EP2549187B1 - Method and apparatus for controlling the air ratio of a burner - Google Patents

Description

The invention relates to a method and a device for controlling the air number of a burner, in particular an oil or gas burner.

Background of the invention

Methods for air number control of burners are known in the art. In these, an air-fuel ratio (so-called air number or lambda) λ of an air-fuel mixture is adjusted to a desired value by varying a fan speed or regulating a fuel valve. Preferred values for the air ratio λ are in a range of 1.15 to 1.3, in which the fuel is burned with excess air. By monitoring and corresponding readjustment of the air ratio can be achieved in terms of pollutant emissions and firing efficiency optimum combustion even in fluctuating environmental conditions and changing fuel quality, such as when switching from the fuel supply of natural gas to liquefied gas.

In the prior art, methods are known in which the detection of the air ratio is effected by measuring an ionization current flowing from an ionization electrode introduced into the combustion chamber. In this case, an alternating voltage is applied to the ionization electrode and detects a current flowing away from the ionization, rectified due to the rectifying property of the flame current as ionization. By means of a control circuit then the measured ionization current is compared with a setpoint of the air ratio corresponding setpoint value for the ionization, and readjusted the composition of the air-fuel mixture accordingly. Such a method is for example in the document DE 44 33 425 A1 disclosed.

A problem with this method results from the fact that during the operating period of the burner, the thermal coupling between the ionization and the burner can change. This is due, inter alia, bending of the ionization electrode, aging, wear and contamination selbiger, and a sooting of the burner. Accordingly, even when the actual air ratio remains the same, the ionization current measured at the ionization electrode changes means that the proportionality factor between the actual air ratio and the measured ionization current is influenced by the above-mentioned effects. Therefore, in order to still be able to readjust the air ratio reliably, a calibration of the determination of the air number, or a determination of an additional proportionality factor between the actual air number and the measured ionization flow, is required.

A method for calibrating the measurement of the ionization current based Luftzahlbestimmung is in the document DE 195 39 568 C1 disclosed. In this method, the air ratio is deliberately lowered in the range λ = 1 (stoichiometric combustion) at regular intervals in order to determine the maximum occurring ionization current. Starting from the value pair determined in this way ( λ = 1 , maximum occurring ionization current), a proportionality factor between the actual air ratio and the measured ionization current can be calculated.

A disadvantage of this method, however, has been found that in the air range λ = 1 of the pollutant emissions compared to the optimized air range, in the combustion takes place with excess air, is significantly increased. Furthermore, operation of the burner in the air-fuel ratio λ = 1 requires increased heat production, for which a corresponding heat-sinking capacity must be provided. Especially during the summer months, in which the burner is typically run in a continuous flow heater, a heat removal capacity required for this purpose is often not available. In particular, in view of a desired reduction of pollutant emissions of the burner, and also with a view to increasing its efficiency in the document DE 195 39 568 C1 Proposed procedures therefore considered to be in need of improvement.

From the publication EP 1811230 A2 a burner with a burner surface and arranged downstream of the burner ignition electrode is known, in which an electrical resistance on the side facing away from the flame of the burner surface is detected. From the detected electrical resistance, the temperature of the burner surface is determined by means of a resistance-temperature relation. In this case, this particular type of temperature determination is selected in order to avoid protrusion of a measuring electrode into the combustion chamber. The detected resistance is further used to detect the flame and to adjust the air-fuel ratio. The latter happens because of first, the air value λ = 1 is approached at which the flame temperature and thus the detected electrical resistance is maximum, and starting from this point, the air-fuel mixture is emaciated in a predetermined ratio, or to a predetermined measured value of the detected electrical resistance is reached. Thus occurs in the burner of the publication EP 1811230 A2 the problem that first the air value λ = 1 must be approached, which is as stated above associated with increased pollutant emissions and unwanted heat dissipation.

The publication DE 10 2008 053 959 B4 discloses a food processor with burner. The burner comprises a cylindrical outer wall and a coaxial to the outer wall, permeable to a combustion fluid inner wall. Within the inner wall, a cavity is formed, in which the combustion takes place mainly. An ignition electrode is arranged so that it projects from the outside through the outer wall and the inner wall into the cavity. This ignition electrode, in addition to its function as an ignition electrode, can be used to measure either an ionization current or the flame temperature. Again, however, there is the problem that in particular the ionization current measurement can be influenced by a change in the thermal coupling between the burner and the ignition electrode, for example by aging of the ignition electrode, and thus not sufficiently high accuracy, such as would be required for air volume control, offers.

From the publication EP 1591723 A2 Finally, an electrode with a Isolierkeramikkörper and acted upon by the flame region of an electrically conductive ceramic body is known. This electrode is particularly resistant to corrosion and can be used in accordance with their specific arrangement in a burner either as an electrode for Ionisationsstrommessung or as part of a Zündelektrodenpaares.

Summary of the invention

It is an object of the present invention to provide a method and apparatus for controlling the air flow rate of a burner, in particular an oil or gas burner, which are free of the above-mentioned problems. It is a further object of the invention, with simple means to a calibration of Luftzahlbestimmung to enable. It is a further object of the invention to increase the quality of air number determination.

To solve these problems, the method according to the invention with the features of claim 1 and the device according to the invention with the features of claim 9 are proposed. Advantageous developments of the invention are the subject of the dependent claims.

