Method and apparatus for adjusting sensitivity of a detector for monitoring a flame in a heater

Abstract

The invention relates to a method and a device for adjusting the sensitivity of a detector (11) for monitoring a flame in a burner (1), wherein an alternating voltage source (12) generates individual alternating voltage pulses (13) of an alternating voltage frequency (F1) and of a predefinable length (L) between an ignition electrode (7) and a counter electrode (9) in a flame region (2), wherein a time interval (T) is between the beginnings of successive alternating voltage pulses (13), and wherein the length (L) and / or the interval (T) of the individual alternating voltage pulses (13) is adjustable. The device in a burner (1) with an air supply (3) and a combustion gas supply (4) comprises an ignition electrode (7), a counter electrode (9), an alternating voltage source (12) and a computing electronics (14) for determining an ionization signal in the flame region (2). The alternating voltage source (12) is configured to generate individual alternating voltage pulses (13) of an alternating voltage frequency (F1), in particular greater than 1 kHz, and of a predefinable length (L) with a time interval (T), wherein the length (L) and / or the time interval (T) of the individual alternating voltage pulses (13) is adjustable. By adjusting the effective amplitude of the alternating voltage source (12) in this way, the sensitivity of the detector (11) can be adjusted.

Description

Technical Field

[0001] This invention relates to the field of regulating or monitoring the combustion process in a heater, and more particularly to a burner for providing hot water or heating in buildings. Combustion quality depends primarily on the ratio of air to combustion gases present during combustion (λ value, also known as the air-fuel ratio). To measure combustion quality, ionization measurements are performed, especially in many heating devices, within the flame zone. This measurement should be able to achieve stable regulation over long periods.

[0002] In addition, flame monitoring is typically performed in the heater, primarily to ensure that combustion gases are not supplied when there is no flame after the heater has been started. This prevents the formation of potentially explosive mixtures and the escape of unburned combustion gases. This can be achieved in various ways, including optical, thermal, and electronic systems. Commonly used electronic flame monitors utilize an existing ignition electrode (which is not needed after the flame is ignited) to generate an ionization signal for monitoring the flame. This specially processed ionization signal can reliably detect not only the presence or extinction of the flame but also, for example, the early measurement of physical weakening of the burner flame due to excessive air supply. Therefore, in cases of flame instability, premature shutdown may occur. Background Technology

[0003] According to existing technology, flame monitoring in operation is typically implemented by applying a constant or adjustable AC voltage in amplitude to the ignition or ionization electrode (hereinafter referred to as the ionization electrode). In the presence of a flame, the ionized flame region has a rectifying effect, causing the ionization current to flow primarily only during the half-wave of the AC current. This current, or the voltage signal derived therefrom (hereinafter referred to as the ionization signal), is measured and, if necessary, further processed in an analog-to-digital converter for flame monitoring after digitization. Specifically, AC voltage sources with high output resistance have been used to date, initially supplying an AC voltage with no DC voltage component to both the ionization electrode and the counter electrode (ground). When a flame appears between them, due to the high output resistance, the voltage drops essentially only during the half-wave due to the rectification effect of the flame, resulting in an AC voltage with a negative DC voltage component being applied to the computing electronics (amplifier and converter). This AC voltage is processed into an ionization signal in the computing electronics and can be converted into a digital signal in the analog-to-digital converter. In known flame monitoring systems, AC voltages with frequencies up to 200 Hz and amplitudes ranging from 50 to 200 volts are typically used. Voltage regulation is desirable to adjust monitoring sensitivity, but this requires significant investment in circuitry and equipment, particularly large transformers. Summary of the Invention

[0004] Here, the present invention aims to provide a remedy to enable the safe and reliable operation of a heater with accurate flame monitoring in terms of quality and / or quantity, with low equipment consumption and low cost.

[0005] The method, apparatus, and computer program product according to the independent claims are used to achieve this objective. Advantageous designs and improvements of the invention are given in their respective dependent claims. The invention is described in the specification, especially in conjunction with the accompanying drawings, and other embodiments are given.

