GB2287831A

GB2287831A - Isolating switch for electricity consumption meter

Info

Publication number: GB2287831A
Application number: GB9405743A
Authority: GB
Inventors: Trevor Walter Palmer; Kenneth Payne
Original assignee: Ampy Automotion Digilog Ltd
Current assignee: Landis and Gyr Ltd
Priority date: 1994-03-23
Filing date: 1994-03-23
Publication date: 1995-09-27
Anticipated expiration: 2014-03-23
Also published as: GB9405743D0; GB2287831B

Abstract

An electrical isolating switch comprises an adjustable electrical path, such as an elongate electrically conductive element (10), electrically operable drive means (38), and a drive transmission means (36) having two stable states corresponding to an open circuit state and a closed circuit state of the electrical path. The drive means is responsive to current pulses to move the drive transmission means so as to close or open the electrical path. Crankshaft movement of a link (24) by the drive transmission means causes opening or closing of the electrical path. The link is connected to the conductive element (10) via a lost motion connection. <IMAGE>

Description

Title: Isolating Switch for Electricity Consumption Meter Field of Invention This invention relates to an isolating switch for electricity consumption meters, wherein the effects of strong magnetic fields in the vicinity of the switch do not cause malfunction.

Background to the Invention When there is a requirement for the control of the electrical supply to a consumer, there is a need for an electrical switch. Typically these switches have a solenoid which is energised by a voltage. This results in a magnetic field being produced which acts upon an armature. This is usually mechanically linked to electrical contracts that allow the passage of electric current when they are closed.

A switch may typically comprise two solenoids that separately control the switch contacts. A short duration voltage pulse, typically 12 volts for 100ms, is applied to one of the two solenoids which when energised will cause the switch to close allowing the passage of current. The second solenoid, when energised, will cause the switch to open such that the passage of current is prevented. This action is typically achieved by use of permanent magnets and/or complicated mechanical spring devices. Magnetic fields, produced when large currents (particularly large current spikes) pass through the switch contacts and associated leads, can interfere with the sensitive permanent magnet holding devices, causing malfunction.

Malfunction can also be caused by the intentional and/or unintentional introduction of powerful permanent magnets in the vicinity of the switch.

It is an object of the present invention to provide an electrical isolating switch that is simple to manufacture and therefore less costly, and is such that it is not affected by externally or internally generated magnetic fields.

Summary of the Invention According to the present invention an electrical isolating switch comprises an adjustable electrical path, electrically operable drive means, and a drive transmission means having two stable states corresponding to an open circuit state and a closed circuit state of the electrical path, wherein the drive means is responsive to a first short duration current pulse to move the drive transmission means so as to close the electrical path and is responsive to a second short duration current pulse to move the drive transmission means so as to open the electrical path.

Non-magnetisable materials are preferably used for the drive transmission means so that it does not respond to the influence of magnetic fields.

The electrical path is preferably provided by an elongate electrically conductive element which can make contact with another electrically conductive member to form the closed path.

In a preferred embodiment the elongate conductive element, typically a metal strip, is fixed at one end to a first fixed mounting which includes or comprises a first terminal and the other end of the conductive element is movable.

The movable end is preferably provided with a contact, with a corresponding contact being secured to a second fixed mounting which includes or comprises a second electrical terminal.

Movement of the drive transmisson means causes the elongate conductive element to move and the contacts to shift, thereby making or breaking the circuit.

The drive transmission means typically includes a link to connect it to the conductive element.

The drive transmission means is preferably attached to the drive means in such a way as to provide a crankshaft movement of the link.

The crankshaft movement is typically achieved by attaching the link to the outboard end of an axially rotatable crank arm and the drive means is arranged to rotate the crank arm.

The radius of the crank arm can be varied in order to provide greater or lesser vertical movement of the link for a given angular rotation thereof.

Rotational movement of the crank arm is limited by interaction of a radial peg rotatable therewith, with two stops placed so as to define the two desired extremes of movement of the crank corresponding to the open and closed positions of the contacts.

Preferably the link is attached to the elongate conductive element through a lost motion connection.

To this end the link is preferably attached to the free end of the conductive element by insertion of the link into an aperture in the conductive element, an end stop and shoulder piece being provided on the link on either side of the aperture so as to ensure that movement of the conductive element occurs as the crank arm is rotated.

Preferably spring means is provided between the shoulder and the strip, so as to ensure that the conductive element is forced into the contacts closed position.

The link may be constructed from electrically insulating material.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a side elevation of an isolating switch embodying the invention as applied to an electricity consumption meter, Figure 2 is an end elevation showing the switch contacts in the open position, Figure 3 is an end elevation showing the switch contacts in the closed position.

Detailed description of a preferred embodiment Figure 1 shows a preferred embodiment of an electrical isolating switch in accordance with the invention. The switch is shown in use in an electricity consumption meter, where a metal strip 10 provides an electrical path between two electrical terminals 12, 14. The strip 10 is connected via a current shunt resistor 16 to the terminal 12. The free end of the strip 10 has a contact 18. A second contact 20 is attached to the terminal 14. When the switch is closed, the contacts 18, 20 are connected and current can flow. The strip 10 is bent so that in its relaxed state the circuit is broken.