According to a first aspect of the invention, a method for controlling the air number of a burner is proposed, in particular a gas or oil burner, with an ignition electrode, means for generating an ignition voltage, which are connectable to the ignition electrode, and an ionization electrode, which is acted upon by an ionization voltage, the method separating the ignition electrode from the means for generating the ignition voltage, detecting a first electrical signal at the ionization electrode and deriving a first air-frequency dependent signal in response to the first electrical signal, detecting a second electrical signal at the ignition electrode, and deriving a second dependent on the air number signal in response to the second electrical signal, determining a control variable for the burner operation in response to the first air-dependent signal and the second dependent on the air number signal, Ver equal to the first air number dependent signal and the second air frequency dependent signal, and if a difference of the first air number dependent signal and the second air frequency dependent signal exceeds a threshold value, performing a calibration process to correct the first air number dependent signal includes.

The invention is based on the finding that, in addition to the ionization current, the flame temperature can be used as a second variable for controlling the air number and for calibrating the determination of the air number. Also, from the flame temperature, with known burner power, the air ratio of the gas-fuel mixture can be reliably derived with high accuracy. However, according to the inventors, the flame temperature per se is not suitable as a reference variable for controlling the air number, since the flame temperature detecting temperature sensor can respond to occurring changes in the flame temperature only with a time delay due to a finite heating. Typically, this results for the Determination of air speed delays of about one to three seconds. An air flow control based solely on the flame temperature would therefore result in increased pollutant emissions and reduced combustion efficiency. Due to the time delay during the detection of the flame temperature, the flame temperature is also not suitable for detecting the flame, ie as a detection variable for a so-called flame detector.

Nevertheless, as the inventors have realized, the flame temperature is very well suited as a calibration variable for determining the air number by means of ionization current measurement. For this purpose, only a stable state of the burner is produced, so that the time delay of the determination of the air number by means of flame temperature measurement has no influence on the determination of the air ratio. In such a stable state, the air number determination can then be calibrated by means of ionization current measurement by comparison of the air value values determined by means of ionization current measurement and flame temperature measurement. Thus, by detecting two independent signals dependent on the air number, the necessity of calibrating the air number determination based on the ionization current can be recognized, and then performed in a simple manner. A lowering of the air ratio in the air range λ = 1 at regular intervals, taking into account the disadvantages described above is thus not required.

Even for the air ratio control itself, there are several advantages of the method according to the invention. First, the simultaneous presence of a first air-mode dependent signal derived from one ionization stream and a second air-mode dependent signal derived from the flame temperature provides a full two-channel system with increased fail safety. In particular, an emergency operation can be maintained in this even in the absence of one of the two signals, for example by a fault in the corresponding electrode or the corresponding signal line, in which the air ratio can be controlled, albeit with restrictions.

In addition, the proposed method advantageously combines the short response time of the ionization current measurement with the reliability and accuracy of the determination of the air number by means of flame temperature measurement. Since the Luftzahlregelung both a first dependent on the air number signal derived from an ionization current, as well as a second dependent on the air number signal from the Flame temperature is derived, are available, opens up many advantageous ways of signal evaluation. For example, it is thus possible to react to changes in ambient conditions or fuel quality, which are reflected in a change in the air number, based on the actual air ratio determined as a function of the ionization current with a very short response time, whereby the burner can always be operated in the range of the optimum air ratio. On the other hand, with constant ambient conditions and consistent fuel quality, the actual air ratio can be determined very accurately by means of flame temperature measurement, which is why the air ratio can be readjusted very accurately. As a result, an improved combustion result can be achieved with constant ambient conditions and consistent fuel quality.

Thus, the inventive method by the simultaneous evaluation of the Ionisationsstrommessung and the flame temperature measurement not only combines the advantages of each Luftzahlbestimmung by Ionisationsstrommessung and an air number determination by means of flame temperature measurement, but also offers other additional benefits that can not be achieved by taking into account only one of the two possibilities for Luftzahlbestimmung would. These additional advantages include, for example, an increased reliability of the burner, a particularly simple possibility calibration air quantity determination during burner operation, a particularly fast responding detection of the extinction of the flame while very accurate determination of the air number, and a particularly fast responding and very accurate air number determination.

In addition, the inventors have recognized that the flame temperature can be determined in a simple manner by utilizing the so-called glow-electric effect by a voltage tapped at the ignition electrode of the burner. This ignition electrode is mandatory in each burner in the burner space and after the air-fuel mixture has been ignited once, for the operation of the burner is no longer needed. This results in particular the advantage that the inventive method can be implemented in a cost effective manner, and no structural changes of the combustion chamber are required to provide the Luftzahlregelung the second dependent of the air ratio signal. This also gives rise to the possibility of retrofitting existing burner systems cost-effectively.

According to an advantageous embodiment of the invention, the calibration process comprises setting a burner power to a predetermined power value, detecting the first electrical signal at the predetermined power value and deriving the first air-frequency dependent signal at the predetermined power value, detecting the second electrical signal at the predetermined power value and Deriving the second air-quantity dependent signal at the predetermined power value, and determining a calibration amount in dependence on the first air-mode dependent signal derived at the predetermined power value and the second air-mode dependent second signal derived at the predetermined power value.

Preferably, the determination of the calibration amount is made by taking a ratio of the first air-mode dependent signal derived at the predetermined power value and the second air-mode-dependent second signal derived at the predetermined power value. Thus, the calibration of the determination of the air number can be carried out in a particularly simple manner.

A further advantage results if the first signal dependent on the air number and the second signal dependent on the air number are present simultaneously in determining the controlled variable for burner operation. In this way, a two-channel system according to EN 60730-1 Annex H to Luftzahlregelung can be created.

