GB2100488A - Flame control device for burners - Google Patents

Abstract

The present invention relates to a flame-control device comprising: - a sequencer 1 adapted to deliver control pulses in the cyclic ratio T1/T; - a logic safety unit 5 receiving as input signals, the output signal of the sequencer and a signal sent by a flame-detection electrodes 17 associated with the burner, - and a cut-out circuit 8 interposed between, on the one hand, a source of power L and, on the other hand, an igniter 14 associated to the burner, and an electrovalve 16 controlling the arrival of gas to the burner. The invention finds a useful application in gas cookers for domestic use. <IMAGE>

Description

SPECIFICATION Flame control device for burners The present invention relates to a flame-control device with sequencer, for use in apparatus equipped with burners, for the cyclic and automatic control, via an appropriate igniter, of the presence and absence of a flame according to an adjustable cyclic ratio, the user being able to determine by a control the ratio ofthe duration T, of the presence of a flame to the total duration T or cycle time.

The apparatus with burners referred to hereinabove can for example be gas cookers, stoves, radiators or the like.

Flame-control devices with sequencers are designed to allow a reduced heating without having to reduce the intensity of the flame. In the case of a cooker, for example, they enable to slow down the cooking of a dish, without lowering the flame. They work according to a time cycle during which a flame is successively present and absent. The cyclic ratio, i.e. the ratio of the period T1 through which there is a flame, to the total cyclic period T, is a number smallet than or equal to 1, proportional to the mean heating power which is required. Thesmallerthis number, the greater the reduced effect.

Some of the advantages of the reduction obtained with a sequencer are important. They are that: 1) The composition of the air-fuel mixture is always optimal since there is no need to reduce the gas flow to excess when producing the flame.

2) The heating surface remains constant and the heat distribution is such that there is no over-heated or under-heated area.

3) The combustion efficiency is maximum, therefore there is a saving of energy compared with the traditional reduction which is obtained by lowering the flame.

4) There is no risk of extinction through draughts, since the flame remains high.

5) the latitude of action of the reduction is very wide, since it is possible to reach cyclic ratios of around 0.1.

The known devices equipped with sequencers work according to a cycle which comprises two consecutive phases: 1) during the first phase, the valve controlling the arrival of gas is closed, there is no heat production, 2) during the second phase, the valve is open and the combustible mixture is ignited by means of an igniter situated close to the burner.

At the end of the second phase, the valve closes up and the cycle starts over again.

The igniting device may be electronic or any other type and does not necessarily operate throughout the whole of the second phase.

The cycle is generally determined by a electromechanical system using an electric motor and cams for programming the cyclic ratio. Installations relying on these electro-mechanical systems are not very practical since they do not afford the possibility of readily changing the cyclic ratio. Moreover, the hand control stops the cycle at any odd point. As a result, the sequencer is also set into operation at any point in the cycle, which means that the immediate opening of the valve and the operation of the igniter are not systematically controlled. And it is sometimes necessary to let 10, 20 or more seconds elapse before the gas is ignited, this being rather unpractical.

In addition, although re-igniting is safe, the arrival of gas cannot be stopped if the ignition has failed, so that all the conditions of safety are not met.

It is the object of the present invention to overcome all the aforesaid disadvantages of the known devices with sequencers, by proposing a flamecontrol device with sequencer of the type defined hereinabove, but comprising: - a sequencer assentially composed of electronic circuits capable of delivering control pusles whose cyclic ratio T1/T may be determined by the user actuating a multi-position switch, - a logic safety unit receiving, for example, as input signals, the output signal of the said sequencer and a signal sent by a flame-detection electrode associated to the burner, this last signal being representative of the presence or of the absence of a flame.

- and at least a cut-out circuit inserted between, on the one hand, a source of power and, on the other hand, an igniter associated to said burner and an electro-valve, or the like, controlling the arrival of the combustible mixture to the burner, said cut-out circuit essentially receiving as control input signal, the output signal of the said logic safety unit.

Such a device, of which the main active parts are in electronic circuit-form will conceivably enable to solve advantageously the aforesaid problem, without any of the limitations and disadvantages of the flame-control devices with electro-mechanical sequencers, this of course, with all the reliability of operation inherent to the currently known electronic components.

