EP3534069B1

EP3534069B1 - Flame monitoring system for a burner of a gas appliance, and control method for a gas appliance

Info

Publication number: EP3534069B1
Application number: EP18382129.7A
Authority: EP
Inventors: José Ignacio Múgica Odriozola; Jesús Ignacio ERRASTI BADIOLA; Iñigo PEÑAGARICANO BADIOLA
Original assignee: Copreci SCL
Current assignee: Copreci SCL
Priority date: 2018-03-01
Filing date: 2018-03-01
Publication date: 2020-07-01
Anticipated expiration: 2038-03-01
Also published as: CN110220221A; EP3534069A1; WO2019166680A1; CN110220221B; ES2817440T3; PL3534069T3

Description

TECHNICAL FIELD

The present invention relates to a flame monitoring system for a burner of a gas appliance, and a control method for a gas appliance.

PRIOR ART

Gas appliances comprising at least one gas burner and a gas valve for each burner are known, said valve being adapted for opening or closing a gas passage to the burner. Likewise, the gas valve is also known to comprise an electromagnetic valve electrically connected to a thermocouple arranged next to the burner, and a manual actuator opening the gas passage when it is moved axially.
Gas appliances of this type comprising a flame reignition system for reigniting the flame if the flame goes out by accident are also known.
W0O1993/012378A1 discloses a device for automatic reignition of a flame that goes out unintentionally for a gas appliance like the one described above. The device comprises a voltage meter electrically connected in parallel with the thermocouple. The device amplifies the voltage value measured by the voltage meter and compares it with the previously measured voltage value such that it can detect a flame that goes out unintentionally and proceed to reignite it.
GB1101908A discloses a safety device for a gas burner. The safety device comprises an electromagnetic valve electrically connected to a thermocouple arranged near a pilot burner. The arrangement is such that the current from the thermocouple is sufficient to open the valve when the pilot burner is on, this latter condition permitting ignition of the main burner. If the pilot burner flame is extinguished by any reason the valve closes. Since, however, the electromagnetic valve has a given inertia, a finite time will elapse before the electromagnetic valve is able to close off the main burner and thus isolate it from the gas supply.

DISCLOSURE OF THE INVENTION

The object of the invention is to provide a flame monitoring system for a burner of a gas appliance, and a control method for a gas appliance, as defined in the claims.
A first aspect of the invention relates to a flame monitoring system for a burner of a gas appliance. The flame monitoring system comprises a thermocouple adapted for being arranged next to the burner and an electromagnetic gas valve adapted for opening or closing a gas passage to said burner, the electromagnetic gas valve being electrically connected with the thermocouple and said electromagnetic gas valve keeping the gas passage open when it receives a specific current from the thermocouple. The flame monitoring system comprises a voltage meter for measuring the voltage of the thermocouple.
The flame monitoring system also comprises interruption means configured for interrupting current flow between the thermocouple and the electromagnetic gas valve during a predetermined time so that the voltage meter can measure the voltage of the thermocouple in vacuum, said predetermined time being such that the electromagnetic gas valve keeps the gas passage open during the interruption by means of the actual inertia of the electromagnetic valve.
A second aspect of the invention relates to a control method for a gas appliance, the gas appliance comprising at least one burner with a thermocouple arranged next to the burner and with an electromagnetic gas valve adapted for opening or closing a gas passage to said burner, the electromagnetic gas valve being electrically connected with the thermocouple and said electromagnetic gas valve keeping the gas passage open when it receives a specific current from the thermocouple.
The method comprises a measuring step for measuring the voltage in the thermocouple. During the measuring step, current flow between the thermocouple and the electromagnetic gas valve is interrupted so that the voltage of the thermocouple is measured in vacuum, said measuring step having a duration such that the electromagnetic gas valve keeps the gas passage open by means of the actual inertia of the electromagnetic valve.
The voltage generated by the thermocouple is very small. Measuring said voltage in vacuum provides a more reliable measurement, with a lower noise level. A good voltage measurement of the thermocouple can thus be obtained in a simple and inexpensive manner.
These and other advantages and features of the invention will become evident in view of the drawings and detailed description of the invention.

