EP0806610B1 - Method for operating a gas burner - Google Patents

Abstract

The method uses a regulation circuit, receiving an ionisation signal (Ui) from an ionisation electrode, for regulation of the gas/air ratio to provide a required lambda value corresponding to a required ionisation signal value (Uis). The regulation is effected within a limited regulation range (RB), for ensuring acceptable emission levels, the upper limit (Uio) of this range lying below the maximum value of the ionisation signal and the lower limit (Uiu) lying above the dangerous emission level. A cut- out signal for the burner is provided when the ionisation signal is outside the regulation range for longer than a given interval.

Description

The invention relates to a method to operate a gas burner with the features of Preamble of claim 1.

Such a method is described in DE 39 37 290 A1 described. There is the ionization electrode in one DC circuit. The evaluation of the ionization current is problematic.

In patent application DE 44 33 425 A1 Improve the evaluability of the over the Ionization electrode flowing current on this one AC voltage applied, which is one of the current of the Ionization electrode dependent DC voltage component overlaid. It becomes an ionization voltage derived a sufficiently accurate image of the respective flame temperature and the air ratio lambda (Gas-air ratio).

It is also known to have a heating output Fan burner of a gas heater using a Control automatic control units according to the heat demand, where the control unit turns the fan speed in Controls dependency on a power setpoint that depends on a room temperature setpoint and one Heating flow temperature and / or heating return temperature and depends on an outside temperature.

DE 195 02 901 C1 is another Control device for a gas burner known. There is based on the fact that the intensity of the Flames always fluctuate, so a flickering picture of flames consists. It is recognized that the amplitudes of this Fluctuations in the gas-air ratio (lambda value) of the Depending on the combustion gas. A Safety flame monitoring for gas shutdown at Flame failure is not mentioned.

As is known, gas appliances must be high Security requirements are sufficient. To The safety regulations (EN 298) go through Flame detector in gas devices for continuous operation during operation at regular intervals, at least once per hour, a self-test. For gas appliances for intermittent operation, the gas burner must be inside Switch off at least once every 24 hours to switch the To be able to check the function of the flame detector. there it is not excluded that during the Burner operation comes to a defect in the flame detector and in addition the flame goes out. The burner control cannot recognize this at first and none Trigger gas shutdown signal, which has the consequence that unburned gas until the next self-check of the Flame detector or burner shutdown flows out.

DE 43 09 454 A1 describes an ionization flame monitor known in which a charged to an operating voltage Capacitor is discharged by the ionization current. The ionization flame monitor can be used during operation checked for function by means of a test signal become. The ionization electrode itself and its Connection cable and in certain malfunctions of the Capacitor cannot be checked. The The flame is only monitored indirectly. Moreover the flame detector is only in by the test signal periodically recurring periods checked.

The object of the invention is to provide an improved method and a device of the type mentioned to propose low-emission combustion to guarantee different operating states.

According to the invention, the above object is achieved by the features of the characterizing part of claim 1. It is thereby achieved that the gas burner can be operated with low emissions at least in the Wobbezahl range of natural gas (10 kWh / m ³ to 15.6 kWh / m ³ ). It is also achieved that the control does not undesirably affect the desired heat output to be provided by the gas heater working with the gas burner, so that the gas heater can cover the heat requirement with the requested heat output.

A further embodiment (cf. FIGS. 9, 10) of the Procedures addresses the following problems:

The control circuit regulates depending on Ionization signal the gas quantity valve so that the Combustion with one for low-emission operation desired lambda setpoint> 1, in particular between 1.1 and 1.35. The control circuit itself serves not dependent on the heat demand Performance adjustment. An adjustment of the heating power of the burner as a function of a power setpoint takes place in a manner known per se by means of Automatic control unit, the fan speed two or multi-stage or infinitely variable. With fast Changes in the performance target and accordingly There may be rapid changes in fan speed erratic control deviations on the control circuit come. These could lead to instabilities in the Control circuit. To avoid the Control circuit must process large control deviations, the reserve share for the Control signal of the gas flow valve regardless of the Control circuit or derived in parallel to this. The The control circuit then only has to be fine-tuned make comparatively small control deviation.

The lead portion of the control signal is easily too win because of the device-specific power control signal characteristic is known by the manufacturer and so that it can be stored in the evaluation circuit.

When there is a change in output or fan speed So the same - regardless of the control circuit - that Control signal for the gas flow valve through this changing reserve proportion adjusted. At a The gas quantity valve will increase performance opened further; if the output is reduced, it will Gas quantity valve closed further. The control circuit even then only needs a fine adjustment to the Lambda setpoint. So it doesn't have to be big, erratic, based on the change in performance Process control deviations.

The power control signal characteristic curve is preferred defines a tolerance band and it becomes when that Actual control signal leaves the tolerance band, on Shutdown signal generated for the burner. The tolerance band is dimensioned so that it is in the normal operation of the Gas blower burner of the gas heater is not left and it will leave if in the course of operating the Gas heaters characteristic curves of the sensors, especially the Ionization electrode and / or the measured value recording, or the actuator system, especially the gas flow valve or the Air path of the fan or the exhaust path or the Change the burner, for example due to contamination. The tolerance band will also fluctuate strongly Wobble payments of the gas, fluctuating strongly Gas supply pressure or fluctuating air resistance or if the control malfunctions. In In all such cases, a shutdown signal for the Burner generated so that this is not in one for one low emission combustion unfavorable area continues to work.

This switch-off signal can be the same or, preferably, if the tolerance band for a certain period of time, for example 5 s, is left to take effect. It is thus safe and low-emission operation of the Brenners guaranteed even after many hours of operation. The control circuit itself can also switch off signals generate if the specified lambda setpoint is not is observable.

The switch switches on a certain time after the switch-off signal Automatic control switch on the gas fan burner again. Do that Switch-off signal several times afterwards, a Lockout may be provided according to which Gas-blown burners only again through service measures can be switched on. By defining the tolerance band other, so far common No need for safety devices.

The tolerance band can be symmetrical or asymmetrical or a desired function according to the Power control signal characteristic curve can be laid.

Through a different or additional configuration (cf. Fig.11 to 14) is to be achieved that a Throttle shutdown signal occurs both when the flame does not exist, and also occurs when a defect consists of a deceptive ionization signal produces a similar signal, such a defect the entire functional range of the Ionization electrode up to a monitoring circuit can be present.

This configuration becomes a characteristic Flame pattern that affects the ionization signal to Monitoring used. There will be fluctuations in the Flame intensity exploited, after one execution the inevitable due to the combustion Flickering fluctuations in the flame pattern, and targeted in the other execution of the flame Modulated fluctuations can be evaluated. Amplitude fluctuations are preferably evaluated. However, it can also, especially when targeted Modulation instead or in addition, the phase or Frequency can be evaluated.

