Magnetic Sensor

Abstract

To prevent the operation of a magnetic sensor from being unstable when a saturable coil is magnetically saturated.SOLUTION: A magnetic sensor includes a magnetic measuring unit 70 that measures magnetism surrounding a saturable coil based on the excitation time of the saturable coil, calculated based on transition of excitation current detected by a current detection circuit. The magnetic measuring unit 70 detects a magnetic saturation state before excitation based on a sum value Tsum obtained by adding a first excitation time Tcw based on a first excitation current and a second excitation time Tccw based on a second excitation current and a magnetic saturation detection threshold Tth for the sum value for detecting the magnetic saturation state before excitation, and detects proximity of a magnetic material based on a difference value Tsub between the first excitation time Tcw and the second excitation time Tccw, a threshold Tdis for detecting proximity of the magnetic material, and a detection result of the magnetic saturation state before excitation.SELECTED DRAWING: Figure 14

Description

Technical Field

[0001] The present invention relates to a magnetic sensor that converts, for example, the magnitude and direction of a magnetic field into an electrical signal, and more particularly to a circuit technique for a magnetic sensor using a saturable coil.

Background Art

[0002] Conventionally, magnetic sensors that detect the magnitude and direction of a magnetic field and convert them into electrical signals have been known. For example, Patent Document 1 discloses a magnetic detection method that applies a saturable coil as a circuit technique for a magnetic sensor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the magnetic detection method using the saturable coil (hereinafter sometimes abbreviated as "coil") described in Patent Document 1, the time T (excitation time) from the start of current excitation of the saturable coil by current excitation to the stop of excitation immediately after magnetic saturation changes linearly depending on the direction and magnitude of the external magnetic field applied to the saturable coil. Measurement was carried out by applying this phenomenon (see, for example, paragraphs

[0017] to

[0050] of Patent Document 1 and FIG. 2). At this time, even if there is a difference in the degree of the direction and magnitude of the external magnetic field to be measured, it was assumed that the saturable coil was in an unsaturated state before current excitation of the saturable coil. If the saturable coil itself was saturated before current excitation, there was a problem that the state of the saturable coil did not transition as assumed in the magnetic sensor described in Patent Document 1 and normal measurement could not be performed.

[0005] In view of the above situation, an object of the present invention is to prevent the operation of a magnetic sensor from becoming unstable when a saturable coil is magnetically saturated.

Means for Solving the Problem

[0006] In order to solve the above problems, a magnetic sensor according to an aspect of the present invention includes a saturable coil, a first excitation current in a first direction, a second excitation current in a second direction opposite to the first direction, an excitation circuit capable of supplying the saturable coil, an external magnetic field applied to the saturable coil, a current detection circuit for detecting an excitation current generated in the saturable coil based on the external magnetic field and the self-induced magnetic field of the saturable coil, and a magnetic measurement unit for measuring the magnetism around the saturable coil based on the excitation time of the saturable coil calculated based on the transition of the excitation current detected by the current detection circuit. The magnetic measurement unit detects the magnetic saturation state before excitation based on an addition value obtained by adding a first excitation time based on the first excitation current and a second excitation time based on the second excitation current, and a magnetic saturation detection threshold value for the addition value for detecting the magnetic saturation state before excitation. The approach of the magnetic body is detected based on the difference value between the first excitation time and the second excitation time, a threshold value for detecting the approach of the magnetic body, and the detection result of the magnetic saturation state before excitation.

[0007] Also, a magnetic sensor according to another aspect of the present invention includes a saturable coil, a first excitation current in a first direction, a second excitation current in a second direction opposite to the first direction, an excitation circuit capable of supplying the saturable coil, an external magnetic field applied to the saturable coil, a current detection circuit for detecting an excitation current generated in the saturable coil based on the external magnetic field and the self-induced magnetic field of the saturable coil, and a magnetic measurement unit for measuring the magnetism around the saturable coil based on the excitation time of the saturable coil calculated based on the transition of the excitation current detected by the current detection circuit. The magnetic measurement unit compares a first excitation time based on a first excitation current with a first individual comparison result obtained by comparing the first excitation time with an individual magnetic saturation detection threshold for detecting a magnetic saturation state before excitation, and a second excitation time based on a second excitation current with a second individual comparison result obtained by comparing the second excitation time with the individual magnetic saturation detection threshold, calculates a logical sum of the comparison results, detects a magnetic saturation state before excitation based on the calculation result of the logical sum, Based on a difference value between the first excitation time and the second excitation time, a threshold for detecting the approach of a magnetic body, and a detection result of the magnetic saturation state before excitation, the approach of the magnetic body is detected.

[0008] Furthermore, a magnetic sensor according to another aspect of the present invention includes a saturable coil, an excitation circuit capable of supplying a first excitation current in a first direction and a second excitation current in a second direction opposite to the first direction to the saturable coil, a current detection circuit that detects an excitation current generated in the saturable coil based on an external magnetic field applied to the saturable coil and a self-induced magnetic field of the saturable coil, and a magnetic measurement unit that measures the magnetism around the saturable coil based on an excitation time of the saturable coil calculated based on a transition of the excitation current detected by the current detection circuit. The magnetic measurement unit compares a first excitation time based on a first excitation current with a first individual comparison result obtained by comparing the first excitation time with an individual magnetic saturation detection threshold for detecting a magnetic saturation state before excitation, and a second excitation time based on a second excitation current with a second individual comparison result obtained by comparing the second excitation time with the individual magnetic saturation detection threshold, calculates a logical sum of the comparison results, detects a first magnetic saturation state before excitation based on the calculation result of the logical sum, Based on a difference value between the first excitation time and the second excitation time, a threshold for detecting the approach of a magnetic body, and a detection result of the first magnetic saturation state before excitation, the approach of the magnetic body is detected. The magnetic measurement unit compares a sum value obtained by adding the first excitation time and the second excitation time with a magnetic saturation detection threshold for the sum value for detecting a magnetic saturation state before excitation, detects a second magnetic saturation state before excitation from the comparison result, calculates a logical product of the detection result of the second magnetic saturation state before excitation and the detection result of the first magnetic saturation state before excitation, and detects a third magnetic saturation state before excitation based on the calculation result of the logical product.

Advantages of the Invention

[0009] According to at least one aspect of the present invention, it is possible to detect the transition of the excitation current when the saturable coil is magnetically saturated at the time before current excitation by an external magnetic field, and it is possible to prevent the operation of the magnetic sensor from becoming unstable when the saturable coil is magnetically saturated. Problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

Brief Description of the Drawings

[0010]

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Embodiments for Carrying Out the Invention

[0011] Hereinafter, examples of embodiments for carrying out the present invention will be described with reference to the accompanying drawings. For components having substantially the same function or configuration in this specification and the accompanying drawings, the same reference numerals are given and redundant descriptions are omitted.

[0012] First, before explaining the embodiments of the present invention, the measurement principle of a general magnetic sensor will be described with reference to FIGS. 1 to 4.

[0013] FIG. 1 is a diagram showing the relationship between the variation in the inductance of a saturable coil and the magnetic flux density inside the saturable coil. FIG. 1 is a graph showing the correspondence between the change in the inductance L of the saturable coil 1 and the change in the magnetic flux density B inside the saturable coil 1 when an external magnetic field (magnetic field H) having two-direction vector components parallel to the axial direction of the saturable coil 1 is applied from the outside. "Lo" is the inductance when not magnetically saturated (non-saturated state), and "Lsat" is the inductance when magnetically saturated.

[0014] When the magnetic field strength inside the saturable coil 1 exceeds a certain value (=|Hsat|) in either direction, the saturable coil 1 undergoes magnetic saturation. Then, as shown in FIG. 1, the inductance L sharply decreases from "Lo" to "Lsat". Applying the phenomenon in which the inductance L varies sharply depending on the magnetic field strength inside the saturable coil 1, the technique described in Patent Document 1 shows a method of sensing the magnetic field strength.

