Apparatus and method for reducing ignitor activation time in an oil-fired burner

Abstract

A controller for an oil fired burner for operating the ignitor initially in an interrupted mode, and instructing the burner to switch to intermittent ignition for a plurality of call-for-heat (CFH) cycles if it is determined that the flame quality is insufficient during the flame-proved period. On the last predetermined iteration cycle, a reset condition occurs; setting a counter back to zero, and a retry ignition is performed to operate once again in interrupted ignition mode. When the apparatus is in interrupted ignition mode, if the current CFH cycle ends normally by satisfying the call, the ignition will remain in the interrupted ignition mode.

Claims

1. A method for controlling a burner ignition system comprising: initially operating said burner in an interrupted ignition mode during a call for heat; switching to an intermittent ignition mode for a plurality of call-for-heat cycles if during a flame proven mode, a flame is determined to be insufficient or confirmed lost; and reverting back to said interrupted ignition mode when a count of said plurality of call-for-heat cycles reaches a predetermined limit.

2. The method of claim 1 including resetting a call-for-heat iteration loop cycle count back to zero when a count of said plurality of call-for-heat cycles reaches a predetermined limit, and operating said ignition system in said interrupted ignition mode.

3. The method of claim 1 including having said ignition system remain in interrupted ignition mode if a current call-for-heat cycle exits due to lost power, lost T-T, or lost limit condition.

4. The method of claim 1 wherein said flame is determined to be insufficient if an average reading of a CAD cell resistance measurements over a first time period is greater than a running average of CAD cell resistance measurements over a second time period, said second time period shorter than said first time period.

5. A burner ignition system comprising: an air-oil mixture nozzle; electrode tips; and a central processing unit implementing a program readable by a machine, tangibly embodying a program of instructions executable by the machine to perform method steps for controlling said burner, said method steps comprising: a) initially operating said burner in an interrupted ignition mode during a call for heat; b) switching to an intermittent ignition mode for a plurality of call-for-heat cycles if during a flame proven mode, a flame is determined to be insufficient or confirmed lost; c) reverting back to said interrupted ignition mode when a count of said plurality of call-for-heat cycles reaches a predetermined limit; and d) having said ignition system remain in interrupted ignition mode if a current call-for-heat cycle exits due to lost power, lost T-T, or lost limit condition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features of the invention believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The figures are for illustration purposes only and are not drawn to scale. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which:

(2) FIG. 1A depicts a logic flow chart of an algorithm of a preferred embodiment of the present invention from the Power On initiation to the Flame Proven mode;

(3) FIG. 1B depicts a logic flow chart of an algorithm of a preferred embodiment of the present invention of the ignition system method steps occurring after the Flame Proven stage.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

(4) In describing the preferred embodiment of the present invention, reference will be made herein to FIG. 1 of the drawings in which like numerals refer to like features of the invention.

(5) It has been shown that in most applications, where intermittent ignition is used in lieu of interrupted ignition, the interrupted mode would have worked well under most circumstances. An ignitor in intermittent mode will activate along with the fan motor. However, this puts the ignitor in a situation where it remains on for long periods of time during a call for heat, causing the ignitor to operate at its maximum temperature and shortening its life. In a preferred embodiment, the present invention introduces operating the ignitor initially in interrupted mode. If the flame quality is not shown to be measurably sufficient when compared to predetermined quality factors during the Flame-Proven period, the apparatus is instructed to switch to intermittent ignition mode for the next call-for-heat (CFH) cycle or for a plurality of call-for-heat cycles, for example n cycles, where n is a constant predetermined limit. On the last or nth cycle, a reset condition is activated, which sets an iteration loop cycle counter back to zero, and a retry ignition step is performed to operate the system once again in interrupted ignition mode. When the apparatus is in interrupted ignition mode, if the current CFH cycle ends normally by satisfying the call-for-heat and not exiting through the recycle state, the ignition will remain in the interrupted ignition mode.

