EP3870899B1 - Method for checking a gas mixture sensor and ionization sensor in a fuel-gas-powered heating device - Google Patents

Description

The invention relates to a method for checking a gas mixture sensor and ionization sensor with regard to their error-free function in a fuel gas-operated heater.

Various control methods for heating devices are known from the prior art, for example from the disclosure according to the publication WO2006/000366A1 . Further printed prior art in the present technical field can be found in the documents DE 20 2019 100 261 U1 and DE 10 2010 046 954 A1 disclosed.

The state of the art is also combustion control according to the so-called SCOT method, in which the amount of air supplied to the burner of the heater is controlled in accordance with the burner output. A flame signal measurement is carried out using an ionization sensor and the gas-air mixture is regulated to a target ionization measurement value stored in a characteristic curve. However, the disadvantage of the SCOT process is that at low burner outputs the flame signal drops sharply and the control therefore becomes unreliable.

The applicant is also responsible for a method for controlling a gas mixture formed from a gas and a fuel gas in a fuel gas-operated heater, in which the gas mixture is generated by providing and mixing a quantity of gas via a first actuator and a quantity of fuel gas via a second actuator. A microthermal gas mixture sensor, which detects at least one material property of the gas mixture, is exposed to the gas mixture and continuously transmits a sensor signal that is dependent on the respective gas mixture to a control unit. The control device compares the detected sensor signal with a target value of the sensor signal and controls at least one of the first and second actuators if the detected sensor signal deviates from the target value of the sensor signal. As a result, the gas mixture is adjusted by increasing or reducing the amount of gas and/or increasing or decreasing the amount of fuel gas until the setpoint of the sensor signal is reached.

The material property of the gas mixture detected by the microthermal gas mixture sensor is preferably the thermal conductivity, the thermal conductivity or the speed of sound of the gas mixture. However, several of these material properties can also be recorded, so that a more precise assignment of the majority of the properties to the gas mixture is possible.

The microthermal gas mixture sensor is designed as a gas mass sensor, which detects both the gas mixture mass supplied to the burner of the heater and other material physical properties. For example, calorimetric microsensors known from the prior art are used for this purpose, which, in addition to the thermal conductivity, also measure the thermal conductivity of the gas mixture. Another possibility is at least one gas mass sensor based on the functional principle of ultrasonic measurement to determine the gas mixture mass and the specific speed of sound that is present depending on the gas mixture.

In the method, the setpoint of the sensor signal is also adjusted by the control unit depending on a composition of the gas or the fuel gas. If the composition of the fuel gas changes (e.g. from propane to butane), the measured properties of the gas mixture change. In addition, other compositions of fuel gas also require different amounts of air for optimal combustion. A new mixing ratio between gas and fuel gas is therefore also required.

Such an adjustment of the target value of the sensor signal is carried out through a calibration process. For this purpose, the control unit changes the first actuator of the gas quantity or the second actuator of the fuel gas quantity until the desired result is achieved. The original setpoint is replaced by the new measured sensor signal for further mixture control.

The calibration process is carried out by controlling the ionization current of a flame signal from a burner of the heater until an ionization setpoint is reached. For this purpose, stoichiometric combustion of the burner of the heater is first set. The flame signal from the burner of the heater and thus a corresponding ionization current are detected via an ionization probe. In stoichiometric combustion, the ionization current is maximum. From this value of the ionization current, an ionization setpoint is calculated using a laboratory-determined percentage and stored as a future ionization current setpoint that must be achieved during the desired combustion. Subsequently, only the amount of gas is reduced by a predetermined factor in order to operate the burner with the desired gas mixture at the predetermined ionization setpoint.

When the ionization setpoint is reached, the at least one material property becomes of the gas mixture is measured using the gas mixture sensor and stored as a new setpoint of the sensor signal in the control unit. The new setpoint is used for further control and replaces the previous setpoint.

