Abstract:
Contamination rate reduction for a flame detection or sensor arrangement using controlled but flexible flame sensor activation. A flame sensor of the subject application is subject to contamination which reduces the lifetime of the sensor. To reduce a contamination rate of the flame sensor, the sensor may be inactivated for certain periods of time when the necessity of flame detection does not appear significant for the use at hand.

Description:
BACKGROUND  
       [0001]     This invention pertains to combustion system flame sensors, and particularly to flame sensor circuits. More particularly, the invention pertains to sensor contamination.  
         [0002]     This invention may be related to U.S. patent application Ser. No. 10/908,463, filed May 12, 2005; U.S. patent application Ser. No. 10/908,465, filed May 12, 2005; U.S. patent application Ser. No. 10/908,466, filed May 12, 2005; and U.S. patent application Ser. No. 10/908,467, filed May 12, 2005. These applications have the same assignee as the present application.  
         [0003]     U.S. patent application Ser. No. 10/908,463, filed May 12, 2005; U.S. patent application Ser. No. 10/908,465, filed May 12, 2005; U.S. patent application Ser. No. 10/908,466, filed May 12, 2005; and U.S. patent application Ser. No. 10/908,467, filed May 12, 2005, are hereby incorporated by reference.  
       SUMMARY  
       [0004]     This invention is an arrangement and approach for reducing a contamination rate in a flame sensor. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0005]      FIG. 1  shows a flame detection or sensing arrangement; and  
         [0006]      FIGS. 2   a ,  2   b ,  2   c  and  2   d  are various timing diagrams of the flame sensor, flame and valve activity. 
     
    
     DESCRIPTION  
       [0007]     Flame rectification type flame sensing arrangements may be subject to continuing performance deterioration due to a build up of contaminants on a flame sensing rod and flame ground area, i.e., proximate to a burner. Over time in the field, the build up may cause intermittent operation or failure of an appliance (e.g., heating unit). Often this problem is not appropriately diagnosed, thus in some cases resulting in repeated service calls and poor customer satisfaction with a system incorporating the flame sensing arrangement.  
         [0008]     In rectification type flame sensors, as noted here, contaminants may accumulate due to ion attraction to an electrically charged flame sensing rod and ground area. When the sensing rod is not energized, contamination rates drop dramatically as the contaminants are not as highly attracted to the rod. However, there still is a continuation of some contamination of the rod. Other flame sensors appear to continuously monitor for a flame during both the normal burner “on” and “off” cycles. Monitoring during the off cycle is considered necessary to detect a flame out of sequence (e.g., a leaky or faulty gas valve). A flame out of sequence may be a rare occurrence, but it needs to be detected when it ever occurs. Thus, various systems maintain energized flame sensing rods whenever the heating unit or appliance is powered. This invention may reduce overall flame sensing rod contamination rates in the field by cycling the flame voltage on and off during a heating off cycle. For example, if a flame voltage (in the off cycle) is imposed in one out of four seconds (i.e., 25 percent duty cycle) rather than continuously, then the rate of flame sensing rod contamination may be significantly reduced. Different duty cycle or time combinations may be used. Reduced duty cycles for flame sensing rod energization may result in a much longer field life of the flame sensor before sensing rod contamination starts to impact performance.  
         [0009]     A flame out of sequence could occur while a burner cycle is ending (i.e., a gas valve does not close properly as expected). The present arrangement may be implemented by maintaining a normal flame sense voltage for a period of time (e.g., 30 seconds or so) after the gas valve is turned off. This approach should detect a problem due to a gas valve failure to immediately close. If no problem is detected during this time period, then a controller may move to the cycling flame voltage sequence of on and off for a reduction of flame sensing rod contamination rates during the rest of the heating off cycle.  
         [0010]     The flame sensor may be on or off while a heating unit or appliance is on. The burner may be on or off while the unit or appliance is on. The sensor may be activated and deactivated for various periods of time while the burner is on and also while it is off. The burner may be a component of the heating unit or appliance. If the heating unit or appliance incorporating a burner is off, then the associated components may be regarded as being effectively off. The heating unit or appliance may be regarded as a part of a larger system (e.g., an HVAC).  
         [0011]      FIG. 1  shows a block diagram of an illustrative example of a flame detector control arrangement  10 . Gas or other fuel may be provided through a conveyance or pipe  11  through a valve  12  to a burner  30  having a flame ground area  13 . Valve  12  may be closed to prevent the flow of gas to the burner  30  and thus extinguish the flame  14 . If the valve  12  is opened, then fuel or gas may be provided to the burner  30 . Valve  12  control may be provided by a signal along a conductor from a controller  16  having a processor  31 , driver circuit  32  and timing circuit  19 . Processor  31  may be connected to temperature and other types of sensors  20 . A power supply  21 , for providing power to the arrangement, may be connected to the processor  31  and driver circuit  32  of controller  16 . Power to the timing circuit  19  and sensors  20  may be controlled and forwarded by the processor  31  from the power supply  21 .  
         [0012]     A spark mechanism in the burner  30  may ignite the gas to bring about the flame  14 . The spark mechanism may receive a sufficient voltage along a conductor  15  from the driver circuit  32 . The flame  14  may be detected by an energized flame sensing rod  17 . If the sensing rod  17  is not energized, it may be energized by a voltage via a conductor  18  from the driver circuit  32 . The timing circuit  19  of controller  16  may provide various patterns for turning on and off the flame sensing rod or flame sensor  17  voltage, along with controlling valve  12 .  