[0015] FIG. 2 is a diagram showing a basic circuit configuration example for causing current excitation of the saturable coil 1. The current excitation circuit 10 shown in FIG. 2 includes, for example, a drive circuit 11 and a current detection circuit 12 connected to the drive circuit 11 via the saturable coil 1. For example, the drive circuit 11 is connected to a constant voltage power supply E and includes a switching circuit using a switching element (for example, a field effect transistor) that is switched by an excitation ON signal. The drive circuit 11 corresponds to the drive circuit of Patent Document 1. The current detection circuit 12 composed of a current detection resistor R and a comparator input (current Id) corresponds to the current detection circuit of Patent Document 1.

[0016] When an excitation current i(t) is input from the drive circuit 11 to the current detection circuit 12, a self-induced magnetic field Hdrv(t) is generated in the saturable coil 1. A unidirectional self-induced magnetic field Hdrv(t) is generated by a unidirectional excitation current i(t).

[0017] FIG. 3 is a diagram showing an example of a circuit configuration when current excitation is performed using an excitation circuit capable of outputting the direction of the excitation current of the saturable coil 1 in two directions (CW direction, CCW direction). The CW direction (first direction) and the CCW direction (second direction) are parallel and opposite to each other.

[0018] In the current excitation circuit 20 shown in FIG. 3, the H-bridge circuit 21 is used to control the direction of current excitation. By changing the direction of generation of the self-induced magnetic field Hdrv(t), the same effect as when the saturable coil 1 is attached in the reverse direction is obtained. A self-induced magnetic field Hdrv(t) with opposite direction vectors is generated by the bidirectional excitation current i(t). As described in paragraph

[0012] of Patent Document 1, in the present invention, sensing is performed by taking the difference (excitation time difference) between the excitation results in the CW direction and the CCW direction of this current excitation circuit 20.

[0019] FIG. 4 is a diagram showing the transition of the coil current when current excitation is alternately performed using the H-bridge circuit 21. The magnitude of the external magnetic field Hex applied to the saturable coil 1 and the combination of the direction of the excitation magnetic field (self-induced magnetic field Hdrv(t)) generated by self-induction from the saturable coil 1 itself due to current excitation cause the excitation time T required until the saturable coil 1 becomes magnetically saturated to vary, as described in the principles described in paragraphs

[0036] to

[0049] of Patent Document 1. The left graph (1) in FIG. 4 shows the transition of the magnetic flux density B and the excitation current i(t) when the external magnetic field Hex is in the positive direction, the central graph (2) in FIG. 4 shows the case where the strength of the external magnetic field Hex is 0, and the right graph (3) in FIG. 4 shows the case where the external magnetic field Hex is in the negative direction.

[0020] As described above, FIG. 4 shows an example in which the excitation time T varies according to the direction and offset amount (gauss) “constant” of the external magnetic field Hex and the direction and offset amount of the self-induced magnetic field Hdrv. In the magnetic sensor, current excitation is performed such that the magnitude of the combined magnetic field obtained by adding the external magnetic field Hex and the self-induced magnetic field Hdrv(t) exceeds |Hsat| indicated by the dashed-dotted line. For example, when |Hsat| is 20 G, when the external magnetic field Hex is “+5 G”, the self-induced magnetic field Hdrv(t) is added with “+15 G”, or the self-induced magnetic field Hdrv(t) is added with “−25 G”, so that the saturable coil 1 is magnetically saturated and the excitation current i(t) immediately rises sharply to the threshold Ith. Then, when the excitation current i(t) reaches the threshold Ith, the current excitation stops.

[0021] Here, in the principle described in Patent Document 1, as an implicit understanding, regarding the scalar value |Hex| of the external magnetic field Hex, |Hex| ≦ |Hsat| was a prerequisite for the initial state of the saturable coil 1 before current excitation. This is because if this condition is not satisfied, that is, the state of |Hex| > |Hsat| indicates that the saturable coil 1 is magnetically saturated by the external magnetic field Hex from the beginning before applying the self-induced magnetic field Hdrv(t). In this case, the time until magnetic saturation by applying the self-induced magnetic field Hdrv(t) cannot be measured.

[0022] In the conventional method, when this prerequisite is not satisfied, that is, when a strong external magnetic field Hex such that |Hex| > |Hsat| is applied to the saturable coil 1, the behavior is not shown. Also, when the magnetic sensor is configured by a mechanism according to the conventional principle, there remain problems in the operation as a magnetic sensor due to the phenomenon described later.

[0023] FIG. 5 is a diagram showing an example of the transition of the excitation current according to the intensity of the external magnetic field Hex in the saturable coil 1 in the magnetically saturated state. Graphs (1) to (3) in Fig. 5 show the transition of the excitation current (hereinafter sometimes referred to as "current transition") when the saturable coil 1 is magnetically saturated from before current excitation by an external magnetic field Hex (|Hex| > |Hsat|), which is not mentioned in Patent Document 1, according to the intensity of the external magnetic field Hex. As shown in Fig. 5, it can be seen that even when the scalar value of the external magnetic field Hex is about the same, the current transition varies greatly depending on the direction of the magnetic vector of the external magnetic field Hex (either the upper side or the lower side of Fig. 5).

[0024] For example, when the directions of the magnetic vectors of the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are the same, there is no significant difference in the excitation time T (upper side of Fig. 5). However, when the directions of the magnetic vectors of the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are opposite, the greater the intensity of the external magnetic field Hex, the shorter the excitation time T for the excitation current i(t) to reach the threshold value Ith and the current excitation to stop (lower side of Fig. 5).

[0025] Fig. 6 is a diagram showing an example of current transition when the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are in the same direction vector. If the directions of the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are the same (upper side of Fig. 5), the saturable coil 1 is always in a saturated state. During current excitation, as shown in Fig. 6, it always remains at a low inductance and the current excitation has ended. This is because if the magnetic field inside the saturable coil 1 is stronger than the magnetic saturation threshold (Hsat), it stabilizes at a constant value while remaining at a low inductance. This is the same as the magnetic saturation phenomenon of a saturable coil 1 with a core material commonly known. Since the inductance of the saturable coil 1 does not change, the rate of increase of the current during current excitation is also constant, and therefore, the excitation time T is also constant in the shortest state. Let this shortest excitation time T in this stable state be "Tmin".

[0026] In the case of opposite vectors to each other, as understood from the graph on the lower side of Fig. 5, the way the excitation current transitions varies greatly depending on the strength of the external magnetic field Hex. The reason for such a transition lies in the fact that the external magnetic field Hex acts so as to cancel out the self-induced magnetic field Hdrv(t). When a reverse self-induced magnetic field Hdrv(t) is applied to the saturable coil 1 that is magnetically saturated by the external magnetic field Hex, the external magnetic field Hex is canceled out and the strength of the magnetic field applied inside the saturable coil 1 becomes smaller. Since the saturable coil 1 saturates magnetically when a magnetic field of a certain strength or more is generated inside the saturable coil 1, conversely, when the internal magnetic field becomes less than a certain strength, the magnetic saturation transitions to an unsaturated state and the inductance rises steeply. Since the way this phenomenon occurs changes depending on the intensity of the external magnetic field Hex, the way the excitation current transitions changes. Accurately grasping this change is an important point of the present invention.

[0027] Hereinafter, with reference to FIGS. 7 to 9, the changes in current transition according to the intensity of the external magnetic field Hex will be described in order. However, in any of the graphs shown on the right side of each of FIGS. 7 to 9, it is assumed that |Hex| > |Hsat| (graph (2)). As a comparison target, on the left side of the graph representing the current transition state for each intensity, a graph (1) in the case where the strength of the external magnetic field Hex is the same as the magnetic saturation threshold Hsat (|Hex| = |Hsat|) is described.

