CN111059993B

CN111059993B - Displacement sensor

Info

Publication number: CN111059993B
Application number: CN201910984281.1A
Authority: CN
Inventors: 久保山丰; 中野泰志; 井上直也; 川口真史
Original assignee: Nabtesco Corp; Shinko Electric Co Ltd
Current assignee: Nabtesco Corp; Shinko Electric Co Ltd
Priority date: 2018-10-16
Filing date: 2019-10-16
Publication date: 2021-12-21
Anticipated expiration: 2039-10-16
Also published as: JP7185872B2; KR102376828B1; JP2020063962A; KR20200042865A; CN111059993A

Abstract

The invention relates to a displacement sensor, which reduces temperature dependence as much as possible to improve the linearity of displacement signals relative to the displacement of a measured object. A displacement sensor (1) is provided with: a rectifier (4) which rectifies a current flowing through a coil that generates an eddy current in the object to be measured and outputs the current from an output terminal; a signal converter for outputting a voltage or a current converted from the output of the rectifier into a displacement of the object to be measured from an output terminal; and a signal characteristic improving unit (8) which is arranged on a path from the output terminal of the rectifier to the output terminal of the signal converter, acquires the temperature around the coil, and improves the output characteristic of the signal converter by increasing the correction value at a higher temperature than at a lower temperature based on the temperature.

Description

Displacement sensor

Technical Field

The present application is based on Japanese patent application (Japanese patent application 2018-195353, application date: 2018/10/16) and enjoys priority benefits based on the application. The entire contents of this application are included by reference thereto.

The present invention relates to a displacement sensor for detecting a gap, which is a distance from a measurement object, in a non-contact manner.

Background

A displacement sensor using a coil includes an oscillator for causing an alternating current to flow through the coil, and a circuit for detecting a signal change caused by a change in impedance of the coil. After the oscillation signal of the oscillator is converted into a dc signal by the rectifier, a signal that linearly changes according to the gap between the objects to be measured is generated by the linearizer (see patent documents 1 and 2).

It is known that the impedance of a coil varies with temperature. Therefore, in patent document 1, the amplitude level of the oscillation signal output from the oscillator having the coil is corrected in accordance with the temperature. In addition, in patent document 2, the output of the linearizer is corrected by a correction value according to the temperature.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2015-137888

Patent document 2: japanese laid-open patent publication No. 8-271204

Disclosure of Invention

Problems to be solved by the invention

In patent document 1, temperature correction is performed at a stage before rectification by a rectifier. Since the signal frequency on the front stage side of the rectifier is high, it is susceptible to the influence of stray capacitance, and when a temperature correction circuit is provided on the front stage side of the rectifier, the circuit tends to be large in size, and is susceptible to the influence of the increase in stray capacitance, and the pattern design of the printed circuit board tends to be difficult.

In patent document 2, although the output voltage of the R-V converter is added to the output voltage of the linearizer to perform the correction process, if the addition process is performed only, the correction process can be performed only with a specific displacement to be corrected, and the input/output characteristics over a wide range cannot be linearized.

In addition, when temperature correction is performed on the output of the linearizer as in patent document 2, a signal that is not subjected to temperature correction is input to the linearizer. Particularly in a high-temperature region, there are concerns that: since the attenuation of the signal from the rectifier circuit increases, the output of the linearizer to which such an attenuated signal is input loses linearity, and accurate temperature correction cannot be performed even if a correction value is added to the signal that loses linearity.

The invention provides a displacement sensor which can reduce temperature dependence as much as possible and improve the linearity of displacement signals relative to the displacement of an object to be measured.

Means for solving the problems

In order to solve the above-described problems, one aspect of the present invention provides a displacement sensor including:

a rectifier for rectifying a current flowing through a coil for generating an eddy current in an object to be measured and outputting the current from an output terminal;

a signal converter for outputting a voltage or a current converted into a displacement of the object to be measured based on an output of the rectifier from an output terminal; and

and a signal characteristic improving unit that is disposed on a path from the output terminal of the rectifier to the output terminal of the signal converter, acquires a temperature around the coil, and improves a characteristic of an output signal of the signal converter by increasing a correction value at a high temperature as compared with a correction value at a low temperature based on the temperature.

Further comprises a temperature measuring device for measuring the temperature around the coil,

the signal converter may be a linearizer,

the signal characteristic improving section may have:

a variable gain amplifier that generates a signal obtained by multiplying the output of the rectifier by a gain; and

a gain adjustment section that adjusts the gain based on the temperature measured by the temperature measurer to improve linearity of the output of the linearizer with respect to the displacement.

