GB2244141A - Measurement of magnetic fields - Google Patents

Abstract

In a device for measuring magnetic fields or flux densities, non linearity errors of a particular Hall element are determined and recorded in a Read Only Memory, and a suitable apparatus e.g. a microprocessor (not shown) is arranged to correct data from the Hall probe using the stored non linearity errors. The error data can be stored in a part of the Hall element assembly itself. <IMAGE>

Description

AN APPARATUS FOR THE MEASUREMENT OF A MAGNETIC FIELD TO ACHIEVE IMPROVED ACCURACY.

THE PRESENT INVENTION RELATES TO THE MEASUREMENT OF MAGNETIC FLUX DENSITY OR MAGNETIC FIELD STRENGTH USING A TECHNIQUE WHICH INCREASES THE ACCURACY AVAILABLE BY A CERTAIN, COMMONLY USED METHOD.

Hall Effect devices exhibit a well known phenomena by which an electrical current, flown as the Hall current, is made to f low through a block of material. usually a seri conductor material and the material is exposed to a Magnetic field having an electrical potential difference, known as the Hall Voltage, this is created across the semi conductor material in a given direction wit respect to the path of the electrical current and the Magnetic Field. further, for a give sample of semi conductor. a known cur rent aro a ven orientation, the potential difference exhibites is approximately proportional to the Magnetic Field Strength.

This principle is widely used in instruments frequently described as Hall Effect Gaussmeters, Hall Effect Tesla meters, Hall Effect Magnetometers etc. and are used in the measurement of Magnetic Field Strengths or Magnetic Flux Density.

Magnetic Field Strengths are measured in units of Oersteds or Amperes per metre. Magnetic Flux Density is measures in suss or Tesla. Both measurements are ciosely related in situations wnere the relative Permeability is that or one or very close to one. Air has such a value and is the medium of measurement for most practical situations. Therefore this principle is widely used for the measurement of both Magnetic Field Strength and Magnetic Flux Density.

In an ideal situation the Hall Effect transducer, based upon a Hall effect device, and the associated electronic circuitry would have a linear characteristic, in a practical situation the Linearity of the Hall Effect Device limits tne accuracy of such a measurement system.

To reduce this non-linearity the specific value of the Hail current used in the Hall Effect Device can be chosen together with a se!ected load resistance placed acros the output terminals carrying the Hall voltage. This arrangement can reduce the errors aue to non-linearity or the Hall Erfect Device but tends to leave signiticant error a higner readings.

According to the present invention it seeks to provide a@ apparatus by which magnetic measurements can be taken which overcomes the non- linearity errors of te Hail Effect Device. The same method can be employed to overcome any iinearity errors in the associated electronic circuitry.

According to one aspect of the present invention a given a.

Effect Device undergoes a setting up proceedure in which it has its individual characteristics measures over a range of Magnetic flux densities. Variations in the output characteristies from a 1 inea. relationship are noted at a number of Magnetic Flux Densities. By this the variations from the ideal are known.

When the Hall Effect Device is to be used for measurement purposes it is connected to some electronic circuitry. The electronics associated with the Hall Effect Device includes an element for digitising the analogue signal. The circuit also includes a storage device such as a "Read Only Memory" (ROM) which will store corrective data or a corrective Algorithm which will uti 1 ise the previousiv measured variations from the ideal for the specific Hal ! Effect Device to be used.

embodiment of the present invention, the Hall Etrect Device is constructed into a practical form suitable for general purpose measurements. The Device ic connected to o the associated electronic circuitry by way of an electrical cable ana its connector. Contained within the connected body is a memory device carrying the corrective information digital form for the individual Hail Effect Device. The advantage of this is that the required data is automatical2y selected when a different Hall Effect Device is connected to the Electronic circuitry.

an embodiment of the present invention will now be more particularly described, b way of example only, with reference to the accompanying 3 wings, in which: Figure 1 is a diagram showing a Hall Effect Device which is supplied with a Hal 1 current and exposed to ar. unknown magnetic field. The Hall voltage generated is supplied to analogue circuits for signal processing. The output of tnese circuits is passed to an Analogue to Digital Converter. The digital representation of the original Hall voltage can now be corrected by the microprocessor system with information stored in the "Read Only Memory" ROM before being sent to tne Output.

Figure @ represent atypical non-i inear characteristics of commercially availabie Hall Eftect Devices.

Claims (3)

1. CLAIMS:

   9008609.1 - APPARATUS FOR THE MEASUREMENT OF A MAGNETIC FIELD TO IMPROVE ACCURACY 1. The output characteristics of a particular Hall device can be determined over a range of magnetic flux densities and that non linearity characteristics be determined by comparison with a more accurate magnetic flux density measurement method and that the resulting data stored in an electronic form.
2. 2. That the non linearity error data claimed in (1) can be used to electronically correct for the errors made in a measurement of magnetic phenomena at the time of the measurement or at a later date.
3. 3. That the non linearity error data claimed in t1i can be stored in an electronic form with the connector plug or other part of a Hall probe assembly so that connecting the Hall probe to a suitable apparatus will also connect the required non linearity error data.