[0028] [When the external magnetic field Hex is small] FIG. 7 is a diagram showing an example of current transition when the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are in the reverse vector direction and the intensity of the external magnetic field is small. The equal signs described on the excitation current i(t) in the figure indicate that the length and slope of the linear part of the excitation current i(t) in the unsaturated state are substantially the same between the right side (graph (2)) and the left side (graph (1)) of FIG. 7, and the inequality signs indicate that the slopes of the excitation current i(t) in the saturated state are substantially the same.

[0029] Here, the current transition when an external magnetic field Hex in the CCW direction that is sufficient to return the saturable coil 1 to the unsaturated state is applied with a relatively small self-induced magnetic field Hdrv(t) is described. The state of the current transition is as shown in Fig. 7. Immediately after current excitation, since it is magnetically saturated, the excitation current i(t) increases with a steep slope (solid line portion). However, as the strength of the synthetic magnetic field returns to the unsaturated state with the minus-side Hsat as the threshold and the inductance sharply increases, the slope of the current increase (dashed line portion) becomes smaller.

[0030] Since the self-induced magnetic field Hdrv(t) increases as long as the current excitation continues, eventually, due to the continuously increasing self-induced magnetic field Hdrv(t), a synthetic magnetic field in the direction opposite to the external magnetic field Hex will flow through the saturable coil 1. Then, when the strength of the synthetic magnetic field exceeds Hsat on the opposite side (plus side), magnetic saturation occurs again and the inductance decreases.

[0031] As a criterion for this (Hex: small) state, whether the saturable coil 1 is magnetically saturated at two points, immediately after the start of excitation and immediately before the end of excitation, is the criterion. The length of the excitation time T in this state can be approximated to be the same as the case of |Hex| = |Hsat|. The reason is that the inductance value is the same regardless of which vector direction the magnetic saturation occurs in, that is, the slope of the excitation current i(t) is the same. As can be seen by comparing the case of |Hex| = |Hsat| shown in the left graph (1) of Fig. 7 and the case of |Hex| > |Hsat| shown in the right graph (2) of Fig. 7, in both cases, a self-induced magnetic field Hdrv(t) of 2×Hsat is generated in the unsaturated state in common.

[0032] Regarding the remaining self-induced magnetic field Hdrv(t) after magnetic saturation, it is only the difference in whether the magnetic field is increased all at once on one side or dispersed and increased at two locations on both sides. Exactly speaking, at the time of the saturation - unsaturation transition, a kink appears in the graph of the excitation current i(t), so the overall excitation time T is slightly longer in the (Hex: small) state where there is one more kink in the graph (2).

[0033] When the external magnetic field Hex becomes even larger and enters the next (Hex: medium) state where magnetic saturation does not occur immediately before excitation stops, the above equilibrium condition regarding the excitation time T is disrupted.

[0034] [When the external magnetic field Hex is medium] Figure 8 is a diagram showing an example of current transition when the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are in opposite direction vectors and the strength of the external magnetic field is medium. When the external magnetic field Hex becomes larger than a certain level, as shown in the graph (2) on the right side of Figure 8, the excitation time T becomes shorter as the external magnetic field Hex increases. As can be seen from looking at the graph (2) on the right side of Figure 8, in order to flow the excitation current i(t) close to the threshold Ith before transitioning from the solid-line magnetic saturation state to the unsaturated state, the excitation current i(t) reaches the threshold Ith and the current excitation stops before magnetic saturation occurs again at the end as in the graph (2) on the right side of Figure 7. Strictly speaking, the excitation time of the solid-line portion increases compared to the case where the above external magnetic field Hex is small and the case where |Hex| = |Hsat|, but due to the inductance (the increase amount of current per unit of excitation time), it is a negligible increase compared to the decrease in the broken-line region. Therefore, overall, the excitation time becomes shorter as the region of the solid-line magnetic saturation state increases (that is, as |Hex| increases).

[0035] When the strength of the external magnetic field Hex becomes even larger, it transitions to the terminal state (Hex: large).

[0036] [When the external magnetic field Hex is large] Figure 9 is a diagram showing an example of current transition when the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are in opposite direction vectors and the strength of the external magnetic field is large. When the external magnetic field Hex becomes even larger and exceeds the self-induced magnetic field Hdrv(t) generated by flowing a current at the threshold Ith, the saturable coil 1 always remains at a low impedance during current excitation. Therefore, the current transition becomes the same as the transition in the case where the directions of the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are the same, and the excitation time T also becomes constant at the minimum value (Tmin). Once the external magnetic field Hex reaches a certain strength and transitions to this state, there will be no significant characteristic change even if the external magnetic field Hex becomes larger hereafter (terminal state). Comparing the state shown in the graph (2) on the right side of Fig. 9 (Hex: large) with the transition when the external magnetic field Hex and the self-induced magnetic field Hdrv(t) have the same vector as shown in the graph (1) on the left side of Fig. 9, it can be seen that both are in a low impedance state during current excitation.

[0037] As shown in Figs. 7 to 9, in the state where the saturable coil 1 is pre-magnetically saturated by the external magnetic field Hex, the transition during current excitation differs depending on its direction. In particular, when the vectors of the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are in opposite directions, the change in the excitation current i(t) until reaching the terminal state varies significantly depending on the strength of the external magnetic field Hex.

[0038] Fig. 10 is a diagram showing an example of the transition of the excitation time T that changes depending on the strength and direction of the external magnetic field Hex. Here, the vector of the self-induced magnetic field Hdrv(t) generated by current excitation is made the same as the positive direction of the external magnetic field Hex axis (horizontal axis) of the graph. Then, we will focus on and explain the regions (a) to (c) where the directions of the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are opposite. Let the approximate value of the excitation time when |Hex| = |Hsat| in the state of region (a) be "Tl", and the excitation time when Hex = 0 be "T0". As can be seen from observing the transition of the strength of the external magnetic field Hex (regions (a) to (c)), the transition after magnetic saturation is in an equilibrium state up to a certain strength. However, it can be seen that the excitation time becomes shorter starting from the state of region (b) where the strength of the external magnetic field Hex in the negative direction is greater than that of region (a), and converges to the shortest excitation time Tmin in region (c).

[0039] FIG. 11 is a diagram showing the relationship between the transition of each excitation time when current is excited in the CW direction and the CCW direction in the H-bridge circuit, the transition of the difference between the respective excitation times, and the intensity of the external magnetic field Hex. In FIG. 11, with the vertical axis (excitation time T axis) as the boundary, if the vector directions of the self-induced magnetic field Hdrv(t) on one side and the external magnetic field Hex are the same, the other side will be opposite, so the transition of the excitation time T will be symmetric to each other.

[0040] As in Patent Document 1, usually, when a differential magnetic sensor is used as a magnetic sensor, as can be seen from the transition of the excitation time T in FIG. 11, after magnetic saturation, only one of the CW direction excitation time and the CCW direction excitation time becomes shorter and the difference shrinks. For this reason, when the external magnetic field Hex is too large as in regions (b) to (c) of FIG. 10, the differential output approaches the state of no magnetic field. As a result, there is a problem that the magnetic sensor misjudges that the inspection target magnetic body is far away even though the inspection target magnetic body is approaching too closely, and the switch of the magnetic sensor returns from the ON state to the OFF state. Also, as shown in FIG. 10, when used as a single pole instead of differential, the transition of the excitation time T changes greatly depending on the direction of the external magnetic field Hex, so the state cannot be estimated. In particular, when the directions of the self-induced magnetic field Hdrv(t) and the external magnetic field Hex are opposite, as in FIG. 11, there is a region (region (b)) where the length of the excitation time T does not change from the non-magnetic field, so the switch ON to OFF due to over-approach occurs.

