GB1600254A - Electronic detection circuits - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO ELECTRONIC DETECTION CIRCUITS (71) We, THE PLESSEY COMPANY LIM ITED, a British Company of, Vicarage Lane, Ilford, Essex IG 1 4AQ, do hereby declare the 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: The present invention relates to electronic detection circuits for detecting differing signalling conditions on a conductor path.

This invention is, for example, particularly applicable to telephone systems and can be used as an electronic equivalent for an electromagnetic relay.

According to the present invention there is provided an electronic detection circuit for detecting idle and seize signalling conditions on a telecommunication junction, extending to a distant outgoing relay set, the detection circuit including an opto-isolator device comprising a light generating semiconductor diode optically coupled to a photo-transistor, the device being connected in the junction, and current regulating means comprising a semiconductor device and a resistor associated with the opto-isolator device, wherein when the idle signalling condition, represented by the application of an earth potential on the negative (- ve) conductor and a negative potential on the positive (+ ve) conductor, is present on the conductor path, the light generating semiconductor diode is conditioned in an OFF state, whereas when the seize signalling condition, represented by the application of a negative potential on the negative (- ve) conductor and an earth potential on the positive (+ ve) conductor, is present on the junction, the light generating semiconductor diode is conditioned in an ON state and wherein regulating means is adapted to regulate the flow of current in the light-generating semiconductor diode when it is conditioned in the ON state, the regulation being effected by shunting current through the semiconductor device in dependence upon flow of said current through the resistor.

The opto-isolator device preferably comprises a light generating semiconductor diode optically coupled to a phototransistor contained in the one package and which is included in a circuit adapted to indicate the signalling condition present on the conductor path. An opto-isolator device suitable for this invention is of the MOTOROLA 4N26 type.

A semiconductor device and resistor are employed in the regulator means which is adapted to shunt the current from the optoisolator. In carrying out the present invention the detection circuit is utilised as an electronic equivalent of an electromagnetic relay.

In one practical application, the circuit is employed for providing several functions provided by a polarised relay (an 'A' relay) in an incoming relay set employed in the signalling system known as DC No. 2 type in a telecommunications system.

In this system signal-conditions are received at the incoming relay set over a junction extending to a distant outgoing relay set.

In operation the electronic circuit caters for reduction of crosstalk.

Again in operation when the electronic circuit is instructed to indicate metering or called subscriber answer conditions the regulating means ensures that the phototransistor is not overloaded.

An embodiment of the invention will now be described by way of example and with reference to the drawing accompanying the provisional specification in which, Figure 1. Illustrates a portion of an electromechanical detection circuit of an incoming relay set of a DC No. 2 System and Figure 2. Illustrates an electronic detection circuit in accordance with this invention and which is an electronic equivalent of the circuit function shown in Figure 1.

Referring to the drawing, in Figure 1 a portion of an electromechanical circuit is shown, where a polarised A relay is connected to a line transformer LT which is connected to a junction (not shown) extending to a distant outgoing relay set (not shown) other relays are not shown but contacts GD, which provides a loop across the - ve and + ve conductors, following its operation when A is operated, is shown. A contact of relay B is also shown and this connects a portion of circuit concerned with metering and called subscriber answer signal conditions.

In the idle state of the distant outgoing relay set, a first signalling condition, represented by the application of an earth potential on the - ve conductor, and a negative potential on the + ve conductor at the incoming relay set. Current flow during this signalling condition is by way of resistor R 1 and through one winding of the A relay to the + ve conductor and thereby to the distant outgoing relay set. The A relay does not operate in these circumstances.

When a sieze or second signalling condition is signalled from the distant outgoing relay set, and represented by the application of a negative potential on the - ve conductor and an earth potential on the + ve conductor at the incoming relay set. Current now flows from the + ve conductor through one of the windings of the A relay, the diode D and another winding of the A relay to the - ve conductor. The A relay operates in these circumstances and contacts Al signal the signalling condition to an output OP. Relays B and GD subsequently operate and prepare the circuit for subsequent operation of relay MA, the contacts of which arrange for the earthing of the loop provided by contacts of relay GD.

Referring now to Figure 2, this illustrates an electronic circuit which provides similar facilities as that provided by the circuit illustrated in Figure 1. It should be noted that the components not designated in this circuit are not essential for the operation of this invention and therefore are only shown by way of explanation.

