EP0197334A1 - Circuit to control a fuel-heated heat source - Google Patents

Abstract

Circuit to control a gas-heated circulating water heater with a relay, the coil of which is connected to an operating voltage via at least one resistance, there being arranged parallel to the coil (15) of the relay both a capacitor (21) and a switch (23) of an air deficiency safety device, a second switch (11/12,30) lying in series with the relay coil (15) in such a manner that the relay has a self- holding circuit (12/13) and that the latter during self-holding separates the relay coil from the capacitor and from the switch (23) by means of the second switch, a third switch (17) being arranged in series with the relay coil (15) and it being possible to pick up a signal for the freeing of the fuel path (3) directly at the connections (7, 8) of the second switch (11/12 or 30). <IMAGE>

Description

The present invention relates to a circuit for controlling a fuel-heated heat source according to the preamble of the main claim.

Such circuits can be used with any type of fuel-heated heat sources, such as water heaters, circulating water heaters, boilers or absorption heat pumps, regardless of whether they are fired with gas or oil. In the case of blower-assisted devices in particular, there is a requirement to ensure that the blower has started before the fuel path is cleared and that the air throughput necessary for the respective combustion is guaranteed.

The present invention is therefore based on the object of specifying a circuit with which the start-up of such a fan can be monitored and the presence of a proper air throughput can be ensured. In the case of fanless devices, the task is accordingly reduced to the presence of a proper air throughput, which of course is then only forced by the burner and its thermal lift.

The problem is solved with the features of the characterizing part of the main claim.

Further refinements and particularly advantageous developments of the invention are the subject of the subclaims or emerge from the following description which explains 5 exemplary embodiments in more detail with reference to FIGS. 1 to 6.

• Figur 1 eine erste Schaltung,
• Figur 2 eine zweite Schaltung
• Figur 3 eine dritte Variante zu den Schaltungen gemäß Figur 1 und 2 und
  die Figuren 4 und 5 weitere Varianten, die alle bezüglich des Grundprinzips gleichwertig, hinsichtlich spezieller weiterer Anforderungen allerdings unterschiedliche Bedeutung aufweisen,
• Figur 6 zeigt ein Ausführungsbeispiel einer Logikschaltung gemäß Figur 4 und Figur 5.

Show it:

• FIG. 1 shows a first circuit,
• Figure 2 shows a second circuit
• Figure 3 shows a third variant of the circuits of Figures 1 and 2 and
  FIGS. 4 and 5 further variants, all of which are equivalent in terms of the basic principle, but have different meanings with regard to special further requirements,
• FIG. 6 shows an exemplary embodiment of a logic circuit according to FIG. 4 and FIG. 5.

The circuit according to FIG. 1 is a gas-heated water heater with an atmospheric burner 1, which lies in the course of a gas line 2, which is controlled by a valve 3 that is opened or closed by an electromagnet 4. This electromagnet 4 is integrated in a line 5. The line 5 leads to a first branch point 7 and to a second branch point 8. From the branch point 7, a line provided with a resistor 9 leads to a positive operating voltage + UB and a further line 10 leads to a contact 11 of a changeover switch 12, the root of which is connected to the Junction 8 is connected. The other contact 13 of the switch 12 is part of a line 14 which is also connected to a positive operating voltage UB. From the branch point 8, a line provided with a relay coil 15 leads to ground 18 via a collector-emitter path 16 of a transistor 17. The transistor 17 is operated as an electronic switch, and can therefore also be represented by a further relay contact. The control electrode 19 of the transistor is connected via a line 20 to a device which emits a signal for starting the water heater. The changeover switch 12 is actuated by the relay coil 15. Furthermore, a relay 26 is actuated by the relay coil 15 via the operative connection 27, which in turn actuates a switching contact 25 via the operative connection 28. Instead of a contact 25, a controllable semiconductor switch can also be used.

