GB2045939A - Gas leak detection and shut-off system - Google Patents

Abstract

An electronic system for detecting gas leaks and automatically operating a valve to cut-off the gas flow when a leak reaches a predetermined level comprises a gas sensor S, which has reduced resistance in the presence of a particular gas, is connected to direct current amplifier AC which triggers SCR memory M when the sensor resistance is so reduced. After triggering, the memory energises direct current power amplifier AP, and continues to do so until cleared by push-button P. When energised, amplifier AP shuts off the source of the gas by closing valve EV and also sounds an audible alarm by means of oscillator O. Visual indication of individual leaks is provided by LED D2. <IMAGE>

Description

SPECIFICATION An electronic circuit for the detecting of a gas leak, said circuit automatically operating a valve which closes the gas distribution The present invention concerns an electronic circuit detecting gas and, more generally, toxic gases, smokes, ect.

Sensitive cells are already well known, said cells being sensitive to the gas concentration, i.e. said cells represent detecting means which provide informations about the toxicity degree caused by the leak of any gas. Nonetheless, said cells are not able, once the toxicity degree has been reached, to automatically operate an interruption of the gas flow in due time, as for that a hand operation is necessary, which represents a considerable disadvantage, most of all for what concerns the safety of the persons who are submitted to said leaks.

The aim of the present invention is to realize an assembly which is able, once a certain gas percentage has been determined, to operate, by means of a particular electronic circuit, a valve placed upstream of the gas distribution as to automatically interrupt the flow, said valve remaining in that blockage position even when the gas percentage lowers, as said valve can be operated again only by hand.

Said device, respectively said assembly is realized, according to the present invention, by means of an electronic circuit, essentially consisting in: - a sensitive cell, - a direct current amplifier, - a memory provided with a pushbutton forthe clearing thereof, - a power amplifier in direct current, - an oscillator for an acoustic signal, - an electronically operated valve.

It should be noted that, on the contrary of the conventional applications in other detecting means, in this case a SCR (a controlled diode) is used, replacing the relais, as said relais may, in the stage of the commutation of the contacts, emit some sparks, which in turn might cause detonations of the escaped gas. The SCR, on the contrary, eliminates this inconvenient as no movable contacts are provided, and furthermore allows to store in a memory the alarm condition, as a hand operation is necessary to stop that alarm condition once the SCR has started the operation thereof.

According to the present invention, once the gas concentration has reached a certain degree, the electronic circuit transmits only one impulse to the valve, causing the mechanic blockage of the gas distribution, said valve remaining in that blockage condition even when the gas concentration lowers; said valve can be disconnected only by hand.

The present invention further provides a device for acoustic signals with a loudspeaker, which in turn may be disconnected only by an ad hoc pushbutton.

The advantages of said invention are evident. Said detecting circuit assures the interruption of any gas distribution since the gas leaks reach a certain concentration degree dangerous in the toxicity thereof; the gas flow can be re-established only by hand operating of the valve upstream of the distribution, even if the concentration is very low. The presence of a dangerous concentration can be furthermore signaled by an acoustic device by a loudspeaker which, in turn, may be disconnected only by hand operating of a pushbutton. Finally, the circuit according to the present invention is simple and cheap in the realization thereof and can be applied in houses, factories, everywhere where gas leaks may represent a danger for persons living or working there.

In the following, an embodiment has been shown according to the enclosed drawing, for exemplifying and not limitative purposes, wherein the figures show: figure 1, a schematic view of the assemblies of the main elements of the circuit according to the present invention; figure 2, a detailed view of the circuit according to the present invention, wherein the assemblies of figure 1 are enclosed in dotted lines.

On the drawing (figure 1), S shows the sensitive cell, AC shows the direct current amplifier, M shows the memory provided with a pushbutton for clearing the same, AP shows the power amplifier in direct current, 0 shows the oscillator for an acoustic signal, and EV the electronically operated valve.

Referring to the elements of the circuit according to figure 2, the functioning thereof will be described hereinbelow. It should be noted that on the drawing R shows the resistances, C the condensers and D the diodes.

Sensitive cell S reduces the resistance thereof in the presence of a gas, so that the tension increases at the ends of the slider of the potentiometer R1 (for the regulation of the sensibility of the circuit).

