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Improvements relating to automatic telephone systems and especially to the substation circuits and substation apparatus used in such systems
Improvements relating to automatic telephone systems and especially to the substation circuits and substation apparatus used in such systems
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机译：与自动电话系统有关的改进，尤其是在这种系统中使用的变电站电路和变电站设备
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904,787. Substation equipment. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. April 10, 1961 [April 14, 1960], No. 13459/60. Class 40 (4). A tuned reed device in a substation comprises digit-transmitting reeds tuned to different voice frequencies and a receiving reed tuned to a particular voice frequency, the transmitting reeds being formed partly or wholly of magnetic material and being positioned in a magnetic circuit so that when they are vibrated by digit keys associated therewith they cause pulses of alternating current to be sent to line due to the change of flux through an inductive winding linking the line and the magnetic circuit, and the receiving reed, also partially or wholly of magnetic material, being vibrated in response to the flux change in the magnetic circuit when ringing current is applied to the line so as to induce an alternating voltage in an output winding associated therewith. A non-magnetic base member 11 (Fig. 1), supports a first permanent magnet 14 having soft iron polepieces 15, 16. A receiving 18 and transmitting reeds 17 all tuned to different voice frequencies and made of magnetic material are attached to polepieces 15 in such a way that they overlie and extend beyond, but do not touch, polepiece 16. The reeds 17 are caused to vibrate by the depression of digit keys 19, the reeds again being vibrated when the keys restore to normal under the action of springs 22. Thus two alternating voltage pulses are sent to line each time a key is operated due to the change of flux in the magnetic circuit, when the reeds vibrate, being detected by a coil I connected in a circuit across the line wires. A second permanent magnet 24 having polepieces 25, 26 and carrying a calling current output winding II is supported below the free end of reed 18 so that when the latter is caused to vibrate by the appearance of ringing current in coil I, a corresponding alternating voltage will appear across coil II. The tuned reed device is indicated by TRD in Fig. 2, coils I and II corresponding to those mentioned above. In the normal condition any noise voltage present on the line wires (connected to B, A) is detected by transformer TXB, rectifiers MR1, MR2 and applied to the base of a transistor TB to maintain this non-conducting. When ringing current of the appropriate frequency, a different frequency being used for each station on a party-line, is applied for a time depending on the time constant of R2, C4 then the output of coil II, after rectification by MR3, MR4, will be sufficient to cause TB to conduct and consequently the blocking oscillator TXA, TA will operate to produce an audible note in the sounder TS.
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