GB2170932A - Status indicators for fuel burning appliances - Google Patents

Abstract

In a fuel burning appliance of the kind in which a flame failure safety system includes a thermocouple 16 heated by a pilot flame 12, and wherein a heat sensing switch 26 is located in the thermocouple circuit:- (a) a pilot flame status indicator 62 is driven by a relay contact 68 in dependance upon the voltage at a point 24 in the thermocouple circuit (b) a thermal switch status indicator 66 is driven by a relay contact 7 in dependance upon the voltage at a contact 28 of the switch. In both cases the voltages are sensed by an operational amplifier acting as a voltage comparator, and the output of which is applied to the relay via a buffer amplifier. <IMAGE>

Description

SPECIFICATION Monitoring fuel-burning appliances This invention relates to monitoring systems for fuel-burning appliances of the kind having a main burner, a pilot burner, and a thermocouple adjacent to the pilot burner for sensing the temperature at the pilot burner.

Such appliances include boilers and water heaters for the heating of water, for use as a hot water supply or for space heating purposes or both, where the fuel is gas, though the invention is not confined to use either with boilers or water heaters, or with gasburning appliances. The appliance may be of any kind in which ignition is effected by the use of a continuously-burning pilot flame, and where there is a requirement that the appliance shall be shut down in the event of failure of the pilot flame.

The means employed in such circumstances at present typically comprises an automatic control unit, together with gas valves and flame detection. These components provide an independent monitoring system arranged to close down the gas supply on failure of the pilot or on indication of an overheat situation in the appliance. These conventional systems are somewhat complicated and consequently are themselves subjected to some danger of failure. They are furthermore comparatively expensive.

According to the invention, there is provided a monitodng system for a fuel-burning appliance having a main burner, a pilot burner, and a thermocouple adjacent to the pilot burner for sensing the temperature at the pilot burner, the system comprising an electronic first switching means having an input terminal and an output terminal and being adapted to give an output signal in response to a predetermined first voltage signal at its said input terminal, and a second switching means connected in an electrical circuit of first operating means for operating when pilot flame is lost, a voltage signal output terminal of the thermocouple, and the- second switching means, being respectively connected to the said input and output terminals of the first switching means.

The thermocouple is preferably connected in series with temperature-responsive changeover switching means having an output terminal such that the change-over switching means applies a second voltage signal at its output terminal when the temperature exceeds a predetermined value, such output terminal being connected with an input terminal of an electronic third switching means having an output terminal and being adapted to give a second output signal in response to said second voltage signal, the output terminal of the third switching means being connected with a fourth switching means connected in an electric circuit of second operating means for operating when said temperature exceeds a predetermined value.

Preferably, the said first switching means is an operational amplifier arranged to go high at its output terminal in response to said first voltage signal. The third switching means is preferably an operational amplifier arranged to go high at its output terminal in response to said second voltage signal. The second switching means is preferably a simple relay, providing low-voltage actuation of a circuit at mains voltage for operation of the first operating means.

The first operating means may for example be a warning device such as a buzzer or a bell or a warning light. Alternatively, or as an additional "first operating means", there may be provided an electrical igniter for the pilot flame, arranged on actuation to make a predetermined number of attempts to restore the pilot flame.

The fourth switching means, where provided, may also be a simple relay, again providing low-voltage actuation of the mains voltage circuit of the second operating means.

The latter may again consist of, or include, a suitable warning device; it may also comprise a suitable device whereby, when ,t,he appliance has cooled to or below its maximum permissible working temperature, the main burner is re-ignited automatically. In this connection it is pointed out that the operation of the changeover switching means when the temperature reaches an unacceptably high value will normally automatically cause the fuel supply to the main burner to be terminated, without interrupting the supply of fuel to the pilot burner. Return of the change-over switching means to its normal condition when the temperature is reduced to an acceptable level will not, however, usually of itself restore the fuel supply since this is only safe when the pilot flame is established.

Warning devices, if provided, may include a suitable device for automatically initiating a telephone or telex warning message to a central switchboard or control centre.

