Fluxgate sensor

Abstract

Sensor with a sensor drive circuit ( 15 ) to measure an external magnetic field applied to the sensor. An alternating current is fed to at least two coils ( 1; 5; 8; 9 ) that are wound around two cores of the sensor. The cores are alternately saturated by the alternating current, wherein the alternating current is assigned to one core each via a sine curve. A first arithmetic mean is an average value of the sine curve signal. A second arithmetic mean is formed from a high peak value of the sine curve of one core and a low peak value of the sine curve of the other core when at least one core is influenced by an external magnetic field.

Description

[0001] Fluxgate sensor

[0002] Description

[0003] The present disclosure refers to a fluxgate sensor with a fluxgate sensor drive circuit to measure an external magnetic field applied to the fluxgate sensor .

[0004] Objective of the present disclosure

[0005] It is the obj ective of the present disclosure to provide a circuit of a magneto-elastic sensor, which requires a reduced number of components and / or parts .

[0006] This significantly reduces the complexity of the sensor .

[0007] It is the intention of the present disclosure to provide a fluxgate sensor drive circuit that measures an external magnetic field applied on a fluxgate .

[0008] The present disclosure therefore assumes that the influence of an external magnetic field is to be measured .

[0009] Another obj ective of the present disclosure is to f ind an alternative way to measure the magnetic field using fluxgate other than measuring the saturation time delay .

[0010] Solution

[0011] The features of claim 1 of the present disclosure achieve these obj ectives .

[0012] Alternating current

[0013] The current to which the present disclosure relates is an alternating current .

[0014] Alternating current (AC ) is an electric current , which periodically reverses its direction . The alternating current (AC) changes its magnitude continuously with time .

[0015] In contrast to alternating current (AC) , direct current ( DC) only flows in one direction .

[0016] The alternating current (AC) of the coil (a) and the coil (b) is each represented as a sine wave, respectively .

[0017] The positive half-period of the sine wave corresponds with the positive direction of the alternating current (AC) .

[0018] The negative half-period of the sine wave corresponds with the negative direction of the alternating current (AC) .

[0019] The full period is referred to as a cycle .

[0020] While the receiver coil (a ) of the core (A) is orientated in one direction, the receiver coil (b) of the other core (B) is orientated in the opposite direction .

[0021] As a result , the two sine curves run in opposite directions .

[0022] Electric drive

[0023] According to the present disclosure, the electric drive is the system used to control the movement and / or to control the function of an electrical arrangement .

[0024] Previous sensor drive circuits for fluxgate sensors usually require at least two drives .

[0025] Previously known sensor drive circuits preferably use two so called harmonic demodulation circuits to sense the magnetic field. The sensor drive circuits known in the art commonly require at least two so-called analogue multiplexer to do so .

[0026] The multiplexer is commonly known as a data selector . The multiplexer selects between analogue and / or digital input signals . It forwards the selected signals to a single output line . The selection done by the multiplexer is directed by a separate set of digital select lines .

[0027] The present disclosure provides a sensor drive circuit for a fluxgate sensor whose functionality requires only a single electric drive .

[0028] Fluxgate sensor and according sensor drive circuit

[0029] Fluxgate sensor

[0030] Following the present disclosure, the fluxgate sensor comprises two, preferably soft magnetic coil cores .

[0031] The cores are periodically driven into magnetic saturation . The magnetic saturation refers to the inf luence of an external magnetic field .

[0032] Saturation magnetisation is a state of the ferromagnetic wave that is reached when an increase in the applied external magnetic field can no longer increase the magnetisation of the ferromagnetic wave .

[0033] If an external magnetic field acts on the fluxgate , it either prevents or promotes the saturation state of the fluxgate .

[0034] According to the present disclosure the core has a receiver coil . One receiver coil is wound around each core .

[0035] The receiver coil (a ) of one core (A) is orientated in one direction, while the receiver coil (b) of the other core ( B) is orientated in the opposite direction . In the absence of an external magnetic field, the voltages induced in the coils ( a ; b) cancel each other out .

[0036] An external magnetic field acts in parallel or in the opposite direction on the magnetic fields of the two coils (a; b) . As a result, if the external magnetic f ield extends parallel to the magnetic field of a first coil (a ) , saturation of the core (A) is reached sooner in the first coil ( a ) .

[0037] In the second coil (b ) , the external field extends antiparallel . Thus , saturation of the second core ( B) is reached later .

[0038] This so-called asymmetry causes a resulting signal in the receiver coils (a ; b) that is proportional to the applied external magnetic field .

[0039] In other words , the fluxgate sensor consists of two, preferably small magnetically susceptible cores (A; B) wrapped by two coils ( a ; b) of wire .

