GB2064140A

GB2064140A - Measuring transducers for measuring magnetic fields

Info

Publication number: GB2064140A
Application number: GB8037315A
Authority: GB
Original assignee: Landis and Gyr AG; LGZ Landis and Gyr Zug AG
Current assignee: Siemens Building Technologies AG; Landis and Gyr AG
Priority date: 1979-11-27
Filing date: 1980-11-20
Publication date: 1981-06-10
Also published as: YU296880A; FR2470387A1; DE2948762C2; CH651152A5; IT8026111A0; GB2064140B; DE2948762A1; IT1134377B; FR2470387B1

Abstract

A measuring transducer for measuring a magnetic field comprises at least one magnetoresistive magnetic film (1) which operates as a magnetic field comparator, a magnetic coil (2) which carries an alternating bias magnetisation current, and a flat conductor (4) carrying a current, which is to be measured, producing the magnetic field to be measured. The resistance of the magnetic film (1) alters abruptly when the external magnetic field passes through zero, the moment at which the resistance alters representing a measurement of the current to be measured. The magnetic film ( 1) is arranged on a semiconductor wafer (5) of a monolithic integrated circuit (IC). The measuring transducer can be manufactured as a mass-produced product by conventional IC- technology. <IMAGE>

Description

SPECIFICATION Measuring transducers for measuring magnetic fields This invention relates to measuring transducers for measuring magnetic fields, for example magnetic fields produced by currents to be measured.

The present applicants' UK Patent Application Publication No. GB 2 000 873 A discloses a measuring transducer for measuring a magnetic field, comprising a magnetic coil for carrying an alternating bias magnetisation current, a current source, and a magnetic field comparator which is connected to the current source, which comprises at least one antisotropic magnetic film of ferromagnetic magnetoresistive material, and which is arranged to be exposed to an external magnetic field corresponding to the sum of the magnetic field to be measured and a bias magnetisation field produced by the bias magnetisation current such that the magnetic film is switched alternately into both directions of saturation by the external field in its magnetic preferential direction and abruptly alters its electrical resistance approximately whenever the external field passes through zero, so that the moment in time of the change in resistance represents a measurement in respect of the magnitude and the sign of the magnetic field to be measured. The abovementioned patent application mentions that the magnetic preferential direction of the magnetic film, that is to say the easy magnetic axis thereof, can extend parallel, perpendicularly or at an angle of for example 450, to the direction of the external magnetic field. In that arrangement, a flat coil comprising a strip or wire or a spiral-shaped copper layer in the nature of an etched printed circuit is provided as a magnetic coil for producing the bias magnetising field.

According to the present invention there is provided a measuring transducer for measuring a magnetic field, comprising a magnetic coil for carrying an alternating bias magnetisation current, a current source, and a magnetic field comparator which is connected to the current source, which comprises at least one antisotropic magnetic film of ferromagnetic magnetoresistive material, and which is arranged to be exposed to an external magnetic field corresponding to the sum of the magnetic field to be measured and a bias magnetisation field produced by the bias magnetisation current such that the magnetic film is switched alternately into both directions of saturation by the external field in its magnetic preferential direction and abruptly alters its electrical resistance approximately whenever the external field passes through zero, so that the moment in time of the change in resistance represents a measurement in respect of the magnitude and the sign of the magnetic field to be measured, the magnetic field comparator being arranged on a semiconductor wafer of a monolithic integrated circuit.

Embodiments of the invention described hereinbelow comprise measuring transducers which can be produced by modern mass production processes and at low manufacturing costs.

The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, which are not to scale, in which: Figure 1 is a basic view illustrating the principle of a measuring transducer embodying the invention; Figures 2 and 3 are cross-sectional views of respective forms of embodiment of the measuring transducer of Figure 1; Figure 4 shows a measuring transducer embodying the invention in conjunction with a conductor for carrying a current to be measured; Figure 5 shows a basic circuit diagram illustrating the principle of a static electricity meter incorporating a measuring transducer embodying the invention; Figure 6 is a cross-sectional view of a further measuring transducer embodying the invention; and Figure 7 is a plan view of the measuring transducer of Figure 6.

Figure 1 shows a measuring transducer for measuring a magnetic field, the transducer comprising an anisotropic magnetic film 1 of ferromagnetic magnetoresistive material which forms a magnetic field comparator and which is connected to a current source (not shown) which feeds into the magnetic film a current lo which flows in the longitudinal direction of the magnetic film 1. The easy magnetic axis EA of the magnetic film 1, that is to say the magnetic preferential direction thereof, includes an angle 13 with respect to the longitudinal direction and with respect to an external magnetic field Ha which is applied to the magnetic film in the longitudinal direction.

