| 摘要 |
<p>The two-tone warning born employs two horns, which are operated alternately via a modulator (3), or a siren (2), the operating frequency of which is varied between two values under the control of a modulator (3). Means are included for inhibiting the modulator (3), pref. controlled by the supply wires to the two horns or the siren, to allow a continuous sound to be provided. Pref. the modulator (3) is inhibited by a bistable relay (5), which is responsive to the supply voltage. The relay working contact (C) is normally closed, but opens when the supply voltage to the siren (2) etc. exceeds a given value, to allow the modulator (3) to be brought into operation.</p> |
