Heating device and method for regulating a fan-operated gas burner

Abstract

A method for regulating a gas burner, wherein the gas burner has a combustion air supply fan whose rotational speed can be set variably, has the following steps: —operating the fan and detecting a fan rotational speed (nVBL); —changing the fan rotational speed; —measuring an ionization voltage (UION) which correlates with an ionization flow in a flame region of the gas burner; —finding a minimum of a gradient of the measured ionization voltage at the current fan rotational speed; —determining an operating point by measuring the current ionization voltage and storing as an operating point; —while the burner is operating, continuously measuring the current ionization voltage; —determining a deviation between the currently measured ionization voltage and the operating point; —checking whether the deviation (Delta UION) is within a predefined limit (UY) and carrying out a case differentiation: +if the deviation is within the predefined limit (UY), continuing the continuous measurement of the current ionization voltage; +if the deviation is not within the predefined limit (UY), repeating the method from the above change in the fan rotational speed.

Claims

1. A method for regulating a gas burner, wherein the gas burner has a combustion air supply fan, the speed of which can be variably set, the method comprising: (a) operating the combustion air supply fan and detecting a fan speed; (b) changing the fan speed; (c) measuring an ionization voltage which correlates to an ionization current in a flame area of the gas burner; (d) finding a minimum of a gradient of the measured ionization voltage with respect to the current change in fan speed; (e) determining an operating point by measuring the current ionization voltage and storing the measured current ionization voltage as an operating point; (f) during operation of the burner, continuously measuring the current ionization voltage; (g) determining a deviation between the currently measured ionization voltage and the operating point; (h) checking whether the deviation lies within a predefined limit and performing a case discrimination, including: if the deviation lies within the predefined limit, continuing the continuous measurement of the current ionization voltage; if the deviation does not lie within the predefined limit, repeating (b) through (h).

2. The method of claim 1, wherein to start the method, the following steps are performed prior to the measurement of the ionization voltage: operating the combustion air supply fan at an output speed; and reducing the fan speed.

3. The method of claim 1, further comprising: after finding the minimum of the gradient of the measured ionization voltage with respect to the current change in fan speed and prior to determining the operating point, increasing the fan speed by an offset value.

4. The method of claim 1, wherein finding the minimum of the gradient of the measured ionization voltage with respect to the current change in fan speed comprises: reducing the fan speed; measuring the current ionization voltage; determining the gradient of the measured ionization voltage with respect to the current change in fan speed; and performing a case discrimination, including: if the gradient is less than zero, reducing the fan speed and repeating the steps of measuring the current ionization voltage and finding the gradient; if the gradient is more than zero, increasing the fan speed and repeating the steps of measuring the current ionization voltage and finding the gradient; if the gradient is equal to zero, determining the gradient as a minimum and continuing the method.

5. The method of claim 1, wherein an output speed of the combustion air supply fan is set to a value in an upper third of a speed range of the combustion air supply fan.

6. The method of claim 1, wherein an output speed of the combustion air supply fan is set to a previously known firing speed.

7. The method of claim 1, wherein the ionization voltage is determined, based on the ionization current, such that: the ionization current is determined as a current flow, which occurs in case of a rectification of an alternating voltage effected by the presence of a flame, which is applied to an ionization electrode arranged in the flame area; and the ionization current is converted into a corresponding ionization voltage by an evaluation circuit.

8. A heating device, comprising: at least one gas burner which has a combustion air supply fan driven by a motor; a flame ionization voltage measuring device configured to detect an ionization voltage which is dependent on a flame generated by the gas burner; and a processing and control unit coupled to the motor and to the flame ionization voltage measuring device, wherein the processing and control unit is configured to: (a) operate the combustion air supply fan and detect a fan speed; (b) change the fan speed; (c) measure an ionization voltage which correlates to an ionization current in a flame area of the gas burner; (d) find a minimum of a gradient of the measured ionization voltage with respect to the current change in fan speed; (e) determine an operating point by measuring the current ionization voltage and storing the measured current ionization voltage as an operating point; (f) during operation of the burner, continuously measure the current ionization voltage; (g) determine a deviation between the currently measured ionization voltage and the operating point; (h) check whether the deviation lies within a predefined limit and performing a case discrimination, including: if the deviation lies within the predefined limit, continue the continuous measurement of the current ionization voltage; if the deviation does not lie within the predefined limit, repeat (b) through (h).