The flame-control device with electronic sequencer, according to the invention, is designed so that the arrival of the combustible mixture to the burner is prevented if the flame has not been lit within a predetermined period, and if necessary after a second unsuccessful attempt to light it, this permitting to fulfill one essential requirement of safety.

Said device according to the invention is also designed so as to obtain an immediate and automatic re-igniting control for the case where the flame goes out due to external causes such as wind for example, whereas the electro-valve still controls the arrival of the combustible mixture to the burner.

Advantageously also, the device according to the invention is provided with a clearing circuit controlled when the multi-position switch, actuated by the operator, stops the arrival of gas to the burner.

Thus it will be possible to overcome the disadvantage indicated hereinabove in connection with the flame-control devices with electro-mechanical sequencers. Indeed, this further disposition of the invention will enable to arrange that each new sequence of operation of the apparatus does not start in any point of the ignition cycle, but on the contrary that it starts always, systematically, at the beginning of a sequence in which the electro-valve controlling the arrival of gas to the burner is opened and at the beginning of an attempt to light the flame.

The invention will be more readily understood on reading the following description with reference to the accompanying drawings in which: - Figure 1 is a block diagram of a flame-control device with electronic sequencer according to the invention, for use, for example, in a gas cooker, - Figure 2 is a diagram of the electronic sequencer proper, - Figure 3 shows some of the signals produced by the said sequencer, - Figure 4 shows in more details a possible embodiment of a logic safety unit, a cut-out circuit, and their respective connections with the igniter and with the electro-valve controlling the arrival of gas to the burner.

- Figure 5 is a diagram showing different stages of operation of the device, - Figures 6 to 8 are diagrams corresponding to the diagrams shown in Figures 1, 2 and 4, but showing variant embodiments of the object of the invention.

Figure 1 shows in 1, the electronic sequencer associated to a multi-position switch 2 which is intended to be operated by the user and to determine the previously defined cyclic ratio. The output 3 of the sequencer is connected to an input 4 of a logical safety unit 5 of which one output 6 is connected to the input 7 of a cut-out circuit 8. Another output 9 of the unit 5 is connected with a pilot light 10, signalling for safety. A push-button 11, connected with another input 12 of the logic safety unit 5, enables to clear manually from the safety position, when the cause of the warning signal issued by the pilot light 10 has been identified.

As shown in the diagram, the cut-out circuit 8 is interposed on a line L supplying the igniter 14, of the automatic re-igniting type and provided with an igniting electrode 15, and the winding 16 of an electrovalve controlling the arrival of gas to the burner of the cooker or of any other apparatus.

A detector electrode 17, detecting the presence of a flame, and situated close to the burner, is connected to another input 18 of the logic safety unit 5. It is thus obvious that the unit 5 is capable of processing the information that it receives from the electronic sequencer 1 and from the detecting electrode 17. Depending on this information and as will be seen hereinafter, the unit 5 will control the opening or closing of the cut-out circuit 8.

The sequencer 1 is an electronic circuit which is designed to give, during a cyle of predetermined duration T, at the most two logical levels 0 and 1 during time periods To and T1, the sum of which is equal to T. At the end of period T, the cycle is continuously repeated in exactly the same way as the preceding one. To each logic level corresponds a position of the valve, for example, closed for state 0 and open for state 1. The action of the sequencer 1 is therefore characterized by the ratio Tt/T of the valve opening time to the total duration of the cycle. At the most, if T1 = 0, the heating power is nil and if T1 = the heating is permanent.

This object is reached with a great variety of electronic circuits. For example, an astable multivibrator could be used if its cyclic ratio is altered.

Another solution could be to use two monostables, each one of which would be controlled by the return of the other one to the stable state. The cycle duration would be equal to the sum of the pulse time of the two monostables. If for example T, and To were the pulse times of two monostables, the cycle duration would be T, + To = T, and the action T1/T of the sequencer would be caused to vary by acting on the times T, and To.

