CH663077A5 - SELF-MONITORING FLAME GUARD. - Google Patents

Description

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

Due to the increase in the price of oil and gas, the efficiency of heating systems is increasingly being taken into account. For this purpose, efforts are being made to reduce the standstill losses of a boiler system, which is achieved by reducing the previously oversized boiler systems and by using such burners, the output of which can be largely adapted to the current heat demand by means of constant control. Such burners only run in the on / off mode at a minimum load and are in continuous operation in the remaining load range. The self-testing of the flame detector for possible component faults, which previously took place during downtime or before each start-up, can no longer be used in continuous operation. Flame monitoring devices are required in such a system, which continuously monitor themselves for component faults even in the operating state. Such flame monitors are known, but still require too much effort for use on small burners or still have technical weaknesses.

So far, it has also been a disadvantage that, in conventional oil atomizing burners, the cost-effective ionization electrode was out of the question because of its coking as a fail-safe flame sensor. However, this type of sensor will also become more important for oil burners with the increasing use of oil gasification or oil evaporation burners, in that then suitable blue-burning flames are achieved for ionization electrodes without any soot formation. Coking of the sensor electrodes then falls away.

A known flame guard (DE-PS 3 026 787) is suitable for both ionization and UV operation. In order to keep its logout time short when the flame goes out of operation, a relatively low resistance is required

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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 complex and takes up a lot of space.

If the known flame monitor does not operate with a UV sensor and a supply without a transformer is selected, there is a risk that the supply voltage will rise in the event of a component fault without being recognized in good time. In the flame relay circuit, this causes an impermissibly long logout time if the flame is extinguished unintentionally. Furthermore, a transformerless direct supply in the known circuit provides a lower ionization sensor voltage, so that the sensor current becomes lower with the same flame quality and is no longer sufficient to ensure the necessary power at the threshold switch fed by the sensor current.

According to DE-OS 2 430 328, a flame detector circuit that can be connected directly to an AC network is known. However, it requires an extremely high-resistance sensor supply circuit so that a good, i.e. relatively low-resistance flame is not recognized as faulty. Due to the high-ohmic sensor supply, there is an extremely low load-bearing capacity with sensor line capacities, and even small insulation fault currents have a significant impact on the useful signal __.

The invention is based on the object of providing a flame monitor for ionization sensors which detects any component failure, can be operated directly from the AC network without a transformer and is largely insensitive to insulation faults and line capacities.

The invention is characterized in claim 1.

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

Show it:

Fig. 1 is a schematically illustrated circuit of a flame detector, broken down into its basic functional groups, and

Fig. 2 is a circuit diagram of an embodiment.

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

1 consists of a flame relay circuit 1, an amplifier circuit 2, an integrator 3 and a pulse generator 4, and an ionization flame sensor, hereinafter referred to as flame sensor 5. The flame sensor 5 forms a parallel circuit with a first capacitor 6 in the amplifier circuit 2, which is connected via a further capacitor 7 to an AC voltage taken directly from the network. The amplifier circuit 2 also contains an amplifier 8 which can be influenced by the voltage across the capacitor 6, the output of which acts on a switching element 9 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, the first of which is connected in series with a first diode 13 and a charging capacitor 14 and a load resistor 15 to a DC voltage source (not shown in FIG. 1). The second winding 12 is also connected in series with the charging capacitor 14 and a second diode 16 which is polarized opposite to the first diode 13 and the load resistor 15, and is therefore also connected to the same DC voltage source. 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 of these circuits, as will be explained further 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 actuates the pulse generator 4 after a period of time which runs independently of the state of charge of the first capacitor 6 when the supply part is working correctly and connected to an AC mains voltage This process is also explained in more detail below with reference to FIG. The triggering of the pulse generator 4 is indicated in FIG. 1 by a switch 18. The pulse generator 4 is assigned a two inputs 19 and 20 of the amplifier 8 short-circuiting switching device 21, which in the closed state pretends to the amplifier 8 a signal “flame extinguished”. The pulse duration is fixed by a timing element, not shown in FIG. 1.

