EP0175890A1 - Method for generate a switch-off signal of a gas-heated apparatus - Google Patents

Abstract

Method for determining a switch-off criterion of a gas-heated apparatus with atmospheric burner and draught diverter, two temperature sensors being used, which are assigned to the waste gas removal device and to the room opening of the draught diverter and the signals from which act on an actuator of the burner via an evaluating circuit. The ruling criterion for switch-off is a temperature difference which is established depending upon the structural characteristics of the apparatus to be monitored and which is varied according to the parameters of apparatus load and apparatus working temperature. After a circuit for implementation of the method, the two temperature sensors are connected to a summing unit via an adaptor, an inverter being provided in the branch of one of the two sensors and the output of the summing unit forming the input of a comparator, the other input of which is acted upon by a reference voltage, and the output of the comparator being connected to an actuator of the heat source via a timing element. <IMAGE>

Description

The present invention relates to a method for determining a switch-off criterion for a gas-heated device and a circuit for carrying out the method according to the preambles of the independent independent claims.

From DE OS 30 20 228, a gas-heated device according to the preamble has become known, the flow control of which has the aforementioned three outlets or inlets, with a temperature sensor being associated with all three openings of the flow control. The temperature sensors are connected to an evaluation circuit by measuring lines, the evaluation circuit being based on the difference between the measured values of two or more temperatures sensor responds and switches off the heat source if the value falls below a setpoint value. This means that a shutdown is carried out regularly and regardless of the operating state of the device and the required power with a constant difference.

It has now been found, however, that this difference would have to be varied in order to still be able to ensure operation of the heat source even in borderline cases or, on the other hand, to be able to initiate an absolutely necessary shutdown.

Accordingly, the present invention has for its object to provide a method with which the shutdown criteria, which are expressed by a temperature difference, can be set, so that on the one hand, an absolutely safe shutdown takes place in dangerous conditions, but on the other hand, even in borderline cases, safe operation of the fuel-heated Heat source is possible. A fuel-heated heat source is understood here to mean any gas-heated device that works with an atmospheric burner and a flow safety device, be it a boiler, circulating water heater, continuous water heater or oven.

The problem is solved with the characteristic Features of the independent claims.

Further refinements and particularly advantageous developments of the invention are the subject of the subclaims or emerge from the following description, which explains an exemplary embodiment of the invention with reference to FIGS. 1 to 10.

• Figur eins eine Prinzipdarstellung eines Wasserheizers,
• Figuren zwei bis acht Diagramme und
• die Figuren neun und zehn Schaltungen zur Durchführung des Verfahrens.

Show it:

• FIG. 1 shows a schematic diagram of a water heater,
• Figures two to eight diagrams and
• Figures nine and ten circuits for performing the method.

In all ten figures, the same reference numerals denote the same details.

According to FIG. 1, a fuel-heated heat source 1 is provided in an installation room, which essentially consists of a heating shaft 2 with an attached flow safety device 3 and a gas burner 4 arranged on its lower part. The heating shaft 2 consists of a more or less hollow cuboid copper shaft, on the top of which a copper lamella heat exchanger is arranged at five, which is either directly from the tap water or from the heating water in the and return of a heating system, not shown, is applied.

The heating shaft 2 thus has an inlet 6 at the bottom and an outlet 7 at the top, the outlet 7 simultaneously forming an inlet 8 for securing the flow. The flow safety device 3 is designed as an essentially cuboid, hollow sheet metal part tapering in the direction of the rising combustion gases 19, which opens at its outlet 9 into an exhaust duct 10, which leads to a chimney (not shown). The design of the fuel-heated heat source as a fanless or with an exhaust gas blower is independent of this. Instead of an exhaust duct, the exhaust gases can also be discharged directly through a wall box to the outside of the building wall.

Sheet metal inserts 11 for deflecting and deflecting the exhaust gas are provided in the interior of the flow safety device. In addition to the inlet 8 for inflowing gas from the heating shaft 2 and the outlet 9 for exhaust gas flowing out into the exhaust shaft, one or more outlets 12 are arranged laterally, from which exhaust gases can escape from the interior 13 of the flow control 3 into the installation space. Both the outlets 12 and the outlet 9 are either from the outer walls of the flow control 3 or formed by the sheet metal insert 11 or by both.

A first temperature sensor 14, which is located approximately in the space between the sheet metal inserts 11 and is directly assigned to the exhaust gas emerging from the heat exchanger, is assigned to the inlet of the flow control 3 assigned to the heat exchanger 5.