It is also proposed that the first air-dependent signal and the second air-dependent signal be weighted with a weighting factor when determining the controlled variable for burner operation. Preferably, these weighting factors are time dependent. For example, during a period in which the burner is in stable operation, the second air-dependent dependent signal may be weighted higher. While this has a longer response time than the first dependent on the air ratio signal on changes in the present air ratio, but on the other hand allows a determination of the air ratio with higher accuracy. Conversely, during a period in which the present air ratio varies widely, the first air-gap dependent signal may be weighted higher.

According to one embodiment of the invention, the air ratio is regulated as a function of the controlled variable for burner operation.

Preferably, the second electrical signal is supplied to an amplifier circuit, and the second air-dependent dependent signal derived from an output signal of the amplifier circuit. This measure is useful, inter alia, because the second electrical signal has been found to be very small compared to the first electrical signal.

It is also proposed that the separation of the ignition electrode from the means for generating the ignition voltage in response to a signal derived from the first electrical signal. The separation preferably takes place when the presence of a flame has been detected on the basis of a flame monitoring based on measurement of the ionization current, and the condition of the burner is found to be stable.

According to a second aspect of the invention, a burner is proposed, in particular a gas or oil burner, with an ignition electrode, means for generating an ignition voltage, which are connectable to the ignition electrode, means for connecting the ignition electrode with the means for generating the ignition voltage and for separating the ignition electrode of the means for generating the ignition voltage, an ionization electrode, which is acted upon by an ionization voltage, a measuring device for detecting a first electrical signal at the ionization electrode and a second electrical signal at the ignition electrode, wherein the ignition electrode is connected as a passive electrode means for deriving a first signal dependent on an air number as a function of the first electrical signal and of a second signal dependent on the air number as a function of the second electrical signal, means for determining a control variable for the burner in response to the first air-dependent signal and the second air-speed dependent signal, means for comparing the first air-dependent signal and the second air-speed dependent signal, and means for performing a calibration process for correcting the first of the air-number dependent signal, provided that a difference of the first air-dependent signal and the second air-dependent signal exceeds a threshold value.

Preferably, the means for performing the calibration operation are configured to set a burner power to a predetermined power value, and to determine a calibration amount depending on the first air-mode dependent signal derived at the predetermined power value and the second air-mode-dependent second power derived at the predetermined power value Signal.

The means for carrying out the calibration procedure are preferably designed to determine the calibration quantity by forming a ratio of the first air-frequency-dependent signal derived at the predetermined power value and the second air-frequency-dependent signal derived at the predetermined power value.

According to a further embodiment of the invention, the burner is designed so that the first dependent of the air ratio signal and the second dependent on the air ratio signal in the determination of the controlled variable for burner operation at the same time applied to the means for determining the controlled variable for burner operation.

Preferably, the means for determining the controlled variable are configured such that the first signal dependent on the air number and the second signal dependent on the air number are weighted in each case with a weighting factor when determining the controlled variable for burner operation.

The burner according to the invention may further comprise means for controlling the air ratio as a function of the controlled variable for burner operation.

Preferably, the burner comprises an amplifier circuit to which the second electrical signal is supplied, wherein the second air-dependent dependent signal is derived from an output signal of the amplifier circuit.

According to a further advantageous embodiment of the invention, the means for separating the ignition electrode from the means for generating the ignition voltage separate the ignition electrode from the means for generating the ignition voltage in response to a signal derived from the first electrical signal.

Short description of the drawing

Figur 1

eine schematische Darstellung des erfindungsgemäßen Brenners

Figur 2

ein Blockschaltbild des erfindungsgemäßen Brenners

Figur 3

ein Flussdiagramm zur Illustration des erfindungsgemäßen Verfahrens

Further advantageous embodiments, but to which the invention is not limited in scope, will become apparent from the following description with reference to the drawing. They show in detail:

FIG. 1

a schematic representation of the burner according to the invention

FIG. 2

a block diagram of the burner according to the invention

FIG. 3

a flowchart for illustrating the method according to the invention

Detailed description of the invention

An inventive burner is in FIG. 1 shown schematically. In the following, reference will only be made to gas burners, but it will be readily apparent to those skilled in the art that, and in what form, the present invention is also applicable to oil burners.

According to FIG. 1 the burner has a combustion chamber 101, in which a combustion process can take place while supplying an air-fuel mixture, and into which an ionization electrode 103 and an ignition electrode 102 protrude. The ionization electrode 103 is connected to means for generating an ionization voltage (not shown) and to a measuring device 106 which detects a first electrical signal 115a from the ionization electrode. In the case of the ionization voltage, this is an alternating voltage, and in the case of the first electrical signal 115a, the ionization current flowing from the ionization electrode, which is a direct current, or a voltage corresponding to the ionization current.

The ignition electrode 102 is connected to a device for generating an ignition voltage 104 in such a way that the ignition electrode 102 can be separated from the means for generating an ignition voltage 104. This can be done by separating means 105 connected between the ignition electrode 102 and the device for generating an ignition voltage 104, which can be realized, for example, as a switch arrangement. In this case, the separating means 105 in particular set up so that after a separation of the ignition electrode 102 from the device for generating an ignition voltage 104, the ignition electrode 102 is connected as a passive electrode. By means of the measuring device 106, a second electrical signal 115b can be detected by the ignition electrode 102, for example, a voltage applied to the passively connected ignition electrode 102, which builds up due to the glow-electric effect, and which is dependent on the temperature of the ignition electrode 102, tapped , Since the voltage picked off at the passively connected ignition electrode 102 is very small compared to the voltage corresponding to the ionization current flowing away from the ionization electrode, it is expedient for the second electrical signal 115b to be supplied to an amplifier circuit. This amplifier circuit may be part of the measuring device 106.

