The present invention relates to the setting of the working 5 point of a burner, especially burners for the heating of houses, where a flue gas detector is used for generating a

-> signal in relation to the CO concentration in the flue gas from the burner, and where the signal is transmitted to an electronic control unit for establishing a working point 10 for the burner in an area with low CO concentration in the gas.

From EP-0 0 156 958 Bl it is known to establish a working point by laying a straight line through two fixed, defined

15 values on the CO axis. The working point is chosen as the point on the lambda axis where the straight line through the two defined CO values intersects the lambda axis. This method is well suited for adjustment when a theoretical curve is used, which is shown in the figures in the EP

20 document. In practice the CO curve will have a course where also with an excessive air flow there is an increasing CO generation at incresing air flow. The EP document mentioned does not take this into consideration, and the regulating system will increase the air flow with increasing CO. If

25 the burner is at the opposite side of the minimum of the CO curve, the increased air flow will result in increased CO generation. This leads to increased air flow etc. The combustion will take place with a fully open damper, and thereby with an excessive air flow.

30

Even if the regulation takes place on the "right" side of the curve, the method is unsuitable in that at a relatively flat CO curve whose minimum lies close to the lower, fixed i, CO value, the intersection of the vertical line will be

35 transposed away from the optimum working point, and the burner will work with an air flow that is far too great, without this being established. The CO curve does not remain constant, but it varies when the burner parameters

are changed. This may be due to changes in the jet, deposits, change of oil type, or change of thermostat setting. The EP document quoted does not take into account that the curve may be transposed during operation, and therefore the method involves a general risk that the working point is set with excessive air flow. In addition to the efficiency being thereby reduced, an excessive air flow also causes increased pollution.

The object of the invention is to achieve a method of regulation which can be used on various types of burners, and which can establish and work in the optimum working point regardless of the course of the CO curve.

This is achieved by a setting of the burner of the type mentioned in the preamble by

1) varying the flow of combustion air stepwise, and for each step is recorded an expression of the CO concentration in a memory circuit together with an identification of the vlo e, indicating the actual air flow and/or fuel flow,

2) establishing the working point of the burner by retriev¬ ing in the memory circuit various delta values for flow identification and comparing the corresponding delta CO values with a previously determined ideal delta value for the CO generation, and defining the working point as one of the two CO values which are linked to the delta value for CO generation that is the closest to the ideal value, and

3) regulating the burner to the established working point by regulation of the air flow and/or fuel flow to the CO value of the working point, and during continued operation to maintain the CO value by regulation of air flow and/or fuel flow.

Hereby it is achieved that the working point is established optimally regardless of the course of the CO curve. This is an advantage because the CO curve of a burner often devi¬ ates considerably from an ideal, theoretical curve. The use

of delta values for flow identification and CO value allows a very fast calculation of the working point in e.g. a microprocessor. The delta values are defined as the dif¬ ference between two actual values. By comparing delta values for flow identification with delta values for CO concentration the working point can be established with certainty, where the CO generation changes very quickly. When the working point has been found, the burner is regul¬ ated to this working point, and during operation the burner is maintained at the working point by maintaining the value found for CO generation for the working point, and regul¬ ated the air flow and/or the fuel flow, so that the CO value is maintained. Thereby the variations in the burner which are caused by climatic variation, such as changes in wind velocity. With the ideal placing of the working point it is achieved that the burner functions with optimum effi¬ ciency. At the same time a number of environmental advant¬ ages are achieved.

The establishing of the working point can take place with advantage with fixed delta values for flow, which have been fixed at a level that allows compensation of irregularities at the values stored in the memory circuit, and the working point is chosen as the lower of the two CO values generated at the fixing of the working point. Hereby it is achieved that sharp breaks on the recorded charactereristic as well as any noise peaks that may have disturbed the fixing of the curve in the memory circuit, are compensated in a simple and certain manner. Hereby it is avoided that the working point is fixed erroneously at an accidental peak on the recorded curve. If a defined value of the change of air flow is used for calculating the working point, it is expedient to define the working point where the magnitude of the change of air flow is equalled by the corresponding change of CO. Here it is necessary to make the choice of either using the upper or the lower value for air flow for establishing the working point. Since the object of the

invention is to work with the lowest possible generation of CO, the higher of the two values for air flow is chosen, but the system can also be used if the higher of the two values is chosen.