At the free end of the strip 10, an aperture 22 is provided through which passes a rod 24 of electrically insulating material. The rod 24 extends through a spring 26, the lower end of which engages the strip 10 around the aperture 22 and the upper end of which is trapped below a shoulder 28 on the rod 24. Beyond this aperture 22 the lower end of the rod 24 is provided with an enlarged end 30.

At the upper end of the rod 24 an aperture 32 is provided within which a peg 34 is a running fit, so as to be rotatable therein. The peg 34 extends from a rotor 36 at a point radially spaced from the axis of rotation of the rotor so as to form a crank. The rotor 26 is rotated by an electric motor 38, which can be made to run clockwise or anti-clockwise according to the polarity of the voltage applied to the motor 38.

A radial peg 40 protruding from the rotor 36 engages end stops 42, 44 which restrict the angular movement of the rotor 36. The end stop 42 limits clockwise rotation of the rotor 36 and the other end stop 44 acts to limit the anti-clockwise rotation. The positions of the end stops 42, 44 are adjustable and as shown in Figure 2 permit angular rotation of the rotor 36 to be in excess of 180 degrees but less than 360 degrees, so that the peg 40 passes through top dead centre and bottom dead centre as the rotor 36 rotates one way and then the other so as to create an over-centre mechanism.

In figure 2, the isolating switch is shown in the open position. The rotor 36 is in the fully clockwise position with the radial peg 40 against the clockwise end stop 42.

Since the rod 24 has rotated beyond top dead centre there is no tendency to rotate anti-clockwise and the stop 42 ensures no further clockwise rotation. The strip 10 is in a relaxed state, there are no internal forces acting to move the contact 18, 20 so they will remain separated.

To close the contacts 18, 20, as shown in Figure 3, a voltage pulse of the correct polarity is applied to the motor 38. This causes anti-clockwise rotation of the rotor 36, until the radial peg 40 hits the anti-clockwise end stop 44. Since the rotor 35 has rotated anticlockwise beyond bottom dead centre there is no tendency for reverse rotation, and as the radial peg has now engaged the stop 44, continual anti-clockwise movement is prevented. The linear motion produced by the rod 24 is transferred to the strip 10 via the shoulder 28 and the spring 26, causing the contacts 18, 20 to close and allowing passage of current between the terminals 12, 14.

Any over travel in the linkage is absorbed by the spring 26, which nevertheless maintains sufficient pressure to keep the contacts 18, 20 closed.

By pre-loading the spring 26, sufficient pressure will be applied to the strip 10 to cause the contact to be closed quickly and releasably.

Claims

1. An electrical isolating switch comprising an adjustable electric path, electrically operable drive means, and a drive transmission means having two stable states corresponding to an open circuit state and a closed circuit state of the electrical path, wherein the drive means is responsive to a first short duration current pulse to move the drive transmission means so as to close the electrical path and is responsive to a second short duration current pulse to move the drive transmission means so as to open the electrical path.

2. An electrical isolating switch according to claim 1, wherein the electrical path is provided by an elongate electrically conductive element which makes contact with another electrically conductive member to form the closed path.

3. An electrical isolating switch according to claim 2, wherein the elongate conductive element is fixed at one end to a first fixed mounting which includes a first terminal and the other end of the conductive element is movable.

4. An electrical isolating switch substantially as herein described with reference to and as illustrated in the accompanying drawings.

4. An electrical isolating switch according to claim 3, wherein the movable end is provided with a contact, with a corresponding contact being secured to a second fixed mounting which includes a second electrical terminal.

5. An electrical isolating switch according to any of claims 2 to 4, wherein movement of the drive transmission means causes the elongate conductive element to move and the contacts to shift, thereby making or breaking the circuit.

6. An electrical isolating switch according to claim 5, wherein the drive transmission means includes a link to connect it to the conductive element.

An electrical isolating switch according to claim 6, wherein the drive transmission means is attached to the drive means to provide a crankshaft movement of the link.

8. An electrical isolating switch according to claim 7, wherein the crankshaft movement is achieved by attaching the link to the outboard end of an axially rotatable crank arm and the drive means is arranged to rotate the crank arm.

9. An electrical isolating switch according to claim 8, wherein rotational movement of the crank arm is limited by interaction of a radial peg rotatable therewith, with two stops placed to define the two desired extremes of movement of the crank corresponding to the open and closed positions of the contacts.

10. An electrical isolating switch according to any of claims 6, 7, 8 or 9, wherein the link is attached to the elongate conductive element through a lost motion connection.

11. An electrical isolating switch according to claim 10, wherein the link is attached to the free end of the conductive element by insertion of the link into an aperture in the conductive element, and an end stop and shoulder piece are provided on the link on either side of the aperture so as to ensure that movement of the conductive element occurs as the crank arm is rotated.

12. An electrical isolating switch according to claim 11, wherein spring means is provided between the shoulder and the strip, so as to ensure that the conductive element is forced into the contacts closed position.

13. An electrical isolating switch according to any of claims 6 to 12, wherein the link is constructed from electrically insulating material