JP7693205B2 - Magnetic Sensors - Google Patents

Description

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 in particular to circuit technology for a magnetic sensor that uses a saturable coil.

Conventionally, magnetic sensors are known that detect the magnitude and direction of a magnetic field and convert it into an electrical signal. For example, Patent Document 1 discloses a magnetic detection method that applies a saturable coil as a circuit technology for a magnetic sensor.

JP 2003-215221 A

In the magnetic detection method using a saturable coil (hereinafter sometimes abbreviated as "coil") described in Patent Document 1, measurements were performed by applying the phenomenon that the time T (excitation time) from the start of current excitation of the saturable coil by current excitation to the end of excitation immediately after magnetic saturation changes linearly depending on the direction and magnitude of the external magnetic field applied to the saturable coil (see, for example, paragraphs [0017] to [0050] and Figure 2 of Patent Document 1). At this time, even if there are differences in the direction and magnitude of the external magnetic field to be measured, it was assumed that the saturable coil was not saturated (non-saturated) before current excitation of the saturable coil. If the saturable coil itself was saturated before current excitation, the state of the saturable coil would not transition according to the phenomenon assumed by the magnetic sensor described in Patent Document 1, and normal measurement would not be possible.

In view of the above situation, the present invention aims to prevent the operation of a magnetic sensor from becoming unstable when a saturable coil becomes magnetically saturated.

In order to solve the above problems, a magnetic sensor of one embodiment of the present invention comprises 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 the excitation current generated in the saturable coil based on an external magnetic field applied to the saturable coil and the self-induced magnetic field of the saturable coil, and a magnetic measurement unit that measures the magnetic field 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 a magnetic saturation state before the excitation based on a sum 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 for the sum detected the magnetic saturation state before the excitation;
The approach of a magnetic body is detected based on a difference value between the first excitation time and the second excitation time, a threshold value for detecting the approach of a magnetic body, and a detection result of the magnetic saturation state before excitation.

In addition, another aspect of the magnetic sensor of the present invention comprises 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 the self-induced magnetic field of the saturable coil, and a magnetic measurement unit that measures the magnetic field 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 calculates a 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 and a second individual comparison result obtained by comparing a second excitation time based on the second excitation current with the individual magnetic saturation detection threshold, and detects a magnetic saturation state before excitation based on the logical sum calculation result;
The approach of a magnetic body is detected based on a difference value between the first excitation time and the second excitation time, a threshold value for detecting the approach of a magnetic body, and a detection result of the magnetic saturation state before excitation.

Furthermore, a magnetic sensor of another aspect of the present invention comprises 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 the self-induced magnetic field of the saturable coil, and a magnetic measurement unit that measures the magnetic field 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 calculates a 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 and a second individual comparison result obtained by comparing a second excitation time based on the second excitation current with the individual magnetic saturation detection threshold, and detects a first magnetic saturation state before excitation based on the logical sum calculation result;
detecting 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 a magnetic body, and a detection result of the first magnetic saturation state before excitation;
The sum of the first excitation time and the second excitation time is compared with a magnetic saturation detection threshold for the sum that detects the magnetic saturation state before excitation, the second magnetic saturation state before excitation is detected from the comparison result, a logical product is calculated between the detection result of the second magnetic saturation state before excitation and the detection result of the first magnetic saturation state before excitation, and a third magnetic saturation state before excitation is detected based on the result of the logical product calculation.

According to at least one aspect of the present invention, it becomes possible to detect the change in excitation current when a saturable coil is magnetically saturated before current excitation by an external magnetic field, thereby preventing instability in the operation of the magnetic sensor when the saturable coil is magnetically saturated.
Problems, configurations and effects other than those described above will become apparent from the following description of the embodiments.

1 is a diagram showing the relationship between the variation in inductance of a saturable coil and the magnetic flux density inside the saturable coil. FIG. 2 is a diagram showing an example of a basic circuit configuration for current excitation of a saturable coil. 1 is a diagram showing an example of a circuit configuration when current excitation is performed using an excitation circuit capable of outputting an excitation current to a saturable coil in two directions (CW and CCW directions). FIG. FIG. 13 is a diagram showing transition of a coil current when current is alternately excited using an H-bridge circuit. 11A and 11B are diagrams showing examples of transitions of excitation currents according to the strength of an external magnetic field Hex in a saturable coil in a magnetically saturated state. 11 is a diagram showing an example of current transition when the external magnetic field Hex and the self-induced magnetic field Hdrv(t) have the same directional vectors. FIG. FIG. 13 is a diagram showing an example of current transition when the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are opposite vectors and the strength of the external magnetic field is small. FIG. 13 is a diagram showing an example of current transition when the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are opposite vectors and the strength of the external magnetic field is medium. FIG. 13 is a diagram showing an example of current transition when the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are opposite vectors and the strength of the external magnetic field is large. 11 is a diagram showing an example of transition of the excitation time T which changes depending on the strength and direction of the external magnetic field Hex. FIG. 11 is a diagram showing the relationship between the transition of the excitation time when current is excited in the CW direction and CCW direction in an H-bridge circuit, the transition of the difference between the excitation times, and the strength of the external magnetic field Hex. FIG. FIG. 13 is a diagram showing the relationship between the transition of the excitation time when current is excited in the CW direction and the CCW direction in an H-bridge circuit, the transition of the sum of the excitation times, and the strength of the external magnetic field Hex. 11 is a diagram showing the difference between an addition method and an individual determination method for magnetic saturation determination according to an embodiment of the present invention. FIG. FIG. 13 is a diagram illustrating an example of the configuration of an addition-type decision block according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an example of the configuration of a judgment block of an individual judgment method according to an embodiment of the present invention. FIG. 13 is a diagram illustrating an example of the configuration of a composite method decision block according to an embodiment of the present invention. 1 is a diagram showing an example of a block configuration of a measurement system of a magnetic sensor according to an embodiment of the present invention; 5 is a flowchart showing an example of a procedure for one-pulse measurement by the magnetic sensor measurement system according to the embodiment of the present invention. 4 is a flowchart showing an example of the overall procedure of a measurement operation by the magnetic sensor measurement system according to the embodiment of the present invention.