The gas cut-off signal that blocks the gas supply not only occurs when the flame goes out. It also occurs if as a result of any technical defect on the real ionization signal there is a deceptively similar signal.

The gas cut-off signal only occurs when the characteristic fluctuations in the flame pattern and not the ionization signal derived from it available. A technical defect in the facility, the the characteristic fluctuations in the flame pattern pretends is excluded in practice.

The entire functional range of the ionization electrode to the evaluation circuit supervised. The gas shutdown signal occurs independently on whether the pretending the ionization signal Defect in the ionization electrode itself or its Connection line or the monitoring circuit or otherwise where is in the system. This makes it a very high one System security achieved, even over the previous ones Safety regulations goes beyond.

The safety flame monitoring is also carried out monitoring for technical defects constantly during burner operation, i.e. with a burning flame. It can So it does not happen that a longer one after a defect There is time for unburned gas to escape. in the If the modulation is specifically applied to the flame it suffices if the modulation signal generates periodically , the time between two consecutive Modulation signals are dimensioned so short that at one No dangerous amount of gas defective during this time emanates unburned.

The ionization signal does not have to be alone or separately for the safety flame monitoring must be generated. It can serve at the same time the combustion control, which in the DE 44 33 425 A1 or DE 195 02 901 C1 is.

Figur 1 einen Regelkreis eines Gasgebläsebrenners für ein Gasheizgerät schematisch,

Figur 2a eine Schaltung zur Gewinnung der Ionisationsspannung mit Ersatzschaltbild der Ionisationselektkrode,

Figur 2b zugehörige Spannungsverläufe,

Figur 3 die Ionisationsspannung in Abhängigkeit von der Luftzahl Lambda,

Figur 4 ein Gas-Zeitdiagramm beim Brennerstart,

Figur 5a ein Regeldiagramm für ein höher- und niederkalorisches Gas,

Figur 5b ein Regeldiagramm bei einer niederen und höheren Heizleistung,

Figur 6 eine Regelkennlinie,

Figur 7 ein Diagramm einer Luftzahlsteuerung bei einem sehr niederkalorischen Gas,

Figur 8 Zeitdiagramme beim Start eines Kalibriervorgangs,

Figur 9 ein Blockschaltbild einer Regelung eines Gasgebläsebrenners,

Figur 10 eine Leistungs-Steuersignal-Kennlinie mit Toleranzband,

Figur 11 ein Blockschaltbild eines ersten Ausführungsbeispiels,

Figur 12 beispielhaft einen Verlauf der Ionisationsspannung mit verbrennungsbedingten Schwankungen (Flackern),

Figur 13 den Verlauf der Ionisationsspannung ohne die Schwankungen und

Figur 14 ein Blockschaltbild eines weiteren Ausführungsbeispiels.

The features of the subclaims relate to further improvements in the operating method in various operating states of the method. They are explained in the following description. The drawing shows:

FIG. 1 schematically shows a control circuit of a gas fan burner for a gas heating device,

FIG. 2a shows a circuit for obtaining the ionization voltage with an equivalent circuit diagram of the ionization electrode,

FIG. 2b associated voltage profiles,

FIG. 3 shows the ionization voltage as a function of the air ratio lambda,

FIG. 4 shows a gas-time diagram when the burner is started,

FIG. 5a shows a control diagram for a higher and lower calorific gas,

FIG. 5b shows a control diagram with a lower and higher heating output,

FIG. 6 shows a control characteristic,

FIG. 7 shows a diagram of an air ratio control for a very low calorific gas,

FIG. 8 time diagrams at the start of a calibration process,

FIG. 9 shows a block diagram of a regulation of a gas fan burner,

FIG. 10 shows a power control signal characteristic curve with a tolerance band,

FIG. 11 shows a block diagram of a first exemplary embodiment,

FIG. 12 shows an example of a course of the ionization voltage with combustion-related fluctuations (flickering),

13 shows the course of the ionization voltage without the fluctuations and

Figure 14 is a block diagram of another embodiment.

A blower is connected to a burner (1) of a gas heater (2) and a gas line (3) connected in the one Gas solenoid valve (4) or another gas control valve is located. There is one in the flame area of the burner (1) Ionization electrode (5) arranged on a Evaluation circuit (6) for the in burner operation between the burner (1) and the ionization electrode (5) flowing Electricity is connected. The evaluation circuit (6) has especially one connected to the AC mains voltage Capacitor (C) and a resistor (R). The Evaluation circuit (6) forms from that of the combustion dependent ionization current an ionization voltage (Ui), which is connected to a control circuit (7). The Evaluation circuit (6) can also be used in the control circuit (7) be integrated.

The control circuit (7) controls by means of a control signal (J), especially control current, the degree of opening of the Gas solenoid valve (4). The power supply is due to the Control circuit (7) the AC mains voltage. It captures also the network frequency and the network amplitude. The Control circuit (7) is, for example, by a digital PI controller, e.g. Microprocessor, realized.

For two-stage or multi-stage control of the fan speed an automatic control device (9) is provided as it is for example under the trade name "Furimat" is known on the market. By means of the control machine (9) is a Safety valve (10) can be switched on and off, whereas with the gas solenoid valve (4) the gas volume flow is infinitely variable is adjustable. At the control automats (9) is a Setpoint generator (8) connected, one of a Target room temperature and / or one Heating flow temperature and / or one Heating return temperature and an outside temperature dependent signal on the control automat (9).

A gas pressure switch (11) is located in the gas line (3) via the control automat (9) during the burning operation switches off insufficient gas pressure. In series with Gas pressure switch (11) is in the control circuit (7) Switch (12) integrated, which in the case of the closer below described control shutdowns and Fault shutdowns the burning operation over the Control automat (9) interrupts.

Via a line (13) gives the control automat (9) to everyone Switching on an ignition pulse to an ignition electrode (14) the burner (1). For flame monitoring is the Ionization electrode (5) placed on the control automat (9) (Line 15). On operated with the mains voltage Safety valve (10) is tapped and connected to the Control circuit (7) laid (line 16). On Speed control signal of the fan (2) is above a Line (17) on the control automat (9) and the Control circuit (7).

The evaluation circuit (6), the control circuit (7) and the Control machine (9) can also be in a single Switchgear can be integrated.

