DE3401603C1 - Self-monitoring flame guard - Google Patents

Description

The invention relates to a self-monitoring flame monitor according to the preamble of Claim 1.

Due to the increase in the price of the energy sources oil and gas, the efficiency of the heating systems is increasing increasingly taken into account. For this purpose, efforts are made to reduce the standstill losses of a boiler system reduce, which leads to the downsizing of the former mostly oversized boiler systems and through the use Such a burner is achieved, the performance of which by means of constant control of the current heat demand can be largely customized. Such burners only run in on / off mode and at a minimum load are in continuous operation in the remaining load range. Previously during the downtime or before commissioning self-testing of the flame monitor for possible component errors is in continuous operation no longer applicable. Flame monitoring devices are required in such a system, which continuously monitor themselves for component errors even when in operation. Such flame keepers are known, but still require too much effort or expense for use on small burners still have technical weaknesses.

Up to now it was also disadvantageous that in conventional oil atomization burners the cost-effective Ionization electrode was out of the question as a fail-safe flame scanner because of its coking. These However, the sensor type is also used for oil burners with increasing use of oil gasification or oil evaporation burners gain in importance by then suitable blue-burning electrodes for ionization electrodes

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de flames can be achieved without any soot formation. There is then no coking of the sensor electrodes.

A known flame monitor (DE-PS 30 26 787) is suitable for both ionization and UV operation. In order to keep the logoff time short when the flame is extinguished from the operating state, a Relatively low-resistance operating voltage source with fail-safe voltage limitation required. Together with the fact that the sensor voltage required for UV operation is higher than the mains voltage, a transformer is required, which is expensive and takes up a lot of space.

If the known flame monitor does not operate with a UV sensor and does not have a power supply Transformer selected, there is a risk that the supply voltage will increase in the event of a component fault, without this being recognized in time. In the flame relay circuit, this results in an inadmissibly long logout time if the flame goes out unintentionally. Furthermore, a transformerless direct supply provides With the known circuit, a lower ionization sensor voltage, so that with the same flame quality the sensor current is lower and to ensure the necessary performance on the one fed by the sensor current Threshold switch is no longer sufficient.

According to DE-OS 24 30 328, a flame monitor circuit that can be connected directly to an alternating current network known. However, it requires an extremely high-resistance sensor feed circuit, so a good one, that is relatively low-resistance flame is not recognized as faulty. Due to the high-resistance sensor supply an extremely low load capacity with sensor line capacitances, and even small insulation fault currents impair the useful signal considerably.

The invention is based on the object of creating a flame monitor for ionization sensors which reduces the space requirement without major circuitry expenditure and reliable self-monitoring is also possible if there is no UV monitoring.

The invention is characterized in claim 1.

An exemplary embodiment of the invention is explained in more detail below with reference to the drawing. It shows

F i g. 1 a schematically illustrated circuit of a flame monitor, broken down into its basic elements Function groups, and

F i g. 2 shows a circuit diagram of an exemplary embodiment.

In the two figures described below, the same reference numerals are used for the same parts.

The flame monitor according to the invention consists according to FIG. 1 from a flame relay circuit 1, an amplifier circuit 2, an integrator 3 and a pulse generator 4, as well as an ionization probe, hereinafter referred to as flame sensor 5. The flame sensor 5 forms with a first capacitor 6 in the amplifier circuit 2 a parallel circuit, which via a further capacitor 7 to a directly dem AC voltage drawn from the mains is connected. The amplifier circuit 2 further includes one of the The voltage across the capacitor 6 can be influenced by the amplifier 8, the output of which is sent to a switching element 9 acts in the flame relay circuit 1 and on the integrator 3 described below.

The flame relay circuit 1 consists of a flame relay 10 with two windings 11 and 12, whose first connected in series with a first diode 13 and a charging capacitor 14 and a load resistor 15 to one in FIG. 1 DC voltage source, not shown, is connected. The second winding 12 is also polarized opposite to the charging capacitor 14 and one of the first diode 13 second diode 16 and the load resistor 15 connected in series and thus also to the same DC voltage source connected. The switching element 9 is parallel to the series connection of the charging capacitor 14 connected to the two windings 11 and 12 and the diodes 13 and 16 and enables bridging these circuits, as will be explained below.

The output of the amplifier 8 also influences a second switching element 17 which triggers the integrator 3.

