WO2000028336A1

WO2000028336A1 - Measuring device, sub-assembly thereof, and method of manufacturing the sub-assembly

Info

Publication number: WO2000028336A1
Application number: PCT/GB1999/003640
Authority: WO
Inventors: Michael Paul Rowles
Original assignee: Howard Butler Limited
Priority date: 1998-11-07
Filing date: 1999-11-04
Publication date: 2000-05-18
Also published as: AU6481099A; GB9824373D0

Abstract

A measuring device, specifically a moving iron ammeter, comprises a fixed iron (18) and a moving iron (22), constituting a responsive member of the device. The moving iron is mounted on a spindle (26), which carries a pointer (28), constituting an indicating member of the device. In accordance with the invention, the moving iron (22), spindle (26) and pointer (28) are produced as a sub-assembly of the device, involving the use of a precision moulding tool, in which the spindle (30) and moving iron (32) are initially located prior to the injection in the mould of plastics moulding material. The plastics moulding material encapsulates the moving iron (32) accurately in relation to the spindle (30), the indicating member (28) of the sub-assembly being provided by moulding material. The sub-assembly so produced is accurate, robust, and may be assembled within the bobbin of the ammeter relatively easily.

Description

Title: Measuring Device, Sub-Assembly thereof, and Method of Manufacturing the Sub- Assembly

Description of Invention

This invention is concerned with improvements relating to measuring devices, particularly of the kind comprising a responsive member mounted for movement about a pivot axis and which moves in response, directly or indirectly, to a change in a parameter being measured, and an indicating member which moves with the responsive member, conveniently across a scale, to indicate the magnitude of movement of the responsive member, and hence the magnitude of change of the parameter being measured.

Such a measuring device is hereinafter referred to as being of the kind specified.

A typical measuring device of the kind specified is a moving iron meter, such as a moving iron ammeter or voltmeter.

Whilst measuring devices of the kind specified are simple in construction and operation, and have been available for many years, they are nonetheless relatively complicated to assemble and/or suffer from unnecessary inaccuracies by virtue of the clearances provided between the various parts thereof, and it is one of the various objects of this invention to provide a measuring device of the kind specified which may be assembled more easily, and/or more accurately, than has heretofore been accomplished.

According to this invention there is provided a measuring device of the kind specified comprising pivot means providing the pivot axis, and wherein at least two of the responsive member, the pivot means and the indicating member are provided by or located within a moulded body of plastics material.

Preferably all three of the responsive member, the pivot means and the indicating member are provided by or located within said moulded body of plastics material. The pivot means may be provided by a taut band, but conveniently is provided by a spindle.

According to this invention there is also provided a sub-assembly for a measuring device of the kind specified, comprising a body of moulded plastics material in which is located the responsive member and pivot means for movement of the responsive member.

The indicating means may similarly be located in the body of moulded plastics material, but more conveniently is provided by the body of moulded plastics material.

In this manner, precision between the responsive member, pivot means and indicating member is readily determined.

According to this invention there is also provided, in a measuring device of the kind comprising a responsive member mounted for movement about a pivot axis and which moves in response, directly or indirectly, to a change in a parameter being measured, and an indicating member which moves with the responsive member to indicate the magnitude of movement of the responsive member, and hence the magnitude of the change of the parameter being measured, a method of manufacturing a sub-assembly for the measuring device, said method involving the steps a) locating the responsive member and the spindle in a mould; and b) injecting plastics material into the mould to provide a moulded body, whereby the relative positions between the spindle means and the responsive member are accurately determined.

The indicating member may also be located in the mould, but preferably the indicating member is provided by the moulded body, whereby movement of the indicating member in response to movement of the responsive member is accurately determined. In this manner a sub-assembly comprising responsive member, spindle and indicating member may readily be assembled in a housing of the measuring device quickly and accurately.

There will now be given a detailed description, to be read with reference to the accompanying drawings, of a measuring device which is a preferred embodiment of this invention, having been selected for the purposes of illustrating the invention by way of example.