The device of Figure 1 is advantageous because of proven control automat (9) with its control and Safety functions for the burner (1) and the fan (2) can continue to be used. The control circuit (7) only needs to control the gas solenoid valve (4). The of her generated shutdown signals are from the Control automats (9) evaluated. It is possible Already existing control automatons (9) Retrofit gas heaters with the control circuit (7).

Figure 2a shows the evaluation circuit (6), the Ionization electrode (5) with its equivalent circuit diagram as Resistor (Ri) and diode (D) is shown. Parallel to Ionization electrode (5 or Ri, D) is inserted Voltage divider made up of resistors (R1, R2). Between the Mains connection (N) and the voltage divider (R1, R2) and the Ionization electrode (5; Ri, D) is the capacitor (C).

As a result of the rectifying effect of the diode (D) shifts the AC line voltage (Un) is one DC voltage component (Ug) to voltage (Ub) (see Fig. 2b), which is detected via the voltage divider (R1, R2) as Uc. The DC voltage component (Ug) is then determined using a Low pass or filtered out by averaging and forms the ionization voltage (Ui). The low pass or Devices for averaging are in the figures not shown. You can in the evaluation circuit (6) or be provided in the control circuit (7). In addition can be provided, the ionization voltage (Ui) according to a possible deviation of the Correct the AC mains voltage from the standard value (230 V). The use of the AC line voltage on the Evaluation circuit (6) is cheap because the AC mains voltage is present anyway. However, it could another sufficiently large AC voltage be used.

FIG. 3 shows the course of the ionization voltage in Dependence on the air ratio Lambda (l) des Combustion state. With stoichiometric combustion (1 = 1) a maximum (Uim) of the ionization voltage occurs (Ui) on. With substoichiometric combustion (l <1) and with overstoichiometric combustion (l> 1) decreases the ionization voltage (Ui). For a low-emission Combustion is a lambda setpoint (ls> 1) between 1.1 and 1.35, e.g. 1.15, is desirable. That corresponds an ionization voltage setpoint (Uis) (see Fig. 3).

There is an approved in the control circuit (7) Control range (RB) for the ionization voltage (Ui) with an upper limit (Uio) and a lower limit Limit value (Uiu) specified. The upper limit (Uio) is below the maximum value (Uim). The lower Limit value (Uiu) lies above the final value (Uie), which occurs when the lambda value (l) is much smaller than 1, the air-gas mixture is therefore due to maximum Gas supply or minimal air supply is so rich that the Combustion is no longer low in emissions.

The ionization voltage (Ui) is very short Time intervals, for example every 50 to 1000 ms, preferably about 100 ms newly acquired. It is with it achieved that the ionization voltage (Ui) never long can be outside the control range (RB), causing over seen every combustion process a low emissions Burning is guaranteed. Move in normal operation the values of the ionization voltage (Ui) in the permitted control range, i.e. between Uio and Uiu, see above that the lambda value (l) correspondingly in the range (lo to lu) is regulated to the lambda setpoint (ls).

If the ionization voltage setpoint (Uis) falls below, then the control circuit (7) opens the control signal (J) continues the gas solenoid valve (4), causing the combustion towards the Lambda setpoint (ls) is controlled. Will the Ionization voltage setpoint (Uis) exceeded, then the control circuit (7) controls the gas solenoid valve (4) in this way indicates that the gas supply is reduced, whereby the Lambda value is regulated again to the lambda setpoint (ls). This applies to the control area (RB) and also to Combustion states outside the control range (RB).

The lower limit (Uiu) of the ionization voltage (Ui) as a result of a lambda value that is greater than lo, falls below, then the control circuit (7) Timer activated, which is also in the control circuit can be realized yourself. In this area I in Figure 3, the gas solenoid valve (4) is opened to to reach the Lambda setpoint (ls) again. Comes the Ionization voltage (Ui) within that of the timer predetermined duration, for example 3 s to 10 s, especially 5 s, then back in the control range (RB) nothing else happens. The burner (1) continues to run and the timer is reset. However, achieve that Ionization voltage (Ui) in this period Control range again, then by opening the Switch (12) a switch-off signal for the burner (1) generated. There is a control shutdown of the Brenners (1). The burner (1) is a short time after Control shutdown, for example 5 to 50 s, again started. Then kick several times, for example three times one after the other, such a shutdown, then the burner (1) no longer restarts automatically, but it will lock out by keeping open of the switch (12) performed and displayed, which itself only by special outside intervention leaves.

If the air ratio lambda (l) drops so far that the Ionization voltage (Ui) becomes greater than the upper one Limit (Uio) of the control range (RB), then again the timer is activated and the control signal (J) (Modulation current) for the gas solenoid valve (4) see above changed that the gas volume flow or gas pressure is reduced in order to increase the lambda setpoint (ls) again to reach. This happens in area II and III of the Figure 3. The adjustment at Ui> Uis is based on the control characteristic curve described in more detail below (cf. Fig. 6) faster than with Ui <Uis. Uim has it highest sensitivity and therefore fastest Correction speed. The air ratio can only be short <lu or <1.

However, becomes the time period specified by the timer exceeded, then a shutdown signal for the burner. This will be after a delay time restarted and done as described above if the shutdown signal then reappears, a Lockout.

If the air ratio becomes 1 due to any circumstances so much <1 that in area IV the ionization voltage (Ui) falls below the setpoint (Uis), then this has - as in area I - a change in the control signal (J) Sequence through which the gas solenoid valve (4) opens further so that the air ratio becomes even smaller. The Control circuit now works with coupling (see area IV in Fig. 3). Due to the high sampling period (100 ms) and the control engineering coupling of the acquisition of the Ionization voltage very quickly becomes the final value (le) of the Air number (l) or the final value (Uie) of the ionization voltage or the maximum value of the control signal (J) is reached, where the gas solenoid valve (4) is fully open. Is the Maximum value of the control signal is reached, then this is detected the control circuit (7) and activates a shutdown signal for the burner. The burner does not have to do this immediately switch off. It is also sufficient if the burner is included one specified by another timer Delay time, for example 5 s, is switched off. This is cheap for the following reason: It is not excluded that the gas solenoid valve (4) when increasing the modulation current (J) that the Control signal is, initially stuck, so that although Modulation current assumes its maximum value, but that Gas solenoid valve does not open further. Within the Delay time has the gas solenoid valve (4) time tarnish, which, if it does, is unnecessary Switching off the burner is avoided.

The occurrence of the minimum value of Control signal (J) recorded electronically and for a Control shutdown evaluated. This will shutdown of the burner (1) is guaranteed if the minimum value of the control signal (J) is reached, however Gas solenoid valve (4) for some reason not closes.

