| 摘要 |
1409608 Burglar alarms MAXIM ALARMS Ltd 30 Aug 1973 [21 Oct 1972] 48583/72 Heading G4N An anti-theft device comprises a base 1, a plurality of light sensitive components 2 present at spaced locations thereon and shieldable from light by a corresponding plurality of articles to be placed on the base 1 and an electrical circuit including an alarm device L or B (see Fig. 3) to which the components 2 are electrically connected in parallel, whereby the alarm device L or B is actuated upon lifting of any one of the articles. The components 2 may be photo resistors or solar cells placed in holes in the base under each article or optically coupled thereto via optical fibres. In operation, when light falls on component 2, the threshold level of an input FET TR1 (see Fig. 3) is exceeded and transistors TR2, TR3 are turned on by amplifying stage IC1 to energize a relay RLA and to close relay contacts A2 for activating a warning lamp L and an audible alarm B. A 4- position switch selectively enables the alarm to be turned off, the lamp, audible alarm to be tested and for the circuit to be made fully operational. The alarm may also be arranged to be triggered if the connecting wires from the sensors are cut. |