Arranged in a plane parallel to the magnetic film 1 is a magnetic coil 2 comprising a conductor track that forms a square or rectangular spiral, the individual turns 3 being disposed perpendicularly to the longitudinal direction of the magnetic film 1 in that region in which the turns 3 are magnetically coupled to the magnetic film 1. The magnetic coil 3 carries an alternating bias magnetisation current lv having a defined curve pattern or waveform. The bias magnetisation current lv produces a bias magnetisation field in the longitudinal direction of the film 1.If, in addition, a magnetic field to be measured is coupled in, in the longitudinal direction of the magnetic film 1, an external magnetic field H a which corresponds to the sum of the magnetic field to be measured and the bias magnetisation field is produced in the longitudinal direction. In the embodiment illustrated, the magnetic field to be measured is produced by a current 1m to be measured, which current flows in a flat conductor 4 perpendicularly to the longitudinal direction of the magnetic film 1.The magnetisation vector M of the film 1, is turned away from the easy magnetic axis EA, through an angle a, by the external field Haw When the external field Ha = 0, the magnetisation vector M of the magnetic film 1 lies in the direction of the axis EA and is therefore turned through the angle,3 with respect to the longitudinal direction of the film 1. If the external magnetic field Ha rises negatively, that is to say in the opposite direction to the preceding direction, the magnetisation vector M is initially constantly turned further, with the angle P rising negatively.

After passing beyond a point of stability which can be determined in accordance with the known Stoner-welfare-model ('Stoner-Wohlfa hrts- Modell'), the magnetisation vector M is turned further in an inconstant manner, that is to say, independently of the speed of change of the external field Hat beyond the hard magnetic axis HA, and very rapidly assumes a new equilibrium position which is shown in broken lines in Figure 1. When this occurs, the magnetic film 1 abruptly alters its ohmic resistance, and this is expressed in a pronounced steep jump in the voltage drop at the magnetic film 1. This jump in voltage can easily be detected and marks the passagethrough-zero of the external field Ha with a high degree of accuracy.The inconstant switching of the magnetic film 1 does not in fact take place precisely when the external field Ha passes through zero, but at a changeover switching field strength Hao. That is to say, there is a hysteresis 2aha0, This is minimal when P = 450 and also depends on the anisotropy field strength of the magnetoresistive material and the so-called demagnetisation effect. A small amount of demagnetisation and thus a small amount of hysteresis means that the thickness of the film 1 is very small in comparison to its width.

If the amount of de-magnetisation is not negligibly small, the influence thereof can be extensively compensated if, instead of the magnetic film 1, use is made of two similar magnetic films which are disposed in an overlapping arrangement and which are separated by a thin, magnetically non-conductive insulating layer, wherein a current equal to 2110 flows in each of the magnetic films and'3 is selected to be equal to 0.

As shown in Figure 2, the magnetic film 1 is arranged on a semiconductor wafer 5 which forms a monolithic integrated circuit (IC) comprising the necessary electronic components of the measuring transducer. Disposed between the film 1 and the semiconductor wafer 5 is an insulating layer 6, for example of silicon dioxide (SiO2).The longitudinal ends of the magnetic film 1 are contacted by conductor tracks 7 and 8 for connecting the magnetic film 1 to a direct current source which provides the current 10. The semiconductor wafer 5 includes inter alia two transistors 9 and 10 of which one is connected by way of the conductor track 7 to the magnetic film 1 and feeds the current lo thereinto, while the other is connected to the magnetic coil 2 by way of a conductor track 1 1 and supplied the bias magnetisation current lv.

The magnetic coil 2 is preferably a flat thin film coil and is arranged together with the magnetic film 1 on the semiconductor wafer 5. In the embodiment shown in Figure 2, the magnetic coil 2 is arranged on the side of the film 1 which is remote from the semiconductor wafer 5 and is insulated therefrom and from the conductor tracks 7 and 8 by an insulating layer 12. The magnetic film 1 is disposed at a defined spacing of, for example, a few microns from the magnetic coil 2 at a position where the bias magnetisation field is virtually constant, over the magnetically active length of the magnetic film 1.