The invention can be embodied by fixing the working point automatically when operation is started, while the burner is working in the established working point until a change takes place or one or several parameters are exceeded, after which the determination of the working point is repeated. Hereby it is achieved that parameter variations are compensated for before they gain any important influ¬ ence on the combustion process. The burner characteristic will change slowly in step with e.g. changes in the jet. Therefore a new fixation of the working point must occur after a short or long period. However, one or several para¬ meters may have changed, such as the thermostat setting, which may lead to a change of the working conditions of the burner. It is therefore expedient automatically to effect a new fixation of the working point at the next starting of the burner. At the same time the flue gas detector will continuously monitor among other things the CO concen¬ tration in the flue gas, and if extreme values or devia¬ tions should occur in excess of what may be expected in the actual measurements, the system will automatically carry out a fixation of the working point at the next start of the burner.

The control system is with advantage equipped with a counter, which counts the number of burner starts, and which when a predetermined number of burner starts is ex¬ ceeded, carries out a new fixation of the working point at the next burner start. It is hereby achieved that the determination of the working point is carried out auto- atically, also if no deviations should be recorded. In this manner it is possible to compensate for the very small variations occurring from one burner operation period to

the next. At the same time the number of burner starts is a parameter which is easily accessible to the control system, and in a simple, economical manner it is possible, e.g. in running a programme, to carry out a determination of the working point when needed.

Advantageously a determination of the working point can be carried out every time the supply voltage to the burner has been interrupted. It is hereby achieved that the working point is fixed from scratch evey time the system has been serviced. At the same time it is ensured that burner systems which during a summer period are replaced by elec¬ trical hot water heating, automatically regulate the work¬ ing point to an optimum at the start of the new heating period.

Hereby the user may activate the control system so that at a subsequent burner start a new determination of the work¬ ing point is carried out. Hereby it is achieved that the user has the possibility of demanding determination of the working point when in his opinion there is a need for this. An example of a need for new determination that the system has no possibility of monitoring is when oil is filled into the tank of an oil burner. Without the user's knowledge there may have been a change of oil type. It is therefore essential that at oil filling a new determination of the working point takes place.

If the burner works continuously, the control system moni- tors the time and/or the degree of load, carrying out renewed determination of the working point at intervals determined by the control system. It is hereby achieved that the regulation system can be used advantageously with gas burners where the flame burns continuously. The output of the burner may be regulated by regulating the gas flow in relation to the actually required output. If the working point is changed slowly due to variations in the gas input

it is necessary to carry out determination of the working point at fixed intervals. However, the burner load may also influence the shift of working point by the fact that combustion products are deposited in burner and flue duct. Jets used for gas will slowly change at normal use. It is therefore an advantage to combine operation period with degree of load in the calculation of the intervals for new determination of working point.

It is advantageous that the flue gas detector should be placed directly in the flue duct, and that there are means of cleaning the flue gas detector, and the cleaning can be carried out at intervals determined by the control system. It is hereby achieved that a relatively low cost flue gas detector can be used, which has no need of filtering and cleaning of the flue gas before the flue gas is passed on to the flue gas detector. Clening of flue gas may be ef¬ fected by heating it to a higher temperature than the operating temperature. Hereby any unwanted compounds and particles are removed from the flue gas detector. If the cleaning of the flue gas detector occurs in operation intervals, this will in no way be disturbing to the normal operation of the system.

Furthermore it is advantageous if the control system has another counter, counting the number of burner starts, and which after a fixed number of burner starts performs the cleaning of the flue gas detector. It is hereby achieved that in a simple manner the control system is able to commence cleaning of the flue gas detector before deposits on it may cause measuring errors proper. At the same time the control system will be allowed in connection with all normal determinations of the working point to commence with cleaning the flue gas detector.

It is expedient that the control system should have means of monitoring fault conditions, which when a fault is

detected transmit a fault signal, and which in the case of faults choose the last known working point. It is heresy achieved that if faults should occur in the flue gas detector or elsewhere, the last known value for deter in- ation of the working point is chosen, because it must be assumed to be the most suitable one for continued opera¬ tion, until the system can be serviced. If the fault is caused by a flue gas detector, the system may for example perform a cleaning of the detector and examine whether acceptable results are then obtained.

It is an advantage that the control system carries out continuous monitoring of the flue gas detector, and at burner starts a pre-ventilation period is used for control- ling the values from the flue gas detector. It is hereby achieved that before burner start it is ensured that there is an active flue gas detector, and by controlling in the pre-ventilation period it is ensured that the CO detector measures correctly at low CO concentrations, because in the pre-ventilation period it is reasonably certain that there are no other combinations of gases in the flue gas duct that may disturb the CO measurement.