Before the details of the circuit according to FIG. 2 are discussed, the basic mode of operation is explained with reference to FIG. 1:

In the idle state, when there is no flame, the switching element 9 remains closed. The voltage across the flame relay circuit 1 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 cannot be charged by the AC voltage applied. There is no voltage at the inputs 19 and 20 of the amplifier 8. With the appearance of the flame, the capacitor 6 charges and the amplifier 8 causes the switching element 9 to open and the switching element 17 to close. The charging capacitor 14 is charged via the high-resistance winding 11 and the diode 13, the charging current being the Flame relay 10 can not turn on. At the same time, the switching element 17 has switched on the integrator 3, which, after reaching a predetermined threshold value, triggers the pulse generator 4 via the switch 18, which in turn actuates the switching device 21 and short-circuits the amplifier inputs 19, 20. The capacitor 6 is only slightly discharged during this short circuit via a limiting resistor 22, 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 via the low-resistance winding 12 and the diode 16 discharges to a residual voltage. The duration of this discharge is given by the pulse duration of the pulse generator 4 and selected so that the flame relay 10 does not drop out. The switching element 17 has at the same time set the integrator 3 to zero and switches it on again at the end of the pulse duration of the pulse generator 4, whereupon the same cycle takes place again, the flame relay 10 always remaining excited due to the holding current through the winding 11. If the flame goes out, the capacitor 6 is no longer recharged, the amplifier 8 leaves the switching element 9 closed and the flame relay 10 switches off after the holding current has fallen below. If the flame is present, only the continuously running cycle can keep the flame relay 10 energized. However, so that a supply part connected directly to the AC mains voltage cannot cause the flame relay 10 to switch on unauthorizedly in the event of a component defect, it is designed in such a way that it must supply two voltages of a certain magnitude that are polarized in opposite directions for the flame detector to operate correctly. Only if this is the case does the cycle described above run smoothly and, if a flame is present, enables the flame relay to be switched on permanently.

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Further details are described below with reference to FIG. 2.

A resistor 23, a capacitor 24, a diode 25 and a first storage capacitor 26 are connected to a mains AC voltage Un as a supply part between a phase conductor Ph and a neutral conductor N in series connection. Furthermore, the series connection of diode 25 and storage capacitor 26 is connected in parallel with a further series connection of a first Zener diode 27, which is polarized opposite to the diode 25, and a second storage capacitor 28, the second storage capacitor 28 additionally being connected by a second Zener diode which limits its charging voltage

29 is bridged.

The first supply voltage U i is tapped across the first storage capacitor 26, that is to say between the neutral conductor N and a conductor 30, and the second supply voltage U2 across the second storage capacitor 28, that is to say between a connection 31 and the neutral conductor N. The two supply voltages Ui and U2 are polarized in opposite directions 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 being connected to the conductor

30 leads. The collector-emitter path of a transistor 32 takes the place of the switching element 9 in FIG. 1.

The series connection of a charging resistor 33 and an integration capacitor 34 is also connected to the first supply voltage U1, the voltage across the integration capacitor 34 being fed via a resistor 35 and via the collector-emitter path of a further transistor 36 to the base of the transistor 32. The base of the transistor 36 is also influenced by the voltage U1 on the conductor 30 via a resistor 37 and is also connected to the neutral conductor N via the drain-source path of a FET transistor 38. Without 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 the connection 31 is used. Furthermore, the gate is connected to the neutral conductor N via the collector-emitter path of a bipolar transistor 40.

It can be seen from the description that the first voltage Ui serves both to supply the flame relay circuit 10 to 16 and the amplifier circuit 2 formed by the transistors 32, 36, 38 and the integration capacitor 34, that is to say the integrator 3.

The base of the transistor 40 forms one input 19 and the neutral conductor N 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 line 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 with 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 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 at a tap 49 of a voltage divider, which consists of a resistor 50 and a diode 51 connected in the flow direction and is connected between the conductor 30 and the neutral conductor N. The pulse generator capacitor 48 forms a timing element together with the resistor 50, 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 N. The transistor 53 is controlled by the timing element 48, 50 and can be influenced by the second supply voltage U2. 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. 1

Another transistor 54 has its base connected via a resistor 55 to the connection between the integration capacitor 34 and the two resistors 33 and 35. Furthermore, the emitter of transistor 54 is connected to conductor 30 via a zener diode 56, while its collector is connected to connection 31 and thus to second supply voltage U2 by a resistor 57. In addition, there is a connection between the collector of transistor 54 and the base of transistor 53 through a diode 58 which, viewed from the collector of transistor 54, is connected in the reverse direction.

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

After the mains AC voltage Un has been applied, the two capacitors 26 and 28 charge via their associated diodes 25 and 27 and supply the two supply voltages Ui and U2 which are polarized opposite one another with respect to the neutral conductor N, hereinafter referred to as voltage Ui and U2.

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

The voltage U2, 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 to say on the base of the transistor 53, and thus also on the amplifier input 38a, which is through the gate of the FET transistor 38 is formed. Thanks to the use of an FET transistor, the negative voltage applied across the resistor 39 enables its blocking. At the base of the downstream transistor 36 there is now a positive voltage, supplied via the resistor 37, and the transistor 36 conducts and, as a result, also the transistor 32. As a result, without the presence of a flame signal, the diode 13 and 16, respectively Windings 11 and 12 and the charging capacitor 14 existing series circuit in the flame relay circuit short-circuited. This prevents any current flow through the flame relay 10.