The gas is preferably air, the fuel gas is preferably liquid gas or natural gas.

In such control methods, the object of the present invention is to check the measured sensor values of the gas mixture sensor and the ionization sensor for plausibility, i.e. with regard to their error-free function, in order to be able to detect errors in the control process.

This task is solved by the combination of features according to claim 1.

According to the invention, a method for checking a gas mixture sensor and ionization sensor with regard to their error-free function in a fuel gas-operated heater is proposed, in which a gas mixture is generated by providing and mixing a quantity of gas via a first actuator and a quantity of fuel gas via a second actuator. The gas mixture sensor is positioned in the gas mixture to detect a material property of the gas mixture and continuously transmits a sensor signal that is dependent on the respective gas mixture to a control device. A flame signal is detected on a burner of the heater via the ionization sensor, an ionization signal is determined from this and transmitted to the control unit. A corresponding ionization signal from the ionization sensor is assigned to the respective sensor signal of the gas mixture sensor. To check the gas mixture sensor and the ionization sensor, the amount of gas or the amount of fuel gas is temporarily changed in a predefined manipulated variable of the first or second actuator, so that the composition of the gas mixture changes. At the same time, the change in the sensor signal of the gas mixture sensor and the ionization signal resulting from the mixture change of the ionization sensor was measured and compared with each other. From the result of the comparison of the respective changes in the sensor values, deviations from target values can be recognized and conclusions can be drawn about a faulty function of the gas mixture sensor or the ionization sensor.

Preferably, in the method, the amount of fuel gas is temporarily changed in a predefined manipulated variable of the first or second actuator, which can be controlled more precisely than the amount of gas, which is usually provided as air via a fan.

If, for example, the proportion of the amount of fuel gas in the gas mixture is increased for the comparison and the ionization signal of the ionization sensor increases as expected without the sensor signal of the gas mixture sensor increasing at the same time, the gas mixture sensor is functioning incorrectly. If, on the other hand, when the gas mixture is changed, only the sensor signal of the gas mixture sensor delivers adjusted signals as expected, without the corresponding adjustment being detectable in the ionization signal of the ionization sensor, there is a faulty function of the ionization sensor, for example the ionization electrode positioned in the burner of the heater. Depending on which of the two sensors delivers an incorrect result, the heater control process can only be carried out via the other sensor until appropriate maintenance has been carried out.

With the method, the absolute magnitude of the deviation of the ionization signal of the ionization sensor or the sensor signal of the gas mixture sensor can also be detected and compared with variables determined or precalculated in the laboratory in order to determine a degree of deviation of the signals from a target value. This makes it possible to set a tolerance range for the signals that are considered normal for regular operation. If the deviation is too large outside the tolerance range, an error diagnosis can be shown on a display of the heater, for example become.

The method according to the invention is preferably used continuously during mixture control and the sensor signal of the gas mixture sensor is regularly compared or checked for plausibility with the ionization signal of the ionization sensor.

A further development of the method provides that, in order to check the gas mixture sensor and the ionization sensor, the amount of gas or the amount of fuel gas is changed cyclically in several steps in predefined manipulated variables of the first or second actuator and the resulting change in the sensor signal of the gas mixture sensor and the ionization signal of the ionization sensor in several of the operating points resulting from the steps are measured and compared with each other.

The calibration process described above by the ionization current control is used in an advantageous embodiment of the method to determine a preliminary assignment of several signal values of the gas mixture sensor and ionization sensor in the different operating points. The calibration process is preferably carried out repeatedly, so that sensor signals of the gas mixture sensor corresponding to several different ionization signals are assigned. The connection between the ionization signal and the sensor signal at the various operating points results in a target characteristic curve in an ionization signal-sensor signal diagram, which is stored in the control unit. At least one tolerance corridor is preferably provided around the target characteristic curve, which characterizes operation outside the normal, so that if the characteristic curve deviates too much from the target characteristic curve, either the mixture control can be calibrated or the heater can even be switched off if necessary.

