Patent GB-453540-A (GB)
Title: Improvements in automatic telephone systems
IPC: H04Q3/00
Filed: 1935-03-18
Abstract: 453,540. Automatic exchange systems. PANSTWOWE ZAKLADY TELE-1 RADJOTECHNICZNE W. WARSZAWIE, 30, Grochowska, and JEDRYCHOWSKI, J., 19, Widok, both in Warsaw. March 18, 1935, No. 8457. [Class 40 (iv) Apparatus in a finder-connector link for small offices is reduced by arranging inter alia that one relay has the combined functions of dialling relay and ring trip relay and another those of finder test relay and release relay and that the circuit for operating a common busy and ringing current generating equipment includes the private wire of a busy line. Operation of call-finder. Combined line and cut-off relay L operates partially in series with the common start relay R and connects its lower winding to the finder bank in place of the normal busy potential. R energizes the line relay I of the first idle link and I completes a self-driving circuit for the finder S over the test wiper gamma. When the calling line is reached, K, which is no longer short-circuited, switches the line and start circuits through and puts busy potential on the C-wiper gamma to operate the cut-off winding of the combined relay. D which is operated by I starts the common tone equipment over a third winding of I, the C-wiper gamma of the final selector and the lead Az so that a tone signal is given by induction from this winding when relay K switches through. Operation of final selector. Dialled impulses are repeated by I to the magnet of the final selector W and to the lower winding of D in parallel. D therefore holds after its circuit is broken at the off-normal springs C. In the case of multi-digit numbers the C-wiper after each digit but the last finds itself in a position over which D is held. At the end of the last digit, however, D falls and completes the test circuit over relay P. If the line is idle, P switches through and starts the ringing equipment, and ringing current is fed to the line over the upper winding of P which now functions as a ring-trip relay and alternately locks over K<1>, P<1> and completes the talking circuit. A ring-back signal is given by the voltage drop across I (upper) which is included in the ringing circuit. If the line is busy, the busy potential is connected over the third winding of the line relay and wire Bz to the common equipment which generates a busy tone signal as described below. Common tone and ringing equipment, Fig. 2. Dialling tone is generated by B which shortcircuits itself on operation when any link requires it. When busy tone is required, battery is connected to Bz. As a result, W1 completes a circuit for magnet O which removes a shunt from W2 which then releases O. W2 is thus again shunted and falls sluggishly owing to a copper slug and interaction continues, causing the switch O to advance slowly. Alternate terminals in bank alpha, the wiper of which is connected to the tone generating relay B are connected to Bz and accordingly a signal in the form of interrupted tone goes back over Bz. Wiper gamma ensures that switch O advances to a definite position whether W1 remains energized or not. When the test relay P in the final selector switches through, a circuit is made from battery over I (upper) via the wanted party's bell and relay D (upper), W1 (lower) and transformer secondary T to + battery on wiper # of switch O. W1 causes the advance of the switch as described above and ringing current is periodically interrupted at # by the disconnection of the transformer. Release. The relapse of K when I is released releases the calling subscriber's individual relay and relay P and makes a homing circuit for the final selector. I is not released until both subscribers have cleared. Rectifiers. Rectifier Pr1 enables the tone and ringing equipment to be operated from a busy C-wire but prevents any shunting effect by other elements over which battery is connected to the C-wire such as the resistance P<11>. The rectifier Pr2 short-circuits the lower winding of W1 as regards the direct current for actuating the ring trip relays to make their operation more certain.