DESCRIPTION OF THE DRAWINGS

Figure 1 schematically shows a first embodiment of the invention.
Figure 2 schematically shows a second embodiment of the invention.

DETAILED DISCLOSURE OF THE INVENTION

Figure 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 cooktop, although it could be incorporated into any other type of gas appliance known in the art, for example a gas oven. Furthermore, the gas appliance may comprise a burner or a plurality of burners, each burner comprising a respective flame monitoring system 1.
The flame monitoring system 1 of the invention comprises a thermocouple 2 adapted for being arranged next to a burner and an electromagnetic gas valve adapted for opening or closing a gas passage to said burner. The electromagnetic gas valve is preferably a safety valve which is part of a gas tap. The user regulates the flow of gas to the burner by acting on the gas tap, and the electromagnetic gas valve closes the gas passage if there is no flame in the burner, thereby preventing gas leak. ES1087355U shows an example of a gas tap with an electromagnetic gas valve.
As it is well known by the skilled person, a thermocouple is a transducer formed by the combination of two different metals which causes a very small potential difference which is a function of the temperature difference between one of the ends, called hot spot, and the other end, called cold spot, i.e., a thermocouple generates a voltage in its terminals when it is subjected to a temperature.
Similarly, it is well known by the skilled person that an electromagnetic gas valve comprises a solenoid coil and a shutter opening or closing the gas passage. The solenoid coil converts electric energy, by means of magnetism, into mechanical energy to act on the shutter and to thereby be able to keep the gas passage open when the voltage it receives reaches a sufficient level.
In the flame monitoring system 1 of the invention, the electromagnetic gas valve is electrically connected with the thermocouple 2, i.e., the solenoid coil 3 of the electromagnetic gas valve is electrically connected with and is powered by the thermocouple 2. In this sense, when the voltage generated by the thermocouple 2 reaches a sufficient level, the solenoid coil 3 of the electromagnetic gas valve actuates the shutter of said electromagnetic gas valve, keeping the gas passage to the corresponding burner open.
So, when the burner is ignited, i.e., when it produces flame, the thermocouple 2 generates a voltage. When the thermocouple 2 reaches a sufficient temperature, it generates a sufficient voltage so that the solenoid coil 3 of the electromagnetic gas valve keeps the gas passage open.
The gas tap comprises a regulator element by means of the rotation of which the gas flow is regulated, and a manual actuator for rotating said regulator element. In addition to regulating the flow, there is also a need to open the electromagnetic valve so that the gas flows to the burner. Preferably, the electromagnetic valve is opened by means of the axial movement of the manual actuator, as occurs in ES1087355U , for example. Once the gas passage to the burner is opened through said manual actuator, the burner generates a flame that heats the thermocouple 2, said thermocouple 2 generating the voltage mentioned above. Until the thermocouple 2 reaches the sufficient temperature, there is a need to keep the gas passage open in other way. The user having to keep the gas passage open by acting on the manual actuator until the thermocouple 2 has reached the sufficient temperature is known in the art. Burners incorporating an ignition assistance system for powering the electromagnetic gas valve by means of an additional power supply while the thermocouple 2 reaches said sufficient temperature, for example, a previously charged capacitor having the ignition assistance function, are also known.
The flame monitoring system 1 comprises a voltage meter 4 for measuring said voltage generated by the thermocouple 2. The flame monitoring system 1 also comprises a control unit 6 and interruption means 5 configured for interrupting current flow between the thermocouple 2 and the electromagnetic gas valve during a predetermined time so that the voltage meter 4 can measure the voltage of the thermocouple 2 in vacuum, said predetermined time being such that the electromagnetic gas valve keeps the gas passage open during the interruption by means of the actual inertia of the electromagnetic gas valve. In other words, the actual inertia of the solenoid coil 3 of the electromagnetic gas valve continues to generate the mechanical energy required for keeping the shutter in an open position despite the fact that it is not electrically powered, provided that said period of time is short.
