Patent Application
20110269080
This invention relates to automatic electronic ignition systems in general and more specifically to automatic electronic ignition systems using hot surface igniters in gas lamps.
Sensing the presence of a flame in a light fixture or appliance may be desirable to ensure that, if the flame goes out, it can be automatically reestablished using an automatic electronic ignition system. Existing automatic ignition systems that rely on additional heat sensing devices such as thermocouples, flame rectification, or light sensors have drawbacks, however. Thermocouples require additional parts and have a slow response time so re-ignition may be unreasonably delayed. Flame rectification requires properly arranged geometries and conducting surfaces near the flame which may make installation troublesome and unreliable. Light sensors may be limited in their effectiveness because they cannot account for external radiation or variation in flame intensity. Thus, there developed a need for an automatic re-ignition system to promptly sense when the flame has gone out and automatically reestablish it without cumbersome secondary parts and systems for doing so.
The following summary provides a brief overview of the claimed apparatus and methods for an automatic ignition system. The summary, however, shall not limit the invention in any respect. A detailed and fully enabling disclosure is set forth in the detailed description of the invention.
In one embodiment, an apparatus for automatically igniting a gas lamp by sensing the presence of a flame may include an igniter, power source, relay, valve controller, pulse-width modulator, and microcontrol unit. The igniter is operatively associated with the power source and converts electricity from the power source into heat. The relay is connected to the power source and the igniter, and relays the electricity supplied from the power source to the igniter. The valve controller is operatively associated with the igniter and controls a supply of a combustible fluid to the igniter. The pulse-width modulator is operatively associated with the power source and the igniter, wherein the pulse-width modulator provides additional power to the igniter.
The microcontrol unit is operatively associated with the igniter, the power source, the valve controller, the relay, and the pulse-width modulator. The microcontrol unit uses the pulse-width modulator to calibrate a total power supply to the igniter and determines the presence of a flame by sensing an electrical resistance of the igniter to the total power supply. The microcontrol unit also controls the amount of electricity supplied to the igniter through the relay and adjusts the amount of combustible fluid supplied to the igniter through the valve controller.
A method for automatically igniting a combustible fluid by sensing the presence of a flame may comprise: controlling a supply of power to an igniter to heat the igniter and ignite the combustible fluid; controlling a supply of the combustible fluid to the igniter; measuring a resistance of the igniter to the supply of power; establishing a range of resistance relating to a temperature range of the igniter; changing the supply of combustible fluid to the igniter when the resistance of the igniter is outside the established range of resistance; supplying power to heat the igniter and automatically ignite the combustible fluid when the resistance of the igniter is outside the range of resistance; and repeating the step of measuring the resistance of the igniter to the supply of power when the resistance of the igniter is within the established range of resistance.
In addition, the method for automatically igniting a combustible fluid may further comprise: calibrating the range of resistance by supplying an additional supply of power through a pulse-width modulator at a specific duty cycle to the igniter; delaying the supply of power to heat the igniter and re-measuring the resistance of the igniter when the combustible fluid is ignited, thereby preventing an unnecessary ignition; and preventing the supply of power and the supply of the combustible fluid when the resistance measurement of the igniter repeatedly falls outside of the established resistance range.
Illustrative and presently preferred embodiments of the invention are shown in the drawings in which:
The present invention comprises automatic electronic ignition system 10 and method 100 to automatically ignite a combustible fluid (e.g., natural gas, propane) in lamps, furnaces, or other similar devices, using a hot surface igniter (HSI) 70. In the present invention HSI 70 not only ignites the combustible fluid in the first instance, but also senses the presence (or absence) of a flame 82 without additional heat sensors, enabling the combustible fluid to be automatically re-ignited if flame 82 goes out. As used in the description of embodiments of the invention, the combustible fluid is gas; however, the present invention should not be viewed as being limited in this respect. Automatic electronic ignition system 10 and method 100 of the present invention are directed to obtaining resistance measurements of HSI 70 over time, calculating any change in resistance, correlating resistance change to temperature change of HSI 70, and using that correlation to determine if flame 82 has gone out. Thus, unlike many other systems and methods, no additional heat sensors are required in the present invention.
