FR2509438A1 - Digital logic controller for gas burner - uses digital logic circuits to monitor burner status and to enable or disable burner operation or ignition - Google Patents

Abstract

At least a solenoid valve regulates the flow of combustible. A flame detector (7), an igniter (21), and a thermostat (22) are provided, the latter controlling an interrupter in the supply circuit. An electrical contactor (23) is mechanically actuated and associated with a tap placed upstream from the solenoid valve. An electromagnet (6) holds the contactor (23) and the tap (1) in the open position when energised. A logic circuit, connected between the thermostat (22) and the flame detector (7) on one side and the electromagnet (6) on the other, comprises logic gates (8,11,12) which drive a timer (24) controlling the electromagnet (6). The logic circuit checks for correct ignition conditions and detects abnormal operating conditions, removing the electromagnet supply to provide fail safe operation.

Description

The present invention relates to a device for controlling a burner. It applies especially, although not exclusively, to the permanent control and to the regulation of the supply of combustible gas (of all types or any other hydrocarbon or mixture of gaseous hydrocarbons) fueling both a gas heater
We know that devices of this type require safety and control systems aimed in particular at preventing the device from being put into the operating position by delivering a combustible gas, while the gas ejected at the burner is not subject immediately upon combustion, this gas could spread into the atmosphere and constitute an obvious danger.

A safety system obtained through the maintenance of a pilot light permanently supplied with combustible gas is commonly used for gas heaters, so as to automatically ignite the gas at the burner main if the gas supply is opened.

Said pilot light is equipped with a system for controlling the presence of a flame, generally consisting of a metal probe forming a thermocouple, the current of which is detected by a monitoring system in the event of the flame heating the probe; if the thermocouple system does not detect the presence of a flame, a controlled solenoid valve constituting a safety valve closes the gas supply downstream.

These known conventional devices have obvious drawbacks: firstly, the permanent maintenance of a pilot light represents a significant gas consumption, all the more so since this pilot light can be incorrectly adjusted.

In addition, thermocouple systems intended to monitor the presence of a flame are of limited reliability and above all of a very long response time, which, in practice, may exceed the standards provided by the distribution organizations of gas.

To avoid these drawbacks, certain other known devices include an arrangement of systematic cyclic emission of sparks in order to be able to relight almost instantaneously a burner whose flame has been extinguished.

Such a spark emission system generates noise and parasites.

Devices are known which are intended to remedy the various drawbacks of the various known devices.

In its French patent N076 03268, the Applicant has already described a device making it possible to unite in a global and compact whole the three functions which were previously isolated namely: the function of automatic ignition of the gas during the putting into operation (previously provided by pilot light or cyclic generation of sparks); -the permanent flame monitoring function (previously provided by thermocouple) -finally, the regulation and modulation function of the gas supply by thermostatic control.

The Applicant has also described in its French patent application N081 02030 a device having the same advantages and functions as that described in French patent N076 03268 but not requiring the use of a special contactor.

These two electrical devices for controlling a burner work perfectly and have given all satisfaction.

However, their electrical supply can only be effected by means of an alternating voltage source such as that of the domestic network for example, in the case of application to water heaters. This electrical supply of known devices has drawbacks
Indeed, on the one hand, these known devices are dependent on the alternative electrical network with the hazards (breakdowns, strikes) that this situation entails, and on the other hand, the intensity or the voltage of the current thus used are relatively high.

The present invention overcomes these drawbacks and in concert a device for controlling a burner whose electrical compost is able to be supplied by energy sources such as batteries or accumulators. The autonomy thus provided allows the device according to the invention to overcome the vagaries of the alternative network, for its operation. This is a major advantage in the event of an interruption, especially a prolonged one, of the alternative electrical supply to the network.