[0040] An alternating electric current is passed through one coil (a) , driving the core (A) through an alternating cycle of magnetic saturation, i . e . magnetised, un-magnetised, inversely magnetised, un-magnetised, magnetised, and so forth .

[0041] The constantly changing field induces a voltage (V) in the second coil (b) , which is measured by a sensor .

[0042] In a magnetically neutral background, the input and output signals of the coils (a ; b) match .

[0043] The signal from the fluxgate magnetic field sensor, which consists of the two cores (A; B) wound around opposite coils (a; b) , has the value 0 .

[0044] However, when the core (A; B) is exposed to an external magnetic field, it is more easily saturated in alignment with the external magnetic field and less easily saturated in opposition to it .

[0045] If the fluxgate sensor is exposed to the external magnetic field, the two alternating current sine curves of the coils ( a; b) of the cores (A; B ) no longer run in opposite directions relative to each other . In the absence of an external magnetic field, the voltages induced in the coils ( a ; b) cancel each other out .

[0046] Under the influence of the external magnetic field, the two alternating current sine curves of the coils (a ; b) of the cores (A; B) shift upwards or downwards .

[0047] Thus , the signal representing the voltage (V) induced in the coil (a ) and the signal representing the voltage (V) induced in the coil (b) do not cancel each other out in view of the external magnetic field .

[0048] The resulting dif ference between the two signals represents the value of the external magnetic field .

[0049] Depending on which of the two coils ( a ; b) or which of the two cores (A; B) is more exposed to the external magnetic field, the alternating current sine curve of the coil ( a ; b) shifts in relation to the alternating current sine curve of the coil (b; a ) ■

[0050] In the presence of the external magnetic field, the resulting signal of the fluxgate sensor has a value not equal to 0 .

[0051] The signal resulting from the fluxgate sensor corresponds to the value of the external magnetic field .

[0052] Alternatively, a so-called fluxgate inductor is driven in and out of magnetic saturation by altering voltage (V) pulses . Of course, multiple fluxgate inductors can also be used .

[0053] Sensor drive circuit

[0054] The sensor drive circuit according to the present disclosure measures the alternating current peaks .

[0055] The alternating current peaks in (V) are referred to as the alternating current high peak value in (V) and the alternating current low peak value in (V) . The external magnetic field is measured using the sensor drive circuit .

[0056] According to the present disclosure, the sensor drive circuit measures the alternating current high and the alternating current low peak changes , which can be used to measure the magnetic field strength .

[0057] A torque and / or a force and / or a current can induce the magnetic field . The magnetic field can also be an external magnetic field .

[0058] The sensor drive circuit can be digitised using a microcontroller or a so called digital signal processing ( DSP) . Digital signal processing refers to the use of digital processing . Digital processing usually refers to a computer and / or a more specialized digital signal processor to perform a wide variety of signal processing operations .

[0059] In the context of the present disclosure , a current voltage (V) represents the current . It goes without saying that another unit can also be used .

[0060] The current to which the present disclosure relates is an alternating current . The alternating current is referred to in more detail above .

[0061] The detection of the alternating current peaks is referred to in more detail below .

[0062] Previously known sensor drive circuits generally require two drives .

[0063] The present disclosure provides for a sensor that only works with a single drive .

[0064] In the following, it is assumed that the alternating current sine curve has a so-called high peak value and a so-called low peak value . The alternating current high peak value is the upper vertex of the respective sine curve .

[0065] The alternating current low peak value is the low vertex of the respective sine curve .

[0066] Peak detection

[0067] Sine wave of alternating current

[0068] The alternating current (AC ) of the coil (a ) and the coil (b) is each represented as a sine wave , respectively .

[0069] The sensor drive circuit according to the present disclosure uses the detection of alternating current peaks to sense an interfering magnetic field .

[0070] Wherein the positive half-period of the sine wave corresponds with the positive direction of the alternating current (AC) , the negative half-period of the sine wave corresponds with the negative direction of the alternating current (AC) .

[0071] The entire period of the alternating current is therefore referred to as a cycle .

[0072] While the receiver coil (a ) of the core (A) is orientated in one direction, the receiver coil (b) of the other core (B) is orientated in the opposite direction .

[0073] As a result , the two alternating current sine curves run in opposite directions .

[0074] In the following, it is assumed that the alternating current sine curve has a so-called high peak value and a so-called low peak value .

[0075] The high peak value is the high vertex of the respective alternating current sine curve . The low peak value is the lower vertex of the respective alternating current sine curve .

[0076] If the two alternating current sine curves are not influenced by an external magnetic field, the alternating current sine curves are arranged in relation to each other so that the signal from the sensor assumes the value 0 .

[0077] Reference value

[0078] When the fluxgate sensor reaches a degree of saturation, at least one alternating current peak is reached .