The conductor tracks 7, 8 and 1 1 and the magnetic coil 2 may comprise for example gold, copper or aluminium and may be applied to the associated one of the insulating layers 6 and 12 using photolithographic processes which are known in the IC-art. The insulating layers 6 and 12 can also be applied using processes which are conventional in the IC-art. It is also possible for the production of the conductor tracks 7, 8 and 1 1, the magnetic coil 2 and the insulating layers 6 and 12 to be combined with corresponding contacting or insulating steps, in the manufacture of the integrated circuit, so that, for the purposes of producing the described measuring transducer, the only additional working operation in comparison with the conventional manufacture of integrated circuits is that of applying the magnetic film 1.

Another measuring transformer shown in Figure 3 differs from that shown in Figure 2 essentially in that the magnetic coil 2 is arranged between the semiconductor wafer 5 and the magnetic film 1. Although the individual layers in Figure 3 are in part of a somewhat different form from those in Figure 2, components in Figure 3 which perform the same function as in Figure 2 are denoted by the same reference numerals for the sake of enhanced clarity.

The semiconductor wafer 5 of Figure 2 or Figure 3 (and also of an embodiment described below with reference to Figures 6 and 7), with the magnetic film 1 and the magnetic coil 2, can be provided with electrical terminals in conventional manner, and encapsulated in a housing. In this respect, the flat conductor 4 (see Figure 1) can serve as part of the housing, similarly to a cooling plate of a power transistor. The flat conductor 4 is advantageously bent into a U-shaped configuration, as shown in Figure 4, and the semiconductor wafer 5 is disposed between the limb portions of the flat conductor 4, with electrical terminals 13 projecting laterally from between the limb portions. The current Im to be measured is passed through the conductor 4 and the magnetic field produced by the current Im is at a maximum between the limb portions of the flat conductor 4 and is virtually zero outside the limb portions. By applying a soft-magnetic layer to the external surfaces of the flat conductor 4, it is possible to provide for an additional magnetic screening action.

The basic electrical circuit diagram of the integrated circuit formed by the semiconductor wafer 5 of any of the embodiments described herein, with the magnetic film 1 and the magnetic coil 2, is shown in Figure 5 within a circuit block 14. The circuit block 14 includes an oscillator 15, a bias magnetisation current source 16, a direct current source 17, an alternating current amplifier 18, a threshold switching means 19, a multiplier 20 or another analog or digital signal processing means, a supply voltage stabiliser 21, and the magnetic film 1 with the conductor tracks 7 and 8 and the magnetic coil 2 which, in the example shown in Figure 5, is a double spiral coil.

The oscillator 1 5 produces a series or train of pulses at a constant frequency for actuating the bias magnetisation current source 16 which supplies the bias magnetisation current lv. The direct current source 17 feeds the current lo into the magnetic film 1. The a c voltage component of the voltage which is dropped across the magnetic film 1 is amplified in the a c voltage ampiifier 18 and passes to the threshold switching means 19 which produces a respective pulse virtually whenever the external field Ha passes through zero.With the alternating bias magnetisation current lv having a defined curve, the points in time at which such pulses occur represent a measurement in respect of the instantaneous value and the mathematical sign of the magnetic field applied to the measuring transducer, or of the current Im flowing in the conductor 4. On the basis of such moments in time, an analog or digital signal representing the instantaneous value of the current Im can be formed in the multiplier or signal processing means 20.

The above-described measuring transducer is extremely suitable for measuring electrical power, for example in static electricity meters. For this purpose, an alternating current to be measured is fed directly into the flat conductor 4 and, as shown in Figure 5, the voltage U to be measured is applied for example by way of a voltage divider 22 to the multiplier 20 and the output thereof is connected to a counting means 23. The multiplier 20 forms the product of the instantaneous value of the alternating current, determined by the measuring transducer, and the instantaneous value of the a c voltage, and the counting means 23 forms the time integral of the product.

For the purposes of energising or feeding power to the circuit block 14, the a c voltage U is converted into a small d c voltage by means of a transformer 24, a rectifier 25 and a capacitor 26, and that voltage is applied to the supply voltage stabiliser 21.

For the purpose of measuring electrical power in a three-phase current mains, a measuring transducer of the kind described is advantageously used for each phase, while the product formation operation for each phase can be effected in the multiplier 20 of the circuit block 14 of the respective phase or in a microcomputer which is common to all phases.

As already mentioned, the windings of the magnetic coil 2, which is in the form of a thin-film coil, can be disposed in a common plane. It is also possible for the individual windings of the thin film coil to be arranged one above the other in an overlapping relationship, in known manner, and to be insulated from each other by a respective interposed insulating layer.

A further advantageous embodiment of a thin film coil will now be described with reference to Figures 6 and 7 in which the same reference numerals as in the preceding figures of the drawings refer to components having the same function.

