186,388. Western Electric Co., Ltd., and Deakin, G. May 28, 1921. Manual exchange systems; metering systems.- In a system for automatically distributing calls amongst those exchange operators who have no call in hand, link-circuits are employed for connecting up the subscriber's lines with the cord circuits, the link-circuits being fewer in number than the cord circuits, and containing such apparatus as the supervisory relays, the repeating-coil and the ringing equipment which are usually associated with the cord-circuits. The subscribers' lines and the link-circuits are arranged in groups, the different linkcircuits of each group being accessible from different groups of subscribers' lines; and the linkcircuits have access to every operator's position, so that every calling line has access to every operator, the operators working as a single team. The link-circuits terminate at one end in callfinder switches which search for the calling line, and at the other end in cord-hunting, switches which select an idle cord-circuit at an idle operator's position. The test circuit of each idle cord includes the winding of a relav in series with back contacts of the corresponding relays of all preceding cords at the same operator's position so that only one such relay can be energized at the same time, thus preventing the seizure of a cord at a position at which the operator is already busy. A similar series connection is provided for the starting circuit of the call-finders to prevent the simultaneous connection of two calling lines to the starting circuit. Means are provided for preventing the employment of an idle linkcircuit to which no idle cord-circuits are available. If, after a link-circuit has been taken into use, all its association cord-circuits become busy, means are provided to release the link-circuit and to extend the call by another link-circuit. The system also includes an operator's listening key for interrupting the conversation, monitoring arrangements by which any faulty cord-circuit may be marked busy and the fault notified at a monitor's desk, and metering arrangements in which in addition to the normal metering of a successful call, an operator's metering-key is provided by which either double metering or, in the case of an ineffective call, no metering may be effected according to the stage in the connection at which the key is depressed. General operation of the system. The Figures illustrate a single system, Fig. 2 being placed below Fig. 1 with Fig. 3 to the right of Fig. 1. The several contacts operated by relays and by sequence switch elements are denoted in the drawings by small reference letters <a>, <b>, &c. and are referred to in the description by these letters in conjunction with the reference numeral denoting the corresponding operating element, for example 205<a> denotes the contact a operated by the relay 205. A pre-selected link-circuit. Figs. 1 and 2, has call-finder brushes 148, 149, 151 which search for the calling line, and a second set of brushes 159 - - 162 which hunt for an idle cordcircuit, Fig. 3, at an idle A-operator's position. The operator's instruments are then automatically connected with the calling line over the selected cord, and the operator inserts the plug 334 in an outgoing trunk which is assigned in the usual manner by a distant B-operator. The callfinde,r switches are of the two-co-ordinate brushchoosing type, each having a capacity of 200 lines, the subscribers line terminals being arranged in groups of ten levels of 20 terminals each, and the line relays 205 being arranged in ten corresponding groups. The call-finders are arranged in pairs so that one finder of a pair hunts first over the terminals of lines in the even hundreds whilst the other hunts first over the odd-hundreds terminals. Allotters 200, 201, Fig. 2, of the sequence-switch type pre-select the next idle link-circuits for connecting with calling lines in odd and even hundreds respectively. Operation of pre-selected link-circuit to seize calling line. When a calling subscriber A, belonging to an even hundred and whose line terminates, it may be supposed, in the third level, removes his receiver, his line relay 205 energizes, placing a selectable potential upon the terminal 151<1> and completing the starting circuit 214<f> 215<f>, 216<f>, - - 216b, 216, 212, 205<c>, 209, for the idle link-circuit preselected by the alotter 201. The battery lead for this starting circuit passes over the series-connected back-contacts of all relays 214, 215, &c., so that only one such relay can remain energized at one time and, in the 'event of simultaneous double connection, only the relay nearest the battery will remain energized, thus preventing the simultaneous connection of two calling-lines to the starting circuit. Relays 209 and 212 energize completing a fundamental circuit 117, 101, 108, 235, 270d, 209a 218, backcontact of relay O<1>, 212<a>. Relay 218 energizes to complete