To this end, according to the invention, the electrical device for controlling a burner, of the type comprising at least one solenoid valve regulating the fuel flow, flame detection means, a fuel ignition member, a thermostat. controlling a switch interposed on the supply circuit, an electrically actuatable contactor associated with a tap arranged upstream of said solenoid valve, said contactor being able to take a first supply position for which the electrical circuit is closed and the tap is open, and a second position for which the circuit is open and the valve is closed, and an electromagnet capable of holding said contactor and said valve in the supply position, is characterized in that it comprises a logic circuit, interposed between the thermostat and the flame detector means on the one hand, and said electromagnet on the other hand, comprising two AND doors, the outputs of which each constitute e the input of an OR gate of the inclusive type if connected to said electromagnet, the two inputs of one of the AND doors being connected, one to the thermostat and the other to the flame detection means, the circuit being suitable to be supplied with low intensity direct current such as a current supplied by a battery or an accumulator.

Also, the logic electric circuit further comprises a time delay device placed between the inclusive OR gate and the electromagnet, an AND gate whose inputs are connected to the output of said OR gate and to the thermostat and whose output is connected to the one of the inputs of an exclusive OR gate, its other input being connected to the flame detection means, the output of said exclusive OU being connected to one of the inputs of an AND gate also connected to an air pressure switch and the output of which is connected to the ignition member.

More specifically, the device comprises two solenoid valves arranged in series and downstream of the contactor, on the fuel supply line of the burner, the first being of the all or nothing type, the second being of the modulating type.

Advantageously, the second modulating solenoid valve is successively connected to the electrical circuit by a timing device and an AND gate, the inputs of which are connected respectively to the first solenoid valve (disposed upstream) and to the flame detection means.

Preferably, the solenoid valves are of the electromagnetic type provided with two coils, or of the mechanically bistable type, and are able to be supplied electrically by a battery or an accumulator.

The invention will be clearly understood in the light of the appended figure.

The single figure represents an overall diagram showing the electrical circuit for controlling the water heater burner, and the members controlled by said circuit.

The device shown in the figure comprises a push-button contactor 23 associated with a tap 1 allowing passage of the fuel in the line 2 leading to the burner 3 downstream of which two solenoid valves V and V2 are placed, the solenoid valve V1 being of the all type or nothing and the solenoid valve V2 being of the modulating type as required.

The contactor 23 pushed manually by the user, on the one hand closes the electrical supply circuit connected to the battery or accumulator 4 and on the other hand, opens the valve 1. An electromagnet 6 allows, when it is excited, to keep the contactor 23 in the closed position of the electrical circuit and open the fuel supply circuit by holding the valve 5.

The electrical circuit comprises a thermostat 22 opening or closing said circuit according to the heat requirements, in the example of application of the device according to the invention to the control of a water heater burner.

The fuel is likely to be ignited by an ignition member 21 (such as an electronic igniter) disposed near the burner 3. Flame detection means constituted in the example of the figures of a current ionization detector 7, are also arranged near the burner 3.

The electrical circuit includes logic elements consisting of "AND" gates, "OR" gates, inverters and a memory.

The thermostat 22 is connected on the one hand to the solenoid valve by interposition of a memory 16 (connected to the flame detector 7), and on the other hand to one of the inputs of two "AND" doors 11 and 12 of which the other two inputs are connected to the flame detector 7. The output of said "AND" doors 11 and 12 constitute the inputs of an "OR" door, the output of which supplies the electromagnet 6 by interposing the timing device 24.

The output of the "OR" door 8 is connected to one of the inputs of an "AND" door 18, the other input of which is connected to the supply branch 19 between the contactor 23 and the thermostat 22. A door "OR", the inputs of which are connected to the output of the "AND" gate 18 and of the flame detector 7, is connected by its output to an "AND" gate 14, the other input of which is connected to a pressure switch contactor air 13. The output of the "AND" door 14 is connected to the ignition member 21.

The modulating solenoid valve V2 is supplied by interposing a time delay relay 25 and an "AND" gate 17, connected on the one hand between the memory 16 and the solenoid valve
V1, and on the other hand at the output of the flame detector 7.

