Patent GB-396776-A (GB)
Title: Improvements in or relating to automatic alarm devices
IPC: H04L15/26
Filed: 1932-02-11
Abstract: 396,776. Selectors responsive to code signals. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London, and HILLS, S. C., 35, Vicarage Road, Chelmsford. Feb. 11, 1932, No. 4132. [Class 40 (iv).] An alarm device responsive only to a particular signal e.g. three dashes of 4 seconds duration separated by 1 second intervals comprises two rotary members moved in one direction by solenoids in response to signal elements and in the other direction by springs and clock-controlled escapements. One of the members moves a step-by-step device which ultimately closes the alarm circuit but if the duration of the signal elements (dashes or spaces) is incorrect, one or other of the rotary members trips the step-by-step device which restores to normal. When no signal is being received, armature RA of the signal relay (not shown) makes contact SC and, assuming key K1 closed, solenoid PRS is energized and shaft SPRS is rotated clockwise into a position in which arm BC on the shaft opens pairs of contacts G, H. Contacts G remove a short-circuit about resistance R2 to reduce current through PRS to a holding value. On receipt of the first dash, RA falls back and releases PRS which moves back under escapement control until it closes contacts D whereupon solenoid SS rotates shaft PS clockwise. An arm SES on shaft PS closes contacts I to hold SS while a second arm SP<1> carries a spring controlled pawl into engagement with rack RM. When the dash ceases, PRS operates again and SS releases whereupon shaft PS moves anticlockwise under escapement control and pawl SP moves rack RM forward one step. This cycle of events continues, if the signal elements are of correct duration, and rack RM opens contacts Z to release a normally operated relay NVRW which closes contacts Y to operate bells B1-B3 and contacts O to hold PRS. The valve filaments of the wireless receiver controlling the signal relay are in series with relay NVRW so that the receiver is now inert. Spark-quenching shunts k are connected across the various contacts. The rack is held in the alarm operating position by a dog RST and the arm ES is prevented from disengaging dog DP by a rod CB which engages beneath it. Dog RST and rod CB are released by a push-button PB through suitable linkwork. The shaft PS is moved counter-clockwise between stops 11, 12, Fig. 3, by a spring 9 and is connected to an escapement by a oneway clutch comprising a drum 1 on the shaft, a member 2 carried by the escapement spindle 3, and spring controlled rollers 5 mounted between inclines on the member 2 and the drum 1. Shaft SPRS is similarly controlled. Rejection of incorrect signals. If a dash is too short, SPRS does not rotate anti-clockwise sufficiently to close contacts D and solenoid SS therefore remains unoperated. If too long, contacts D are opened but SS holds over contacts H, I until arm PE on shaft SPRS opens contacts C, and arm BC operating through lever PR trips the dog DP which permits rack RM to restore under spring control. The dog is held disengaged by a catch OMHP. If a space is too long an adjustable stud ESS on an arm ES rigid with shaft PS trips the dog DP. In order that the rack RM may be restored without giving the alarm if the last dash is too long, contacts X closed simultaneously with contacts I by energization of SS are arranged in shunt of the contacts Z controlling relay NVRW and remain closed until after Z opens. This allows the dog DP to be tripped by an overlong last dash before the alarm is actuated.