430,295. Telegraph exchange systems. SIEMENS & HALSKE AKT.-GES., Siemensstadt, Herlin. Nov. 8, 1934, No. 32131. Convention date, Nov. 8, 1933. [Class 40 (iii)] In a metering system in which the called station sends back over the b leg and earth a reply signal for initiating the metering action at the calling station as described in Specification 394,785, this reply signal is sent under the control of a slow-release relay U2 which may be the relay that diverts the last group of dialled impulses from the lifting- magnet H2 to the rotary magnet D2 in the final line-selector LW. The end of the reply signal is determined by the relay U2, while its beginning is determined by the pulling up of the test relay P2 of the line selector LW upon completion of the exchange connection. An additional slow-release relay F2 ensures that until the reply signal has been sent, the leg b over which it is sent shall be cut off from the contact er2 that normally sends on signals from the called to the calling station. Setting up exchange connection ; action at calling exchange. On the initiation of a call, the calling subscriber's preselector VW1 hunts for a free group selector GW and the sending-on contact er1 is reversed so that positive (spacing) polarity is applied to leg a, over which the outgoing selecting impulses are sent with earth return, while the incoming impulses for setting the meter are received over leg b and earth. When a free group selector is found, relay T1 pulls up and makes fast the connection with aid of relay C1 provided that wiper Z2 of the meter is on its zero contact ; but if the meter has not been zeroized the circuit of T1 is disabled at this point. The slow-release supervisory relay L1 in leg b pulls up and starts the local motor. The first group of dialled impulses is sent on by relay A1 whose armature a11 operates the lifting magnet H1 of the group selector and raises the latter to the selected level, the offnormal contacts k1, k2, being then operated. A relay U, (not shown), then switches the rotary magnet D1 on to the interrupter UGW so that the group selector hunts for the next stage in the selector system ; and relay P1 pulls up when this is found. Relay A1 is cut out by the rotary off-normal contact w so that subsequent groups of dialled impulses passing to the stage VA1 select first the trunk FL and then, through the line selector LW, the called subscriber associated with the preselector VW2. Setting up exchange connection ; action at called exchange. Dialling-impulses sent on by armature er1 over leg a and earth reach relay A2, so that armature a21 impulses the lifting-magnet H2 and the slow-release relay V2 which at v21 disables relay U2 ; but when the group of impulses is complete, relay V2 releases and relay U2 is energized through v21 and off-normal contact k3. The next group of impulses passes to the rotary magnet D2 to select the required subscriber. A slowrelease relay F2 is energized through u21 and ensures that contact er2 shall not be connected to the b leg until it has been reversed to the positive or spacing position by the action of relay ES2 and of the called subscriber's station (not shown). When dialling has ceased relay V2 releases and slow-release relay U2, whoso winding I is cut off by the off-normal contact w2, has its hold-on winding II cut off at v22. Test relay P2 is energized via v23 if the called subscriber is free, completing the connections and causing the slowrelease supervisory relay L2 to pull up. The arrangements are such that positive (spacing) potential is continuously applied to leg b, except during the negative reply impulse described below. Release. The c circuit is broken at either station when a supervisory relay L1 or L2 receives a marking impulse considerably longer than the meter-preparing impulse referred to below. The exchange circuits and metering circuits are then restored to normal in an obvious manner. Metering. The meter circuits ZE are shown as associated with one group selector GW, but may be arranged for selective connection by means of selector switches. At the calling station closure of contact c12 causes relay E to pull up and prepare at e4 a circuit for the subscriber's meter-actuating magnet ZT. As soon as the off-normal contact k2 is restored, winding I of relay F1 energizes this relay, which holds on until the reply impulse arrives to start the metering action ; the clockwork switch uk closes periodically for the purpose of effecting metering, and when relays E, F1 have pulled up it energizes relay B via e6, f13, and this relay then holds on via e3 until the exchange connection is eventually released. A negative reply impulse is sent back over leg b as follows. At the called station the slow-release relay U2 pulled up temporarily, as described above, during the establishment of the connection, and during this time positive potential was applied to the b leg through the off-normal contact w1 and contact f 21, which were operated. When, however, the test relay P2 pulls up, a negative impulse is sent over the b leg through contact u21, and this endures until the release of the slowrelease relay U2 has been completed. The length of the impulse, as determined by the release time of relay U2, is not great enough to release the supervisory relays L1, L2, but is great enough to release relay F1 at the calling station. The clockwork contact uk thereupon energizes relay B via f 13, and relay V1 is cut off at b2 but with slow release ; and in the interval during which B and V1 are both energized an impulse through b3, v11 and Z2 operates the meter-switch magnet DZ, shifting the wipers Z1, Z2 by one step. The next two steps are effected automatically by the interrupter UZ, and in this way three impulses are sent by wiper Z1 through meter magnet ZT for the purpose of registering the basic charge. Thereafter impulses depending on lapse of time are sent, the wipers Z1, Z2, being stepped forward by the magnet DZ energized by the clockwork switch uk at intervals. For the night tariff, contact nk is closed and relay B acts to disconnect certain of the contacts associated with wiper Z1. The invention may also be applied to zone metering systems; thus a relay contact v associated with the group selector may, for calls other than trunk calls, cut off the switch Z1 except in the zero position. On release of the exchange connection relay E releases and the wipers Zl, Z2 are stepped home under the influence of interrupter UZ.