The "OR" gate 15 is of the exclusive type while the "OR" gate 8 is of the inclusive type.

Two logic inverters 9 and 10 are each arranged on an input of the "AND" door 12, connected respectively to the thermostat 22 and to the flame detector 7.

On startup, the operation of the device according to the invention is as follows
The device is started up by manual pressure on the contactor 23 (against a compression spring) which then closes the circuit and supplies the latter with electrical energy supplied by the battery 4. The translation of the contactor 23 causes the opening of the valve 1, thus leaving passage to the fuel up to the first solenoid valve V1 which is at this instant in the closed position.

Two cases can arise, depending on whether there is a heat demand or not, detected by the thermostat.

If the thermostat 21 is open (no heat demand), there is normally no flame and therefore no ionization current; the winding of the solenoid valve 6 is food keeping the contactor 23 in the pressed position. The supply current of the electromagnet 6 is obtained after passing through the "AND" gates 11 and 12, the inverters 9 and 10 and the "OR" gate 8. Always in this same case of opening the thermostat, if there is a flame at the burner 3: this is then a fault, because there is no request for heat. The electromagnet 6 must therefore be de-energized in order to close the valve 5 of the tap 1. This result is obtained by the set of logic components 8, 9, 10, 11 and 12. In fact, the "AND" doors 11 and 12 then each have a powered input and the other is unpowered respectively. Their receiving outputs are therefore not powered, which makes it possible to obtain a zero current at the output of the "OR" gate 8, and therefore to de-energize the electromagnet 6 after a given time via the timing device 25.

The fuel supply is cut off. It is then necessary to press the switch 23 manually to switch on the device again.

The second possible case likely to arise is that where there is a demand for heat, therefore the thermostat 22 is closed as well as the supply circuit.

Memory 16, located between the thermostat and the solenoid valve
V1 is able to record the passage of the ionization current from the flame detector 7, when the thermostat 22 is closed. Thus, the supply by the thermostat 22 of the solenoid valve V1 depends on the existence or the absence an ionization current at this instant, that is to say the absence of flame or not at the burner 3. The memory 16 authorizes the passage of the current if, at the instant when the thermostat 22 closes , There is no ionization current (i.e. if there is no flame). If there is a flame at this time, the solenoid valve V1 is not supplied.

This is logical, since the presence of a flame at this instant would be proof that the flame existed while the thermostat was open (just before it was closed), this is the malfunction described above (no heat demand and presence flame). In this case, the electromagnet 6 is de-energized according to the process previously described.

If it is assumed that this fault does not appear, the thermostat closing and in the absence of ionization current, the solenoid valve V1 is supplied (thanks to memory 16).

It has been noted that the open thermostat 22 and the absence of a flame cause the electromagnet 6 to be excited, and that after the thermostat has been closed (without the presence of a flame), the de-excitation of said electromagnet only takes place after a given time (thanks to device 24).

Thus, when the thermostat 22 is closed, the electromagnet 6 remains energized for a given time, the branch 20 then remains supplied. The "AND" door 18 is supplied on its two inputs (branch 20 and thermostat). The "OR" gate 15 receives a power supply on one of its inputs (the one connected to the output of the "AND" gate 18), the other input being unpowered (no ionization current). The “AND” door 14 therefore receives a supply on its two inputs (assuming the air pressure switch engaged) and then supplies the ignition member 21 which ignites the fuel.

The free passage of the fuel is obtained because the valve 5 and the solenoid valve V1 are open. The presence of a flame causes an ionization current, which makes it possible to maintain: excited the electromagnet 6, since the two inputs of the "AND" gate 11 are supplied, and on the other hand to cut off the supply of the ignition device 21, since the two inputs of the "exclusive OR" door 15 are supplied, eliminating the supply of one of the inputs (and therefore of the output) of the "AND" door 14.

