Patent GB-715805-A (GB)
Title: Improvements in apparatus for signalling the escape of illuminating gas and other similar combustible gases
IPC: G01N25/46
Filed: 1949-08-10
Abstract: <PICT:0715805/III/1> <PICT:0715805/III/2> <PICT:0715805/III/3> In a device for signalling the escape of illuminating gas comprising a differential thermometer having two gas filled bulbs connected by a capillary tube one of the bulbs being surrounded by a catalyst, the temperature of both bulbs is kept above that of the surrounding air by the provision of electric resistances wound around the catalyst and around the other of the two gases containing bulbs, which resistances are connected to a constant source of electric current. In Fig. 2 gas filled bulbs A and B are connected by a capillary tube containing mercury 34.  Two electrical connections are provided between which the mercury can make contact when a temperature differential exists between A and B.  Resistances 29 and 30 are wound around bulbs A and B and are connected through variable resistances 31 and 32 to a source of electric current; the variable resistances permit the position of the mercury globule in the tube to be adjusted.  In Fig. 1 the heating resistances 29 and 30 and the catalyst surrounding bulb A. have been omitted for clarity, and the construction of the warning device associated with the differential thermometer is shown. Bulbs A and B are of coiled form and are provided with resistances 8 and 9, resistance 9 being slightly greater than resistance 8; these resistances are connected to platinum contacts in the capillary tube 16 and are in circuit with a warning light 11, a transformer 12 and a resistance 13.  The latter is associated with a thermometer 14 which when heated due to current flowing in resistance 13 operates warning bell 17; 15 is an insulating covering.  In operation, when gas escapes the temperature of bulb A which is covered with a catalyst is increased, thereby forcing the mercury to the right and completing the circuit including the resistances 8 and 9, thereby through resistance 13 heating thermometer 14 which when a predetermined temperature is reached operates warning bell 17.  If the temperature of A rises due to some other cause such as radiant heat the circuit will be closed as before but in such a case resistance 9 being greater than resistance 8 will heat bulb B quicker than A thereby forcing the mercury back to the original position before resistance 13 has heated thermometer 14 to the temperature required to operate the bell 17.  The bulbs may be interlaced as shown in Fig. 5, where bulb A is surrounded by the two halves of the bulb B.  The bulbs may be connected to the capillary by means of metal tubes which may have a spherical enlargment at 27 to trap mercury, these metal tubes serving also as contact members.  The whole device may be protected against false alarms by surrounding it with metal grills containing a porous heat insulating material such as glass wool, silk, wool, or asbestos fibres.  Additionally the catalyst covered bulb may be surrounded by a coating of cotton wool the outside of which is coated with ferric oxide; the catalyst itself is preferably a platinum sponge.  The device may be associated with means for closing gas cocks, switching on and off safety lights, operating air conditioning systems and opening and shutting windows. Specification 480,335 is referred to.