[0041] <One Embodiment of the Present Invention> Therefore, in the present invention, in order to solve the above-described problems, it is detected that the saturable coil 1 is magnetically saturated before current excitation, false determination of the magnetic sensor is prevented, and safety is provided in the operation as a magnetic proximity switch sensor. That is, in the present invention, when the saturable coil 1 is magnetically saturated before current excitation, even if the difference in the excitation time T is below the switch-on threshold value ΔTth shown in FIG. 11, it is determined that a strong magnetic field is being received and the ON state can be maintained without change.

[0042] [Determination by Addition Method] As already described, it is difficult to uniquely detect magnetic saturation of a magnetic sensor by reading differential output. As can be seen in Fig. 11, in region (c) symmetric with respect to the vertical axis (excitation time T axis), the difference becomes extremely small, making it impossible to distinguish from the zero magnetic field state.

[0043] On the other hand, looking at the characteristic change of the excitation time T after magnetic saturation from Fig. 11, the side with the same magnetic field direction (vector) is fixed at the shortest excitation time Tmin. On the other hand, the reverse direction side is fixed at the external magnetic field Hex, and the reverse direction side changes according to the magnitude of the external magnetic field Hex, corresponding to each intensity level of the external magnetic field Hex. That is, since only one side changes while the other side is a fixed parameter, when taking the sum of the CW direction excitation time Tcw and the CCW direction excitation time Tccw, the excitation time T after magnetic saturation becomes a parameter showing a unique change, especially between (Hex: medium) and (Hex: large).

[0044] Here, considering the added value Tsum of the excitation times T in the same direction and the reverse direction, on the same direction side, the shortest excitation time Tmin is a fixed value and does not move, so only the fluctuation of the excitation time T on the substantially reverse direction side remains as the variable component of the added value Tsum. Fig. 12 shows the relationship between the external magnetic field Hex and the added value Tsum when the sum of the excitation time Tcw and the excitation time Tccw of the H-bridge circuit in Fig. 11 is taken as the added value Tsum.

[0045] Fig. 12 is a diagram showing the relationship between the transition of each excitation time when current excitation is performed in the CW direction and the CCW direction in the H-bridge circuit, the transition of the sum of each excitation time, and the intensity level of the external magnetic field Hex. Looking at the change of the added value Tsum in Fig. 12, as can be seen, after magnetic saturation, the added value Tsum decreases in regions (b) to (c), so it does not cross the threshold before and after magnetic saturation like the difference between the excitation time Tcw and the excitation time Tccw shown in Fig. 10. From Fig. 12, it can be seen that if only one threshold Tth is set on the added value Tsum axis (vertical axis), magnetic saturation can be easily detected in regions (b) to (c).

[0046] The advantage of this method is that regardless of the direction of the external magnetic field Hex, the behavior of the addition value Tsum is symmetric about the excitation time T axis (vertical axis). Therefore, it is possible to determine magnetic saturation simply by adding two values (excitation time Tcw and excitation time Tccw). Also, as additional circuits from the conventional method (subtraction circuit for calculating differential output), only one addition circuit for obtaining the sum of two excitation times T (excitation time Tcw, excitation time Tccw) and an OR circuit (logical sum circuit) with the magnetic detection output result of the conventional differential circuit are required. Compared with the individual determination method described later, since all circuits are relatively common circuits as analog arithmetic circuits, they are easy to implement.

[0047] As a criterion for the threshold value of the addition value Tsum, it is set in the region where the addition value Tsum decreases in regions (b) to (c). Also, while the current excitation of the saturable coil 1 can be normally performed according to FIG. 12, the value of the addition value Tsum is at most within the range of about 2T. When the current excitation cannot be normally performed due to a disconnection of the saturable coil 1, etc., since the excitation current cannot flow, no trigger signal for stopping the excitation pulse is applied as in paragraph

[0046] of Patent Document 1, and the excitation signal never stops, that is, the excitation time T becomes extremely long and cannot be a normal behavior (in an actual circuit, it is usually set to turn off after a certain time, so this itself does not cause a problem in circuit operation).

[0048] If this extremely long addition value Tsum can be detected as a threshold value (threshold value Tdis in FIG. 12), there is a secondary effect that the disconnection detection of the saturable coil 1 can be easily self-diagnosed. In the conventional differential method, even an extremely long excitation time T becomes zero when taking the difference between magnitudes of the same degree, so it cannot be detected.

[0049] [Determination by individual determination method] In the magnetic saturation measurement by the addition method, although the circuit function can be simplified, the (Hex: small) region is not regarded as magnetically saturated due to its structure. What is common to the regions (a) to (c) in Fig. 12 is that the excitation time T on one side (CW direction or CCW direction) across the vertical axis (excitation time T axis) is fixed at the shortest excitation time Tmin. If the saturable coil 1 is excited in both directions in the magnetically saturated state, the excitation time in either direction will be the shortest excitation time Tmin. Therefore, although individual determination is necessary, a method is proposed in which if there is even one (unidirectional) shortest excitation time Tmin among the measurement results in both directions, it is regarded as magnetically saturated.

[0050] The advantage of this method is that it can immediately capture the saturated state of the saturable coil 1, which is advantageous in a solution where the accuracy of analog data has great significance. That is, there is no case where the saturable coil 1 is half magnetically saturated like the (Hex: small) state (= region (a)) and appears not to be magnetically saturated on the surface. This point is clear when compared with the determination by the addition method shown in Fig. 13. In practice, the excitation time threshold tth for magnetic saturation detection is set slightly longer than the shortest excitation time Tmin.

[0051] [Differences in Magnetic Saturation Determination between Addition Method and Individual Determination Method] Fig. 13 is a diagram showing the differences in magnetic saturation determination between the addition method and the individual determination method according to an embodiment of the present invention. In Fig. 13, the region Ar1 of the addition method and the region Ar2 of the individual determination method each represent a region where the saturable coil 1 is regarded as not magnetically saturated in each determination. In the determination by the addition method on the lower side of Fig. 13, it is determined whether the intensity of the external magnetic field Hex in the CW direction and the CCW direction reaches a level that penetrates into the region (b) shown in Fig. 12. If the addition value Tsum obtained by adding the excitation time Tcw and the excitation time Tccw exceeds the excitation time threshold Tsum, the intensity of the external magnetic field Hex is within the region Ar1, and the saturable coil 1 is not magnetically saturated. For stable determination, the excitation time threshold Tth may be set so that the region Ar1 has a predetermined margin and covers the region (b).

[0052] Also, in the determination by the individual determination method on the upper side of FIG. 13, it is determined whether the intensity of the external magnetic field Hex in the CW direction and the CCW direction exceeds the threshold value |Hsat| and penetrates into the region (a). If the individual excitation times Tcw and Tccw respectively exceed the excitation time threshold value tth, the intensity of the external magnetic field Hex is within the region Ar2, and the saturable coil 1 is not magnetically saturated. For stable determination, the excitation time threshold value tth may be set so that the region Ar2 has a predetermined margin and is inside the threshold value |Hsat|.

[0053] [Specific Example of Processing by Addition Method] Hereinafter, a specific example of the processing by the addition method will be described with reference to FIG. 14. FIG. 14 is a diagram showing a configuration example of a determination block of the addition method according to an embodiment of the present invention.

[0054] As described in the above-mentioned [Determination by Addition Method], in the addition method of the present embodiment, in a form that prioritizes the threshold determination (analog switch determination) of the differential analog data (let Tsub = Tcw - Tccw) of the excitation times Tcw and Tccw at the time of the conventional CW and CCW bidirectional output, a switch-on determination (magnetic saturation switch determination) by magnetic saturation detection based on the sum of the outputs (let Tsum = Tcw + Tccw) is added. Specifically, by calculating the logical sum of the analog switch determination and the magnetic saturation switch determination, if either switch determination is ON, the switch output becomes ON (the logical sum is the true value).

[0055] Also, in the determination by the addition value Tsum, separately from the magnetic saturation switch determination, when the excitation time T is so long that it cannot be obtained if a current is flowing through the saturable coil 1 (threshold value Tdis in [Determination by Addition Method]), an error determination (disconnection detection determination) for determining that the saturable coil 1 is disconnected is also performed simultaneously.