A further development of the method is characterized in that an additional gas sensor and/or a fuel gas sensor for detecting at least one of the material property of the gas or the fuel gas is used. In a solution with both additional sensors, ie gas sensor and fuel gas sensor, the material property of the gas is measured via the gas sensor and the material property of the fuel gas is measured via the fuel gas sensor, whereby it is advantageous that the respective end points are determined from the signals from the gas sensor and fuel gas sensor the sensor characteristic curve of the sensor signal of the gas mixture sensor can be determined. The first end point is determined by pure fuel gas, the second end point by pure gas, especially air. Thus, an expected course of the sensor characteristic curve of the gas mixture sensor when changing the amount of fuel gas or gas amount for carrying out the method according to the invention can be predetermined from measurements determined in the laboratory with the comparison of the change in the sensor signal of the gas mixture sensor and the ionization signal of the ionization sensor.

Even with a step-by-step change to achieve and measure several specific operating points, the characteristic curve and thus the operating points expected on the characteristic can be calculated in advance, so that a target sensor signal is determined for each of the operating points resulting from the steps.

Alternatively, one embodiment of the method provides that only one additional sensor, ie only the gas sensor or only the fuel gas sensor, is added. This is more cost-effective. At the same time, it offers the advantageous possibility of determining at least one end point of the sensor characteristic curve of the sensor signal of the gas mixture sensor, from which the step-by-step change, for example in the amount of fuel gas, can be predicted more precisely. In addition, taking into account the end point of the sensor characteristic curve, just one step of changing, for example, the amount of fuel gas can be sufficient to detect the deviations in the sensor signal of the gas mixture sensor. It is advantageous here that the checking of the gas mixture sensor and the ionization sensor does not take place in the area of the maximum of the ionization signal comparatively high exhaust gas values must be carried out, but rather the plausibility test can be carried out with a first increase, for example in the amount of fuel gas.

In a further development of the method, the gas mixture sensor, the gas sensor and/or the fuel gas sensor are provided redundantly. Each of the redundantly provided gas mixture sensors, gas sensors and/or fuel gas sensors conveniently supplies its own signal to the control unit, which is checked for plausibility and therefore the sensors are checked for error-free function.

Fig. 1

ein prinzipieller Aufbau zur Durchführung der Gemischregelung,

Fig. 2

einen Aufbau eines Heizgerätes zur Durchführung des Verfahrens,

Fig. 3

eine Regelungskennlinie des Sensorsignals des Gasgem ischsensors,

Fig. 4

eine Regelungskennlinie des Sensorsignals des Gasgem ischsensors,

Fig. 5

eine Kennlinie der Ionisationsstromregelung,

Fig. 6

eine Kennlinie zur Brenngasmengenerhöhung zur Durchführung des Verfahrens,

Fig. 7

eine resultierende Kennlinie des Sensorsignals des Gasgemischsensors bei der Brenngasmengenerhöhung gemäß Fig. 6,

Fig. 8

eine resultierende Kennlinie des Ionisationssignals des Ionisationssensors bei der Brenngasmengenerhöhung gemäß Fig. 6,

Fig. 9

eine Kennlinie im Diagramm lonisationssignal-Sensorsignal mit Toleranzkorridor.

Other advantageous developments of the invention are characterized in the subclaims or are shown in more detail below together with the description of the preferred embodiment of the invention with reference to the figures. Show it:

Fig. 1

a basic structure for carrying out the mixture control,

Fig. 2

a structure of a heating device for carrying out the process,

Fig. 3

a control characteristic curve of the sensor signal of the gas mixture sensor,

Fig. 4

a control characteristic curve of the sensor signal of the gas mixture sensor,

Fig. 5

a characteristic curve of the ionization current control,

Fig. 6

a characteristic curve for increasing the amount of fuel gas to carry out the process,

Fig. 7

a resulting characteristic curve of the sensor signal of the gas mixture sensor when the fuel gas quantity is increased Fig. 6 ,

Fig. 8

a resulting characteristic curve of the ionization signal of the ionization sensor when increasing the amount of fuel gas Fig. 6 ,

Fig. 9

a characteristic curve in the ionization signal-sensor signal diagram with tolerance corridor.

