IE51864B1 - Electronic telecommunications dc loop signalling circuit - Google Patents

Abstract

Electronic SVI/CNI DC loop signalling circuit uses opto-couplers OCT1- OCT4 to provide the polarised relay functions of the known Strowger circuit. The circuit has one opto-coupler OCT1 which continuously conducts during the idle state of the circuit. The opto- coupler also automatically busies the circuit under fault conditions.

Description

TITLE: ELECTRONIC TELBGOMMGNICATIONS DC LOOP SIGNALLING CIRCUIT.

Tbe present invention relates to electronic telecommunications NO loop signalling circuits.

The known Strowger NO 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 hoard end and respond to change in direction of current and changes of resistance. The line monitoring polarised relay has three windings, one of which is used as a bias winding. The bias wincH hg uses its own power supply and not that of tbe distant exchange, thus segregating the exchange batteries and thereby avoiding earth potential difference problems.

Accordingly an aim of the present invention is to provide an electronic equivalent circuit of the Strowger NO loop signalling circuit which does not require the use of polarised relays.

According th the present invention there is provided a telecommunications direct current loop signalling circnit 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 loop and which becomes nonconductive if the loop becomes faulty.

Referring to the drawing the relay contacts SZ1 to SZJ and NA1 to NA5 are shown in the idle state. In the idle state, a 33k loop is provided via resistor R and opto-coupler 0CT1.

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 EL of the loop. Opto-coupler OCT1 conducts and transmits a negative potential to the common control CO indicating that the circuit is free.

Tn the idle condition opto-coupler OCT1 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 E to be short-circuited. Optocoupler 00T1 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 El 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 M operates, contacteMl to M3 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 (SVI).

If the subscriber rejects the call, the operator applies the answer condition and opto-coupler 00T2 switches On as before and indicates to the common control CC to connect the caller. The operator informs the caller that he cannot he 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 hy the potentials Ί0 of the answer condition reversed. Opto-coupler 0CT2 switches On and transmits a signal to the common control OC. In less than 500 ms, opto-coupler 00T3 and 00T4 and transistor TE switch On as a result of the reversed answer condition and indicate to the common control CO to connect the caller to the Ί5 subscriber on SVI.

If the call was set up hy an operator, the interception operator after having trunk offered TEO, may want to recall the originating operator. This is achieved hy 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 ohm negative battery on the positive leg Hi of the loop, followed hy a 9070 ohm earth on the positive leg H of the loop and a 9070 ohm negative battery on the negative leg EL of the loop, witt-in -150 ms of the first application, Opto-coupler 00T2 switches On in response to the 270 ohm earth and battery on the negative and positive legs, El, H respectively and transmits a signal to the common control - 5 CC. For the 90?0 ohm earth and. battery, opto-coupler OOTJ switches On which switches transistor TR On. The switching On of transistor TR within 150 ms of opto-coupler 00T2 switching On maintains relay BA in a held condition.

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

The circuit meets the line condition 0 to 5·2 K. Biodes B 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 ZB is provided to ensure that the opto-coupler 0CT4 does not switch when the 9070 ohm earth and battery potentials are applied.

Claims (7)

1. WHAT WE CLAIM IS:1. A telecommunications direct current loop signalling circuit comprising a plurality of opto-ooupling devices arranged to respond to signal conditions applied to the loop and one opto-coupler device is arranged to he continuously conducting during an idle state of the loop and which becomes non-conductive if the loop becomes faulty.

2. A telecommunications direct current loop signalling circuit according to claim Ί 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 is used to signal a busy condition.

4. A telecommunications direct current loop signalling circuit as claimed in claim 3 wherein said one optocoupling 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 optocoupling 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-ooupling devices provide an output signal indicative of a transfer to a subscriber on service interception, the third opto-coupling device being used to maintain the 81864 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.