GB2153145A - Magnetic field trimmer in a Hall effect device - Google Patents

Abstract

A Hall effect device, such as a relay, includes mechanically adjustable means (9) for trimming the magnetic flux through the Hall element (8) in order to obtain switching at a predetermined coil (1) current. The means may comprise a magnetically soft screw (9) or a non-magnetic screw employed to adjust the width of the air gap in which the Hall element is disposed when two yoke members are axially movable with respect to one another. Only a screw driver and voltmeter to indicate switching are required to perform the adjustment. <IMAGE>

Description

SPECIFICATION Hall effect device This invention relates to Hall effect devices and in particular, but not exclusively, to Hall effect relays and to methods of adjusting the switching threshold.

According to one aspect of the present invention there is provided a Hall effect device including a Hall effect element, means for generating magnetic flux relative to the element whereby when the element is carrying a current it generates a Hall voltage corresponding to the magnetic flux, and including mechanically adjustable means for trimming the magnetic flux through the element.

According to another aspect of the present invention there is provided a method of adjusting a Hall effect relay whereby to cause it to switch at a predetermined coil current, the relay comprising a coil, a magnetic circuit including a member extending through the coil and an air gap, a Hall element disposed in the air gap, which element when carrying a current generates a Hall voltage corresponding to the coil current, Hall voltage amplifying means and means for comparing the amplified Hall voltage with a reference value, the method comprising the steps of assembling the relay such that it switches at an applied coil current slightly less than the predetermined coil current, and, with the coil current adjusted to the predetermined value, trimming the magnetic flux through the element by operation of mechanically adjustable means whereby to correspondingly reduce the Hall voltage until a value thereof is reached at which switching reoccurs.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which Fig. 1 illustrates a known Hall effect relay; Fig. 2 illustrates a first embodiment of adjustable Hall effect relay according to the present invention, and Fig. 3 illustrates a second embodiment of adjustable Hall effect relay according to the present invention.

A possible application for a Hall effect device is as a transducer of current to voltage.

This is accomplished by passing the current to be sensed through the windings of a solenoid to generate a magnetic field. If this field is suitably applied to a semiconductor chip (Hall effect device) carrying a current then a voltage (the Hall voltage) is generated. Alternatively, the isolation between the input, or current carrying, circuit, and the output circuit, of which the Hall effect device is an element, allows the design of unidirectional solid state transformers. Applications for such devices have, in particular, been identified in telecommunications systems. An example of such use is the substitution of a Hall effect device for the springset of a dialling register relay, the so-called A-relay, to provide a Hall effect relay, as described in our co-pending Application No. 8324783 (Serial No. ) (M.P.

Dyer-P.J. Etter 7-2) which, in general, relates to electrical circuits for detecting changes in the state of a telecommunications line between the unlooped and the looped state. The present invention is concerned with the nonlinear, or switching character, of a Hall effect relay.

It is commonly the case that a relay is required to switch its contacts at a specified current in its field coil. In the solid state version this switching action can be simulated, very simply, by amplifying the Hall voltage to a suitable magnitude and then comparing it with a reference voltage. Whilst this technique is effective, it has one weakness when implemented in a manufacturing process. In practice, the amplified output voltages of a number of Hall effect relays will differ, due to the sum of the various tolerances involved. These include natural variations in Hall effect sensitivity between semiconductor chips and in their offset voltages, plus variations derived from tolerances in the amplifier components. The net effect is that relays, which are intended to be identical, in fact vary in the coil current required for switching.

Two methods are basically available to keep the variation in the coil current required for switching within acceptable limits. Either the components of the system must be specified to tolerances which will guarantee the overall behaviour, or a "set-on-test" procedure must be adopted. An example of the latter would be to determine the necessary value of a resistor which sets the reference voltage with which the amplified Hall voltage is compared.

Although usually cheaper than close tolerancing all components, this procedure can still contribute significantly to the cost of the completed unit.