In the Figure 1 A basic structure for implementing mixture control is shown. In the following description of the figures, air is always assumed to be the gas, even if other gases can theoretically also be used.

In Figure 1 The actuator 4 for supplying a controllable amount of air 2 and the actuator 3 for supplying a controllable amount of fuel gas 1 are regulated in their respective opening positions via the control device 11 in order to produce the gas mixture 9 in a specific fuel gas-air mixture ratio. The gas mixture sensor 10 is positioned in the area of the gas mixture 9 and is supplied with the gas mixture 9. The fuel gas sensor 6 is also positioned in the fuel gas path 5 and the gas sensor 8 is positioned in the gas path 7, which also deliver signals to the control unit 11. The control device 11 and the control system are monitored via a process monitoring unit 12.

Figure 2 shows a specific embodiment of a fuel gas-operated heater 200 with a gas safety valve 101, a gas control valve 102 as an actuator for the amount of fuel gas 103, a mixing fan 107 for sucking in air 104 and mixing it with the fuel gas 103 to generate the gas mixture 105. About the speed of the mixing fan 107 the air volume is adjustable; it therefore provides the actuator for the air supply. The heater 200 includes the microthermal gas mixture sensor 106, with a second gas mixture sensor 108 being shown as an alternative installation position in the exhaust area of the mixing fan 107. In principle, however, a second gas mixture sensor is not required. The mixing fan 107 conveys the gas mixture 105 to the burner 109, on which the ionization sensor 111 with the ionization electrode is installed in order to monitor the burner flame. In addition, the signal lines to and from the control device 100, which processes the control of the gas mixture 105, are shown via arrows.

The following describes the components of the basic structure Figure 1 Reference is made, however, directly to the heater 200 according to Figure 2 are transferable.

In Figure 3 is in a diagram 30 a simplified linear relationship used for the control between the sensor signal 31 detected by the gas mixture sensor 10 for pure air 2 (reference number 34 corresponds to 100% air) and the sensor signal 32 for pure fuel gas 1 (reference number 36 corresponds to 100% fuel gas) shown. For the gas mixture 9 (reference number 35 corresponds to 40% air and 60% fuel gas), the sensor signal 33 lies in between. The amounts of air 2 and fuel gas 1 are adjusted via the respective actuators 3 and/or 4 until the mixture properties of the desired mixing ratio required by the process are detected by the gas mixture sensor 10. Figure 3 shows a linear course of the characteristic curve of the sensor signal, but non-linear characteristic curves are also possible, which enable control of the corresponding positions of the actuators 3, 4, for example using value tables.

According to Figure 3 the sensor signal decreases the more fuel gas 1 is supplied. The sensor signal is shown, for example, as dependent on the thermal conductivity as a material property of the gas mixture 9, the fuel gas being, for example, liquid gas and the thermal conductivity of liquid gas being lower than that of air. However, there are also types of gas for which the direction of action of the control is reversed, as in Figure 4 shown. Here the fuel gas 1 is natural gas, whose thermal conductivity is higher than that of air. In diagram 40 according to Figure 4 a simplified linear relationship used for the control between that detected by the gas mixture sensor 10 Sensor signal 42 for pure air 2 (reference number 44 corresponds to 100% air) and the sensor signal 41 for pure fuel gas 1 (reference number 46 corresponds to 100% fuel gas/natural gas). For the gas mixture 9 (reference number 45 corresponds to 75% air and 25% fuel gas/natural gas), the sensor signal 43 is in between, but close to the sensor signal 41 of pure fuel gas 1. For control with natural gas, the control unit 11 uses the signal change of the gas mixture sensor 10 at the Increasing the amount of fuel gas determines the direction of action of the control and is used as a basis for further mixture control.

