378,532. Electric signalling systems. ASSOCIATED TELEPHONE & TELEGRAPH CO., 1033, West Van Buren Street, Chicago, U.S.A. May 15, 1931, No. 14495. Convention date, May 31, 1930. Addition to 371,844. [Class 40 (i).] In a system of the type described in the parent Specification, in which a power circuit is represented on an indicator board in the form of a circuit diagram and in which the effect on the whole system of the movement of a switch is automatically indicated, when a particular unit on the indicator board is selected, a control circuit is simultaneously extended to the actual unit represented and a lamp is illuminated if the indicator and the controlled unit are not in agreement. If a remote unit should change its condition automatically, the relative indicator symbol is altered and an alarm lamp is lit. A unit cannot be controlled from the central station unless the indicator equipment is first altered to show the required indication so that the alarm lamp is illuminated. Selection of indicator unit. Assuming the switch symbol B010 of station 01, Fig. 5, is required, the operator operates key K3 and then dials on CD the number of the station and of the unit. The first 2 digits, 0 and 1, set the selector S1 to the first contact on its tenth level, 251 is operated over 155 and lamp 428 lights to indicate that station 01 has been selected. Relay 251 closes a chain circuit for 9 similar relays, each of which has contacts extending the circuits from S2 to 100 different leads. The outlets from 10 contacts on one level are shown in the drawing. 100 of such groups of relays may be accessible to wiper 127, the particular group selected depending on the position to which S1 is set. Selector S2 responds to the next two digits and wipers 227, 228,229 are set to the tenth contact in the " B " level. A circuit is thus completed over 227 and 234 for 321 which completes circuits for similar relays for the same purpose as described above for relay 251. The impulsing leads are extended to S3 and the last two digits, namely 1 and 0, step this selector to the tenth contact in the first level, completing a circuit over 154 and 363, from K4 to magnet 8010 which controls the notching relay relative to indication BO10. Checking selection. The key K4 is moved to the right and springs 131 connect interrupter 140 to magnet 8010. The cams controlled by the notching relay are moved rapidly through their various positions, changing the lamp signals behind B010 in rapid succession. The cams controlled by 8010 are not shown but they are similar to 51, 52 and 53. The operation of notching relays is described in the parent Specification. Selection and control of remote unit. When the operator is satisfied that the correct signal has been selected the key K4 is moved to the left, disconnecting the interrupter 140 and sending a single pulse over 154 to step 8010. If switch B010 is to be moved from the " out " to the " in " position the springs 130 are operated a sufficient number of times to move the cams into position 4 in which the green lamp 583 and the white alarm lamp 594 are illuminated. The apparatus is illustrated in this position. Key K5 is now operated completing a circuit for relay 507 to positive at 521, which enables relay 606 at the station 01 to energize over 652 and 657. Relay 606 completes a circuit for polarized relays 604 and 605 in series over line S and these relays enable magnets 603 and 608 to step wipers 651 .. 655 and 656 .. 660 respectively on to the next terminals. A circuit is now completed for 604 and 605 to energize in the opposite direction and the two switches are stepped forward step-by-step in synchronism. The contacts wiped by 655 are connected to battery through contacts of relays such as 507 and when contact 8 is reached 655 fails to find battery, as the circuit is broken at 516, and the switches stop. In this position a circuit is completed for 601 over line I, and either contacts 682 or 683 of the pallet switch PS, the direction of current flow depending on whether B010 is in or out. Relay 601 energizes and as the indication on the indicator board is a true presentation of the switch condition, its armature remains as shown. To close the oil switch the key K1 is operated and 602 energizes. Relay 602 completes a circuit for 611, the direction of flow being such that contacts 651 close and relay 612 pulls up. Relay 612 completes a circuit for solenoid 615 which closes the oil switch. The changing over of the oil switch reverses the direction of current flow over line I and 601 changes over its armature. Relay 505 releases breaking the circuits for the green lamp 583 and the white lamp 594. The signal is dark to indicate the switch is in. If the operator now wishes to trip the switch, key K4 is operated a sufficient number of times to move the notching relay cams to position 3. Alarm lamp 594 lights to indicate disagreement. Key K1 is then operated to energize 602 which completes a circuit over line C to energize 611 to make contact 653, whereupon the oil switch is tripped by 614. An indicator signal is returned to 601 as previously explained, relay 505 energizes to extinguish 594 and light green lamp 583. The release of key K5 allows 507 to de-energize and the distributer switches step on until their home positions are reached. The connections to the notching relays of associated apparatus are interwired so that indications of controlled apparatus change as the controlling switches are moved. This interconnection is described in the parent Specification. The selectors S2, S3 are released by the restoration of key K3 but S1 is held until K2 is operated. A number of indicators at station 01 can thus be reached with a single setting of S1. Automatic indication of change over. Should a switch such as BO10 at station 01 suddenly change its position, due, for example, to overload conditions, the relay 610 is de-energized and a circuit is completed over the pallet switch contacts for relay 607. Relay 607 closes a circuit, in parallel to that closed by 606, for relays 604 and 605 which step the distributer switches at the two stations. As no relay such as 607 is operated, a complete cycle is traversed. When the switches reach their eighth contacts a circuit is completed over I to cause relay 601 to change over. Relay 505 de-energizes, or energizes if it is already back, closing in either case a circuit for the alarm lamp and circuits to bring the indicator lamps into their correct condition to represent the new position of the switch. To extinguish the alarm lamp the operator must move the relative notching relay cams into the position indicative of the new position of the oil switch.