IE52445B1

IE52445B1 - Inflammable gas detector device

Info

Publication number: IE52445B1
Application number: IE1010/82A
Authority: IE
Original assignee: Conte Franco Maria
Priority date: 1981-05-05
Filing date: 1982-04-29
Publication date: 1987-10-28
Also published as: NZ200307A; NO153236C; DE3266133D1; IT8109399A0; IT1167878B; ATE15562T1; IL65497A0; FI75430B; FI75430C; ES511787A0; AU1843388A; CA1237505A; DK185582A; YU44342B; JPS57186160A; NO821461L; JPH0424439Y2; JPH0374352U; EP0065497A1; DK159167C

Abstract

The detector (R) is formed of a spiral of thin platinum alloy wire enclosed in a Davy cage of fine metallic grids to prevent flame propagation in the event of ignition within. It is connected in a bridge circuit with potentiometer (R3) and two fixed resistor (R2, R4), supplied with rectified AC from a series transistor (T1) and Zener diode stabiliser (Z1). The unbalance of the bridge is monitored by a differential amplifier (Ad) which controls a low-frequency tone generator (IC2). When the threshold of unbalance is exceeded due to a concn. of gas within the detector, an alarm is given by an electroacoustic device (TA). A standby battery and delay circuit may be provided to ensure operation following failure of the AC supply or rectifier.

Description

This invention relates to a detector device for the detection of inflammable gas.

It is known - in both industrial and domestic use of combustible gases - that the high degree of safety needed in the operation of equipment utilising an inflammable gas is a technical problem of primary importance since it is necessary to minimize the possibility of a spill and consequent fires or damage to objects and/or people as the inflammable gases are often highly toxic.

Accordingly, prevention devices which are able to detect the presence of a dangerous concentration of gas and, thus, control the operation of warning means or more complex safety apparatus, are of particular importance especially when equipment using inflammable gas is operated in un15 ventilated rooms. It is clear that a high sensitivity and high degree of operation reliability are the basic constant characteristics that the detector device must have.

Accordingly, the invention provides an inflammable gas detector device comprising a resistor bridge circuit, one arm of which comprises a gas detector element formed by a coil of platinum alloy wire, and an alarm transducer, a first circuit connected to the bridge circuit and operating as a variable threshold differential amplifier uses the imbalance occurring between the terminals of said first circuit when the quantity of gas in the vicinity of the detector element exceeds the preset limit, in order to trigger a second circuit which operates as a low-frequency oscillator and which actuates the alarm transducer.

The detector apparatus of the present invention meets the above mentioned requirements to a high standard for it involves the use of a particular electric sensor as part of such a prevention device and which is capable of changing its sensitivity; in addition, the electronic operation of the apparatus ensures a quick and reliable response and great flexibility in use.

The detector element of the device is essentially made up of a platinum alloy wire wound to form a closed coil, which is able to change its resistance - once the electric current is made to flow through it - as a function of the density (%) of inflammable qas surrounding said coil.

This sensing detector - once inserted in a branch of a bridge circuit made up of resistors having constant resistance - is able to produce a control signal in the form of a variation in resistance of the sensor which is due to the presence of traces of gas, for the control of electronic circuits which are provided for alarm or intervention in a plurality of practical uses.

The invention will now be described with reference to the accompanying drawings which show schematically a preferred embodiment of the invention given only as a practical demonstration and not to be considered in a limiting sense; wherein: - Fig. 1 shows a block diagram of the inflammable gas detector device according to the invention; Fig. 2 is a circuit diagram of said detector device of Fig. 1.

Reduced to its basic structure and with reference to the accompanying drawings, the invention comprises: - a supply section including a mains feeder (A) provided with a rectification bridge transformer suitably stabilized by means of known electronic circuits; - a bridge circuit having resistors (PM), a branch of which is made up of a S2445 - 4 detector element (R) for detecting the gas, said detector element being shaped as a coil consisting of a thin wire of platinum alloy and enclosed in a cage of metallic net (Davy's type) which, is known per se in order to prevent flame prqp5 agation in the case of gas ignition around the coil; optional sucking and conveying means for the ambient air to be controlled, including a sucking pump and canalization ducts for increasing the sensitivity of said detector element (R); - a note oscillator (G) and an associated electroacoustic transducer cascade (TA) .

More particularly, and according to a preferred embodiment of the invention, the mains feeder (A) is provided - in order to obtain an elevated stability - with a transistor (T1), a Zeener diode (Z1) and an integrated circuit (ICI).

The bridge circuit (PM) is made up of two resistors (R2) and (R4) having constant resistance, a resistor (R3) having variable resistance and the above mentioned detector (R); two vertices of the bridge being connected to the input terminals (2-3) of a differential amplifier (Ad) whose output (6) is brought to the terminal (4) of an integrated circuit (Ic2, of the note oscillator (G) which operates as a generator of low frequency oscillations; and the output (3) of said integrated circuit (Ic2) being connected, through a condenser (C8) and a resistor (R7) in series, to the above mentioned electroacoustic device (TA).

In order to avoid a possible fault in the operation of the apparatus owing to a power drop, an ancillary supply •Section (A1) is provided including; a battery backup connected to the automatic recharge circuit, a 30 warning device of mains power drop and battery breakdown and a timer circuit (Tp) providing for the activation of the ancillary supply section through an intermittance adjustable at will. - 5 The operation is as follows. In the case of an increase of inflammable gas concentration around the sensor (R), which brings about a resistance variation of sensor (R), an electric voltage imbalance is produced between the terminals (2) and (3) of the amplifier (Ad) which gives rise to an electric voltage signal? and this signal, suitably amplified, triggers the working of the note oscillator (G) which, in turn, activates the transducer (TA), Such an operating condition will be maintained throughout the time the sensor detects a gas percentage greater than a predetermined one, the latter being set up at wi’l by varying the intervention threshold which is obtained acting on the balance condition of the bridge by means of the potentiometer (R3).

Example Values of the essential components which are used in an embodiment of the invention follows: C1 C2 = 2200 |iF = c3 = C6 = C7 = 10 nF R5 = 10 K ohm R6 = 100 K ohm = 0.1 liF R? = 22 Ohm 1/2 W c8 = 100 llF T1 = BC 140R1 = 470 Ohm Z1 = Zeener 12 V/0.4 W *2 = 220 Ohm Ad = (1A741 *3 = 100 + 470 Ohm ^cl - LM 340T5.0 r4 = 6.8 Ohm Ic2 = • NE555

Claims

1. CLAIMS;

1. An inflammable gas detector device comprising a resistor bridge circuit, one arm of which comprises a gas detector element formed by a coil of platinum alloy wire, and an alarm transducer,· a first circuit connected to the bridge circuit and operating as a variable threshold differential amplifier uses the imbalance occurring between the terminals of said first circuit when the quantity of gas in the vicinity of the detector element exceeds the preset limit, in order to trigger a second circuit which operates as a low-frequency oscillator and which actuates the alarm transducer.

2. An inflammable gas detector device according to claim 1, wherein the first and second circuits are integrated circuits.

3. An inflammable gas detector device according to claim 1, wherein the threshold of said first circuit is variable by means of a potentiometer.

4. An inflammable gas detector device according to claim 1, wherein the gas detector element is housed in a Davy cage.

5. An inflammable gas detector device according to claim 1, wherein means for conveying the ambient air to the actual detector element are associated with said gas detector element.

6. An inflammable gas detector device according to claim 1, substantially as hereinbefore described with particular reference to and as illustrated in the accompanying drawings. F. R. KELLY S CO.,