Another good and practical solution, which is precisely illustrated in Figure 2, consists in counting the pulses of a clock. If the clock time is TH, the cyle time T is equal to NTH, N being an integer, and the valveopening sequence time will be T, = MTH, M being an integer between 0 and N. For example, if T = 30 seconds and N = 1,500, this gives TH = 20 milliseconds, and T, can in theory take on any value between 0 and 30 seconds, in 20 milliseconds increments. In practice, three intermediate values are sufficient, for example 20 seconds, 10 seconds and 5 seconds. It follows from the foregoing that if the clock period TH = 20 milliseconds is selected, it can be supplied by the 50 Hz alternating supply system 13.

Figure 2 gives an example of sequencer 1 which uses a binary counter 19. The circuits are fed from the system 13 via a D.C. supplying unit 20, which also feeds the logic safety unit 5.

Said unit 20 is fed from one ofthe secondary windings of a transformer T of which the other secondary winding, which has a point in common with the first, supplies a shaping circuit 21 and the line L. Said shaping circuit 21 sends to the binary counter 19 pulses synchronous with the alternating current of the supply system. Said binary counter 19 delivers signals whose frequency is the result of divisions by integral powers of 2 of the frequency of the supply system. In the illustrated example, outputs 22, 23 and 24 of the dividers by 512, 1024, and 2048 are used and processed by a logic circuit 25. The switch 2 permits to select the opening sequences of the valve 16.The positions successively correspond to the stop, permanent operation, and opening of the valve during the first half, or the first quarter or the first eighth of the cycle time.

The cycle time in this particular example is 40.96 seconds (= 20 ms x 2048).

The corresponding outputs that the operator can connect selectively to the output 3 of the sequencer 1 via the switch 2, have therefore been given the respective reference numbers 26, 27,28, 29 and 30.

The last three are outputs of the logic circuit 25. A clearing circuit 31, connected as indicated in Figure 2, is provided so that the first cycle of operation starts systematically at the beginning of an igniting and electro-valve opening phase.

Figure 3 shows the logic states (0 or 1) on the one hand, on the outputs 22 to 24 of the binary dividing counter 19, and, on the other hand, on the outputs 26 to 30 of the logic circuit 25 (output 3). The diagrams bear the corresponding reference numbers and are self-explanatory.

Figure 4 gives a possible representation of the cut-out circuit 8 which controls the current passing through the igniter 14 and into the electro-valve 16.

The conduction of the triac 32 is dependent on the logic levels applied between the base and the transmitter of transistor 33, which base is connected to the aforementioned input 7. If a level 0 is applied to the base, the transistor is blocked, no current controls the triac gate and said triac blocks the passage of the current. If, on the contrary, a level 1 is applied on the base of the transistor 33, said latter becomes conducting and allows the current through the gate of the triac 32, this allowing the current to pass through the electro-valve 16 and into the igniter 14.

Resistors 34 and 35 are used to limit the currents in the gate of the triac and in the base oftransistor 33.

Figure 4 also shows a diagram of the safety logic afforded by the logic unit 5, and the connections with the other sub-units of the device shown in Figure 1.

The cut-out circuit 8 is opened if either one of the following conditions is met: - if the sequencer 1 gives on its output 3 a logic state 0, this occurring in the stop position and through the periods To of the cycle of operation, - if the output of gate 36 is in the 0 state (safety signal).

On the contrary, the cut-out circuit 8 is closed when either one of the following conditions is met: - if the sequencer 1 gives at its output 3 a state 1 (permanent operation or operation through times T1 of the cycle), - if the output of gate 36 is in state 1.

When power is applied, capacitor 37 forces input 38 of gate 39 to pass to state 1. Capacitor 40 places input 12 of gate 36 in the 0 state.

The output of gate 36 and as a result input 41 of gate 39 are both in the 0 state. The output of gate 39 connected to the other input 42 of gate 36 is then in the 0 state and the output of said latter remains in state 1 whereas capacitor 40 is charged through resistor 43, causing input 12 of gate 36 to pass to state 1. The output state of gate 36 is thereafter connected to the logic state of input 38 of gate 39.

During time T, or in permanent operation, input 44 of gate 45 is controlled to state 1 by the sequencer 1.

When a flame is detected, the detection circuit, which detects by ionization ofthe electrode 17 causes a logic state 0 to appear at input 18. The output of gate 45 passes to state 1, so that input 38 of gate 39 remains in state 1. The output of gate 36 also remains in state 1. The electrovalve 16 is power-fed and controls the arrival of gas to the burner.