The aforementioned glow electric effect (also Richardson effect, Edison effect or Edison Richardson effect, see for example Neil W. Ashcroft, N. David Mermin: Solid State Physics. Saunders College Publishing, New York 1976, pp. 362-364 ) denotes the fact that electrons can overcome the work function from a heated metal electrode above a material-dependent minimum temperature, and can escape from the electrode. The current generated thereby allows to close the temperature of the electrode.

Furthermore, the separating means 105 communicate with the measuring device 106 and can receive signals from the measuring device 106. Thus, in response to a signal derived from the first electrical signal 115a detected by the ionization electrode, which may be used in a manner known in the art to detect a flame in the combustion chamber 101, the ignition electrode 102 may be provided by the means for generating a Ignition voltage 104 are separated by means of the separation means 105. Specifically, according to the invention, the ignition electrode 102 is then disconnected from the ignition voltage generating means 104 when a stable flame has been detected by ionization current measurement.

The measuring device 106 is connected to a device for deriving signals 107 which, depending on the first electrical signal 115a detected by the measuring device 106, is a first signal 116a dependent on the air number and detected by the measuring device 106 second electrical signal 115b, a second air-dependent signal 116b derived. For this purpose, 107 characteristic curves are stored in the device for deriving signals, which allow the number of air to be dissipated, given known burner output, from the electrical signals 115a, 115b detected by the ionization electrode 103 and the ignition electrode 102. Correspondingly, the device for deriving signals 107 for a number of burner outputs can in each case refer to a characteristic which relates the ionization current and the air ratio to each other, and a characteristic curve the flame temperature, or the current flowing out from the ignition electrode 102, and the air ratio in relation to each other. If no characteristic curves are available for an actual burner output, the air ratio is determined in each case by interpolation of the characteristic curves corresponding to the nearest burner output.

The means for deriving signals 107, in turn, is in communication with means for determining a burner operation control amount 108 and a comparator 109 to which the first air number dependent signal 116a and the second air number dependent signal 116b are respectively transmitted.

Depending on the first air quantity dependent signal 116a and the second airspeed dependent signal 116b, the means for determining a controlled variable 108 determines a controlled variable for burner operation. In addition, a power specification of the burner or a fan speed corresponding to the instantaneous power can be included in the determination of the controlled variable. The device for determining a controlled variable 108 is in communication with a burner control 112 and transmits a signal corresponding to the controlled variable for burner operation to the burner control 112, which controls the burner in dependence on this signal / controlled variable. The burner control 112 will be described later on the basis of FIG. 2 be described in more detail.

During burner operation, the relationship between the air ratio and the measured ionization current may change. This can occur, for example, due to aging, wear, contamination or bending of the ionization electrode 103 or due to sooting of the combustion chamber 101. Consequently, the air number indexed by the first air-amount dependent signal 116a may differ from the actual air-fuel ratio in the air-fuel mixture of the combustion chamber 101, thereby deteriorating the quality of the air number control. The above Adverse effects which influence the determination of the air number by means of ionization current measurement, however, hardly have any influence on the air number determination by means of flame temperature measurement. A deviation between the air ratio determined by ionization current measurement and the air ratio determined by means of flame temperature measurement therefore suggests the necessity of a recalibration of the air ratio determination by means of ionization current measurement.

Accordingly, the comparator 109 compares the first air-number dependent signal 116a and the second air-number dependent signal 116b with each other. Unless otherwise explicitly stated below, such a comparison can also be based on the comparison of an air ratio λ_Ion, which is obtained from the first air-dependent signal 116a, and an air ratio λ_Temp, which is obtained from the second air-dependent signal 116b will, refer. If, in the comparison, a deviation is detected which exceeds a predetermined level, a signal is output to a calibration device 110 which is in connection with the comparator 109. In response to this signal, the calibration device 110 performs a calibration process. In order to carry out the calibration process, the calibration device 110 must be able to transmit control commands to the burner control 112, to the measuring device 106 and to the device 107 for deriving signals 107. To ensure this, the calibration device 110 is in communication with the burner controller 112 and can transmit to it parameters for operating parameters, such as the burner output. As it stands, though in FIG. 1 Not explicitly shown, the calibration device 110 also communicates with the measuring device 106 and the means for deriving signals 107 and may be commands, for example for detecting the first and second electrical signal 115a, 115b or for deriving the first and second dependent on the air number signal 116a, 116b, each transmitted to this.

To assess whether there is a predetermined amount of deviation between the first air-number dependent signal 116a and the second air-number dependent signal 116b, the comparator 109 may be configured to perform a number of comparison methods. For example, the difference between the two signals can be compared with a predetermined threshold value. The predetermined threshold can be determined by the actual burner power, or an average of the two air-dependent signals 116a, 116b dependent. It is also conceivable that the comparator 109 compares the second air-gap-dependent signal 116b, which corresponds to a current time, with the first air-number-dependent signal 116a, which corresponds to a time difference Δt before the current time so to take into account the delayed response of Luftzahlbestimmung by flame temperature measurement. As noted above, the comparison methods described here can also be made in the light of from the first depending on the air ratio signal 116a air ratio λ_Ion and recovered from the second dependent on the air ratio signal 116b air ratio λ_Temp.

The means for deriving signals 107, the means for determining a controlled variable 108, the comparator 109 and the calibration means 110 are components of a control circuit 111. This control circuit 111 may be implemented as hardware, software, or a combination of the two.