When the tension reaches the value of the threshold of the darlington transistor T1 (around 1, 2 Volts), said transistor enters the conduction and the tension begins increasing, on the sender thereof, from 0 Volts up to positive values. When the tension of the SCR reaches the value necessary for starting the function, said SCR enters the conduction and, consequently, all the units of the circuit depending thereon, start functioning. The SCR must perform two functions: the first one is a trigger function, i.e.

the function of preventing intermediate potentials present on the sender of T1 from reaching successive stages, as T1 functions either at a blockage condition (minimum of tension), orata maximum tension, but not at all in linear conditions. The second function is the one of the memory as, once a tension is present on gateg, and that, consequently, said gate is functioning, even if said tension is lacking, the SCR still remains in the conduction, i.e. said SCR stores in the memory a momentart lack of tension.

Pushbutton P is provided in the circuit with the purpose of clearing the same.

Once the SCR is in the condUction, the base tension lacks on T2 and said T2 passes from a stage of maximum tension to a blockage condition (minimum of tension) cutting off the ground contact and bringing the darlington T3 into a momentary conduction (saturation) (due to C9) by means of the base polarization. The current flow, of a high intensity, on collector T3, operates the valve which interrupts the gas flow, said valve remaining closed even when T3 returns to the interdict position thereof, i.e.

of the minimum tension.

It has been shown how, replacing a relais used according to the conventional applications of similar circuits, in this case a SCR has been used; it must be pointed out that such a replacing has been provided by the present invention as to prevent the formation of sparks which can be caused by the movable contacts of a relais during the commutation. As the SCR does not have any movable contact, the formation of sparks is excluded a priori and, consequently, also the danger of a detonation, which could be caused by said sparks.

The oscillator shown by circuit NE555 starts oscillating as a consequence of the charge and discharge cycle of condensator C7; said succession is however not possible as the charge is not possible as for the ground contact of C7 on the side of T2 by D8; in the presence of gas, as already said, T2 is open and C7 is no more connected in ground contact by D8. In such conditions above cycle may work and the oscillation may take place; said oscillation is amplified by the NE555 which transmits the same, through C8 and R15, to the loudspeaker which, in turn, performs the acoustic transduction thereof.

The LED D2 lights only in the presence of gas, while LED D1 has the function of a signal lamp and diode D12 assures that the current flow takes place only in the direction of the battery towards the circuit and notviceversa.

A circuit assuring the charging of the battery has not been shown nor described, the same being already well known.

Sensitive cell S still intercepts the gas leaks, but said cell does not have (as for the independance thereof) sufficient current as to operate the memory.

It is for this purpose that current amplifier AC has been provided in the circuit.

Memory M "remembers" all the gas leaks, the continuous as well as the momentary ones. The memory operates power amplifier AP which, in turn, operates, by the two outlets thereof, valve EV and the start of oscillator 0.

For what concerns the realization form in direct current, a battery may be interposed between the ground contact and the upper connection of valve EV, as can be seen on figure 2.

The above described embodiment shows an exemplifying and not limitative realization of the present invention; it is understood that other shapes, proportions and dispositions can be adopted without going out of the limits of the present invention.

Claims (6)

1. An electronic circuit for detecting gas leaks, said circuit operating automatically and in due time a valve placed upstream of the gas distribution, said valve cutting off the gas flow once the concentration, due to the gas leaks, has reached a predetermined degree, essentially consisting in: -a sensitive cell (S); - a direct current amplifier (AC); - a memory (M) provided with a pushbutton (P) for clearing the same; - a power amplifier (AP) in direct current; -an oscillator (0) for an acoustic signal; - a valve (EV) electronically operated.

2. An electronic circuit according to claim 1, wherein valve (EV) placed upstream of the gas distribution, said valve receiving from the circuit the mechanic blockage impulse of the gas flow, remains in that blockage position even if the concentration of the escaped gas lowers, and may be disengaged only by hand operation.

3. An electronic circuit according to claims 1 and L 2, wherein an acousticalarm signal is provided, which can be disconnected only by means of a hand operated pushbutton.

4. An electronic circuit according to claims 1 to 3, wherein the feeding of the circuit may take place by means of the main electric energy source, as well as by means of a battery.

5. An electric circuit according to claims 1 to 4, wherein the conventionally used relais is replaced by a SCR as to prevent the formation of sparks due to the movable contacts.

6. An electronic circuit for detecting gas leaks substantially as described herein with reference to and as illustrated in the accompanying drawings.