232,691. Coventry Automatic Telephones, Ltd., Collyer, J. E., and Wilman, C. W. Jan. 25, 1924. Automatic and semi-automatic exchange systems; metering.-In a system in which the metering or non-metering of a call is determined by the simultaneous or successive energization of two back-bridge relays, metering is also dependent upon an additional meter-preparing operation which takes place at the conclusion of dialling so that, even if the back-bridge relays are subjected to the metering conditions at any time during the establishment of the connection, no operation of the meter takes places at this time. According to one arrangement, Figs. 1 - - 3, the meter-preparing operation is effected by the energization of one back-bridge relay whilst the other is de-energized. In a second arrangement, Figs. 4 and 5, the back-bridge relays are normally disconnected from the talking wires and are connected thereto by a polarized relay which operates by reversal of current at the conclusion of dialling. First arrangement; call to automatic subscriber; metering.-The call is extended in known manner to a first selector, Fig. 1, at which relays 101, 103, 107 energize, the latter connecting up dialling tone. The first series of impulses is repeated to the vertical magnet 110 in parallel with relay 111, which completes a circuit 105, 114, 112 for relay 113, which locks up over contacts 118, 115. Upon the relapse of relay 111, hunting takes place in the usual manner under the combined control of relay 113 and magnet 116, and when an idle final selector, Fig. 2, is reached, relay 120 operates and switches through. Relay 153 energizes over the grounded test wire 178 and completes a circuit for relay 156. which connects relay 158 in series with one back-bridge relay 124. Relays 158, 160 operate, and the next series of impulses is repeated at contact 125 to relay 158 and thence over contacts 164, 165, 162 to the vertical magnet 163. The relapse of relay 160 at the end of the digit causes the impulses of the final digit to pass to the rotary magnet 167. Relay 156 relapsing at the end of this digit either closes a locking circuit for the test relay 169 in case the wanted line is busy or, if the line is idle, completes a circuit for the upper winding of switching relay 176 which, by opening a shortcircuiting contact 177, holds over its lower winding. Relay 176 connects ringing current to the wanted line and at armature 193 connects a ring- back battery-connected signal to the upper talking conductor. The consequent operation of one back-bridge relay 128 with the other 124 disconnected constitutes the meter-preparing operation and causes the release of relay 107 and the operation of relay 130. When the called subscriber replies, the ring-cut-off relay 186 operates, and both back-bridge relays 128, 124 energize in series over the called loop. Relay 107 again energizes, and the metering circuit 105, 132, 134, 135, 136 is closed during the time of release of relay 130. Call to operator's position; prevention of automatic metering; metering by operator. When a first selector, Fig. 1, gains access to an operator's position, Fig. 3, relay 351 energizes in series with relay 128 to establish the meter-preparing operation as before, and closes circuits for relay 354 and lamp 353. The insertion of a plug 355 energizes relay 361 which disconnects relay 351. During the interval before relay 354 (which is very slow) releases, relay 124 is energized and relay 128 disconnected so that relay 130 is released by the operation of relay 107 and, when relay 128 subsequently operates, the meter circuit is open at contact 134. The operator may operate the meter one or more times by means of a key which opens the lower line conductor, thereby establishing again the meter-preparing condition. Second arrangement. When a first selector, Fig. 4, is seized, relays 201, 203, 205, 207 operate, and a circuit is completed for the lower winding of polarized relay 226 which does not operate. The vertical and rotarv movements take place in a similar manner to that described above for the first arrangement and, when an idle final selector, Fig. 5, has been selected, relay 220 switches through and completes a circuit over lead 257 for relay 258 which energizes relay 260. Relay 251 energizes over both talking conductors in series with the bridged upper winding of polarized relay 226 and completes a circuit for relay 262. The tens and units impulses are repeated to relay 251 at contact 228 and thence at contact 2'66 to the vertical and rotary magnets 264, 268, relay 262 relapsing at the end of the tens digit. The relapse of relay 260 at the end of the units digit either locks up busy relay 269 or completes a circuit for the switching relay 275, the latter connecting up ringing current at contacts 278, 277 and at contacts 252, 255 reversing the battery and ground connections of relay 251 to the talking leads, so that polarized relay 226 now responds, holds over its lower winding by short-circuiting resistance 242. disconnects its upper winding, and connects the back-bridge relays 230, 231 to the talking leads. When the called subscribed replies, relays 230, 231 operate and open the circuit of relay 207 so that, during the time of release of the latter relay, a metering impulse is transmitted over contacts 238, 237, 236, contacts 228 being short-circuited at this time to prevent the calling subscriber from interfering with the metering. Specifications 208,075, 221,362, 224,692, and 233,467 are referred to.