NZ196834A - Loop signalling circuit with opto-couplers - Google Patents

Description

.T 1 96834 Priority Da. Jfr .t'. fP.

CompSsto S^ccirjc3l':cn Fi!sd: 15 ;t;$i Class: . tf.°. ... «.-Tngi Publication Date: \ "R -T1 | P.O. Journal, Ko: ..J£f£ Patents Form No. 3 * NOTE: CMGE OF WKZ OF XFFLlC&m ;LIMITED to pic ;PATENTS ACT 1955 COMPLETE SPECIFICATION ;£#r«r> ;ELECTRONIC TELECOMMUNICATIONS DC LOOP SIGNALLING CIBCUIT ;We, THE PLESSEY COMPANY LIMITED, a British Company of Vicarage Lane, Ilford, Essex, England, hereby declare this invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- ;- 1 - ;1 ;34 ;TITLE: ELECTRONIC TELECOMMUNICATIONS DC LOOP SIGNALLING CIRCUIT. ;The present invention relates to electronic telecommunications DC loop signalling circuits. ;5 The known Strowger DC loop signalling circuit consits of three polarised relays and a four diode "bridge arrangement together with associated circuitry. The polarised relays are used to monitor the potential of the manual "board end and respond to change in direction of current and changes of 10 resistance. The line monitoring polarised relay has three windings, one of which is used as a bias winding. The bias winding uses its own power supply and not that of the distant exchange, thus segregating the exchange batteries and thereby avoiding earth potential difference problems. 15 Accordingly an aim of the present invention is to provide an electronic equivalent circuit of the Strowger DC loop signalling circuit which does not require the use of polarised relays. ;According tb. the present invention there is provided 20 a telecommunications direct current loop signalling circuit comprising a plurality of opto-coupling devices arranged to respond to signal conditions applied to the loop and one opto-coupling device is arranged to be continuously conducting during an idle state of the circuit and which 25 becomes nonconductive if the circuit becomes faulty. ;Referring to the drawing the relay contacts SZ1 to SZ3 and DA1 to DA3 are shown in the idle state. In the idle state, a 33k loop is provided via resistor R and opto-coupler 0CT1. ;- 3 - ;f 96834 ;The loop maintains a polarised relay, in the operators position circuit, (not shown), in the non operated state, providing a 650 ohm earth on the positive leg PL of the loop and a 650 ohm negative battery on the negative leg UL of the loop. Opto-coupler OCT-1 conducts and transmits a negative potential to the common control CC indicating that the circuit is free. ;In the idle condition opto-coupler 0CT1 continuously conducts. If the opto-coupler fails or the circuit is disconnected opto-coupler 0CT1 becomes non-conductive and a busy indication is given preventing the circuit being taken into use. ;When the circuit is seized, relay SZ operates and relay contacts SZ1 to SZJ switch to the other state. This enables opto-coupler 0CT1 and resister R to be short-circuited. Opto-coupler 0CT1 ceases to conduct and the negative potential signal is not transmitted to the common control CC indicating that the circuit is busy. When the operator answers, a 270 ohm earth appears on the negative leg HL of the loop and a 270 ohm negative battery appears on the positive leg PL of the loop. The above condition switches opto-coupler 0CT2 On and relay DA operates, contactsLAl to DA3 change to the other state and a negative potential signal indicating an answer signal is passed to common control CC. ;A speech path is now set up between the manual board and the originator of the call. The operator ascertains details from the caller and either gives the new number if the call was due to a changed number, and the operator and caller ;then clear, or the following procedure is adopted if the call was to a subscriber on service interception (SVT). ;If the subscriber rejects the call, the operator applies the answer condition and opto-coupler 0CT2 switches On as before and indicates to the common control CC to connect the caller. The operator informs the caller that he cannot be connected. If the subscriber accepts the call the operator transfers the call by operating and releasing the transfer key, which sends an answer condition followed by the potentials of the answer condition reversed. Opto-coupler 0CT2 switches On and transmits a signal to the common control CC. In less than 300 ms, opto-coupler 0CT3 and 0CT4 and transistor IE switch On els a result of the reversed answer condition and indicate to the common control CO to connect the caller to the subscriber on S"VT. ;If the call was set up by an operator, the interception operator after having trunk offered TKO, may want to recall the originating operator. Mais is achieved by operating and releasing the ring key for the second time. (The ring key would have been initially operated to provide the trunk offer facility). This applies a 270 ohm earth on the negative leg HL of the loop and a 270 phm negative battery on the positive leg PL of the loop, followed by a 9070 ohm earth on the positive leg PL of the loop and a 9070 ohm negative battery on the negative leg HL of the loop, within 150 ms of the first application* Opto-coupler 0CT2 switches On in response to the 270 ohm earth and battery on the negative and positive legs, ■HL, PL respectively and transmits a signal to the common control 1968 3 4 CO. For the 9070 ohm earth and battery, opto-coupler 0CT3 switches On which switches transistor TR On. The switching On of transistor TE within 150 ms of opto-coupler 0CT2 switching On maintains relay DA in a held condition.

When the operator clears the potentials applied to the positive leg PL and negative leg INL are removed for a minimum period of 160 ms.

The circuit meets the line condition 0 to 5-2 E. Diodes D are provided in series and in parallel with the opto-couplers to protect them when the line current reverses. A 0.1 jif capacitor C is provided to prevent the opto-couplers and transistors switching due to "battery noise or transients in the supply voltage and a 10 volt zener diode ZD is provided to ensure that the opto-coupler 0CT4- does not switch when the 9070 ohm earth and "battery potentials are applied. 1 O/C ^834

Claims (7)

WHAT WE CLAIM IS:-

1. A telecommunications direct current loop signalling circuit comprising a plurality of opto-coupling devices arranged to respond to signal conditions applied to the loop and one opto-coupler device is arranged to be continuously conducting during an idle state of the circuit and if non-conductive indicates a fault or busy condition of the circuit.

2. A telecommunications direct current loop signalling circuit according to claim 1 used for subscriber service interception.

3. A telecommunications direct current loop signalling circuit as claimed in claim 2 wherein the non-conductive state of said one opto-coupling device provides a busy condition signal.

4-. A -telecommunications direct current loop signalling circuit as claimed in claim 3 wherein said one opto-coupling device becomes non-conducting when the circuit is seized.

5- A telecommunications direct current loop signalling circuit as claimed in claim 4- wherein a second opto-coupling device provides an output signal indicative of an answer request.

6. A telecommunications direct current loop signalling circuit as claimed in claim 5 wherein third and fourth opto-coupling devices provide an output signal indicative of a transfer to a subscriber on service interception, the third opto-coupling device being used topgaintjgi.n the " 7 t 96834 answer condition.

7. A telecommunications direct current loop signalling circuit as claimed in any preceding claim substantially as described with reference to the accompanying drawing. ON « CAajv II