Method, apparatus, and computer program product for correcting a fuel gas to air ratio

Abstract

The invention relates to a method for recalibrating calibration data of a first measuring system (S1) for measuring a first ionization signal in the flame region (2) of a heater (1) operated with combustion air and gas, wherein the first measuring system (S1) measures a first ionization signal (I1) which is derived from a first ion current flowing from an ionization electrode (8) to a counter electrode (9) through the flame region (2) and from which a combustion air to gas ratio (λ) is determined and adjusted during combustion in the heater (1) using calibration data, the first measuring system (S1) being recalibrated at least according to a predeterminable standard or at predeterminable time intervals, and the recalibration is carried out using an ignition electrode (7) for ignition in the heater (1), which is operated to generate a second ionization signal (I2). The invention also relates to a device, in particular for carrying out the aforementioned method.

Description

Technical Field

[0001] The present invention relates to the field of regulating the gas-air mixture for combustion processes in heaters, in particular in combustion chambers in heaters for heating water or buildings. To measure the combustion quality, which depends primarily on the ratio of air to gas during combustion (the lambda value, also known as the air-fuel ratio), ionization measurements are performed in the flame region, particularly in many heaters. Such measurements must enable stable regulation over long periods of time, which necessitates detecting slow changes in the measuring system and enabling recalibration. Background Art

[0002] According to the prior art, ionization electrodes determine the actual value of ionization in the flame region, which is proportional to the currently existing lambda value. Therefore, the currently existing lambda value can be derived from the ionization measurement. Therefore, the lambda value can be measured through calibration and adjusted to the target value via a control loop. Here, an AC voltage is applied to the ionization electrodes. The ionized flame region, when a flame is present, has a rectifying effect, causing the ionization signal to flow primarily only during the half-wave of the AC current. The current and the resulting proportional voltage signal (hereinafter referred to as the ionization signal) are measured and, if necessary, digitized in an analog-to-digital converter before being further processed as the ionization signal. The air and / or gas supply is then modified using appropriate controls until the desired lambda target value is achieved. Typically, a lambda value > 1 (1 corresponds to the stoichiometric ratio), for example, lambda = 1.3, is sought to ensure sufficient air for clean combustion with essentially no carbon monoxide production. However, lambda must be kept low to ensure stable combustion. This regulation can be performed, in particular, via a valve for the gas supply and / or a blower for the ambient air supply.

[0003] For example, EP 0 770 824 B1 and EP 2 466 204 B1 disclose such a heater, the basic structure of a measuring system for ionization measurements, and its use for regulation. They also describe how the regulation accuracy can vary over time due to various influences, particularly those affecting the state or shape of the ionization electrodes. Various methods for recalibration are proposed, but they all involve relatively high costs and / or may have the disadvantage that, during recalibration, the heater must temporarily be operated at a lambda value of 1 or lower, which can also lead to temporary, undesirable formation of carbon monoxide. Furthermore, very high flame temperatures occur in this region, which can additionally damage the ionization electrodes during calibration.

[0004] EP 2 014 985 B1 discloses a control concept which allows operation and adjustment without causing the combustion to approach the lambda value 1, so that even during adjustment, almost no carbon monoxide is produced. However, it is not always possible to maintain the optimal lambda value. Summary of the Invention

[0005] The object of the present invention is to provide a method for quickly recalibrating an existing control concept or correcting a calibration curve on which it is based, which method can be implemented with little additional equipment expenditure.

[0006] The methods, devices, and computer program products according to the independent claims are used to achieve the above-mentioned objects. Advantageous embodiments and improvements of the invention are given in the corresponding dependent claims. The description, in particular with reference to the drawings, explains the invention and specifies further exemplary embodiments.

[0007] The method according to the invention is for recalibrating calibration data of a first measuring system for measuring a first ionization signal in the flame region of a heater operated with combustion air and gas. The first measuring system measures the ionization signal, which is derived from a first ion current flowing from an ionization electrode to a counter electrode through the flame region, and uses the calibration data to determine and regulate the combustion air to gas ratio (λ) during combustion in the heater. The first measuring system is recalibrated at least according to predefined criteria or at predefined time intervals, and the recalibration is performed by an ignition electrode used for ignition in the heater, which is operated to generate a second ionization signal. In some heaters, the second ionization signal is already measured to determine and monitor the presence of a flame.