Automatic electronic ignition system 10 will now be described in an embodiment comprising gas lamp 22, as shown in
Gas supply 78 supplies gas for flame 82 through gas valve 74 which regulates the flow of gas in gas supply 78. Gas valve 74 is controlled by ignition control unit 18, which also controls the power supply to HSI 70. As is explained in more detail below, in conjunction with the ignition control unit 18, HSI 70 automatically ignites gas from gas supply 78 to form flame 82. Thereafter, ignition control unit 18 collects data about the temperature (resistance measurements) of HSI 70 which can then be used to determine the condition of flame 82 and to re-ignite the gas when flame 82 has gone out.
Ignition control unit 18 comprises transformer 46, regulator 62, relay 54, microcontrol unit 34, watchdog programmable interface controller (PIC) 50, and valve control 58, as
Power source 66 supplies current to heat HSI 70 via ignition control unit 18 through relay 54, which may be an electromagnetic or solid state device. HSI 70 acts as a resistor, converting current from power source 66 into heat until HSI 70 reaches a temperature high enough to ignite the gas. Temperatures generally suitable for igniting propane or natural gas are in the range of about 450° C. to about 650° C., for example.
In addition to directing current to HSI 70 directly from power source 66, relay 54 also directs current from microcontrol unit 34 to HSI 70 to collect data (e.g., resistance measurements) from HSI 70 that can then be used to determine the condition of flame 82, as will be explained in more detail below. Resistance measurements from HSI 70 correspond to the temperature of HSI 70 at the point in time in which any resistance measurement is made. Resistance measurements may vary in view of the presence of flame 82, as well as ambient temperature or the model of HSI 70 used in any particular embodiment of the present invention. After obtaining resistance measurements from HSI 70, microcontrol unit 34 correlates any change in resistance measurements over time to a change in temperature of HSI 70 and thereby determines whether flame 82 has been extinguished or not.
Microcontrol unit 34 is operatively associated (1) with power supply 66 through regulator 62 and transformer 46, (2) with HSI 70 through relay 54, (3) with gas supply 78 through gas valve 74, and (4) with watchdog PIC 50. In the embodiment shown in
Microcontrol unit 34 is connected to HSI 70 through relay 54 so that microcontrol unit 34 can (1) calibrate the total voltage supply to HSI 70, (2) obtain resistance measurements from HSI 70, and (3) send instructions to relay 54 when it is time to automatically ignite or re-ignite gas from gas supply 78. In one embodiment, microcontrol unit 34 comprises a central processing unit, a timer, input and output ports, and an analog-to-digital converter and a digital-to-analog converter, which act as a pulse-width modulator to offset the voltage supply to HSI 70 and calibrate the total voltage supply to HSI 70. After offsetting the total voltage supply to HSI 70, power source 66 sends current directly to HSI 70 via relay 54 while delaying the opening of gas valve 74. Delaying the opening of gas valve 74 reduces gas accumulation by allowing HSI 70 to reach ignition temperature before being introduced to gas from gas supply 78. Once the total voltage supply is calibrated, microcontrol unit 34 may obtain resistance measurements from HSI 70 at predetermined intervals. The central processing unit of microcontrol unit 34 processes the resistance measurements in accordance with the instructions embedded in its firmware or software to determine whether flame 82 has gone out.
If microcontrol unit 34 determines by following method 100 of the present invention that flame 82 has gone out, then microcontrol unit 34 signals relay 54 that HSI 70 needs to automatically re-ignite gas from gas supply 78 to form flame 82. Microcontrol unit 34 sends an electronic signal through the various output ports to relay 54, thereby reconnecting HSI 70 to power source 66 through relay 54. The connection between HSI 70 and power source 66 provides an increased amount of current to HSI 70, thereby heating HSI 70 to the ignition temperature.
In order for HSI 70 to re-ignite the gas, gas valve 74 must be opened. In that instance, microcontrol unit 34 sends a signal to valve control 58 to open gas valve 74. Valve control 58 opens gas valve 74, thereby allowing gas to flow through gas supply 78 to HSI 70. Gas valve 74 may comprise an electromechanical valve, such as a solenoid valve, that is operatively associated with valve control 58. If, on the other hand, microcontrol unit 34 determines that flame 82 remains lit and has not been extinguished, then microcontrol unit 34 continues sending a signal to valve control 58 to maintain the flow of gas through gas supply 78 to HSI 70.