If no flame has appeared, a logic level 1 is found at input 18 of gate 45 and the output of said latter passes to the 0 state. After a few seconds, determined by elements 37 and 46, input 38 of gate 39 passes to the 0 state, as well as the output of gate 36. The valve closes up and the light 10 indicates the safety state. It is then necessary to actuate the push-button 11 to reset the circuit.

If the flame happens to disappear due to external causes during the time T, of the cycle or whilst in permanent operation, as in the preceding case, the output of gate 45 passes to the 0 state, since the detection electrode 17 transmits to input 18 a new logic level 1. The igniter, which has detected the disappearance of the flame, attempts to re-light it. If the attempt is successful before input 38 of gate 39 reaches the 0 state, input 18 of gate 45 receives once again a logic level 0 and its output retruns to state 1, this imposing the same state to input 38 of gate 39.

Gate 36 then remains in state 1 so that the switch 8 is kept closed whilst keeping up the supply to winding 16 of the electrovalve. If, on the contrary, the attempt to relighting has failed, input 38 passes to the 0 state after a period of time determined by resistor 46 and capacitor 37: the output of gate 39 passes to state 1 and the output of gate 36 passes to state 0, which leads to the signal for safety issued by the pilot light 10.

During time T,, input 44 of gate 45 receives a level 0. Input 18 receives alternating current and passes from 0 to 1 at the frequency of the supply system.

The output of gate 45 changes from 1 to 0 at the same frequency. Diode 48 and capacitor 37 force input 38 to remain in state 1. The output of gate 39 is therefore at 0 and the output of gate 36 at 1. The logic level which is applied to input 44 of gate 45 is also transmitted to the switch 8 by way of a diode 49.

The switch 8 is then opened and the electrovalve is not fed. When To come to an end, there follows a time T1 with the operations described hereinabove.

If the safety state was caused by the unprogrammed disappearance of the flame, the output of gate 36 has passed to the 0 state, this meaning that its two inputs are in state 1. To re-set the device, it suf fixes to momentarily cause input 12 of gate 36 to pass to the 0 state by actuating push-button 11.

Figure 5 shows the operational diagram of the device in the different examples given hereinabove.

With the example just described, it is possible to regulate a burner whilst retaining all the aforesaid advantages. In practice, for example in the field of household electrical appliances, it is normal to design and produce heating apparatus with multiple burners, which can be lit by a single igniter. In general, such apparatus have at least three, and mostly four burners.

With these apparatus, it is considered unnecessary to regulate each burner by its own means, and on the contrary it appears to be sufficient for only one burner in any heating apparatus to be controlled.

It is therefore possible to envisage fitting the sequencer described hereinabove for controlling one burner, using the conventional electronic igniting means for the others. This however leads to duplicating the igniting means in one heating apparatus and unnecessarily increases the cost thereof.

One attractive solution to solve this problem would be to couple the conventioally known single igniter with the device according to the invention, in order to obtain the burner sequential-control function, whilst permitting to ignite the other noncontrol led burners in the same apparatus, by using the single igniter of the device. But then, it becomes necessary to provide means for selectively controlling and regulating the igniter and to use the electrode of the igniter specially allocated to the controlled burner as a means to detect the presence of a flame for the logic safety unit.

This object is reached according to an other embodiment of the invention illustrated in Figures 6 to 8. In these figures, the logic safety unit 5 has a first output 6 which leads to the input 7 of the switch 8 described hereinabove. Said switch 8 only controls, from terminals 13, the circuit supplying the electrovalve 16 which controls the arrival of gas to the burner.

The logic safety unit 5 also has a second output 6a connected to the input 7a of a second switch 8a identical to switch 8, as can be seen in Figure 8. Switch 8a controls the supply circuit of an igniter 14a which, contrary to the preceding example, is not of the selfreigniting type. Said igniter, of the conventional type with controlled re-ignition, comprises a first electrode 51 which produces sparks and enables to detect the presence of a flame in a controlled burner.

Said electrode is connected, as in the preceding example, to the input 18 of gate 45. In addition, a spark-gap 52 is interposed between the output of igniter 14a and the junction circuit between electrode 51 and input 18. Said spark-gap is provided to isolate the transmission circuit leading to the input 18 from any "presence of flame" information which could be sent by electrodes 511-512-51n connected to the output of igniter 14a and ensuring the igniting of n hand-controlled burners forming part of the same apparatus. These different electrodes are connected to the outputs of igniter 14a.

