EP0664422B1 - Compound pressure sensor - Google Patents

Abstract

The monitor monitors the relationship between the static combustion fuel pressure and the static combustion air pressure shortly before the bringing together of fuel and combustion air in a combustion heat producer. It has two regulating membranes (4', 6') which, via a lever mechanism with fixed or alterable lever arm ratio, are joined to one another. On one side of the first regulating membrane (6'), the fuel pressure acts and on the second regulating membrane (4'), the combustion air pressure works. On one arm of a weighing beam (8) a spring device (11) and a counter bearing (16) are so arranged that they counteract any possible disengagement of the weighing beam.

Description

The present invention relates to a device for permanently monitoring the relationship between the static fuel pressure p _br and the static combustion air pressure p _l shortly before the combination of fuel and combustion air in a combustion heat generator.

Pressure switches for gas and air pressures are known, for example the "Compact pressure switch for gases and air type GW A4" and the "Differential pressure switch for air type LGW A1" from DUNGS, which are to be set to a defined pressure value and when this is reached Set pressure forward an electrical signal by closing a contact. These pressure switches are not suitable for monitoring a control pressure range.

Pressure sensors that convert the pending media pressure into an analog electrical output signal can be used for the intended application, but must be connected to one another via logic.

This combination of a gas pressure sensor with an air pressure sensor is not the subject of the present invention.

Rather, the present invention relates to the mechanical implementation of a permanent pressure ratio monitoring in which the absolute pressure values are irrelevant. Deviations in the equilibrium of moments, caused by excessive air pressure or excessive gas pressure, should be able to be detected and generate electrical signals which may switch off the combustion heat generator.

In contrast to single-stage combustion, with which a heat requirement is adjusted by switching a fan burner on and off, this only happens very rarely in the case of burners which work in a modulating or modulating manner, since the heat is required by flexibly adapting the heat output of the burner. It is important that the proportions of fuel and the required amount of air are repeatedly controlled in each burner load position so that always one hygienic combustion exists.

Variable outputs are controlled via air volume metering, for example by operating a blower motor at different speeds or by connecting or closing an air damper to a blower when the blower motor is running at a constant speed.

The reference variable for all pneumatic compound controls is the combustion air pressure, which is set in the burner tube after the flap in accordance with the flap position. All compound controls, in which the pressures of the two mixture components air and gas are used as control variables, work on the same principle, regardless of how the two control membranes are spatially assigned to each other and whether they are in a fixed or changeable force-lever arm ratio or not .

Common to all pneumatic compound controls is the possibility of considering the pressures in the combustion chamber of e.g. Boiler so that the pressure difference that is decisive for the mass flow from the burner into the combustion chamber can also be taken into account in the mixture composition.

Static pressures are used to regulate and control the combustion mixture, which are in a fixed, adjusted relationship to one another. The mode of operation of the pneumatic compound control, as is known for example from DE 25 47 075 C3, is based on the equilibrium between the two moments of the forces on the air membrane times the lever arm on the air side and the forces on the gas membrane times the lever arm on the gas side of the balance beam.

The object of the present invention is to present a monitoring device of the type described at the outset, with which not only a defined operating point of the combustion heat generator, but an entire operating range can be monitored, the same gas-to-air pressure settings which should also be comprehensible and which also have a compound control system .

This object is achieved in that the device described at the outset has two control membranes which are mechanically connected to one another and on one side of which the fuel pressure p _br acts in the first control membrane, the combustion air pressure p _l acts in the second control membrane, and with a switching mechanism which is acted upon by one of the two control membranes, preferably by the second, with the combustion air pressure p _l , the switching mechanism emitting a signal to the outside depending on the switching state.

The device according to the invention thus has the great advantage that the ratio between the static fuel pressure p _br and the static combustion air pressure p _l can be permanently monitored, with no additional external auxiliary energy being required. Deviations from a permanently adjusted ratio can be communicated to a user or a corresponding control device via the switching mechanism. Furthermore, it is particularly advantageous that, in the device according to the invention, essential parts of the compound control devices known per se can be adopted directly.

