RU2084912C1 - Magnetic field sensor - Google Patents

Abstract

FIELD: instruments, in particular, devices which measure magnetic field, electric current, linear and angular movements. SUBSTANCE: device has magnetoresistive member which is made from magnetic film using bridge circuit and permanent magnet, which generate bias field which level depends on temperature. Bias magnetic field level and temperature coefficient of rest inductance of magnet conform to equation which include temperature coefficient of magnetic resistor sensitivity for constant bias field and coefficient of dependency of sensitivity on bias field for constant temperature. Presence of magnet and use of Permalloy magnetoresistive element results in temperature compensation of sensitivity by factor of 10 to level of 0.01 % for grad. EFFECT: increased precision. 2 dwg

Description

 The invention relates to the field of measuring transducers and can be used in devices for converting electric current, measuring the magnitude and power of electric current, measuring the strength and orientation of the magnetic field vector, measuring linear and angular displacements.

 Thin-film magnetoresistors made according to a bridge circuit are known. Such a scheme is necessary to compensate for the temperature drift of "zero", which occurs due to a change in the nominal electrical resistance R with temperature. As a rule, magnetoresistors, in addition to the magnetoresistive (MR) element, contain additional electric or magnetic elements for linearizing the useful signal (Lenz D. E. Review of magnetic sensors. TIIER, 1990-T. 78, No. 6, pp. 87-102). However, along with those taken into account, there is another source of converter error, which is caused by the temperature dependence of the anisotropy of the magnetoresistance ΔR. It leads to a change in the sensitivity of the magnetoresistor with temperature. In known designs of magnetoresistors, temperature compensation of sensitivity is not performed.

 The closest in design features to the claimed one is a magnetoresistor containing a permalloy film MR element in the form of a four-armed bridge and a system of film permanent magnets. Hill E.W. Britwistle J.K. Spattered permanent magnet arrays for MR sensor bias. IEEE Tr. Magn 1987. V. 23, No. 5, P. 2419-2421.

 PtCo magnets are designed to create a bias magnetic field (magnetic bias) and thereby to provide a bipolar and linear useful signal. The parameters and arrangement of the magnets are selected from the calculation of obtaining the optimal sensitivity of the magnetoresistor at room temperature. The temperature dependence of sensitivity is not taken into account. Based on the temperature dependence ΔR of permalloy films, this leads to an error in the conversion of the magnetoresistor of more than 0.1% deg.

 The technical result consists in reducing the conversion error by thermal compensation of the sensitivity of the magnetoresistor.

где для магниторезистора α_т температурный коэффициент чувствительности при постоянном смещающем поле;
α_н(T_o) коэффициент зависимости чувствительности от смещающего поля при фиксированной температуре.This result is achieved in that the magnetic field sensor containing a magnetoresistive element and a permanent magnet is characterized in that a permanent magnet is used, the temperature coefficient of residual induction α _in , and which the biasing field H _b (T ₀ ) created by it at a fixed temperature T ₀ satisfies the ratio:

where for the magnetoresistor α _{t the} temperature coefficient of sensitivity at a constant bias field;
α _n (T _o ) is the coefficient of the dependence of sensitivity on the biasing field at a fixed temperature.

где η(T_o, H_во) значение чувствительности при фиксированных температурах и смещающем поле. Кроме того, смещающее поле выбирается линейно зависящим от температуры
H_в(T) = H_в(T_o)[1+α_в(T-T_o)] (3)
где H_b(T₀) значение смещающего поля при фиксированной температуре. Совокупности (2) и (3) приводят к отсутствию температурной зависимости чувствительности, если выполняется (1). Таким образом изменение чувствительности из-за температурной зависимости МР эффекта компенсируется соответствующим температурным ходом смещающего поля.Relation (1) is based on the fact that the sensitivity of the magnetoresistor in the working range of temperatures and bias fields is considered as a linear function of these parameters

where η (T _o , H _in ) is the sensitivity value at fixed temperatures and biasing field. In addition, the bias field is linearly dependent on temperature.
H _a (T) = H _a (T _o) [1 + α _in (TT _o)] (3)
where H _b (T ₀ ) is the value of the bias field at a fixed temperature. Combinations (2) and (3) lead to the absence of a temperature dependence of sensitivity if (1) is satisfied. Thus, a change in sensitivity due to the temperature dependence of the MR effect is compensated by the corresponding temperature behavior of the biasing field.

 The presence in the sensor of a permanent magnet (PM "with a certain relationship between the temperature coefficient of the residual product and the bias field created by it is an essential feature that distinguishes the claimed invention from the prototype and determines its compliance with the criterion of" novelty ".

На фиг. 2 представлены зависимости чувствительности магниторезистора от температуры для случаев создания смещающего поля катушками Гельмгольца (кривая 1) и магнитом из феррита бария (кривая 2).In FIG. 1 is a schematic representation of a sensor including an MR element 1 on a substrate 2 and a permanent magnet 3 with magnetization

In FIG. Figure 2 shows the temperature dependence of the magnetoresistor sensitivity for cases of creating a biasing field by Helmholtz coils (curve 1) and a barium ferrite magnet (curve 2).

 The sensor includes a magnetoresistive element 1 on the substrate 2 and a permanent magnet 3 with magnetization.

Его величина составила 10% мТл.A sensor is made containing a permalloy film magnetoresistive (MR) element 1 and a composite permanent magnet 3 (PM) from barium ferrite. A schematic representation thereof is shown in FIG. 1. The MR element was obtained on a silicon substrate by projection photolithography. It has the structure of a four-armed bridge, each of the shoulders of which is made in the form of an inclined meander. The temperature dependence of the sensitivity of such an element is shown in FIG. 2 (curve 1). It is measured at a constant bias field (6.5 mT), which was created by Helmholtz coils (in the absence of PM), and gives α _t -0.13% / deg. The coefficient α _n (T _o ) was determined at room temperature (T ₀ = 20 ^o C) from the experimental dependence

Its value was 10% mT.

Composite PM is made by metal-plastic technology from barium ferrite powder, which has an α _of -0.2% / deg. According to formula (1), for the indicated values of the coefficients, thermal compensation of sensitivity is realized if the PM creates a bias field with an induction of 6.5 mT. In particular, such a bias field was obtained from a plate with a residual induction of 0.01 T and dimensions 6x5x0.6 mm, located at a distance L = 1.1 mm from the MR element.

 The dependence η (T) (for a thermally compensated magnetoresistor is shown in Fig. 2 (curve 2). The value of the temperature coefficient of sensitivity for it is 0.01% / deg, which is an order of magnitude lower than for a magnetoresistor without temperature compensation. Accordingly, it decreased 10 times conversion error due to temperature dependence of sensitivity.

Claims (1)

Magnetic field sensor comprising a magnetoresistive element and a magnet, wherein the permanent magnet is used, the temperature coefficient α remanence and _in which generated them at a fixed temperature T _o biasing _field H (T _o) satisfy the relation

where for the magnetoresistor
α _t is the temperature coefficient of sensitivity at a constant bias field;
α _n (T _o ) - (coefficient of the dependence of sensitivity on the biasing field at a fixed temperature.

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