GB2228337A

GB2228337A - Hall-effect apparatus for measuring direct current

Info

Publication number: GB2228337A
Application number: GB9002590A
Authority: GB
Inventors: Walter Fleischmann; Andreas Kraus; Jurgen Ludwig
Original assignee: Diehl GmbH and Co
Current assignee: Diehl Verwaltungs Stiftung
Priority date: 1989-02-18
Filing date: 1990-02-06
Publication date: 1990-08-22
Anticipated expiration: 2010-02-06
Also published as: FR2643460B1; DE3905060A1; DE3905060C2; GB2228337B; GB9002590D0; FR2643460A1

Description

1 APPARATUS FOR THE NON-CONTACT MEASURING OF A DIRECT CURRENT The

invention relates to apparatus for the non- contact measuring of a direct current at or during a measuring time, of a kind comprising a Hall effect sensor which is arranged in an air gap or between poles of a magnetic device such as an annular magnet.

An item of equipment is described in the literary passage Siemens, Schaltungen mit Halbleiterbauelementen "'Circuits having Semi-conductor Components"), volume 2, 4th edition, 1970, pages 186 to 189. There a special circuit for generating the control current necessary foi the Hall effect sensor is described, and the ohmic zero component of the Hall voltage is compensated for by means of a voltage divider.

It is already known, in the case of such known items of equipment, that currents, to be measured, under 50A produce in an annular magnet no magnetic field which is sufficiently strong for an accurate measurement, if the conductor carrying the measuring current is not laid in coils around the magnet. Laying of the conductor in coils is, however, not practicable in some circumstances. For example, such items of equipment are not suitable for measuring, battery rest charging-currents or residualcharge currents in starter circuits which are designed for high nominal currents, for example several hundreds 1. 1 2 to several thousands of amperes, as is the case, f or example, with aircraft on-board mains or vehicle on-board mains. The battery charging currents that are to be measured are considerably smaller than the nominal currents. The charging currents are, for example, smaller than 5A. The conductors carrying the direct currents that are to be measured are designed for the said high currents and are correspondingly thick and strong. They can, for measuring purposes, hardly be laid in coils around a magnet.

An object of the invention is to propose apparatus, of the kind mentioned at the beginning hereof, which allows a measurement of a direct current f lowing in the conductor which is small in comparison with the nominal current f or which the conductor is designed, without the conductor having to be placed in coils around the annular magnet or other magnetic device.

In accordance with the invention there is provided apparatus, of said kind, which is characterised in that the magnetic device carries a calibrating winding, to which a predetermined calibrating current is applied, at times not coincident with measuring times, by a control and evaluating circuit; in that the control and evaluating circuit detects the Hall voltage produced by the Hall effect sensor in response to the calibrating current, and detects the offset Hall voltage; in that the control and evaluating circuit prior to each 1 1 z 3 measuring time by way of an impulse generator premagnetises the magnetic device to maximum remanence; and in that the control and evaluating circuit in the measuring time detects the Hall voltage based on the direct current that is to be measured.

The control and evaluating circuit thus detects the Hall voltage based on the known calibrating current, the offset Hall voltage which occurs when the measuring current is zero and the Hall voltage based on the direct current that is to be measured. From these values the control and evaluating circuit calculates the direct current flowing through the conductor. The result achieved is sufficiently accurate even of comparatively small currents and measurement in the case even when the conductor is placed in a coil-free manner through the magnetic device. This is because, in the case of the equipment, influences of the temperature drift and sample assessment or control on the one hand of the offset voltage and on the other hand of the proportionality factor explained in more detail below are detected. Moreover, because of the premagnetisation of the magnetic device to produce maximum remanence flux or remanence induction at the gap, the result is achieved that an uncertain remanence flux or induction does not have an effect on the measurement result. Ageing phenomena are also compensated for.

It is not absolutely necessary for the calibrating 4 current to be applied to the calibrating winding prior to each measurement. It is sufficient to undertake the calibration at specific time intervals. The impulse which pre-magnetises the magnetic device in a specific 5 manner is preferably applied prior to each measurement. When the impulse generator pre-magnetises the magnetic device, the calibrating current is switched off.

In development of the invention the impulse 10 generator is connected to the calibrating winding. In this way a further winding on the magnetic device for the pre-magnetisation, is avoided. It is, however, also possible to provide the magnetic device with an additional winding for such pre-magnetisation.

The invention will. be described further, by way of example, with reference to the accompanying diagrammatic drawings, wherein:- FIGURE 1 shows a block wiring diagram of apparatus of the invention, and FIGURE 2 shows the magnetic hysteresis curve of an annular magnet of the apparatus.

An annular magnet 1 has an air gap 2 in which a Hall effect sensor 3 is arranged. The Hall effect sensor 3 is an integrated component part, and the generation of its control current is not shown in more detail. The output Hall voltage of the Hall effect sensor 3 is connected by way of an amplifier 4 and an analog/digital converter 5 to a control and evaluating circuit 6 which is formed by a microprocessor.