A particularly preferred embodiment of the invention is characterized in that on the other side of the two control membranes, the combustion chamber pressure p _{f of} the heat generator acts. This allows the pressure p _f in the combustion chamber, for example of a boiler, to be included in the permanent monitoring, so that the pressure difference in the mixture composition, which is decisive for the mass flow from the burner into the combustion chamber, can also be taken into account. In this embodiment, the ratio (p _br - p _f ) / (p _l - p _f ) is then monitored. For p _f << p _br , p _l this monitoring ratio changes into the ratio p _br / p _l . Instead of applying the combustion chamber pressure p _f to the room on the other side of the two control membranes, this room can be connected to the atmospheric pressure, so that in this embodiment it is alternatively possible to monitor the ratio p _br / p _l .

The control membranes are preferably subjected to the combustion chamber pressure p _f on their underside, while the burner pressure p _{br is} applied to the top of the first control membrane and the combustion air pressure p _l is applied to the top of the second control membrane. Among other things, this enables geometrically particularly simple pressure feeds.

In a very simple embodiment of the device according to the invention, the mechanical connection of the two control membranes comprises a lever mechanism with a fixed lever arm ratio. The device can then be operated at a specific, predetermined gas / air pressure ratio.

In a somewhat more comfortable embodiment, the lever arm ratio of the lever mechanism can be changed. This allows a desired operating point to be set within certain limits.

A further development of this embodiment is preferred, in which the lever mechanism comprises a balance beam resting on an in particular horizontally displaceable cutting edge bearing. Such a scale construction is particularly sensitive and technically relatively easy to manufacture.

A further development is preferred in which a spring device is provided on one of the two balance arms, preferably on the side of the first control membrane, for balancing the moments and for zero point adjustment of the moment balance on the balance beam. In particular, a spring, preferably the first control membrane, can be acted upon. Such an arrangement allows a characteristic parallel shift in the mixture offered in the burner in the direction of a gas or air excess.

A particularly preferred embodiment of the invention is characterized in that an actuator of the switching mechanism is connected to a control membrane, preferably the second. The actuator then follows the corresponding travel of the control diaphragm, so that the position of the actuator can be used to display the position of the control diaphragm in the switching mechanism. The switching mechanism is preferably designed as an electrical switch.

The switching mechanism preferably has at least two switching states in order to be able to indicate a positive or negative deviation from a set pressure ratio. It is also possible to provide further switching states which permit a finer deviation scaling, as a result of which different displays or reactions are possible according to the deviation amount.

The invention is not only limited to a combustion heat generator, but can in principle be used wherever a certain set pressure ratio is to be monitored or regulated.

Further advantages result from the description and the attached drawing. Likewise, the features mentioned above and those listed further can be used individually according to the invention or in any combination with one another. The embodiment mentioned is not to be understood as a final example, but rather has an exemplary character.

Fig. 1

einen Schnitt durch die erfindungsgemäße Vorrichtung zur permanenten Überwachung des Brennstoff-Verbrennungsluft-Druckverhältnisses; und

Fig. 2

eine schematische Darstellung eines Gasgebläsebrenners mit druckseitiger Luftklappe.

The invention is illustrated in the drawing and is explained in more detail using an exemplary embodiment. Show it:

Fig. 1

a section through the inventive device for permanent monitoring of the fuel-combustion air pressure ratio; and

Fig. 2

a schematic representation of a gas fan burner with pressure-side air flap.

In Fig. 1, 1 shows a device according to the invention for the permanent monitoring of mixture pressures, hereinafter referred to as compound pressure switch, which can be used in a combustion heat generator.

The gas fan burner 50 shown in FIG. 2 can be used as such a combustion heat generator, for example. In this gas fan burner 50, a radial fan 51, shown schematically in FIG. 2, draws in the ambient air and presses the compressed air through an air flap 52 through a flow channel 53 into a combustion chamber 54 of a boiler 55. The constriction, which determines the flow, forms a baffle plate 56 in the flow channel 53, which has a special design for intensive mixing of the air with the fuel gas. In the case of fans which are not speed-controlled, a motor-operated air flap arranged on the suction or pressure side of the fan 51 adjusts the required amount of air.

The blower 51 has the sole task of providing the combustion air in sufficient quantity. The instantaneous volume flow is represented in the flow channel 53 in front of the baffle plate 56 by a static pressure component, which is measured at the tap 58 as a representative measured variable for the air pressure p _l .

According to FIG. 2, the narrowest point for the gas flow is a gas nozzle 59, which can be composed of several individual bores. The pressure gradient determining the volume flow is determined by the static pressure p _br (tap 61) measured in the gas supply 60 in a smooth pipeline and the pressure p _f forming in the combustion chamber 54. The pressure energy contained in both media is used to overcome flow losses and to form a mixture.