Below, examples of embodiments of the present invention will be described with reference to the accompanying drawings. In this specification and the accompanying drawings, components having substantially the same functions or configurations are designated by the same reference numerals and duplicate descriptions will be omitted.

First, before explaining the embodiment of the present invention, the measurement principle of a general magnetic sensor will be explained with reference to Figures 1 to 4.

FIG. 1 is a diagram showing the relationship between the variation in inductance of a saturable coil and the magnetic flux density inside the saturable coil.
1 is a graph showing the correspondence between the change in inductance L of the saturable coil 1 and the change in magnetic flux density B inside the saturable coil 1 when an external magnetic field (magnetic field H) with vector components in two directions parallel to the axial direction of the saturable coil 1 is applied from the outside. "Lo" is the inductance when there is no magnetic saturation (unsaturated state), and "Lsat" is the inductance when there is magnetic saturation.

When the magnetic field strength inside the saturable coil 1 exceeds a certain value (= |Hsat|) in either direction, the saturable coil 1 becomes magnetically saturated. Then, as shown in Figure 1, the inductance L drops sharply from "Lo" to "Lsat." The technology described in Patent Document 1 applies this phenomenon in which the inductance L changes sharply depending on the magnetic field strength inside the saturable coil 1 to provide a method for sensing the magnetic field strength.

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

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 the unidirectional excitation current i(t).

Figure 3 shows an example of a circuit configuration when current excitation is performed using an excitation circuit that can output the excitation current of the saturable coil 1 in two directions (CW direction and CCW direction). The CW direction (first direction) and CCW direction (second direction) are parallel and opposite to each other.

The current excitation circuit 20 shown in FIG. 3 is configured to be able to control the direction of current excitation using an H-bridge circuit 21, and by varying the direction in which the self-induced magnetic field Hdrv(t) is generated, the same effect can be obtained as when the saturable coil 1 is attached in the opposite direction. The bidirectional excitation current i(t) generates a self-induced magnetic field Hdrv(t) with opposite vectors. 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 and CCW directions of this current excitation circuit 20.

FIG. 4 is a diagram showing the transition of the coil current when current is alternately excited using the H-bridge circuit 21.
The excitation time T required for the saturable coil 1 to become magnetically saturated varies depending on the combination of the magnitude of the external magnetic field Hex applied to the saturable coil 1 and 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, as per the principle described in paragraphs [0036] to [0049] of Patent Document 1. Graph (1) on the left side of 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, graph (2) in the center of 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, graph (2) in the center of 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 negative direction, respectively.

Thus, FIG. 4 shows an example in which the excitation time T varies depending on the direction and offset amount (Gauss) of the external magnetic field Hex, which is "constant," and the direction and offset amount of the self-induced magnetic field Hdrv. In the magnetic sensor, current excitation is performed so that the magnitude of the composite magnetic field obtained by adding the external magnetic field Hex and the self-induced magnetic field Hdrv(t) exceeds |Hsat|, which is shown by the dashed line. For example, if |Hsat| is 20 G, when the external magnetic field Hex is "+5 G," adding "+15 G" to the self-induced magnetic field Hdrv(t) or "-25 G" to the self-induced magnetic field Hdrv(t) causes the saturable coil 1 to become magnetically saturated, and the excitation current i(t) immediately rises to the threshold value Ith. Then, when the excitation current i(t) reaches the threshold value Ith, the current excitation stops.

Here, in the principle described in Patent Document 1, it is implicitly understood that, with respect to the scalar value |Hex| of the external magnetic field Hex, |Hex|≦|Hsat| is a prerequisite for the initial state of the saturable coil 1 before current excitation. This is because if this condition does not hold, that is, if |Hex|>|Hsat|, it indicates that the saturable coil 1 is magnetically saturated by the external magnetic field Hex from the very beginning, before the self-induced magnetic field Hdrv(t) is applied. In this case, it is not possible to measure the time it takes to become magnetically saturated by applying the self-induced magnetic field Hdrv(t).

Conventional methods do not show the behavior when this precondition does not hold, that is, when a strong external magnetic field Hex such that |Hex|>|Hsat| is applied to the saturable coil 1. Furthermore, when a magnetic sensor is constructed using a mechanism based on conventional principles, there remain issues with its operation as a magnetic sensor due to the phenomenon described below.

FIG. 5 is a diagram showing an example of transition of the excitation current according to the strength of the external magnetic field Hex in the saturable coil 1 in a magnetically saturated state.
Graphs (1) to (3) in Fig. 5 show the transition of the excitation current (hereinafter sometimes referred to as "current transition") for each degree of strength of the external magnetic field Hex when the saturable coil 1 is magnetically saturated (|Hex|>|Hsat|) before current excitation by the external magnetic field Hex, which is not mentioned in Patent Document 1. As shown in Fig. 5, even if the scalar value of the external magnetic field Hex is about the same, the current transition differs greatly depending on the direction of the magnetic vector of the external magnetic field Hex (either the upper side or the lower side in Fig. 5).

For example, when the magnetic vectors of the external magnetic field Hex and the self-induced magnetic field Hdrv(t) have the same direction, there is no significant difference in the excitation time T (upper part of Figure 5). However, when the magnetic vectors of the external magnetic field Hex and the self-induced magnetic field Hdrv(t) have opposite directions, the greater the strength of the external magnetic field Hex, the shorter the excitation time T at which the excitation current i(t) reaches the threshold Ith and the current excitation stops (lower part of Figure 5).