The circuit supplying the igniter 14a controlled by the switch 8a further comprises, in parallel from terminals 13, a secondary control circuit controlled by a hand-operated switch 56.

The output 6a of the unit 5 corresponds to that of a gate 55 whose inputs 53 and 54 are respectively connected upstream of diode 48 and downstream of gate 39 to which is also connected the pilot light 10.

In this type of fitting, the input 41 of gate 39 is con nected to the output of gate 36.

As in the preceding example, the cut-out circuit 8 is opened if either one of the two following conditions is met: - if the sequencer 1 gives on its output 3 a logic state 0, - if the output of gate 36 is in the 0 state (safety signal).

On the contrary, the cut-out circuit 8 is closed if either one of the two following conditions is met: - if the sequencer 1 gives on output 3 a state 1 (permanent operation or during times T1 of the cycle), - if the output of gate 36 is in state 1.

To close the switch 8a, one of the three following conditions should be met: - a flame should be detected by electrode 51 during a cycle T of operation, - the sequencer 1 should give on its output 3 a logic state 0 (as with switch 8), outside the igniting sequence, - the output of gate 36 should be at 0 (as with switch 8) in the safety state.

To the two conditions required for switch 8 to open is added a restriction for switch 8a: the system should not have detected a flame and output 6a of gate 55 should be in the 0 state.

By moving switch 2 from the stop point towards any one of the sequential positions, it is automatic to start with an igniting cycle T,. The input 4 of gate 45 is controlled in state 1 by the output 3 of sequencer 1. When a flame is detected, electrode 51 causes a logic state 0 to appear on input 18. The output of gate 45 passes to state 1. The output of gate 36 also stays at 1. Electrovalve 16 is current-fed and controls the arrival of gas to the burner. Gate 55 which, before the appearance of the flame, was in state 1, passes to state 0 at the same time as gate 45 passes to 1. Then, igniter 14a is no longer controlled and the production of sparks stops.

If no flame has appeared, a logic level 1 is found at input 18 of gate 45 and the output passes to the 0 state. After a few seconds, the exact number of which is determined by elements 37 and 46, input 38 of gate 39 passes to 0, as well as the output of gate 36. The valve closes and the light 10 signals for safety. At the same time, inputs 53-54 of gate 55 are respectively set to 0 by 45 and to 1 by 39, this imposing a 0 on the output of gate 55 and as a result the opening of switch 8a and the switching off of igniter 1 4a. It will be necessary to cut off the supply to the electronic system to re-set the circuit.

If the flame happens to disappear due to external causes during time T1 of the cycle or whilst in permanent operation, as in the preceding case, the output of gate 45 passes to 0, gate 55 will then pass to state 1 and will control the igniter 14a via the switch 8a. If this attempt at re-igniting is successful before input 38 of gate 39 has reached the 0 state, input 18 of gate 45 receives once again a logic level 0 and its output returns to state 1, this imposing the same state to input 38 of gate 39. Valve 16 remains open whereas, gate 55 having passed to the 0 state, the igniter will no longer function.

If on the contrary the attempt at re-igniting has failed, input 38 passes to the 0 state at the end of the time period determined by resistor 46 and capacitor 37, the output of gate 39 passes to state 1, that of gate 36 passes to state 0, thus causing a safety signal.

During time T,, input 44 of gate 45 receives a level 0, input 18, directly connected to level 1 by a resistor, will then bring the output of gate 45 to state 1.

Input 38 of gate 39 being then in state 1, the output of gate 39 is then at 0 and the output of gate 36 is at 1. The logic level which is applied to input 44 of gate 45 is also transmitted to switches 8 and 8a via diode 49. Said swtiches are then opened and there is neither any gas flowing nor sparks produced, When To comes to an end, a time T1 follows, with the operations described hereinabove.

If the safety signal has been caused by the unprogrammed disappearance of the flame, the output of gate 36 has passed to the 0 state, this meaning that its two inputs are in state 1. To re-set the device, it suffices to cause input 12 of gate 36 to pass momentarilyto the 0 state.