Principally it has been ensured that at starting the control system chooses an air flow and/or a fuel flow that differs from the calculated working point, and after a determined operating time is regulates the air flow and/or the fuel flow to the determined value. It is hereby achieved that at burner start it is possible to operate with either a too small or a too large air flow. It is therefore possible to let the burner start take place optimally, because the burning parameters may be different in a cold and a hot combustion chamber. It is therefore very advantageous to regulate to the optimum working point only after a determined period.

Apparatus for setting the working point of a burner, espe-

cially for burners for houses, where a flue gas detector is used for generating a signal in relation to the CO concen¬ tration in flue gas from the burner, and where the signal is transmitted to an electronic control unit for determin- ation of a working point for the burner in an area with low CO concentration in the flue gas, in that

1) The burner has means of regulating the flow of cumbust- ion air and/or fuel εtepwise, and for each step an expres¬ sion of the CO concentration is recorded in a memory cir- cuit together with a flow identification, which indicates the actual flow of air or fuel,

2) The working point of the burner is determined by searching in the memory circuit for various delta values for flow identification, and comparing the corresponding delta CO values with a pre-determined ideal delta value of the CO generation, and the working point is defined as one of the two CO values attached to the delta value of CO generation that is closest to the ideal value, and

3) The burner is regulated to the determined working point by regulation of the flow of air and/or fuel to the CO value of the working point, and during continued operation the CO value is maintained by regulating the flow of air and/or fuel.

It is hereby achieved that the working point of the burner is optimally determined regardless of the course of the CO curve of the burner. At the same time the optimum determin¬ ation of the working point means optimum burner efficiency, and at the same time environmental advantages are thereby obtained in that the flow of unburned hydrocarbons in the flue gas is minimal, while at the same time the CO content in the flue gas is maintained at a very low value. By main¬ taining during operation the CO value defined in the work¬ ing point, the advantage is achieved that parameter vari- ations in the burner are compensated for without shifting the working point. Another advantage of the apparatus described is that it is possible to install flue gas

detector and control electronics together with a flow identification unit in an air/fuel supply system, so that the invention can also be used on existing plant, which require a minimum of modifications.

At a possible exa plary embodiment the air flow is regul¬ ated by means of a damper, based on signals from the elec¬ tronic control unit, and the electronic control unit re¬ ceives signals indicating the flow identification from a damper regulating unit. A simple method of air flow regu¬ lation is hereby achieved. Correspondingly is is relatively simple to install a flow identification unit on a damper. A distinct advantage of the damper regulation is that the method can be used at modification of existing burners. However, the flow regulation can also be achieved by speed regulation of the blower unit of the burner. Hereby the flow identification can be derived directly from a speed indication from the blower.

The flue gas detector can be placed with advantage direct in the flue gas duct, and the flue gas detector consists of a CO sensor with a built-in heater element and a tempera¬ ture sensor. It is hereby achieved that a relatively simpel and low-cost flue gas detector can be used, which does not require filters or other flue gas cleaning equipment. To allow the CO sensor to work it is necessary that it is heated to operating temperature, and therefore a heating element is built into the CO sensor. At the same time there is a temperature sensor in the CO sensor unit to allow te - perature control in the flue gas duct.

The control system has means of regulating and maintaining a defined temperature in the smoke gas detector. It is hereby achieved that the temperature of the CO sensor is maintained within a specified temperature range regardless of the conditions in the flue gas duct. In the flue gas duct there may be considerable temperature differences

between the operating period of the burner and the stand¬ still period of the burner. It is therefore necessary to have a control system that takes care of this temperature regulation.

The invention is explained in more detail below by means of drawings showing in

fig. 1 an exemplary embodiment of a burner which is regulated by the method indicated,

fig. 2 two possible courses of CO generation in relat¬ ion to air flow and regulation according to the state of the art,

fig. 3 the same two curves, but indicating a regulation according to the present invention, and

fig. 4 an exemplary embodiment of the electronic control unit.

Fig. 1 shows a combustion chamber 1, which is supplied with fuel from a fuel flow regulation unit 2 through a fuel supply line 3. Correspondingly two starting electrodes 4 are shown, which are in connection with the electronic control unit 13. 5 indicates a connection to a fuel storage or a fuel source. The drawing also shows a fuel vapori¬ sation or atomisation unit (7) , which is placed in the combustion chamber 1, and the purpose of which is as far as possible to ensure that the fuel supplied is evaporated in the combustion chamber 1. An air supply unit with air flow regulation 8 supplies through air supply duct 9 the com¬ bustion chamber 1 with combustion air. The air is drawn from an air induction duct 10. In the flue gas duct 12 there is a flue gas detector 11, which is connected to the electronic control unit 13 via the signal wire 14. The elec-