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) have the same directional vector.
If the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are in the same direction (upper side of Figure 5), the saturable coil 1 is always in a saturated state, and during current excitation, as shown in Figure 6, the inductance always remains low and the current excitation is completed. This is because if the magnetic field inside the saturable coil 1 is stronger than the magnetic saturation threshold (Hsat), the inductance remains low and stable at a constant value. This is similar to the commonly known magnetic saturation phenomenon of the cored saturable coil 1. Since the inductance of the saturable coil 1 does not change, the rate of current increase during current excitation is also constant, and therefore the excitation time T is also constant at the shortest state. The shortest excitation time T in this stable state is designated as "Tmin".

In the case of mutually opposite vectors, as can be seen from the graph in the lower part of FIG. 5, the manner in which the excitation current transitions varies greatly depending on the strength of the external magnetic field Hex.
The reason for this transition is that the self-induced magnetic field Hdrv(t) acts to cancel out the external magnetic field Hex. When the opposite self-induced magnetic field Hdrv(t) is applied to the saturable coil 1, which 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. The saturable coil 1 becomes magnetically saturated when a magnetic field of a certain strength or more is generated inside the saturable coil 1, so conversely, when the internal magnetic field falls below a certain strength, the magnetic saturation transitions to a non-saturated state and the inductance rises sharply. The way in which this phenomenon occurs changes depending on the strength of the external magnetic field Hex, so the way in which the excitation current transitions changes. Accurately grasping this change is an important point of the present invention.

Below, we will explain the change in current transition depending on the strength of the external magnetic field Hex with reference to Figures 7 to 9. However, in all of the graphs shown on the right side of Figures 7 to 9, |Hex|>|Hsat| (graph (2)). For comparison, on the left side of the graphs showing the state of the current transition for each strength level, we have shown graph (1) where the strength of the external magnetic field Hex is the same as the magnetic saturation threshold Hsat (|Hex|=|Hsat|).

[When the external magnetic field Hex is small]
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 opposite vectors and the strength of the external magnetic field is small. The equal sign written on the excitation current i(t) in the figure indicates that the length and the slope of the linear part of the excitation current i(t) in the non-saturated state are almost the same on the right side (graph (2)) and the left side (graph (1)) of FIG. 7, and the inequality sign indicates that the slope of the excitation current i(t) in the saturated state is almost the same.

Here, we will describe the current transition when an external magnetic field Hex in the CCW direction is applied to the saturable coil 1, which is strong enough to return the coil to a non-saturated state with a relatively small self-induction magnetic field Hdrv(t). The current transition is as shown in Figure 7. Immediately after current excitation, the coil is magnetically saturated, so the excitation current i(t) increases at a steep slope (solid line). However, the strength of the composite magnetic field returns to a non-saturated state with the negative Hsat as its threshold, and the inductance rises sharply, so the slope of the current increase (dashed line) becomes smaller.

The self-induced magnetic field Hdrv(t) increases as long as current excitation continues, and eventually the ever-increasing self-induced magnetic field Hdrv(t) causes a resultant magnetic field in the opposite direction to the external magnetic field Hex to flow through the saturable coil 1. Then, when the strength of the resultant magnetic field exceeds Hsat on the opposite side (positive side), magnetic saturation occurs again and the inductance decreases.

The standard for this (Hex: small) state is whether or not the saturable coil 1 is magnetically saturated at two points: immediately after excitation begins and immediately before excitation stops. The length of the excitation time T in this state can be approximated as being the same as when |Hex| = |Hsat|. The reason for this is that the inductance value is the same regardless of which vector direction is magnetically saturated, 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 graph (1) on the left side of Figure 7 with the case of |Hex| > |Hsat| shown in graph (2) on the right side of Figure 7, a self-induced magnetic field Hdrv(t) of 2 x Hsat is commonly generated in a non-saturated state in both cases.

As for the remaining self-induced magnetic field Hdrv(t) after magnetic saturation, the only difference is whether the magnetic field is increased all at once on one side, or whether it is distributed and increased in two places on both sides. To be precise, when the saturation-non-saturation transition occurs, an inflection point appears on the graph of the excitation current i(t), so when there is one more inflection point in graph (2) (Hex: small), the total excitation time T is slightly longer.

When the external magnetic field Hex becomes even larger and the next state (Hex: medium) is reached where magnetic saturation no longer occurs just before the excitation is stopped, the above equilibrium condition for the excitation time T is lost.

[When the external magnetic field Hex is medium]
FIG. 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 opposite vectors and the strength of the external magnetic field is medium.
When the external magnetic field Hex becomes larger than a certain level, the excitation time T becomes shorter as the external magnetic field Hex becomes larger, as shown in the graph (2) on the right side of FIG. 8. As can be seen from the graph (2) on the right side of FIG. 8, the excitation current i(t) flows close to the threshold Ith before transitioning from the magnetic saturation state of the solid line to the non-saturation state, so that the excitation current i(t) reaches the threshold Ith and current excitation stops before magnetic saturation occurs again at the end as shown in the graph (2) on the right side of FIG. 7. Strictly speaking, the excitation time of the solid line portion increases compared to when the external magnetic field Hex is small and when |Hex|=|Hsat|, but due to the inductance (=increase in current per excitation time), the increase is insignificant compared to the decrease in the dashed line area. Therefore, overall, the excitation time becomes shorter as the area of the magnetic saturation state of the solid line increases (i.e., |Hex| becomes larger).

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

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

As shown in Figures 7 to 9, when the saturable coil 1 is in a state where it is magnetically saturated in advance by the external magnetic field Hex, the transition during current excitation differs depending on its direction. In particular, when the vector directions of the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are opposite, the change in the excitation current i(t) until the terminal state is reached differs greatly depending on the strength of the external magnetic field Hex.

FIG. 10 is a diagram showing an example of transition of the excitation time T which 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 the same as the positive direction of the external magnetic field Hex axis (horizontal axis) of the graph. The explanation will be focused on the regions (a) to (c) where the external magnetic field Hex and the self-induced magnetic field Hdrv(t) are in the opposite directions. The approximate value of the excitation time when |Hex|=|Hsat| in the state of region (a) is "Tl", and the excitation time when Hex=0 is "T0". As can be seen from the transition of the strength degree of the external magnetic field Hex (regions (a) to (c)), the transition after magnetic saturation is in a state of equilibrium up to a certain level of strength. However, it can be seen that the excitation time becomes shorter from the state of region (b) where the strength degree of the external magnetic field Hex in the negative direction is greater than that of region (a), and further converges to the shortest excitation time Tmin in region (c).

