GB2254499A - Electric circuit monitoring devices - Google Patents

Abstract

A monitoring device (20) for an electric circuit, for example, the circuit of a storage heater, furnace or oven, in which there is a group of heating elements, (4-10), indicates the failure of one of the elements. The device comprises a first coil (22) which carries current at a level appropriate to the number of elements functioning correctly in the group. A second coil (24) carries current at a constant level so as to produce a fixed magnetic attractive force below that produced by the first coil when all elements are operating correctly but above that of the first coil if one element fails. Movable armature means (26, 28) are normally attracted towards the first coil (22), but when an element fails, move towards the second coil (24), causing an indicator (36) to move into a visible position. <IMAGE>

Description

ELECTRIC CIRCUIT MONITORING DEVICES The invention is concerned with improvements in or relating to electric circuit monitoring devices, particularly but not exclusively, devices suitable for use in heating devices in a domestic or industrial environment and including at least two energisable heating members in the circuit.

By way of example, so-called night storage heaters are in popular use to gain benefit from their use of electricity at off-peak periods, and, during day-time hours, the steady release of heat stored by suitable refractory blocks provided within the heater housing. In many examples of storage heaters of this kind, the blocks are heated by at least two, and conveniently four, heating elements. When, in the normal course of use, one or even two of the elements fail(s), the effect of this is not immediately felt, since two or three elements are still operational. The heating means is however operating at reduced efficiency, the desired room temperature is not reached or if reached is not sustained, and the user, while dissatisfied with the performance, is unaware that there is a remediable fault.

The invention provides a monitoring device for electric circuits comprising a plurality of heat producing elements, wherein there is provided an electromagnetic indicator device including a first coil adapted to carry current at any one of plurality of predetermined levels according to operating conditions, said levels including a first, relatively high, level at which a magnetic force of a first value is produced, and a second, lesser, level, at which a second, lower, magnetic force is produced and a second coil adapted to carry current at a constant level to produce a magnetic force at a level between that of said first and second forces there being further provided armature means mounted for movement between a first position and a second position and indicator means operative in response to movement of said armature means between said first and second positions to indicate a change of current level in said first coil, wherein current is carried by the first coil at said first level so that said armature means is attracted into said first position when said plurality of heating elements are all functioning correctly, and wherein the current, and therefore also the magnetic force, is reduced to said second level or below when one or more of said elements ceases to function correctly, the arrangement being that when the condition of the elements is such that the first coil carries current at said second, lower, level, the armature means is moved to said second position under the influence of the magnetic force in said second coil.

Conveniently, said indicator means may comprise a visual marker device which may exhibit a change of colour to an observer. Other indicating means may however be provided, if preferred.

Advantageously, the invention may find application in heating devices comprising a body of heat retaining refractory material heated by a plurality of heating elements during predetermined heating periods (off-peak power) to allow dissipation of heat from the body during intervals between said periods. The invention may also find application in electric ovens or furnaces, wherever the condition of an element in a group of elements is not visually evident to the observer.

There will now be described an example of several devices according to the invention. It will be understood that the description, which is to be read with reference to the drawings, is given by way of example only and not by way of limitation.

In the drawings: Figure 1 is a schematic circuit diagram of a heating device used with an electromagnetic monitoring device; Figure 2 is a schematic diagram of a first example of a monitoring device arrangement; and Figures 3 to 5 are schematic diagrams of second, third and fourth examples of indicator device arrangements.

The heating device illustrated in Figure 1 is a storage-type heater comprising a body of refractory material indicated in broken lines at 2. The body 2 is heated at off-peak times in the conventional manner by four elements 4,6,8,10. The energisation of the elements is regulated by a charge controller 12 in the usual way.

The circuitry includes a live lead 14 and a neutral 16, with an earth 18. Inserted in the lead 14 is an electromagnetic indicator device indicated at 20 in Figure 1, (shown in schematic detail in Figure 2), a neutral line 21 connecting with line 16.

The indicating device 20 comprises a first coil which may conveniently be referred to as the current coil 22, which is in series with the heating elements and is arranged to carry current at a first level, say, 14 amps, when all four heating elements 4,6,8 and 10 are energised and also to carry current at a lower level, in the present example, approximately 11 amps, when one or more elements fail or are otherwise inoperative. The device further comprises a second (voltage) coil 24 which has a lower amp-turn rating than coil 22. When energised, the coil 24 produces a magnetic force lower than that produced by the first level of current in the coil 22.It is arranged that the second coil 24, which may be referred to as the voltage coil, carries current at a substantially constant value, which may be at any suitable level, in the example about 100 mA, so that there is no change in the magnetic force of coil 24 when elements fail.

Positioned between the coils 22 and 24 is a movable armature arrangement comprising in the present example two armatures 26 and 28 each pivotted about a point 30, 32 respectively and linked by a tie member 34.

An indicating flag 36 having a push member 38 is movably mounted adjacent to the free end of the armature 28. The flag 36, is of a distinctive colour, in this example, red. An aperture 40 is provided in the casing of the device 20, through which aperture the flag 36 cannot normally be seen.

In operation, the armatures 26 and 28 are in their full-line positions, i.e. the armature 26 is pulled towards the coil 22 which carries current at the first, higher, level when all four elements 4,6,8, and 10 are energised and therefore produces a magnetic force at said first value.