The variable gain amplifier may have an analog multiplier or a multiplying D/a converter for generating a signal obtained by multiplying the output of the rectifier by the gain,

the output of the analog multiplier or the multiplication-type D/a converter is input to the linearizer.

The temperature sensor may further include a correlation storage unit that stores a correlation between the temperature around the coil and the gain adjusted by the gain adjustment unit,

the gain adjustment unit acquires the gain corresponding to the temperature measured by the temperature measuring device from the correlation storage unit.

The temperature measuring device may further include a temperature measuring device for measuring a temperature around the coil,

the signal converter is a linearizer that is,

the signal characteristic improving section corrects the input-output characteristic of the linearizer according to the temperature measured by the temperature measuring device.

The signal characteristic improving section may correct an input/output characteristic of the linearizer to improve linearity of the input/output characteristic of the linearizer.

The signal characteristic improving unit may convert the level of the output of the rectifier based on a polygonal function in which the input/output characteristic changes at a reference signal level that differs according to the temperature measured by the temperature measuring unit, and output the converted output.

The signal characteristic improving unit may decrease the reference signal level of the polygonal line function as the temperature measured by the temperature measuring unit increases.

The signal characteristic improving unit may perform level conversion on the output of the rectifier based on a polygonal function whose slope changes in accordance with the temperature measured by the temperature measuring unit at a reference signal level, and output the converted output.

The present invention may further include:

a substrate on which the coil, the rectifier, and the signal converter are mounted; and

a substrate temperature measuring device that measures a temperature of the substrate,

wherein the signal characteristic improving section improves the output characteristic of the signal converter based on the temperature of the coil measured by the temperature measuring instrument and the temperature of the substrate measured by the substrate temperature measuring instrument.

The apparatus may further comprise a self-excited oscillation circuit that outputs an oscillation signal by performing an oscillation operation using an impedance of the coil,

the oscillation level of the self-oscillation circuit changes under the influence of a change in impedance of the coil caused by eddy currents generated in the object.

The coil may be a coreless coil or a cored coil.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, the linearity of the displacement signal with respect to the displacement of the object to be measured can be improved by reducing the temperature dependence as much as possible.

Drawings

Fig. 1 is a block diagram showing a schematic configuration of a displacement sensor according to a first embodiment.

Fig. 2 is a block diagram showing a first specific example of the linearity improving unit of fig. 1.

Fig. 3 is a block diagram of a second example further embodying fig. 2.

Fig. 4 is a block diagram of a modification of fig. 3.

Fig. 5 is a diagram showing input/output characteristics of a displacement sensor not provided with the signal characteristic improving section and the linearizer of fig. 1.

Fig. 6 is a diagram showing characteristics of the displacement sensor according to the present embodiment including the linearity improving unit.

Fig. 7 is a diagram showing characteristics of the displacement sensor according to the present embodiment including the linearity improving unit.

Fig. 8 is a diagram showing characteristics of a displacement sensor according to a comparative example not including the linearity improving unit.

Fig. 9 is a diagram showing characteristics of a displacement sensor according to a comparative example not including a linearity improving unit.

Fig. 10 is a block diagram showing a schematic configuration of a displacement sensor according to the second embodiment.

Fig. 11 is a graph showing an example of the input/output characteristics of the linearizer adjusted by the input/output characteristic correcting section.

Fig. 12 is a graph showing the characteristics of the linearizer in the absence of a sensitivity change.

Fig. 13 is a graph showing the characteristics of the linearizer in the case where the sensitivity is decreased by 10%.

Fig. 14 is a graph showing the characteristics of the linearizer in the case where the sensitivity is decreased by 20%.

Fig. 15 is a circuit diagram of a linearizer having the characteristics of fig. 10 to 13.

Fig. 16 is a circuit diagram of a linearizer according to a modification.

Fig. 17 is a diagram showing a polyline function according to a modification.

Fig. 18 is a block diagram showing a schematic configuration of a displacement sensor according to the third embodiment.

Description of the reference numerals

1: a displacement sensor; 2: a coil; 3: an oscillator; 4: a rectifier; 5: a linearizer; 6: an output amplifier; 7: a temperature measurer; 8: a signal characteristic improving section; 11: a variable gain amplifier; 12: a gain adjustment unit; 13: a correlation storage unit; 14: MCU; 15: an A/D converter; 16: a D/A converter; 17: a multiplying type D/A converter; 18: an input/output characteristic correction unit.