FIG. 11 is a diagram showing the relationship between the transition of the 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 excitation times, and the strength of the external magnetic field Hex.
In FIG. 11, when the vector directions of the self-induced magnetic field Hdrv(t) and the external magnetic field Hex are the same on one side of the vertical axis (excitation time T axis), they are opposite on the other side, so the transitions of the excitation time T are symmetrical with each other.

As in Patent Document 1, when a differential type 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 and CCW excitation times becomes shorter, and the difference is reduced. Therefore, when the external magnetic field Hex is too large as in the region (b) to (c) in FIG. 10, the differential output becomes close to a state of no magnetic field. As a result, the magnetic sensor has a problem in that the switch of the magnetic sensor returns from the ON state to the OFF state because it considers the magnetic body to be inspected to be far away even though it is too close. In addition, even when used as a single pole as in FIG. 10 instead of differential, the transition of the excitation time T changes significantly depending on the direction of the external magnetic field Hex, so it is not possible to estimate the state. In particular, when the directions of the self-induced magnetic field Hdrv(t) and the external magnetic field Hex are opposite, there is a region (region (b)) where the length of the excitation time T is the same as that of no magnetic field, as in FIG. 11, so the switch is switched from ON to OFF due to excessive proximity.

<One embodiment of the present invention>
In this invention, to solve the above problem, the saturable coil 1 is detected as being magnetically saturated before current excitation, preventing erroneous determination by the magnetic sensor and ensuring safety in operation as a magnetic proximity switch sensor. In other words, in the case where the saturable coil 1 is magnetically saturated before current excitation, even if the difference in excitation time T is below the switch-on threshold ΔTth shown in Fig. 11, the present invention can determine that the saturable coil 1 is receiving a strong magnetic field and can maintain the ON state.

[Determination by Addition Method]
As already mentioned, it is difficult to uniquely detect the magnetic saturation of the magnetic sensor by reading the differential output. As can be seen from Fig. 11, the difference becomes minimal in the region (c) symmetrical with respect to the vertical axis (excitation time T axis), and it becomes impossible to distinguish from no magnetic field.

On the other hand, looking at the characteristic change in the excitation time T after magnetic saturation from Figure 11, the side with the same magnetic field direction (vector) is fixed at the shortest excitation time Tmin. On the other hand, the opposite direction side is fixed by the external magnetic field Hex, and the opposite direction side changes according to the strength of the external magnetic field Hex. In other words, since only one side changes and the other side is a fixed parameter, when the CW direction excitation time Tcw and the CCW direction excitation time Tccw are added, the excitation time T after magnetic saturation becomes a parameter that shows a unique change, especially between (Hex: medium) and (Hex: large).

If we consider the sum Tsum of the excitation times T in the same and opposite directions, since the shortest excitation time Tmin on the same direction side is a fixed value and does not change, only the fluctuation of the excitation time T on the opposite direction side remains as a variable component of the sum Tsum. Figure 12 shows the relationship with the external magnetic field Hex when the sum Tsum is the sum of the excitation times Tcw and Tccw of the H-bridge circuit in Figure 11.

FIG. 12 is a diagram showing the relationship between the transition of the excitation time when current is excited in the CW direction and the CCW direction in the H-bridge circuit, the transition of the sum of the excitation times, and the strength of the external magnetic field Hex.
As can be seen from the change in the added value Tsum in Fig. 12, the added value Tsum after magnetic saturation decreases in the region (b) to (c), and therefore 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. Fig. 12 shows that magnetic saturation can be easily detected in the region (b) to (c) by setting only one threshold Tth on the added value Tsum axis (vertical axis).

The advantage of this method is that since the behavior of the sum value Tsum is symmetrical around the excitation time T axis (vertical axis) regardless of the direction of the external magnetic field Hex, magnetic saturation can be determined simply by adding two values (excitation time Tcw and excitation time Tccw). In addition, the only circuitry added to the conventional method (subtraction circuit for calculating differential output) is one addition circuit that calculates the sum of the 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. Compared to the individual determination method described below, all of the circuits are relatively common analog arithmetic circuits, making them easy to implement.

The threshold value of the added value Tsum is set to the region where the added value Tsum decreases in the region (b) to (c). Also, as shown in FIG. 12, while current excitation of the saturable coil 1 is performed normally, the maximum value of the added value Tsum is within a range of about 2T. If current excitation cannot be performed normally due to a break in the saturable coil 1, the excitation current cannot flow, and as described in paragraph [0046] of Patent Document 1, a trigger signal to stop the excitation pulse is not applied, and the excitation signal does not stop indefinitely. In other words, the excitation time T becomes so long that it is impossible for normal behavior to occur (in actual circuits, the excitation is usually set to turn off after a certain time, so this in itself does not pose a problem in terms of circuit operation).

If this extremely long sum Tsum can be detected as a threshold (threshold Tdis in FIG. 12), it has the secondary effect of making it easy to self-diagnose the detection of a broken wire in the saturable coil 1. With conventional differentials, an extremely long excitation time T cannot be detected because the difference between the two values is of similar magnitude and becomes zero.

[Judgment by individual judgment method]
In magnetic saturation measurement by the addition method, the circuit function can be simplified, but the (Hex: small) region is not considered to be magnetically saturated due to the mechanism. What is common to the regions (a) to (c) in Figure 12 is that the excitation time T on one side (CW direction or CCW direction) of 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 while it is magnetically saturated, the excitation time in either direction will be the shortest excitation time Tmin. Therefore, although it is necessary to judge individually, we propose a method in which it is considered to be magnetically saturated if even one (unidirectional) of the bidirectional measurement results has the shortest excitation time Tmin.