This temperature sensor 14 is connected to an evaluation circuit 16 via a measuring line 15. Furthermore, a side outlet 12, which is provided for the exhaust gas outlet in the direction of the installation space, is assigned a temperature sensor 17, which is also connected to the evaluation circuit 16 via a line 18. The temperature sensor 14 can detect the temperature of the gas flowing from the interior 13 through the outlet 9 into the exhaust duct 10. The temperature sensor 17 can detect the temperature of part or all of the gas which passes through the interior 13 of the flow safety device or leaves this interior through the opening 12.

The temperature sensors 14 and 17 are designed as temperature-dependent semiconductor resistors. They are either thermally insulated on the inside of the outer jacket for flow protection 3 or on the sheet metal inserts 11 attached to have the smallest possible thermal inertia.

The evaluation circuit 16 is connected via a line 20 to an electromagnet 21, which in turn acts by means of an actuating rod 22 on a solenoid valve 23 which is arranged in the course of a gas line 24 which leads to the gas burner 4. The direction of buoyancy of the gases within the heating shaft 2 is indicated by the arrow 19.

To clarify the functioning of the evaluation circuit 16, reference is made to the diagrams in FIGS. Two to five.

A diagram is shown in FIG. Two, the exhaust gas outlet being shown in percent on the abscissa and the temperature difference relating to a reference temperature To being plotted on the ordinate. The percentage corresponds to the ratio between the exhaust gas volume flow exiting at the lateral opening 12 and the total exhaust gas volume flow passing through the inlet 8. There are three curves 30, 31 and 32. The same dependencies are set up in FIG. 3, but here the corresponding curves 33 to 35 are at a lower level. The difference between the two diagrams is that the device performance has been varied. That is the case FIG. 2 shows an appliance power close to the nominal power and in FIG. three an appliance partial power has been assumed. It is the same device. The conditions can be transferred to any other device, the curves will be approximately similar. Curves 30 and 33 occur at the maximum possible flow temperature of the heat source or the maximum possible tap water temperature. Curves 31 and 34 result at a medium flow or tap water temperature and curves 32 and 35 at the lowest possible tap water or flow temperature. In all cases, the temperature difference is the difference between the signals measured by the temperature sensors 14 and 17 and determined in the evaluation circuit 16.

It is clear from the diagrams that, for example, at full load, i.e. in the case of the representation according to FIG. 2, with an assumed or presumed or officially determined exhaust gas outlet percentage of 20% with the minimal device load according to curve 32, a temperature difference of 0.35 ° To is still permissible, at a larger temperature difference, however, must be switched off. To give another example: With a partial device output according to FIG. 3, with an average device load according to curve 34, with a si ₉ viewed exit rate of 10% of the exhaust gas at a temperature difference of 0.30 ° To shutdown.

It follows directly from the above that, if the special device is known, this shutdown can be carried out differently according to the possible parameters, by first specifying a hazardous gas leakage rate, if this is exceeded, and then depending on the load condition of the device (work - or flow temperature) and the degree of load on the device then switches off in detail by setting the associated temperature difference.

From the figure four, which has the same diagram for the content, the curves emerge as curves 36 to 38, specifically with an average load. In this way, it is possible to record intermediate part outputs in addition to the limit value loads (minimum and maximum) and thus to determine the temperature difference when the exhaust gas outlet is set as desired, and if this is exceeded, it must be switched off. This makes it possible to adapt the device series to a wide variety of approval regulations at home and abroad.

Another diagram emerges from FIG represents the absolute sensor temperature in ° C in the ordinate as a function of the exhaust gas leakage rate in percent, whereby a certain flow or tap water temperature was assumed. There are three curves 39, 40 and 41, which run almost parallel to one another and whose distance is determined only by the device power. In this way, curve 39 arises at maximum device output or load, curve 40 at medium device output and curve 41 is assigned to the minimum device output. The curves 39 to 41 appear as a straight line in contrast to the curves 30 to 38 of the figures two to four. It follows from FIG. Five that curve 41 with the lowest absolute values includes low exhaust gas temperatures and thus also low temperature differences. The reverse applies to curve 39, which can be assigned to the diagram according to FIG. This unpredictable relationship leads to the fact that by weighting the family of curves according to the figures two to four, depending on the absolute sensor temperature according to the curves according to figure five, a uniform switch-off criterion, i.e. a clear dependency of the temperature difference on the exhaust gas outlet temperature, can be specified . Based on these inventive considerations, curve 42 according to FIG. Eight could be developed. This curve shows the relationship between the difference of the measurement signals of the sensors 14 and 17 in the ordinate and the exhaust gas temperature in the abscissa. The exhaust gas temperature is measured by the sensor 14 alone. However, the curve assumes that a certain maximum rate of the permissible exhaust gas outlet has been agreed, or in the case of variations in the maximum exhaust gas outlet rate which is regarded as permissible, different curves 42 result. The slope of the curve 42 varies with the change in the exhaust gas outlet rate. The curve 42 has been found by laboratory measurements on a specific device, specifically on the basis of the measurements according to the diagrams in FIGS. Two to four. The curve is almost a straight line. It is essential that two areas 43 and 44 are separated from one another by the curve, it being possible to assume with sufficient certainty that no exhaust gas exit into the installation space takes place in area 43, whereas such an exhaust gas exit takes place in area 44, in accordance with the criteria, as they were previously developed and defined. It is now possible to determine the temperature difference for a specific device, if it is exceeded, it is necessary to switch off the device depending on the absolute exhaust gas temperature.

