Patent GB-661103-A (GB)
Title: Improvements in or relating to electrical signalling systems
Filed: 1949-05-28
Abstract: 661,103. Electric selective signalling. ERICSSON TELEPHONES Ltd., and STEVENS, J. R. H. May 28, 1949. No. 14741/48. Class 40 (i). [Also in Group XXXIX] A telephone substation equipped with apparatus which on the receipt of a normal call from a manual or automatic C.B. exchange operates automatically to return to the calling station an audible signal indicative of the numerical setting of one or more measuring devices associated with the said substation returns a different audible signal if a fault exists at the substation. The substation may also be used for outgoing and incoming telephone calls in the normal way, taking down of the handset initiating the disconnection of the signalling equipment from the line. Layout of equipment. In the embodiment leads LA, LB are connected to the A and B wires of a normal subscriber's line, leads TA, TB to the A and B line terminals of the telephone set, and lead TE to the extension bell terminal thereof. An earthed battery is connected to leads PMB and CBB leading to an associated water-level indicator and the extension call bell respectively. Lead CBA is also connected to the extension bell. Leads XO, X1, ... X9, and UO, U1, ... U9 are connected to contacts of the indicator associated with digits nought to nine on the "tens feet" and "units feet" scales respectively ; and leads HO, H1, ... H11 to similar contacts associated with "inches" nought to eleven. The indicator (not shown) is one of known type which applies a marking to contacts on its scales i accordance with the current liquid level. Lead PMA is connected to a device which locks the marking contacts of the indicator at their current setting as long as the lead is grounded. Call incoming to station. Relay R responds to the ringing current and brings up N over wiper and contact 1 of Pl. The two selectors included in the circuit of the station will for convenience be termed the primary (P) and secondary (S) selectors. The former is a 50 point uniselector with four pairs of wipers, the odd-numbered wipers wiping over contacts 1-25, and the even-numbered wipers over contacts 26-50; while the latter is a 25 point uniselector with 8 wipers, each wiping concurrently over contacts 1-25. Relay R releases at the end of the ringing period and completes a self-interrupted drive circuit over P1.1 whereupon P steps to contact 2, and N locks up over P1 and P2 until P steps to contact 50, or the release relay Z operates. The release of R also connects retard coil TF and relay L across the loop to the exchange to trip the ringing and operate L. Operation of N brings up A which thereupon interacts with B these relays having operate and release times of the order of 100 and 200 milliseconds respectively ; and also extends earth over PMA to lock the indicator, and over P7.2 to wiper S1. If the selector S is off-normal at this time a self-drive circuit is completed and S homes to contact 1, whereupon P steps to contact 3 over S1.1. With P5 on contact 3 relay T pulls up over S4.1 and grounds wiper S6 so that S steps to contact 2 under control of relays A and B. The next operation of A locks SDM operated until B operates to release SDM and step S to contact 3. However, with A up relay C is operated over P3.3 and S8.2 and when S steps to contact 3 capacitor QE discharges through C and holds C up for about 2 seconds during which time B is held also. The subsequent release of B reoperates A thus energising SDM over P7.3 and S6.3. Reoperation of B opens this circuit and S steps to contact 4. The inclusion of relay C thus provides an interval of about 2 seconds before the transmission of the audible signal commences. Relay D comes up over P7.3 and S6.4; locks under control of N; modifies the circuit of L to allow high-speed release thereof at a later stage ; and steps S to contact 5. The movement of wiper S4 to contact 5 releases T which extends ground over P7.3 and S7.5 to step S to contact 6. Transmission of audible signals : "Tens feet" zero. Test relay T is now connected over P5.3 and S4.6 to lead XO the zero lead of the "tens feet" scale. Should the level of the associated indicator stand at zero on this scale the lead XO is marked by battery from lead PMB and T operates, bringing up C over P3.3 and 88.6 to retard the subsequent release of B by about 2 seconds. When relay A releases (with B still up) relay BZ is operated over S2.6, opens its own circuit, and then reoperates ; this cycle continuing at 400 cycles per second since the BZ contact is mounted on a tuned reed. An audio-frequency tone is thus induced in the second winding of BZ and passed to line via retard coil TF. The duration of the tone pulse is determined by the time that B is up and A released, in this case about 2 seconds. With relay C unoperated the duration is of the order of 200 milli-seconds. The long pulse indicates a zero setting of the "tens feet" scale. The subsequent release of C and B terminates the pulse and P steps to contact 4 over P7.3 and S6.6. Relay T remains up and P steps to contact 5 over P7.4 where a self-drive homing circuit for S is completed over P7.5 and S1, P stepping to contact 6 as soon as S has homed. "Tens feet" not zero. With S in position 6 T does not operate and S steps to contact 7 of P7.3 and S7.6 under control of A and B. During the release period of B a short pulse of tone is sent to line. Wiper S7 at contact 7 extends ground over P7.3 to step P to contact 4 where a circuit is completed over contacts 7 to 24 of S6 to allow S to be driven under control of A and B. A short pulse of tone is transmitted at each step of S and the leads X1 to X9 are tested in turn. Relay T pulls up to the marked X lead, cuts the drive of S, and steps P to contact 5 thus disconnecting BZ and homing S to contact 1, whereafter P steps to contact 6. The number of pulses sent to line is equivalent to the digit marked on the "tens feet" scale and the conclusion of the signal is followed by an interdigital pause. "Units feet" signal. Wiper P7 at contact 6 extends earth over S7 to step S to contacts 2 and 3 under control of A and B and then automatically to contact 6. Contacts 6, 7 and 8 of P7 are connected similarly to contacts 3, 4 and 5 respectively and the "units feet" signal is transmitted in a manner similar to that described for the "tens feet" signal, P stepping to 7, 8 and 9. "Inches" signal. This is transmitted in like manner contacts 9, 10, 11 of P7 being utilized and P stepping to contact 12 at the end of the signal. Relay T then comes up over P5.12 and S4.1 and S steps from contact 1 to contact 2 under control of A and B. Relay C pulls up over P3.12 and S8.2 and holds B so that the subsequent stepping of S is delayed by about 2 seconds to provide a long pause before the signals are re-transmitted. When S steps to contact 3 relay C is disconnected at S8, and S steps on to 4 and 5 whereupon T is released and steps S to contact 6. Repetition of signals. This is similar to the first transmission, the operative contacts of P3 and P5 being 12, 13, 15, 16, 18 and 19 for the second transmission, and 21, 22, 24 and 25 with 27 and 28 of P4 and P6 for the third; and those of P7 being 11 to 19, and 20 to 25 with 26 to 28 of P8 respectively. After the third transmission of the "inches" signal P steps to contact 29 and S homes to contact 1. P is then self-driven to contact 50 where N releases and steps P to contact 1. The release of N opens the loop to the exchange and reconnects the telephone set to the line. Relays A, Band D release and restore the circuit to normal. Premature clearing during transmission. Interruption of the calling loop for a period exceeding 2 milli-seconds releases L which opens its own circuit to prevent its re-operation. When the exchange battery is reconnected to the line release relay Z pulls up and releases N. P then self-drives to contact 50 and thence to contact 1. Telephone calls. During the operation of the apparatus earth is applied intermittently to a local call bell over lead CBA. When the telephone handset is taken down to answer a call, Z pulls up to the telephone loop, and releases N which switches the telephone through to the line. Outgoing calls may be made without interference to, or from, the signalling equipment. Signalling existence of fault in equipment. Should relay T fail to respond to a marked lead, S steps on to contact 25 so that a train of 19 tone pulses is transmitted. Since the longest normal train is of 11 pulses the caller recognises this as a fault signal.