The advantage of this method is that it can instantly capture the saturated state of the saturable coil 1, making it advantageous in solutions where the accuracy of analog data is of great importance. In other words, it eliminates cases where the saturable coil 1 is partially magnetically saturated, such as in the (Hex: small) state (= area (a)), and appears not to be magnetically saturated. This is clear when compared to the determination using the addition method shown in Figure 13. In practice, the excitation time threshold tth for magnetic saturation detection is set slightly longer than the shortest excitation time Tmin.

[Difference between additive and individual magnetic saturation determination methods]
FIG. 13 is a diagram showing the difference between the addition method and the individual determination method for magnetic saturation determination according to an embodiment of the present invention.
In Fig. 13, the region Ar1 of the additive method and the region Ar2 of the individual judgment method each represent a region where the saturable coil 1 is considered not to be magnetically saturated in each judgment. In the judgment of the additive method in the lower part of Fig. 13, it is judged whether the strength of the external magnetic field Hex in the CW direction and the CCW direction is at a level that cuts into the region (b) shown in Fig. 12. If the sum Tsum obtained by adding the excitation time Tcw and the excitation time Tccw exceeds the excitation time threshold Tsum, the strength of the external magnetic field Hex is within the region Ar1, and the saturable coil 1 is not magnetically saturated. For stable judgment, it is preferable to set the excitation time threshold Tth so that the region Ar1 overlaps the region (b) with a predetermined margin.

In addition, in the judgment by the individual judgment method in the upper part of FIG. 13, it is judged whether the strength of the external magnetic field Hex in the CW direction and CCW direction exceeds the threshold value |Hsat| and enters into the region (a). If the individual excitation time Tcw and excitation time Tccw each exceed the excitation time threshold value tth, the strength of the external magnetic field Hex is within the region Ar2, and the saturable coil 1 is not magnetically saturated. For stable judgment, it is preferable to set the excitation time threshold value tth so that the region Ar2 is inside the threshold value |Hsat| with a certain margin.

[Example of processing using the addition method]
A specific example of the process using the addition method will be described below with reference to FIG.
FIG. 14 is a diagram showing an example of the configuration of an addition-type decision block according to an embodiment of the present invention.

As described above in [Determination by Addition Method], in the addition method of this embodiment, a switch-on determination (magnetic saturation switch determination) is added by detecting magnetic saturation using the sum of the outputs (Tsum = Tcw + Tccw) in a manner that takes precedence over the threshold determination (analog switch determination) of the differential analog data (Tsub = Tcw - Tccw) of the excitation times Tcw and Tccw during conventional bidirectional CW and CCW output. 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 is ON (logical sum is the true value).

In addition, when making a judgment based on the sum value Tsum, if the excitation time T is so long that it cannot be obtained if current is flowing through the saturable coil 1 (threshold value Tdis in [judgment based on the addition method]), an error judgment (breakdown detection judgment) is also made at the same time to determine that the saturable coil 1 has been broken, in addition to the magnetic saturation switch judgment.

The additive type judgment block 30 shown in FIG. 14 includes a first comparator 31, a second comparator 32, a third comparator 33, and a logical OR circuit 34. The first comparator 31 performs conventional analog switch judgment, comparing the difference value Tsub between the excitation times Tcw and Tccw with the switch-on threshold value ΔTth, and outputting an ON signal when |Tsub|>ΔTth.

The second comparator 32 is a block added in the present invention, which compares a sum Tsum, which is the sum of the excitation times Tcw and Tccw, with a 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, and indicates, for example, that a magnetic body is suspected of being too close.
The third comparator 33 is a block added in the present invention, which compares a sum Tsum, which is the sum of the excitation times T in two directions, with a threshold value Tdis, and outputs an ON signal (an error output for disconnection detection) when Tsum>Tdis.
The logical sum circuit 34 compares the outputs of the first comparator 31 and the second comparator 32, and if either comparator outputs an ON signal, outputs an ON signal (switch output).

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

As described above in [Determination by individual determination method], a determination (unidirectional magnetic saturation switch determination) is added that takes precedence over the analog switch determination in [Specific processing by addition method], in which if only one of the excitation times Tcw, Tccw is less than the threshold tth that is close to the shortest excitation time Tmin, it is deemed to be magnetically saturated. Specifically, the configuration is such that a logical sum is calculated from the results of the analog switch determination and the unidirectional magnetic saturation switch determination for the excitation times Tcw, Tccw.

The judgment block 40 of the individual judgment method shown in FIG. 15 includes a first comparator 41, a second comparator 42, a third comparator 43, a logical sum circuit 44, and a logical sum circuit 45. The first comparator 41 performs conventional analog switch judgment like the first comparator 31 shown in FIG. 14, and 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.

The second comparator 42 is a block added in the present invention, which compares the excitation time Tcw with a 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, and indicates, for example, that a magnetic body is suspected of being too close.
The third comparator 43 is a block added in the present invention, which compares the excitation time Tccw with a threshold value tth, and outputs an ON signal when Tccw<tth.

The OR circuit 44 compares the outputs of the second comparator 42 and the third comparator 43, 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, and indicates, for example, that a magnetic body is suspected to be excessively close.
The logical sum circuit 45 compares the outputs of the first comparator 41 and the logical sum circuit 44, and outputs an ON signal if either output is ON (switch output).

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

One case in which this type of combined method is used is when it is necessary to accurately detect the magnetic saturation of the saturable coil 1 while simultaneously performing error diagnosis of the saturable coil 1, as shown in Figure 12. In this case, the output of the individual judgment method is used to judge magnetic saturation detection, and the error detection function of the additive judgment method is also used.

