Patent Application
20070028858
This invention relates to controllers for gas fired heaters, and more particularly to controllers for either 120 volt or 240 volt gas fired water heater applications.
Gas fired water heating appliances such as a pool water heater typically have a controller for controlling the supply of gas and an igniter for igniting the gas. An igniter known in the art that is capable of warming up quickly is a silicon nitride hot surface igniter. While such an igniter is desirable because of its mechanical strength and durability, it has a critical temperature limitation which must be avoided. Specifically the silicon nitride igniter must remain below approximately 1350° Celsius. If the igniter temperature repeatedly approaches 1350° C., the igniter will cease to ignite prematurely. Thus, electrical power to the igniter must be controlled to provide an igniter temperature that is sufficient to ignite gas and is below the 1350° C. temperature limitation.
Gas fired water heaters for pools typically require either a 120 volt or 240 volt alternating current power source for pump motors and other components. Controllers for such pool water heaters therefore had to be configured in either a 120 volt or 240 volt embodiment, for controlling the application of power to related components such as an igniter. This is particularly the case with the silicon nitride hot surface igniter, which requires careful control of power applied to the igniter to avoid its critical temperature. Such controllers are typically required to switch power to the igniter to provide an averaged applied voltage of a predetermined level from the line voltage power source. Therefore, the line voltage level of an existing pool water heater that is to be replaced is significant to the selection of the replacement water heater controller.
The present invention relates to a controller for controlling the operation of a gas-fired water heating appliance. In one embodiment of the present invention, a controller is provided that comprises a switching means for connecting an electrical power source to an igniter for igniting gas, a voltage sensing means for sensing the voltage value of the electrical power source, and a processor that is capable of determining whether the power source is of a first rated voltage level or a second rated voltage level. The processor is capable of responsively selecting an appropriate switching sequence from a look-up table having a plurality of switching sequences corresponding to a plurality of voltage values for either the first rated voltage or the second rated voltage, where the processor controls the switching means based on the selected switching sequence to effect switching of power to supply an average predetermined voltage to the igniter that will heat the igniter to a desired temperature.
The controller further comprises means for determining whether the electrical power source is of a first or second rated voltage level through one of either an Analog-to-Digital input to the processor for sensing the voltage level of the power source, a voltage comparator circuit that provides a voltage level signal to the processor, or a voltage detection circuit for sensing the connection of either voltage source.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
One embodiment of a controller for a gas-fired water heater appliance in accordance with the principles of the present invention is indicated generally as 20 in
The controller 20 comprises a non-linear op amp 32 configured as a comparator circuit, for comparing the line voltage from terminals 24 to determine whether the power source is of either a first rated voltage or a second rated voltage. Specifically, the line voltage connection at terminals 24 may be input to a non-linear Op-amp, which provides an input to the plus pin 34 and an input to the minus pin 36 of the comparator 32. The comparator circuit provides an output at 38 to the processor 30, which determines whether the power source is of either a first rated voltage or a second rated voltage based on the output signal at 38. The processor 30 may then determine which look up table to use in selecting a switching sequence, which will control switching of power to the igniter 26 based on the actual line voltage value.
The controller further comprises a second non-linear op amp 40 configured as a comparator circuit, for comparing a reference voltage at plus pin 42 to a representative fraction of the line voltage value at minus pin 44, for determining the actual value of either the first rated voltage or the second rated voltage. The output signal of the op amp 40 is a sine wave that varies in amplitude, and may be input to the processor for evaluation. In the preferred embodiment of the present invention, the arrangement of the non-linear op amp 40 is preferably configured to sense a 1/100 fractional portion of the line voltage value and compare the fractional amount to a 5 volt direct current reference, where the output signal may be input to an Analog-to-Digital converter in the processor 30 such that digital values are established for the actual voltage at a resolution of at least two percent of the line voltage. Thus, for every two percent change in actual line voltage value, the processor 30 would be capable of correspondingly select a different switching sequence to apply pulsed power to the igniter 26 at a desired averaged voltage.
The controller 20 further comprises a switching means 22 for switching line voltage to the hot surface igniter 26. The switching means 22 may comprise a single triac that can be gated to conduct either positive or negative voltage. The switching means 22 could also comprise first and second SCR's, wherein the first provides for switching one direction of an alternating current source and the second provides for switch the opposite direction of an alternating current source. The processor 30 controls the switching of a transistor 50 for switching low voltage power from a power supply 48 to a light emitting diode 52, which may be part of an opto-isolator or other similar switching component. For example, the triac 54 and LED 52 may be a single phot-gating component. By controlling the switching of a transistor 50, the processor 30 is capable of controlling the switching means 22 to either effect continuous conduction through the switching means 22 to supply continuous alternating current to the igniter during warm up, or to effect periodic intermittent conduction through the switching means 22 to supply intermittent alternating current to the igniter. Specifically, the processor 30 controls intermittent switching of power to the igniter 26 by using an appropriate switching sequence, having a series of on and off half-wave periods of an alternating current source. Each switching sequence corresponding to a given voltage value comprises a duty cycle of on and off half wave periods of an alternating current source, where the duty cycle of intermittent voltage application to the igniter provides a desired averaged voltage or RMS voltage to the igniter. Thus, for any actual voltage value for either the first rated voltage or the second rated voltage, the processor may select a switching sequence having a duty cycle that will provide a predetermined voltage to the igniter 26 that will heat the igniter 26 to a desired temperature.
An example of a switching sequence having a duty cycle of on and off half wave periods of an alternating current source is illustrated in
In operation, the processor 30 determines whether the power source 24 is of either a first rated voltage of 120 volts or a second rated voltage of 240 volts (alternating current), and also determines the actual peak line voltage value of the alternating current waveform. From the actual voltage value determined via the input signal at 46 to the processor 30, the processor 30 looks up an appropriate switching sequence from either a first look-up table corresponding to the first rated voltage or a second look-up table corresponding to the second rated voltage. In the preferred embodiment, the first look-up table is for a rated voltage of 120 vac, and the second look-up table is for a rated voltage of 240 vac. From the first or second table, the processor 30 selects an appropriate switching sequence from a plurality of switching sequences corresponding to a plurality of voltage values, where the selected switching sequence corresponds to the actual line voltage value determined by the processor 30. The processor 30 is capable of responsively selecting an appropriate switching sequence from a look-up table having a plurality of switching sequences corresponding to a plurality of voltage values for either the first rated voltage or the second rated voltage, where the processor 30 controls the switching means 22 based on the selected switching sequence to effect switching of power to supply an average predetermined voltage to the igniter 26 that will heat the igniter 26 to a desired temperature. By intermittently switching line voltage to the igniter at a predetermined duty cycle, the controller 20 provides a predetermined averaged voltage to the igniter that will heat the igniter to a desired temperature.
The preferred embodiment of the present invention may also be capable of determining polarity and voltages that are not compatible with the controller 20, such as a three phase power source. If such a power source is connected to the controller 20, the processor will establish a lock-out of igniter and water heater operation. Likewise, the processor 30 may determine a disagreement between the comparator output signal 38 representing a first or second rated voltage and the comparator output signal 46 representative of the actual voltage level, to provide a redundant measurement and accordingly lock out operation of the water heater when not in agreement.
The advantages of the above described embodiment and improvements should be readily apparent to one skilled in the art, as to enabling control of application of either a first or second rated power source to an igniter for a gas fired water heater. Additional design considerations may be incorporated without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited by the particular embodiment or form described above, but by the appended claims.