[0008] Independent of the known function as a flame monitor, this second ionization current is also used for other purposes during operation, in particular for recalibrating the calibration data of the original control concept. This allows the first ionization signal to be corrected at any time by comparison with the second ionization signal, optionally supplemented with (already stored) empirical values for both ionization signals and their changes over time.

[0009] In a preferred embodiment, the ignition electrode is operated in a second measurement system to measure a second ionization signal. This allows not only changes in the ionization electrode itself but also changes in its electronics, particularly long-term drift, to be detected and corrected. This second measurement system, which is also commonly used for flame monitoring, operates according to the following principle.

[0010] An AC voltage without a DC voltage component is applied from a voltage source with a high output impedance between the ignition electrode and ground. Due to the rectification effect of the flame plasma during flame combustion, ionization current flows toward ground during each positive half-wave of the AC voltage. The voltage amplitude of each positive half-wave decreases due to the high output impedance of the voltage source, while the negative half-wave remains unchanged. As a result, the AC voltage exhibits a negative DC voltage component. The amplitude of the negative DC voltage component is converted as an average value using an amplifier circuit. Based on its characteristic curve, this voltage signal can be used as a second ionization signal for the purposes described herein when the gas supply remains unchanged and the air supply increases. Typically, the signal is digitized using an analog-to-digital converter (e.g., with a value between 0 and 1023) so that it can be further processed in a microprocessor.

[0011] The characteristic curve of the signal is derived from a combination of various effects. On the one hand, when combustion occurs with a stoichiometric ratio of gas to combustion air, the ionization of the flame region is most intense. On the other hand, as the gas velocity increases (greater gas volume per unit time), the flame moves away from the gas outlet opening (which forms an electronic ground in the system), reducing the ion current. The temperature of the flame and ignition electrode also sometimes contributes to this rectifying effect. This results in a curve with a highly reproducible minimum that lies near the typical lambda value for continuous operation.

[0012] In a preferred embodiment, the combustion in the heater enters at least one constant combustion state, which can be predetermined by a first measurement system. While maintaining or selectively changing this state, a second ionization signal from a second measurement system is measured. This results in two comparable measured values for the same state. If the second ionization signal is deemed more reliable, the measured value calculated from the first ionization signal can provide a corresponding correction for future measurements. However, at least any deviation between the two measured values can be determined, and measures can be derived from this deviation.

[0013] It is particularly advantageous if the first measuring system successively brings the combustion into several different constant states and, in each of these states, switches on the second measuring system, measures the second ionization signal in this state and / or when this state changes, and determines any deviations from the first ionization signal. This allows the relationship between the air-fuel ratio and the first ionization signal, i.e., the calibration curve of the first measuring system, to be checked with appropriate accuracy depending on the number and spacing of the states (so-called support points) and, if necessary, fully corrected.

[0014] In a preferred embodiment, the different constant states are different load levels of the heater, which are determined by different constant speeds of the fan and / or different constant quantities of gas supplied per unit time by means of different constant settings of the gas valve.

[0015] In this way, the entire characteristic field of the first measuring system can be recalibrated in conjunction with different load levels. Calibration data for the relationship between the ionization signal and the ratio of combustion air to gas under different load conditions are stored in the first and second measuring systems, and during each recalibration, a comparison is made between the measured values determined by the two measuring systems. If there are deviations, the first measuring system is recalibrated using the data of the second measuring system.

[0016] Furthermore, a device is proposed, in particular a device configured to carry out the method described herein, comprising a heater with an air supply and a gas supply, the air supply and the gas supply being regulated by a control unit, and a first measuring system comprising an ionization electrode, a counter-electrode, a first alternating voltage source, and first electronic evaluation devices for determining a first ionization signal, which can be provided to the control unit, wherein a second measuring system is present for measuring a second ionization signal, which can be generated between an ignition electrode used for ignition and a counter-electrode from the second measuring system, and the first and second systems are each configured for determining a lambda value.