One embodiment of the invention will now be described, by way of example only, with reference to the drawing of this Application, which is a schematic diagram illustrating a monitoring system according to the invention for a gas-fired central heating boiler.

The boiler in this example need not be described in detaii. It has a main gas burner 10, ignited by a pilot flame 1 2 at a pilot burner 14 when the main gas valve (not shown) is opened, this being effected in the conventional way in response to the heating by the pilot flame of the hot junction 16 of a thermocouple 18, the cold junction 20 of which is maintained at ambient temperature.

The hot junction 16 and the cold junction 20 of the thermocouple are connected in series with resistive load 22, so as to estab lish an output voltage signal at an output tapping 24 when the hot junction is heated.

Connected between the cold junction 20 and the load 22 is a thermal cut-out switch 26, which is of the normally-closed type but which opens when the surrounding temperature rises above a predetermined maximum acceptable value. The cut-out switch 26 is mounted in a part of the boiler where it will respond to variations in a chosen temperature, such as that of the heated water, so that it opens upon the water becoming over-heated.

The thermal cut-out switch 26 is provided with an additional contact 28 connected to the input 48 of the differential amplifier 36 through a second output terminal 30. The switch is thus in the form of a change-over contact switch whereby the contact 28 becomes connected to contact 26 and draws input 48 to earth hence causing the relay 38 to de-energise.

The monitoring system includes: an electronic first switching means, namely an operational amplifier 32; a second switching means comprising a "lost pilot" relay 34; an electronic third switching means in the form of an operational amplifier 36; and a fourth switching means comprising an "overheat" relay 38.

Each of the operational amplifiers 32 and 36 has a reference voltage input terminal 40 connected through a pair of resistors in a lowvoltage electrical circuit 50 such that the resistors define a predetermined reference voltage at the input terminal 40. The pairs of resistors thus associated with the amplifier 32 are indicated at 42, and those associated with the amplifier 36 are indicated at 44. The resistors 42 may be of different values, and the resistors 44 may be of different values. The amplifiers 32 and 36 need not be identical with each other.

The operational amplifier 32 has a further input terminal 46, which is connected to the voltage signal output terminal 24 of the thermocouple 18. The operational amplifier 36 also has a further input terminal, which is indicated at 48. The terminal 48 is connected with the output terminal 30 of the change over switch 26.

The output terminals of the operational amplifiers 32 and 36 are indicated at 52 and 54 respectively. These are connected through respective simple amplifiers 56, 58 with the low-voltage control coils of the relays 34 and 38 respectively. The "lost pilot" relay 34 is in this example provided with normally-closed contacts 68 arranged to operate a flasher 60 which controls a flashing warning light 62 at mains voltage indicating loss of pilot flame.

The "overheat" relay 38 in this example is provided with normally-open contacts 70 arranged to operate a flasher 64 which controls a flashing warning light 66 at mains voltage indicating that the boiler has become overheated.

In normal operation of the boiler, the change-over switch 26 is closed, i.e. its output terminal 30 is isolated. When the pilot flame 12 is burning and the hot junction 16 of the thermocouple is thereby heated, a voltage is established, via the output terminal 24, at the input 46 of the operational amplifier 32.

This voltage is greater than the reference voltage at the terminal 40 of the amplifier 32, which accordingly goes high at its output terminal 52 so as to cause the coil of the "lost pilot" relay 34 to be energised. In this condition the relay 34 has its contacts open so that the warning light 62 is not energised.

If the boiler is switched on (so that the control circuit 50 is energised), but there is no pilot flame 12, the hot junction 16 will not be heated sufficiently to establish the voltage at the input 46 of the operational amplifier 32 necessary to maintain the coil of the relay 34 energised. Thus, when the boiler is initially switched on, the relay 34 will be in a deenergised condition so that the warning light 62 will glow. This will continue until the pilot flame 12 has been established for a sufficiently long period of time for the coil of the relay 34 to become energised, whereupon the light 62 ceases to operate.

Similarly, if the pilot flame 62 is extinguished (or if it is weak), while the boiler is switched on, the hot junction 16 cools down and causes the signal voltage at the input terminal 46 of the operational amplifier 32 to decrease in value. When this voltage becomes smaller than the reference voltage applied at the input terminal 40, the amplifier 32 cause the coil of the relay 34 to be de-energised, and the warning light 62 consequently glows a warning that the pilot flame has been lost.