In the embodiment shown in
Having described automatic electronic ignition system 10, method 100 for igniting the combustible fluid (e.g., gas) will now be described. Method 100 comprises (1) calibrating automatic electronic ignition system 10, (2) processing resistance readings related to HSI 70 to predict the presence of flame 82, and (3) re-igniting gas lamp 22 in the absence of flame 82.
The step of calibrating automatic electronic ignition system 10 includes using offset nulling to offset the resistance reference readings of HSI 70 by offsetting the total voltage supply to HSI 70. The total voltage supply to HSI 70 is offset until the summed output voltage is similar regardless of the type of HSI 70 or ambient temperature. In one embodiment, microcontrol unit 34 offsets the total voltage supply to HSI 70 through pulse-width modulation, which provides HSI 70 with an intermediate supply of current from power source 66. The offset voltage is accordingly used to calibrate automatic electronic ignition system 10 regardless of the model of HSI 70 used or the ambient temperature.
Different HSI 70 models may have predictable trends relating to changes in resistance relative to changes in temperature. However, the initial resistance reading of any particular HSI 70 may be affected by the model of HSI 70 or ambient temperature. For example, while a resistance measurement increase of 30 ohms in HSI 70 may indicate the presence of flame 82, the beginning resistance reference reading may vary by more than 150 ohms depending on the model of HSI 70 or ambient temperature. While a fixed circuit could measure a wide range of resistance expected from various models of HSI 70 and changes in ambient temperature, such a circuit would not accurately and efficiently predict the presence of flame 82 because of the wide range of resistance measurements needed. In order to narrow the range of resistance measurements needed to indicate the presence of flame 82, method 100 further comprises calibrating automatic electronic ignition system 10 using offset nulling, thereby creating a more precise and efficient automatic electronic ignition system 10.
The calibrating step occurs when gas valve 74 is closed and relay 54 restricts any current from power source 66 to HSI 70. In one embodiment, the calibrating step comprises continuously sending current to HSI 70 (e.g., through microcontrol unit 34) while measuring the resistance of HSI 70 to establish an initial reference point before igniting the gas. The current may also be sent to HSI 70 at periodic intervals as would be apparent to a person skilled in the art after having read the present disclosure.
Sending current from microcontrol unit 34 to HSI 70 is not for igniting the gas but rather for obtaining resistance measurements that vary due to the ambient temperature, the model of HSI 70, and the presence of flame 82. After establishing the initial reference point, method 100 comprises determining if the voltage supply to HSI 70 should be offset. The voltage supply to HSI 70 is offset if the initial reference point is outside a predefined range of resistance. The predefined range of resistance is set depending on the model of HSI 70 used for specific gas lamp 22.
Offsetting the total voltage supply to HSI 70 helps ensure subsequent resistance (temperature) readings fall within the predefined resistance range. Having the subsequent resistance readings fall within the predefined range of resistance allows method 100 to more efficiently and accurately predict the presence of flame 82 regardless of ambient temperature or model of HSI 70. For example, if the ambient temperature is 150° C. rather than room temperature (20° C. to 25° C.), the resistance of HSI 70 will rise. The rise in resistance will cause microcontrol unit 34 to offset the total voltage supply to compensate for the change in resistance due to the rise in ambient temperature. Once offset, the resistance readings of HSI 70 will fall within a smaller window of resistance, which allows microcontrol unit 34 to more efficiently determine the presence of flame 82.
