Detailed Description
Fig. 1 shows a first embodiment of a flame monitoring system 1 according to the invention for a burner of a gas appliance.
The gas appliance incorporating the flame monitoring system 1 is preferably an electronic gas range, although the flame monitoring system 1 may be incorporated into any other type of gas appliance known in the art, such as a gas stove. Furthermore, the gas appliance may comprise one burner or a plurality of burners, each comprising a respective flame monitoring system 1.
The flame monitoring system 1 of the present invention comprises a thermocouple 2 arranged beside the burner and an electromagnetic gas valve for opening or closing the gas passage to said burner. The solenoid gas valve is preferably a safety valve that is part of a gas tap. The user adjusts the gas flow rate to the burner by operating the gas cock, and if there is no flame in the burner, the electromagnetic gas valve closes the gas passage, thereby preventing gas leakage. ES1087355U shows an example of a gas tap with an electromagnetic gas valve.
As is well known to those skilled in the art, a thermocouple is a transducer formed by the combination of two different metals, the thermocouple causing a very small potential difference which is a function of the temperature difference between one of the two ends, called the hot spot, and the other end, called the cold spot, i.e. when the thermocouple is subjected to temperature, it generates a voltage in its terminals.
Similarly, as is well known to those skilled in the art, an electromagnetic gas valve includes an electromagnetic coil and a shutter (shutter) that opens or closes a gas passage. The solenoid converts the electrical energy into mechanical energy by means of magnetic force to act on the shutter, so as to be able to keep the gas passage open when the voltage received by the solenoid reaches a sufficient level.
In the flame monitoring system 1 of the present invention, the electromagnetic gas valve is electrically connected to the thermocouple 2, that is, the electromagnetic coil 3 of the electromagnetic gas valve is electrically connected to the thermocouple 2 and is powered by the thermocouple 2. In this case, when the voltage generated by the thermocouple 2 reaches a sufficient level, the solenoid 3 of the solenoid gas valve actuates the shutter of said solenoid gas valve, thus maintaining the gas passage to the corresponding burner in an open condition.
Thus, when the burner is ignited (i.e., when the burner produces a flame), the thermocouple 2 generates a voltage. When the thermocouple 2 reaches a sufficient temperature, it generates a sufficient voltage so that the solenoid 3 of the solenoid gas valve keeps the gas passage in an open state.
The gas tap comprises an adjustment element for adjusting the gas flow by means of rotation and a manual actuator for rotating said adjustment element. In addition to regulating the flow, it is also necessary to open the solenoid valve to allow the gas to flow to the burner. For example, as described in ES1087355U, it is preferable that the solenoid valve is opened by axial movement of a manual actuator. As soon as the gas passage to the burner is opened by said manual actuator, the burner generates a flame that heats the thermocouple 2, said thermocouple 2 generating the above-mentioned voltage. It is necessary to keep the gas channel open in another way before the thermocouple 2 reaches a sufficient temperature. The user must keep the gas channel open by operating the manual actuator until the thermocouple 2 reaches a sufficient temperature, as is known in the art. Burners are also known which incorporate an ignition-assist system for powering the solenoid gas valve by means of an additional power source (for example a pre-charged capacitor with ignition-assist function) during the time when the thermocouple 2 reaches said sufficient temperature.
The flame monitoring system 1 comprises a voltmeter 4 for measuring said voltage generated by the thermocouple 2. The flame monitoring system 1 further comprises a control unit 6 and an interruption device 5, the interruption device 5 being configured to interrupt the flow of current between the thermocouple 2 and the electromagnetic gas valve during a predetermined time, the predetermined time being the time during which the electromagnetic gas valve keeps the gas channel in an open state by means of the actual inertia of the electromagnetic gas valve during the interruption, so that the voltmeter 4 can measure the voltage of the thermocouple 2 in an isolated state. In other words, as long as said period of time is sufficiently short, the actual inertia of the solenoid 3 of the solenoid gas valve continues to generate the mechanical energy required to keep the shutter in the open position, although the latter is not powered.
As described above, the voltage generated by the thermocouple 2 is small. Measuring the voltage in the isolated state provides a more reliable measurement value with a lower noise level. Thus, good voltage measurements of the thermocouple 2 can be obtained in a simple and inexpensive manner.
As mentioned above, the thermocouple 2 generates a voltage in its terminals according to the temperature to which it is subjected (here due to the flame generated by the burner). The voltage measurement of the thermocouple 2 thus makes it possible to monitor the flame condition of the burner and to detect possible anomalies (for example, the flame being inadvertently extinguished due to gas flows or liquid spills). Monitoring the flame condition of the burner enables the control unit 6 to perform advanced functions (e.g. re-igniting the flame if it is inadvertently extinguished).
Electronic gas appliances comprising advanced functions usually comprise a control circuit which is responsible for supplying the electromagnetic coil of the electromagnetic gas valve, i.e. which receives the voltage generated by the thermocouple and, according to an operating algorithm, generates an electrical signal which is fed to the electromagnetic coil of the electromagnetic gas valve. Gas appliances of this type must comply with very strict regulations in order to prevent malfunctions related to unintentional electromagnetic gas valve opening due to errors in the control circuit or control algorithm. In the case of an electromagnetic coil of an electromagnetic gas valve which is supplied with power only by a thermocouple, this type of malfunction does not occur, and therefore the safety standards to be adhered to are less stringent. Thus, a gas appliance incorporating the flame monitoring system 1 of the present invention may perform advanced functions (e.g., re-igniting a flame if it is inadvertently extinguished) while belonging to a category in which safety standards to be adhered to are less stringent.
