GB2141854A - Gas accident prevention - Google Patents

Abstract

An electrode 8 is mounted so as to project into the flame of a gas burner 7. A voltage is applied to the burner 7 through power circuit 13 and a current passes from the burner 7 to the electrode 8. A fall in this current indicates a fall in the oxygen content of the atmosphere supporting combustion. This current is passed through an amplifier 14 to a decision circuit 15. If the current is outside certain preset limits, it passes through an NAND circuit 16 to operate a buzzer 21 and alarm lamp 22. If the current is within these limits, it passes to an OR circuit 17 and an AND circuit 18 and thence past a gas in use lamp 24 and ventilator 25 to open an electromagnetic valve 3 controlling a passage 2 from a gas cylinder 1 to a cock 5. A vibration detector 19 actuates the valve 3 in the event of an earthquake. A switching circuit 11 and a one shot multi-vibrator 12 control an ignition device 9 for the burner 7. <IMAGE>

Description

SPECIFICATION Gas accident prevention The invention relates to apparatus for preventing accidents such as explosions and poisoning due to the escape of gas from burners.

In the flame of a gas burner, there are ions in a plasma state which migrate in a certain direction and make the flame electrically conductive with a rectifying effect. The generation of the ions is influenced by the oxygen content of the atmosphere supporting combustion. A fall in oxygen content reduces conduction, and is utilized in apparatus according to the invention to cut off the gas supply.

Apparatus according to the invention comprises an electrode mounted so as to project into the flame of a gas burner, means for applying a voltage to the burner, means for detecting a fall in electric current passing from the burner to the electrode, and a valve actuable by the detecting means for cutting off the supply of gas to the burner.

The apparatus may also include a vibration detector, and means for actuating the valve to cut off the gas in the event of vibration due to an earthquake.

The valve preferably comprises an electromagnetic coil having a core fast on a valve member and slidable with respect to a permanent magnet on actuation of the valve.

Drawings: Figure lisa schematic diagram of apparatus according to the invention; Figure 2 is a more detailed diagram of a power supply circuit 10 in Figure 1; Figure 3 is a similar diagram of a switch 4 in Figure 1: Figure 4 is a similar diagram of an alternating current power circuit 13, an amplifier 14 and a decision circuit 15 in Figure 1; Figure 5 is a similar diagram of an alternative direct current power circuit 13 and amplifier 14for Figure 1; Figure 6 is a schematic diagram of a vibration detector 19 in Figure 1; and Figure 7 is a section through a valve 3 in Figure 1.

With particular reference to Figure 1, a propane gas cylinder 1 is shown feeding through a passage 2, a valve 3, a switch 4 having a knob 6, and a cock 5, a gas burner 7. The cylinder 1 is of course for illustration only as it could be replaced by a public service gas supply pipe. An electrode 8 is mounted so as to project into the flame of the burner 7. A power circuit 13 applies a voltage to the burner 7, an amplifier 14 amplifies the current passing from the burner 7 to the electrode 8, and a decision circuit 15 detects a fall in that current. In normal operation,the decision circuit 15 feeds an OR circuit 17, and thus an AND circuit 18 which keep open the valve 3 and operate a lamp 24 indicating that gas is in use, a ventilator 25 and any other devices actuated by the use of gas.If the current passing from the burner 7 to the electrode 8 falls below a level indicating a dangerous oxygen level in the atmosphere supporting combustion, the decision circuit 15 also operates a NAND circuit 16, an alarm buzzer 21 and lamp 22, and causes the valve 3 to be closed. A vibration detector 19 and a gas control board 20 each also actuate the AND circuit 18 to close the valve 3 in the event of an earthquake or unauthorized interference with the gas supply, for example by a child.

The burner 7 is also provided with an ignition device 9 powered by a one shot multi-vibrator 12 fed through a switch circuit 11 from the switch 4. The switch circuit 11 also powers the OR circuit 17 through an i nverter 66. The switch 4 has internal switches S1,S2 and S3 for ON, OFF and ignition conditions, and is powered through a circuit 10 as is shown in more detail in Figure 2.

Turning now to Figure 2, the power supply circuit 10 comprises a mains electric plug 23 coupled to a transformer 28 through a fuse 26 and a switch 27.