9. The heating device of claim 8, wherein to start the heating device, the processing and control unit is configured to operate the combustion air supply fan at an output speed and reduce the fan speed, bot prior to the measurement of the ionization voltage.

10. The heating device of claim 8, the processing and control unit is further configured to: after finding the minimum of the gradient of the measured ionization voltage with respect to the current change in fan speed and prior to determining the operating point, increase the fan speed by an offset value.

11. The heating device of claim 8, wherein the processing and control unit is configured to: reduce the fan speed; measure the current ionization voltage; determine the gradient of the measured ionization voltage with respect to the current change in fan speed; and perform a case discrimination, including: if the gradient is less than zero, reduce the fan speed and repeating the steps of measuring the current ionization voltage and finding the gradient; if the gradient is more than zero, increase the fan speed and repeating the steps of measuring the current ionization voltage and finding the gradient; if the gradient is equal to zero, determine the gradient as a minimum and continuing the heating device.

12. The heating device of claim 8, wherein the processing and control unit is configured to set an output speed of the combustion air supply fan to a value in an upper third of a speed range of the combustion air supply fan.

13. The heating device of claim 8, wherein the processing and control unit is configured to set an output speed of the combustion air supply fan to a previously known firing speed.

14. The heating device of claim 8, wherein the processing and control unit is configured to determine the ionization voltage, based on the ionization current, such that: the ionization current is determined as a current flow, which occurs in case of a rectification of an alternating voltage effected by the presence of a flame, which is applied to an ionization electrode arranged in the flame area; and the ionization current is converted into a corresponding ionization voltage by an evaluation circuit.

Description

(1) These and additional advantages and features of the invention will be explained in more detail in the following text based on examples with the aid of the accompanying figures, in which:

(2) FIG. 1 shows a schematic block diagram of a regulation system for regulating a gas burner; and

(3) FIG. 2 shows a flow diagram with a regulation method for a fan-operated gas burner.

(4) FIG. 1 shows a very rough representation of the principal structure of a regulation system on which the method according to the invention for regulating a fan-operated gas burner can be performed.

(5) The regulation system has a processing and control unit 1. In addition, a sensor 2 is provided with which the ionization current in the area of a flame generated by the burner is measured and converted into an ionization voltage U.sub.ION with the aid of a suitable evaluation circuit. The ionization voltage U.sub.ION is outputted as a measured value and supplied to the processing and control unit 1.

(6) In a practical application, the ionization voltage U.sub.ION can, for example, lie in the range between 0.3V to 3.3V depending on the quality of combustion at the output of the measurement circuit when a flame is present. At voltages less than 0.3V, the flame is detected as extinct. To increase the robustness of the detection, a hysteresis window of, for example, 0.3V to 0.7V is provided. This means that in a first-time detection, the flame will only be detected as existing if the ionization voltage reaches at least 0.7V. In contrast, the flame will only be detected as extinct when falling below 0.3V.

(7) The processing and control unit 1 is further connected to a motor 3 of a combustion air fan not shown. In particular, the processing and control unit 1 can control the speed of the motor 3 and thus of the combustion air fan. Conversely, it is required that the processing and control unit 1 receives information about the speed n.sub.VBL of the motor 3 and thus of the combustion air fan. The speed information can be determined in a suitable manner. Thus, it is possible that the processing and control unit 1 already itself specifies the speed through a corresponding control of the motor 3. Similarly, sensors (e.g. one or more Hall sensors) can be provided on the motor 3 to determine the speed of the motor 3. For this purpose, different possibilities are known which need not be explored at this point.