         [0013]      FIGS. 2   a ,  2   b ,  2   c  and  2   d  provide several illustrative examples of timing of the flame sensor or sensing rod  17  energizing together with the timing of gas valve  12  opening and closure, and the presence of flame  14 . The timing signals are of the flame sensing rod  17 , flame  14 , and gas valve  12 , which are designated with reference numerals  27 ,  24  and  22 , respectively. The existence of the flame  14  may be assumed independently of detection by the flame sensing rod  17  for illustrative purposes. The timing graphs have “H” and “L” (e.g., high and low) level indications. “H” indicates that flame sensing rod  17  is energized according to the flame sensing rod timing signal  27 . “L” indicates that flame sensing rod  17  is not energized according to the flame sensing rod timing signal  27 . Similarly, “H” and “L” indicate that the flame  14  is present and not present, respectively, according to the flame timing signal  24 . Likewise, “H” and “L” indicate that the valve  12  is open and closed, respectively, according to the valve timing signal  22 .  
         [0014]     In  FIG. 2   a , the gas valve  12  is indicated as “on” at the left portion of the valve timing signal  22 . Also, the flame sensing rod  17  is energized according to the timing signal  27  and the flame  14  is present according to timing signal  24 . One may note that the flame  14  presence may continue briefly according to signal  24  after gas valve  12  is closed at time line  23  according to signal  22  at that time. The flame presence  14  may continue for an additional period of time up to time line  25  according to timing signal  24 , possibly due to remaining gas in the pipe  11  between the valve  12  and the burner  30 , or due to a slow closure of valve  12 . The flame  14  may stay on if the valve  12  is stuck open, and likewise flame sensor  17  will remain on as long as the flame  14  is sensed by the flame sensor  17 . The flame sensor or sensing rod  17  may purposely remain energized, even if valve  12  is appropriately closed, for a period as indicated by signal  27  up to at least time line  26 . Such period of time may be  15 ,  30  or more or less seconds. After the time line  26 , which is an “burner off” cycle, assuming the flame  14  to be extinguished, the arrangement may energize the flame sensing rod  17  just periodically (rather than continually) for flame detection to reduce rod contamination. For an illustrative example, the energization signal  27  for the flame sensing rod may have a  25  percent duty cycle, i.e., the sensing rod  17  may be energized for one second, deenergized for three seconds, periodically, until the gas valve  12  is turned on as indicated by signal  22  at a time line  28 . The duty cycle may be some other percentage as appropriate for reliable monitoring of the burner  30 . The flame  14  may ignite at time line  29 .  
         [0015]      FIG. 2   b  shows another example of timing of the flame sensing rod  17  energization signal  27  relative to the flame  14  indication signal  24  and gas valve  12  activation signal  22 . A significant difference between this diagram and that of  FIG. 1   a , is that during the “burner on” period up to the time line  23 , the flame sensing rod  17  energization signal  27  may have a duty cycle, such as 25 percent, where it is energized for a period of time and then deenergized for another period of time in a periodic fashion, to reduce the rate of contamination of the flame sensing rod  17 . However, as in  FIG. 2   a , the sensing rod  17  energization signal  27  may remain on continually for a period of time after the gas valve  12  closure. Various other patterns of timing signals may be implemented for an arrangement or system. Also, such timing may be non-periodic.  
         [0016]      FIGS. 2   c  and  2   d  show other illustrative examples of timing diagrams of flame sensing rod  17  energization signals  27  that might not have consistent, regular, or periodic patterns. The deenerization and energization of the flame sensing rod  17  may be indicated by timing circuit  19  signals via controller  16  that may provide a good timing profile of signal  27  in view of other parameters, such as those noted by sensors  20 , from or to the flame detector control arrangement  10 . The signal  27  profile may be dynamic in pattern. Also, the time lines  23 ,  25 ,  26 ,  28  and  29  may be shifted or be dynamically shifting from time to time in accordance with signals of the controller  16  for one reason or another. There may be various combinations of timing diagrams in a sensing arrangement or system.  
         [0017]     A need or an estimated need for flame sensing may be a basis for a timing pattern for energization of the flame sensor  17 . Such timing pattern could be but would not necessarily be regular or periodic. Controller  16  may control the energization or activation of the flame sensor  17  with approaches that indicate the times when to activate and inactivate the flame sensor  17  in order to maximize the monitoring of the burner  30  and its flame  14 , if there is a flame, and minimize the contamination rate of the sensor  17 , in conjunction with a number of variables and fixed parameters. Some of the flame sensor energization and deenergization timing techniques involving variables and parameters for controlling the flame sensor  17 , valve  12  and burner  30 , incorporated in controller  16 , may include model predictive control (MPC) and optimization, proportional-integral-derivative (PID) tuning and control, fuzzy logic control, neural network control, and the like. Examples of applications, arrangements or systems related to the control strategy of controller  16  applicable to flame sensor  17  activation and inactivation, relative to burner  30  flame  14  status, may be based on principles and concepts disclosed in U.S patent application Ser. No. 11/014,336, filed Dec. 16, 2004; U.S. Pat. No. 5,351,184, issued Sep. 27, 1994; U.S. Pat. No. 5,561,599, issued Oct. 1, 1996; U.S. Pat. No. 5,574,638, issued Nov. 12, 1996; U.S. Pat. No. 5,572,420, issued Nov. 5, 1996; U.S. Pat. No. 5,758,047, issued May 26, 1998; U.S. Pat. No. 6,122,555, issued Sep. 19, 2000; U.S. Pat. No. 6,055,483, issued Apr. 25, 2000; U.S. Pat. No. 6,253,113, issued Jun. 26, 2001; U.S. Pat. No. 6,542,782, issued Apr. 1, 2003; and U.S. patent application Ser. No. 11/323,280, filed Dec. 30, 2005; all of which are hereby incorporated by reference. These patents and applications are assigned to the assignee of the present invention.  
         [0018]     In the present specification, some of the matter may be of a hypothetical or prophetic nature although stated in another manner or tense.  
         [0019]     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.