As a result of the conductive transistor 32, the voltage Ui is largely above the resistor 15, and this load initially results in a relatively small value of Ui. Because transistors 32 and 36 are conductive and resistor 35 is relatively low-resistance, the base of transistor 54 is almost at the potential of neutral conductor N and transistor 54 is conductive. The Zener voltage at the Zener diode 56 is exceeded and the voltage U1 therefore causes a further current through 30, 56, 54, 57, 29, the greatest voltage drop occurring across the resistor 57. The potential at the cathode of the diode 58 thus becomes positive, and this prevents the transistor 53 from being influenced by this circuit.

Furthermore, the voltage U1 across the resistor 50 charges the pulse generator capacitor 48, 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.

In the state described so far, the circuit remains until after the flame 46 is ignited, the capacitor 6 charges and its control voltage U3 via the resistor

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41 modulates the bipolar transistor 40. This transmits the flame signal to the amplifier input 38a. At the same time, the base-emitter diode of the transistor 40 limits a further rise in the control voltage Lb. This is important because a higher control voltage U3 would result in an inadmissibly long logout time when the flame goes out 5, self-monitoring also taking place here because the base is interrupted -Emitter diode is recognized. It would cause the flame relay 10 to drop 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. This blocks the transistors 36 and 32. is The load on the source of Ui through the resistor 35 is eliminated. The pulse generator capacitor 48 charges via the resistor 15, which is much smaller than the resistor 50,

as well as via diode 51. The integration capacitor 34 is likewise charged via the resistor 33. In addition, a charging current arises through the diode 13 and the winding 11 to the charging capacitor 14, this current flow not being sufficient to pull up the flame relay 10. With increasing charge of the integration capacitor 34, the base of the transistor 54 assumes an increasingly positive value, namely until the Zener voltage across the Zener diode 56 is undershot, which triggers the blocking of the transistor 54. The time until this occurs is given by the integration capacitor 34. The positive voltage across resistor 57 is eliminated by blocking transistor 54 30. The transistor 53 is driven via the diode 58. Since it is now conducting, it forms a short-circuit switch for the base-emitter path of the transistor 40, whereby it connects the base of the transistor 40 to the neutral conductor for a time determined by the pulse generator described below. 35 As a result, transistors 40 and 38 block, while transistors 32 and 36 become conductive. The charging capacitor 14 discharges via 12, 16, 32 and its current causes the flame relay 10 to open, while the integration capacitor 34 discharges very quickly via 35, 36, 32. 40 At the same time that the transistors 32 and 36 become conductive, the pulse generator capacitor 48 begins to be recharged, in that its right electrode in FIG. 2 is connected to the potential of the neutral conductor N via the transistor 32. The supply voltage Ui is reduced due to the 45 load which arises as a result of the transistor 32 becoming conductive. This promotes the blocking of the transistor 54 by means of a positive feedback effect and causes a desired toggle effect for its switching operation and a sufficiently long stay in the blocking state. so

The recharging of the pulse generator capacitor 48 takes much longer than the very rapid discharge of the integration capacitor 34, the latter of which has the consequence that the positive voltage at the base of the transistor 54 drops rapidly to such an extent that it becomes more negative than at the emitter. The transistor 54 thus becomes conductive again, and the voltage U1 acts again via the resistor 57. The connection between the resistor 57 and the diode 58 is now at the positive potential, but this cannot influence the transistor 53 by blocking the diode 58. This is important because the time during which transistor 54 is blocking 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 transferred via the resistor 52 to the base of the transistor 53. The transistor 53 is therefore probably with the blocking of the

Transistor 54 is conductive, but remains conductive for a longer period beyond the short blocking pulse of transistor 54, until the charge of the pulse generator capacitor 48 at the tap 49 has risen again to a potential of approximately 0.5 volts. Then the transistor 53 turns off again.

During the time in which the transistor 53 was conductive, the capacitor 6 has discharged only slightly through the resistor 41. Therefore, after the transistor 53 has been blocked at the base of the transistor 40, again only the size of the control voltage U3 which can be tapped off via the capacitor 6 is decisive, although, as described above, both the transistor 53 and the control voltage U3 act on the base of the transistor 40. That is, provided that the flame 46 is still present, the transistors 40 and 38 become conductive again, while the transistors 36 and 32 block again.

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

The flame relay 10 can therefore only remain in the excited state if the transistor 40 is periodically blocked for a short time. Any fault in 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 Ui and U2, is thus also monitored, since each failure of one of its elements leads to a fault in this cycle and therefore to a decrease in the flame relay 10.