The - ve and + ve conductors are again connected to a line transformer LT which is in turn connected to ajunction extending to a distant outgoing relay set. In the idle or first signalling condition of the outgoing relay set (as defined previously), the current flow in the + ve conductor is by way of resistor R1 diode D2 and the junction to the distant outgoing relay set. With this first signalling condition present, the opto-isolator OI, having no current passing through the lightdiode LD, takes up a first state in which the photo-transistor PT is switched off. No significant output appears at OP.

When a seize or second signalling condition is signalled from the distant outgoing relay set (as previously defined), the current now flowing in the - ve conductor comprises of the current through resistor R1 and that from the distant outgoing relay set earth via the + ve conductor over the junction. Accordingly this current flows through the light diode LD, resistor R2 and over the junction to the distant outgoing relay set negative potential. This current is at its minimum value when the distant exchange battery is at its minimum voltage and the line resistance over the junction is comparatively high.

With very small values of current flowing in the + ve conductor, insufficient voltage is developed across resistor R2 to cause transistor TRl to start conducting. However, this current is sufficient to be satisfactorily detected by the opto-isolator OI i.e. the current through the light diode LD is sufficient to activate the photo-transistor PT to be switched ON resulting in the opto-isolator OI taking up a second state, enabling a significant output to appear at OP.

As a result of the significant output appearing at OP, and a relay sequence (not shown), relay GD is subsequently operated.

Contacts GOD 1 disconnects resistor R1 and places a loop across the - ve and + ve conductors giving rise to the current in the - ve and + ve conductors becoming identical.

On short junctions, when line resistance is comparatively low, the line current is comparatively high which in turn increases the voltages drop across resistor R2, as a result of which the p.n.p. transistor TRI conducts prior to relay GD operating. The effect of transistor TR1 conducting tends to reduce the current flow through the light diode LD of the opto-isolator OI with the effect that more current is taken by transitor TR1. In effect the current through the opto-isolator OI is automatically regulated enabling the light diode LD portion to be protected from damage as a result of high currents which may normally be expected using short junctions or under overload conditions. This gives a greater operational life for the optoisolator. Typically, the maximum current that can flow through the light diode LD (within practical limits) is that current, which when multiplied by the resistance of resistor R2, is equivalent to the maximum base/einitter voltage drop of the transistor type employed, plus the small base current of transistor TR1.

The diode combination comprising diodes Dla, Dlb and D2 is used to electrically balance the circuit to reduce crosstalk. Thus, current flowing through the diodes Dla and Dlb in the +ve conductor, is matched with that flowing through the light diode LD and the base/emitter diode of transistor TR 1 in the - ve conductor.

Similarly, current flow through the diode D2, in the + ve conductor matches the effect of diode D3 in the - ve conductor. Thus, contacts GD2, and the circuitry associated with it, are, therefore, connected at the balanced portion of the loop, irrespective of the direction of current flow in the loop.

A further signalling requirement of the circuit is that metering and called subscriber answer conditions, which give rise to potential opto-isolator current overload, should be catered for. This is achieved by signalling by way of conductor MA to transistor TR2.

When a significant signal is applied over conductor MA to the base electrode of the p.n.p. transistor TR2 it is caused to conduct thereby connecting an earth potential, by way of the high impedance coil HI and contacts GD2, to the balance portion of the loop. Although the current in the - ve conductor increases as a result of these further signalling conditions, the current through the light diode LD only increases by a small amount as the regulating circuit ensures that the increase in current in the - ve conductor is passed by transistor TR1.

It should be appreciated that if digit signals are being transmitted over the junction the first and second signalling conditions will appear alternately and the circuit will operate as already described for these two signalling conditions.

Various alternatives to the described embodiment will appear to those skilled in the art and it should therefore be understood that the described embodiment is not intended to be a limitation on the scope of this invention.

For instance although the opto-isolator device OI is shown as a unitary device, the same result can be achieved by utilising discrete components.

Again transistors TRI and TR2 can be replaced by n.p.n. transistor types by suitable rearrangement of the supply voltages.