In the control circuit (7) there is a starting gas ramp given (see Fig. 4), according to which in a Safety time (T) by controlling the gas quantity valve (4) each time the burner (1) starts, the gas pressure or Gas volume flow is continuously increased from pmin to pmax. pmin and pmax are dimensioned in such a way that with each Wobbe number the gas family in question, for example natural gas, the Burner starts safely.

Each time the burner is started, the fan (2) starts up a constant speed. After a pre-wash for the combustion chamber becomes the gas solenoid valve at time (t0) (4) increasingly open. With a higher calorific gas is the optimum at time (t1) (gas 1) Gas-air mixture reached so that the ignition takes place. The corresponding gas solenoid valve position remains at the end of Maintain safety time (T). Only after that sets the regulation described above. At a low-calorific gas is the ignitable mixture for example, only reached at time (t2). It then the ignition and this occurs Gas solenoid valve position will continue until the end of Maintain safety time (T). With every wobbe number of the Ignition is guaranteed for each gas.

The control circuit (7) works as, preferably digital, PI controller, which uses the ionization voltage a sampling period of, for example, those mentioned above 100 ms detected and with the same frequency the new one Value for the control signal (J) calculated. The respective Control signal change (dJ) consists of the by the I control part caused changes and that compared to last control value changed P control portion together.

At a certain desired output of the burner is the same for a higher calorific gas Ionization voltage setpoint (Uis) (gas 1 in Fig. 5a) smaller control signal (J1) is required than with a low calorific gas (gas 2 in Fig. 5a). At the low calorific gas is the higher control signal for Uis (J2) necessary (see Fig.5a). This takes into account the Control circuit.

The situation is similar when the burner (1) in a performance level (S1) higher performance and in one Power level (S2) of lower power through appropriate Fan speed setting should be operated (see Fig.5b). The control circuit (7) detects the Fan speed or determines the load from the position of the connected gas solenoid valve (4) via the Line (17) and provides the same Ionization voltage setpoint (Uis) in the larger Power level (S1) higher values of the control signal (J) than in the lower power level (S2) (see Fig.5b).

Figure 6 shows the control signal change (dJ) in Dependence on the control deviation (d) of the respective Ionization voltage (Ui) from the target ionization voltage (Uis). It can be seen that with the same size positive and negative control deviations (d) the Control signal change (dJ) with positive control deviations (above dp1) is greater than with the same negative Control deviations (below dn1). Figure 6 also shows that the P control part only starts from a certain positive or negative control deviation (dp1, dn1) becomes active. There is no difference between the control deviations (dnl and dp1) Control signal change (dJ). This ensures that the control signal (J) in the inevitable scatter of the Measured values of the ionization voltage (Ui) are not constant is changed and therefore not the gas solenoid valve (4) every little one, no matter how short Control deviation that affects the low-emission operation of the Brenner is practically without influence, is adjusted.

The P control component is shown in dotted lines in FIG. 6. The I control component is with a solid line indicated. In the event of negative system deviations, the I control component for a longer reset time than for positive control deviations.

The modulation current (J) is an alternating current, for example with the network frequency of the Control circuit (7) superimposed. The amplitude of the superimposed AC component is much smaller as the control signal (J) as such, for example is between 30 mA and 150 mA. Through the overlaid AC component is due to the mechanical structure of the gas solenoid valve (4) conditional valve hysteresis reduced so that the gas solenoid valve (4) Control signal changes (dJ) quickly in both directions appeals.

The burner becomes a very low calorific gas delivered and the fan speed can not be lower to maintain full load, then it can even when the gas solenoid valve is opened to the maximum (4) or maximum control signal (J) that the Combustion is switched off. To avoid this, so Maintaining the heating operation is for one a higher value of the air ratio is permitted for a limited time. Accordingly, the control circuit for the ionization voltage setpoint (Uis) for a limited time. The relationships are shown in FIG. 7. In the Control circuit (7) are threshold values (J1, J2) for the Control signal (J) specified. Occurs at Ionization voltage setpoint (Uis) low calorific gas on, which lead to a regular shutdown of the combustion can, then the control circuit (7) first increases that Control signal (J) in the manner described to the Increase gas supply accordingly. However, the top Threshold (J1) is reached, then the Control circuit (7) the ionization voltage setpoint Uisn (a in Fig. 7). This is a minor one Linked to increase in lambda, however it is ensures that the burner (1) continues to burn. The Control signal (J) will then move towards the decrease the lower threshold (J2) if the gas is not becomes even lower calorific (arrow b in Fig. 7), which leads to a control shutdown or a lockout would lead. Then the lower threshold (J2) reached, then the control circuit (7) switches (see c in Fig.7) back to the original Ionization voltage setpoint (Uis) back.

The relationships between the Ionization electrode (5) and that of the gas solenoid valve (4) set gas flow, for example by Combustion residues on the ionization electrode (5) and / or their bending and / or wear or Move deposits in the gas quantity valve (4). It is therefore a calibration function in the control circuit (7) integrated. The calibration function is in regular Intervals, through an event counter, for example Counter of the switch-on or switch-off processes, or by a Operating hours counter activated. During calibration the control function described is switched off. The Calibration is preferably not done by itself changing speed of the fan (2) to the influence of Fan (2) to suppress the combustion. Cheap is to calibrate at a medium speed perform so as not to turn on during calibration Modulation limits of the control signal (J). The Calibration can also be done while switching the Blower (2) from one power level to the other Power level take place because the speed change in Compared to the calibration process is slow, so that the Speed virtually constant during the calibration process is.

The calibration process is carried out at time (t1) (see Fig. 8) from the event or operating hours counter during the transition from the full load level to the partial load level of the blower (2) started when the decreasing modulation current (J) reached a low value (Jk). This value is from the control circuit. It is then from the Control circuit (7) the modulation current (J) and thus over the gas solenoid valve (4) increases the gas supply, causing the Ionization voltage (Ui) increases accordingly. To the At time (t2) the ionization voltage (Ui) reaches one predetermined value, for example 0.9 Uimax. The Time period (t1 to t2) serves to start the preheating the ionization electrode (5). From the time (t2) until the time (t3) the modulation current (J) remains constant held. During this period (t2 to t3) it heats up the ionization electrode (5) to a stable temperature and thereby guarantees reproducible measured values.

After the time (t3) the modulation current (J) of the control circuit (7) increased so that the Drive over the maximum value (Uimax) of the ionization voltage (Ui) becomes. This - new - maximum value (Uimax) and / or the measured values resulting in the time period (t3 to t4) will be used for further processing in the calibration process saved.