Figure 5 shows a diagram 20 for calibration by means of ionization current control with a characteristic curve of the ionization signal (Io signal) detected by the ionization electrode in the burner flame versus the fuel gas-air ratio λ. Since the basic structure is according to Figure 1 shows no ionization electrode, the heater 200 is shown below Figure 2 referred. The control unit 100 controls the amount of air 104 to a predetermined value during burner operation, measures the ionization signal at the ionization electrode of the ionization sensor 111 on the burner 109 and increases the amount of fuel gas 103 until the ionization signal differs from the originally existing ionization value 21 at a Fuel gas-air ratio 24 has increased to the maximum 22. From this value, the ionization setpoint 23 is calculated using a laboratory-determined percentage and stored as a future ionization current setpoint, which must achieve the desired fuel gas-air ratio 25 with a higher excess of air. At the same time, a corresponding sensor signal from the gas mixture sensor 108 is stored for each value of the ionization signal.

In the Figures 6-9 Characteristic curves are shown in diagrams which provide an exemplary embodiment of the method for checking the gas mixture sensor 108 and ionization sensor 111 with regard to their error-free function in the fuel gas-operated heater 200. The amount of fuel gas is increased as a parameter. Alternatively, the procedure is carried out in the same way The air volume can be changed.

According to Figure 6 To carry out the method, the gas control valve 102 is controlled via the control device 100 in such a way that the amount of fuel gas F increases depending on the opening position P of the gas control valve 102. The characteristic curve 80 represents a flow characteristic curve of the fuel gas. In the embodiment shown, the increase occurs gradually from points a, b, c, d, e, with the amount of fuel gas F increasing essentially constantly over a fixed amount 81.

If the amount of air remains unchanged, the change in the amount of fuel gas causes a shift in the mixture composition in % of fuel gas and air and thus a changing sensor signal S of the gas mixture sensor 108, as in Figure 7 shown. The two end points 61, 65 of the sensor characteristic curve 60 determine the mixture composition in % at reference number 65 pure air or at reference number 66 pure fuel gas. Starting from the target mixture composition at point a Figure 6 , marked in Figure 7 With reference number 69, the amount of fuel is reduced in partial steps abcd to the test mixture composition 67, marked in Figure 7 with reference number 67, increased, with the sensor signal S changing by a signal difference 72 in error-free operation. At the same time increases, as in Figure 8 shown, the ionization signal from a value indicated at reference numeral 23 at point a to a maximum value of stoichiometric combustion, which is indicated at reference numeral 22 at point d. If the gas mixture is further enriched to point e, the ionization signal drops again.

Referring to Figure 9 The target characteristic curve 95 results from each step a, b, c, d, e of the assignment of the respective sensor signal (S) of the gas mixture sensor 108 to the corresponding ionization signal (Io signal) of the ionization sensor 111. In addition, there are two tolerance limits T1 in dashed lines and T2 are shown to determine the tolerance corridor. If there is a deviation in the direction of arrow A, this is a function of the gas mixture sensor 108 outside the normal values, as the amount of fuel gas increases Figure 7 the ionization signal increases significantly more than the sensor signal. If there is a deviation in the direction of arrow B, the ionization sensor 111 is functioning outside the normal values, since an increase in the amount of fuel gas occurs according to Figure 7 the sensor signal increases significantly more than the ionization signal. A deviation in the direction of arrow A indicates a faulty function of the gas mixture sensor 108, a deviation in the direction of arrow B indicates a faulty function of the ionization sensor 111. The mixture control of the heater 200 by the control device 100 then takes place via the sensor, which is not working incorrectly, until the necessary maintenance has been carried out. The error and maintenance requirement is displayed visually on the heater 200, for example via the display, and/or transmitted directly to the manufacturer. If the comparison result of the sensor values is outside the tolerance corridor determined by the tolerance limits T1, T2, the heater 200 is switched off.

