Patent GB-680295-A (GB)
Title: Improvements in electrical signalling and indicating arrangements
Inventor: PREIST THOMAS PHILIP
IPC: E21F17/18
Filed: 1949-11-23
Abstract: 680,295. Electric selective signalling. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Oct. 25, 1950 [Nov. 23, 1949], No. 30076/49. Class 40 (i). A signalling system indicates which motor has failed in a conveyer system having a plurality of conveyers in tandem each driven by a separate motor and each arranged upon stoppage to stop those conveyer motors which precede it in the sequence by means of centrifugal or like switches; the said switches are arranged to vary the resistance of a signalling line and centralized indicating equipment is variably set thereby. In the embodiment of Fig. 1 motor contacts BF1-BF5 are arranged on stoppage of the respective motor to connect one or more of equal resistances YA-YD selectively into the signalling line circuit and thus operate relay L which completes a Wheatstone bridge network comprising balancing resistances YF-YJ of similar value as resistances YA-YD and with relay BR connected across the diagonal. Relay BR is polarized and is adapted to operate only when the resistance in the signalling line arm of the bridge is equal to or below the sum of resistances YF-YJ and the winding of relay L. Thus if motor contacts BF1 close the relay BR operates immediately after L has operated and causes lamp LPA to light. If motor contacts BF5 close maximum resistance is inserted in the signalling line and relay BR does not operate immediately. Instead, after relay L has operated the bridge-balancing relays A-D operate in sequence as follows. Relay A operates, shorts out resistance YJ and energizes relay B. Relay B then shorts out resistance YH and energizes relay C, which similarly shorts resistance YG and energizes relay D. When relay D shorts out resistance YF conditions for operation of relay BR hold and, since relay D is operated, the lamp LPE lights. If any intermediate motor contacts close the conditions to operate relay BR would be reached at a corresponding earlier stage in the sequence of operation of the bridge-balancing relays and the appropriate lamp LPB, LPC or LPD would light. Fig. 2 (not shown) illustrates a modification of the system of Fig. 1 for ten motors using only six bridge-balancing relays. The embodiment of Fig. 3 is a simpler system wherein motor contacts CS2-CS6 normally short-circuit respective resistances YB-YF in series in a signalling line which is open circuited on operation of motor contacts CS1. An ammeter MA connected in series with the line is fed from A.C. mains via a suitable rectifier RB and a variable resistance YA is adjusted to give full scale reading with all contacts CS1-CS6 closed. When any motor stops the preceding motors automatically stop and thus contacts are opened and corresponding resistance inserted in the line causing the ammeter to indicate the number of conveyers still in operation. When the remotest motor stops contacts CS6 also close a circuit to an alarm AB. Alternatively, signalling resistance may be wired, as in Fig. 1 and a contact voltmeter connected across a further series resistance so that whenever the needle leaves the zero position the contacts complete an alarm circuit and the actual reading indicates the motor concerned.