IE51189B1 - Electronic detection circuit - Google Patents

Description

TITLE: ELECTRONIC DETECTION CIRCUIT The present invention relates to electronic detection circuits for detecting differing signalling conditions on a conductor path.

The invention finds application in telephone systems and can be used as an electronic equivalent for an electromechanical relay.

An electronic equivalent for an electromechanical relay is disclosed in co-pending Application No. 44492/77.

The electronic equivalent uses an opto-coupler which does not switch ON until the current rises to a threshold level and which switches OFE when it falls below the threshold level. Consequently the width of the pulse produced by the relay is reduced and pulse width distortion is experienced.

Accordingly an aim of the present invention is to provide an electronic equivalent for an electromechanical relay which overcomes the above mentioned pulse width reduction and distortion.

According to the present invention there is provided an electronic detection circuit for detecting first and second signalling conditions on a conductor path, the detection circuit including a first opto-coupler and a second optocoupler connected to the conductor path, and a bistable device connected to the opto-couplers for providing an output signal; wherein when the first signalling condition is present on the conductor path the first opto-coupler is conditioned in an ON state which sets the bistable device, - 5 and when the second signalling condition is present on the conductor path the second opto-coupler is conditioned in an ON state, which resets the bistable device, the setting and resetting of the bistable device provides the output signal which is dependent upon the detected first and second signal conditions.

According to an aspect of this invention the first and second opto-couplers are provided with current protection means.

In one practical application the electronic detection circuit is employed for providing the functions provided by a polarised relay (an Ά' relay) in an incoming relay set employed in a signalling system, known as DC No.2 type, in a telecommunications system. In this type of system, signal conditions are received at the incoming relay set over a junction extending to a distant outgoing relay set.

An embodiment of the invention will now be described with reference to the accompanying drawing which shows an electronic detection circuit according to the invention.

In an idle condition the above mentioned distant outgoing relay set provides the line with an earth on the negative leg NL and a negative potential on the positive leg PL. This permits current to flow via resistor S . and the positive leg PL to the distant relay set.

The distant relay set initiates a telephone line seizure condition by replacing the earth potential with a negative potential on negative leg NL, and by replacing the negative potential by an earth on the positive leg PL. This - Aallows current to flow via resistors S and El to the negative potential of the distant end via opto-cou.pler OCTI and negative leg Hl. When opto-coupler OCTI conducts, transistor TE2 of the bistable device switches OH and transistor TE5 switches OPP. The output 0/P changes from OV to -50V and remains at the latter potential until optocoupler 0CT2 conducts. As a result of the voltage change relay GD is caused to operate. The contacts of relay GD which are shown, are nov; operated, placing control of the bistable device under the control of opto-couplers OCTI and 0CT2.

When the distant end starts pulsing for the first break,the current reverses and is detected by opto-coupler 0CT2. Opto-coupler 0CT2 is switched OH and transistor TE1 of the bistable device is also switched OH. At this instant transistor TE2 is switched OFF and transistor TSJ switched OH. This process alternates giving earth and -50V potentials at the output 0/P at a speed of lOpps.

In practice the line resistances can vary from 0 to 8.2E ohms consequently if the line resistance is zero ohms, the line current would be in the order of 126 mA. If this current was allowed to pass through opto-couplers OCTI and 0CT2 they would deteriorate rapidly resulting in a reduced life span. Therefore, means such as resistor El, in the order of 100 ohms, is used in conjunction with transistors TE4- and ΤΞ5 and any current greater than 10 mA can be made to by-pass opto-coupler OCTI because transistors TEA and TE5 would switch, and their respective base - 5emitter voltages would be greater than 1 volt. Transistors TE4 and TH5 are connected in parallel enabling the load to be shared by both transistors. This prevents excessive current being passed through one oi the transistors and prevents excessive power dissipation. Eesistor 52 and transistors TE6 and TE7 are provided to protect optocoupler 0CT2 when the current is in the reverse direction.

The above description has been of one embodiment only and is not intended to limit the scope of the invention.

For example, each transistor pair, TE4 and TE5 or TE6 and TE? could be replaced by a high power transistor.

Claims (5)

1. WHAT WE CLAIM IS:1. An electronic detection circuit for detecting first and second signalling conditions on a conductor path., the detection circuit including a first opto-coupler and a second opto-coupler connected to the conductor path, and a bistable device connected to the opto-couplers for providing an output signal, wherein when the first signalling condition is present on the conductor path the first opto-coupler is conditioned in an OH state which sets the bistable device and when the second signalling condition is present on the conductor path the second optocoupler is conditioned in an OH state which resets the bistable device, the setting and resetting of the bistable device provides the output signal which is dependent upon the detected first and second signal conditions.

2. An electronic detection circuit as claimed in claim 1 for detecting first and second signalling conditions on a telephone line. J. An electronic detection circuit as claimed in claim 2 wherein the first signalling condition is indicative of telephone line seizure.

3. 4. An electronic detection circuit as claimed in claim 2 wherein the second signalling condition is indicative of a first break condition on the telephone line.

4.

5. An electronic detection circuit as claimed in claim d wherein each opto-coupler is connected to a current protection circuit which enables current exceeding a predetermined amount to by-pass the respective opto-coupler