The solenoid valve V2 is started up via the "AND" gate 17, the two inputs of which are then supplied
We have described above, a process of ignition, flame detection, then cutting the power to the ignition device. But one can imagine that as a result, or during this process, the flame disappears. The ionization current then disappears, again causing the supply (gate "OR" 15 and "AND" 14) of the ignition device 21 for a new boom. But in addition, the absence of ionization current (while the thermostat 22 is closed) provokes the de-excitation of the electromagnet 6 after a given time. If at the end of this given time interval the fuel is not ignited by the member 21, the electromagnet 6 de-energizes causing the return of the valve 5 (of the tap 1) on its seat, blocking the passage of the fuel, and cutting the general power supply
It can be seen that the electrical supply of fuel is cut off as soon as a malfunction occurs.

The modulating solenoid valve V2 is put into service when at the same time the first solenoid valve V1, of the all or nothing type, is supplied and there is an ionization current and therefore a flame. This bet. in service is carried out after a given time by the delay device 25. If the flame were to disappear, the "AND" door 17 (not supplied on one of its inputs) would cut off the supply to the solenoid valve V2 and the ignition attempt would only take place with the solenoid valve V1 open.

It can be seen that, whatever the various possible cases that may arise, the device according to the invention has complete safety in use.

The solenoid valves used are advantageously supplied electrically by battery or accumulator.

They can be of the magnetic resonance type with two coils, or of the mechanical bistable type.

Thanks to the electric power supply by battery or accumulator, the device according to the invention, because of its logical electrical components and of the solenoid valves designed for this purpose, is able to overcome the vagaries of the alternative electrical network.

Claims (5)

1.-Electrical device for controlling a burner, of the type comprising at least one solenoid valve regulating the fuel flow, flame detection means (7), a fuel ignition member (21), a thermostat (22) controlling a switch interposed on the supply circuit, an electrical contactor (23) operable mechanically associated with a tap disposed upstream of said solenoid valve said contactor (23) being able to assume a first supply position for which the electrical circuit is closed and the valve (1) open, and a second position for which the electrical circuit is open and the valve (1) closed, and an electromagnet (6) capable of holding said contactor (23) and said valve ( 1) in the supply position characterized in that it comprises a logic circuit, interpc between the thermostat (22) and the flame detector means (7) on the one hand, and said electromagnet (6) on the other hand , comprising two AND gates (11,12) whose s nettles each constitute the input of an OR door (8) of the inclusive type connected to said electromagnet (6), the two inputs of one of the AND doors (12) being connected, one to the thermost (22) and the other to the flame detection means (7) and the circuit being able to be supplied with low intensity direct current such as a current supplied by a battery (4) or an accumulator. 2.- Device according to claim 1, characterized in that the logic electric circuit further comprises a timing device (24) placed between the inclusive OR gate (8) and the electromagnet (6), an AND gate (18) whose inputs are connected respectively to the output of said OR gate (8) and to the thermostat (22) and whose output is connected to one of the inputs of an exclusive OR gate (15), its other input being connected to flame detection means (7), the output of said exclusive OU (15) being connected to one of the inputs of an AND gate (14) also connected to an air pressure switch (13) and the output of which is connected to the 'ignition member (21). 3.- Device according to one of claims 1 or 2, characterized in that it comprises two solenoid valves V1 and V2 arranged in series, and downstream of the contactor (23), on the fuel supply line (2) of the burner (3), the first V1 being of the all-or-nothing type the second V2 being of the modulating type. 4.- Device according to claim 3, characterized in that the second modulating solenoid valve v2 is connected to the electrical circuit successively by a timing device (25) and an AND gate (17) whose inputs are connected respectively to the first solenoid valve V1 (arranged upstream) and to the flame detection means (7). 5.- Device according to one of claims I to 4, characterized in that the solenoid valves V1, V2 are of the magnetic resonance type provided with two coils, or of the mechanically bistable type and are capable of being electrically powered by a battery (4 ) or an accumulator.