turned off to aid in faster charging of capacitor  22 . The microcontroller  16  may be programmed to control various aspects of ignition and sensing of the system  10 . Controller  16  may contain a control algorithm to effect various controls in the system for more efficient and effective igniting and sensing of a flame. The algorithm may be implemented with software or in another manner.  
         [0026]     Independently from adjustment of applied spark energy, the invention above may include adaptive flame sensing with a constant-current mode. Given the capability to measure the strength of the flame signal from the flame sensing circuit  64 , the microcontroller in this system may use control line  18  and feedback connection  57  to adjust the applied voltage to the flame sensing circuit. Applying lower voltage to a flame rod in flame rectification may significantly extend the life of the appliance, yet as contamination builds up on the flame rod  45 , a higher voltage may be needed to detect the presence of a flame. Thus, with this circuit one may use the ADC connection  57  to sense voltage at node  53 , and note that the voltage on capacitor  37  is close to double that of node  53  to control the voltage applied to the flame rod  45 . An algorithm in the microcontroller may measure the flame strength seen from sensing circuit  64  and adjust the applied voltage through control line  18  such that the signal is always within a pre-programmed range. This algorithm may effectively produce a constant net flame current, increasing voltage only as necessary to break through contamination build up on the flame rod.  
         [0027]     One may note that the spark and flame sensing would not occur at the same time. Therefore, the voltage at node  53  may be controlled to different levels at different time. For example, when higher spark energy is needed, the voltage at node  53  may be regulated at 170 volts or higher. After the flame is sensed, spark may be stopped. If the flame current is strong, the voltage at node  53  may be controlled at a much lower level, such as 70 volts, so that the voltage at node  61  is only about 140 volts, as long as the flame current sensed is still within the pre-determined range. The controller  16  may continuously sense the voltage at node  53  and adjust control line  18  to regulate voltage at node  53  to meet the dynamic voltage or energy needs required by the spark and flame sensing circuits.  
         [0028]      FIG. 2  is a block flow diagram of certain activity in the adaptive spark ignition and/or flame sensing signal generation system  10 . The arrows show a flow of one block to another. The order shown is an illustrative example; however, the order may take various forms, and different kinds of activity may be indicated in the blocks. Block  71  indicates converting a low input AC voltage to a low DC voltage. Block  72  shows converting the low DC voltage to a first high DC voltage. Block  73  indicates storing the first high DC voltage charge on a spark capacitor. Block  74  shows discharging the charge on the spark capacitor through a primary winding of a step-up transformer. Block  75  indicates providing an ignition spark from a secondary winding of the step-up transformer. Block  76  shows multiplying the voltage on the spark capacitor with a diode-capacitor circuit to a second high DC voltage. Block  77  indicates converting the second high DC voltage into a chopped voltage. Block  78  shows providing the chopped voltage to a flame sensor. Block  79  indicates monitoring a flame sensor output to determine flame presence. Block  80  shows adjusting spark energy, duration, and/or rate according to the flame sensor output. Block  81  indicates engaging or stopping a chopping of the second high DC voltage as sought or desired according to the spark energy, duration and/or rate. Block  82  shows adjusting the first high voltage to control the amplitude of the chopped voltage to control the flame current to a predetermined range. In other words, regulating the first high DC voltage and the second high DC voltage may be done to control the amplitude of the chopped voltage to limit the flame current within the pre-determined range. Adjusting the first high voltage may directly affect the second high voltage to control the amplitude of the flame current.  
         [0029]      FIG. 3  is a flow diagram of the spark generation as it may be related to a burner. An adaptive spark energy algorithm may be started in block  84 . The spark may be started at a saved voltage as indicated in block  85 . As the spark is started, a timer of block  86  may be started. A sensing of a flame may be checked in diamond  87 . If a flame is not sensed, then the timer may be continued as indicated in block  88 . The time on the timer may be noted to see if it exceeds the spark time allowed as indicated in diamond  89 . If not, then one may again check for a flame in diamond  87 . If the time is greater than the spark time allowed as in block  89 , then the spark voltage may be increased one step as in block  91 . After this, then one may again check for a flame in diamond  87 . If the answer to whether the flame is sensed in diamond  87  is yes, then the sparking may be stopped as indicated in block  95 . Then the time may be checked as to whether it is less than the time allowed or not in diamond  92 . If not then storage may take place as in block  94 . If so, then the spark voltage may be reduced in block  93  and then stored as in block  94 . The adaptive spark energy algorithm may end in block  83 .  