a circuit for counting relay 2 which closes a circuit for counting relay 2<1> which, however, does not yet energize being short-circuited over contacts 212<c>, 218<c>. Relay 101 energizes driving the sequence switch 100 into its second position in which the trip-spindle magnet 102 energizes to rotate the trip-spindle which intermittingly short circuits the fundamental circuit over the interrupter springs 104. At the first interruption, relay 218 de-energizes breaking the short-circuit on counting relay 2<1> which locks up and transfers the impulse-counting circuit to relays 1, 1<1>. which operate in a similar manner for the next impulse. After three interruptions, relay O<1> energizes and permanently breaks the fundamental circuit. Relay 101 de-energizes driving the switch 100 to its third position in which the motor magnet 121 rotates the tripped set of brushes over the third level of contacts. When the test brush 151 reaches the test terminal 151<1> of the calling line, relay 101 energizes in series with the subscriber's cut-off relay 112 in a circuit 128<a>, 101, 131, 151, 205<a>, 112, and drives the switch 100 to its sixth position. The cut-off relay 112 locks up and de-energizes the line relay 205 which restores to normal the starting circuit of the group of link-circuits. As the switch 100 passes through its fourth and fifth positions, calling supervisory relay 145 energizes and closes a circuit 158, 132<b>, 145<c>, 140<b> 144, 129, 128 for relay 158; and a preliminary test is made as described later in case the call has been abandoned. Allotter; operation when all the call-finders which hunt first over the even hundreds are engaged. In the third position of switch 100, earth 164 is converted to the contact 233 of the allotter switch 201 which energizes to hunt for the next idle link-circuit. If all the call-finders which normally hunt first over the even hundreds are busy. relay 207 energiezs over series contacts 163, 163<1>, &c. and opens the circuit of allotterswitch 201 which, therefore, does not hunt. If, whilst all these call-finders are engaged, a further call is n ade on an even-hundreds line, part of the fundamental circuit previously traced is replaced by a path over contacts 209<a>, 207<c>, 222<b>, 241 leading to a call-finder which normally rotates first over the odd-hundreds terminals. Relays 222, 223, open the fundamental circuit whilst the switches 200, 201 are in motion. Operation of link-circuit to seize idle cordcircuit; completion of connection. In the 6th position of the switch 100, motor magnet 125 rotates the brushes 159, - - - 162, and when an idle coro-circuit is reached, relays 130, 309 energize in a circuit 128, 129. 130, 152<d>, 158<e>, 162, 317, 309, 310<k>, 311<h> - - -, 306. The battery lead from key 306 passes through the back-contacts of relays 309, 310, &c., in series, so that only one relay can energize at the same moment and double connection is prevented. Relay 130 energizes relay 101 in a locking circuit 130<c>, 101, 128, to stop the brushes and drive the switch 100 into its 8th position in which it waits until the operator extends the call. In passing through its 7th position, a test is made for double connection. If two link-circuits have seized the same idle cord, two relays 130 have their low-resistance left-hand windings parallel and the current being insufficient to hold both, one will fall back deenergizing its corresponding relay 101 which energizes the release relay 132 over a circuit 101<b>, 135 and releases the link-circuit. Relav 309 lights the calling lamp 330 in series with the relay 325 which energizes to light the operator's pilot lamp 326, and to put earth over contacts 310b, &c., upon the second terminals 316 of all the idle cord-circuits. If the brushes 315 are resting upon the terminals of an idle cord, relay 303 energizes in a circuit 302d, 310<b>, 325<c> and energizes motor magnet 305 which rotates the brushes 315 until they reach the terminals of the selected cord when relay 303 relapses to stop the brushes and energize relay 301 which connects the operator's speaking set 340 with the calling subscriber. The operator enquires the wanted number, depresses an order-wire key 312 connecting her set 340 over an order-wire 341 to a distant B-operator, an earth connection on the key 312 energizing relay 313 which disconnects the set 340 from the calling subscriber. The A-operator then inserts the plug 334 in the jack of the assigned trunk. Relay 332 energizes in the sleeve circuit and completes a circuit 324, 332<c>, 328, 161, 158 for the calling supervisory lamp 328 which does not light, being shortcircuited over contacts 145<c>, 140<b>, 129, 128. High-impedance relay 331 locks up in a circuit 331, 162, 152<d>, 109, 101, 123 and reduces the current through the relay 101 which falls back driving the switch 100 from its 8th position. If no automatic ringing is provided, the switch is energized in its 9th and 10th p