Detailed Description

The following describes embodiments of the present invention in detail.

(first embodiment)

Fig. 1 is a block diagram showing a schematic configuration of a displacement sensor 1 according to a first embodiment. The displacement sensor 1 shown in fig. 1 includes a coil 2, an oscillator 3, a rectifier 4, a linearizer 5, an output amplifier 6, a temperature measuring instrument 7, and a signal characteristic improving unit 8.

The oscillator 3 is constituted by, for example, a self-excited oscillation circuit. Compared with the independent-excitation type oscillation circuit, the self-excitation type oscillation circuit can simplify the circuit structure and reduce the installation area and the component cost. Further, since resonance of the coil is utilized, there is an advantage that a change in voltage level of the oscillation signal caused by a change in distance from the object to be measured can be increased. The specific circuit configuration of the self-excited oscillation circuit is not particularly limited, and, for example, a colpitts oscillation circuit can be applied.

The oscillator 3 incorporates a resonance circuit formed by the coil 2 and a capacitor not shown. An alternating current of a resonance frequency flows through the coil 2. Therefore, the coil 2 generates a magnetic flux corresponding to the alternating current, and an eddy current is generated in the object to be measured disposed in the vicinity of the coil 2 due to the magnetic flux. When an eddy current is generated in the object to be measured, the impedance of the coil 2 changes under the influence of the eddy current, and the voltage level of the oscillation signal of the oscillation circuit also changes. In this manner, an alternating current is supplied to the coil 2 to generate an alternating magnetic field in the coil 2, thereby generating an output corresponding to an eddy current induced in the object to be measured in accordance with the displacement of the position of the object to be measured.

Since eddy current is not generated when the object to be measured is an insulator, the object to be measured, which can detect displacement, that is, a gap by using the displacement sensor 1 of fig. 1, is limited to a conductor. Further, even if the inside of the object to be measured is an insulator, since eddy current is generated as long as the surface is a conductor, displacement can be detected by the displacement sensor 1 of fig. 1. The object to be measured may be a conductive body, and may be a non-magnetic body or a magnetic body.

The rectifier 4 rectifies a current flowing through the coil 2 that generates an eddy current in the object to be measured, and outputs the current from an output terminal. That is, the rectifier 4 rectifies the oscillation signal of the oscillator 3, that is, the output of the coil 2, and converts the rectified signal into a dc signal. The signal converter such as the linearizer 5 outputs a voltage or a current converted into a displacement of the object to be measured based on the output of the rectifier 4 from the output terminal. In the case of using the linearizer 5 as the signal converter, the linearizer 5 generates a displacement signal whose signal level linearly changes in accordance with the displacement of the object to be measured, based on the output of the rectifier 4. Ideally, the linearizer 5 generates a displacement signal whose signal level linearly changes in accordance with the displacement of the object to be measured. However, since the output of the rectifier 4 varies due to the impedance variation of the coil 2 caused by the temperature change, the actual output signal level of the linearizer 5 is not linear with respect to the displacement of the object to be measured even in the same temperature environment. Therefore, the present embodiment includes temperature measuring instrument 7 and signal characteristic improving unit 8.

The signal converter is not necessarily limited to the linearizer 5. For example, a signal converter that performs arbitrary signal conversion processing on an input signal and outputs the signal may be provided instead of the linearizer 5. The arbitrary signal conversion processing refers to, for example, processing for converting an input signal into a sine wave signal.

The temperature measurer 7 measures the temperature of the periphery of the coil 2. When the displacement sensor 1 of fig. 1 is used to measure, for example, the displacement of the valve of the engine, the temperature around the coil 2 may be high enough to exceed 100 ℃. As described above, the dc resistance of the coil 2 varies depending on the temperature, and the output signal level of the displacement sensor 1 also varies. Therefore, it is desirable to measure the temperature of the coil 2 itself or the temperature of a place as close to the coil 2 as possible in the use environment of the displacement sensor 1.