The arrangements of the second embodiment of the invention have the following advantages.

If the cycle of the controlled burner is in phase T,, the switch 8a is open. The user can nevertheless control the igniter 14a with a view to igniting a noncontrolled burner by hand-operating the switch 56.

Of course a spark will be produced simultaneously to the other burners, but without any results since these burners, whether or not they are controlled, are in the position where they are not fed with gas.

The cycle of the controlled burner will automatically be resumed as previously indicated as the electrovalve 16 opens and as the switch 8a is controlled to closure. Only the controlled burner will receive the benefit of the operation of the safety elements since the spark-gap 52 filters by its presence any spurious current which could be due to the operation of at least one of the controlled burners and which could come from the corresponding igniting electrode and be applied to the input 18.

If the cycle of the controlled burner is in phase T1, the user can always actuate in the same way the hand switch 56 to cause the voluntary ignition of a controlled burner.

The present invention is in no way limited to the description given hereinabove and on the contrary covers any modifications that can be brought thereto of equivalent technique. For example, the emobidments of the unit 5 and NAND type gates at two inputs. It is obvious that such unit could comprise NOR type gates working in the same way and giving the same results.

Claims (8)

1. Flame-control device with sequencer for use in apparatus equipped with burners, for the cyclic and automatic control, via an appropriate igniter, of the presence and absence of a flame according to an adjustable cyclic ratio, the user being able to determine by a control the ratio of the duration T1 of the presence of a flame to the total duration T or cycle time, comprising: - a sequencer essentially composed of electronic circuits capable of delivering control pulses whose cyclic ratio T1/T may be determined by the user actuating a multi-position switch, - a logic safety unit receiving, for example, as input signals, the output signal of the said sequencer and a signal sent by a flame-detection electrode associated to the burner, this last signal being representative of the presence or of the absence of a flame.

- and at least a cut-out circuit inserted between, on the one hand, a source of power and, on the other hand, an igniter associated to said burner and an electro-valve, or the like, controlling the arrival of the combustible mixture to the burner, said cut-out circuit essentially receiving as control input signal, the output signal of the said logic safety unit.

2. Device according to claim 1, wherein said device comprises a logic safety circuit composed of a circuit with successive gates delivering a logic signal controlling the closing of the switch under the simultaneous influence of the signal controlling the operation of the sequencer and the detection of a flame by the detector electrode.

3. Device according to claim 1 or 2, wherein said logic safety circuit comprising a circuit with successive gates is provided with a first gate which receives the signals from the sequencer and from the detector electrode, and of which the output is connected to one of the inputs of a second gate via a timing circuit which delays the application to the said input of a signal indicating the change of state of the first gate consecutively to the change of state of the input of the first gate following a detection of absence of flame.

4. Device according to claim 1, wherein a sequencer is provided which comprises an automatic clearing circuit.

5. Device according to any one of claims 1 to 4, wherein said device comprises: - a first cut-out circuit controlled by the logic safety unit and provided to supply an electrovalve supplying combustible gas to a controlled burner and to sequentially stop said supply whenever an absence of flame is detected in said burner, - a second cut-out circuit controlled by said logic unit and provided to supply a sequential igniting and re-igniting member, - an igniter, controlled for re-igniting, and provided with at least one igniting electrode which is also adapted to detect the presence of a flame.

6. Device according to claim 5, wherein a second cut-out circuit is provided which is controlled by the logic safety unit, said latter being provided to this effect with a control circuit shunted on the circuit with successive gates and depending on the action of a timing circuit for controlling and renewing the supply to the igniter during the action of said timing circuit.

7. Device according to any one of claims 5 and 6, wherein said device comprises: - an igniter with controlled ignition composed of at least one igniting and detecting electrode which is allocated to one controlled burner and of at least one other igniting electrode allocated to at least one burner with controlled ignition, - a device interposed between the igniter and the electric connection between the circuit with successive gates and the electrode of the controlled burner, in order to oppose the transmission to the logic safety unit of any spurious information resulting from the presence of a flame on at least one of the non-controlled burners, - and a handcontrolled switch shunted on the circuit ofthe automatically-operating ignition switch between the source of power and the igniter with controlled ignition.

8. Device substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.