Burner controller 112 includes a fan controller 113 for controlling the speed of an air blower 232 (see FIG FIG. 2 ), which regulates the amount of air blown into the combustion chamber 101, and thus the burner output, and a valve controller 114 for controlling a gas valve 243 (see FIG FIG. 2 ), which regulates the amount of gas flowing into the combustion chamber 101. The burner control 112 is based on the FIG. 2 be described in more detail.

FIG. 2 shows a block diagram of the burner according to the invention. Elements of the burner containing the in FIG. 1 shown are indicated by like reference numerals. Main components of the burner of the FIG. 2 are the combustion chamber 101, the blower control 113, the valve control 114 and the means for determining a controlled variable 108.

The blower control 113 comprises a blower 232, a speed sensor 233, and a regulator 231. The blower 232 blows combustion air into the combustion chamber 101, or into an antechamber connected thereto, in which the combustion air is premixed with gas as the fuel. The rotational speed sensor 233, which may be designed as a Hall sensor, detects the instantaneous rotational speed of the blower 232. The actual burner output is dependent on the rotational speed of the blower 232. Accordingly, the controller 231 a Power setting 210 can be specified. The controller 231 transmits the power demand 210 to a fan speed specification using, for example, a fan speed-power curve, and controls the fan in accordance with the fan speed specification and the instantaneous fan speed sensed by the speed sensor 233. The controller 231 may be a proportional-integral-derivative (PID) controller, and the control of the fan can be done by means of pulse width modulation (PWM).

The valve controller 114 comprises a gas valve 243, an opening degree / gas valve setting means 242, an opening degree sensor 244, and a regulator 241. Gas is flowed through the gas valve 243 into the combustion chamber 101, or into an antechamber connected thereto, in which the gas flows is premixed with combustion air. The opening degree sensor 244 detects the current opening degree / of the gas valve 243. The controller 241 can be given a manipulated variable, for example a specification for the opening degree I. The controller 241 controls the gas valve 243 by means of the gas valve opening degree setting means 242 in response to the current opening degree I detected by the opening degree sensor 244 and the opening degree I. The controller 241 may be a PID controller and the controller the gas valve 243 can be done by means of PWM. If the control of the gas valve 243 by means of PWM, the opening degree sensor 244 may detect a current of the opening degree / gas valve setting means 242 and transmit it to the controller 241, and the opening degree / gas valve 243 specification may be a default for the modulation current , The gas valve opening degree setting means 242 and the gas valve 243 constitute a modulating valve in this case.

The means for determining a control variable 108 comprises a determination device 282 for determining a relative fan speed N_rel, based on a maximum fan speed N_max, a determination device 284 for determining a combustion air flow rate Q_Air, a determination device 281 for determining a flow rate ratio K, a determination device 283 for determining a gas flow rate Q_Gas, a determining means 285 for determining a relative degree of opening of the gas valve _ I rel with respect to a maximum opening degree I_max, and determining means 286 for determining an opening degree I of the gas valve.

The determining means 282 for determining a relative fan speed I _ rel receives the current blower speed N indicative signal from the fan controller 113, determined on the basis of this signal and the stored maximum fan speed N_max an instantaneous relative fan speed N _ rel, and inputs the thus determined current Relative fan speed N_rel indicating signal to the determination device 284 for determining the combustion air flow rate Q_Airc . The determining means 284 for determining the combustion air flow rate Q_Luft determined using a blower characteristic curve, from the instantaneous relative fan speed N_rel the current air flow rate Q_Luft and enters the thus determined current air flow Q_Luft signal indicating the determining means 283 for determining the gas flow rate Q_Gas from. The blower characteristic curve includes a plurality of pairs of values (N _ rel, Q_Luft), and so sets the relative fan speed N_rel and the air flow rate Q _ air in relation to each other.

The first air-mode dependent signal 116a derived from the detected ionization current and the second air-mode signal 116b derived from the detected flame temperature are supplied to the flow rate determining means 281. On the basis of these signals 116a, 116b, the instantaneous air ratio is determined, for example by averaging the air numbers λ_Ion and λ_Temp determined in accordance with the two signals 116a, 116b . For this purpose, dependent on the air ratio signals 116a, 116b, or the respective dependent on the air speed signals 116a may 116b correspondingly determined air ratios λ _ ion and λ_Temp are each provided with a weighting factor, so that for example, the air ratio determination by ionisation may be weighted higher as the air number determination by means of flame temperature measurement, or vice versa.

As stated above, the determination of the air number by means of ionization current measurement has the advantage that it follows fluctuations of the actual air number with a very short time delay, while the air number determination by means of flame temperature measurement follows the actual development of the air number with some time delay (about one to three seconds), but has the advantage of greater accuracy and reliability. Thus, it has to be advantageous proved to change the weighting factors as a function of changes in the air ratio over time. For example, in periods of only small fluctuations in the air number, the determination of the air number by means of flame temperature measurement can be weighted correspondingly higher, which improves the accuracy and reliability of the air number determination. On the other hand, in periods of large variations in the air ratio, the air number determination by ionization current measurement can be weighted correspondingly higher in order to improve the response of the air ratio control. Conclusions on the magnitude of the fluctuations of the actual air number can be drawn from both the air-number dependent signals 116a, 116b, but especially from the first air-number dependent signal 116a.

