Patent GB-596444-A (GB)
Title: Telecommunication switching systems
IPC: H04Q1/38
Filed: 1945-03-02
Abstract: 596,444. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. March 2, 1945, No. 5242. Convention date, April 21, 1944. [Class 40 (iv)] In a telecommunication switching system, a controller, having a plurality of selectable operating positions, applies a different potential to one electrode of a discharge device for each position, a source of current applies a succession of potentials to a second electrode of the device and a relay is operated to effect a switching operation when the potentials bear a predetermined relation to each other. The key sender has a characteristic resistance individual to each key which is connected into the line circuit, on operation of the key, by opening a short-circuiting contact. Each key, on its return stroke after being depressed, holds one contact open for keys 1 ... 5, and, in the case of keys 6 ... 9, it opens two contacts, one of which breaks the line circuit for the first quarter of the movement but holds only the second contact open for the remainder of the stroke to connect the resistance in the line. This is done in the latter case by a pin 35, Fig. 3, on the key 26 which, during the first part of the return stroke, rises under an inclined lug 20, Fig. 2, on one spring 38, thereby breaking contact with the fixed contact spring 37. A further lug 40, Fig. 3, holds the second contact spring 36 also open. After the initial part of the return movement of the key the first spring 20 is released but the second remains held open by continued engagement with the pin 35. In the case of keys 1 to 5, only one movable contact spring is used and this is held open in a similar manner during the entire return stroke. The rate at which a depressed key can rise is controlled by a frictional or other governor. As described, a member 29 on each key engages a rubber wheel 31 on a spindle 32 and rotates a disc 33 against which a friction spring 34 presses. In the register controller, Fig. 7, RAR releases and RBR operates when the calling line is connected. AR then operates and locks in series with the line after which its operating circuit is broken by BR. RBR also applies high tension to the discharge tube arrangement V1, V2. RIR is operated by AR and remains energized during operation of the register. When a button is released after depression, AR releases due either to the opening of the line circuit or the high resistance inserted and connects battery over resistance RN1 to the line. The appropriate potential is thus applied to the grid of V2 and a chain of counting relays CR1 ... CR9 operate in turn to connect a series of matching potentials P1 ... P10 to the grid of V1. When the potentials on the two grids are the same, gas valve GV fires and operates GVR. This stops the relay chain, operates the corresponding XR relay and connects up relay GSR, which re-operates AR and establishes the conditions for the reception of the next digit. Relay XR locks in series with transfer relay TR 1. When a P.B.X. is equipped for calling by the system of the invention, trunk calls may be made either by installing an ordinary dial or by adapting the local register circuit to convert ten-button pulses into dial impulses. Specifications 598,188, 601,906 and 628,174 are referred to.