The essence of simplification from figure eight is to be seen in the fact that the representation of the variation of the temperature difference is now only necessary from the device exhaust gas temperature. There is no separate determination of the device performance or device load and the level of the flow temperature or tap water temperature.

A check shows that the simplification according to FIG. 8 is also possible. The diagrams according to FIGS. Six and seven, which show the dependence of the differential temperature signal or the differential voltage obtained therefrom on the exhaust gas discharge rate, are used as proof. In the diagram according to FIG. Six, the exhaust gas outlet is shown in percent on the abscissa and the output voltage in volts is shown on the ordinate. The curves 45 to 48 shown in FIG. 6 are obtained by subtracting five values from the curves 39 and 40 in FIG. The size of these corresponds to the level of the exhaust gas temperature. The subtracted values increase accordingly with the level of the exhaust gas temperature. This subtraction makes it possible to obtain five correction factors from the differences between the curves 39 and 40 or 40 and 41 of the figure, by means of which the existing differences between the sets of curves in the figures two, three and four are brought to zero. This is only possible for egg NEN point, which is advantageously considered as the point of the maximum allowed exhaust gas rate. It goes without saying that this point cannot be defined as a mathematically exact point, but rather has a permissible spread.

The curve 45 in FIG. 6 represents the dependence of any output voltage in volts, which can no longer be assigned to an absolute temperature or a temperature difference, as a function of the exhaust gas outlet rate, the parameters being the device load and the flow or tap water temperature. While curve 45 is assigned the maximum device load and the highest possible flow temperature, curve 48 is assigned the minimum device load with the lowest flow temperature. The curve 47 is also associated with the minimum device load with the highest possible flow temperature, while curve 46 occurs with the maximum device load and the lowest possible flow or tap water temperature. It turns out, however, that the curves 45 to 48 can be brought almost to a point at a point with about 15% exhaust gas leakage into the room. If you select this point as the switch-off threshold, the fuel-heated heat source is switched off when the voltage threshold is exceeded;

It should be indicated that the point in question of the exhaust gas outlet threshold depends very much on the positioning of the sensors and the structural conditions of the fuel-heated heat source.

The same conditions are plotted in FIG. Seven, only the type of gas has been changed. This shows that the same considerations apply to a wide variety of gases, be it city gas, natural gas with high or low calorific values. If a different exhaust gas exit rate is considered to be just permissible, the weighting of curves 39 to 41 in FIG. Five or curves 30 to 38 of FIGS. Two to four must accordingly be carried out, which inevitably also results in a different position of curves 42. The accuracy of this consideration can be proven by experimental re-measurement, from which other figures six and seven or other curves 45 to 48 with an intersecting point 49 which is shifted as desired, result.

• Zum Vergleich möge die Kurve 30 in Figur zwei in Verbindung mit der Kurve 39 in Figur fünf gelten. Das Ziel ist, von der Kurve 30 in Figur zwei einen solchen Wert zu subtrahieren, daß die Kurve mindestens im Bereich der kritischen Abschaltschwelle der Kurve 33 in Figur drei etwa entspricht. Das zugehörige Subtraktionssignal wird aus der Differenz der Kurven 39 und 41 in Figur fünf gewonnen. Diese Differenz beträgt unabhängig von der Abgasaustrittsrate etwa 45 °C. In der Auswerteschaltung könnte man definieren, daß man die Differenz der aktuellen Ist-Abgasaustrittstemperatur bis zu einer unteren festgelegten und gerätetypischen gespeicherten Größe bildet und diese Differenz mit einem Korrekturfaktor kleiner als eins wichtet und diesen Wert von den Werten der Kurve 30 in Figur zwei abzieht. Das bedeutet, daß man beispielsweise bei hoher Gerätebelastung (Figur zwei) und entsprechend hohen Abgastemperaturen (Kurve 39 in Figur fünf) hohe Korrekturdifferenzwerte bekommt. Das bedeutet andererseits, daß man mit niedriger werdender Gerätebelastung immer kleinere Beträge von den Kurven der Figuren zwei bis vier abzieht. Hieraus resultiert ein quasi Aufeinanderfallen der Kurvenscharen dieser Figuren in einem bestimmten Punkt, der so zu wählen ist, daß dort die maximal zulässige Abgasaustrittsrate auftritt.