Diodes 29 and a condensor C1 complete the mains power circuit, but a battery 30, a resistor R3 and a diode 60 provide an alternative secondary source of power, the battery 30 normally being charged by the mains. The outputs of the transformer 28 are connected to the anodes of thyristors SCR1 and SCR2, the cathodes of which are connected through resistors R1 and R2 and a start switch 63 to high potential. Manual operation of the start switch 63 sets switches S4 and S5 to ON, and puts a constant voltage through a safety device 61 to an output terminal 62. In the event of a mains power cut, the battery 30 supplies the output terminal 62, but when the mains power supply is restored, the valve 3 is not opened until the start switch 63 has been manually operated.

Figure 3 shows in more detail the connection of the switches S1, 52 and S3 in the switch 4. They are connected on the input side to a terminal 31 through resistors R4, R5 and R6, and on the output side respectively to terminals 32, 33 and 34. The ignition switch S3 is connected through the terminal 32 to an input terminal 35 of the one shot multi-vibrator 12.

The terminal 35 leads to an inverter 36, a resistor R7 and an inverter 37. Before the inverter 37, the circuit is earthed through a condensor C2. The inverters 36 and 37 feed an AND circuit 38, and so produce at an output 39 of the vibrator 12 a pulse signal of a width determined by the time constant of the resistor R7 and the condensor C2. These pulse signals actuate the valve 3 and the ignition device 9 which produces a spark discharge while the gas is flowing from the valve 3 to the burner 7. Thus when the cock 5 is moved to the ignition position, one pulse signal is produced from the vibrator 12, and the ignition device 9 will ignite gas in the burner 7. It is best if the ignition device 9 discharges sparks sychronized with the end of the pulse signal if the distance between the valve 3 and the burner 7 is long.

In Figure 4 alternating current is supplied to an input terminal 40 of the power circuit 13. This is fed to a primary coil of a transformer 46 by an oscillator circuit comprising inverters 41,42 and 43, transistors 44,45, resistors R7, R8 and a condensor C3. An amplified alternating current is induced in the secondart coil of the transformer 46 through a resistor R9 between an earth terminal 59 and an out terminal 64 leading to the burner 7 shown with a gas flame F. A weak current of from 3 to 9 mA flows at from 10 to 79 V between the burner7 and the electrode 8. This is amplified by the amplifier 14 and fed to the decision circuit 15.The amplifier 14 has an input terminal 47 connected to the electrode 8, whence the current is transformed by a resistor R10, smoothed by a condensor C4, and amplified by a buffer amplifier or differential amplifying circuit 48 and lead to an output terminal 49. The decision circuit 15 has an input terminal 50 leading to a pair of variable resistors 52, 53 connected in series and to a power input terminal 51. The output of the variable resistors 52,53 is coupled respectively to comparator circuits 54,55, the comparator 54 setting a standard current valve as a low limit, and the comparator 55 an upper limit for the variable resistors.The comparators 54,55 are each individually coupled to the input terminal 50. The output of the comparator 54 is connected to one side of an AND circuit 57, and that of the comparator 55 through an inverter 56 to the other side of the AND circuit 57 so that the output at a terminal 58 is only present when the signals are below the lower limit value or above the upper limit valve set by the variable resistors 52,53. The output of the terminal 58 is connected through the OR circuit 17 and the AND circuit 18 to the valve 3. It is also coupled to the NAND circuit 16 and the alarm indicators such as the buzzer 21 and lamp 22.

The alternative DC power circuit of Figure 5 is shown as consisting of the power circuit 13 and amplifier 14, and including the secondary coil of the transformer 46. The differential amplifier 48 and resistor R10 are also shown. A diode 65, smoothing condensor C5, and resistor R11 are also shown. The condensors C4, C5 buffer sudden changes in current due to transient effects such as wind.

The vibration detector 19 in Figure 6 comprises a base 67 and three mutually perpendicular flexible strips 68 each ending in a plate 69 and having a strain gauge 70 secured thereto. The strain gauges 70 comprise a thin layer of copper, nickel or silicon on a sheet of plastics material or paper which changes in resistance on distortion or bending. The strain gauges 70 and a resistor R18 are connected to a power input terminal 76 and amplified by differential amplifier circuit 71,72 to eliminate comparatively slow voltage changes such as those due to temperature variations by passing them through a time constant circuit consisting of a condensor C6 and a resistor R1 2. The amount of amplification is determined by resistors R13, R14, and amplified signals are obtained at the output of the circuit 71.The signal is synthesized by the diodes 77,78 with that passing through a phase inversion circuit comprising resistors R15, R16 and the amplifying circuit 72, and reset the input of a flip-flop 73 which provides the input of the pulse signal for ignition. The distortion gauges 70 react when the detector 19 is vibrated. If the peak voltage exceeds the input voltage of the flip-flop 73, the flip-flop 73 is activated and keeps an output terminal 74 at a low voltage unless another pulse signal for ignition is received.