In the measuring transducer shown in Figures 6 and 7, the thin film coil comprises a first group of parallel conductor tracks 27 which are disposed in a first plane, and a second group of parallel conductor tracks 28 which are disposed in a second plane. The conductor tracks 27 are disposed below the magnetic film 1 on the insulating layer 6 which is applied to the semiconductor wafer 5, and are insulated from the film 1 by the insulating layer 12. The conductor tracks 28 are arranged on an insulating layer 29, above the film 1. The insulating layers 12 and 29 do not compietely cover the conductor tracks 27, but leave the ends thereof freely accessible. The two ends of the conductor tracks 28 are bent into a Z-shaped configuration and are each connected to a respective end of two successive conductor tracks 27. With the same number of windings, the magnetic coil comprising the conductor tracks 27 and 28 has a conductor length which is smaller by a multiple than that of the flat magnetic coil 2.

Claims

1. A measuring transducer for measuring a magnetic field, comprising a magnetic coil for carrying an alternating bias magnetisation current, a current source, and a magnetic field comparator which is connected to the current source, which comprises at least one antisotropic magnetic film of ferro-magnetic magnetoresistive material, and which is arranged to be exposed to an external magnetic field corresponding to the sum of the magnetic field to be measured and a bias magnetisation field produced by the bias magnetisation current such that the magnetic film is switched alternately into both directions of saturation by the external field in its magnetic preferential direction and abruptly alters its electrical resistance approximately whenever the external field passes through zero, so that the moment in time of the change in resistance represents a measurement in respect of the magnitude and the sign of the magnetic field to be measured, the magnetic field comparator being arranged on a semiconductor wafer of a monolithic integrated circuit.

2. A measuring transducer according to claim 1, wherein the magnetic coil is a thin film coil which is arranged on the semiconductor wafer and which is disposed in one or more planes.

3. A measuring transducer according to claim 2, wherein the magnetic coil comprises two groups of parallel conductor tracks which are disposed in respective planes, wherein the conductor tracks of one of the groups are arranged on one side of the magnetic film and the conductor tracks of the other group are arranged on the other side of the magnetic film, and the two ends of the conductor tracks of one group are connected respectively to an end of two different conductor tracks of the other group.

4. A measuring transformer according to claim 1, claim 2 or claim 3, wherein the integrated circuit comprises a source of the bias magnetisation current, the current source connected to the magnetic field comparator, an amplifier, a threshold switching means and/or a digital or analog signal processing means.

5. A measuring transducer according to claim 4, wherein the signal processing means is a multiplier.

6. A measuring transducer according to claim 5, for measuring a magnetic field produced by an alternating current to be measured, wherein the integrated circuit comprises a multiplier for forming the product of the instantaneous value of said alternating current, determined by the measuring transducer, and the instantaneous value of an alternating voltage, and a counting means is connected downstream of the multiplier for forming the time integral of the product.

7. A measuring transducer according to any one of the preceding claims, wherein the semiconductor wafer is arranged between limb portions of a flat conductor which is bent into a Ushaped configuration and which is intended to carry a current, which is to be measured, for producing the magnetic field to be measured.

8. A measuring transducer for measuring a magnetic field, the transducer being substantially as herein described with reference to Figures 1 and 2 of the accompanying drawings.

9. A measuring transducer for measuring a magnetic field, the transducer being substantially as herein described with reference to Figures 1 and 3 of the accompanying drawings.

10. A measuring transducer for a magnetic field, the transducer being substantially as herein described with reference to Figures 1, 6 and 7 of the accompanying drawings.

11. A measuring transducer for measuring a magnetic field the transducer being substantially as herein described with reference to Figures 1, 2 and 4 of the accompanying drawings.

12. A measuring transducer for measuring a magnetic field, the transducer being substantially as herein described with reference to Figures 1, 3 and 4 of the accompanying drawings.

13. A measuring transducer for measuring a magnetic field, the transducer being substantially as herein described with reference to Figures 1, 4, 6 and 7 of the accompanying drawings.

14. A measuring transducer for measuring a magnetic field, the transducer being substantially as herein described with reference to Figures 1, 2, 4 and 5 of the accompanying drawings.

1 5. A measuring transducer for measuring a magnetic field, the transducer being substantially as herein described with reference to Figures 1, 3, 4 and 5 of the accompanying drawings.

16. A measuring transducer for measuring a magnetic field, the transducer being substantially as herein described with reference to Figures 1, 4, 5, 6 and 7 of the accompanying drawings.