The modulation current (J) is increased further until the Ionization voltage (Ui) again about 10% below that Uimax value, which is in Figure 8 at time (t4) Case is. The lambda value is in the period (t3 to t4) the incineration itself is unfavorable, but this does not ins Weight drops because this time span is at most a few Takes seconds.

After the time (t4) the control circuit (7) switches including the previously saved Modulation current (JK) again on the above described Control process back. This starts when the Time (t5) the ionization voltage (Ui), the Modulation current (J) and the gas pressure (p) stabilized to have.

From the stored - new - maximum value of Ionization voltage or from the in the period (t3 to t4) Measured values obtained are directed by the control circuit (7) a correspondingly adjusted new setpoint for the Ionization voltage (Uis).

Because of the short sampling period mentioned Control circuit (7) will also change in the period (t3 to t4) result in a series of measured values. Compared to the other measured values of the series strongly differing measured values are suppressed because they rely on external electrical Interference may be based.

To the influence of only temporarily occurring, though unusual, but still tolerable calibration measurement series can decrease, averaging between the new measurement series and the measurement series previous calibration operations.

Before with the new calibration value, which from the new Maximum value of the ionization voltage or from the Series of measurements can actually be derived Recalibration of the setpoint of the ionization voltage (Uis) is made, two handover criteria of the control circuit (7) checked.

The first transfer criterion detects a sudden one Change all components of the control loop. It is fulfilled if the deviation of the new calibration value is sufficiently small from the previous calibration values.

The second handover criterion records a "creeping Drift "of the system (burner control), which in the event of deviation sufficient from the values provided by the manufacturer is small.

Only if both handover criteria are met will the Burner operation continued with recalibration. Is If one of the handover criteria is not met, then the Burner operation first through a control shutdown and after repeated repetition by a lockout interrupted.

The burner (1) shutdowns are summarized the following:

The control unit (9) switches the safety valve (10) and the blower (2) depending on the heat requirement and the gas pressure in the usual way ("normal Control shutdown ").

a) im Regelvorgang der Regelbereich(RB) bei positiven oder negativen Regelabweichungen länger als eine vorbestimmte Zeit, beispielsweise 5s, verlassen wird oder

b) im Regelvorgang der Maximalwert oder der Minimalwert des Steuersignals(J) länger als eine vorbestimmte Zeit, beispielsweise 5s, erreicht ist oder

c) sich im Kalibriervorgang die Ionisationsspannung(Ui) während der Vorwärmzeit(t2 bis t3) der Ionisationselektrode(5) stark ändert oder

d) im Kalibriervorgang der Maximalwert des Steuersignals (J) erreicht wird oder

e) im Kalibriervorgang das erste oder zweite Übergabekriterium nicht erfüllt wird.

The control circuit (7) performs a control shutdown by opening the switch (12) for a limited time, if

a) in the control process the control range (RB) is left longer than a predetermined time, for example 5s, in the case of positive or negative control deviations or

b) in the control process, the maximum value or the minimum value of the control signal (J) has been reached for longer than a predetermined time, for example 5 seconds, or

c) the ionization voltage (Ui) changes significantly during the preheating time (t2 to t3) of the ionization electrode (5) or

d) the maximum value of the control signal (J) is reached in the calibration process or

e) the first or second transfer criterion is not met in the calibration process.

After a control shutdown, the control automat (9) the burner (1) again.

f) eine mehrmalige, beispielsweise dreimalige, Regelabschaltung nach a erfolgte oder

g) eine mehrmalige, beispielsweise dreimalige, Regelabschaltung nach b erfolgte oder

h) eine mehrmalige, beispielsweise dreimalige, Regelabschaltung nach c, d, e erfolgte.

The control circuit (7) leads to a lockout that can only be remedied by special measures, for example by permanently opening the switch (12), if

f) a repeated, for example three times, shutdown according to a or

g) repeated, for example three times, control shutdown according to b or

h) there was a repeated, for example three, control shutdown according to c, d, e.

The repeated shutdowns are controlled by counters detected. The counters for the control shutdown a, b, or Lockouts f, g, are caused by any "normal Control shutdown "of the control automat (9) reset. The counter for the control shutdowns c, d, e, or Lockout h, is with a valid calibration reset.

The lockout can also be initiated by that the control circuit (7) by means of the gas solenoid valve (4) of the minimum value of the control signal (J) closes. The Contact of the gas pressure switch (11) initially remains closed. The control unit (9) then provides the Line (15) an extinguishing of the burner flame firmly, whereupon he closes the safety valve (10). The tax automat (9) then tries to ignite the burner (1) again, whereby the safety valve (10) is connected to the mains voltage, which also through the line (16) Control circuit (7) is transmitted. The attempt to ignite can not succeed because the gas solenoid valve (4) closed is. After several, for example four, The ignition controller (9) opens in vain attempts to ignite "Fault" and reports "Ignition not possible". The Control circuit (7) counts the ignition attempts of the Control automaton (9) and then opens after a certain one Time, for example 10s after the end of the fourth Try the switch (12) so that the control unit (9) now for safety also the safety valve (10) closes. It is therefore a high level of operational security reached, the existing in the control automat (9) Security features are exploited.

The exemplary embodiment according to FIGS. 9 and 10:

A blower is connected to a burner (1) of a gas heater (2) and a gas line (3) connected in the one Gas solenoid valve (4) as a gas quantity valve. in the Flame area of the burner (1) is one Ionization electrode (5) arranged on a Control circuit (7) is connected. About the Line (6 ') is the signal of the ionization electrode (5) also to those described in more detail below Automatic burner controls (9). In the burner control (9) there is thus the possibility of opening the burner (1) Presence or absence of a flame monitor. The control circuit (7) controls in Dependence on one in the burning operation over the 'Ionization electrode (5) flowing current and a preset lambda setpoint using a Control signal (J), especially control current, the degree of opening the gas solenoid valve (4). The control circuit (7) is for example a digital PI controller that realized, for example, by a microprocessor is. Through the control circuit (7) is a low emissions Combustion, for example with a lambda setpoint between 1.1 and 1.35, preferably at 1.15, guaranteed.

For two or multi-stage or for stepless The fan speed is controlled by an automatic control unit (9) provided, as for example under the trade name "Furimat" is known on the market. Using the control machine (9) a safety valve (10) can be switched on and off, whereas with the gas solenoid valve (4) the gas volume flow is continuously adjustable. At the control automat (9) a setpoint generator (8) connected, one of a Target room temperature and / or one Heating flow temperature and / or one Heating return temperature and an outside temperature dependent signal on the control automat (9).