[0017] The second measuring system is preferably constructed independently of the first measuring system, ie, has no common parts therewith except the counter-electrode. This also allows, at least within certain limits, errors in the electronics of the first measuring system to be detected and corrected.

[0018] However, it is particularly preferred if the second measuring system is designed differently from the first, i.e., has as few or no components as possible in common with it. By using different electronic components and / or a different structure and / or a different measuring principle, even systematic defects (e.g., slow drift of amplifiers, resistors, or other components) can be detected and compensated.

[0019] In a preferred embodiment, a comparator is present, to which the measured values of the first and second measuring systems can be fed, and when a deviation between the two measured values is detected, the calibration data of the first measuring system are readjusted using the correction unit.

[0020] The invention also relates to a computer program product comprising instructions for causing the described apparatus to perform the method proposed herein.Modern heaters usually comprise an electronic controller containing at least one programmable microprocessor controllable by such a computer program product. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Illustrative embodiments of the present invention (but not limited thereto) and the working principle of the method according to the present invention are described in detail herein with reference to the accompanying drawings. In which:

[0022] Figure 1 Schematically illustrates a device according to the present invention;

[0023] Figure 2 A graph (normal and drifting) is shown for explaining how the first ionization signal changes with the blower speed at a specific air-fuel ratio (λ);

[0024] Figure 3 shows a schematic circuit for generating an ionization signal in the second measurement system S2;

[0025] Figure 4 A diagram illustrating a measurement process using the second measurement system S2 is shown;

[0026] Figure 5 The diagram shows a calibration curve for the calibration of the first measuring system S1 . DETAILED DESCRIPTION

[0027] Figure 1An exemplary embodiment of the proposed device is schematically illustrated. During operation, a flame region 2 forms in a heater 1 that burns gas with air. Air enters the combustion chamber 1 via an air supply 3 and a blower 5. Gas is mixed with the air via a gas inlet 4 and a gas valve 6. An ignition electrode 7 ignites the mixture at the start of the combustion process and subsequently serves, for example, as a component of a flame monitoring system. The first ionization signal in the flame region 2 is measured by an ionization electrode 8. For this purpose, a first measuring system S1 is used, which applies an AC voltage from a first AC voltage source to the ionization electrode 8. First electronic processing units 13 measure the generated ionization signal and convert it into a lambda value, or the air-fuel mixture ratio, based on stored calibration data (control curves). Using this value as the actual value, a control unit 17 adjusts the blower 5 and / or the gas valve 6 to achieve the desired target value for lambda. To ensure long-term reliable operation, the control curve must be adjusted at regular intervals, which can be selected based on, for example, the operating time of the heater 1 and / or other parameters. This is due, in part, to the fact that the ionization electrode 8 can change during operation, for example due to thermal deflection and / or the growth of an oxide layer on the surface. The electronics may also change. Unfortunately, automatic and absolute calibration is difficult to perform using existing equipment. Therefore, the present invention utilizes the ignition electrode 7 to generate a second ionization signal as a novel approach for recalibration. To this end, the second measuring system S2 is put into operation via a conversion unit 10, which connects a second AC voltage source 12 to the ignition electrode 7 instead of the ignition electronics (as long as this is no longer used for flame monitoring). The second ionization signal is measured and evaluated in the second processing electronics 14 and also provides the actual value of lambda. Ideally, the two actual values provided by measuring systems S1 and S2 are identical or in a ratio that has not changed since the last calibration, so that the control curve in the first measuring system S1 remains unchanged. However, if a deviation or ratio between the two measured values is detected in the comparator 15, a correction factor can be determined by the correction unit 16. This correction unit can correct the control curve so that the control unit 17 can use the corrected control curve for further adjustments using the first measuring system. It is assumed that the second measuring system S2 measures more reliably than the first measuring system S1, and therefore S1 is corrected towards the actual value of S2. Using empirical values and / or theoretical considerations, this correction value can be weakened by a damping value if the entire calculated correction is not applied or not applied immediately.