The terminal 74 is connected to an input of the AND circuit 18, and closes the valve 3 and shuts off the gas supply even if the flame F continues burning.

The flip-flop 73 has a further terminal 75, and is connected through diodes 77, 78.

The valve shown in Figure 7 comprises a housing 100 having a gas inlet 102 and outlet 103 separated by a seat 104 and controlled by a valve member 110.

An electromagnetic coil 108 has a core 114 fast on a stem 111 of the valve member 110. The coil 108, and with it the valve member 110, are slidable with respect to a permanent magnet 106 mounted on a magnetic substance 107 and surrounded buy a permanent magnet 105. At a lower end of the permanent magnet 106 is a magnetic substance 121, and below that a coil spring 109 contacting an upper end of the valve member stem 111. The permanent magnet 105 is surrounded by an outercase 112. The coil 108 is powered from terminals 115 which pass through seals 120a, 120b on wiring inserts into the valve housing 100.Upper and lower parts of the housing 100, and a base cover 124, are held together by screws and sealed by means of packings 119a, 11 9b and 11 9c. In the lower part of the housing 100, a diaphragm 116 extends across a branch of the gas outlet 103, and has fast thereon distortion gauge 117. The gauge 117 is connected to electric terminals 118 to give a signal output indicative of gas pressure.

Spaces 122 and 123 respectively surround the gauge 117 and coil 108.

The permanent magnet 105 generates a magnetic field having lines of force normal to the valve seat 104. The permanent magnet 106 has as one pole the magnetic substance 107 and as the other the magnetic substance 121. The passage of electric current through the coil 108 serves to raise the valve member 110, and the spring 109 to lower it and shut the valve. If the passage of electric current in either direction is used to raise and lower the valve member 110, the spring 109 can be omitted. The distortion or strain gauge 117 functions in the same way as the strain gauges 70 of Figure 6 to produce a signal indicative of outlet gas pressure.

Reverting to Figure 3, the output terminal 33 of the switching circuit 11 is connected to one end of the NAND circuit 16 in Figure 1, while the output terminal 34 is connected to the OR circuit 17 through an inverter 66. Thus in a two-burner gas range, one only of the burners can be used, and the apparatus remain effective. Two electrodes 8 as shown in Figures 4 and 5 can be used, one operating on alternating and the other on direct current so as to ensure complete control of the valve 3.

In operation, the cock 5 is moved from the closed to the ignition position, the switch S3 is set to ON, and the valve 3 is opened. A pulse signal operates the ignition device 9. If the ignition should fail for some reason to produce a flame F, the valve 3 remains open only for a length of time corresponding to the width of the pulse signal, and will not stay open even if the cock 5 is held in the ignition position although it usually returns to the closed position when released due to spring pressure. The electric current flowing from the burner 7 to the electrode 8 depends upon the burning conditions, and if it is outside the set limits, the decision circuit 15 closes the valve 3 and stops the gas supply. The NAND circuit 16 operates the buzzer 21 and alarm lamp 22.

Vibration due to an earthquake produces a low level output at the terminal 74 of the detector 19, and closes the valve 3 through the AND circuit 18. At night, or when the apparatus is not in use, the control board 20 can be set, and the AND circuit 18 will not produce a signal to open the valve 3 and so prevents abuse for example by children. When the gas is no longer used, and the cock is closed to stop burning, the output signal from the decision circuit 15 is at a low level and closes the valve 3.

Claims (4)

1. Apparatus for preventing gas accidents which comprises an electrode mounted so as to project into the flame of a gas burner, means for applying a voltage to the burner, means for detecting a fall in electric current passing from the burner to the electrode, and a valve actuable by the detecting means for cutting off the supply of gas to the burner.

2. Apparatus according to claim 1 which includes a vibration detector, and means for actuating the valve to cut off the gas in the event of vibration due to an earthquake.

3. Apparatus according to claim 1 or 2 in which the valve comprises an electromagnetic coil having a core fast on a valve member and slidable with respect to a permanent magnet on actuation of the valve.

4. Apparatus for preventing gas accidents substantially as herein described with reference to the drawings.