By comparing the instantaneous air ratio thus determined with a predetermined (optimal) air ratio, the determination means 281 determines a flow rate K setpoint indicative of the ratio of gas flow rate Q_gas to air flow rate Q_air or a specification of a relative change in the instantaneous flow rate Throughput ratio K, and outputs this specification, or a signal indicative of the default, to the determining means 283 for determining the gas flow rate Q_Gas . The gas flow rate determining means 283 determines a gas flow rate setting Q_Gas based on the current air flow rate Q_Air supplied by the combustion air flow rate Q_Air determining means 284 and the flow rate setting K, or the instantaneous flow ratio relative change specification and outputs a signal indicating this specification to the determining means 285 for determining the relative opening degree I_rel of the gas valve.

Determining the relative opening degree I_rel of the gas valve 285 determines, by using a gas valve characteristic from the gas flow rate Q_Gas or the relative gas velocity instant Q_gas, a specification for a relative opening degree I_rel of the gas valve 243 and outputs such certain default indicative signal to the determining means 286 for determining the opening degree I of the gas valve. The gas valve characteristic includes a plurality of value pairs ( I_rel, Q_Gas ), and thus sets the relative opening degree I_rel of the gas valve 243 and the gas flow rate Q_Gas in relation to each other.

The determining means 286 for determining the degree of opening I of the gas valve is determined, based on the specification for the relative degree of opening I _ rel of the gas valve 243 and the stored maximum opening degree I_max of the gas valve 243 a specification for the opening degree I of the gas valve 243 as a manipulated variable for the gas valve 243 and outputs a signal indicative of the predetermined value to the controller 241 in the gas valve controller 114.

Thus, the means for determining a controlled variable 108 on the basis of the first air-dependent signal 116a and the second air-dependent signal 116b deviations of the instantaneous air number from the predetermined (optimal) air ratio and readjust the air ratio accordingly. If the current air ratio is above the predetermined air ratio, the air ratio can be lowered, for example, by increasing the gas supply. In the other case, if the instantaneous air ratio is below the predetermined air ratio, the air ratio can be increased, for example, by reducing the gas supply.

In the flowchart of the FIG. 3 a method according to the invention for operating the burner, in particular for calibrating the determination of the air number, is shown.

First, (in FIG. 3 not shown) the ignition electrode 102 from the means for generating an ignition voltage 104 by means of the separation means 105 separated. Specifically, the separation of the ignition electrode 102 according to the invention is then carried out by the device for generating the ignition voltage 104 when a stable flame has been detected by ionization current measurement.

Subsequently, in step S301, the first electric signal 115a (from the ionization electrode 103) and the second electric signal 115b (from the ignition electrode 102) are detected. In the following step S302, the first air-signal-dependent signal 116a is derived from the first electrical signal 115a, and the second air-frequency-dependent signal 116b is derived from the second electrical signal 115b. For this purpose, characteristic curves are stored, which allow for each known burner power from the detected at the ionization electrode 103 and the ignition electrode 102 electrical signals 115a, 115b, respectively, the air ratio derive. Correspondingly, one characteristic curve can be used for a number of burner outputs, which sets the ionization current and the air ratio relative to each other, and a characteristic curve which relates the flame temperature, or the current flowing out from the ignition electrode 102, and the air ratio to one another. If no characteristic curves are available for an actual burner output, the air ratio is determined in each case by interpolation of the characteristic curves corresponding to the nearest burner output.

The first air-mode dependent signal 116a and the second air-mode dependent signal 116b, respectively, and the air-data obtained from the two air-mode dependent signals 116a, 116b are compared with each other in step S303, and it is determined whether a predetermined amount Exceeding deviation between the two air-dependent signals 116a, 116b, or the respectively obtained therefrom air figures λ_Ion, λ_Temp, is present. If there is no such deviation, the process proceeds to step S304, otherwise to step S305.

The determination as to whether there is a deviation between the two signals 116a, 116b which depend on the air number and which exceeds the predetermined amount can be effected in various ways. Thus, for example, a comparison of the difference of the two air-dependent signals 116a, 116b, or the air ratios λ_Ion, λ_Temp derived therefrom, can take place with a predetermined threshold value. In this case, the predetermined threshold value of the actual burner power, or an average of the two air-dependent signals 116a, 116b, or the air ratios λ_Ion, λ_Temp, derived therefrom, may be dependent. It is also conceivable that a comparison between the second air-dependent signal 116b (or the air ratio λ_temp derived therefrom) corresponding to a current time and the first air-number-dependent signal 116a (or the air ratio λ_Ion derived therefrom) a time corresponding to a time difference .DELTA.t before the current time is performed, so as to take into account the delayed response of Luftzahlbestimmung by flame temperature measurement.

In step S304, a control amount for burner operation is determined in response to the first air-amount dependent signal 116a and the second air-amount-dependent signal 116b. For this purpose, one based on the two of the Air number dependent signals 116a, 116b determined air ratio compared with a specification for the air ratio, and determines the controlled variable depending on the result of this comparison. The controlled variable can be, for example, a specification for a gas throughput Q_Gas , a specification for a relative opening degree I_rel of the gas valve 243, a specification for an opening degree I of the gas valve 243, or a specification of a control or manipulated variable for the gas valve 243, like a modulation current, act. Also, the controlled variable may be a specification for a relative change of the above variables. In the determination of the controlled variable, in addition to the two air-dependent signals 116a, 116b, the instantaneous burner output or the instantaneous fan speed N, via which the instantaneous burner output can be controlled, are included.