[0079] The present disclosure measures the high peak value of the alternating current in (V) and a corresponding low peak value of the alternating current in (V) of the sinusoidal curves of the alternating current .

[0080] An arithmetic mean is formed from a high peak value and a low peak value, neither of which is influenced by the external magnetic field . This value is referred to as the reference value in (V) .

[0081] Then another arithmetic mean is formed from a high peak value and a low peak value , both of which are influenced by the external magnetic field .

[0082] A first arithmetic mean is an average value of the sine curve signal .

[0083] The first arithmetic mean (reference voltage ) is determined by averaging the sine curve .

[0084] It goes without saying that the first arithmetic mean may also be determined by using a voltage devider or a so called voltage reference IC . The voltage reference IC is an electronic device that provides a steady voltage that other ICs can use to make measurements with the required accuracy . A second arithmetic mean is formed from ( a ) a high peak value of the sine curve of one core and (b) a low peak value of the sine curve of the other core when at least one core is inf luenced by an external magnetic field .

[0085] It goes without saying that the first arithmetic mean and the second arithmetic mean are dif ferent values .

[0086] The first arithmetic mean is a reference value ( reference voltage ) for the second arithmetic mean .

[0087] To determine the value of the external magnetic field, the difference between the reference value in (V) and the second arithmetic mean value in (V) is formed, the later ( second arithmetic mean value ) resulting from the alternating current high peak value in (V) and the alternating current low peak value in (V) , both of which were measured under the influence of the external magnetic field .

[0088] The resulting difference is the value of the external magnetic field in (V) .

[0089] The magnetic field is thus measured by measuring the alternating current peaks .

[0090] In the state of the art , the time dif ference between the signals was measured, whereas the present disclosure envisages determining the differences between the voltage values .

[0091] According to the present disclosure, alternating current high peak values in (V) and alternating current low peak values in (V) are measured instead of the time delay until a magnetic saturation . Connection, of coils

[0092] In previously known sensor drive circuits , the connection of the coils requires at least one drive arranged at each end of the coils .

[0093] In the state of the art , the signal is taken from the middle connection arranged between the pairs of individual coils .

[0094] The sensor drive circuit of the present disclosure employs a single drive only .

[0095] The coils relating to the present disclosure are connected in series and / or in parallel .

[0096] The output signal is taken from the opposite end of the connection .

[0097] Diode , Resistor and Capacitor

[0098] Diode : The present disclosure understands the diode to be a two- terminal electronic component . The diode conducts a current in one direction . In the context of the present disclosure , the current is an alternating current .

[0099] The diode has a low resistance in one direction . The diode has a high resistance in the other direction .

[0100] The diode allows the alternating current to pass in one direction while blocking it in the opposite direction .

[0101] As the diode receives alternating current , the diode allows the current to pass alternately in one direction, while the diode blocks the current in the opposite direction .

[0102] The direction in which the diode lets the current through or in which the diode blocks the current changes continuously . Resistor : The resistor is a passive two-terminal electrical component . The resistor implements an electrical resistance as a circuit element .

[0103] The main electrical function of the resistor is to provide an electrical resistance .

[0104] Capacitor : According to the present disclosure, the capacitor is an electronic device that stores electrical energy in an electric field . The electric energy is stored by accumulating electric charges , preferably on two closely spaced surfaces that are insulated from each other . The capacitor is a passive electronic component comprising two terminals .

[0105] Preferably, the capacitor comprises conductors separated by a non-conductive region .

[0106] Advantages of the present disclosure

[0107] A smaller sensor drive circuit enables the arrangement of a smaller sensor .

[0108] Also, a higher immunity of electromagnetic compatibility ( EMC) can be achieved .

[0109] In addition, greater immunity to interference can be achieved with regard to electromagnetic compatibility (EMC ) .

[0110] Better functional safety can be achieved .

[0111] The present disclosure can be used for all kinds of sensors .

[0112] In particular, torque and force sensors can be combined with magneto-elastic technology .

[0113] The new sensor drive circuit allows compliance with modern, high electromagnetic compatibility and / or with Automotive Safety Integrity Level (ASIL) requirements to fulfil a high level of functional safety . ASIL is a ris k classification system defined by the known ISO 26262 standard for the functional safety of road vehicles .

[0114] The present disclosure leads to a reduction in the complexity of the sensor drive circuit .

[0115] The sensor drive circuit requires a smaller number of components . The reduced number of installed components enables the development of smaller sensors .

[0116] Previously, the printed circuit board ( PCB) required a greater number of components .

[0117] Drawings

[0118] Further examples and advantageous embodiments of the present disclosure are described in more detail below with reference to the figures . These show :

[0119] Fig . 1 a simplified fluxgate sensor drive circuit according to the present disclosure ,

[0120] Fig . 2 a coil connection according to the state of the art ,

[0121] Fig . 3 a coil connection according to the present disclosure and

[0122] Fig . 4 to Fig . 8 show coils of the coil connection arranged in series and / or in parallel .