The integrator 3 serves as a timing element and is actuated when it is working correctly on an AC mains voltage connected feed part after a running independently of the state of charge of the first capacitor 6 Time the pulse generator 4. This process is also described below with reference to FIGS. 2 explained in more detail. The triggering of the pulse generator 4 is shown in FIG. 1 indicated by a switch 18. The pulse generator 4 a switching device 21 short-circuiting two inputs 19 and 20 of the amplifier 8 is assigned to the in the closed state, the amplifier 8 simulates a "flame extinguished" signal. The pulse duration is by a in the F i g. 1 timer, not shown, is fixed.

Before going to the details of the circuit according to FIG. 2 is entered, an explanation of the follows basic mode of operation based on the F i g. 1.

In the idle state, when there is no flame, the switching element 9 remains closed. The ones on the flame relay circuit 1 voltage appears at the load resistor 15 and the flame relay 10 is not energized. The voltage at the integrator 3 is zero and the switching device 21 is open. As long as there is no flame, the capacitor 6 can move away from the Do not charge the applied AC voltage. There is no span at the inputs 19 and 20 of the amplifier 8 tion. With the appearance of the flame, the capacitor 6 charges up and the amplifier 8 causes a load Opening the switching element 9 and closing the switching element 17. The charging capacitor 14 is over the high-resistance winding 11 and the diode 13 are charged, with the charging current not affecting the flame relay 10 can turn on. At the same time, the switching element 17 has switched on the integrator 3, the after reaching a predetermined threshold value

so via the switch 18 controls the pulse generator 4, which in turn actuates the switching device 21 and the Amplifier inputs 19, 20 short-circuited. The capacitor 6 is during this short circuit via a Limiting resistor 22 discharged only insignificantly, but the amplifier 8 actuates the switching elements 9 and 17. In the flame relay circuit 1, this causes the flame relay 10 to be switched on by the charging capacitor 14 discharges through the low-resistance winding 12 and the diode 16 to a residual voltage. The duration this discharge is given by the pulse duration of the pulse generator 4 and selected so that the flame relay 10 does not fall off. The switching element 17 has simultaneously set the integrator 3 to zero and switches it at the end of the pulse duration of the pulse generator 4 again, whereupon the same cycle runs again, with the Flame relay 10 always remains energized thanks to the holding current through the winding 11. The flame goes out then the capacitor 6 is no longer recharged,

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the amplifier 8 leaves the switching element 9 closed and the flame relay 10 switches after falling below of the holding current. If there is a flame, only the continuously running cycle can control the flame relay 10 keep excited. But it also means a power supply that is directly connected to the AC mains voltage cannot cause unauthorized switching on of the flame relay 10 in the event of a component defect, this is designed so that it has two voltages of opposite polarity for correct operation of the flame detector must deliver a certain size. Only if this is the case does the cycle described above run smoothly and enables the flame relay to switch on permanently if a flame is present.

Further details are given below with reference to FIGS. 2 described.

A resistor 23, a capacitor 24, a diode 25 and a first storage capacitor 26 are connected in series to an AC mains voltage Un as a feed part between a phase conductor Ph and a neutral conductor N. Furthermore, the series circuit of diode 25 and storage capacitor 26 is connected in parallel with a further series circuit of a first Zener diode 27 with opposing polarity to diode 25 and a second storage capacitor 28, the second storage capacitor 28 being additionally bridged by a second Zener diode 29 which limits its charge voltage.

The first supply voltage U \ is tapped via the first storage capacitor 26, i.e. between the neutral conductor N and a conductor 30, and the second supply voltage Uz via the second storage capacitor 28, i.e. between a connection 31 and the neutral conductor //. The two supply voltages Ui and Uz are polarized opposite to one another with respect to the neutral conductor N.

The flame relay circuit 1 with the switching elements 10 to 16 according to FIG. 1 is connected between the conductor 30 and the neutral conductor N , the resistor 15 leading to the conductor 30. Instead of the switching element 9 of FIG. 1 the collector-emitter path of a transistor 32 occurs.

The series circuit of a charging resistor 33 and an integration capacitor 34 is also connected to the first supply voltage U \ , the voltage across the integration capacitor 34 being fed to the base of the transistor 32 via a resistor 35 and via the collector-emitter path of a further transistor 36. The base of the transistor 36 is also influenced by the voltage U \ on the conductor 30 via a resistor 37 and is also connected to the neutral conductor N via the drain-source path of an FET transistor 38. In the absence of a flame, the gate of the FET transistor 38 is biased more negatively than the potential at the neutral conductor N , for which purpose a resistor 39 connected between the gate and connection 31 is used. Furthermore, the gate is connected to the neutral conductor // via the collector-emitter path of a bipolar transistor 40.

