Patent GB-673954-A (GB)
Title: Improvements in automatic telephone alarm signalling apparatus
IPC: G08B19/00
Filed: 1949-03-09
Abstract: 673,954. Automatic exchange systems. McSORLEY, D. J., and ROBINS, J. T. May 22, 1950 [March 9, 1949; June 10, 1949], Nos. 6429/49 and 15531/49. Addition to 638,155. Class 40 (iv). [Also in Group XXXVIII] In a gramophone type of automatic alarm which transmits a recorded message to a selected telephone substation, the pick-up carries an impulsing contact which co-operates with a number of cam elements attached to a disc gramophone record before the pick-up stylus enters a recorded portion of the groove. As shown in Figs. 4 and 5, the record comprises an outer portion 16 provided with a widely spaced groove 23 which leads into an inner portion 15 containing the warning message. Impulsing according to the substation required is effected by the cam elements which comprise bent wires 25 inserted as necessary in radially spaced holes 32 provided in a sector A of the outer portion and located between the grooves. The remainder of the outer portion is imperforate and provides a pause period between each group of impulses. The outer portion may be formed integral with the inner portion or may be made separately from a light alloy. The impulsing contacts are mounted on a pick-up arm 17, Fig. 6, and comprise springs 26 operated by a feeler 27 whenever it engages a cam element during the transverse movement of the arm as a reproducing stylus 24 follows the groove in the outer portion. The gramophone may be spring or electrically driven and is housed in a partitioned case .(not shown) which also contains batteries for an amplifier 19, Fig. 11. Speed control at 40 R.P.M. is effected by a governor, Fig. 9, comprising a centrifugally-controlled brake disc 10, movement of the disc also controlling contacts t<SP>1</SP>-t<SP>5</SP> of a contact stack 48 through a cranked arm 49. An alarm signal at terminals S pulls up relay 35 which locks mechanically until released by a push button (not shown) and starts the gramophone by disengagement of the relay armature from a pin (not shown) on the motor spindle. Relay 35 also isolates the alarm signal circuit and closes a local bell circuit through a thermal delay switch 51. When the drive motor has attained a suitable speed, the brake disc operates contacts t<SP>1</SP>-t<SP>5</SP> which switch on amplifier 19 and connect the impulsing contacts 26 and an output transformer 20 to the telephone lines a, c. The bell of the local telephone set is also shortcircuited at terminal b and the local bell circuit isolated before the thermal delay switch has time to operate. Before impulsing commences the pick-up runs inoperatively through an outer groove 28 and this pause period allows the seizure of exchange equipment. When impulsing is completed, the transverse movement of the pick-up arm frees contacts 54 from a ramp 55 and a short circuit across the output transformer is removed. With clockwork mechanisms, running down occurs after the message is transmitted and the governor brake disc is disengaged from contacts t<SP>1</SP>-t<SP>5</SP>, thereby restoring the telephone line to normal and permitting the local bell to ring after a delay period determined by the thermal switch 51. If electric drive is provided, automatic stopping may be effected by movement of the pick-up arm.