The determination of the instantaneous air ratio on the basis of the two air-frequency-dependent signals 116a, 116b can be done by averaging the two air-frequency-dependent signals 116a, 116b. In this case, the first signal 116a dependent on the air number and the second signal 116b dependent on the air number, or the air numbers λ_Ion, λ_Temp derived therefrom, can be weighted differently. For example, the instantaneous air ratio can be determined as follows. From the first air-mode dependent signal 116a, the air ratio determined by ionization current measurement is λ _Ion, and from the second air- mode dependent signal 116b, the air ratio λ_Temp determined by flame temperature measurement is extracted. The instantaneous air ratio λ can then be determined by means of the equation λ = (A · λ_Ion + B · λ_Temp) / (A + B) . It has proven advantageous to make the weighting of the signals dependent on the air number signals 116a, 116b as a function of changes in the air ratio over time. In periods of only small fluctuations of the air number, the determination of the air value by means of flame temperature measurement can be weighted correspondingly higher ( B> A ), which improves the accuracy and reliability of the air number determination. On the other hand, in periods of large variations of the air ratio, the air number determination by ionization current measurement can be weighted correspondingly higher ( A> B ) to improve the response of the air ratio control. Conclusions on the magnitude of the fluctuations of the actual air number can be drawn from both the air-number dependent signals 116a, 116b, but especially from the first air-number dependent signal 116a. In extreme cases, one of the two weighting factors A , B can be set to zero, for example in emergency mode. After determining the controlled variable for burner operation, the inventive method returns to its starting point and can be run again.

In steps S305 to S309, a calibration process for calibrating the air number determination by ionization current measurement is performed. In step S305, a predetermined, predetermined burner power is approached for this purpose. The choice of this predetermined burner output can be based on which burner outputs have characteristic curves which relate the air ratio and the detected ionization current, or the air ratio and the detected flame temperature, to one another. Furthermore, the predetermined burner power can be selected so that the burner is in this burner power in the most stable operation and the actual air ratio is subjected to the lowest possible fluctuations. Another criterion for the selection of the predetermined burner output may be that the predetermined burner output should correspond to a commonly present, average burner output.

In steps S306 and S307, in correspondence to steps S301 and S302, at the present predetermined burner power, the first and second electric signals 115a, 115b are detected, and from this, the first and second air-number dependent signals 116a, 116b are derived.

In step S308, a calibration amount is determined from the air-number dependent signals derived in step S307. This can be achieved by forming a quotient of the first air-quantity-dependent signal 116a and the second air-speed-dependent signal 116b, or by forming a quotient of the air ratio λ_Ion obtained from the first air-dependent signal 116a and the second from the air number dependent signal 116b obtained air ratio λ_Temp happen. In other words, a calibration factor can be obtained by quotient formation of the air ratio λ_Ion determined by ionization current measurement and the air ratio λ_Temp determined by means of flame temperature measurement, the air ratio λ_Temp determined by means of flame temperature measurement being assumed to be the actual air ratio . The thus determined calibration variable can then be used to adjust the derivative of the first air-dependent signal 116a from the first electrical signal 115a accordingly, that is, for example, by dividing the detected based on a stored characteristic Air ratio λ _ Ion by the calibration factor. In this case, the calibration device 110 sends a signal indicating the calibration size to the device 107 for deriving signals 107, in which the currently valid calibration variable is stored. Deviating from this, the calibration variable can also be used to correspondingly adapt the determination of the controlled variable for the burner operation, that is to say by dividing the air ratio λ_Ion determined by ionization current measurement by the calibration factor before the step of the averaging described above in step S304. In this case, the calibration quantity is also to be taken into account in the comparison of the two air-frequency-dependent signals 116a, 116b in a corresponding manner. Correspondingly, the calibration device 110 sends a signal indicating the calibration variable to the device for determining a controlled variable 108 and the comparator 109, in which the currently valid calibration variable is stored in each case.

The calibration process ends with step S309, in which the original burner power, which is determined before the deviation between the first air-fuel-dependent signal 116a and the second air-signal-dependent signal 116b is determined in step S303, ends.

After completion of the calibration process, a new comparison of the first air-quantity-dependent signal 116a with the second air-speed-dependent signal 116b, or a comparison of the air data obtained from these signals, can take place in step S310. For this purpose (in FIG. 3 not shown), the first and second electrical signals 115a, 115b are first detected according to steps S301 and S302, and the first and second air-number dependent signals 116a, 116b are derived therefrom. The derived signals are then compared again, in step S303 (in FIG. 3 Not shown). It should be noted that the calibration variable obtained during the calibration process either in the derivation of the first air-dependent signal 116a from the first electrical signal 115a, or in the comparison of the air-number dependent signals 116a, 116b, or the air ratios obtained therefrom λ_Ion , λ_Temp, corresponding to input finds.

If, in step S310, that is to say after passing through the calibration process of steps S305 to S308, there is also a deviation between the air ratio dependent signals 116a, 116b, or the airborne numbers obtained therefrom, various steps can be performed. For example, a calibration of the air number measurement by means of ionization current measurement can take place by starting the air range λ = 1 , as in step S311 of FIG FIG. 3 shown. Alternatively, since the persistent deviation may indicate a defect of the ionization electrode, an alarm signal may be issued and / or an emergency stop of the burner or start of an emergency operation may be performed. In this emergency mode, the air ratio may still be controlled, albeit with limitations, based on the flame temperature measurement. Otherwise, if no unacceptable deviation has been detected in step S310, the inventive method returns to its starting point and can be run again.