WHAT WE CLAIM IS: 1. An electronic detection circuit for detecting idle and seize signalling conditions on a tclecommunication junction, extending to a distant outgoing relay set, the detection circuit including an opto-isolator device comprising a light generating semiconductor diode optically coupled to a photo-transistor, the device being connected in the junction, and current regulating means comprising a semiconductor device and a resistor associated with the opto-isolator device, wherein whe. the idle signalling condition, represented by the application of an earth potential on the negative (vie) conductor and a negative potential on the positive (+ ve) conductor, is present on the junction, the light generating semiconductor diode is conditioned in an OFF state, whereas when the seize signalling condition, represented by the application of a negative potential on the negative (- ve) conductor and an earth potential on the positive. (+ ve) conductor, is present on the junction, the light generating semiconductor diode is conditioned in an ON state and wherein the regulating means is adapted to regulate the flow of current in the light generating semiconductor diode when it is conditioned in the ON state, the regulating being effected by shunting current through the semiconductor device in dependence upon flow of said current through the resistor.

2. An electronic detection circuit as claimed in claim 1 in which when the detection circuit is instructed to indicate metering or called subscriber answer conditions the regulating means ensures that the photo-transistor is not overloaded.

3. An electronic detection circuit as claimed in any one of claim 2 in which when the opto-isolator device is conditioned in its first state the photo-transistor is switched-off.

4. An electronic detection circuit as claimed in claim 3 in which when the optoisolator device is conditioned in its second state the photo-transistor is switched-on.

5. An electronic detection circuit as claimed in any preceding claim in which the electronic detection circuit is an electronic equivalent of an electromagnetic relay circuit forming part of an incoming relay set.

6. An electronic detection circuit substantially as described herein, with reference to, and as shown, in the drawing accompanying the provisional specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. Similarly, current flow through the diode D2, in the + ve conductor matches the effect of diode D3 in the - ve conductor. Thus, contacts GD2, and the circuitry associated with it, are, therefore, connected at the balanced portion of the loop, irrespective of the direction of current flow in the loop. A further signalling requirement of the circuit is that metering and called subscriber answer conditions, which give rise to potential opto-isolator current overload, should be catered for. This is achieved by signalling by way of conductor MA to transistor TR2. When a significant signal is applied over conductor MA to the base electrode of the p.n.p. transistor TR2 it is caused to conduct thereby connecting an earth potential, by way of the high impedance coil HI and contacts GD2, to the balance portion of the loop. Although the current in the - ve conductor increases as a result of these further signalling conditions, the current through the light diode LD only increases by a small amount as the regulating circuit ensures that the increase in current in the - ve conductor is passed by transistor TR1. It should be appreciated that if digit signals are being transmitted over the junction the first and second signalling conditions will appear alternately and the circuit will operate as already described for these two signalling conditions. Various alternatives to the described embodiment will appear to those skilled in the art and it should therefore be understood that the described embodiment is not intended to be a limitation on the scope of this invention. For instance although the opto-isolator device OI is shown as a unitary device, the same result can be achieved by utilising discrete components. Again transistors TRI and TR2 can be replaced by n.p.n. transistor types by suitable rearrangement of the supply voltages. WHAT WE CLAIM IS:

1. An electronic detection circuit for detecting idle and seize signalling conditions on a tclecommunication junction, extending to a distant outgoing relay set, the detection circuit including an opto-isolator device comprising a light generating semiconductor diode optically coupled to a photo-transistor, the device being connected in the junction, and current regulating means comprising a semiconductor device and a resistor associated with the opto-isolator device, wherein whe. the idle signalling condition, represented by the application of an earth potential on the negative (vie) conductor and a negative potential on the positive (+ ve) conductor, is present on the junction, the light generating semiconductor diode is conditioned in an OFF state, whereas when the seize signalling condition, represented by the application of a negative potential on the negative (- ve) conductor and an earth potential on the positive. (+ ve) conductor, is present on the junction, the light generating semiconductor diode is conditioned in an ON state and wherein the regulating means is adapted to regulate the flow of current in the light generating semiconductor diode when it is conditioned in the ON state, the regulating being effected by shunting current through the semiconductor device in dependence upon flow of said current through the resistor.

2. An electronic detection circuit as claimed in claim 1 in which when the detection circuit is instructed to indicate metering or called subscriber answer conditions the regulating means ensures that the photo-transistor is not overloaded.

3. An electronic detection circuit as claimed in any one of claim 2 in which when the opto-isolator device is conditioned in its first state the photo-transistor is switched-off.

4. An electronic detection circuit as claimed in claim 3 in which when the optoisolator device is conditioned in its second state the photo-transistor is switched-on.

5. An electronic detection circuit as claimed in any preceding claim in which the electronic detection circuit is an electronic equivalent of an electromagnetic relay circuit forming part of an incoming relay set.

6. An electronic detection circuit substantially as described herein, with reference to, and as shown, in the drawing accompanying the provisional specification.