[0006] The method according to the invention for adjusting or adapting the sensitivity of a detector for monitoring a flame in a heater is characterized in that an AC voltage source generates a plurality of AC voltage pulses of a predetermined frequency and a predetermined length, the predetermined length being located between the ignition electrode and the counter electrode in the flame region, wherein a time interval exists between the beginnings of the plurality of AC voltage pulses, and wherein the length and / or interval of each AC voltage pulse is adjustable. In this way, the effective amplitude of the AC voltage can be adjusted, allowing for a simpler and particularly less costly structural approach than when using conventional AC voltage sources with adjustable amplitude. It has been found that the accuracy of desired flame monitoring does not depend on whether the AC voltage is sinusoidal and continuous. What matters is only the effective amplitude, i.e., the integral of each amplitude can be reproducibly adjusted over time, and the integrals of the positive and negative half-waves are also substantially constant over time, i.e., the negative and positive half-waves occur approximately the same. Conversely, the shape of the AC voltage pulses is not important, so each pulse can, for example, have a decreasing amplitude. With the shape and length of each AC voltage pulse remaining constant, the effective amplitude of the AC voltage can be adjusted by changing the time interval between the AC voltage pulses. This effective amplitude acts solely on the ionization signal. Therefore, the measurement sensitivity can be adjusted during operation.

[0007] Preferably, the AC voltage frequency is higher than the repetition frequency generated by the time interval of the AC voltage pulses, especially greater than 1 kHz. Compared to low frequencies, smaller transformers can be used to generate frequencies in the kHz range, thus making smaller circuits possible overall.

[0008] In a particular embodiment of the invention, the AC voltage frequency is greater than 15 kHz. This can generate pulses comprising several consecutive waves, which may decay in amplitude, and can be repeated at appropriate time intervals.

[0009] The appropriate spacing is particularly important at repetition frequencies between 0.2 and 15 kHz. The effective amplitude (voltage) of the AC voltage can be adjusted over a wide range using these values.

[0010] In a preferred embodiment of the present invention, the maximum amplitude of the AC voltage pulse is between 50 and 300 volts [V], preferably between 100 and 200V.

[0011] Preferably, each AC voltage pulse should be substantially free of DC voltage components so that the rectification effect of the flame can be easily measured and calculated. Any small DC voltage components that may exist should, in any case, be constant so that they can be compensated for if necessary.

[0012] In a particular embodiment of the invention, each AC voltage pulse has a decreasing amplitude over its length. Such pulses can be generated, for example, based on the principle of a so-called "flyback converter." Using a simple microcontroller, the effective amplitude can be easily adjusted by changing the time interval of the AC voltage pulses.

[0013] The apparatus according to the invention for adjusting the sensitivity of a detector for monitoring a flame in a heater having an air supply and a combustion gas supply comprises: an ignition electrode, a counter electrode, an AC voltage source, and computational electronics for determining an ionization signal in the flame region. The AC voltage source is configured to generate a plurality of AC voltage pulses of a frequency, particularly greater than 1 kHz, and of a predetermined length at time intervals. The length and / or spacing of the plurality of AC voltage pulses are adjustable. A so-called duty cycle, derived from the pulse length and time interval, is used to adjust the desired effective amplitude of the AC voltage, thereby allowing the measurement sensitivity to be matched to the operating conditions.

[0014] Preferably, the AC voltage source is designed to provide AC voltage pulses of a frequency greater than 15 kHz and a constant length when adjusting the time interval of the AC voltage pulses.

[0015] In a preferred embodiment, the time interval between the start of two consecutive AC voltage pulses can be adjusted between 0.005 and 5 milliseconds [ms], preferably between 0.05 and 1 ms.

[0016] The present invention also relates to a computer program product comprising instructions that cause a heater to perform the method having the aforementioned apparatus. Attached Figure Description

[0017] The illustrative embodiments of the present invention and the working principle of the method according to the present invention will now be described in detail with reference to the accompanying drawings. The present invention is not limited to the illustrative embodiments described. Wherein:

[0018] Figure 1 : A heater with a flame monitoring device is shown schematically.