In contrast to what is known, in the case of the flame monitor described, the transistor 32 connected in parallel with the flame relay circuit was selected such that it is conductive when there is no flame signal. As a result, the deregistration time is no longer determined by the large charging time constant of the charging capacitor 14, but rather only by its short discharge time constant. Therefore, the source of the supply voltage U1 can be selected to have a high resistance and, consequently, a relatively flat course of the charging curve of the charging capacitor 14 can be used. This enables the cycle repetition time of the cycle to be increased, that is, to be selected 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, that is to say a lower energy consumption from this circuit, and thus a lower load on the sensor signal and an increased sensitivity. The logoff time is now mainly determined by the discharge time constant resulting from the resistor 41 and the capacitor 6.

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

In order to achieve this behavior, it is important that the triggering of the discharge process at the charging capacitor 14 is not derived from the voltage at this capacitor, but from the independent integration capacitor 34. In addition, it is important that the duration of the discharge process does not depend on the voltage at the charging capacitor 14, but on the separate time circuit of the pulse generator capacitor 48 and its resistor 50.

The arrangement described can be produced inexpensively and, despite the power supply without a transformer, guarantees that an unacceptable increase in the operating voltage and the consequent increase in the logoff time cannot occur in the event of a component fault.

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Claims (8)

663077 PATENT CLAIMS 1. Self-monitoring flame monitor for monitoring the flame of an oil evaporation or gas burner, with an ionization flame sensor and a parallel connection of the flame sensor to an AC voltage, with a first capacitor, the charging of which depends on the ionization current of the flame sensor, with one influenced by a control voltage across the first capacitor Amplifier in an amplifier circuit with an output switching element which is connected in parallel as part of a flame relay circuit of a series circuit of at least one diode, a partial winding of a flame relay and a charging capacitor, while a further series circuit 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 pulse which periodically opens and closes the output switching element in the presence of an ionization current Sensor, characterized in that a charge is independent of the state of charge of the first capacitor (6) which can be charged by the ionization current, but is independent of the initial state of the amplifier (8; 36; 38) influenced integrator (3; 34) is arranged, which triggers a pulse generator (4; 54) with a pulse duration predetermined by a timing element (50,48), and that one of the pulse generator (4; 54) can be actuated during the pulse duration Inputs (19, 20; 38a) of the amplifier (8; 36, 38) short-circuiting and thus pretending to the amplifier (8; 38; 36) a signal "flame extinguished", pretending switching device (21; 53) is present, and that the flame detector is also present has a supply part which can be connected to the mains AC voltage (Un) and which supplies two voltages (Ui, U2) which must have two specific sizes for the flame detector to operate correctly. 2. Flame detector according to claim 1, characterized in that the two voltages (Ui, U2) of a certain size are polarized in opposite directions and the first voltage (Ui) for supplying the flame relay circuit (1.10 ... 16), the Amplifier circuit (2; 36; 38), the pulse generator (4; 54; 48; 50) and the integrator (3; 34), and the second supply voltage (U2) to that of the pulse generator (4; 54,48,50) influenced switching device (21; 53) and thus acts on the amplifier input (19, 20; 38a). 3. Flame detector according to claim 1 or 2, characterized in that the supply part of a series circuit of a resistor (23), a second capacitor (24), a diode (25) and a first storage capacitor connected to the mains AC voltage (Un) (26) and that the series connection of the diode (25) and the first storage capacitor (26) is connected in parallel with a further series connection of one of the diodes (25) with opposite polarity, the first zener diode (27) and a second storage capacitor (28), the second Storage capacitor (28) is additionally bridged by a second zener diode (29) limiting its charging voltage, and that the first supply voltage (U1) across the first storage capacitor (26) and the second, oppositely polarized supply voltage (U2) across the second storage capacitor (28) is tapped. 4. Flame detector according to claim 3, characterized in that the parallel connection of the flame sensor (5) and its ionization path (5, 46, 47) with the first capacitor (6) supplying the control voltage (U3) via at least one resistor (42, 43) can be connected in series with a further capacitor (7) to the mains AC voltage (Ün). 5. flame guard according to one of claims 1 to 4, characterized in that the output circuit element (9; 32) connected in parallel to the series circuit in the flame relay circuit (1), which consists of the diodes (13, 16), the windings (11, 12) and the charging capacitor (14) is a transistor (32) conducting without the presence of a flame signal. 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 basis thereof Both the switching device (21; 53) which can be actuated by the pulse generator (4; 54) and the control voltage (U3) which can be tapped via the first capacitor (6) act, the base-emitter path of the bipolar transistor (40) simultaneously limiting the control voltage ( U3) serves. 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 the timer (48, 50) is controlled and can be influenced by the second supply voltage (U2). 8. Flame detector according to claim 7, characterized in that the input (38a) of the amplifier (32,36,38) is the gate of a FET (38) which can be driven with the second, negative supply voltage (U2).