When the boiler becomes overheated while the pilot flame 12 is burning, so that a voltage signal appears at the output terminal 30 in the manner already described above, this signal, being of a higher voltage than the reference voltage at the terminal 40 of the "overheat" operational amplifier 36, causes the latter to go high and so to transmit a current to energise the coil of the overheat relay 38. The relay contacts 70 close, and the overheat warning light commences glowing.

This continues so long as the overheating condition persists.

If desired, the relay 38 may be of the kind which requires to be positively reset to the normal open condition of its contact 70, even when the previously-energised relay coil has become de-energised as a result of the boiler temperature becoming reduced so that the cut-out switch 26 reverts to its normal or closed condition.

Claims (2)

1. A monitoring system for a fuel-burning appliance having a main burner, a pilot burner, and a thermocouple adjacent to the pilot burner for sensing the temperature at the pilot burner, the system comprising an electronic first switching means to given an input terminal and an output terminal and being adapted having an output signal in response to a predetermined first voltage signal at its said input terminal, and a second switching means connected in an electrical circuit of first operating means for operating when pilot flame is lost, a voltage signal output terminal of the thermocouple, and the second switching means, being respectively connected to the said input and output terminals of the first switching means.

2. A monitoring system according to Claim 1, wherein the thermocouple is connected in series with temperature-responsive, electrical change-over switching means having an output terminal such that the change-over switching means applies a second voltage signal at its output terminal when the temperature exceeds a predetermined value, such output terminal being connected with an input terminal of an electronic third switching means having an output terminal and being adapted to give a second electrical output signal in response to said second voltage signal, the output terminal of the third switching means being connected with an electrical fourth switching means connected in an electrical circuit of second operating means for operating when said temperature exceeds a predetermined value.

2. A monitoring system according to Claim 1, wherein the thermocouple is connected in series with temperature-responsive changeover switching means having an output terminal such that the change-over switching means applied a second voltage signal at its output terminal when the temperature exceeds a predetermined value, such output terminal being connected with an input terminal of an electronic third switching means having an output terminal and being adapted to give a second output signal in response to said second voltage signal, the output terminal of the third switching means being connected with a fourth switching means connected in an electrical circuit of second operating means for operating when said temperature exceeds a predetermined value.

3. A monitoring system according to Claim 1 or Claim 2, wherein said first switching means is an operational amplifier arranged to go high at its output terminal in response to said first voltage signal.

4. A monitoring system according to Claim 2, wherein said third switching means is an operational amplifier arranged to go high at its output terminal in response to said second voltage signal.

5. A monitoring system according to any one of the preceding claims, wherein the second switching means is a simple relay.

6. A monitoring system according to any one of the preceding claims, wherein the first operating means is a warning device.

7. A monitoring system according to Claim 2 or Claim 4, wherein the fourth switching means is a simple relay.

8. A monitoring system according to any one of Claims 2, 4 and 7, wherein the second operating means is a warning device.

9. A monitoring system for a gas-burning boiler, constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, the drawing of this Application.

10. A gas-burning boiler having a main burner and a pilot burner, incorporating a monitoring system according to any one of the preceding claims.

CLAIMS Amendments to the claims have been filed, and have the following effect: (a) Claims 1 and 2 above have been textually amended.

(b) Textually amended claims have been filed as follows:

1. A monitoring system for a domestic fuel-burning appliance having a main burner, a pilot burner, and a thermocouple adjacent to the pilot burner for directly sensing the temperature at the pilot burner, the system comprising an electronic first switching means having an input terminal and an output terminal and being adapted to give an electrical output signal in response to a predetermined first voltage signal at its said input terminal, and an electronic second switching means connected in an electrical circuit of a first operating means for operating when pilot flame is lost, the input terminal of the first switching means being connected directly into a predetermined point of the thermocouple to receive a voltage signal directly therefrom, and the second switching means being connected to the said output terminal of the first switching means.