[0056] The addition method determination block 30 shown in FIG. 14 includes a first comparator 31, a second comparator 32, a third comparator 33, and an OR circuit 34. The first comparator 31 performs conventional analog switch determination. It compares the difference value Tsub between the excitation times Tcw and Tccw with the switch-on threshold value ΔTth, and outputs an ON signal when |Tsub| > ΔTth.

[0057] The second comparator 32 is a block added in the present invention. It compares the addition value Tsum, which is the sum of the excitation times Tcw and Tccw, with the threshold value Tth, and outputs an ON signal when Tsum < Tth. The ON signal of the second comparator 32 is a magnetic saturation detection output. For example, it is suspected that there is an over-approach of a magnetic material. The third comparator 33 is a block added in the present invention. It compares the addition value Tsum, which is the sum of the excitation times T in two directions, with the threshold value Tdis, and outputs an ON signal (error output for open-circuit detection) when Tsum > Tdis. The OR circuit 34 compares the outputs of the first comparator 31 and the second comparator 32 respectively, and outputs an ON signal (switch output) if either comparator outputs an ON signal.

[0058] [Specific processing by individual determination method] Next, a specific example of the processing by the individual determination method will be described with reference to FIG. 15. FIG. 15 is a diagram showing a configuration example of a determination block of an individual determination method according to an embodiment of the present invention.

[0059] As described in the above [Determination by individual determination method], in a form that prioritizes the analog switch determination in [Specific processing by addition method], when either one of the excitation times Tcw and Tccw is less than the threshold value tth close to the shortest excitation time Tmin, a determination (unidirectional magnetic saturation switch determination) that assumes magnetic saturation is added. Specifically, it is configured to calculate the logical sum from the results of the analog switch determination and the unidirectional magnetic saturation switch determination in the excitation times Tcw and Tccw respectively.

[0060] The determination block 40 of the individual determination method shown in FIG. 15 includes a first comparator 41, a second comparator 42, a third comparator 43, an OR circuit 44, and an OR circuit 45. The first comparator 41 performs the conventional analog switch determination in the same manner as the first comparator 31 shown in FIG. 14. It compares the difference value Tsub between the excitation times Tcw and Tccw with the switch-on threshold value ΔTth, and outputs an ON signal when |Tsub| > ΔTth.

[0061] The second comparator 42 is a block added in the present invention. It compares the excitation time Tcw with the threshold value tth and outputs an ON signal when Tcw < tth. The ON signal of the second comparator 32 is a magnetic saturation detection output. For example, an over-approach of a magnetic material is suspected. The third comparator 43 is a block added in the present invention. It compares the excitation time Tccw with the threshold value tth and outputs an ON signal when Tccw < tth.

[0062] The OR circuit 44 compares the outputs of the second comparator 42 and the third comparator 43 respectively, and outputs an ON signal if either comparator outputs an ON signal. The ON signal of the OR circuit 44 is a unidirectional magnetic saturation detection output. For example, an over-approach of a magnetic material is suspected. The OR circuit 45 compares the outputs of the first comparator 41 and the OR circuit 44 respectively, and outputs an ON signal if either output is ON (switch output).

[0063] [Specific processing by the composite method] Next, a specific example of the processing incorporating the functions of both the addition method and the individual determination method will be described with reference to FIG. 16. FIG. 16 is a diagram showing a configuration example of a determination block of the composite method according to an embodiment of the present invention.

[0064] As a case where such a composite method is used, it is assumed that, as shown in FIG. 12, while sensitively capturing the magnetic saturation of the saturable coil 1, it is also desired to simultaneously perform the error diagnosis of the saturable coil 1. In this case, the output of the individual determination method is used for the determination of magnetic saturation detection, and the error detection function of the addition determination method is used in combination.

[0065] Also, as shown in FIG. 13, by utilizing the difference between the magnetic saturation detection regions Ar1 and Ar2 in the addition method and the individual determination method, it is also possible for this composite method to stepwise evaluate the strength of the external magnetic field Hex causing magnetic saturation. That is, it becomes possible to output as new measurement information whether it is a mild magnetic saturation that only catches in the determination of the addition method or a severe magnetic saturation that also catches in the individual determination method. This determination can be easily implemented by taking the logical product of the addition method and the individual determination method, as shown by the broken line portion in FIG. 16. Such detailed measurement information such as the degree of magnetic saturation of the saturable coil 1 is not necessarily used because the number of signal lines increases in a binary sensor where one conventional signal line corresponds to 1-bit H (high) / L (low) information. However, it can be useful in a high information density method such as the serial output method.

[0066] The determination block 50 of the composite method shown in FIG. 16 includes a first comparator 51, a second comparator 52, a third comparator 53, a fourth comparator 54, a fifth comparator 55, an OR circuit 56, an OR circuit 57, and an AND circuit 58.

[0067] The first comparator 51, the second comparator 52, and the third comparator 53 are the same as the blocks used in the individual determination method shown in FIG. 15. Since the first comparator 51, the second comparator 52, and the third comparator 53 have the same configurations as the first comparator 41, the second comparator 42, and the third comparator 43 shown in FIG. 15 respectively, detailed descriptions thereof are omitted.

[0068] The fourth comparator 54 and the fifth comparator 55 are the same as the blocks used in the addition method shown in FIG. 14. Since the fourth comparator 54 and the fifth comparator 55 have the same configurations as the second comparator 32 and the third comparator 33 shown in FIG. 14 respectively, detailed descriptions thereof are omitted.

[0069] The OR circuits 56 and 57 are the same as the blocks used in the individual determination method shown in FIG. 15. Since the OR circuits 56 and 57 have the same configurations as the OR circuits 44 and 45 shown in FIG. 15, respectively, detailed descriptions thereof are omitted.

[0070] The AND circuit 58 compares the outputs of the fourth comparator 54 and the OR circuit 56, and outputs an ON signal if both outputs are ON. This ON output is a magnetic saturation detection output caused by a strong magnetic field.

[0071] [Configuration of Measurement System] Next, the measurement system of an actual magnetic sensor will be described with reference to FIG. 17. FIG. 17 is a diagram showing a block configuration example of a measurement system of a magnetic sensor according to an embodiment of the present invention.

[0072] In the measurement system of an actual magnetic sensor, as in the application described in paragraphs

[0053] to

[0054] of Patent Document 1, once the excitation time T is converted into a voltage value by a sample-and-hold circuit or the like, it is then converted into digital data by an ADC or the like, taken into a microcontroller (hereinafter abbreviated as "microcomputer") as measurement data, and compared and determined with a threshold value of digital data pre-recorded in the microcomputer.

[0073] For the microcomputer, addition, subtraction, or comparison and determination processing of individual values of digital data are all easy. Within the range allowed by the processing time, as described in [Specific Processing by Composite Method], determination is made in a composite manner. That is, in FIG. 13, the individual determination method is adopted for the determination of magnetic saturation detection, and the addition method is applied as the self-diagnosis function of the saturable coil 1.

[0074] The measurement system of the magnetic sensor 60 shown in FIG. 17 includes a microcomputer 70, an RS flip-flop circuit 80, a demultiplexer (referred to as "DEMUX" in the figure) 90, an excitation circuit 100, a current detection circuit 110, a sample-and-hold circuit 120, and an OR circuit 130.

[0075] The RS flip-flop circuit 80 has the same function as the RS flip-flop circuit in FIG. 1 of Patent Document 1. That is, the function of the RS flip-flop circuit 80 is to start current excitation (Set) by an excitation start trigger signal input from the microcomputer 70, and to stop the excitation pulse by detecting the threshold current from the current detection circuit 110 or by a sequentially issued excitation stop trigger signal after a certain period of time has elapsed (Reset). The output Q of this RS flip-flop circuit 80 is branched by the demultiplexer 90 in the CW or CCW direction to drive the excitation circuit 100 composed of an H-bridge circuit. Also, the pulse width from Set to Reset of the output Q itself corresponds to the excitation time T for one measurement.