From what has been described it can be seen that the first voltage U \ serves to supply the flame relay circuit 10 to 16 as well as the amplifier circuit 2 formed by the transistors 32,36,38 and the integration capacitor 34, i.e. the integrator 3.

The base of the transistor 40 forms one input 19 and the neutral conductor N forms the other input 20 of the amplifier 8 according to FIG. 1. The voltage tapped at the first capacitor 6 acts between these two inputs.

The capacitor 6 is connected in series with a resistor 42 and the capacitor 7 to the AC mains voltage Un , the ionization path being tapped at the connection point between the capacitor 7 and the resistor 42 via a resistor 43 and thus connected in parallel to the first capacitor 6. The ionization path consists of the flame sensor 5 immersed in a flame 46 and a burner mouth 47 which is connected to earth or to the neutral conductor N.

The circuit also has a pulse generator capacitor 48 which is connected on one side to the connection between the load resistor 15 and the two diodes 13 and 16. Its second connection is to a tap 49 of a voltage divider, which consists of a resistor 50 and a diode 51 connected in the flow direction and is switched off between the conductor 30 and the neutral conductor. The pulse generator capacitor 48 together with the resistor 50 forms a timing element, and the switching device to be influenced by this timing element consists of a transistor 53, the emitter-collector path of which is connected between the base of the transistor 40 and the neutral conductor JV. The transistor 53 is controlled by the timing element 48, 50 and can be influenced by the second supply voltage Ut . For this purpose, the tap 49 is connected to the base of the transistor 53 via a resistor 52. The transistor 53 corresponds to the switching device 21 in Fig.l.

Another transistor 54 has its base connected to the connection between the integration capacitor 34 and the two resistors 33 and 35 via a resistor 55. Furthermore, the emitter of the transistor 54 is connected to the conductor 30 via a Zener diode 56, while its collector is connected to the connection 31 and thus to the second supply voltage Uz through a resistor 57. In addition, there is a connection between the collector of the transistor 54 and the base of the transistor 53 through a diode 58 which, starting from the collector of the transistor 54, is connected in the reverse direction.

The flame monitor described according to FIG. 2 works as follows:

After the application of the AC voltage Un, the two capacitors load 26 and 28 via their associated diodes 25 and 27 and deliver the two-to-neutral together of opposite polarity supply voltages U \ and Uz in the following voltage U \ and £ / 2 called

It is assumed that there is no flame for the time being.

The voltage Uz, the size of which is limited by the Zener diode 29, acts on the switching device influenced by the pulse generator described below, that is, on the base of the transistor 53, and thus also on the amplifier input 38a, which is passed through the gate of the FET transistor 38 is formed. Thanks to the use of an FET transistor, the negative voltage applied across resistor 39 enables it to be blocked. A positive voltage is now applied to the base of the downstream transistor 36, fed in via the resistor 37, and the transistor 36 conducts and, as a result, the transistor 32 as well Windings 11 and 12 and the charging capacitor 14 existing series circuit in the flame relay circuit short-circuited. Everyone

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Current flow through the flame relay 10 is prevented. ·

As a result of the conductive transistor 32, the voltage U \ is largely above the resistor 15, and this load initially results in a relatively small value of U \ . Because the transistors 32 and 36 are conductive and the resistor 35 has a relatively low resistance, the base of the transistor 54 is almost at the potential of the neutral conductor N, and the transistor 54 conducts. The Zener voltage at the Zener diode 56 is exceeded and the voltage U \ therefore causes a further current through 30,56,54,57,29, with the greatest voltage drop across the resistor 57 occurring. The potential at the cathode of the diode 58 is thus positive, and this prevents the transistor 53 from being influenced by this circuit.

Furthermore, the voltage U \ across the resistor 50 causes the pulse generator capacitor 48 to be charged, the charging voltage of which is limited by the diode 51. The voltage drop across the diode 51, that is to say the voltage at the tap 49, keeps the base of the transistor 53 positive via the resistor 52 to such an extent that the latter remains blocked.

The circuit remains in the previously described state until, after the flame 46 has been ignited, the capacitor 6 charges and its control voltage £ / 3 controls the bipolar transistor 40 via the resistor 41. This then transmits the flame signal to the amplifier input 38a. At the same time, the base-emitter diode of the transistor 40 limits a further increase in the control voltage Uz- This is important because a higher control voltage £ / 3 would lead to an inadmissibly long log-off time when the flame is extinguished, with self-monitoring taking place here as well, because an interruption the base emitter diode is recognized. It would lead to the flame relay 10 dropping out because the pulse cycle described below would then no longer take place.