As shown in FIG. 13, this combined method also makes it possible to evaluate the strength of the external magnetic field Hex that is causing magnetic saturation in stages by utilizing the difference between the magnetic saturation detection areas Ar1 and Ar2 in the additive method and the individual judgment method. In other words, it is possible to output new measurement information as to whether the magnetic saturation is mild enough to be detected by the additive method alone, or severe enough to be detected by the individual judgment method. This judgment can be easily implemented by taking the logical product of the additive method and the individual judgment method, as shown by the dashed line in FIG. 16. This kind of detailed measurement information, such as the degree of magnetic saturation of the saturable coil 1, is not necessarily used in conventional binary sensors in which one signal line corresponds to 1-bit H (high)/L (low) information, because the number of signal lines increases. However, it can be useful in methods with high information density such as serial output methods.

The composite method judgment block 50 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, a logical OR circuit 56, a logical OR circuit 57, and a logical AND circuit 58.

The first comparator 51, the second comparator 52, and the third comparator 53 are the same as the blocks used in the individual judgment method shown in FIG. 15. The first comparator 51, the second comparator 52, and the third comparator 53 have the same configuration as the first comparator 41, the second comparator 42, and the third comparator 43 shown in FIG. 15, respectively, so detailed explanations are omitted.

The fourth comparator 54 and the fifth comparator 55 are the same as the blocks used in the addition method shown in FIG. 14. The fourth comparator 54 and the fifth comparator 55 have the same configuration as the second comparator 32 and the third comparator 33 shown in FIG. 14, respectively, so a detailed description is omitted.

The logical sum circuit 56 and the logical sum circuit 57 are the same as the blocks used in the individual determination method shown in FIG. 15. The logical sum circuit 56 and the logical sum circuit 57 have the same configuration as the logical sum circuit 44 and the logical sum circuit 45 shown in FIG. 15, respectively, and therefore a detailed description thereof will be omitted.

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.

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

In an actual magnetic sensor measurement system, as in the application described in paragraphs [0053] to [0054] of Patent Document 1, the excitation time T is first converted into a voltage value using a sample-and-hold circuit or the like, then converted into digital data using an ADC or the like, which is then taken into a microcontroller (hereafter abbreviated as "microcomputer") as measurement data and compared with a threshold value of the digital data previously recorded in the microcomputer for judgment.

For a microcontroller, it is easy to perform the process of adding or subtracting digital data, or comparing and judging individual values. To the extent that processing time allows, a composite judgment is performed as described in [Specific processing using the composite method]. In other words, in FIG. 13, the individual judgment method is used to judge magnetic saturation detection, and the addition method is used as a self-diagnosis function for the saturable coil 1.

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

The RS flip-flop circuit 80 has the same role as the RS flip-flop circuit in FIG. 1 of Patent Document 1. That is, the role of the RS flip-flop circuit 80 is to start current excitation by an excitation start trigger signal input from the microcomputer 70 (Set), and to stop the excitation pulse by detecting a threshold current from the current detection circuit 110 or by an excitation stop trigger signal that is issued sequentially 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 consisting of an H-bridge circuit. Also, the pulse width of the output Q itself from Set to Reset corresponds to the excitation time T for one measurement.

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 or 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 according to the magnitude and direction of the external magnetic field Hex and the direction of the current excitation is generated in the saturable coil 1.

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

The sample-and-hold circuit 120 converts the output signal T (corresponding to information on the excitation time T) from the RS flip-flop circuit 80 from time information to voltage information, and holds the voltage value until it is read by the ADC 740 of the microcomputer 70. The held voltage value is reset by a reset trigger signal from the microcomputer 70.

The logical sum 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 microcontroller 70 is input.

[Internal structure of the microcontroller]
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 operation of each block of the microcomputer 70 is synchronized by a clock signal from the clock 700. In addition, by counting the number of clocks, it is possible to measure time according to the number of clocks.

The processor 710 (an example of a control unit) reads out a control program recorded in the flash ROM 720 into the RAM 760 and executes it, thereby controlling the overall progress of the sensing operation (e.g., sequence control). In order to execute the processing of the flowcharts shown in Figures 18 and 19, the processor 710 appropriately executes processing such as giving direction instructions to the CW/CCW selector 730, resetting the held value of the sample-and-hold circuit 120, controlling the excitation pulse from start to stop, taking in analog data from the ADC 740, and storing the measurement results in the Tcw storage memory 761 and the Tccw storage memory 762.

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

The CW/CCW selector 730 controls the excitation direction of the excitation circuit 100 (H-bridge circuit) and whether the read result of the sample-and-hold circuit 120 is stored in the Tcw storage memory 761 or the Tccw storage memory 762. In reality, the CW/CCW selector 730 is incorporated into the sequence operation of the processor 710, so it can be considered conceptual.

The ADC 740 acquires the voltage information (measurement data) of the output signal T held by the sample-and-hold circuit 120 and converts it from an analog signal to digital data. The digitally converted measurement data is allocated and stored in a storage memory for CW or CCW via a demultiplexer 750 inside the microcomputer 70 according to an instruction from the CW/CCW selector 730.

The Tcw storage memory 761 and the Tccw storage memory 762 are configured as predetermined memory areas of the RAM 760, and temporarily store the measurement results obtained by the measurement system of the magnetic sensor 60. The measurement results are used as input variables in the comparison operation circuit 770.

Flash ROM 780 stores set thresholds for performing the difference calculation of the conventional technology, the addition calculation and addition method judgment added in this embodiment, and each judgment of the individual judgment method. The set thresholds are read into the comparison calculation circuit 770 and become the reference value for each judgment.

The comparison calculation circuit 770 performs magnetic saturation judgment using the addition method and the individual judgment method, and magnetic detection judgment using the difference value of the conventional technology. The internal processing logic is based on the configuration of the judgment block of the composite method shown in FIG. 16. The input parameters of the comparison calculation circuit 770 include a total of four judgment parameters for the excitation time Tcw and the excitation time Tccw, which are the measurement data acquired from the RAM 760, the sum value Tsum and the difference value Tsub derived from the measurement data by the internal calculation circuit, and four threshold parameters corresponding to the judgment logic (FIGS. 14 to 16) stored in the flash ROM 780.