A gas pressure switch (11) is located in the gas line (3) via the control automat (9) during the burning operation switches off insufficient gas pressure. In the control circuit (7) a switch (12) is integrated, which over the Control unit (9) interrupts the burning operation when the desired lambda setpoint cannot be guaranteed.

Via a line (13), the control automat (9) gives each Switching on an ignition pulse to an ignition electrode (14) the burner (1). On the speed of the fan (2) determining signal is from the control machine (9) via a line (17 ') on the one hand to the blower (2) and on the other hand, placed on an evaluation circuit (18).

The device-specific is in the evaluation circuit (18) Speed, i.e. Power control signal characteristic curve (K) filed. This characteristic curve - regardless of the respective setting of the control circuit (7) - the Connection between the at a respective Fan speed for reaching the desired one Burner output necessary opening degree of Gas solenoid valve (4). The evaluation circuit (18) generates a reference signal according to the characteristic (K) (J '). It detects the change in a circuit part (19) of the reference signal (J ') against the previous one Status. This corresponds to the change in speed Change (dJ ') has a positive or negative impact on you Adders (20) to the control signal (J) as a reserve component. This makes the control signal (J) corresponding to the Speed change parallel to the control circuit (7) to the desired power or the fan speed adjusted.

The gas solenoid valve (4) is one of the desired Change in service approximately corresponding amount further opened or closed. The control circuit (7) must therefore change the desired performance itself do not process. It regulates the respective Power setting the gas solenoid valve (4) to the for a low-emission combustion necessary lambda setpoint.

The reference signal (J ') and that around the reserve component (dJ') changed control signal (J) are sent to a comparator (21) placed. This is connected to a correlator (22) in which is a tolerance band with an upper tolerance limit (To) and a lower tolerance limit (Tu) is stored (see Fig. 2). The correlator (22) detects whether the respective value still within the tolerance band (To, Tu) lies, or migrated outside the tolerance band is. Is the respective value of the reserve share (dJ ') changed control signal (J) from the by Characteristic curve (K) hiked tolerance band, then this is a sign that due to any Malfunctions a low-emission combustion in the desired Dimensions is no longer guaranteed. This can for example on deposits or wear in the Area of the burner (1), the ionization electrode (5), the Fan (2), the gas solenoid valve (4) or air duct or for malfunctions occurring in the electronics or based on gas ratios. Anyway, there is Correlator (22) a shutdown signal in the event of such interference via the line (23) to the control automat (9). This must not immediately at the beginning of the fault. It is preferably only switched off when the Malfunction lasts for a certain time, e.g. 5s.

It can be provided that the automatic control unit (9) after a certain time after switching off the burner (1) starts again. Then the shutdown signal from Correlator (22) several times, for example three times, then the automatic control unit (9) is switched to malfunction, so that the burner (1) only again by service personnel can be switched on.

The functions of the evaluation circuit (18) with the Storage of the characteristic (K), the circuit part (19), the Adder (20), the comparator (21) and the correlator (22) can be implemented in a microprocessor that at the same time the functions of the control circuit (7) takes over.

The characteristic curve (K) is shown in FIG. 10, in which Point I the blower (2) at a speed (D1) for one low power level is running. This corresponds ideally Case - without the necessary by the control circuit (7) Readjustment - a control signal reference signal (J'1). At a higher speed (D2) for a larger one The power level results from the characteristic curve (K) (cf. Point II) corresponding to a reference signal (J'2). Between points I and II the characteristic (K) runs in essentially linear. But this does not necessarily have to be rather, it can also have a kinking curve. This is above and below the characteristic curve (K) Tolerance band with its upper tolerance limit (To) and its lower tolerance limit (Tu). Within the Tolerance limits are that of the control circuit (7) dominant control range. The tolerance band does not have to run symmetrically to the characteristic (K). It can vary the specific device properties also asymmetrical or even spread or according to special functions be defined.

As long as the control signal effective at the gas solenoid valve (4) (J + dJ ') lies within the tolerance band, the Correlator (22) no switch-off signal. Comes this value however at the speed (D1) or the speed (D2) or an intermediate speed outside the Tolerance band, then the shutdown signal is initiated.

The exemplary embodiment according to FIGS. 11 to 14:

There is a gas burner (1) for a gas heater Gas line (3) connected in which a switchable and adjustable gas valve (4), for example solenoid valve, lies. At the gas burner (1) are an air connection (2 ') and possibly an air-promoting, speed-controllable Blower (2) arranged. The blower (2) is not in everyone Case necessary; it can also be one act atmospheric gas burner.

One protrudes into the flame area of the gas burner (1) Ionization electrode (5). On the ionization electrode (5) is a via a capacitive coupling element (27) AC voltage, preferably the mains AC voltage (U), activated. The coupling element (27) consists of a Capacitor and a resistor. The coupling link (27) is connected via a resistor (28), like the gas burner (1), electrically to earth.

At the ionization electrode (5) is a voltage divider (29) connected to the voltage that occurs, for example, reduced by a factor of 10. With the Voltage divider (29) is connected to a filter (210) the frequency of the coupled AC voltage (50 Hz) sieves.

At the outlet (211) of the filter (210) is burning Flame an ionization signal (ionization voltage Uio), as shown for example in Figure 12. The The ionization signal inevitably fluctuates accordingly flickering flames (fluctuations in Flame intensity) around an average (M). in the Fluctuation curve occur weaker one after the other Fluctuations caused by the bandwidth (S1) in Figure 12 are indicated, and stronger fluctuations due to the bandwidth (S2) are shown in Figure 12.

Apart from that, the bandwidth changes to Dependence on the lambda value, which is described in DE 195 02 901 C1 is described.

An example of a decreasing temporal is in FIG The course of the mean (M) is shown, which is at a change in the excess air (lambda value) of the the respective combustion process and the respective lambda value is proportional.

At the output (211) there is a first function block (212), the the fluctuations caused by the flickering rectifies or filters that at the output (213) of the first function block (212) the above average (M) is available.

The output (213) of the first function block (212) is on second function block (214) downstream, the one around the mean (M) lying amplitude tolerance band generated, the width of which is denoted by B in FIG. The tolerance range (B) is such that it is smaller than the smallest bandwidth (S1) Fluctuations.

The output (215) of the function block (214) is at one Comparator function block (216), on which the Exit (211) is. The comparator function block (216) is on the output side. at a reset input of a Timer (217) which is based on a control device (218) for the gas valve (4) acts. Such a control device (218) is common as a "burner control".

In the context of interest here, the Control device (218) only the output signal of the Timer (217) in a shutdown signal for the Convert the gas valve (4).