As described above, the magnitude of the voltage generated by the thermocouple 2 is small. Measuring said voltage in vacuum provides a more reliable measurement, with a lower noise level. A good voltage measurement of the thermocouple 2 can thus be obtained in a simple and inexpensive manner.
As described above, the thermocouple 2 generates a voltage in its terminals depending on the temperature to which it is subjected, in this case due to the flame produced by the burner. The voltage measurement of the thermocouple 2 thereby allows monitoring the situation of the flame of the burner and detecting possible anomalies therein, for example, the flame going out unintentionally due to a stream of air or a liquid overflow. Monitoring the situation of the flame of the burner allows the control unit 6 to perform advanced functions such as reigniting the flame if it goes out unintentionally, for example.
Electric gas appliances including advanced functions usually comprise a control circuit which is responsible for powering the solenoid coil of the electromagnetic gas valve, i.e., the control circuit receives the voltage generated by the thermocouple, and depending on the operation algorithm, the control circuit generates an electric signal to feed the solenoid coil of the electromagnetic gas valve. Gas appliances of this type must comply with very strict regulations to prevent failures relating to unintentional electromagnetic gas valve opening derived from errors in the control circuit or in the control algorithm. In the cases in which the solenoid coil of the electromagnetic gas valve is powered only through the thermocouple, this type of failures will not occur, and therefore the safety standard to be complied with is less strict. A gas appliance incorporating the flame monitoring system 1 of the invention can therefore perform advanced functions such as reigniting the flame if it goes out unintentionally, and at the same time, falls within the category in which the safety standards to be complied with are less strict.
Preferably, in the absence of grid power supply, the interruption means 5 of the flame monitoring system 1 allow current flow between the thermocouple 2 and the electromagnetic gas valve at least during a predetermined time interval, i.e., the gas appliance in which the flame monitoring system 1 is incorporated can work in the absence of grid power supply at least during a predetermined time interval. A gas appliance which, when electrically powered by the power grid, has advanced functions, such as for example, the reignition of the flame if it goes out unintentionally, but at the same time allows the user to use the basic functions of the gas appliance in the absence of grid electric current at least during a period of time, can thus be obtained.
The interruption means 5 preferably comprise a switch electrically connected in series between the thermocouple 2 and the electromagnetic gas valve, the voltage meter 4 being arranged parallel to the thermocouple 2. In other embodiments not shown in the drawings, the interruption means comprise a commutator which electrically connects the thermocouple with the electromagnetic gas valve in a first position, and connects the thermocouple with the voltage meter in a second position.
In the first embodiment of the invention shown in Figure 1, the switch comprises a normally open MOSFET 50 configured for allowing and interrupting current flow between the thermocouple 2 and the electromagnetic gas valve.
In this first embodiment, since the MOSFET 50 is a normally open type, in order to for the thermocouple 2 to be able to electrically connect to the electromagnetic gas valve without grid power supply, i.e., in order for the gas appliance to be able to work at least during a predetermined time interval, the MOSFET 50 is also powered by an additional power supply circuit comprising an additional power supply 7 other than the power grid powering said MOSFET 50 during a predetermined time in the absence of power grid current. Said power supply 7 is preferably a battery or a previously charged capacitor. The gas appliance incorporating the flame monitoring system 1 shown in Figure 1 can therefore work in the most basic mode in the absence of grid electric current at least during a time interval since the additional power supply 7 will allow the normally open MOSFET 50 to be closed, and the thermocouple 2 can thus be connected to the electromagnetic gas valve. The additional power supply will preferably be in charge of the normal operation of the gas appliance when it is powered by the grid electric current.