With the modulation of the transistor 40, the amplifier input 38a, that is to say the gate of the FET transistor 38, becomes more positive and its drain-source path goes into the conductive state. As a result, the transistors 36 and 32 block. The load on the source of U \ by the resistor 35 is eliminated. The impulse relay 10, while the integration capacitor 34 discharges very quickly through 35,36,32. Simultaneously with the conduction of the transistors 32 and 36, a charge reversal of the pulse generator capacitor 48 begins, in that its in the FIG. 2 right electrode is deposited via the transistor 32 to the potential of the neutral conductor. The load resulting from the transistor 32 becoming conductive reduces the supply voltage U \. This promotes the blocking ίο of the transistor 54 through a positive feedback effect and causes a desired toggle effect for its switching process and a sufficiently long dwell in the blocked state

The charge reversal of the pulse generator capacitor 48 takes much longer than the very rapid discharge of the integration capacitor 34, the latter having the consequence that the positive voltage at the base of the transistor 54 rapidly drops so far that it becomes more negative than at the emitter. The transistor 54 thus becomes conductive again, and the voltage U \ acts again across the resistor 57. The connection between the resistor 57 and the diode 58 is now at the positive potential, but this cannot affect the transistor 53 due to the blocking of the diode 58. This is important because the time during which the transistor 54 blocks is shorter than the desired pulse length of the pulse generator should be. The reloading of the pulse generator capacitor 48, which takes place relatively slowly for this purpose, takes place via the resistor 50, the voltage potential at the tap 49 initially being negative and changing towards positive values, which is transmitted via the resistor 52 to the base of the transistor 53. The transistor 53 therefore becomes conductive when the transistor 54 is blocked, but remains conductive for longer after the short blocking pulse of the transistor 54, until the charge reversal of the pulse generator capacitor 48 at tap 49 again to a potential of about 0, 5 volts has risen. Then the transistor 53 blocks again.
During the time in which the transistor 53 was conductive, the capacitor 6 has discharged only insignificantly via the resistor 41. Therefore, after the blocking of the transistor 53 at the base of the transistor 40, only the size of the control voltage U ₃ that can be attacked via the capacitor 6 is decisive, although

Transmitter capacitor 48 is charged via resistor 15, 45, as described above, as is transistor 53 which is much smaller than the resistor 50, as well as via the as well as the control voltage t / 3 on the basis of the transi-

Diode 51 on. The integration capacitor 34 is also charged via the resistor 33. Also arises a charging current through the diode 13 and the winding 11 to the charging capacitor 14, this current flow to pull up the flame relay 10 is not sufficient. With increasing charge of the integration capacitor 34, the base of transistor 54 assumes an increasingly positive value, until the The Zener voltage across the Zener diode 56 has fallen below, which triggers the blocking of the transistor 54. The time, until this occurs is given by the integration capacitor. The positive voltage across resistor 57 is eliminated by the blocking of the transistor 54. The transistor 53 is activated via the diode 58. Because he now conducts, it forms a short-circuit switch for the base-emitter path of the transistor 40, where it is the Base of transistor 40 during a time determined by the pulse generator described below Sets neutral. As a result, the transistors 40 and 38 block, while the transistors 32 and 36 become conductive. The charging capacitor 14 discharges via 12, 16, and its current causes the flame shutter to be opened 40 act. That is, provided that the flame 46 is still present, the transistors will 40 and 28 conductive again, while transistors 36 and 32 block again.

The charging current flowing through the winding 11 for the charging capacitor 14 now holds the flame relay 10 in an excited state. Then the whole cycle repeats itself again.

The flame relay 10 can therefore only remain in the energized state if the transistor 40 is blocked periodically for a short time. Any disturbance of the cycle described, which takes place in a certain time, causes the flame relay 10 to drop out. The power supply unit, which supplies the two supply voltages U \ and Ui , is thus also monitored, because any failure of one of its elements leads to a disruption of this cycle and therefore to the flame relay 10 dropping out.

In contrast to the familiar, the flame monitor described was the flame relay circuit transistor 32 connected in parallel is selected so that it is conductive when no flame signal is present. Through this the logoff time is no longer from the big one

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The charging time constant of the charging capacitor 14 is determined, but only from its short discharging time constant. The source of the supply voltage U \ can therefore be selected to be high-resistance and, as a result, a relatively flat course of the charging curve of the charging capacitor 14 can be used. This enables the cycle repetition time to be increased, ie to be greater than one second. This in turn results in a more favorable ratio of the charging time to the discharging time of the capacitor 6 charged by the ionization circuit than a lower energy consumption from this circuit, and thus a lower load on the sensor signal and increased sensitivity. The logoff time is now mainly determined by the discharge time constant resulting from the resistor 41 and the capacitor 6.

