DE4102928A1 - Magnetic field measuring device - has core acting as flux divider with flux gate in auxiliary flux path - Google Patents

Abstract

The magnetic field measuring device uses a flux gate magnetometer with a magnetic core (1) would with an energising winding (8) and a measuring winding (9) associated with a flux gate (4, 8). The energising winding (8) is coupled to an energising source (10), so that an AC signal is obtained in the measuring winding (9) which is proportional to the flux variation, converted by an evaluation circuit (11) into a corresponding display value. The core (1) acts as a flux divider with the full flux fed along a measuring path (3) and part of the flux fed through the flux gate (4, 8). USE - For measuring relatively small DC magnetic fields.

Description

The invention relates to a device for measurement magnetic fields according to the preamble of claim 1.

Such devices are suitable for measuring magnetic Fields, especially of equal fields. Depending on the type of Setup, the sensitivity is different.

With devices for measuring magnetic fields is often the principle of the fluxgate magnetometer (fluxgate) is used. An element becomes in the magnetic circuit to be measured inserted periodically into the magnetic by means of a coil Saturation is brought. This will make the flow to be measured periodically interrupted. Another coil can be used AC voltage signal are taken from that to be measured Flow is proportional. A facility of this type is out EP-PS 00 65 589 known.

Such a measurement inevitably finds one Interruption of the flow to be measured takes place, whereby the Skin effect occurs and the measurement accuracy adversely affected becomes. That is why there are limits to the measurement of small flows. In certain applications, such as measuring oxygen held in gases, become magnetic bridge circuits used where it is strictly required that the person to be measured River is not interrupted.

The invention has for its object one for measurement smallest rivers, especially of equal fields, suitable To create device that does not affect the magnetic circuit and their output signal in a simple way for definitive Measured variable can be converted.

The stated object is achieved by the features of Claim 1 solved. Advantageous developments of the invention result from the subclaims.

An exemplary embodiment of the invention is described below the drawing explained in more detail.

It shows

Fig. 1 is a diagram of a device for measuring magnetic fields,

Fig. 2 shows the field line course in the core of the sensor, switch off the flux gate,

Fig. 3 shows the field line course in the core of the sensor when the river gate is energized.

In FIG. 1, 1 is a core. This is a flat, thin sheet and is made of a magnetically conductive material, such as Mumetall. Advantageously, the core 1 is made of metal glass, because it can suppress the skin effect better at high excitation frequencies. The core 1 has a first cutout 2 through which the core 1 is divided in its longitudinal direction into two branches, namely into a measuring strand 3 and into a secondary strand 4 . Two further cutouts 5 are arranged within the secondary line 4 , the longitudinal axis of which is arranged transversely to the direction of flow 6 . Through these cutouts 5 , a web 7 is formed within the secondary strand 4 , which represents the core of an excitation winding 8 . The secondary line 4 thus forms a river gate together with the excitation winding 8 .

A measuring winding 9 is placed around the measuring strand 3 . The excitation winding 8 is fed by an excitation source 10 . The signal from the measuring winding 9 is fed to an evaluation circuit 11 .

If the excitation winding 8 is not excited, the flow through the core 1 shown in FIG. 2 results. The flow is divided equally between the measuring line 3 and the secondary line 4 . The distribution ratio can be influenced by the geometric design. From the total flow Φ _tot , a partial flow Φ _m passes through the measuring line 3 , the other partial flow Φ ₁ through the secondary line 4 .

If the excitation winding 8 is excited so much that the web 7 goes into saturation, the total flux Φ _{tot is passed} through the measuring strand 3 according to FIG. 3. In addition to the partial flow Φ _m , the partial flow Φ _{1 also} passes through the measuring line 3 . If the excitation source 10 now gives a sinusoidal voltage to the excitation winding 8 , the voltage being slightly greater than is necessary to achieve the saturation field strength H _sat , a voltage is induced in the measuring winding 9 , the magnitude of which is the product of the number of turns of the measuring winding 9 , the frequency of the excitation voltage and the flux difference Φ _tot -Φ _{m is} proportional. This flow difference is the same as the partial flow Φ ₁ . The following applies: u = 4 × n × f × u ₁ , where u is the induced voltage, n the number of turns of the measuring winding 9 , f the excitation frequency and Φ _{1 is} the diverted partial flow already mentioned.