tronic control unit 13 is connected via the signal wire 15 to the air supply unit 8, and via the signal wire 16 the electronic control unit 13 is connected to the fuel flow regulation unit 2. The electronic control unit 13 is also connected to display 17, which can show the operating con¬ ditions of the burner regulation system. Correspondingly there is connection to the electronic control unit 13 from a keyboard 18, which can be used for indication of inform¬ ation to the burner regulation system. A thermostat 19 is also connected to the electronic control unit 13. A burner regulation as shown in fig. 1 may operate in the manner that at starting the characteristics are first determined by running through the procedure that the burner is started with excessive air from the air supply unit 8. The air flow is recorded in the electronic control unit 13, and at the same time the CO content in the flue gas is recorded from the flue gas detector 11. By slowly changing the air flow via the air supply unit 8 and at the same time continuously make recordings from the flue gas detector 11, and storing the values for air flow together with the corresponding CO values in a memory unit, a characteristic of the burner is recorded. Then the electronic control unit 13 performs a calculation of the values of the recorded curve. This takes place by comparing the air flow changes with the changes in the CO generation in the flue gas. In the point where a change established by the system corresponds with the pre¬ determined CO content determined by the system, the working point is chosen. Then the air supply unit 8 is regulated to this working point, and the combustion now takes place in this working point, while the flue gas detector 11 monitors the CO content of the flue gas. The CO concentration is maintained in the working point by regulation of the air flow and/or the fuel flow.

Determination of the working point in the electronic con¬ trol unit 13 is performed with a certain minimum value for change of air flow. This is done in order to compensate any

breaks on the recorded curve while at the same time in this manner to compensate for any noise deviations. At the same time it is achieved that the working point will not be de¬ termined on an accidental peak or on a far too sharp break on the course of the curve. When the corresponding values for air flow change and CO content change have been found, the electronic control unit 13 automatically chooses the lower of the two air flow values that have been compared with the CO changes. Hereby a small CO generation in the flue gas is obtained.

The electronic control unit 13 monitors the number of burner starts, and after a number of burner starts deter¬ mined by the system a new determination of the working point is performed. However, changes may have occurred of burner parameters, either by a change of thermostat setting 19 or because extreme values have been arrived at, e.g. from flue gas detector 11. If the invention is to be used for an oil burner it is necessary by change of oil type to carry out a new determination of the working point. There¬ fore there is a keyboard 18, from which the user may demand a new fixation of the working point. The system will auto¬ matically perform a new determination of the working point if the supply voltage to the burner unit has been inter- rupted. In this manner it is ensured that in the case of service of the plant the working point will be optimally determined.

The flue gas detector 11, which is installed direct in the flue gas duct 12, can be chosen as a type that can be installed direct in the flue gas duct 12 without requiring filtering. It is possible to use a flue gas detector 11, which is sensitive to several gas components at the same time, but since the CO generation changes very much around the optimum working point, it is possible to exploit with advantage the fact that the detector changes its signal values substantially in the area around the ideal working

point. Changes of other parameters that influence the de¬ tector at the same time are very small in this area. There¬ fore it is possible to use a relatively simple, low-cost flue gas detector. Mounting direct in flue gas duct 12 has the disadvantage, however, that unburned hydrocarbons and sulphur compounds will collect on flue gas detector 11. It is therefore necessary to clean the detector, and this can be done by heating the detector to a temperature which is higher than the normal operating temperature. It is pos- sible in this manner to burn away all polluting particles from the surface of the flue gas detector 11. Therefore there is in the electronic control unit 13 a counter that counts the number of burner starts, and which, when a defined number of burner starts is exceeded, performs a cleaning of flue gas detector 11 during a subsequent operation pause. If the regulation system is used for con¬ tinuous operation, the cleaning of the detector can be performed with fixed time intervals.

Fig. 2 shows a coordinate system where CO values are shown in relation to the air flow. Two curves 20 and 21 are drawn, where curve 20 is a theoretical curve known from the state of the art. Curve 21 is a corresponding CO curve, but of a shape occurring often in practice. In fig. 2 there is a tentative representation of how the regulation will occur on the two curves if the regulation is performed according to the state of the art. According to the state of the art the working point is found by drawing a straight line through two fixed points on the CO curve. The state of the art states that these two points may be for example 25 and 50 ppm. Then a straight line 26 or 27 is laid through the two fixed values on the CO curve. The working point is chosen as the air flow that corresponds to the intersection of curve 26 or 27 with the air flow axis for CO = 0. In this manner the working point 22 appears on the theoretical curve, and the working point 23 on the practical curve. It is shown here that if a regulation system chooses an air

flow corresponding to working point 23, the combustion takes place with an inappropriately large air flow.