The branch point 7 is connected to ground 18 via a capacitor 21, an anemometer contact 23 being connected in parallel via a line 22. Instead of a contact 23, a controllable semiconductor can also be used. The contact 23 is actuated in any case when an air throughput sufficient for the fuel throughput from the burner 1 is determined in the supply line or exhaust line. Any other air flow meter can be used instead of an anemometer. The switch contact 25 is connected in parallel to the anemometer contact 23 via a line.

The present invention has for its object to monitor the proper functioning of this contact 23 or its technical equivalents. It can be assumed here that this monitoring cannot take place during ongoing operation of the heat source or at standstill, but only when the state changes, with the change in state of the contact 23 being monitored. It is essential for the circuit that both the anemometer contact 23 such as the capacitor 21 and the coil 15 of the relay are parallel to one another, the coil 15 in turn being in series with a switch 17 and the branch Junction point 7 can be decoupled from the relay coil via a switching contact 11 and the coil 4 of the gas solenoid valve is parallel to this contact 11/12.

To operate the circuit according to FIG. 1, the following must be carried out, starting from the idle state (contacts 23 and 25 open, changeover switch 12 on contact 11, coil 15 de-energized, switch 17 open, solenoid valve de-energized):

The presence of positive operating voltage + UB leads to charging of the capacitor 21 via the resistor 9, provided the switches 23 and 25 are open, but this is the case when the combustion air is not flowing due to the extinguished burner and the uncontrolled timer 26. The electronic switch 16 is blocked so that the coil 15 cannot be energized and the solenoid valve 4 cannot be opened. The level of the resistance value of the resistor 9 is dimensioned such that neither the solenoid valve 4 and the relay 15/12 can be switched on or off via the resistor. On the other hand, the resistor 9 must be dimensioned as small as possible in order to enable the capacitor 21 to be charged quickly. If the capacitor 21 is charged and the electronic switch (17) is turned on by a corresponding signal on the line 20, both the capacitor 21, which is now discharging, and the additional current flow through the resistor 9 cause the coil 15 to be energized and thus activated Switching the changeover switch 12 to the contact 13. This first switches off the pull-in path for the coil 15, and on the other hand switches a latching circuit for this coil, in that the latching now takes place via the line 14 and the contact 12/13. It is assumed that the relay in FIG. 1 completes the switching process that has started once, despite opening contact 11, that is, contact 11 only opens after contact 13 closes. The relay now remains in this switching state for as long as electronic switch 17 is conductive. Simultaneously with the switch 12 being switched over, the timer 26 is actuated via the active connection 27, with the result that the switch 25 is closed for a specific delay time via the active connection 28.

Now the coil 4 is excited by + UB via line 14, via contact 12/13, point 8, line 5, point 7, line 24 and contact 25, which is now closed. After the delay time initiated in the timer expires, the contact 25 opens again. If sufficient air throughput has occurred due to the fuel escaping from the burner 1, which is ignited, and the resulting thermals, the contact 23 of the anemometer has now been actuated and takes over the line connection for the opening, parallel-connected contact 25.

If there is not sufficient air throughput, the anemometer contact 23 does not close and the solenoid valve is closed again when the contact 25 is opened.

The solenoid valve 4 or the relay 15 can only be de-energized with sufficient air throughput by the disappearance of the control deviation signal on the line 20. With each new start of the circuit or each time the burner is started, a change of contact of the contact 23 is urgently necessary and also monitored, since otherwise the capacitor cannot be charged when the contact 23 remains closed, but this in turn is a prerequisite for the excitation of the coil 15 . The energization of this coil and thus the switching of the switch 12 are in turn a prerequisite for a current flow through the magnet 4 of the valve 3.

In the exemplary embodiment according to FIG. 2, the circuit has been modified to the extent that the changeover switch 12 has been replaced by a pure make contact in connection with a diode 30. This diode is in the forward direction from point 7 towards point 8. If the polarity between UB and ground is reversed, the diode must be switched in the reverse direction. The same applies to the polarity of transistor 17.

