GB297092A - Improvements in or relating to means for electrically producing sounds by acoustic warning or signalling apparatus - Google Patents

Abstract

297,092. Blondel, A. Sept. 14, 1927, [Convention date]. Audible signalling systems.-An electromagnetically operated sound producer is operated from a power supply of commercial frequency through the intermediary of a frequency changer. As shown in Fig. 1, the vibrator V of the sound producer P is operated by an electromagnet E which is supplied through a frequency changing transformer T<1> from a source A of low frequency current. The secondary circuit is tuned to an harmonic of the supply frequency by a condenser Cm and the corresponding high frequency is produced by reason of the saturated condition of the transformer core. An inductive coil L prevents the higher frequency current from passing to the supply source. In a modification (Fig. 2, not shown) the transformer T<1> is replaced by an auto-transformer and in a further arrangement (Fig. 3, not shown) the electromagnet E performs the dual function of operating unit for the sound producer and raising the frequency. A battery H may be provided to saturate the core of the frequency changer or polarize the electromagnet E or perform both functions simultaneously. If desired the frequency changer may be supplied through a transformer T<2> which is shunted by condensers C<1>, C<2>. Reference has been directed by the Comptroller to Specification 178,235, [Class 13, Bells &c.].