[0123] Fig . 1 shows a fluxgate sensor drive circuit 15 according to the present disclosure .

[0124] The one Opamp required by the present disclosure is shown by reference 5.

[0125] The Opamp 5 is a so called operational amplifier .

[0126] The Opamp 5 compares the reference signal and a so called assymetrique point . The Opamp 5 makes sure that the reference signal and the assymetrique point are equal by correcting the coils 10, 11, 12, 13 output through a feedback.

[0127] In the following, the operational amplifier is referred to as Opamp .

[0128] The one Opamp required by the present disclosure is shown by reference 5.

[0129] Preferably, but not exclusively, Opamp 5 is a direct current (DC) -coupled high-gain electronic voltage amplifier.

[0130] Preferably, the direct current (DC) -coupled high-gain electronic voltage amplifier has a differential input. Usually, it has a single-ended output.

[0131] Fig. 1 shows a two sensor coil setup, with coils 10, 11, 12, 13. The output goes to a High / Low peak detection.

[0132] The middle point between both point is determined.

[0133] The diodes 6 and capacitors 7 are also shown in Fig. 1.

[0134] Fig. 2 shows a coil connection according to the state of the art .

[0135] In the previously known sensor drive circuit 15, the connection of the coils 10; 11; 12; 13 requires one diode 8 and one diode 9, arranged at one end of the connection of the coils 10; 11; 12; 13, respectively.

[0136] In the state of the art, the signal 16 is taken from the middle connection arranged between the pairs of individual coils 10; 11; 12; 13.

[0137] The individual coils 10; 11; 12; 13 of the connection of the coils are arranged in series 17. Fig. 3 shows a coil connection according to the present disclosure .

[0138] The connection of the coils 10; 11; 12; 13 of the sensor drive circuit 15 according to the present disclosure requires only one diode .

[0139] According to the present disclosure, the signal 16 is taken from the middle connection arranged between the pairs of individual coils 10; 11; 12; 13.

[0140] The individual coils 10; 12 and 11; 13 of the connection of the coils are arranged in series 17.

[0141] In Fig. 3 the individual coils 10; 11 and 12; 13 of the connection of the coils are also arranged in parallel 18.

[0142] Fig. 4 to Fig. 8 show coils 10; 11; 12; 13 of the coil connection arranged in series 17 and / or in parallel 18.

[0143] The coils 10; 11; 12; 13 that are also marked with reference 17 are arranged in series with one another.

[0144] The coils 10; 11; 12; 13 that are marked with reference 18 are arranged in parallel with one another.

[0145] Bridges 19 are shown in Fig. 6 and 8. The bridges 19 offer the opportunity that the number of coils 10; 11; 12; 13 can be increased or decreased within the connection of the coils 10; 11; 12; 13. List of reference

[0146] 1 free

[0147] 2 free

[0148] 3 free

[0149] 4 free

[0150] 5 OPAP

[0151] 6 Diode

[0152] 7 Capacitor

[0153] 8 Diode

[0154] 9 Diode

[0155] 10 Coil

[0156] 11 Coil

[0157] 12 Coil

[0158] 13 Coil

[0159] 14 free

[0160] 15 Fluxgate sensor drive circuit

[0161] 16 Signal

[0162] 17 Arrangement in series

[0163] 18 Arrangement in parallel

[0164] 19 Bridge

[0165] 20 Substrate

Claims

Claims1. Sensor with a sensor drive circuit (15) to measure an external magnetic field applied to the sensor, wherein alternating current is fed to at least two coils (1; 5;8; 9) that are wound around two cores of the sensor, and the cores are alternately saturated by the alternating current, wherein the alternating current is assigned to one core each via a sine curve, characterized in that, a first arithmetic mean is an average value of the sine curve signal, and a second arithmetic mean is formed from a high peak value of the sine curve of one core and a low peak value of the sine curve of the other core when at least one core is influenced by an external magnetic field.

2. Sensor according to claim 1 characterized in that the coils (1; 5; 8; 9) are arranged in series (17) .

3. Sensor according to claim 1 characterized in that the coils (1; 5; 8; 9) are arranged in parallel (18) .

4. Sensor according to claim 1 characterized in that the coils (1; 5; 8; 9) are connected via a bridge (19) .

5. Sensor according to claim 1 characterized in that the coils (1; 5; 8; 9) are separated via a substrate (20) .

6. Sensor according to claim 1 characterized in that the fluxgate sensor has one single fluxgate sensor drive (1; 5; 8; 9) .Sensor according to claim 1 characterized in that the fluxgate sensor drive circuit (15) has at least one diode (6) and / or at least one capacitor (7) and / or at least one resistor.

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