When adjusting the gas blower burner 50 with the gas-air composite fitting described, it cannot be determined when adjusting the maximum output whether the gas pressure p _br after the fitting also changes in the selected ratio when the air flap 52 is opened further and thus with increasing air pressure p _l Has. This means that it can happen that the gas fitting was already fully open at an angle of the air flap 52 of, for example, 70 °, so that a further increase in the air flap angle increases the amount of air but not the amount of gas.

In order to prevent this, the gas-air composite fitting of the fan burner 50 is connected to the composite pressure switch 1 according to the invention shown in FIG. 1.

The static pressure of the combustion air p _{1 is introduced} into a first chamber 3 ′ of the composite pressure monitor 1 via an opening 3 formed in the housing 2 of the composite pressure monitor 1. This air-side chamber 3 'is closed at the bottom by a membrane plate 4, on which a control membrane 4' rests. The pressure of the fuel gas p _{br is introduced} into a second chamber 5 ′ of the composite pressure monitor 1 via a second opening 5 in the housing 2. This gas-side chamber 5 'is closed at the same height as the first membrane plate 4 by a second membrane plate 6, on which a control membrane 6' also rests. The combustion chamber pressure p _f prevailing in the combustion chamber 55 of the boiler is passed via a third opening 7 into the space 7 'under the two membrane plates 4, 6. The two chambers 3 ', 7' and 5 ', 7' are each separated from each other by the two control membranes 4 ', 6' resting on the membrane plates 4, 6, whereas the two chambers 3 ', 5' are separated by a partition 2 ' are separated from each other.

The two membrane plates 4, 6 of the same area are arranged horizontally at the same height and are non-positively coupled to one another via a balance beam 8. The two control diaphragms 4 ', 6' are so elastic, for example due to excess material, that they do not hinder the movements of the diaphragm plates 4, 6. The balance beam 8 rests on a displaceable cutting edge bearing 9. Via a support adjustment mechanism 10, the lever arm ratio of the balance beam 8 can be adjusted from the outside via a slotted screw 10 '. If membrane plates 4, 6 do not have the same area, the lever arm ratio is shifted in accordance with the area ratio of both membrane plates 4, 6.

A spring device 11 and a counter bearing 16 are provided on the right arm of the balance beam 8 for balancing the moments on the balance beam 8 and for zero point adjustment of the moment balance. The spring device 11 consists of a bolt 13, which is acted upon by a spring 12 in the direction of the right diaphragm plate 6 and has an enlarged central section 13a. This middle section 13a cooperates with a stop 14 fixed to the housing, as a result of which the movement of the bolt 13 in the direction of the diaphragm plate 6 is limited. The tension of the spring 12 can be adjusted from the outside via an adjusting screw 15 sealed with respect to the chamber 7 '. The counter bearing 16 to the spring device 11 is formed by a bolt 18 acted upon by a spring 17, which engages on the upper side of the right diaphragm plate 6. The prestressing force of the spring 17 can be set in a defined manner from the outside by means of an adjusting screw 15a, which is sealed with respect to the chamber 5 '. The travel of the pin 18 is limited by the fact that its enlarged middle section 18a cooperates with a stop 19 fixed to the housing. The forces of the springs 15, 17 only become effective when the balance beam 8 is deflected, since the spring forces acting on the bolts 13, 18 are absorbed by the stops 14, 19 in the equilibrium position of the balance beam 8, that is to say internal forces are involved.

The two stops 14, 19 fixed to the housing also limit the possible deflections of the balance beam 8 downwards or upwards, the stop 14 interacting with the balance beam 8, the stop 19 interacting with the diaphragm plate 6.

A switching mechanism is coupled to the left diaphragm plate 4. For this purpose, a switching pin 21 rests on the top of the diaphragm plate 4, the upper end and the central section of which each have a thickening 21a, b. The switching pin 21 is subjected to a downward force via a spring 22. Two electrical contact springs 23, 24 can be deflected via the two thickenings 23a, b. The contact springs 23, 24 are acted upon upwards or downwards via the upward or downward arc springs 23a or 24a. In the horizontal position of the balance beam 8, the upper contact spring 23 therefore bears against an upper contact element 25, and the lower contact spring 24 bears against a lower contact element 26.