The fact that the magnitude of the induced voltage depends on the frequency is advantageously used to adjust the sensitivity. The higher the frequency, the greater the sensitivity. The sensitivity that can be achieved at an excitation frequency of 200 kHz is approximately 200 volts per turn and Tesla. This allows magnetic fields of the order of 10 ^-5 to 10 ^-7 Tesla to be measured.

The division of the partial flows Φ _m and Φ ₁ depends on the geometry of the core 1 and can be determined once. It results from the dimensioning of the core 1 with a constant thickness, from the ratio of the width of the measuring strand 3 and the narrowest point of the secondary strand 4 . The narrowest point is that next to cutouts 5 . Thus the ratio x = Φ ₁ / Φ _tot can also be determined. The value x is a key figure for the facility. In this way, measurements of the flow change Φ ₁ can be deduced from the total flow Φ _tot . The sensitivity can also be influenced by this ratio.

When the excitation winding 8 is excited with a sinusoidal voltage, a sinusoidal voltage is induced in the measuring winding 9 . Since the deviation of this voltage from the sinusoidal shape is only small, it is advantageous at low frequencies (less than 10 kHz) to measure the voltage directly using an AC rms value measuring device. In this case, the evaluation circuit 11 is such an AC rms value measuring device. At frequencies higher than 10 kHz, a rectifying amplifier stage with subsequent smoothing and a moving coil instrument detecting the peak value of the measuring voltage are advantageously used as the evaluation circuit 11 . In any case, there is still an amplifier stage in the evaluation circuit 11 , the gain factor of which corresponds to the value 1 / x = Φ _tot / Φ ₁ .

The core 1 advantageously has a thickness of 15 to 100 μm. In connection with the use of metal glass, which has already been mentioned as advantageous, it is achieved that the demagnetization factor is also small.

The device described can be understood as a shunted fluxgate magnetometer, in which the magnetic flux to be measured is never interrupted. By closing the flux gate, the partial magnetic current Φ _{1 is} diverted from the secondary line 4 to the measuring line 3 .

Claims (8)

1. Establishment magnetic measurement fields, consisting of a magnetizable core (1), a, a flux gate (4, 8) associated with the excitation winding (8), a measuring winding (9), an excitation source (10) and an evaluation circuit (11) whereby upon excitation of the excitation winding ( 8 ) by means of the excitation source ( 10 ) by an alternating current in the measuring winding ( 9 ) an alternating current proportional to the flux (Φ ₁ ) is generated, which is converted by the evaluation circuit ( 11 ) into a display variable, thereby characterized in that the core ( 1 ) is designed as a flow divider in which a partial flow (Φ ₁ ) through the flow gate ( 4 , 8 ) can be interrupted, so that the total flow (Φ _tot ) flows through a measuring line ( 3 ). 2. Device according to claim 1, characterized in that the core ( 1 ) is a flat, thin sheet and has a cutout ( 2 ) through which the magnetic flux Φ _dead when the flux gate ( 4 , 8 ) is not energized is divisible into one a partial flow Φ _m flowing in a measuring line ( 3 ) and a partial flow Φ ₁ flowing in a secondary line ( 4 ). 3. Device according to claim 2, characterized in that the core ( 1 ) consists of metal glass. 4. Device according to claim 3, characterized in that the core ( 1 ) has a thickness of 15 to 100 microns. 5. Device according to one of claims 1 to 4, characterized in that the evaluation device ( 11 ) divides a value representing the device x = Φ1 / Φ _tot or multiplied by its reciprocal. 6. Device according to one of claims 1 to 5, characterized in that the excitation source ( 10 ) a sinusoidal voltage with a frequency equal to or less than 10 kHz can be removed and that the evaluation circuit contains an alternating voltage effective value measuring device. 7. Device according to one of claims 1 to 5, characterized in that the excitation source ( 10 ) a sinusoidal voltage with a frequency greater than 10 kHz can be removed and that the evaluation circuit ( 11 ) a rectifying amplifier stage with subsequent smoothing and a the peak value of Contains measuring voltage sensing display element. 8. Device according to claim 7, that the display element Moving coil instrument is.