Figure 2 shows a second embodiment of the flame monitoring system 1. The second embodiment differs from the first embodiment in the interruption means 5. The rest of the features are analogous to those of the first embodiment so it is not considered necessary to describe them again.
In this second embodiment, the interruption means 5 comprise, in addition to a normally open MOSFET 50, a normally closed relay 51, the relay 51 and the MOSFET 50 being electrically connected in parallel. So, in the absence of electric current in the grid, the relay 51, being a normally closed type, allows current flow between the thermocouple 2 and the electromagnetic gas valve, such that the gas appliance in which the flame monitoring system 1 is incorporated can work despite the absence of grid electric current. In contrast, when the interruption means 5 are powered by the grid electric current, the relay 51 will open, and the MOSFET 50 will be in charge of allowing or preventing current flow between the thermocouple 2 and the electromagnetic gas valve. This second embodiment allows the gas appliance in which the flame monitoring system 1 is incorporated to work at all times, regardless of whether or not there is grid electric current, i.e., it is not limited to the energy stored in an additional power supply like in the embodiment of Figure 1. A gas appliance incorporating the flame monitoring system 1 which always works in the absence of grid electric current is therefore obtained.
The interruption means 5 preferably have an ON resistance less than half the resistance of the electromagnetic gas valve when they allow current flow between the thermocouple 2 and the electromagnetic gas valve. The maintenance of this proportion assures that the voltage reaching the electromagnetic gas valve is sufficient for the correct operation of the system.
As described above, measuring the voltage of the thermocouple 2 by means of the voltage meter 4 allows monitoring the situation of the flame of the burner, where possible anomalies therein, for example the flame going out unintentionally due to a stream of air or a liquid overflow, can be detected by means of said measurement. The flame monitoring system 1 may preferably comprise a flame reignition device for the burner. The flame reignition device comprises a spark generator adapted for being connected to the burner. The reignition device is configured for reigniting the flame if the flame goes out by accident. The reignition device can therefore be activated depending on the evolution of the voltage of the thermocouple 2 measured by the voltage meter 4.
The flame monitoring system 1 may preferably comprise a timer configured for closing the gas passage when a time pre-established by the user has elapsed. The flame monitoring system 1 can be configured for considering that the pre-established time has elapsed if the flame cannot be reignited after it goes out by accident. In this way it is prevented that the timer continues to work when the flame has gone out. The flame monitoring system 1 can be configured also for considering that the pre-established time has elapsed if grid power supply is lost.
Preferably, the timer opens the interruption means 5 for closing the gas passage once the pre-established time has passed.
The invention also relates to a gas appliance comprising at least one burner comprising the flame monitoring system 1 described in any of the embodiments thereof.
The control method for a gas appliance incorporating a monitoring system 1 like the one described above, comprises a measuring step for measuring the voltage in the thermocouple 2. During the measuring step, current flow between the thermocouple 2 and the electromagnetic gas valve is interrupted, said measuring step having a duration such that the electromagnetic gas valve keeps the gas passage open by means of the actual inertia of the electromagnetic gas valve.
Optionally, the control method may comprise a flame reignition step if the measured voltage of the thermocouple 2 complies with certain predefined criteria.
The measuring step preferably has a maximum duration of 300 µs. As mentioned above, the duration of the interruption must be short so that the electromagnetic gas valve keeps the gas passage open through the actual inertia thereof.
The measuring step is also preferably performed periodically with a frequency of 100 ms. It is important for the interval between measurements to be short, since the flame possibly going out must be detected in the shortest time possible.