(6) During the Flame-Proven state, the CAD cell resistance is monitored to assess analytically potential flame loss. A CAD cell is a light-sensitive cell that changes its resistance in the presence of light. In most cases, the resistance decreases as the cell views the light. The CAD cell is used to detect the ignition of the oil burner. In this manner, the quality of the flame is assessed, rather than simply a flame-on or flame-out status, and the system operation alters depending upon the measured flame integrity. As an illustrative example, if at any time during the Flame Proven state, the short term resistance (received in the last second) exceeds a 5 second running average by a predetermined offset resistance value, the ignition mode would be changed to intermittent ignition for the remainder of the CFH cycle currently engaged, and for the next m cycle, where m is a predetermined constant limit. This is neither a flame-on or flame-out condition; rather, it reflects and makes an assessment on the existing quality of the flame at the time of measurement.

(7) FIG. 1A depicts a logic flow chart of an algorithm of a preferred embodiment of the present invention from the Power On initiation to the Flame Proven mode, for addressing and mitigating an undesirably long time period in which an ignitor may be on during a call for heat.

(8) In a first step at initial power on (step 10), an iteration loop cycle count is set to a nonvolatile value of the count, which is initially set to zero (step 12). A call-for-heat signal is then monitored (step 20). If there is a call-for-heat (CFH) signal, a first action is required (step 22). In order to analytically assess the flame quality at interim intervals, the CAD cell resistance is periodically measured (step 24). CAD cell resistances are captured and continuously averaged. In one embodiment, the CAD cell resistance measurements are taken (update) at 50 millisecond intervals, and a running 5 second average is calculated. Upon further inquiry, a quarter-second CAD cell resistance running average is generated with the same sampled data, referred to as the short-term resistance, is also taken, which is ultimately compared to the five second running average for a later assessment of flame quality. This is a measured assessment of flame loss predictability. In this manner, system action may still be required even if the flame is on, since the flame may be of questionable quality.

(9) The system then determines if a try-for-ignition (TFI) period is complete (step 26). The TFI period is complete when flame stabilization is complete. If the TFI period is not complete 28, the algorithm reverts back step 22 to determine if there still is a CFH signal. If the TFI period is complete 30, the iteration loop cycle count is checked to see if this is the first time through this iteration loop (step 32), that is, if the iteration loop cycle count is still zero.

(10) If it is the first time through this iteration loop, the cycle count would still be zero, and the system is directed to assess the flame in the Flame Proven mode (step 34). If it is not the first time through the iteration loop (the iteration loop cycle count does not equal zero), the iteration loop cycle count is incremented (step 36), and compared to a predetermined limit to assess if it has exceeded the predetermined limit (step 38). If the iteration loop cycle count has not exceed the predetermined limit, the nonvolatile value of the count is set equal to the loop cycle count value (step 40), and the system is directed to assess the flame in the Flame Proven mode (step 34). If the iteration loop count exceeds the predetermined limit 42, the iteration loop cycle count is set to zero (step 44), and the nonvolatile value of the count is set equal to the loop cycle count (step 40). Although the predetermined limit may be any value set for continuous operation of the ignition system, preferably, the predetermined limit is in the range of n=2 to 250, and more preferably, the predetermined limit is in the range of n=5 to 50. In one embodiment, the predetermined limit for the iteration loop counter was set at 10.

(11) If, at an interim power on, which is not the initial power on (step 10), there is no call for heat 50, or if upon exit from a prior call-for-heat there is no new call-for-heat, the ignition system is effectively in standby mode. While in standby mode, the system tests to determine if the reset button has been activated which would reset the iteration loop cycle count (step 52). The system determines if the room temperature control thermostat input (T-T) is open (step 54). If the T-T is not open, the system reverts to waiting for a call-for-heat (step 22). If the T-T is open 56, the system determines if a reset condition has been activated (step 58).