Even if in Figure 1 and Figure 2 separate fuel gas sensors 6, 103 and gas sensors 8, 106 are provided, the method also includes versions without these additional sensors or with only one fuel gas sensor or gas sensor.

Claims (12)

1. A method for checking a gas mixture sensor and ionization sensor regarding their error-free functioning in a fuel-gas-powered heating device,

   wherein a gas mixture is created by providing a gas amount via a first actuator (4, 107) and a fuel gas amount via a second actuator (3, 102) and mixing them,

   wherein the gas mixture sensor (10, 106) is positioned in the gas mixture for detecting a material characteristic of the gas mixture (5, 105) and continuously transmits a sensor signal which is dependent from the respective gas mixture to a control device (7, 100),

   wherein a flame signal is detected at a burner (109) of the heating device (200) via the ionization sensor (111) and an ionization signal is determined therefrom and transmitted to the control device (11, 100),

   wherein a corresponding ionization signal of the ionization sensor (111) is assigned to the respective sensor signal of the gas mixture sensor (10, 106),

   and wherein for checking the gas mixture sensor and the ionization sensor the gas amount or the fuel gas amount is temporarily changed in a pre-defined actuating variable of the first or the second actuator so that the gas mixture changes, and at the same time the respective resulting change of the sensor signal of the gas mixture sensor and of the ionization signal of the ionization sensor are measured and compared to one another.
2. The method according to claim 1, wherein for checking the gas mixture sensor (10, 106) and the ionization sensor (111) the gas amount or the fuel gas amount is cyclically changed in several steps in pre-defined actuating variables of the first or the second actuator and the respective setting change of the sensor signal of the gas mixture sensor and of the ionization signal of the ionization sensor is measured in several ones of the operating points resulting from the steps and compared to one another.
3. The method according to claim 1 or 2, further comprising a calibration process occurring through an ionization current regulation of the flame signal of the burner (109) of the heating device (200) until a nominal value of the ionization signal is reached.
4. The method according to claim 3, wherein, when reaching the nominal value of the ionization signal, a corresponding sensor signal of the gas mixture sensor is assigned.
5. The method according to claim 4, wherein the calibration process is repeatedly executed during operation of the heating device and the sensor signal of the gas mixture sensor (10, 106) is assigned when the respective nominal value of the ionization signal is reached so that corresponding sensor signals of the gas mixture sensor are assigned to several different ionization signals.
6. The method according to any one of claims 2 to 5, wherein a characteristic curve with a tolerance corridor surrounding the characteristic curve is formed from the connection between the ionization signal and the sensor signal in the different operating points.
7. The method according to any one of the preceding claims, wherein a gas sensor (8) and/or a fuel gas sensor (6) for detecting at least one of the material characteristics of the gas or of the fuel gas is provided.
8. The method according to any one of the preceding claims 1 to 6, wherein a gas sensor (8) detects the material characteristic of the gas and a fuel gas sensor (6) detects the material characteristic of the fuel gas and end points of a characteristic sensor curve of the sensor signal of the gas mixture sensor (10, 106) are determined therefrom.
9. The method according to the preceding claim, wherein a target sensor signal for each of the operating points resulting from the steps is determined from the course of the characteristic sensor curve of the sensor signal of the gas mixture sensor.
10. The method according to any one the preceding claims 6 to 9, wherein the heating device (200) is switched off when the tolerance corridor is left.
11. The method according to any one the preceding claims 7 to 10, wherein the gas mixture sensor, the gas sensor and/or the fuel gas sensor are redundantly provided.
12. The method according to the preceding claim, wherein each of the redundantly provided gas mixture sensors, gas sensors and/or fuel gas sensors delivers their own signal to the control device and is checked regarding their error-free functioning.

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