As part of offsetting the current supply to HSI 70, method 100 further comprises creating a variable voltage at a specific duty cycle from pulse-width modulation. Creating the variable voltage may comprise microcontrol unit 34 acting as a pulse-width modulator to create the variable voltage at the specific duty cycle. Pulse-width modulation provides an intermediate supply of voltage from microcontrol unit 34 to HSI 70. A change in the duty cycle affects the intermediate supply of electrical power from power source 66. An increase in duty cycle will increase the pulse-width modulation and accordingly increase the intermediate supply of electrical power. Initially, setting the duty cycle comprises adding a small amount of voltage from pulse-width modulation to the voltage generated by passing a constant current through HSI 70 (e.g., microcontrol unit 34) in order to measure the resistance of HSI 70. Establishing the specific duty cycle comprises adjusting the pulse-width modulation variable voltage until the summed output voltage is similar regardless of the HSI 70 model or ambient temperature. If microcontrol unit 34 detects a new HSI 70 model, or a substantial change in ambient temperature then the specific duty cycle is adjusted. Thus, by offsetting the current supply with pulse-width modulation at a specific duty cycle, resistance readings may be efficiently and accurately obtained from HSI 70 regardless of the ambient temperature or model of HSI 70.
Once automatic electronic ignition system 10 is calibrated, method 100 further comprises processing resistance readings from HSI 70. Processing the resistance readings comprises automatically predicting the presence of flame 82 by analyzing trends in resistance measurements at specific instances in time (i.e., instantaneous trend of resistance analysis), using instructions embedded in firmware or software. In one embodiment, the firmware is embedded in ignition control unit 18 and is written in a high-level procedural computer programming language containing instructions for adjusting the voltage supply to HSI 70, and for signaling relay 54 and valve control 58. Such high-level procedural computer programming firmware allows a user to preset calibration parameters relating to resistance readings and to preset time delays in opening gas valve 74 before igniting the gas. Once parameters are set, resistance readings can be processed automatically using the instantaneous trend of resistance analysis to predict the presence of flame 82.
By analyzing trends in resistance measurements at specific instances in time, a HSI 70 temperature (Tp) can be predicted automatically based on a real-time temperature (Tc), a first derivative of the real-time temperature (dT), and a second derivative of the real-time temperature (d2T). Calculating the first derivative (dT) and second derivative (d2T) may comprise obtaining at least three temperature (resistance) samples of HSI 70 at one second intervals and feeding the samples into a first-order exponential decay curve using the equation (Tp)=(Tc)−((dT)̂2)/(d2T) to predict HSI 70 temperature (Tp). While the present example employs one second intervals, other intervals may be employed.
A hypothetical first-order exponential decay model 200 is shown in
If the result of method 100 predicts that flame 82 is present, then method 100 comprises continuing to process resistance readings from HSI 70. Otherwise, method 100 further comprises re-igniting gas lamp 22 by sending a signal to valve control 58 to shut gas valve 74 and restrict the flow of gas from gas supply 78, and by sending a signal to relay 54 to direct current from power source 66 to HSI 70. Once HSI 70 reaches an acceptable temperature range (resistance range) for ignition then the signal is sent to valve control 58 to open gas valve 74 and allow gas to flow from gas supply 78 to HSI 70. Delaying the opening gas valve 74 minimizes gas accumulation in the vicinity of HSI 70 by allowing HSI 70 to reach ignition temperature before being introduced to gas from gas supply 78.
In addition, if the gas is not ignited within the predetermined time frame or after at least two consecutive tries, method 100 may further comprise stopping the gas flow by closing gas valve 74 and stopping the transmission of current to HSI 70 from power source 66. Stopping the gas flow and closing gas valve 74 may comprise overriding microcontrol unit 34 with watchdog PIC 50. For example, in one embodiment, if microcontrol unit 34 opens gas valve 74 and signals relay 54 to heat HSI 70 for more than a predetermined number of consecutive tries (e.g., three) without ignition then watchdog PIC 50 will override microcontrol unit 34 to shut gas valve 74 and stop sending additional current to HSI 70.
Thus, as
While the present invention only illustrates certain embodiments, it will be apparent to those skilled in the art after having read this disclosure that various changes and modifications can be made without departing from the claimed scope of the invention. For example, a skilled person in the art may change the size, shape, location or orientation of the various components without departing from the scope of the present invention. Likewise, the present invention may include structures between components that are shown directly connected or contacting each other without departing from the scope of the invention.
Having set forth the various embodiments, the present invention anticipates suitable modifications which remain within the scope of the invention. Therefore, a person skilled in the art should only construe this invention in accordance with the following claims.