[0028] Figure 2The graph shows how the first ionization signal (and the similarly formed second ionization signal) depends on the rotational speed of the fan 5. This rotational speed typically ranges from 1,000 to 10,000 revolutions per minute (rpm). The determined rotational speeds can be used as support points i1, i2, ..., i10 for checking and recalibration. The upper curve A shows the dependence for a new ionization electrode 8, while the lower curve B shows the dependence for a used and slightly aged (e.g., oxidized or warped) ionization electrode 8. If the ionization signal I1 is converted to the lambda value shown in calibration curve A, an incorrect actual value is obtained if the ionization electrode 8 is aged, which can lead to suboptimal regulation.

[0029] The following describes a typical process for recalibrating the control curve in the first measuring system according to the present invention by way of example. However, the present invention is not limited to this specific process, as there are numerous possible options for recalibrating using the ignition electrode 7. In the exemplary embodiment selected here, the heater is initially in normal operation with a specific gas supply and associated speed of the fan 5. The ionization signal I1 is then regulated by means of the first measuring system S1 to a value predetermined as a setpoint value, for example, 100 µA (microamperes), corresponding to this state, by adjusting the fan speed and / or fuel supply. If calibration data (characteristic field, control curve) is available, this type of regulation ensures that the desired lambda value is maintained over a wide load range.

[0030] However, recalibration can be triggered if a certain number of heater operating times has been exceeded, a restart is performed, or for other reasons. In the exemplary embodiment described here, a single control curve is corrected based on so-called support points i1, i2, ..., i10 on the x-axis (blower speed), so that the values i1, i2, ..., i10 between the support points can be obtained by interpolation as needed. For a speed range between 1000 and 10,000 rpm (revolutions per minute), for example, up to 10 support points can be used within a suitable time interval to achieve sufficiently accurate recalibration, but more or fewer support points can of course be used. For each support point, for example, at a speed of 3000 rpm, recalibration is performed at a suitable time, such as when a load of a suitable size is currently in use or can be removed. If the recalibration conditions are met, the system switches from normal operation (measuring system S1 is used to set a constant lambda value, for example, lambda = 1.3, and this value is precisely adjusted to the actual value for the relevant speed according to the valid calibration curve) to the recalibration process. In this case, the gas supply remains constant during the entire readjustment period, and the blower speed is then also kept constant. The first measuring system S1 is then switched to the second measuring system S2. At the start of the readjustment, the second measuring system determines the second ionization signal I2, which is determined with the aid of the ignition electrode 7. If, due to changes in the measuring system S1, the desired lambda value is no longer achieved precisely, this can be detected and corrected with the aid of the measuring system S2. For this purpose, the gas supply remains constant, while the blower speed is reduced in a defined manner until a value below the desired lambda value is reliably reached, which is always significantly above the stoichiometric ratio of air to gas, so that in the process virtually no carbon monoxide is produced and the flame temperature does not increase excessively (see Figure 4 Based on the above-mentioned λ value, the speed of the blower 5 is increased until the second ionization signal is detected to be away from the burner 9 due to a large increase (see Figure 4 From this point, the speed of the blower 5 is reduced again, wherein the ionization signal is observed in order to determine the exact position of the (absolute) minimum of the ionization signal and to adjust the setpoint value to this minimum or in its vicinity (see Figure 4 At this point, a check is then performed to determine whether the actually existing rotational speed of the blower 5 corresponds to the expected rotational speed of, for example, approximately 6000 rpm.

[0031] In terms of control technology, it is easy to use a value in the vicinity of the minimum in the side wall as a setpoint value (here in particular in the side wall towards the oil-rich mixture, that is, at Figure 4between points "1" and "3"), because then, when the actual value changes (positive or negative), it is clear in which direction the correction must be made. In each case, a desired lambda value of around 1.4 can be set without producing carbon monoxide in the process.

[0032] The original speed resulting from the control can now be compared with the speed thus found, and corrections can be made at each point (support point) on the calibration curve. This process can be repeated at the appropriate time in other load states (support points), so that the calibration can be corrected accordingly there as well.