When one elements fails, the level of current in the coil 22 falls to the second level. Because the constant magnetic force in the (voltage) coil 24 is at a higher level than that produced at the (current) coil 22 at its second current-carrying level, the attraction of the armature 28 to the coil 24 will be greater than the attraction of armature 26 to the coil 22 and, next time the heating elements are switched on, the two armatures pivot clockwise as shown in Figure 2 into the chain-dotted position, 26', 28'.

As a result, the flag 36 moves to broken-line position 36', and becomes visible in the aperture 40, thus indicating to the user that an element of the heater device has failed.

Figure 3 shows a second example in which there are provided a first (current) coil 42 and a second (voltage) coil 44. A movable armature arrangement is positioned between the two coils 42,44 and comprises two armature members 46 and 48, each pivotally mounted at 50 and 52 respectively and linked by a tie member 54. An indicating flag 56 is provided at an end portion of a control rod 58 slidably supported on support locations 60, 62. In this arrangement which may be termed a force opposition arrangement, it is the average value of the magnetising force which is important in determining the position of the armature 46, 48.

When the full current is flowing in the heating elements and therefore the coil 42 is fully energised, the armature is attracted to the right and the flag is in an obscured position. When the current in the elements drops, the magnetic field of the coil 44 operates to draw the armature to the left, thus pushing the rod 58 into a position where the flag is visible.

Figure 4 is a third example which shows a force comparison arrangement in which a control rod 64 is pivotable about a point 66. The magnetic force in a (current) coil 68 draws the right-hand side of the rod downwardly. A flag 70 mounted on a pivotal mounting 72 is in an obscured position when all elements are operating but when one fails the magnetic force in the (voltage) coil 74 acts to draw the left-hand side of the rod downwardly towards it, this displacing the flag 70 into a visible position.

In Figure 5, an arrangement is shown in which two coils, 76 (current coil) and 78 (voltage coil) are wound so as to produce a condition of phase opposition in the circuit. The coils are mounted on a support 80 and a control rod 82 is mounted for sliding movement with respect to the support 80. A flag 84 is provided on the free end of the rod 82, when all the elements are operating, the condition of the circuit is such that there are equal and opposite magnetic forces, but when one element fails and the current in the coil 76 is reduced, there is then produced a net magnetic attraction which causes the armature 86 to move to the left, contacting the rod 82 and moving the flag 84 into a visible position.

Various modifications may be made within the scope of the invention as defined by the following claims. It will be understood that the indicator device arrangements according to the invention may be incorporated in an article at the point of manufacture or an article may be converted to make use of the advantages accruing from the invention.

Claims (9)

CLAIMS:

1. A monitoring device for electric circuits comprising a plurality of heat producing elements, wherein there is provided an electromagnetic indicator device including a first coil adapted to carry current at any one of plurality of predetermined levels according to operating conditions, said levels including a first, relatively high, level at which a magnetic force of a first value is produced, and a second, lesser, level, at which a second, lower, magnetic force is produced and a second coil adapted to carry current at a constant level to produce a magnetic force at a level between that of said first and second forces there being further provided armature means mounted for movement between a first position and a second position and indicator means operative in response to movement of said armature means between said first and second positions to indicate a change of current level in said first coil, wherein current is carried by the first coil at said first level so that said armature means is attracted into said first position when said plurality of heating elements are all functioning correctly, and wherein the current and therefore the magnetic force is reduced to said second level or below when one or more of said elements ceases to function correctly, the arrangement being that when the condition of the elements is such that the first coil carries current at said second, lower, level, the armature means is moved to said second position under the influence of the magnetic force in said second coil.

2. A device as claimed in claim 1, wherein said indicator means comprises a visual marker device adapted to exhibit one of a range of coloured signals.

3. A device as claimed in either of claims 1 and 2, wherein the said second coil has a lower amp/turn rating than said first coil.

4. A device as claimed in any one of the preceding claims, wherein the moveable armature means is mounted for pivotal movement between said positions, movement towards said second position causing physical contact with a support member for the indicator means, causing movement of said indicator means.

5. A device as claimed in claim 4, wherein said indicator means moves from an out-of-sight position to a visible position, and is adapted to be re-set by return to said out-of-sight position when all elements resume normal functioning.

6. A device as claimed in claim 5, wherein said indicator means is in the form of a flag, the device including a housing having an aperture through which the flag is visible when the armature means is in its second position.

7. A device as claimed in claim 1, wherein when the elements are in an un-energised state, the armature means is biased towards an intermediate position, the construction and arrangement being such that on energisation of the elements when in a correctly functioning condition, the armature moves to said first position and when said elements are not all in a correctly functioning condition, the armature moves to said second position.

8. A device as claimed in either one of claims 1 and 7, wherein the first and second coils are wound in phase opposition to produce equal and opposite force when all elements are functioning correctly, failure of one or more elements thus producing a net magnetic force adapted to move the armature means.

9. A monitoring device for an electric circuit comprising a plurality of heat-producing elements, constructed and arranged substantially as hereinbefore described with reference to a) Figures 1 and 2 b) Figure 3 c) Figure 4 d) Figure 5 of the drawings.