[0076] The excitation circuit 100 is composed of, for example, an H-bridge circuit. The excitation circuit 100 current-excites the saturable coil 1 in the CW direction or the CCW direction based on the output Q of the RS flip-flop circuit. A self-induced magnetic field Hdrv(t) having a strength and direction corresponding to the magnitude and direction of the external magnetic field Hex and the direction of current excitation is generated in the saturable coil 1.

[0077] The current detection circuit 110 monitors the drive current flowing through the H-bridge circuit (excitation circuit 100) and outputs a trigger pulse for stopping current excitation when a current equal to or greater than the threshold current Ith flows. For example, the current detection circuit 110 is composed of a current detection resistor R and a comparator (see FIG. 3) not shown.

[0078] The sample and hold circuit 120 converts the output signal T (corresponding to the information of the excitation time T) from the RS flip-flop circuit 80 from time information to voltage information and holds it so that the voltage value can be read by the ADC740 of the microcomputer 70. The held voltage value is reset by a reset trigger signal from the microcomputer 70.

[0079] The OR circuit 130 outputs a reset signal to the RS flip-flop circuit 80 when either the excitation stop trigger signal from the current detection circuit 110 or the excitation stop trigger signal from the microcomputer 70 is input.

[0080] [Internal Structure of Microcomputer] The microcomputer 70 includes a clock 700, a processor 710, a flash ROM 720, a CW / CCW selector 730, an ADC 740, a demultiplexer 750, a RAM 760, a comparison operation circuit 770, a flash ROM 780, and an I / F circuit 790. The operations of each block of the microcomputer 70 are synchronized by the clock signal of the clock 700. Also, by counting the number of clocks, time can be measured according to the number of clocks.

[0081] The processor 710 (an example of a control unit) reads the control program recorded in the flash ROM 720 into the RAM 760 and executes it, thereby performing overall progress control (e.g., sequence control) of the sensing operation. The processor 710 appropriately executes processes such as direction instructions to the CW / CCW selector 730, resetting the hold value of the sample and hold circuit 120, control from the start to the stop of the excitation pulse, capturing of analog data by the ADC 740, and saving of measurement results to the Tcw storage memory 761 and the Tccw storage memory 762 in order to execute the processes of the flowcharts shown in FIGS. 18 and 19.

[0082] The flash ROM 720 is used as an example of a computer-readable non-transitory recording medium that stores the program executed by the processor 710. Note that, as the processor 710, a CPU (Central Processing Unit), an MPU (Micro Processing Unit), or the like can be used.

[0083] The CW / CCW selector 730 controls the excitation direction of the excitation circuit 100 (H-bridge circuit) and which of the Tcw storage memory 761 or the Tccw storage memory 762 to save the read result of the sample and hold circuit 120. Actually, since the CW / CCW selector 730 is incorporated in the sequence operation of the processor 710, it can be considered a conceptual one without problem.

[0084] The ADC740 acquires the voltage information (measurement data) of the output signal T held in the sample-and-hold circuit 120 and converts it from an analog signal to digital data. The measurement data converted to digital is allocated and stored in the CW or CCW storage memory via the demultiplexer 750 inside the microcomputer 70 according to the instruction from the CW / CCW selector 730.

[0085] The Tcw storage memory 761 and the Tccw storage memory 762 are configured as a predetermined memory area of the RAM 760 and temporarily store the measurement results of the measurement system of the magnetic sensor 60. The measurement results are used as input variables in the comparison operation circuit 770.

[0086] The flash ROM 780 stores the setting thresholds for performing the differential operation of the prior art, the addition operation and the determination of the addition method added according to the present embodiment, and each determination of the individual determination method. The setting threshold is read into the comparison operation circuit 770 and becomes the reference value for each determination.

[0087] The comparison operation circuit 770 performs the magnetic saturation determination of the addition method and the individual determination method, and the magnetic detection determination based on the differential value of the prior art. The internal processing logic conforms to the configuration of the composite method determination block shown in FIG. 16. As the input parameters of the comparison operation circuit 770, there are a total of four determination parameters for the excitation time Tcw and the excitation time Tccw, which are the measurement data obtained from the RAM 760, and the addition value Tsum and the differential value Tsub derived by the internal operation circuit from these measurement data, and four threshold parameters corresponding to the determination logic (FIGS. 14 to 16) stored in the flash ROM 780.

[0088] Based on the determination result and operation of the operation circuit inside the comparison operation circuit 770, a difference value Tsub can be obtained between each switching determination result in FIGS. 14 to 16 and the analog measurement data of the external magnetic field Hex. The operation result is processed as a sensor output from the digital information data in the next-stage I / F circuit 790 according to the sensor configuration. In this embodiment, any one of an addition method (FIG. 14), an individual determination method (FIG. 15), or a composite method (FIG. 16) of determination blocks is implemented in the comparison operation circuit 770. However, all types of determination blocks may be implemented in the comparison operation circuit 770, and the processor 710 may be configured to switch the determination blocks arbitrarily or according to a user's instruction.

[0089] The I / F circuit 790 (interface circuit) converts the determination result in the microcomputer 70 into an electrical signal to obtain a sensor output. For example, GPIO can be used for a switch output, and DAC can be used for an analog output. In an actual magnetic sensor, in the peripheral devices of the microcomputer 70, there are often cases where the electrical characteristics are inferior or special electrical control such as the serial communication standard RS-485 is required. Therefore, usually, it may also be used as a sensor output via an I / F circuit composed of another analog element or a dedicated communication IC.

[0090] For example, in the magnetic sensor 60, an interface can be adopted in which one sensor output signal line called IO-Link defined in IEC61131-9 can be arbitrarily switched between serial communication output and switching output. In this case, in the communication mode, the switching output, the strength and direction of the external magnetic field Hex, the presence or absence of magnetic saturation of the saturable coil 1, and the presence or absence of a disconnection error of the saturable coil 1 can be encapsulated in the same packet data as serial communication data. In the switch sensor mode, the ON / OFF signal of the switching output can be output from one signal line. In the comparison operation circuit 770, it is assumed that an analog output can also be obtained although it is a switching sensor, which means that it can support an output form capable of transmitting a large amount of information density, such as a serial communication method.

[0091] [One-Pulse Measurement of Magnetic Sensor] Next, the procedure of the measurement operation by the measurement system of the magnetic sensor 60 will be described. The one-pulse measurement shown in FIG. 18 shows the measurement operation once in the CW or CCW direction, and FIG. 19 is a flowchart of the entire operation as a magnetic sensor. As shown in the flowchart of FIG. 19, the one-pulse measurement is performed a plurality of times while changing the excitation direction setting by the CW / CCW selector 730 to the CW or CCW direction, and the measurement results are saved.

[0092] First, the procedure of the one-pulse measurement by the measurement system of the magnetic sensor 60 will be described with reference to FIG. 18. FIG. 18 is a flowchart showing an example of the procedure of the one-pulse measurement by the measurement system of the magnetic sensor 60 according to an embodiment of the present invention.

[0093] First, when the processor 710 of the microcomputer 70 starts the one-pulse measurement process, it outputs a reset trigger signal to the sample hold circuit 120 to reset the sample hold circuit 120 (S1). Next, the processor 710 inputs an excitation start trigger pulse to the RS flip-flop circuit 80 (S2). Next, the processor 710 determines whether a certain time has elapsed since the start of excitation (S3), and if the certain time has not elapsed (NO in S3), the determination process in step S3 is repeated.

[0094] On the other hand, when a certain time has elapsed since the start of excitation (YES in S3), the processor 710 inputs an excitation stop trigger pulse to the RS flip-flop circuit 80 (S4). Next, the processor 710 captures the measurement data output from the sample hold circuit 120 by the ADC 740 and stores it in the Tcw storage memory 761 or the Tccw storage memory 762 of the RAM 760 via the demultiplexer 750. After the process of step S5, the process of this flowchart ends.

