GB2213943A

GB2213943A - Hall-effect arrangements

Info

Publication number: GB2213943A
Application number: GB8900498A
Authority: GB
Inventors: Peter John Kerr
Original assignee: YORKSHIRE WATER AUTHORITY
Current assignee: YORKSHIRE WATER AUTHORITY
Priority date: 1988-01-14
Filing date: 1989-01-10
Publication date: 1989-08-23
Also published as: GB8800845D0; GB8900498D0

Abstract

A Hall-effect arrangement for sensing signals on a transmission line T comprises an inductance and, electrically isolated therefrom, a Hall-effect device He powered from its own voltage supply and exposed to any magnetic field from the inductance. Any circuit connected to the Hall-effect device is exposed only to the output voltage thereof and is thereby protected regardless of the voltage supplied to the inductance or of its rise time. <IMAGE>

Description

GALVANIC ISOLATOR The present invention relates to a galvanic isolator for an electrical circuit.

Signal transmission lines such as used in telecommunications, instrumentation monitoring and control engineering, are often connected to expensive electronic equipment, which is prone to damage by an overvoltage on the signal line. In the case, for instance, of a transmission line buried in the ground, such an overvoltage may be induced by lightning striking the ground in the vicinity of the line.

Although electronic devices are known for protecting a circuit against an undue input voltage, they may not necessarily protect a circuit in these circumstances since the rise time of the overvoltage may be faster than the time the devices take to operate. In this instance, the full magnitude of the overvoltage would be applied to the apparently protected circuit.

It is an object of the present invention to provide a circuit isolator effective to protect a circuit against an overvoltage regardless of the rise time thereof.

There is provided by the present invention a galvanic isolator comprising an inductance to generate a magnetic field on the application of a voltage thereto and, electrically isolated therefrom, a Hall effect device powered from its own voltage supply and positioned in relation to the inductance to be exposed.

to any magnetic field from the inductance and thereby produce a current in response to a magnetic field from the inductance.

It will be appreciated that the device of the present invention provides no current conducting pathway between the inductance and the Hall-effect device and that the voltage of the latter is limited to that of its own voltage supply.

Thus, any circuit connected to the Hall-effect device would be exposed only to the output voltage thereof and could therefore be protected regardless of the voltage supplied to the inductance, or of its rise time.

The present invention is considered to be particularly useful for signal transmission lines, in which case, the inductance would terminate a line and the Hall -effect device would be connected to the circuitry being served by the line.

The present invention will now be described, by way of example only, with reference to an embodiment thereof as illustrated in the accompanying drawing in which the sole figure is a circuit diagram of the embodiment.

Referring now to the sole figure, the embodiment comprises an inductance in the form of a coil L connected to terminate a signal transmission line generally indicated at T. The embodiment further comprises a Hall-effect device He provided with its own voltage source, in this instance shown as 5 V +.

The Hall-effect device provides an output to an amplifier OpA, in this instance having an ammeter Am connected across its output to provide a measure of analogue signals normally to be transmitted by the transmission line.

The coil, which may be mounted on a suitable core, is configured to produce a concentrated magnetic field, and the Hall-effect device is located to be exposed to the field produced by the coil and thereby produce a current in responses thereto. In this instance, the Hall-effect device is such as to vary its current output in response to the varying magnetic field from the coil produced by the current through the coil.

The amplifier may modify the signal if the need arises to compensate for remanance in the inductance and could be used otherwise to condition or "tailor" the output signal.

The illustrated embodiment provides isolation from any overvoltages on the transmission line of the amplifier regardless of the overvoltage rise time or magnitude and, in this instance, also constitues a linear analogue communication path between the signal line and the amplifier for A.C. and D.C. signals.

Claims

1 A galvanic isolator comprising an inductance to generate a magnetic field on the application of a voltage thereto and, electrically isolated therefrom, a Hall-effect device powered from its own voltage supply and positioned in relation to the inductance to be exposed to any magnetic field from the inductance and thereby produce a current in response to a magnetic field from the inductance.

2 A galvanic isolator according to Claim 1, wherein the inductance is a coil.

3 A galvanic isolator according to Claim 2, wherein the coil is mounted on a core.

4 A galvanic isolator according to any of the preceding claims, wherein the Hall-effect device is connected to an amplifier to provide an input thereto.

5 A galvanic isolator according to Claim 4, wherein the amplifier is such that it may be used to modify the signal from the Hall-effect device in some predetermined manner.

6 A galvanic isolator according to Claim 5, wherein the amplifier is such that it may be used to compensate the input signal thereto for remanance in the inductor.

7 A galvanic isolator substantially as hereinbefore described with reference to the sole figure of the accompanying drawing.

8 An electrical-signal transmission line providing a signal to an electronic device and comprising a galvanic isolator according to any of the preceding claims with the inductor terminating the transmission line and the Hall-effect device providing the input to the electronic device.