NZ200307A - Inflammable gas detection alarm - Google Patents

Description

200307 Priority Date|s): .^TvY.^ I Complete Specification Ftled: l^T.^ Class: fTJ. .. Publication Date: $85 P.O. Journal,- Ko: ,(?V3£?.* Patents Act 1953 COMPLETE SPECIFICATION DETECTOR APPARATUS OF INFLAMMABLE GAS I, FRANCO MARIA OONTE1, of Via L. Carrand 3, Fierenze, Italy, an Italian citizen hereby declare the invention for which I pray that a patent may be granted to me and the method by which it is to be performed, to be particularly described in and by the following statement:- 200307 t t m This invention relates to apparatus for detecting inflammable gases.

It is well known that it is of the greatest inportance in the operation of any plant, whether industrial or domestic, which handles combustible 5 gases, to ensure that the leakage of such gases is kept to a minimum to avoid fires and other damage to things, and also to avoid injury to persons because such gases are often highly toxic. Devices which are of particular importance in this connection, especially where inflammable gases are released into confined spaces, are those which detect the 10 presence of dangerous concentrations of gas and consequently control alarms or more complex emergency apparatus. Such devices mast be and remain highly sensitive and must also be highly reliable in operation. The detector apparatus of the present invention meets these requirements because, firstly, it uses an electrical sensor of adjustable sensitivity 15 and, secondly it operates electronically and therefore has both a fast and reliable response and great flexibility in use.

The sensor of this invention essentially, comprises a platinum alloy wire which is wound to form a tight coil and the electrical resistance of 20 which varies as a function of the concentration (%) of inflammable gas surrounding the coil. This sensor, inserted in a branch of a fixed resistance bridge circuit, is able to generate control signals according to the concentration of the gas, the control signals being usable to operate an alarm or for other practical uses. r: LJ4JANi9g5 200307 An embodiment of the invention is hereunder described, by way of example only, with reference to the accompanying drawings wherein: Figure 1 is a block diagram of an apparatus for detecting Figure 2 is a circuit diagram of the same apparatus.

Reduced to its basic structure and with reference to the accompanying 10 drawings, the invention comprises: a power supply including a mains feeder (A) equipped with a rectification bridge transformer which is suitably stabilised by means of known electronic circuits; a resistive bridge circuit having resistors (PM), a branch of which is formed by a gas detector element (R) which is a coil of fine platinum alloy wire 15 which is preferably contained in a metal mesh cage (Davy's type) in order to prevent the propogation of flame in the event of gas igniting around the coil; optionally an aspirator including a gas pump (As) which draws air and any gas entrained in the air through ducts in which the detector element (R) is located; an audio oscillator (G) and an 20 electroacoustic transducer (TA) connected in cascade.

To increase the stability of the device, the mains feeder A is preferably provided with a transistor (Tl) , a Zener diode (Zl) and an integrated circuit (Ic^). inflairanable gases according to the invention; and 200307 The bridge circuit (PM) is made up of two fixed resistors (R2) and (R4), a variable resistor (R3) , 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 supplied to the terminal 5 (4) of an integrated circuit (IC2) of the audio frequency oscillator (G); and the output (3) of such integrated circuit (Ic2) being connected to the said electroacoustic transducer (TA) through a capacitor (C8) and a resistor (R7) in series. To avoid faulty operation of the apparatus in the event of a mains power failure, an auxiliary pcwer supply (A1) is 10 provided, including a battery which is connected through a buffer to a corresponding automatic recharging circuit, a device to signal a mains power failure or failure of the battery, and a timing circuit (Tc) which is adapted to activate the auxilliary power supply at adjustable intervals.

The apparatus operates as follows. An increase in the concentration of inflammable gas about the sensor (R) induces a variation in the resistance of the sensor (R) which results in a voltage unbalance between the terminals (2) and (3) of the amplifier (Ad) , and this 20 signal, suitably amplified, triggers the audio oscillator (G) which in turnr activates the transducer (TA).

The device will remain in this state for so long as the sensor continues to detect a concentration of gas which is greater than the predetermined 25 concentration, the latter being set by adjustment of the variable JW, kJI+MNm 200307 resistor (R3).

Construction example The following are the values of essential components which are used in an embodiment of the invention: Cj = 2200 jj. F R5 - 10 Kohm C2 = C3 = Cg = Cj = 10 JUL? Rg = 100 Kohm C4 = 0.1 yM.F R^ = 22 Ohm 1/2 W Cg = 100 jmF Tx = BC 140 R1 = 470 Ohm = Zener 12 V/0.4 W R2 = 220 Ohm Ad = Z^741 R^ = 100 + 470 Ohm 1^ = LM340T5.0 R^ = 6,8 Ohm Ic^ = NE555 In practice, the form, dimensions, weight, characteristics, disposition, nature and value of individual components may be varied without departing frcm the scope of the invention as defined in the claims.

Claims (7)

4 • o r 7 2 G u o u / WHAT I CLAIM IS:

1. Apparatus for detecting inflammable gas, comprising in combination an electrical power supply, a resistive bridge circuit having two input 5 vertices connected to the power supply and two output vertices and a branch of which comprises a detector element the electrical resistance of which varies in dependence on the concentration of inflammable gas surrounding the element, a differential amplifier the inputs of which are connected to the output vertices of the bridge circuit such that the 10 output voltage of the differential amplifier is dependent on a voltage unbalance between the output vertices of the bridge circuit, an audio frequency oscillator which is triggered to oscillate by the output of the differential amplifier, and an electroacoustic transducer which is driven by the oscillator; whereby when the concentration of inflammable 15 gas surrounding the said element exceeds a pre-determined level, the audio oscillator operates to drive the transducer to emit an audible alarm signal.

2. Apparatus according to claim 1, wherein the differential amplifier 20 and the audio oscillator are integrated circuits.

3. Apparatus according to claim 1 or claim 2, wherein a further branch of the bridge circuit comprises a variable resistor for adjusting the balance condition of the bridge circuit and thereby the sensitivity 25 threshold of the apparatus. 2 003

4. Apparatus according to any preceeding claim, wherein the gas

5. Apparatus according to claim 4, wherein the gas detector element is enclosed in a Davy cage.

6. Apparatus according to any preceeding claim, further comprising means for conveying ambient air in which the inflanmable gas may be entrained, onto and to surround the gas detector element.

7. Apparatus for detecting inflammable gas substantially as hereinbefore described with reference to the accompanying drawings. detector elsrient is a ccil of platinum alloy wire FRANCO MARIA OONTE* by his authorized agents, J. D. HARDIE & COMPANY