Claims (16)

1. A method for controlling an air ratio of a burner, in particular a gas or oil burner, comprising
   an ignition electrode (102),
   means for generating an ignition voltage (104) connectable to said ignition electrode (102), and
   an ionization electrode (103) which can be supplied with an ionization voltage,
   characterized in that said method comprises:

   disconnecting said ignition electrode (102) from said means for generating said ignition voltage (104),

   detecting a first electrical signal (115a) at said ionization electrode (103), and deriving a first signal dependent on said air ratio based on said first electrical signal (115a),

   detecting a second electrical signal (115b) at said ignition electrode (102), and deriving a second signal dependent on said air ratio based on said second electrical signal (115b),

   determining a control variable for the burner operation based on said first signal (116a) dependent on said air ratio and said second signal (116b) dependent on said air ratio,

   comparing said first signal (116a) dependent on said air ratio and said second signal (116b) dependent on said air ratio, and

   if a difference between said first signal (116a) dependent on said air ratio and said second signal (116b) dependent on said air ratio exceeds a threshold value, performing a calibration process in order to correct said first signal (116a) dependent on said air ratio.
2. The method according to claim 1, wherein said calibration process comprises:

   setting a burner power to a predetermined power value,

   detecting said first electrical signal (115a) at said predetermined power value and deriving said first signal (116a) dependent on said air ratio at said predetermined power value,

   detecting said second electrical signal (115b) at said predetermined power value and deriving said second signal (116b) dependent on said air ratio at said predetermined power value, and

   determining a calibration variable based on said first signal (116a) dependent on said air ratio derived at said predetermined power value and said second signal (116b) dependent on said air ratio derived at said predetermined power value.
3. The method according to claim 2, wherein determining said calibration variable is performed by forming a ratio of said first signal (116a) dependent on said air ratio derived at said predetermined power value and said second signal (116b) dependent on said air ratio derived at said predetermined power value.
4. The method according to one of the preceding claims, wherein said first signal (116a) dependent on said air ratio and said second signal (116b) dependent on said air ratio are simultaneously available for determining said control variable for the burner operation.
5. The method according to one of the preceding claims, wherein said first signal (116a) dependent on said air ratio and said second signal (116b) dependent on said air ratio are respectively weighted with a weighting factor for determining said control variable for the burner operation.
6. The method according to one of the preceding claims, wherein said air ratio is controlled based on said control variable for the burner operation.
7. The method according to one of the preceding claims, wherein said second electrical signal (115b) is supplied to an amplifier circuit, and said second signal (116b) dependent on said air ratio is derived from an output signal of said amplifier circuit.
8. The method according to one of the preceding claims, wherein disconnecting said ignition electrode (102) from said means for generating said ignition voltage (104) is carried out based on a signal derived from said first electrical signal (115a).
9. A burner, in particular a gas or oil burner, comprising an ignition electrode (102),
   means for generating an ignition voltage (104) connectable to said ignition electrode (102), and
   an ionization electrode (103) which can be supplied with an ionization voltage,
   characterized by

   a switch arrangement (105) for connecting said ignition electrode (102) to said means for generating said ignition voltage (104) and for disconnecting said ignition electrode (102) from said means for generating said ignition voltage (104),

   measuring means (106) for detecting a first electrical signal (115a) at said ionization electrode (103) and a second electrical signal (115b) at said ignition electrode (102), wherein said ignition electrode (102) is configured as a passive electrode,

   a first component of a control circuit (107) for deriving a first signal (116a) dependent on an air ratio based on said first electrical signal (115a) and a second signal (116b) dependent on said air ratio based on said second electrical signal (115b),

   a second component of a control circuit (108) for determining a control variable for the burner operation based on said first signal (116a) dependent on said air ratio and said second signal (116b) dependent on said air ratio,

   a comparator (109) for comparing said first signal (116a) dependent on said air ratio and said second signal (116b) dependent on said air ratio, and

   calibration means (110) for performing a calibration process in order to correct said first signal (116a) dependent on said air ratio, if a difference between said first signal (116a) dependent on said air ratio and said second signal (116b) dependent on said air ratio exceeds a threshold value.
10. The burner according to claim 9, wherein said calibration means (110) for performing said calibration process are configured to:

    setting a burner power to a predetermined power value, and

    determining a calibration variable based on said first signal (116a) dependent on said air ratio derived at said predetermined power value and said second signal (116b) dependent on said air ratio derived at said predetermined power value.
11. The burner according to claim 10, wherein determining said calibration variable is performed by forming a ratio of said first signal (116a) dependent on said air ratio derived at said predetermined power value and said second signal (116b) dependent on said air ratio derived at said predetermined power value.
12. The burner according to one of claims 9 to 11, wherein said first signal (116a) dependent on said air ratio and said second signal (116b) dependent on said air ratio are simultaneously available at said second component of a control circuit (108) for determining said control variable for the burner operation.
13. The burner according to one of claims 9 to 12, wherein said first signal (116a) dependent on said air ratio and said second signal (116b) dependent on said air ratio are respectively weighted with a weighting factor for determining said control variable for the burner operation.
14. The burner according to one of claims 9 to 13, further comprising a burner controller (112) for controlling said air ratio based on said control variable for the burner operation.
15. The burner according to one of claims 9 to 14, wherein said second electrical signal (115b) is supplied to an amplifier circuit, and said second signal (116b) dependent on said air ratio is derived from an output signal of said amplifier circuit.
16. The burner according to one of claims 9 to 15, wherein said switch arrangement (105) for disconnecting said ignition electrode (102) from said means for generating said ignition voltage (104) disconnects said ignition electrode (102) from said means for generating said ignition voltage (104) based on a signal derived from said first electrical signal (115a).

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