The present invention is concerned with a "set-on-test" operation, which is, however, reduced to a simple screw adjustment.

Referring now to the drawings and in particular to Fig. 1 which shows a side view of a Hall effect relay as described in our co-pending Application No. 8324783 referred to above. The relay has a coil 1 wound on a core 2 of magnetically soft iron. The structure also has a yoke 3, also of soft iron, on which is mounted a module 4 which contains the Hall effect element and amplification and comparison circuitry. This module 4 is L shaped with a notch so that it fits on the yoke 3 as shown.

The "base" of the L, which faces the end of the core 2, contains a portion of magnetically soft iron (not shown) embedded in a moulding and so located as to provide a gap between one of its ends and the left hand end of core 2. The other end of this portion of iron is aligned with the end of the yoke 3. A Hall effect element, not shown, which may be of gallium arsenide, silicon or other semiconductor, is located in the magnetic gap thus formed in the magnetic circuit produced by the field coil 1 of the relay and including extending through the core 2, the yoke 3 and the portion of soft iron embedded in the moulding. The elements 1, 2 and 3 may be identical to those of a conventional A relay, the module 4 replacing the armature and pileup of the conventional A relay.

The Hall effect relay shown in Fig. 2 and incorporating a simple "set-on-test" screw adjuster employs a coil 1, core 2 and yoke 3 which, as described with respect to Fig. 1 may be identical to those of a conventional A relay. Instead of the module 4 of Fig. 1, however, a further yoke member 5 of magnetically soft iron, which is generally L-shaped and provided with a notch to aid in location on the yoke 3, is secured to the yoke 3 so that an air gap 6 is obtained between the base 7 of the armature and the left hand end of the core 2. A Hall effect element 8 is mounted in the air gap 6 comprising a gap in the magnetic circuit produced by the coil 1 and extending through the core 2, the yoke 3 and the member 5.The amplifier and comparator circuitry (not shown) for the generated Hall voltage may be disposed within a portion of the member 5 in order to provide a complete unit electrically equivalent to an A relay and of similar dimensions.

The coil 1, core 2, yoke 3, member 5 and Hall effect element and amplifier and comparator circuitry are assembled such that the relay initially switches at an applied coil current slightly less than the desired value. The applied coil current is then increased to the desired switching value and a screw 9 of magnetically soft ferro-magnetic material is inserted through the member 5 beside the Hall effect element 8. As the screw 9 penetrates across the gap 6, magnetic flux is concentrated in it, thus starving the Hall effect element 8. The effect of this is to reduce the Hall voltage. The screw 9 is screwed in until switching reoccurs as indicated by a voltmeter. Thus all units of a batch of relays all initially assembled to switch at some current slightly less than the desired value can be rendered identical quickly and simply using only a screwdriver and a voltmeter.

Alternatively, a reduction of the amplified Hall voltage may be achieved by means of a screw 10 (Fig. 3) of non-magnetic material disposed in the same position as screw 9. The embodiment of Fig. 3 employs a coil 1, core 2 2 and yoke 3 which, as described with respect to Fig. 1, may be identical to those of a conventional A relay. A generally L shaped further yoke member 11 of soft magnetic material can be secured to the yoke 3, but provision is made for there to be a relative sliding action between yoke 3 and member 11 such that the size of the air gap 12 between the base 13 of member 11 and the left hand end of core 2 is adjustable. The sliding action may be achieved by means of elongate slots (not shown) in the member 11 through which securing screws 14 extend.

The non-magnetic screw 10, which is positioned beside Hall effect element 15, affords a means of controllably increasing the size of the air gap 12, when being screwed in and the screws 14 are not tightened thus permitting relative sliding of the member 11 and yoke 3, and hence adjusting the switching threshold due to the increased reluctance of the magnetic circuit. Once the required switching threshold is reached the securing screws 14 are tightened. The air gap may be adjusted without the use of screw 10, simply by adjusting the relative positions of members 11 and 3, however the use of a screw 10 facilitates the adjustment by enabling fine control thereof.