Preferably, the interruption means 5 of the flame monitoring system 1 allows a current flow between the thermocouple 2 and the electromagnetic gas valve at least during a predetermined time interval in the absence of mains power, i.e. a gas appliance incorporating the flame monitoring system 1 may be operated in the absence of mains power at least for a predetermined period of time. Thus, a gas appliance can be obtained: the gas appliance has advanced functionality when powered by the grid (e.g., re-igniting the flame if it is inadvertently extinguished), but at the same time allows the user to use the basic functionality of the gas appliance at least for a period of time without grid current.
The interruption means 5 preferably comprise a switch electrically connected in series between the thermocouple 2 and the electromagnetic gas valve, the voltmeter 4 being arranged in parallel with the thermocouple 2. In other embodiments, not shown, the interrupting device includes a diverter that electrically connects the thermocouple with the electromagnetic gas valve in a first position and connects the thermocouple with the voltmeter in a second position.
In a first embodiment of the invention, shown in figure 1, the switch comprises a normally-on MOSFET 50, the normally-on MOSFET 50 being configured to allow and interrupt the flow of current between the thermocouple 2 and the electromagnetic gas valve.
In this first embodiment, since the MOSFET 50 is of the normally open type, in order to enable the thermocouple 2 to be electrically connected to the electromagnetic gas valve without mains power (i.e. in order to enable the gas appliance to operate at least for a predetermined period of time), the MOSFET 50 is also powered by an additional power supply circuit comprising an additional power supply 7 other than the mains, which supplies said MOSFET 50 during a predetermined period of time in the absence of mains current. The power source 7 is preferably a battery or a pre-charged capacitor. Thus, a gas appliance incorporating the flame monitoring system 1 shown in fig. 1 may operate in the most basic mode, at least for a certain period of time, in the absence of mains current, since the additional power supply 7 will allow the normally open MOSFET 50 to close, whereby the thermocouple 2 may be connected to the electromagnetic gas valve. When the gas appliance is powered by mains current, the additional power supply will preferably be responsible for the normal operation of the gas appliance.
Fig. 2 shows a second embodiment of the flame monitoring system 1. The second embodiment differs from the first embodiment in the interrupting device 5. The remaining features are similar to those of the first embodiment and therefore it is not considered necessary to describe them again.
In this second embodiment, the interrupting device 5 includes a normally closed relay 51 in addition to the normally open MOSFET 50, the relay 51 being electrically connected in parallel with the MOSFET 50. Thus, in the absence of grid current, the normally closed relay 51 allows current flow between the thermocouple 2 and the electromagnetic gas valve, so that the gas appliance incorporating the flame monitoring system 1 can operate despite the absence of grid current. Conversely, when the interrupting device 5 is powered by the mains current, the relay 51 will open and the MOSFET 50 will be responsible for allowing or preventing the flow of current between the thermocouple 2 and the electromagnetic gas valve. This second embodiment allows a gas appliance incorporating the flame monitoring system 1 to operate at all times regardless of the presence of grid current (i.e., without limitation, energy stored in an additional power source as in the embodiment of fig. 1). A gas appliance incorporating a flame monitoring system 1 is thus obtained which can always operate without mains current.
When the interrupting device 5 allows a current to flow between the thermocouple 2 and the electromagnetic gas valve, the interrupting device 5 preferably has an on-resistance that is less than half the resistance of the electromagnetic gas valve. The maintenance of this ratio ensures that the voltage to the solenoid gas valve is sufficient for the system to function properly.
As mentioned above, measuring the voltage of the thermocouple 2 by means of the voltmeter 4 enables monitoring the flame condition of the burner, wherein possible anomalies (for example, the flame inadvertently extinguishing due to gas flows or liquid spills) can be detected by means of said measurements. The flame monitoring system 1 may preferably comprise flame re-ignition means for the burner. The flame reignition device comprises a spark generator connected to the burner. The reignition device is configured to reignite the flame when the flame is accidentally extinguished. Therefore, the re-ignition means can be activated according to the change in the voltage of the thermocouple 2 measured by the voltmeter 4.
The flame monitoring system 1 may preferably include a timer configured to close the gas passageway when a user preset time has elapsed. The flame monitoring system 1 may be configured to consider a predetermined time to have elapsed if the flame cannot be re-ignited after an accidental extinction. This prevents the timer from continuing to operate when the flame is extinguished. The flame monitoring system 1 may also be configured to consider a predetermined time to have elapsed if the grid power is lost.
Preferably, the timer disconnects the interruption means 5 to close the gas passage when a preset time has elapsed.
The invention also relates to a gas-fired appliance comprising at least one burner comprising a flame monitoring system 1 as described in any of the embodiments.
The control method for a gas appliance incorporating a monitoring system 1 as described above comprises a measurement step of measuring the voltage in the thermocouple 2. The flow of current between the thermocouple 2 and the electromagnetic gas valve is interrupted during a measurement step of duration such that the electromagnetic gas valve keeps the gas passage in an open state by means of the actual inertia of the electromagnetic gas valve.
Alternatively, the control method may comprise a flame reignition step if the measured voltage of the thermocouple 2 meets certain predetermined criteria.
The measuring step preferably lasts at most 300 mus. As mentioned above, the duration of the interruption must be short, so that the solenoid gas valve keeps the gas passage in the open state by actual inertia.
The measuring step is also preferably performed periodically at a frequency of 100 ms. It is important that the interval between measurements is short, because a potentially extinguished flame must be detected in the shortest possible time.