The judgment results and calculations of the calculation circuit inside the comparison calculation circuit 770 provide the switching judgment results of Figures 14 to 16 and the difference value Tsub as analog measurement data of the external magnetic field Hex. The calculation results are processed in the next stage I/F circuit 790 from digital information data to sensor output depending on the sensor configuration. In this embodiment, the comparison calculation circuit 770 is implemented with a judgment block of either the addition method (Figure 14), the individual judgment method (Figure 15), or the composite method (Figure 16). However, the comparison calculation circuit 770 may be implemented with judgment blocks of all methods and configured so that the processor 710 can switch judgment blocks arbitrarily or at the user's command.

The I/F circuit 790 (interface circuit) converts the judgment result in the microcontroller 70 into an electrical signal and outputs it as the sensor output. A GPIO can be used for switch output, and a DAC can be used for analog output. In actual magnetic sensors, the electrical characteristics of the peripheral devices of the microcontroller 70 are often inferior, or special electrical control such as the serial communication standard RS-485 is often required. For this reason, the sensor output may usually be output via an I/F circuit using one more stage of analog elements or a dedicated communication IC.

For example, the magnetic sensor 60 can employ an interface in which a single sensor output signal line, called an IO-Link as defined in IEC 61131-9, can be arbitrarily switched between serial communication output and switching output. In this case, in communication mode, the switching output, the strength and direction of the external magnetic field Hex, the presence or absence of magnetic saturation in the saturable coil 1, and the presence or absence of a disconnection error in the saturable coil 1 can be encapsulated in the same packet data to output serial communication data, while in switch sensor mode, the ON/OFF signal of the switching output can be output from a single signal line. The comparison calculation circuit 770 is a switching sensor but is also able to obtain analog output because it can accommodate output formats that can transmit high information density, such as serial communication methods.

[One-pulse measurement of magnetic sensor]
Next, a procedure for the measurement operation by the measurement system of the magnetic sensor 60 will be described.
The one-pulse measurement shown in Fig. 18 shows one measurement operation in the CW or CCW direction, and Fig. 19 is a flowchart of the overall operation of the magnetic sensor. As shown in the flowchart in Fig. 19, one-pulse measurement is performed multiple 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.

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

First, when the processor 710 of the microcomputer 70 starts the one-pulse measurement process, it outputs a reset trigger signal to the sample-and-hold circuit 120, resetting the sample-and-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 amount of time has passed since the start of excitation (S3), and if the certain amount of time has not passed (NO in S3), repeats the determination process of step S3.

On the other hand, if 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 loads the measurement data output from the sample-and-hold circuit 120 into the ADC 740, and stores it in the Tcw storage memory 761 or Tccw storage memory 762 of the RAM 760 via the demultiplexer 750. After the processing of step S5, the processing of this flowchart ends.

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

First, the processor 710 of the microcomputer 70 sets the CW/CCW selector 730 to 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.

Next, the processor 710 stores the measurement results of the one-pulse measurement in the RAM 760 (S13). Next, the processor 710 sets the CW/CCW selector 730 to the opposite direction to the previous direction, in this case the CCW direction (S14).

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

On the other hand, if measurements have been completed for both CW and CCW (YES in S15), the comparison calculation circuit 770 performs a judgment using the addition method, the individual judgment method, or the combined method (S16). Next, the comparison calculation circuit 770 outputs the judgment result as the calculation result to the I/F circuit 790 (S17). The I/F circuit 790 then converts the calculation result input from the comparison calculation circuit 770 into an electrical signal, which is used as the sensor output. After the processing of step S17, the processing of this flowchart ends.

As described above, the magnetic sensor according to one embodiment of the present invention follows the measurement principle of the magnetic sensor in Patent Document 1, while resolving the problem of unstable operation of the magnetic sensor when the saturable coil is magnetically saturated, which was an operational constraint in application to a magnetic detection switch sensor. In other words, the inventors of the present application focused on the peculiarities 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 when the saturable coil is magnetically saturated before current excitation by an external magnetic field, which was not mentioned in the prior art, and by actively applying this, they were able to newly add a magnetic saturation detection function for the saturable coil.

The magnetic sensor according to this embodiment, configured as described above, detects the transition of the excitation current when the saturable coil is magnetically saturated by such an external magnetic field before current excitation, thereby preventing the magnetic sensor from becoming unstable when the saturable coil is magnetically saturated, and ensuring safety when applied to a switch sensor. For example, normal switch operation can be continued even when a magnetic body is too close to the saturable coil or when a ferromagnetic body is close. Furthermore, the magnetic sensor according to this embodiment makes it possible to obtain the detailed state of the saturable coil itself (magnetic saturation, open circuit failure) as a new measurement parameter.

As an embodiment of the present invention, the following configuration may also be adopted.
One embodiment of the present invention comprises a saturable coil, a pulse generator, a two-way current excitation unit, a pulse width modulation unit, a current detection unit, and a calculation unit capable of calculating the difference (differential value) and sum (additive value) of two pulse widths.

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

The pulse generator has a mechanism that generates an OFF-ON rising signal with any pulse start trigger, generates an ON-OFF falling signal with any pulse stop trigger, and generates one square wave pulse signal with two trigger inputs. For example, the pulse generator can be configured using an RS flip-flop circuit 80.

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

The pulse width modulation unit excites the saturable coil and outputs a pulse width modulated signal whose pulse width is the time until 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.

The pulse width of the pulse-width modulated signal changes due to the inductance, which changes depending on the strength of the self-induced magnetic field generated by current excitation of the saturable coil and the combined magnetic field due to the external magnetic field Hex, and the difference in excitation time until the threshold current is reached, which arises from differences in the transition of the excitation current amount.