In the exemplary embodiment according to FIG. 3, a resistor 40 is looped into the line 20 and the relay 15 is provided with an additional normally open contact 41 which is looped into the line 5 of the electromagnet 4. The line 5 runs from the branch point 7 via the electromagnet of the solenoid valve and the contact 41 at + UB.

This circuit has the advantage that a malfunction of the transistor 17 can also be monitored, since in this embodiment the energy requirement of the latch circuit is taken from the control signal on the line 20. After actuation of the associated latching contact 13, the coil 15 receives its excitation energy via the path of the transistor 17, the contact 13 and the line 42.

The exemplary embodiment according to FIG. 4 relates to a gas-heated circulating water heater with combustion air supply or removal via a fan. The difference to Figures 1 to 3 is that there is no automatic air supply due to thermals. This means that the anemometer contact remains open without fan control, but that on the other hand a proper air supply and thus closing the anemometer contact is a prerequisite for enabling the fuel path. The anemometer is therefore not operated indirectly by the thermal of the burner, but by a separate blower motor. A point of charge meter 53 is connected to point 7 via a resistor 52 located in a line 51, and is connected on the other side via a line 54 to a logic 55, the output line 56 of which is connected to the base 19 of the transistor: 17. Another input 57 of logic 55 is connected to a connection point 58 which is connected to the emitter of transistor 17, a resistor 59 being situated between the latter and ground 18. A controller 61 is connected to the collector of the transistor 17 via a line 60, with which a motor of the fan 62 can be started, which is responsible for the combustion air supply to the burner 1, which runs in a channel 63, in this channel the anemometer 64 is provided. In the course of line 5, a normally open contact 6 is additionally provided, which can be actuated by a controller 65. It is closed when the burner is to be switched on. The logic 55 has a further input line 66, which is connected to the controller 65 once and is connected to the normally open contact 13 via the line 42.

With regard to the function of the circuit according to FIG. 4, it should be noted that the line 66 to the logic 55 leads to a signal which serves to prepare the start-up of the heat source and which leads the actual burner switch-on signal on the active line 67, in particular in order to ensure, for example, the air throughput and the purging times. This signal can also be used to ventilate the combustion chamber.

• Unter der Voraussetzung, daß, zurückgreifend auf Figur 3, ein Einschaltsignal auf der Leitung 20 erfolgt, bevor der Kondensator 21 geladen ist, so kann die Relaisspule 15 nicht erregt werden, da durch das Einschalten des Tansistors 17 über die Leitung 60 gleichermaßen ein Ein schaltsignal an die Steuerung 61 des Gebläses 62 gelegt wird, was infolge der sich im Luftkanal 63 einstellenden Luftströmung das Nichtöffnen des Anemometerkontaktes 23 bewirkt. Um das auszuschließen, wird über den Ladezustandsmesser 53 die Spannung des Kondensators 21 erfaßt und ein Betätigen des elektronischen Schalters 17 erst dann zugelassen, wenn ein für das Anziehen des Relais ausreichender Ladezustand des Kondensators erreicht ist. Das Einschalten der Relaisspule 15 führt aber zu einem Stromfluß im Widerstand 59 und damit zu einem Spannungspotential am Punkt 58, womit über die Leitung 57 der Logik 55 ein Signal zugeführt wird, durch das die von der Ladekontrolle 53 des Kondensators abgegebenen Signale hinsichtlich ihrer Auswirkung auf den elektronischen Schalter 17 unwirksam gemacht werden. Es wird nämlich, da über die Leitung 60 der Lüfter mittlerweile angelaufen ist, durch Einschalten des Kontaktes 23 des Anemometers der Kondensator entladen, wobei die Ladezustandskontrolle 53 über die Leitung 54 wieder ein Sperrsignal abgibt, das nach erfolgtem Relaisanzug jedoch unwirksam bleiben muß. Durch entsprechende Beschaltung der Steuerung 61 wird sichergestellt, daß der Lüfter 62 nur dann anlaufen kann, wenn der Transistor 17 leitend geworden ist . Nunmehr kann durch Betätigen des Schalters 6 die Wärmequelle durch Öffnen des Gasventils in Betrieb gehen.

