TRAP SWITCH CONSTRUCTIONS IN THE NORMALLY CLOSED PROTECTIVE CIRCUIT OF BURGLAR ALARM SYSTEMS

摘要

The trap includes a pliable elongated member which may be a wire, cord or tape having a steel terminal element serving as an armature releasably held by a permanent magnet structure which constitutes one end support holding the elongated member taut. When the armature is detached from the magnet by movement of some part of the protected structure, as for instance a window, a venetian blind or by movement of an intruder, the protective circuit will open, thereby actuating the alarm circuit. The magnet is one terminal of the trap switch. The armature is conductively connected in some manner to the other switch terminal. The pliable elongated member may be a wire offering part of the circuit path while the armature and magnet are engaged. Parts of the protected structure may serve as the pliable member or the armature, as for instance in an example shown, the ladder tapes of a venetian blind serve as the elongated pliable member, while the blind's base rail serves as the armature. Both supports for the pliable member may comprise a magnet and armature. In embodiments shown, a single armature is used to shunt two spaced magnets, in which instances, such pair of magnets constitute the switch terminals. The magnet structures preferrably comprise a magnetic block carried in a sheet steel channel having mounting lugs for various placements. The line of direction of the elongated pliable member, is not limited. Force required to dislodge the armature is adjustable.