Whilst the embodiment of Fig. 2 has been described as having a separate yoke 3 and member 5 which are secured together, alternatively a single equivalent generally Ushaped element may be employed

Claims (14)

1. A Hall effect device including a Hall effect element, means for generating magnetic flux relative to the element whereby when the element is carrying a current it generates a Hall voltage corresponding to the magnetic flux, and including mechanically adjustable means for trimming the magnetic flux through the element.

2. A Hall effect device as claimed in claim 1 and comprising a Hall effect relay, the magnetic flux generating means comprising a relay coil and a magnetic circuit, including a core member extending through the coil and an air gap in which the element is disposed, and wherein the mechanically adjustable means comprises a screw adjustably extending in the magnetic circuit at the air gap.

3. A Hall effect device as claimed in claim 2, wherein the screw is of magnetically-soft ferro-magnetic material.

4. A Hall effect device as claimed in claim 2, wherein the magnetic circuit further includes a generally U-shaped member having the end of one leg thereof coupled to the core member at one end of the coil, the air gap being disposed between the end of the other leg of the U-shaped member and the core member at the other end of the coil, the Hall element being mounted to the other leg end and the screw being disposed beside the Hall element and screwable extending through the other leg end and into the air gap.

5. A Hall effect device as claimed in claim 2, wherein the screw is of non-magnetic material, and wherein the width of the air gap is adjustable upon screwing of the screw.

6. A Hall effect device as claimed in claim 3 wherein the magnetic circuit further includes a generally U-shaped member the length of the base of which is adjustable, the end of one leg of the U-shaped member being coupled to the core member at one end of the coil, the air gap being disposed between the end of the other leg of the U-shaped member and the core member at the other end of the coil, the Hall element being mounted to the other leg end and the screw being disposed beside the Hall element and screwable extending through the other leg end, across the air gap and up to the core member at the other end of the coil.

7. A Hall effect device as claimed in claim 1 and comprising a Hall effect relay, the magnetic flux generating means comprising a relay coil and a magnetic circuit, including a core member extending through the coil and an air gap in which the element is disposed, and wherein the mechanically adjustable means comprises a member of the magnetic circuit whose length is adjustable, adjustment thereof producing corresponding adjustment of the width of the air gap.

8. A method of adjusting a Hall effect relay whereby to cause it to switch at a predetermined coil current, the relay comprising a coil, a magnetic circuit including a member extending through the coil and an air gap, a Hall element disposed in the air gap, which element when carrying a current generates a Hall voltage corresponding to the coil current, Hall voltage amplifying means and means for comparing the amplified Hall voltage with a reference value, the method comprising the steps of assembling the relay such that it switches at an applied coil current slightly less than the predetermined coil current, and, with the coil current adjusted to the predetermined value, trimming the magnetic flux through the element by operation of mechanically adjustable means whereby to correspondingly reduce the Hall voltage until a value thereof is reached at which switching reoccurs.

9. A method as claimed in claim 8, wherein the mechanically adjustable means comprises a screw of a magnetically soft ferromagnetic material arranged to extend into the air gap, beside the Hall element, by a variable amount.

10. A method as claimed in claim 8, wherein the mechanically adjustable means serves to adjust the width of the air gap.

11. A method as claimed in claim 10 wherein the magnetic circuit includes a member whose length is adjustable, and adjustment thereof producing corresponding adjustment of the width of the air gap.

12. A method as claimed in claim 11.

wherein the mechanically adjustable means comprises a screw of non-magnetic material extending across the air gap, screwing of said screw causing adjustment of the length of the adjustable length member and the width of the air gap.

13. A Hall effect relay substantially as herein described with reference to and as illustrated in Fig. 2 or Fig. 3 of the accompanying drawings.

14. A method of adjusting a Hall effect relay whereby to cause it to switch at a predetermined coil current substantially as herein described with reference to and as illustrated in Fig. 2 or Fig. 3 of the accompanying drawings.