The individual weighting is as follows:

• For comparison, curve 30 in FIG. 2 may apply in conjunction with curve 39 in FIG. The goal is to subtract such a value from curve 30 in FIG. 2 that the curve at least in the region of the kri table turn-off threshold of curve 33 in Figure three corresponds approximately. The associated subtraction signal is obtained from the difference between curves 39 and 41 in FIG. This difference is about 45 ° C regardless of the exhaust gas leak rate. In the evaluation circuit it could be defined that the difference between the current actual exhaust gas outlet temperature is formed up to a lower fixed and device-specific stored value and this difference is weighted with a correction factor less than one and this value is subtracted from the values of curve 30 in FIG. This means that, for example, high correction difference values are obtained with high equipment loads (figure two) and correspondingly high exhaust gas temperatures (curve 39 in figure five). On the other hand, this means that with decreasing equipment load, smaller and smaller amounts are subtracted from the curves of the figures two to four. This results in a quasi collapse of the family of curves of these figures at a certain point, which is to be selected so that the maximum permissible exhaust gas leak rate occurs there.

The great advantage of the invention is that it is no longer necessary to record the current device load, which could be achieved, for example, by sensing the position of the solenoid valve. Furthermore, it is no longer necessary to set the amount of the lead or Detect the tap temperature and also feed it to the evaluation circuit.

• Die beioen Meßfühler 14 und 17 geben die registrierten Meßwerte über die Anpassungsstufe 50 und 51 nach Invertierung in dem einen Zweig auf den Summierer 53, wobei die Signaldifferenz auf dem einen Eingang des Komparators 55 ansteht und mit einer Referenzspannung 56 verglichen wird. Die Referenzspannung entspricht in ihrer Höhe der festgelegten Gasaustrittsrate gemäß den Punkten 49 in Figuren sechs und sieben.

The associated evaluation circuit is shown in principle in FIGS. Nine and ten, with FIG. 9 representing the general version and FIG. 10 a specially adapted circuit. In the figure nine, the two temperature sensors 14 and 17 are initially provided, which are connected to adaptation stages 50 and 51 via the two lines 15 and 18. The measurement signals are converted in the adaptation stages, and the measurement value conversion can be different. At the outputs of the adaptation stages 50 and 51 there are voltages which correspond to the temperatures at the sensors 14 and 17 and which are linearly dependent on the measured temperatures, the proportionality factors being different. The output of the adaptation stage 50 is given via a line 52 to an input of a summer 53, while the output of the adaptation stage 51 is connected to the other input of the summer 1 with the interposition of an inverter 54. A comparator 55 is connected downstream of the summer, one input of the summer and the other input of which is supplied with a reference voltage 56. The output of the comparator is connected to a relay 58 via a timing element 57. The circuit of Figure nine works like follows:

• The two sensors 14 and 17 transmit the registered measured values via the adaptation stages 50 and 51 after inversion in one branch to the summer 53, the signal difference being present at one input of the comparator 55 and being compared with a reference voltage 56. The height of the reference voltage corresponds to the fixed gas discharge rate according to points 49 in FIGS. Six and seven.

If it is to be switched off at a different exhaust gas exit rate, in addition to a change in the reference voltage 56, another adjustment in stages 50 and 51 is also necessary, specifically by selecting other coefficients.

The circuit according to FIG. 10 is simplified in that the active elements of the adaptation stages 50 and 51 have been omitted. The sensors 14 and 17 are arranged in a bridge circuit, and the bridge diagonal is given to an operational amplifier 59. The output of the operational amplifier is connected to the comparator 55, which in turn has its output connected to the relay 58. If the relay responds, the fuel-heated heat source is switched off. The reference voltage 56 is through a voltage divider, be standing from resistors 60 and 61, predetermined and is at the other input of the comparator 55. The coefficients of the adaptation stages 50 and 51 according to FIG. 9 are formed in FIG. 10 by the resistor network consisting of the resistors 62, 63, 64 and 65, the resistor 62 being located in the course of the inverting input of the operational amplifier 59 to a connection point 66 , which is on the one hand connected to the sensor resistor 14 and a fixed value resistor 67, while the resistor 63 connects the other input of the operational amplifier 59 to a connection point 68, to which on the one side the other temperature sensor 17 and another fixed value resistor 69 are connected, which together form one Form the branch of the bridge circuit 70, while the other branch is formed by the fixed value resistor 67 with the associated temperature sensor.