Claims

Flame monitoring system for a burner of a gas appliance, the flame monitoring system comprising a thermocouple (2) adapted for being arranged next to the burner and an electromagnetic gas valve adapted for opening or closing a gas passage to said burner, the electromagnetic gas valve being electrically connected with the thermocouple (2) and said electromagnetic gas valve keeping the gas passage open when it receives a specific current from the thermocouple (2), the flame monitoring system (1) also comprising a voltage meter (4) for measuring the voltage of the thermocouple (2), characterised in that the flame monitoring system (1) also comprises interruption means (5) configured for interrupting current flow between the thermocouple (2) and the electromagnetic gas valve during a predetermined time so that the voltage meter (4) can measure the voltage of the thermocouple (2) in vacuum, said predetermined time being such that the electromagnetic gas valve keeps the gas passage open during the interruption by means of the actual inertia of the electromagnetic gas valve.
Flame monitoring system according to claim 1, wherein the interruption means (5) allow current flow between the thermocouple (2) and the electromagnetic gas valve when said interruption means (5) are not powered by the power grid at least during a predetermined time interval, such that the gas appliance can work in the absence of grid power supply during said period.
Flame monitoring system according to claim 1 or 2, wherein the interruption means (5) comprise a switch electrically connected between the thermocouple (2) and the electromagnetic gas valve, the voltage meter (4) being arranged parallel to the thermocouple (2).
Flame monitoring system according to claim 3, wherein the switch comprises a normally open MOSFET (50) configured for allowing or interrupting current flow between the thermocouple (2) and the electromagnetic gas valve.
Flame monitoring system according to claim 4, wherein the MOSFET (50) is powered by a power supply circuit comprising a power supply (7) powering said MOSFET (50) during a predetermined time in the absence of power grid current, said power supply (7) preferably being a battery or a previously charged capacitor.
Flame monitoring system according to claim 4, wherein the switch also comprises a normally closed relay (51) which allows current flow between the thermocouple (2) and the electromagnetic gas valve when said interruption means (5) are not electrically powered, the relay (51) and the MOSFET (50) being electrically connected in parallel, and the relay (51) being kept open when the interruption means (5) are electrically powered.
Flame monitoring system according to claim 1 or 2, wherein the interruption means (5) comprise a commutator which electrically connects the thermocouple (2) with the electromagnetic gas valve in a first position, and connects the thermocouple (2) with the voltage meter (4) in a second position.
Flame monitoring system according to any of the preceding claims, wherein the interruption means (5) have an ON resistance less than half the resistance of the electromagnetic gas valve when they allow current flow between the thermocouple (2) and the electromagnetic gas valve.
Flame monitoring system according to any of the preceding claims, comprising a flame reignition device for the burner, said reignition device comprising a spark generator adapted for being connected to the burner, and said flame reignition device being configured for reigniting the flame if the flame goes out by accident, the reignition device being activated depending on the evolution of the voltage of the thermocouple (2) measured by the voltage meter (4).
Flame monitoring system according to claim 9, comprising a timer configured for closing the gas passage when a time pre-established by the user has elapsed, the flame monitoring system being configured for considering that the pre-established time has ended if the flame cannot be reignited after it goes out by accident or if grid power supply is lost, the gas passage being closed by means of the opening of the interruption means (5).
Gas appliance, characterised in that it comprises at least one burner comprising a flame monitoring system according to any of the preceding claims.
Control method for a gas appliance, the gas appliance comprising at least one burner with a thermocouple (2) arranged next to the burner and with an electromagnetic gas valve adapted for opening or closing a gas passage to said burner, the electromagnetic gas valve being electrically connected with the thermocouple (2) and said electromagnetic gas valve keeping the gas passage open when it receives a current from the thermocouple (2), the method comprising a measuring step for measuring the voltage in the thermocouple (2), characterised in that during the measuring step current flow between the thermocouple (2) and the electromagnetic gas valve is interrupted so that the voltage of the thermocouple (2) is measured in vacuum, said measuring step having a duration such that the electromagnetic gas valve keeps the gas passage open by means of the actual inertia of the electromagnetic gas valve.
Control method according to claim 12, comprising a flame reignition step if the measured voltage of the thermocouple (2) complies with certain predefined criteria.
Control method according to claim 12 or 13, wherein the measuring step has a maximum duration of 300 µs.
Control method according to any of claims 12 to 14, wherein the measuring step is performed periodically with a frequency of at least 100 ms.