The comparator function block (216) constantly compares whether an amplitude fluctuation in the ionization signal (Ui) occurs that the amplitude tolerance band (B) over or falls below. Such an amplitude fluctuation occurs on, the comparator function block (216) inputs Reset signal to the timer (217).

The timer (217) is activated by each reset signal of the Comparator function blocks (216) set to zero and then starts counting again and again. Is that on Timer (217) preset duration, for example 5 s, has expired and is not in this period Reset signal occurred, then the timer (217) a gas shutdown signal to the controller (218) that then the gas valve (4) closes. The said The time period is set in such a way that undisturbed burner operation an amplitude fluctuation of the Ionization signal occurs safely. To the It is also possible to avoid making the sensitivity too high be provided that the gas valve is only switched off if some, for example two or three Sequence of gas cut-off signals.

a) Im regelmäßigen, ungestörten Brennerbetrieb, wenn also die Flamme vorliegt, erkennt der Komparator-Funktionsblock(216), daß die Amplitudenschwankungen auftreten und daß diese das vorgegebene Toleranzband(B) über- bzw. unterschreiten. Dies geschieht unabhängig von der jeweiligen Höhe des Mittelwerts(M) des Ionisationssignals, was wichtig ist, weil sich das Ionisationssignal, d.h. dessen Mittelwert(M), im normalen Brennerbetrieb ändern kann, wobei eine solche Änderung nicht zu einer Sicherheitsabschaltung führen soll. Der Komparator-Funktionsblock(216) gibt bei jeder Amplitudenschwankung immer wieder ein Rücksetzsignal an den Zeitgeber(217), bevor die an diesem eingestellte Zeitdauer abgelaufen ist. Es tritt also ein Gasabschaltsignal nicht auf.

b) Erlischt die Flamme, dann liegt kein Ionisationssignal vor, so daß der Komparator-Funktionsblock(216) kein Rücksetzsignal erzeugt. Dementsprechend läuft der Zeitgeber(217) ab und gibt bei Erreichen der eingestellten Zeitdauer ein Gasabschaltsignal an die Steuervorrichtung (218). Das Gasventil(4) wird geschlossen.

c) Besteht in der Einrichtung bei brennender oder nicht brennender Flamme ein Defekt, beispielsweise in der Ionisationselektrode(5), deren Anschlußleitung oder den sonstigen Einrichtungen(27 bis 216), der zu einem dem Ionisationssignal(Ui) am Ausgang(211) nur ähnlichen Signal oder dem Ausgang(215) ähnlichen Signal führt, dann erkennt der Komparator-Funktionsblock(216), daß die charakteristischen Amplitudenschwankungen fehlen und gibt kein Rücksetzsignal an den Zeitgeber(217), so daß das Gasabschaltsignal auftritt. Ein Gasabschaltsignal tritt also bei unterschiedlichen Störungen oder Defekten immer dann auf, wenn die Amplitudenschwankungen nicht vorliegen bzw. nicht erkannt werden, oder zwar vorliegen, aber nicht das Toleranzband (B) über- bzw. unterschreiten.

The described device works essentially as follows:

a) In regular, undisturbed burner operation, ie when the flame is present, the comparator function block (216) recognizes that the amplitude fluctuations occur and that these exceed or fall below the predetermined tolerance band (B). This happens regardless of the respective level of the mean value (M) of the ionization signal, which is important because the ionization signal, ie its mean value (M), can change during normal burner operation, such a change should not lead to a safety shutdown. The comparator function block (216) always sends a reset signal to the timer (217) whenever the amplitude fluctuates before the time period set thereon has expired. So a gas shutdown signal does not occur.

b) If the flame goes out, then there is no ionization signal, so that the comparator function block (216) does not generate a reset signal. Accordingly, the timer (217) runs and sends a gas cut-off signal to the control device (218) when the set time period is reached. The gas valve (4) is closed.

c) If there is a defect in the device with a burning or non-burning flame, for example in the ionization electrode (5), its connecting line or the other devices (27 to 216), which is only similar to the ionization signal (Ui) at the output (211) Signal or the signal similar to the output (215), then the comparator function block (216) recognizes that the characteristic amplitude fluctuations are missing and does not give a reset signal to the timer (217), so that the gas cut-off signal occurs. A gas shutdown signal therefore always occurs in the case of different faults or defects when the amplitude fluctuations are not present or are not recognized, or are present but do not exceed or fall below the tolerance band (B).

According to FIG. 11 there is an output (213) Control circuit (219 or 7), such as in the DE 44 33 425 A1 is described. With this it will Gas valve (4) and / or the blower (2) regulated so that different gas qualities and different environmental conditions Combustion at a desired lambda setpoint results.

The control circuit (219) and the components described (29 to 217) can be in a microcontroller or Realize microprocessor. The effort for that Safety flame monitoring is therefore low.

Figure 14 shows a further embodiment schematically. Figure 11 corresponding parts are with the provided there reference numerals. To the gas valve (4) a modulator (220) connected. This modulates the Gas supply to the gas burner (1) so that fluctuations in the Flame intensity result. Such deliberate fluctuations the flame intensity can also be achieved that the air supply, for example by means of the blower (2) (see Fig. 11), is specifically modulated.

These fluctuations specifically modulated onto the flame image form in the undisturbed burner operation in Ionization signal (Ui). One on the modulator (220) matched demodulator (221) detects this characteristic fluctuations. One to the Demodulator (221) connected Flame monitoring circuit (222) monitors whether the from Modulator (220) produces fluctuations in the demodulator (221) occur and gives a gas shutdown signal over the Modulator (220) or directly to the gas valve (4) if the Fluctuations are not recognized by the demodulator (221).

a) Im ungestörten Brennerbetrieb, bei vorhandener Flamme, tritt ein Gasabschaltsignal nicht auf, weil der Demodulator(221) die vom Modulator(220) verursachten Schwankungen erfaßt.

b) Erlischt die Flamme, dann können die vom Modulator (220) verursachten Schwankungen nicht zum Demodulator (221) gelangen. Dies hat zur Folge, daß die Flammenüberwachungsschaltung(222) ein Gasabschaltsignal erzeugt.

c) Bei irgendeinem Defekt im Wirkungskreis Modulator-Gasventil-Flamme-Ionisationselektrode-Demodulator-Flammenüberwachungsschaltung des Systems kommt das Modulationssignal nicht richtig zum Demodulator(221). Es wird dann ein Gasabschaltsignal ausgelöst.