The inverting input of the operational amplifier 59 is connected to its output via a feedback resistor 71. The function of the circuit according to Figure ten is approximately identical to that of Figure nine. The reference voltage can be adjusted by varying the value of one of the resistors 60 and 61. The timer 57 is used, especially when starting up the device, to briefly override the switch-off criterion or to ensure in normal operation that only when before are a shutdown condition for a predetermined time the heat source is switched off.

If the heat source 1 is switched on during operation by a signal from a controller, for example a room thermostat or storage thermostat for a domestic hot water tank, then this switch-on command is given electrically on a line parallel to the line 20, so that the electromagnet 21 is energized and the gas solenoid valve 23 is opened. As a result, 6as flows via line 24 to burner 4, where it is ignited and burned by means not shown. It goes without saying that the burning flame is monitored by a thermoelectric fuse or ionization path. The exhaust gas flows through the interior of the heating shaft 2 and the heat exchanger 5 and passes from there via the outlet 7 and the inlet 8 into the interior 13 of the flow control device 3. In normal operating conditions, the exhaust gas leaves the interior 13 through the two paths left and right of the central one Sheet metal insert 11 below the outlet 9 through this in the direction of the exhaust duct 10. Since the amount of gas passing there is greater than the amount of exhaust gas that passes through the heat exchanger 5 due to the train in the exhaust duct, tertiary air is discharged from the installation space of the heat source via the outlet openings 12 Interior 13 of the Flow protection sucked and leaves this interior in the same way as the exhaust gas from burner 4. The temperature of this tertiary air can be between 0 and 40 ° C. The gas flowing in through the opening 8 can be in a temperature range of 150 to 300 ° C.

Claims (9)

1.Procedure for determining a switch-off criterion for a gas-fired device with an atmospheric burner and a heat exchanger and a flow safety device which has an opening assigned to the device, one of the exhaust gas discharge device and one or more openings associated with the installation space of the device, to which two temperature sensors are assigned, the signals of which are transmitted via one An evaluation circuit act on an actuator of the burner, characterized in that, given the structural properties of the device, a temperature difference serves as a criterion, which is varied in accordance with the parameters of the device load and the device working temperature. 2. The method according to claim one, characterized in that sensors (14, 17) for determining the size of the temperature difference are available, which with a gas throughput to the burner (4) varying signal and a device-specific with the temperature (flow, return , Middle and tap water) variable signal is changeable. 3. A method for determining the parameters device load and device-specific temperature, characterized in that the critical temperature difference is variable with the value of the exhaust gas temperature at a predetermined maximum allowable exhaust gas outlet rate. 4. The method according to claim one or three, characterized in that the actual value of the temperature difference is corrected with a factor which is measured according to the difference between the actual device temperature and the lowest possible device temperature. 5. The method according to any one of claims one to four, characterized in that the one exhaust gas temperature sensor (14, 17) is used twice by once for measuring the temperature difference, on the other hand serves to measure the absolute level of the exhaust gas temperature. 6. Circuit for performing the method according to one of claims one to five, characterized in that the two sensors (14, 17) are connected to an adder with the interposition of a matching stage (50, 51), with one of the two sensors in the branch an inverter (54) is provided, and that the output of the summer forms an input of a comparator (55), the other input of which is formed by a reference voltage (56) and that the output of the comparator is connected via a timing element to an actuator (58) Heat source (1) is switched. 7. Circuit according to claim six, characterized in that the adaptation stages (50, 51) carry out different measured value conversions. 8. A circuit according to claim six, characterized in that the two sensors (14, 17) together with fixed value resistors (69, 67) form branches of a bridge and that the bridge diagonal points (66, 68) via correction resistors (62, 63) on the two Inputs of an operation amplifier (59), the two inputs being connected to a reference voltage via bleeder resistors (64, 65). 9. Circuit according to claim eight, characterized in that the output of the operational amplifier is connected via a feedback resistor (71) to the inverting input and that the output of the operational amplifier forms an input of the comparator, the other input of which is provided by a voltage divider (60, 61) is formed.

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