(12) If the reset has not been activated 60, a visual indicator 62 is removed. Preferably, the visual indicator is a light indicator, but other visual indicators are not precluded. The ignition system then reverts back to waiting for the next call-for-heat (step 22).

(13) If the reset has been activated 64, the user is notified by the visual indicator (step 66), preferably a light indicator. The iteration loop cycle count is set to zero, and the nonvolatile value of the cycle count is set equal to the iteration loop cycle count (step 68). The ignition system then reverts back to waiting for the next call-for-heat (step 22).

(14) FIG. 1B depicts a logic flow chart of an algorithm of a preferred embodiment of the present invention of the ignition system method steps occurring after the Flame Proven stage. Referring to FIG. 1B, at the Flame Proven stage (step 34), the ignition system checks if the iteration loop cycle count is at zero (step 70). If the iteration loop cycle count is not zero, this means the ignition control is currently in intermittent ignition mode. Consequently, there is no need to monitor the CAD cell resistance for flame quality or flame loss predictability. If the iteration loop cycle count is zero (step 72), the CAD cell resistance is captured for different time intervals (step 74) for two separate calculations: a running average for a first time period; and a second average over a second time period shorter than the first time period. The first calculation is considered a CAD cell resistance running average, while the second calculation is considered a CAD cell resistance read. If the read average is greater than the running average by a predetermined offset limit 76, the iteration loop cycle count is set to 1 and the nonvolatile value of the count is set to the count, i.e., set to 1 (step 78). If the read average is less than or equal to the running average 80, the iteration loop cycle count remains at 0. The running average 80 may include an offset value.

(15) Depending upon the value of the iteration loop cycle count, the ignition mode is adjusted accordingly, such that the ignition mode is in interrupt ignition if the iteration loop cycle count is 0 and in intermittent ignition mode if the iteration loop cycle count is some other count value (step 82). The ignition system next checks to determine if the current call-for-heat has ended (step 84). If the current call-for-heat has not ended, the Flame Proven cycle repeats 86 starting at step 34; else, the nature of how the call-for-heat exited is determined (step 88). If, when proceeding to the exit mode, the resultant activity was determined to be due to lost power 90, the ignition system is powered off (step 92). Power can be lost because either the service switch was open or if control power is governed by a limit string and the limit has been reached. Power loss is not considered an abnormal call-for-heat exit.

(16) If, when proceeding to the exit mode, the resultant activity was determined to be due to lost T-T or reached a boiler condition limit 94, such as for example boiler temperature, exhaust stack pressure, and furnace heat exchanger temperature, to name a few, the ignition system reverts back to waiting for the next call-for-heat (step 20). Limit signals are normally-closed contacts that open when a limit condition is reached. If, when proceeding to the exit mode, the resultant activity was determined to be due to a lost flame condition 96, the ignition system algorithm enters a recycle mode, which turns off the valve, motor and igniter, and sets the iteration loop cycle count to one, and the nonvolatile value of the cycle count to the cycle count, i.e., 1 (step 98). After a predetermined period of time, the ignition system then reverts back to waiting for the next call-for-heat (step 20).

(17) The preferred embodiment described above represents an algorithm that allows the ignition system of an oil-fired burner to operate initially in interrupted ignition mode, and switch to intermittent ignition mode in lieu of an interrupted ignition mode if and when the quality of the flame is measurably insufficient, in which case a flame loss is predictable and anticipated, or the flame is completely lost, and remain in intermittent ignition mode for a predetermined number of call-for-heat cycles. Once the predetermined limit for call-for-heat cycles in intermittent ignition mode is reached, the ignition system is set back to interrupted ignition mode.

(18) Modifications to the algorithm may be made while maintaining the salient features of the present invention to operate a burner initially in the interrupted mode, and switch to an intermittent mode if flame quality is determined to be insufficient during the Flame Proven period. The intermittent mode is used on a cycled basis until a call-for-heat is satisfied or a cycle count reaches a predetermined limit.

(19) While the present invention has been particularly described, in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.