In the accompanying drawings:-

FIGURE 1 is a view of a bobbin assembly of the preferred embodiment, parts being shown in exploded position for clarity;

FIGURE 2 is a vertical sectional view of the bobbin; and

FIGURES 3a, 3b and 3c are respective plan side elevation and end elevational views of a sub-assembly of the measuring device, which is also illustrative of certain aspects of the invention.

The measuring device which is the preferred embodiment of this invention is of the kind specified, specifically a moving iron ammeter, comprising in conventional manner a hollow plastic moulded bobbin 6 having upper and lower flanges 8, 10, around the body of which in use a coil (not shown) is wound, through which the current to be measured is in the use of the device passed.

Mounted on the wall portion 14 of the bobbin projecting beyond the flange 8 is a toothed gear wheel 16, from which depends in a downward direction a curved, generally triangular fixed iron 18, said curvature being about a longitudinal axis L/A passing centrally through the bobbin 6.

The fixed iron 18 may be moved around the axis by rotation of the gear wheel 16, to adjust the setting of the ammeter in a conventional manner.

Mounted beneath the gear wheel 16 is a gear ring 20 of magnetic material, which may be rotated to finely adjust the magnetic field of the device, again in known manner. The measuring device which is the preferred embodiment of this invention comprises a sub-assembly comprising moving iron 22, constituting a responsive member of the device, spindle 26, constituting the pivot axis of the sub-assembly, and pointer 28, constituting an indicating member of the device. The spindle 26 is inserted downwardly into a bore 40 provided in a lower cap portion 42 of the bobbin, and is located upwardly in a bore 44 extending into a cap 46 located in a complimentary bore 47 in the clamping head 48 of the device, in conventional manner.

In accordance with this invention, particularly as is shown in Figure 3a, 3b and 3c, the sub-assembly is moulded in a precision moulding tool, in which the spindle 26 and moving iron 32 are initially located prior to the injection into the mould cavity of plastics moulding material, to provide a body 30 of moulded plastics material within which part at least of the moving iron 32 and the spindle 36 are located, part of the body 30 providing the indicator member. In this manner it may be ensured that the moving iron 32 is accurately located in relation to the spindle 26, and movement of the moving iron 32 about the axis L/A is accurately transferred to movement of the indicator member (pointer 28).

By the use of the invention above described not only is the sub-assembly more reliably accurate and more robust than has heretofore been found practical, but additionally the sub-assembly is more robust than has heretofore been readily obtainable, providing a moving iron ammeter which is significantly superior.

In particular, the sub-assembly may be assembled within the bobbin relatively easily, by location of the lower end portion of the spindle 30 in the bore 40 in the underside of the bobbin, and at an upper end portion within the bore 44, ensuring automatically a correct positioning of the moving iron 22 relative to the longitudinal axis L/A. The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1 A measuring device comprising a responsive member mounted for movement about a pivot axis, and an indicating member which moves with the responsive member, characterised in that at least two of the responsive member, the pivot means and the indicating member are provided by or located within a moulded body of plastics material.

2 A device according to claim 1 wherein all three of the responsive member, the pivot means and the indicating member are provided by or located within said moulded body of plastics material.

3 A measuring device according to claim 1 wherein the pivot means is provided by a spindle.

4 A sub-assembly for a measuring device of the kind comprising a responsive member mounted for movement about a pivot axis and which moves in response, directly or indirectly, to a change in a parameter being measured, and an indicating member which moves with the responsive member, conveniently across a scale, to indicate the magnitude of movement of the responsive member, the sub-assembly comprising a body of moulded plastics material in which is located the responsive member and the pivot means.

5 A sub-assembly according to claim 4 wherein the indicating means is located in the body of moulded plastics material.

6 A sub-assembly according to claim 4 wherein the indicating means is provided by the body of moulded plastics material. 7 In a measuring device of the kind comprising a responsive member mounted for movement about a pivot axis, and which moves in response to a change in a parameter being measured, and an indicating member which moves with the responsive member, a method of manufacturing a sub-assembly for the measuring device, said method involving the steps: a) locating the responsive member and the spindle in a mould; and b) injecting plastics material into the mould to provide a moulded body.

8 A method according to claim 7 wherein the indicating member is located in the mould.

9 A method according to claim 7 wherein the indicating member is provided by the moulded body.