[0019] Figure 2 A schematic circuit for generating an ionization signal according to the present invention is shown, and

[0020] Figure 3 The diagram illustrates the variation in the effective amplitude of AC voltage by comparing the prior art with that of the present invention. Detailed Implementation

[0021] Figure 1 An embodiment of the device proposed herein is schematically illustrated. In a heater 1 for igniting a combustion gas mixed with air, a flame zone 2 is formed during operation. Air reaches the heater 1 via an air supply unit 3 and a blower 5. The combustion gas is mixed with the air via a combustion gas supply unit 4 and a combustion gas valve 6. An ignition electrode 7 ignites the mixture at the start of the combustion process and is subsequently used, for example, as part of a flame monitoring device 11. In conventional devices, an ionization signal in the flame zone 2 is typically measured by means of an ionization electrode 8, which is used to adjust the λ value during heater operation. An adjustment unit 10 is then used to adjust the blower 5 and / or the combustion gas valve 6 accordingly. The flame monitoring device 11 according to the invention ensures that only combustion gas is supplied when a stable flame is detected. For this purpose, an additional ionization electrode is used, often the ignition electrode 7, to generate an additional ionization signal whose electronic processing is specifically designed for flame monitoring purposes. In particular, an AC voltage source 12 is designed for this purpose.

[0022] Figure 2An embodiment of a circuit suitable for a flame monitoring device is schematically illustrated. An AC voltage source 12 with high output resistance initially supplies an AC voltage, essentially devoid of a DC voltage component, to the ignition electrode 7 and the counter electrode 9 (ground). When a flame is present between them (shown here as equivalent circuit diagram 16), the voltage, due to the rectification effect of the flame (shown as a diode in the equivalent circuit diagram), drops only halfway through the wave, resulting in an AC voltage with a negative DC voltage component at the input of a computational electronics device 14 (amplifier and converter). This AC voltage is converted into the desired ionization signal in the computational electronics device 14 and converted in an analog-to-digital converter (ADC) 15, and can then be further processed. This overall arrangement forms a detector for a flame monitoring device, which then provides an ionization signal only in the presence of a flame, wherein the ionization signal also has a typical trend from which, for example, the initial physical weakening of the flame at the gas outlet can be identified, thus allowing for shutdown even if instability begins due to excessive gas velocity or an excessively high λ value. However, the sensitivity of the detector depends on the amplitude of the AC voltage used, and therefore in the prior art, the amplitude of the AC voltage can typically be adjusted, for example, between 50V and 200V at a frequency of, for example, 200Hz. According to the invention, an AC voltage source 12 is now used, comprising an AC voltage pulse generator 17, a microcontroller 18, and a regulator 19. This configuration results in a low-cost and space-saving AC voltage source 12 in which the effective amplitude can be adjusted according to the desired detector sensitivity. Although the effective amplitude does not have the typical form of a generally sinusoidal AC voltage, it induces the same ionization signal upon further processing as a sinusoidal AC voltage with that amplitude.

[0023] Figure 3 Qualitatively describe what happens during the adjustment of the effective amplitude according to the present invention. Figure 3 The upper section shows how the sinusoidal AC voltage with amplitude U1 changes as the amplitude decreases to value U2. The graph plots the voltage U as a function of time t.

[0024] exist Figure 3 The following section illustrates how the effective amplitude of the AC voltage formed by the individual AC voltage pulses 13 of length L can be adjusted by changing the interval T (e.g., T1 and T2) between the individual AC voltage pulses 13. A larger effective amplitude is produced in interval T1 than in the larger interval T2. If the maximum amplitude Umax of each AC voltage pulse 13 is appropriately selected, and if necessary, the frequency F1 of the AC voltage pulses is also selected, then the effective amplitude can be adjusted accordingly. Figure 3The effective amplitude is adjusted by a sinusoidal AC voltage shown in the upper part. Furthermore, the AC voltage frequency F1 is higher than the repetition frequency F2 generated by the time interval T of the AC voltage pulses 13.

[0025] Therefore, the present invention realizes a cost-effective alternative to an adjustable AC voltage source in a detector for flame monitoring in a heater.