(8) The control of the rotation speed of the motor 3 and thus of the speed of the combustion air fan can, for example, be specified by a pulse width modulation in a range from 0% to 100% of the rotation speed. Alternatively, the drive voltage of the motor 3 or the drive current of the motor for speed regulation can also be set directly.

(9) FIG. 2 shows a flow diagram with a method for regulating a fan-operated gas burner.

(10) At the start of the method, the combustion air fan is, at a starting point SO, operated at an output speed which should correspond to a relatively high speed.

(11) Based on this speed, the speed n.sub.VBL is reduced in step S10. In step S20, the ionization voltage U.sub.ION is measured in the aforedescribed manner.

(12) In the following text, a gradient of the ionization voltage U.sub.ION is determined with respect to the speed n.sub.VBL in step S30. If the gradient is less than 0, the method proceeds to step S10, so that the speed n.sub.VBL is further reduced.

(13) If, however, the gradient in step S30 is more than 0, the speed is increased in step S40. In the following text, the ionization voltage U.sub.ION is measured in step S50 again, and the gradient is determined in step S60.

(14) If the gradient is then still more than 0, the speed is further increased in step S40, and a gradient is determined in step S60 again.

(15) If it has been detected in step S30 or S60 that the gradient is 0 or very close to 0, this is detected as the minimum of the gradient (related to the amount value) and thus as the optimum. At the same time, this point also corresponds to a minimum speed for the fan speed.

(16) In this process, the “minimum of the gradient” is to be understood as the absolute value. Thus, the minimum of the gradient is found at the value 0, while values more or less than 0 lie above the minimum.

(17) This operating point thus detected means that the ratio between air supply (specified by the combustion air fan) and combustion gas supply for the burner is optimal, so that the energy content of the combustion gas can be optimally exploited with minimal exhaust emission at the same time. Thus, the burner is operated in an optimal operation state.

(18) A further reduction of the fan speed would result in too little combustion air being supplied, so that the mixture to be burnt would be set too rich. An unnecessarily high consumption of combustion gas would be the consequence.

(19) In step S70, the speed is changed with the aid of an offset speed n.sub.X. This change in step S70 is optional and need not necessarily be performed. However, it has transpired that in the case of common burners during operation in the aforedescribed minimum speed, small deviations, for example, with regard to the ambient parameters, may result in the combustion behavior of the burner changing drastically. To allow greater tolerance and thus a gentler behavior, the minimum value for the speed just found within the scope of step S30 or S60 is increased by the offset value n.sub.X. The n.sub.X value emerges from operational-test measurements of the type of burner used and can be determined by the manufacturer depending on the design target.

(20) In the following text, the ionization voltage for the “optimal” speed thus newly determined is measured and stored as the operating point U.sub.B in step S80.

(21) At this operating point, the burner can be optimally operated, on the condition that the ambient parameters do not change or only change slightly.

(22) During the subsequent operation, the ionization voltage is continuously measured in step S90 and thus the quality of the flame detected. In this process, the ionization voltage can be measured continuously or at regular or otherwise specified time intervals.

(23) A difference between the ionization voltage U.sub.ION measured in step S90 and the ionization voltage determined as the operating point U.sub.B in step S80 is determined in the form of the value of delta U.sub.ION in step S100. This deviation of the ionization voltage values is then compared to a value U.sub.Y which is a decision criterion for the admissible change in the ionization voltage.

(24) If it is determined in step S100 that the deviation of the current ionization voltage U.sub.ION from the ionization voltage specified for the operating point is less than or equal to the value U.sub.Y, the measurement in step S90 is further continued and the operation of the burner maintained unchanged.

(25) If, however, it is determined in step S100 that the deviation is too large, the method determines that readjustment of the operating point is required. A reason for this can, for example, be a change of one or more ambient parameters which results in the burner not being able to be operated anymore at the optimal operating point at this point in time.

(26) Thereupon, the method is performed again by reducing the speed in step S10. Prior to that, the speed can reasonably be increased to a higher value (output speed) again in order to be able to conduct a change in speed over a larger range.