The annular magnet 1 carries a calibrating winding 7 having n turns. Connected to the calibrating winding 7 is a constant current source 8 which can be switched on and of f by the microprocessor 6 by way of a lead 9.

Parallel to the constant current source 8 an impulse generator 10 is connected to the calibrating winding 7, which impulse generator can be switched on and off by way of a lead 11 from the microprocessor 6. The microprocessor 6 does not switch the two current sources 8,10 on simultaneously.

Through the annular magnet 1 there extends in a coil-free manner a conductor 12 which carries the direct current that is to be measured, hereinafter called the measured current IM The Hall voltage UH occurring at the output of the Hall ef fect sensor 3 as a result of a measuring current IM follows the relation:

UH = UO + k IM, (1) in which respect UO is the offset Hall voltage which occurs when the measured current IM is zero, and k is a proportionality factor.

1 6 Prior to a measurement of the measured current IM, a known calibrating current IK is applied to the calibrating winding 7 by the constant current source 8. There thereby arises at the output of the Hall effect sensor 3 a calibrating voltage UK. This is initially stored in the microprocessor 6. The proportionality factor k turns out as:

k = UK/IK. (2) From this there results with the above relation (l):

IM (UH-UO) IK n/UK. (3) is Then also the of úset Hall voltage UO is stored in the microprocessor 6.

As a result of the calibrating current IK the magnetic circuit of the annular magnet 1 is magnetised in an undefined non-specific manner, so that the remanence flux assumes an arbitrary value between +Br(max) and Br(max) (see FIGURE 2).

After the switching-off of the constant current course 8 the impulse generator 10 is switched on. This now gives a current impulse to the calibrating winding 7. The current impulse can be either positive or negative. As a result of the current impulse the magnetic circuit is pre-magnetised by the induction to the one point of 7 maximum remanence flux Br(max), so that the working straight line is the limiting curve of the hysteresis through this point of maximum remanence (see FIGURE 2).

Subsequently then the measured current IM is switched on or respectively the conductor 12 is conducted through the annular magnet 1 and the then arising Hall voltage UH is stored in the microprocessor 6. Also the value of the calibrating current IK and the number n of the coils of the calibrating winding 7 are stored in the microprocessor 6. The microprocessor 6 then ascertains from the values UH, UO, IK, n and UK the flowing current IM in accordance with the above relation (3).

In the case of the described item of equipment a calibration of the connection between the measured current IM and the initial variable UH is achieved in that the measured value is put into relationship with a magnetic field based on a known calibrating current 1K.

The temperature drift and the sample assessment or control of the proportionality factor are compensated for. As a result of the detection of the offset voltage, also the temperature drift and sample assessment or control are taken into consideration. The remanence of the magnetic circuit is adjusted by the specific premagnetisation. Thus, even ageing phenomena scarcely have any effect on the measurement result.

The invention is not confined to details of the 8 foregoing example and many variations are possible within the scope of the invention as def ined by the appended claims. For example, the magnetic device may be of any form, other than an annular magnet, arranged to actuate a 5 Hall generator and accept the conductor 12.

t is 9

Claims

1. Apparatus for the non-contact measuring of a direct current in a measuring time by means of a Hall ef fect sensor which is arranged in an air gap or between poles of a magnetic device which is arranged so that a conductor carrying a direct current that is to be measured extends through or can be passed through the device, characterised in that the device carries a calibrating winding, to which a predetermined calibrating current is applied at times not coincident with measuring times, by a control and evaluating circuit; in that the control and evaluating circuit detects the Hall voltage produced by the Hall ef f ect sensor in response to the calibrating current, and detects the offset Hall voltage; in that the control and evaluating circuit prior to each measuring time by way of an impulse generator premagnetises the magnetic device to a point of maximum remanence; and in that the control and evaluating circuit in the measuring time detects the Hall voltage based on the direct current that is to be measured.

2. Apparatus as claimed in Claim 1, characterised in that the impulse generator is connected to the calibrating winding.

3. Apparatus as claimed in Claim 1 or 2, characterised in that the impulse generator pre-magnetises the annular magnet at least after each switch-on of the calibrating current.

4. Apparatus as claimed in any preceding claim, characterised in that the control and evaluating circuit has a microprocessor which, outside the measuring times, alternately connects a constant current source and the impulse generator to the calibratini winding.

5. Apparatus for non-contact measuring of a direct 10 current substantially as hereinbefore described with reference to the accompanying drawings.

4 Published 1990atThe Patent Office. State House. 6671 HighEolborn. London WC1R4TP.Purther copies maybe obtained from The Patent OfriceSales Branch. St Mary Cray. Orpington. Kent BR5 3RD Printed by Multiplex techniques ltd. st mary Cray. Kent, Con. 187