GB557852A - Improvements relating to devices for periodically opening and closing an electric circuit and selective apparatus employing such devices - Google Patents

Abstract

557,852. Electric signalling systems. STANDARD TELEPHONES & CABLES, Ltd., HARTLEY, G. C., LOWRY, L. P., and BRAY, F. H. June 4, 1942, No. 7599. [Class 40 (i)] [Also in Group XXXVII] A polarized relay for periodically opening and closing a circuit has two windings controlled directly or indirectly over contacts operated by the relay so that in alternate periods terminated by change-over of the contacts (1) current from a source traverses one winding and is opposed by a condenser-charging current in the other winding, and (2) the current traverses the first winding in the reverse direction and is opposed by discharge current in the other winding. The durations of the periods depend on the times required for the charging and discharging currents to decay to a value less by a predetermined amount than the current in the first winding so that the periods are independent of fluctuations of the source, and adjustment is effected by a potentiometer which feeds the first winding. As shown in Fig. 1, the relay P in its inactive condition is maintained with contact p<SP>1</SP> in one position by current from potentiometer PR over winding 1. When start relay ST is operated the current over 1 is reversed and a shunt on condenser C is removed so that charging current flows over 2. When the charging current has sufficiently decayed contacts p<SP>1</SP> change over followed by pp which cause the reversal of conditions described above. The overall period of the relay and the ratio of the two periods referred to above are varied by adjustment of the potentiometer. The periods also depend on the value of resistance R3 and capacity C. Receiver, Fig. 3, responsive only to a signal comprising marks and spaces of pre-determined duration. The marks are of 4 secs. duration with a tolerance of Œ ¢ sec. and the spaces of 1 sec. duration with a limit of 1¢ secs. Two impulsing relays, P (580 milli. seconds) and PA (495 milli. seconds), arranged as in Fig. 1 and fed by a battery of higher voltage than other relays, are used to time the marks and spaces respectively in conjunction with relay chains TA, SA-TC, SC and RA, QA, RB, QB. The periods of operation of the pairs in the chains are shown in Fig. 4; each pair beats at half the frequency of the preceding pair. When a dash is received, potential is applied to terminal RC to operate HR quickly and R relatively slowly to avoid response to momentary interference; R makes itself quick to release. Start relay ST pulls up (key KS has been thrown) and relay P sends timed pulses to the first relay chain. After the sixth period of PP (3¢ secs. and SB, TB, TC operated), D pulls up and locks and prepares a circuit for PZ in series with ST. If the dash now terminates and releases R, PZ operates and locks independently of ST which releases. If the dash lasts longer than 8 periods of P (4¢ seconds, with TB back), DD pulls up to prevent operation of PZ, ST releases when the termination of the dash releases R and the circuits restore to normal, the counting chain being restored in any case by the release of ST. The operation of PZ thus registers an acceptable dash and starts up relay PA to send pulses to the second chain for timing a space. The minimum period is provided for by the operation of PZ, the release of ST and the first chain, and re-operation of ST. After the third period of PT (1¢ seconds and QA, RA, RB operated) the locking circuit of PZ is opened and the relapse of this relay operates M in series with L which was previously operated by PZ, the circuit of M being conditional on the re-operation of ST to signify the commencement of another dash. An acceptable pause is therefore registered by the operation of both L and M. The operation of PZ on the next dash if acceptable releases L but holds M until N pulls up and releases it. N registers the second dash. If PZ does not operate, ST on relapse releases both M and L. On the next pause if acceptable, PL is released before ST is re-operated and holds N which thus registers a further pause, but if it lasts too long ST operates first and releases N. The third dash if acceptable operates L when PZ pulls up so that N continues to be held and the alarm circuit over terminal AA in closed.