The function of the circuit according to Figure 4 is as follows:

• Provided that, based on FIG. 3, a switch-on signal occurs on line 20 before capacitor 21 is charged, relay coil 15 cannot be energized, since switching on transistor 17 via line 60 likewise causes a switch-on signal is placed on the controller 61 of the fan 62, which causes the anemometer contact 23 not to open as a result of the air flow occurring in the air duct 63. To rule this out, the voltage of the capacitor 21 is detected via the state-of-charge meter 53 and actuation of the electronic switch 17 is only permitted when a sufficient state of charge of the capacitor has been reached for the relay to be energized. Switching on the relay coil 15, however, leads to a current flow in the resistor 59 and thus to a voltage potential at the point 58, with the result that a signal is supplied to the logic 55 via the line 57, through which the signals emitted by the charge control 53 of the capacitor relate to their effect the electronic switch 17 are made ineffective. It is namely, since the fan has meanwhile started up via line 60, the capacitor is discharged by switching on the contact 23 of the anemometer, the state of charge control 53 again issuing a blocking signal via line 54 which, however, must remain ineffective after relay activation has taken place. Appropriate wiring of the controller 61 ensures that the fan 62 can only start when the transistor 17 has become conductive. The heat source can now be operated by opening the gas valve by actuating the switch 6.

In the exemplary embodiment according to FIG. 5, the circuit is modified in that the resistor 9 is split into two resistors 70 and 71 and the line 51 is connected to the connection point 72 of both resistors. The resistor 52 is omitted, the charging voltage control 53 is connected directly to + UB via a line 73. The advantage of this circuit lies in the fact that, in contrast to the exemplary embodiment according to FIG. 4, in which both resistors 9 and 52 must be designed to be short-circuit proof, only resistor 71 need be designed to be short-circuit proof.

The circuit 53 is designed such that it acts as a Schmitt trigger and switches off only when a certain voltage drop across the resistor 71 is exceeded, that is to say gives a switch-off signal on the line 54 and only switches on again as a switch-on voltage value when there is a smaller voltage drop across the resistor 71.

FIG. 6 shows the exemplary embodiment of a logic circuit 55, which on the one hand has the task of preventing the switching on of the transistor 17 when the relay 21 is not activated and the capacitor 21 is not sufficiently charged, but on the other hand it blocks the switching off of the transistor 17 when the capacitor 21 is discharged once it has been tightened . In this way it is ensured that the fan is switched off and remains on when the relay has dropped, for example by briefly interrupting the heat request signal on line 20. After the mechanical run-on time of the blower has expired, the anemometer 64 again reports a lack of air, that is to say the Switch 23 opens. Only then are the prerequisites for a new start-up given, including charging the capacitor, switching on the relay and controlling the fan.

It is also conceivable to provide the logic circuit with a further input 87, at which a signal can be fed in which leads to the transistor 17 being switched off. This input is connected to the anemometer output - (23) with the interposition of an edge-triggered timing element, so that a short switch-off pulse is switched to the base of the transistor 17 when the contact 23 is opened. With this measure, after an air deficiency message (23 opens), a renewed start-up is forced during burner operation, as already explained above.