The flame monitor described continuously monitors itself, because every short circuit or interruption of any semiconductor or capacitor as well as any interruption of any resistance disturbs the for the Flame relay circuit necessary cycle so that the flame relay is no longer energized.

In order to achieve this behavior, it is important that the discharge process is triggered on the charging capacitor 14 not from the voltage across this capacitor, but from the independent integration capacitor 34 is derived. It is also important that the duration of the discharge process does not depend on the Voltage on the charging capacitor 14, but from the separate timing circuit of the pulse generator capacitor 48 and its resistance 50 is dependent.

The arrangement described is inexpensive to manufacture and, despite the power supply, offers no Transformer guarantees that in the event of a component fault there will be no unacceptable increase in the operating voltage and the resulting extension of the log-off time can occur.

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Claims (8)

34 Ol 603 claims: 1. Self-monitoring flame monitor for monitoring the flame of an oil evaporation or gas burner, with an ionization probe that can be connected to an alternating voltage source and a capacitor that can be charged depending on the ionization current of the flame scanner, with an amplifier with an output switching element that can be influenced by a control voltage via the capacitor, as part of a flame relay circuit of the series connection of at least one diode, the partial winding of a flame relay and a charging capacitor is connected in parallel, while the series connection of at least one further diode with a further partial winding of the flame relay and the charging capacitor is connected to a supply voltage charging the charging capacitor, and with a periodic output switching element when an ionization current is present switching pulse generator, characterized that the alternating voltage source (23, 24, 26, 27, 28, 29 ) supplies two oppositely polarized supply voltages (U \, Ui) of a certain size for the flame relay (10), that the pulse duration of the pulse generator (4; 54) can be set by a timing element (48, 50), that the amplifier (8; 36, 38) controls an integrator (3; 34) that is essentially independent of the charge state of the capacitor (6), which actuates the pulse generator (4; 54) which, during the pulse duration, confirms a switching device (21; 53) which short-circuits the amplifier input (19, 20; 3Sa) to simulate a signal "flame extinguished". 2. Flame monitor according to claim 1, characterized in that the output switching element is a the flame relay circuit (11,12,13,14,16) parallel The transistor (32) is brought into the conductive state in the absence of a signal “flame is burning” is. 3. Flame detector according to claim 2, characterized in that the supply voltage (U \) the flame relay circuit (11,12,13,14,16), the amplifier circuit (2; 36, 38), the pulse generator (4; 54, 48, 50) and feeds the integrator (3; 34), while the oppositely polarized supply voltage (Ui ) acts on the switching device (21; 53) which can be actuated by the pulse generator (4; 54, 48, 50). 4. Flame monitor according to one of the preceding claims, characterized in that the feed part of a load connected to the mains AC voltage (Un) series circuit of a resistor (23), a second capacitor (24) and a diode (25) and a first storage capacitor ( 26) consists in that the series connection of the diode (25) and the storage capacitor (26) is connected in parallel with a further series connection of a Zener diode (27) with opposing polarity to the diode (25) and a further storage capacitor (28), which is additionally connected by its charging voltage limited further Zener diode (29) can be bridged, and that a supply voltage (Ut) via the first storage capacitor (26) and the oppositely polarized supply voltage (U2) via the further storage capacitor (26) can be tapped. 5. Flame monitor according to claim 4, characterized in that the parallel connection of the flame sensor (5) and its ionization path (5; 46, 47) with the control voltage (U3) supplying the first capacitor (6) via at least one resistor (42, 43) can be connected in series with a further capacitor (7) to the mains alternating voltage (Un) . 6. Flame detector according to claim 5, characterized in that a bipolar transistor (40) is used to transmit the flame signal to the amplifier input (38a,), the collector-emitter path of which is connected between the amplifier input (38a,) and the neutral conductor (N) and on the base of which both the switching device (21; 53) operable by the pulse generator (4; 54) and the control voltage (t / 3) that can be tapped via the first capacitor (6) act, the base-emitter path of the bipolar transistor (40) at the same time Limitation of the control voltage (U3) is used. 7. Flame detector according to claim 6, characterized in that a further transistor (53) serves as the switching device (21), the emitter-collector path of which is connected between the base of the bipolar transistor (40) and the neutral conductor (N) and the base of which is connected through the timing element (48, 50) is controlled and can be influenced by the second supply voltage (Ui) . 8. Flame detector according to claim 7, characterized in that the input (38a,) of the amplifier (32, 36) is the gate of an FET transistor (38) which can be controlled with the second, negative supply voltage (U2).