[0033] To determine the required correction, consider the I2 / I1 ratio, for example. For example, increase the blower speed (increasing the air volume and reducing the risk of unintentional carbon monoxide emissions) until the I2 / I1 ratio increases by 5 percentage points. Then, determine the blower speed at which this increase occurs. The starting speed (here: 3000 rpm) and the final speed (here: 4000 rpm) are converted into a ratio (resulting in 0.75) and compared with a previously saved reference value (e.g., 0.7). This correction factor (here: 0.7 / 0.75 = 0.93) relative to the newly measured reference value of the ratio is used to correct the original value of the calibration curve at this support point (100 µA). This results in the new, recalibrated value of the calibration curve (93.3 µA). If you do not want to completely recalibrate the calibration curve immediately, you can set a so-called damping factor between 0 and 1. In this way, the influence of each recalibration on the calibration curve is correspondingly smaller, which means that the adverse effects of any errors during the recalibration are also mitigated, and the correct new calibration curve is only obtained during the course of several recalibrations.

[0034] Figure 3 The schematic diagram shows a circuit as it can be used in a measuring system S2. A second AC voltage source 12 with a high output resistor 18 initially provides an AC voltage without a DC voltage component, which is applied to the ignition electrode 7 and the counter electrode 9 (ground). When a flame appears between the ignition electrode and the counter electrode (shown here as an alternative circuit diagram), the voltage drops only in half-waves due to the rectifying effect of the flame (shown as a diode in the alternative circuit diagram). As a result, an AC voltage with a negative DC voltage component is applied to the input of the second electronic processing unit 14 (amplifier and converter). This AC voltage is converted into a second ionization signal in the processing electronics 14 and converted in an analog-to-digital converter 20, which can then be processed further.

[0035] Figure 4The following diagram qualitatively illustrates what occurs during a recalibration process using the second measuring system S2. In the diagram, the second ionization signal I2 (in digitized form, e.g., a number between 0 and 1023) is plotted on the Y-axis against the blower speed on the X-axis, with constant gas flow. The resulting characteristic diagram shows an almost constant initial range, a decrease to a minimum (point "3"), and a subsequent increase. Experience has shown that the minimum is approximately at the typically desired lambda value of between 1.3 and 1.4, while the constant range extends further to the left, e.g., at point "1," away from lambda = 1. During the rising section, e.g., at point "2," the flame, which could become unstable with increasing air flow, begins to dissipate. However, between points "1" and "2," the air flow can be varied without generating carbon monoxide or causing instabilities, in order to find the minimum at point "3" and use it for recalibration. Instead of the blower speed, the lambda value can be used as the unit on the X-axis based on the relationships described.

[0036] Figure 5 The result of a recalibration of the support point at a blower speed of 3000 rpm is shown. Recalibration at this support point means that the desired constant lambda value of 1.3 can no longer be achieved with an ionization signal of 100 µA, whereas this lambda value is achieved with an ionization signal of 93.3 µA. After recalibration, this value is the new setpoint at this point, and the values around the blower speed are adjusted accordingly. When recalibrating at several support points, a new calibration curve is generated for the desired lambda value, which takes into account the Figure 2 Drift of measuring system S1 is shown.

[0037] The present invention makes it possible to reliably recalibrate existing conventional control systems simply by using additional electronics, without having to modify the heater itself. The ignition electrode is used to generate a second ionization signal in the flame region, which can be used to correct any long-term drift of the existing control system at predetermined intervals. The second ionization signal is already used in many applications for flame monitoring, so only a few additional components are required to recalibrate conventional control systems, in particular to correct for long-term drift.