Claims (20)

1. Circuit for controlling a fuel-heated heat source with a relay which is connected to at least one resistor at an operating voltage, characterized in that both a capacitor (21) and a switch (23) of an air deficiency fuse are arranged in parallel with the coil (15) of the relay are that in series with the relay coil (15) is a second switch (11/12; 30), that the relay has a latching circuit (12/13) and that this latches the relay coil through the second switch from the capacitor and from the switch (23) separates that a third switch (17) is arranged in series with the relay coil and that a signal for the release of the fuel path (3) at the connections (7, 8) of the second switch (11/12 or 30), is immediately decreased. 2. Circuit for controlling a fuel-heated heat source with a relay which is connected to at least one resistor at an operating voltage, characterized in that both a capacitor (21) and a switch (23) of an air deficiency fuse are arranged in parallel with the coil (15) of the relay are that in series with the relay coil (15) is a second switch (11/12; 30), that the relay has a latching circuit (12/13) and that this latches the relay coil through the second switch from the capacitor and from the switch (23) separates that the relay has a second make contact (41) and that a signal for releasing the fuel path (3) between a connection of the switch (23) and the second make contact (41) is removed. 3. A circuit according to claim 1 or 2, characterized in that the circuit has a control input (20) and that the third switch - (17) is a controllable switch which can be actuated by the signal at the control input (20). 4.- Circuit according to claim 3, characterized in that the self-holding circuit of the relay is fed from the control input (20). 5. Circuit according to one of claims 1 to 4, characterized in that the second switch - (11/12; 30) is a controllable (transistor) or non-controllable (diode) semiconductor switch. 6. Circuit according to one of claims 1 to 5, characterized in that a timing element (26) is present, which is actuated by the relay coil (15), and in that a further switch (25) is arranged in parallel with the switch (23) of the air deficiency fuse is actuated by the timer. 7. Circuit according to one of claims 1 to 5, characterized in that a logic circuit - (55) in the control circuit (56) of the switch (17) is provided, which has a signal input (66) for the signal at the control input (20) of the circuit has and further inputs (54, 57) for status signals of the circuit. 8. A circuit according to claim 7, characterized in that a state of charge transmitter (53) is provided for monitoring the state of charge of the capacitor (21) and that the output (54) of the state of charge transmitter is connected to an input of the logic circuit (55). 9. Circuit according to claim 8, characterized in that the state-of-charge transmitter (53) monitors the voltage across the capacitor (21). 10. The circuit according to claim 8, characterized in that the state-of-charge sensor (53) monitors the charging current of the capacitor or the voltage drop across the resistor (9). 11. The circuit according to claim 10, characterized in that the resistor (9) is designed as a voltage divider (70, 71), the output signal of which represents an input signal for the state-of-charge transmitter (53). 12. Circuit according to one of claims 8 to 11, characterized in that the state-of-charge transmitter (53) has Schmitt trigger behavior. 13. Circuit according to one of claims 7 to 12, characterized in that switching means - (59) are provided which emit a signal when the relay is energized, and that the output of these switching means is connected to an input (57) of the logic circuit (55) is. 14. Circuit according to claim 13, characterized in that the switching means (59) consist of a shunt resistor, which is flowed through by the coil current of the relay. 15. Circuit according to one of claims 7 to 14, characterized in that at the output (60) of the . third switch (17) a control signal for a fresh air or exhaust fan (62) is removed. 16. Circuit according to one of claims 7 to 15, characterized in that the control signal for the switch 17 is derived from a voltage divider (82, 84), the divider ratio of which can be changed by a controllable resistor (80). 17. The circuit according to claim 16, characterized in that the control signal for the controllable resistor (80) from a voltage divider - (85, 86) is derived, the parts ratio of which is variable by a controllable resistor (81), the control electrode at an input ( 57) the logic circuit is connected. 18. Circuit according to one of claims 7 to 17, characterized in that the logic circuit - (55) has a further input (87), the actuation of which prevents the third switch - (17) from being switched on. 19. Circuit according to claim 18, characterized in that an edge-triggered further timing element is provided, which is connected to the switch (23) of the air snail safety device and is triggered by opening this switch (23) and its output signal with the input (87) of the logic circuit (55) is connected. 20. Circuit according to one of claims 1 to 19, characterized in that a further resistor is connected in series with the capacitor (21).

Images