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Telecommunications Line Monitor

IP.com Disclosure Number: IPCOM000060872D
Original Publication Date: 1986-May-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Shah, VV: AUTHOR

Abstract

Telecommunication systems are widely used for information transfer. As a consequence, circuits which can be interfaced with such systems and which provide means of reliable line monitoring are of significant importance. The present circuit is one which can be used to monitor a telephone line for the purpose of dialled digit logging, though it has numerous other applications, because it is capable of operating with a variety of line types. Operating and detecting ranges are selectable by simple component changes. The circuit is designed to utilize wide tolerance components, and it exhibits stable performance over a wide range of temperatures. An opto-coupler is used to provide electrical isolation of the logging circuitry from the telephone line.

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Telecommunications Line Monitor

Telecommunication systems are widely used for information transfer. As a consequence, circuits which can be interfaced with such systems and which provide means of reliable line monitoring are of significant importance. The present circuit is one which can be used to monitor a telephone line for the purpose of dialled digit logging, though it has numerous other applications, because it is capable of operating with a variety of line types. Operating and detecting ranges are selectable by simple component changes. The circuit is designed to utilize wide tolerance components, and it exhibits stable performance over a wide range of temperatures. An opto-coupler is used to provide electrical isolation of the logging circuitry from the telephone line. The circuit is connected in series with the line 1 and provides outputs for line currents in either direction. A transistor 2 has its emitter connected to one part of the line 1 and its collector through a diode 3 to the other part. A resistor 4 connects the base to the emitter of the transistor 2, and the base is also connected to the other part of the line 1 through a light-emitting diode (LED) 5 forming part of an opto-coupler 6. A second transistor 7 is arranged with similar components, but in the opposite direction. A shunt resistor 12 connects the two parts of the line 1. The shunt resistor 12 ensures that the circuit does not respond to line leakage currents. The value of the resistor 12 is selected so that the maximum voltage drop developed across it by leakage current is insufficient to illuminate an opto-coupler LED 5 or 10. At higher line current levels, the voltage drop across resistor 12 increases to the extent that the LED threshold is exceeded. By means of normal opto-coupler action, this can be detected at the opto-coupler output. A further increase in the line curre...