The calculation unit, which can calculate the difference (differential value) and sum (additive value) of the two pulse widths, stores the pulse width due to the excitation for each direction of the current that excited the saturable coil. The calculation unit is configured to have an error detection function that calculates the sum and difference of the two pulse widths and, based on the judgment result, detects a state in which the saturable coil is in a magnetically saturated state before excitation and normal measurement is not possible due to the approach of a ferromagnetic body, or an error of a broken wire failure in which an excitation current cannot flow through the saturable coil. The calculation unit detects the approach of a magnetic body, including magnetic saturation due to a ferromagnetic body, and outputs the result as a switch output signal. For example, this calculation unit can be configured using a comparison calculation circuit 770.

Furthermore, as an embodiment of the present invention, the following configuration can also be adopted.
(1) (Additive 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 (e.g., a microcomputer 70) that measures a magnetic field 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 includes:
detecting a magnetic saturation state before the excitation based on a sum 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 for the sum for detecting a magnetic saturation state before the excitation;
a magnetic sensor that 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 a magnetic body, and a detection result of a magnetic saturation state before the excitation.
(2) (Disconnection detection)
The magnetic sensor described in (1) above, wherein the magnetic measurement unit detects a break in the saturable coil based on a result of comparing a sum of the first excitation time and the second excitation time with a threshold for detecting a break in the saturable coil.
(3) (Individual judgment 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 (e.g., a microcomputer 70) that measures a magnetic field 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 includes:
a logical sum is calculated between 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 and a second individual comparison result obtained by comparing a second excitation time based on the second excitation current with the individual magnetic saturation detection threshold, and the magnetic saturation state before the excitation is detected based on the logical sum calculation result;
a magnetic sensor that 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 a magnetic body, and a detection result of a magnetic saturation state before the excitation.
(4) (Combined 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 (e.g., a microcomputer 70) that measures a magnetic field 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 includes:
a logical sum is calculated between 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 and a second individual comparison result obtained by comparing a second excitation time based on the second excitation current with the individual magnetic saturation detection threshold, and the first magnetic saturation state before the excitation is detected based on the logical sum calculation result;
detecting 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 first magnetic saturation state before the excitation;
A magnetic detection sensor that compares a sum obtained by adding the first excitation time and the second excitation time with a magnetic saturation detection threshold for the sum that detects a magnetic saturation state before excitation, detects a second magnetic saturation state before the excitation from the comparison result, calculates a logical product of a detection result of the second magnetic saturation state before the excitation and a detection result of the first magnetic saturation state before the excitation, and detects a third magnetic saturation state before the excitation based on a result of the logical product.
(5) (Disconnection detection)
The magnetic sensor described in (4) above, wherein the magnetic measurement unit detects a break in the saturable coil based on a result of comparing the sum of the first excitation time and the second excitation time with a threshold value for detecting a break in the saturable coil.

The present invention is not limited to the above-described embodiment, and various other applications and modifications are possible without departing from the gist of the present invention as described in the claims. For example, the above-described embodiment describes in detail and specifically the configuration of the magnetic sensor measurement system in order to explain the present invention in an easy-to-understand manner, and is not necessarily limited to having all of the components described.

Furthermore, the above-mentioned configurations, functions, processing units, etc. may be realized in part or in whole by hardware, for example by designing them as integrated circuits. As hardware, a broad processor device such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) may be used. Furthermore, the processing performed by a certain processing unit may be realized by a single piece of hardware, or may be realized by distributed processing using multiple pieces of hardware.

1...saturable coil, 10...current excitation circuit, 11...drive circuit, 12...current detection circuit, 20...current excitation circuit, 21...H-bridge circuit, 30...addition type judgment block, 31...first comparator, 32...second comparator, 33...third comparator, 34...logical OR circuit, 40...individual judgment type judgment block, 41...first comparator, 42...second comparator, 43...third comparator, 44...logical OR circuit, 45...logical OR circuit, 50...combined type judgment block, 51...first comparator, 52...second comparator, 53...third comparator, 54...fourth comparator, 55...fifth comparator, 56...logical OR circuit, 57...logical OR circuit, 58...logical 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...logical 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...area, Ar2...area, Hex...external magnetic field, Hdrv(t)...self-induced magnetic field (excitation magnetic field), i(t)...excitation current

Claims (5)

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 that measures a magnetic field 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 includes:
detecting a magnetic saturation state before excitation based on a sum 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 sum value for detecting a magnetic saturation state before excitation;
a magnetic sensor that 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 a magnetic body, and a detection result of a magnetic saturation state before the excitation. The magnetic sensor according to claim 1 , wherein the magnetic measurement unit detects an open circuit in the saturable coil based on a result of comparing a sum of the first excitation time and the second excitation time with a threshold value for detecting an open circuit in the saturable coil. 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 that measures a magnetic field 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 includes:
a logical sum is calculated between 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 and a second individual comparison result obtained by comparing a second excitation time based on the second excitation current with the individual magnetic saturation detection threshold, and the magnetic saturation state before the excitation is detected based on the logical sum calculation result;
a magnetic sensor that 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 a magnetic body, and a detection result of a magnetic saturation state before the excitation. 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 that measures a magnetic field 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 includes:
a logical sum is calculated between 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 and a second individual comparison result obtained by comparing a second excitation time based on the second excitation current with the individual magnetic saturation detection threshold, and the first magnetic saturation state before excitation is detected based on the logical sum calculation result;
detecting 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 first magnetic saturation state before the excitation;
A magnetic sensor that compares a sum obtained by adding up the first excitation time and the second excitation time with a magnetic saturation detection threshold for the sum that detects a magnetic saturation state before excitation, detects a second magnetic saturation state before excitation from the comparison result, calculates a logical product of a detection result of the second magnetic saturation state before excitation and a detection result of the first magnetic saturation state before excitation, and detects a third magnetic saturation state before excitation based on a result of the logical product. The magnetic sensor according to claim 4 , wherein the magnetic measurement unit detects an open circuit in the saturable coil based on a result of comparing a sum of the first excitation time and the second excitation time with a threshold value for detecting an open circuit in the saturable coil.

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