Fig. 3 shows the same system of co-ordinates as fig. 2 with the same two curves 20 and 21. It is indicated here how the working point is found by using fixed changes of the air flow and measuring the corresponding changes in the CO generation. It appears that if the regulation takes place on curve 20, a change of air flow of a magnitude as indi- cated by 28 will cause a CO change as indicated by 33. In the same manner an air flow change 29 will cause a CO change 34. The air flow change indicated by 30 causes a CO change 35, and this change corresponds to the value fixed by the system, after which the working point is chosen as the higher of the two air flow values that have been used for fixing the change on the CO axis. This is how the work¬ ing point 24 is determined. Correspondingly it appears from fig. 3 that an air flow change 31 corresponds to a very large change in CO 36. In order to make the drawing reason- ably clear, curve 21 shows only the air flow change cor¬ responding to the correct CO change as defined by the system. This air flow is shown here by 32, corresponding to a CO change 37. The working point is chosen as already stated, and as designated here by 25. Now if working point 25 is compared with the working point 23 shown in fig. 2, the implication of the invention sketched is understood, because the working point is chosen correctly regardless of the course of the CO curve. In fig. 3 it can also be seen that the working point 24 has not been shifted very much in relation to working point 25. Both points lie approximately at an optimum on the curves sketched.

Fig. 4 shows an exemplary embodiment of an electronic con¬ trol unit 13, which can be used for the regulation method specified. The block diagram is built up from a number of input units 11, 39, 40, 41, which shall perform signal con¬ version and amplification of the signals received. Then

there is an arithmetic unit 47 with memory 6, and there are output units 17, 49, 50, which perform signal conversion and amplification of the signals required for regulation of air supply unit 9 and fuel regulation unit 2. At the same time a display 17 is indicated, which can communicate to the system user. Also shown is a safety system 48, which monitors any fault conditions in the individual electronic modules.

Here follows a detailed explanation of fig. 4, which shows a flue gas detector 11, here indicated as a CO sensor. This flue gas detector also contains a heater element, which is connected with a temperature regulation unit 38, the pur¬ pose of which is the maintenance of a predetermined tempe- rature in the flue gas detector 11. At the same time the temperature regulation unit 38 has the function that when cleaning of the flue gas detector 11 is required, it in¬ creases the temperature in the flue gas detector 11 until the flue gas detector 11 is cleaned of sulphur compounds and any hydrocarbon compounds which may be deposited on the detector 11. The measuring signal from the flue gas detec¬ tor 11 is taken via a signal wire 14 to a signal amplifier and signal converter 45.

Also in fig. 4 a flue gas temperature sensor 39 is shown, which is also connected to signal amplifier and signal converter 45. Correspondingly, two input modules 40 and 41 are indicated, which process signals from air supply unit and fuel supply unit, giving feedback about the supplies of fuel and/or air supplied at any time. These signals are also sent to signal amplifier and signal converter 45.

Fig. 4 also shows a burner control unit 42, which contains the high voltage generator for the ignition electrodes 4. The burner control unit 42 is connected via a galvanic separator 43 to the safety system 48. There is another connection from the galvanic separator 43 to the arithmetic

unit 47. The arithmetic unit 47 is also connected to the signal amplifier and signal converter 45. Likewise, the arithmetic unit 47 is connected to the temperature regu¬ lator unit 38. The arithmetic 47 is fed from a time control unit 46 with the required time dependent signals. The arithmetic unit 47 has also connection to memory 6. The memory unit is necessary for storing the recorded charac¬ teristic of the burner process and possibly for inter- storage of data from the arithmetic unit 47.

The arithmetic unit 47 has a number of shown outputs, which are connected to signal converter and amplifier units 49, 50. Here a signal converter 49 is shown, which converts and amplifies the signals to the air supply unit 9. Similarly a signal converter 50 is shown, which performs processing and amplification of signals to fuel regulation unit 2. The arithmetic unit 47 is also connected to a control panel, which contains display 17 and keyboard 18. The display 17 is equipped with a number of signal lamps and an analog display which can show the actual condition. On the display panel there is a keyboard 18 with a number of pushbuttons, which can be used for example by the user for new deter¬ mination of working point. A current supply unit 44 pro¬ vides supply voltages for the various modules. The safety system 48 monitors fault conditions, and if faults should occur this is communicated to the display and on to a pos¬ sible alarm unit 51.