If the balance beam 8 is balanced, there will be no deflection which causes one of the two spring contacts 23, 24 to switch over. Only a change in the equilibrium will produce a deflection of the balance beam 8, which is sufficient to trigger a switching process of a contact spring 23, 24. If the left diaphragm plate 4 is deflected downward, the upper contact spring 23 is deflected downward against the arc spring 23a via the upper thickening 21a of the switching bolt 21 and comes into contact with a central contact element 27. The contact spring 24 is still in contact with the lower contact element 26. If, on the other hand, the left diaphragm plate 4 is deflected upward, the lower contact spring 24 is deflected upward against the arc spring 24a via the thickening 21b of the switching bolt 21 and in turn comes into contact with the middle contact element 27. The contact spring 23 now remains in contact with the upper contact element 25.

The contacts 25, 26, 27 are guided through the housing 2 to the outside, and the mutually conductively connected contact springs 23, 24 are also guided to the outside via a common line 22, so that the switching state of the switching mechanism 20 and thus the position of the balance beam 8 can be displayed outside the housing 2 via an electrical signal.

In the embodiment of the invention shown in FIG. 1, the fuel pressure p _br acts on the upper side of the left diaphragm plate 4 and the combustion air pressure p _l acts on the upper side of the right diaphragm plate 6. The underside of both diaphragm plates 4, 6 is subjected to the combustion chamber pressure p _{f of} the heat generator. The ratio (p _br - p _f ) / (p _l - p _f ) is thereby monitored via the lever mechanism 8, 9 described above, and both positive and negative deviations from a set ratio can be indicated via the switching mechanism 20 outside the housing 2 or further processable. If, for example, the air pressure component p _l predominates, the composite pressure monitor 1 is out of balance and the spring preload of the spring 17 is overcome, so that the switching mechanism 20 of the composite pressure monitor 1 switches.

The monitoring ratio for p _f << p _br , p _{l changes} into the ratio p _br / p _l . Instead of applying the combustion chamber pressure p _f to the chamber 7 'on the underside of the two membranes 4, 6, this chamber 7' can be connected to the atmospheric pressure, so that in this embodiment an alternative It is also possible to monitor the exact ratio p _br / p _l .

A device 1 for the permanent monitoring of the relationship between the static fuel pressure p _br and the static combustion air pressure p _l shortly before the combination of fuel and combustion air in a combustion heat generator 50 has two control diaphragms 4 ', 6', which are mechanically connected to one another and on one of them Side in the first control membrane 6 'the fuel pressure p _br , in the second control membrane 4' the combustion air pressure p _l acts, and a switching mechanism 20 which is acted upon by the second control membrane 4 'with the combustion air pressure p _l , the switching mechanism 20 each emits a signal to the outside after switching status. The monitoring of the pressure ratio therefore does not require any additional auxiliary energy, and deviations from a fixedly adjusted ratio can be recorded and further processed via the switching mechanism 20.

Claims (6)

1. Device (1) for continuous monitoring of the ratio between the static fuel pressure p_br and the static combustion air pressure p₁ immediately prior to the mixing of fuel and combustion air in a combustion heat unit (50), having two regulation diaphragms (4', 6') which are connected to each other by means of a lever mechanism having fixed or variable lever arm ratio and including a balance arm (8) seated on a knife-edge bearing (9) with the fuel pressure p_br acting on one side at the first regulation diaphragm (6') and the combustion air pressure p₁ acting on the second regulation diaphragm (4'), wherein a spring means (11) and a thrust bearing (16) are arranged at one arm of the balance arm (8) in such a fashion that they oppose possible deflections of the balance arm (8), and having a switching mechanism (20) subjected to the combustion air pressure p₁ by means of one of the two regulation diaphragms (4', 6'), preferentially the second (4'), wherein the switching mechanism (20) issues an external signal in dependence on the switching state.
2. Device according to claim 1, characterized in that, in each case, the furnace pressure p_f of the combustion heat unit (50) acts on the other side of the two regulation diaphragms (4', 6').
3. Device according to claim 2, characterized in that the regulation diaphragms (4', 6') are each subjected to the furnace pressure p_f at their lower sides.
4. Device according to one of the preceding claims, characterized in that the knife-edge bearing (9) is displaceable in a horizontal manner.
5. Device according to one of the preceding claims, characterized in that an actuator (21) of the switching mechanism (20) is connected to a regulation diaphragm, preferentially to the second (4').
6. Device according to claim 5, characterized in that the switching mechanism (20) is configured as an electrical switch (23, 24, 25, 26, 27, 28).

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