[0095] [Overall Measurement Operation of Magnetic Sensor] Next, the procedure of the overall measurement operation by the measurement system of the magnetic sensor 60 will be described with reference to FIG. 19. FIG. 19 is a flowchart showing an example of the procedure of the entire measurement operation by the measurement system of the magnetic sensor 60 according to an embodiment of the present invention.

[0096] First, the processor 710 of the microcomputer 70 sets the CW / CCW selector 730 in the CW direction (S11). Next, the processor 710 performs the one-pulse measurement shown in FIG. 18 (S12). When the one-pulse measurement in FIG. 18 is completed, the process proceeds to step S13 in FIG. 19.

[0097] Next, the processor 710 stores the measurement result of the one-pulse measurement in the RAM 760 (S13). Next, the processor 710 sets the CW / CCW selector 730 in the determination direction opposite to the previous one, here the CCW direction (S14).

[0098] Next, the processor 710 determines whether the measurements for both CW and CCW are completed (S15). If the measurement for either CW or CCW is not completed (NO in S15), the process returns to the one-pulse measurement in step S12.

[0099] On the other hand, when the measurements for both CW and CCW are completed (YES in S15), the comparison operation circuit 770 performs a determination by an addition method, an individual determination method, or a composite method (S16). Next, the comparison operation circuit 770 outputs the determination result as an operation result to the I / F circuit 790 (S17). Then, the I / F circuit 790 converts the operation result input from the comparison operation circuit 770 into an electrical signal to obtain a sensor output. After the process of step S17, the process of this flowchart ends.

[0100] As described above, while following the measurement principle of the magnetic sensor in Patent Document 1, the magnetic sensor according to an embodiment of the present invention has solved the problem of the operation instability of the magnetic sensor at the time of magnetic saturation of the saturable coil, which was an operational constraint in the application to the magnetic detection type switch sensor. That is, the inventor of the present application has focused on the specificity of the transition of the excitation current due to the combination of the direction and magnitude of the external magnetic field and the self-induced magnetic field in the case where the saturable coil was magnetically saturated at the time before current excitation by the external magnetic field, which was not mentioned in the prior art, and by actively applying this, it has been possible to newly add a magnetic saturation detection function to the saturable coil.

[0101] According to the magnetic sensor according to the present embodiment having the above configuration, by detecting the transition of the excitation current in the case where the saturable coil was magnetically saturated at the time before current excitation by such an external magnetic field, it is possible to prevent the operation instability of the magnetic sensor at the time of magnetic saturation of the saturable coil and ensure safety in the application to the switch sensor. For example, even when a magnetic body approaches the saturable coil or a ferromagnetic body approaches, it is possible to continue the normal switch operation. Moreover, the magnetic sensor according to the present embodiment enables newly obtaining the detailed state (magnetic saturation, open circuit failure) of the saturable coil itself as a measurement parameter.

[0102] Note that, as an embodiment of the present invention, the following configuration can also be adopted. One embodiment of the present invention includes a saturable coil, a pulse generator, a two-direction current excitation unit, a pulse width modulation unit, a current detection unit, and an arithmetic unit capable of calculating the difference (difference value) and sum (addition value) of two pulse widths.

[0103] The current excitation unit is configured to excite currents from two directions to the saturable coil so that the magnetic vector direction of the self-induced magnetic field Hdrv(t) generated by the current excitation can be arbitrarily set. For example, the current excitation unit can be configured using a CW / CCW selector 730 and an excitation circuit 100.

[0104] The pulse generator is assumed to have a mechanism that generates an OFF-ON rising signal by an arbitrary pulse start trigger, generates an ON-OFF falling signal by an arbitrary pulse stop trigger, and generates one rectangular wave pulse signal by two trigger inputs. For example, the pulse generator can be configured using an RS flip-flop circuit 80.

[0105] The current detection unit is configured to detect the current flowing through the saturable coil and issue a pulse stop trigger of the pulse generator to stop the excitation when the amount of the current exceeds a certain threshold value. The threshold value is set to a current value at which it can be determined that the excitation current amount has increased significantly and the saturable coil has become magnetically saturated. For example, the current detection unit can be configured using a current detection circuit 110.

[0106] The pulse width modulation unit excites the saturable coil and outputs a pulse width modulation signal having a pulse width that is the time until the excitation is stopped by the pulse stop trigger of the pulse generator. For example, the pulse width modulation unit can be configured using a sample and hold circuit 120.

[0107] The pulse width of the pulse width modulation signal varies depending on the inductance that changes according to the strength of the synthetic magnetic field formed by the self-induced magnetic field generated by current-exciting the saturable coil and the external magnetic field Hex, and the difference in the excitation time until reaching the threshold current caused by the difference in the transition of the excitation current amount.

[0108] The arithmetic unit capable of calculating the difference (difference value) and sum (addition value) of two pulse widths stores the pulse width due to the excitation for each direction of the current that excited the saturable coil. Then, the arithmetic unit calculates the sum and difference of the two pulse widths, and is configured to have an error detection function that detects an error in a state where normal measurement cannot be performed due to the ferromagnetic substance approaching the saturable coil and causing magnetic saturation from before excitation, or a disconnection fault where no excitation current can flow through the saturable coil, based on the determination result. And the arithmetic unit detects the approach of the magnetic substance including magnetic saturation by the ferromagnetic substance and outputs it as a switch output signal. For example, this arithmetic unit can be configured using a comparison arithmetic circuit 770.

[0109] Furthermore, as one embodiment of the present invention, the following configuration can also be adopted. (1) (Addition method) A saturable coil, An excitation circuit capable of supplying a first excitation current in a first direction and a second excitation current in a second direction opposite to the first direction to the saturable coil, A current detection circuit that detects an excitation current generated in the saturable coil based on an external magnetic field applied to the saturable coil and a self-induced magnetic field of the saturable coil, A magnetic measurement unit (for example, microcomputer 70) that measures the magnetism around the saturable coil based on the excitation time of the saturable coil calculated based on the transition of the excitation current detected by the current detection circuit, The magnetic measurement unit Detects the magnetic saturation state before excitation based on an added value obtained by adding a first excitation time based on the first excitation current and a second excitation time based on the second excitation current, and a magnetic saturation detection threshold value for the added value for detecting the magnetic saturation state before excitation, Detects the approach of the magnetic body based on a difference value between the first excitation time and the second excitation time, a threshold value for detecting the approach of the magnetic body, and a detection result of the magnetic saturation state before excitation Magnetic sensor. (2) (Open circuit detection) The magnetic measurement unit detects an open circuit of the saturable coil based on a result of comparing an added value of the first excitation time and the second excitation time with a threshold value for detecting an open circuit of the saturable coil The magnetic sensor according to (1) above. (3) (Individual determination method) A saturable coil, An excitation circuit capable of supplying a first excitation current in a first direction and a second excitation current in a second direction opposite to the first direction to the saturable coil, A current detection circuit that detects an excitation current generated in the saturable coil based on an external magnetic field applied to the saturable coil and a self-induced magnetic field of the saturable coil, Based on the excitation time of the saturable coil calculated based on the transition of the excitation current detected by the current detection circuit, a magnetic measurement unit (for example, microcomputer 70) that measures the magnetism around the saturable coil is provided. The magnetic measurement unit calculates the logical sum of a first individual comparison result obtained by comparing a first excitation time based on the first excitation current with an individual magnetic saturation detection threshold for detecting a magnetic saturation state before excitation, a second excitation time based on the second excitation current, and a second individual comparison result obtained by comparing the second excitation time with the individual magnetic saturation detection threshold, and detects the magnetic saturation state before excitation based on the calculation result of the logical sum. Based on the difference value between the first excitation time and the second excitation time, a threshold for detecting the approach of a magnetic body, and the detection result of the magnetic saturation state before excitation, the approach of the magnetic body is detected. Magnetic sensor. (4) (Composite method) A saturable coil, an excitation circuit capable of supplying a first excitation current in a first direction and a second excitation current in a second direction opposite to the first direction to the saturable coil, a current detection circuit that detects an excitation current generated in the saturable coil based on an external magnetic field applied to the saturable coil and a self-induced magnetic field of the saturable coil, Based on the excitation time of the saturable coil calculated based on the transition of the excitation current detected by the current detection circuit, a magnetic measurement unit (for example, microcomputer 70) that measures the magnetism around the saturable coil is provided. The magnetic measurement unit calculates the logical sum of a first individual comparison result obtained by comparing a first excitation time based on the first excitation current with an individual magnetic saturation detection threshold for detecting a first magnetic saturation state before excitation, a second excitation time based on the second excitation current, and a second individual comparison result obtained by comparing the second excitation time with the individual magnetic saturation detection threshold, and detects the first magnetic saturation state before excitation based on the calculation result of the logical sum. Based on the difference value between the first excitation time and the second excitation time, a threshold for detecting the approach of a magnetic body, and the detection result of the first magnetic saturation state before excitation, the approach of the magnetic body is detected. Compare the added value obtained by adding the first excitation time and the second excitation time with the magnetic saturation detection threshold value for the added value that detects the magnetic saturation state before excitation, detect the second magnetic saturation state before excitation from the comparison result, calculate the logical product of the detection result of the second magnetic saturation state before excitation and the detection result of the first magnetic saturation state before excitation, and detect the third magnetic saturation state before excitation based on the calculation result of the logical product. Magnetic detection sensor. (5) Open circuit detection The magnetic measurement unit detects the open circuit of the saturable coil based on the result of comparing the added value of the first excitation time and the second excitation time with the threshold value for detecting the open circuit of the saturable coil. The magnetic sensor according to (4) above.