[0026] List of reference numerals

[0027] 1 heater

[0028] 2 Flame Zones

[0029] 3. Air Supply Department

[0030] 4. Combustion Gas Supply Department

[0031] 5 blowers

[0032] 6. Combustion Gas Valve

[0033] 7 Ignition Electrodes

[0034] 8 ionization electrodes

[0035] 9. Burner / Reverse Electrode

[0036] 10 adjustment units

[0037] 11 Detectors / Flame Monitoring Devices

[0038] 12 AC voltage sources

[0039] 13 AC voltage pulses

[0040] 14 Computing Electronic Devices

[0041] 15 Analog / Digital Converters

[0042] 16. Equivalent circuit diagram of a flame

[0043] 17 AC voltage pulse generator

[0044] 18 microcontrollers

[0045] 19 regulators

[0046] U1 first amplitude

[0047] U2 second amplitude

[0048] Umax maximum amplitude

[0049] T1 First time interval

[0050] T2 Second time interval

Claims

1. A method for adjusting the sensitivity of a detector (11) for monitoring a flame in a heater (1), characterized in that, An AC voltage source (12) generates AC voltage pulses (13) of a pre-defined AC voltage frequency (F1) and a pre-defined length (L), the pre-defined length (L) being located between the ignition electrode (7) and the counter electrode (9) in the flame region (2), wherein the time interval (T) is located between the beginnings of consecutive AC voltage pulses (13), and wherein the pre-defined length (L) and / or the time interval (T) of the respective AC voltage pulses (13) are adjustable to allow adjustment of the effective amplitude of the AC voltage corresponding to the desired sensitivity of the detector (11), the effective amplitude being the integral of the respective amplitude, which can be reproducibly adjusted over a certain period of time.

2. The method according to claim 1, characterized in that, The pre-given AC voltage frequency (F1) is higher than the repetition frequency (F2) generated by the time interval (T) of the AC voltage pulse (13).

3. The method according to claim 1 or 2, characterized in that, The pre-defined AC voltage frequency (F1) is greater than 1 kHz.

4. The method according to claim 1, characterized in that, The pre-defined AC voltage frequency (F1) is greater than 15 kHz.

5. The method according to claim 2, characterized in that, The repetition frequency (F2) is between 0.2 kHz and 15 kHz.

6. The method according to claim 1, characterized in that, The maximum amplitude (Umax) of the AC voltage pulse (13) is between 50 and 300 volts.

7. The method according to claim 1, characterized in that, Each AC voltage pulse (13) has essentially no DC voltage component.

8. The method according to claim 1, characterized in that, Each AC voltage pulse (13) has a decreasing amplitude (U) during its pre-given length (L).

9. An apparatus for adjusting the sensitivity of a detector (11) for monitoring a flame in a heater (1), the heater having an air supply (3) and a combustion gas supply (4), the apparatus comprising an ignition electrode (7), a counter electrode (9), an AC voltage source (12) in a flame region (2), and computational electronics (14) for determining an ionization signal, characterized in that, The AC voltage source (12) is configured to generate AC voltage pulses (13) with a predetermined AC voltage frequency (F1) and a predetermined length (L) at time intervals (T), and the predetermined length (L) and / or time interval (T) of the AC voltage pulses (13) can be adjusted to allow adjustment of the effective amplitude of the AC voltage corresponding to the desired sensitivity of the detector (11), the effective amplitude being the integral of the individual amplitudes, which can be reproducibly adjusted over a certain time.

10. The device according to claim 9, characterized in that, The AC voltage source is designed to generate AC voltage pulses (13) with a frequency greater than 15 kHz and a pre-given length (L) that can be adjusted in time interval (T) of the AC voltage pulses (13).

11. The device according to claim 9 or 10, characterized in that, The time interval (T) between the start of two consecutive AC voltage pulses can be adjusted between 0.005 milliseconds and 5 milliseconds.

12. A computer program product, comprising instructions, characterized in that, The instructions cause the device according to any one of claims 9 to 11 to perform the method according to any one of claims 1 to 8.

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