         [0030]      FIG. 4  is a graph of certain items noted in  FIG. 3 . The start of a gas flow to a burner or the like is shown by waveform  96 . The spark may be started about the same time as shown by the lines  97  and waveform  98 . The spark may be continued for a period of time as shown by length  101  until a flame is sensed. The voltage applied to the spark mechanism may continue for about a time period as shown by length  99 . That voltage may be sustained for about three seconds or any other amount of time as desired. If a flame is not sensed, the voltage may be incremented in steps as shown by the flow diagram of  FIG. 3 . Curves  103 ,  104  and  105  show examples of a start of flame presence. Curve  106  shows a sustained flame presence. The example flame curves  103 ,  104 , and  105  have corresponding spark times of  101 ,  107 , and  108  respectively.  
         [0031]      FIG. 5  shows the various flame thresholds (FT) for flame sensing. The first threshold FT 1  may reveal flame loss or un-sensed presence of a flame. The second threshold FT 2  may reveal a flame of the pilot level and here the sparking may cease. This may be regarded as a flame proved  1 . The third threshold FT 3  may be regarded as a flame proved  2 . Here the pilot may be sufficient to light a burner. The fourth threshold FT 4  may indicate a weak flame and the fifth threshold FT 5  may indicate a flame low. The sixth threshold FT 6  may indicate a flame high. In this invention the flame sense voltage may be adjusted to maintain the flame current between FT 5  and FT 6  by the algorithm previously described. Reduction of voltage may result in a lower contamination rate of the flame rod  45 . A weak flame could indicate a significantly contaminated rod  45 .  
         [0032]      FIG. 6  is a flow diagram of an adaptive flame sensing approach. It may begin with a start of trial of ignition  111  which may lead to a block  112  which sets the flame voltage at a default value. From block  112  may be question  113  whether the flame is greater than a high threshold. If the answer is yes, then the flame voltage may be decreased as shown in block  114 . After this is the question  113  again as to whether the flame exceeds the high threshold. If the answer is no, then a question  115  of whether the flame is less than the low threshold may be asked. If the answer is no, the question  113  may be asked again. If the answer to the question  115  is yes, then the flame voltage may be increased as indicated in block  116 . After block  116 , then a return to the question of block  113  may be made again.  
         [0033]      FIG. 7  is a flow diagram of an adaptive flame sensing approach indicated in more detail than the one in  FIG. 6 . After the start of trial for ignition  111 , the flame voltage may be set at a default value as indicated in block  112 . Then a question  117  of whether the flame is greater than the flame prove  1  (FT 2 ) may be asked. If the answer is no, then there may be a return to an input of the question  117 . If the answer is yes, then there may be a delay of a short time (e.g., ˜2 sec.) in block  118 . After block  118 , then a question  119  of whether the flame is greater than flame high (FT 6 ) may be asked. If the answer is yes, then the flame voltage may be decreased by one step (the flame voltage should not be lower than the minimum flame voltage) in block  120 . Then there may be return to the question  119 . If the answer is no to question  119 , then a question  121  of whether the flame is less than a flame low (FT 5 ) may be asked. If the answer is no to question  121 , then there may be a return to question  119 . If the answer to question  121  is yes, then another question  122  of whether the flame is less than a flame weak (FT 4 ) may be asked. If the answer is no, then block  123  may be proceeded to where the flame voltage may be increased one step (the maximum flame voltage is not to be exceeded). After block  123 , then the question  119  may be asked and so on. If the answer to the question  122  is yes, then the flame voltage may be increased to a maximum in block  116 . After block  116 , then the question  119  may be asked again and so forth.  
         [0034]     In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense.  
         [0035]     Although the invention has been described with respect to at least one illustrative example, many variations and modifications will become apparent to those skilled in the art upon reading the present specification. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.