[0110] Note that the present invention is not limited to the above-described embodiments, and various other application examples and modification examples can be taken without departing from the gist of the present invention described in the claims. For example, the above-described embodiments have described the configuration of the measurement system of the magnetic sensor in detail and specifically in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the components described.

[0111] In addition, each of the above configurations, functions, processing units, etc. may be realized in hardware by designing part or all of them, for example, by an integrated circuit. As the hardware, a processor device in a broad sense such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) may be used. Further, the processing performed by a certain processing unit may be realized by one piece of hardware or by distributed processing by a plurality of pieces of hardware.

Explanation of reference numerals

[0112] 1…Saturable coil, 10…Current excitation circuit, 11…Drive circuit, 12…Current detection circuit, 20…Current excitation circuit, 21…H-bridge circuit, 30…Addition method determination block, 31…First comparator, 32…Second comparator, 33…Third comparator, 34…OR circuit, 40…Individual determination method determination block, 41…First comparator, 42…Second comparator, 43…Third comparator, 44…OR circuit, 45…OR circuit, 50…Composite method determination block, 51…First comparator, 52…Second comparator, 53…Third comparator, 54…Fourth comparator, 55…Fifth comparator, 56…OR circuit, 57…OR circuit, 58…AND circuit, 60…Magnetic sensor, 70…Microcomputer, 80…RS flip-flop circuit, 90…Demultiplexer, 100…Excitation circuit, 110…Current detection circuit, 120…Sample and hold circuit, 130…OR circuit, 700…Clock, 710…Processor, 720…Flash ROM, 730…CW / CCW selector, 740…ADC, 750…Demultiplexer, 760…RAM, 761…Tcw storage memory, 762…Tccw storage memory, 770…Comparison operation circuit, 780…Flash ROM, 790…I / F circuit, Ar1…Region, Ar2…Region, Hex…External magnetic field, Hdrv(t)…Self-induced magnetic field (excitation magnetic field), i(t)…Excitation current

Claims

1. A saturable coil, an excitation circuit capable of supplying a first excitation current in a first direction and a second excitation current in a second direction opposite to the first direction to the saturable coil, a current detection circuit for detecting an excitation current generated in the saturable coil based on an external magnetic field applied to the saturable coil and a self-induced magnetic field of the saturable coil, a magnetic measurement unit for measuring magnetism around the saturable coil based on an excitation time of the saturable coil calculated based on a transition of the excitation current detected by the current detection circuit, wherein the magnetic measurement unit detects a magnetic saturation state before excitation based on an added value obtained by adding a first excitation time based on the first excitation current and a second excitation time based on the second excitation current, and a magnetic saturation detection threshold value for the added value for detecting a magnetic saturation state before excitation, and detects the approach of a magnetic body based on a difference value between the first excitation time and the second excitation time, a threshold value for detecting the approach of the magnetic body, and a detection result of the magnetic saturation state before excitation magnetic sensor.

2. The magnetic measurement unit detects a disconnection of the saturable coil based on a result of comparing an added value of the first excitation time and the second excitation time with a threshold value for detecting a disconnection of the saturable coil The magnetic sensor according to claim 1.

3. A saturable coil, an excitation circuit capable of supplying a first excitation current in a first direction and a second excitation current in a second direction opposite to the first direction to the saturable coil, a current detection circuit for detecting an excitation current generated in the saturable coil based on an external magnetic field applied to the saturable coil and a self-induced magnetic field of the saturable coil, a magnetic measurement unit for measuring magnetism around the saturable coil based on an excitation time of the saturable coil calculated based on a transition of the excitation current detected by the current detection circuit, The magnetic measurement unit compares a first excitation time based on the first excitation current with an individual magnetic saturation detection threshold for detecting a magnetic saturation state before excitation to obtain a first individual comparison result, and compares a second excitation time based on the second excitation current with the individual magnetic saturation detection threshold to obtain a second individual comparison result, calculates a logical sum of the first and second individual comparison results, detects the magnetic saturation state before excitation based on the calculation result of the logical sum, and detects the approach of the magnetic body based on a difference value between the first excitation time and the second excitation time, a threshold for detecting the approach of the magnetic body, and a detection result of the magnetic saturation state before excitation. A magnetic sensor.

4. A saturable coil, an excitation circuit capable of supplying a first excitation current in a first direction and a second excitation current in a second direction opposite to the first direction to the saturable coil, a current detection circuit that detects an excitation current generated in the saturable coil based on an external magnetic field applied to the saturable coil and a self-induced magnetic field of the saturable coil, and a magnetic measurement unit that measures the magnetism around the saturable coil based on an excitation time of the saturable coil calculated based on a transition of the excitation current detected by the current detection circuit. The magnetic measurement unit compares a first excitation time based on the first excitation current with an individual magnetic saturation detection threshold for detecting a magnetic saturation state before excitation to obtain a first individual comparison result, and compares a second excitation time based on the second excitation current with the individual magnetic saturation detection threshold to obtain a second individual comparison result, calculates a logical sum of the first and second individual comparison results, detects the first magnetic saturation state before excitation based on the calculation result of the logical sum, and detects the approach of the magnetic body based on a difference value between the first excitation time and the second excitation time, a threshold for detecting the approach of the magnetic body, and a detection result of the first magnetic saturation state before excitation. Add the added value obtained by adding the first excitation time and the second excitation time, and compare it with the magnetic saturation detection threshold value for the added value for detecting the magnetic saturation state before excitation. Detect the second magnetic saturation state before excitation from the comparison result, calculate the logical product of the detection result of the second magnetic saturation state before excitation and the detection result of the first magnetic saturation state before excitation, and based on the calculation result of the logical product, detect the third magnetic saturation state before excitation. Magnetic sensor.

5. The magnetic measurement unit detects a disconnection of the saturable coil based on a result of comparing an added value of the first excitation time and the second excitation time with a threshold value for detecting a disconnection of the saturable coil. The magnetic sensor according to claim 4.

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