[0038] 1 heater

[0039] 2 Flame Area

[0040] 3 Air delivery unit

[0041] 4 Gas Transportation Department

[0042] 5 Blower

[0043] 6 Gas valve

[0044] 7 Ignition electrode

[0045] 8 Ionization electrode

[0046] 9 Pairing electrodes

[0047] 10 Conversion Unit

[0048] 11. First AC voltage source

[0049] 12 Second AC voltage source

[0050] 13 First computing electronic device

[0051] 14 Second computing electronic device

[0052] 15 Comparator

[0053] 16 calibration units

[0054] 17 Adjustment Unit

[0055] 18 Output resistance

[0056] 19 Flame Alternative Circuit Diagram

[0057] 20 Analog-to-digital converters

[0058] S1 First measuring system

[0059] S2 Second measurement system

[0060] I1 first ionization signal

[0061] I2 Second ionization signal

[0062] A. Calibration curve for a new ionization electrode

[0063] B Calibration curve of used ionization electrodes

Claims

1. A method for recalibrating calibration data of a first measuring system (S1) for measuring a first ionization signal in the flame region (2) of a heater (1) operated with combustion air and gas, characterized in that The first measuring system (S1) measures a first ionization signal (I1), which is derived from a first ionization current flowing from an ionization electrode (8) to a counter electrode (9) through a flame region (2), and from which a ratio (λ) of combustion air to gas is determined and adjusted with the aid of calibration data when combustion occurs in the heater (1). The first measuring system (S1) is readjusted at least according to a predeterminable standard or at predeterminable time intervals, and the readjustment is carried out with the aid of an ignition electrode (7) for ignition in the heater (1), which is operated to generate a second Ionization signal (I2); wherein the ignition electrode (7) is operated in the second measuring system (S2) for measuring the second ionization signal (I2); in the first measuring system (S1) and the second measuring system (S2), calibration data of the relationship between the ionization signal (I1 or I2) and the ratio of combustion air to gas under different load conditions are stored, and during each recalibration, a comparison is made between the measured values determined by the two measuring systems (S1, S2), and if there is a deviation, the first measuring system (S1) is recalibrated with the data of the second measuring system (S2).

2. The method according to claim 1, characterized in that The combustion in the heater (1) is brought into at least one constant combustion state which can be predetermined by a first measuring system (S1), and a second ionization signal (I2) of a second measuring system (S2) is then measured while maintaining or changing said state in a targeted manner.

3. The method according to claim 1, characterized in that The combustion is brought into a plurality of different constant states successively by means of a first measuring system (S1), and in each of the states a second ionization signal (I2) measures the state at least in the state or when the state changes.

4. The method according to claim 1, wherein The different constant states are different load levels of the heater (1), which are determined by different constant settings of the gas valve (6) at least by different constant speeds of the fan (5) and / or different constant quantities of gas supplied per unit time.

5. The method according to claim 1, wherein After a constant state has been established, the ratio of combustion air to gas (λ) is first reduced by a predetermined value and then continuously or stepwise increased in order to curve the second ionization signal (I2) as a function of the λ value and to identify predeterminable characteristic points of the curve.

6. A device with a heater (1), the heater having an air supply (3) and a gas supply (4), the air supply and the gas supply being regulated by a regulating unit (17), the device also having a first measuring system (S1), the first measuring system comprising an ionization electrode (8), a counter electrode (9), a first alternating voltage source (11) and first electronic computing means (13) for determining a first ionization signal (I1), the first ionization signal being capable of being supplied to the regulating unit (17), wherein: A second measuring system (S2) is provided for measuring a second ionization signal (I2), which can be generated between an ignition electrode (7) for ignition and a counter electrode (9) of the second measuring system (S2), and the first measuring system (S1) and the second measuring system (S2) are respectively configured to determine the ratio of combustion air to gas; the device is also provided with a comparator (15) capable of supplying measurement values of the first measuring system (S1) and the second measuring system (S2) related to the predetermined ratio of combustion air to gas to the comparator, and a correction unit (16) is provided for recalibrating the calibration data of the first measuring system (S1) when a deviation between the two measurement values is found.

7. The device according to claim 6, wherein The second measuring system (S2) is designed independently of the first measuring system (S1), ie, apart from the counter electrode (9), it has no components in common with the first measuring system.

8. The device according to claim 6 or 7, wherein: The second measuring system ( S2 ) is designed differently from the first measuring system ( S1 ), ie, has as few or no common components with the first measuring system and / or operates according to a different principle.

9. A computer program product comprising instructions for causing an apparatus according to any one of claims 6 to 8 to perform a method according to any one of claims 1 to 5.

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