Here too, the principle of operation is as follows:

a) In the undisturbed burner operation, with a flame present, a gas shutdown signal does not occur because the demodulator (221) detects the fluctuations caused by the modulator (220).

b) If the flame goes out, the fluctuations caused by the modulator (220) cannot reach the demodulator (221). As a result, the flame monitoring circuit (222) generates a gas cut-off signal.

c) If there is any defect in the modulator-gas valve-flame-ionization-electrode-demodulator-flame monitoring circuit of the system, the modulation signal does not come properly to the demodulator (221). A gas cut-off signal is then triggered.

The modulation can be continuous or periodic, for example every 5 s to 10 s during one in contrast, a short time, for example 1 s to 3 s, respectively. By periodic modulation ensures that over the burn time seen the Modulation has only a slight influence on the lambda value of the combustion process.

The control circuit (219 or 7) is not in FIG. 14 shown. You can also in this embodiment to be available. The control circuit works with one Microprocessor or microcontroller, then can also this embodiment, the function of the safety flame monitoring simply be integrated into it.

Claims (17)

1. Method of operating a gas burner, in particular gas fan burner (1), wherein a control circuit (7) picks up an ionisation signal (Ui) derived from an ionisation electrode ( 5) disposed in the flame region and the gas-air ratio (lambda I) is adjusted by varying the gas and/or air flow volume supplied to the burner (1) to a lambda reference value > 1 to which a reference value (Uis) of the ionisation signal corresponds, characterised in that a permitted adjustment region (RB) of the ionisation signal (Ui) is established, whose upper limit value (Uio) is smaller than the maximum value (Uim) of the ionisation signal (Ui) and whose lower limit value (Uiu), whilst still ensuring a low-emission operation, is above a final value (Uie) at which combustion is no longer low-emission, and in that the control circuit (7) generates a cut-out signal for the burner (1) if the ionisation signal (Ui) ieaves the permitted adjustment region (RB) for longer than a specified duration, and that if the ionisation signal (Ui) falls short of the lower limit value (Uiu) and if the ionisation signal (Ui) falls short of the reference value (Uis) at a lambda value <1, due to positive feedback of the control circuit (7) the gas flow volume is increased or the air flow volume is throttled, in particular up to the final value (le or Uie), at which combustion is no longer low-emission and upon reaching which a further cut-out signal is generated by the control circuit (7) for the burner (1).
2. Method according to claim 1, characterised in that after the cut-out signal the control circuit (7) re-starts the burner (1) and in that when a series of such control cut-outs occur one after another, the control circuit (7) performs a fault cut-out.
3. Method according to claim lor 2, characterised in that a timer determining the specified duration is reset if the ionisation signal (Ui) returns to the adjustment region (RB) within the specified duration.
4. Method according to one of the preceding claims, characterised in that the final value is a maximum value and/or minimum value of a control signal (J) for the magnetic gas valve (4).
5. Method according to claim 4, characterised in that when the minimum value of the control signal (J) of the magnetic gas valve (4) is reached, this is electronically detected and the burner (1) is turned off by closing a gas safety valve (10).
6. Method according to one of the preceding claims, characterised in that at a start signal for the burner (1) the gas flow volume is increased in a slope-like manner with constant fan speed until the burner ignites and thereafter the gas flow volume is kept constant until the expiry of a specified safety time (T).
7. Method according to one of the preceding claims, characterised in that when an upper threshold value (J1) of the control signal (J) is reached the control circuit (7) switches over to a low reference value (Uisn) of the ionisation signal (Ui) and thereafter, when a lower threshold (J2) of the control signal (j) is reached, switches back to the previous reference value (Uis) of the ionisation signal (Ui).
8. Method according to one of the preceding claims, characterised in that the control circuit (7) switches over at regular intervals to a calibration operation for the ionisation signal (Ui).
9. Method according to claim 8, characterised in that in each calibration operation the control signal (J) for the magnetic gas valve (4) is first set to a value suited for pre-heating of the ionisation electrode (5) and then the control signal (J) is increased until the maximum value of the ionisation signal (Ui) has been passed through and the resultant value is evaluated for calibration.
10. Method according to one of the preceding claims, characterised in that in order to control the gas burner (1) an automatic control device ( 9) with a safety valve (10) and gas pressure control device (11) is provided, and in that the control circuit (7) controls a magnetic gas valve (4) and the cut-out signal generated thereby is applied to the automatic control device (9).
11. Method according to one of the preceding claims, characterised in that an automatic control device (9) controls the fan speed according to the power reference value and in that by means of an evaluation circuit (18), from the respective change in fan speed, a lead component (dJ') for the control signal (J) is generated, wherein, if the fan speed is increasing, the lead component (dJ') varies the control signal (J) in the direction of a larger gas flow volume, and if the fan speed is decreasing, in the direction of a smaller gas flow volume.
12. Method according to claim 11, characterised in that a tolerance belt is defined around a power/control signal characteristic curve, and in that when an actual control signal leaves the tolerance belt, a cut-out signal is generated for the burner.
13. Method according to one of the preceding claims for safety flame-monitoring in a gas burner (1) with the ionisation electrode (5) in the flame region, by means of which during burner operation an ionisation signal (Ui) is derived, characterised in that while the burner is operating, the fluctuations of the electrical ionisation signal (Ui) derived arising from fluctuations in the flame intensity are monitored, and in that when such fluctuations of the ionisation signal (Ui) do not arise, a gas cut-out signal is transmitted.
14. Method according to claim 13, characterised in that the ionisation signal (Ui) is also evaluated in order to adjust the combustion to a lambda reference value (Is).
15. Method according to claim 13 or 14, characterised in that the monitored fluctuations are such fluctuations of the ionisation signal (Ui) as arise from a modulation impressed on the combustion gas and/or combustion air supply.
16. Method according to one of the preceding claims 13 to 15, characterised in that a first function block (12) suppresses or rectifies the fluctuations of the ionisation signal (Ui), in that a second function block (14) in series generates an amplitude tolerance belt (B) around the output signal of the first function block (12), wherein the amplitude tolerance belt (B) is so dimensioned that it is smaller than the ever-recurring amplitude fluctuations in the ionisation signal (Ui), in that the output signal of the second function block (14) and the ionisation signal (Ui) containing the fluctuations are applied to a comparator function block (16), which then sends a reset signal to a timer (17) if an amplitude fluctuation of the ionisation signal (Ui) goes beyond or falls short of the amplitude tolerance belt (B), and in that the timer (17), if it does not receive a reset signal after a pre-set duration, then transmits the gas cut-out signal.
17. Method according to claim 15, characterised in that in the combustion gas and/ or combustion air supply of the gas burner (1), a modulator (20) is disposed, with which a demodulator (21) for the ionisation signal (Ui) is associated, which transmits the gas cut-out signal if it does not recognise the modulation signal.

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