The signal characteristic improving unit 8 is disposed on a path from the output terminal of the rectifier 4 to the output terminal of the signal converter, acquires the temperature around the coil 2, and improves the output characteristic of the signal converter by increasing the correction value at a higher temperature than at a lower temperature based on the temperature. For example, the signal characteristic improving unit 8 improves the characteristic of the output of the signal converter such as the linearizer 5 based on the temperature measured by the temperature measuring unit 7. More specifically, the signal characteristic improving unit 8 is disposed in a signal path from the output node of the rectifier 4 to the output node of the linearizer 5, and improves the characteristic of the output of the linearizer 5 with respect to the displacement of the object to be measured based on the temperature measured by the temperature measuring unit 7. Here, the improvement of the characteristics means, for example, improving the linearity of the output of the linearizer 5 with respect to the displacement of the object to be measured, that is, improving the linearity. Although fig. 1 shows an example in which the signal characteristic improving section 8 is disposed between the rectifier 4 and the linearizer 5, the signal characteristic improving section 8 may be provided inside the linearizer 5. In the second embodiment described later, an example in which the signal characteristic improving section 8 is provided inside the linearizer 5 is described, and in the present embodiment, an example in which the signal characteristic improving section 8 is disposed between the rectifier 4 and the linearizer 5 is described.

The signal characteristic improving section 8 according to the present embodiment improves the linearity of the output of the linearizer 5 with respect to the displacement of the object to be measured. Ideally, the signal characteristic improving unit 8 performs a predetermined linearity improving process so that the linearizer 5 outputs a signal that linearly changes in accordance with the displacement of the object to be measured.

Fig. 2 is a block diagram showing a first specific example of the signal characteristic improving unit 8 shown in fig. 1. The signal characteristic improving section 8 of fig. 2 has a variable gain amplifier 11 and a gain adjusting section 12. In addition, the signal characteristic improving unit 8 in fig. 2 may include a correlation storage unit 13.

The variable gain amplifier 11 generates a signal obtained by multiplying the dc signal output from the rectifier 4 by an adjustable gain. The variable gain amplifier 11 can include, for example, an analog multiplier.

The gain adjustment unit 12 adjusts the gain based on the temperature measured by the temperature measuring device 7 to improve the linearity of the output of the linearizer 5 with respect to the displacement of the object to be measured.

The correlation storage unit 13 stores in advance a relative relationship between the temperature and the gain of the variable gain amplifier 11. The method of generating data stored in the correlation storage unit 13 will be described in detail later, and the temperature of the coil 2 is supplied to the correlation storage unit 13, whereby the gain of the corresponding variable gain amplifier 11 can be extracted. As described above, if the correlation storage unit 13 is provided in advance, the gain adjustment unit 12 can quickly acquire the gain corresponding to the temperature measured by the temperature measuring instrument 7 from the correlation storage unit 13, and can easily perform the gain adjustment of the variable gain amplifier 11.

Fig. 3 is a block diagram of a second example further embodying fig. 2. The displacement sensor 1 shown in fig. 3 includes an MCU (Micro Control Unit) 14 functioning as a gain adjustment Unit 12. The MCU 14 performs the processing operation of the gain adjustment unit 12 by digital signal processing. Therefore, in the displacement sensor 1 of fig. 3, an a/D converter 15 for converting the output of the temperature measuring instrument 7 into a digital signal is connected to the front stage side of the MCU 14, and a D/a converter 16 for converting the output signal of the MCU 14 into an analog signal is connected to the rear stage side of the MCU 14. The gain of the variable gain amplifier 11 is adjusted by the output signal of the D/a converter 16. The MCU 14 refers to the internal or external correlation storage unit 13 to set a gain according to the temperature of the coil 2.

Fig. 4 is a block diagram of a modification of fig. 3. The signal characteristic improving section 8 in fig. 4 is obtained by replacing the variable gain amplifier 11 and the D/a converter 16 in fig. 3 with a multiplying D/a converter 17. By using the multiplication-type D/a converter 17, the frame structure can be made simpler than that of fig. 3. The basic operation principle of the displacement sensor 1 of fig. 3 and 4 is the same as that of fig. 1 and 2. As a modification of fig. 3 and 4, the output of the rectifier 4 may be converted into a digital signal by an a/D converter and input to the MCU 14, the gain may be digitally adjusted by the MCU 14, and the gain-adjusted digital signal may be converted into an analog signal by a D/a converter and input to the linearizer 5. Thus, the variable gain amplifier 11 is not required to be provided.

Fig. 5 is a diagram showing input/output characteristics of a displacement sensor not provided with the signal characteristic improving section 8 and the linearizer 5 of fig. 1. In fig. 5, the horizontal axis represents the distance (mm) between the object and the object, and the vertical axis represents the output signal level. FIG. 5 shows 5 graphs w 1-w 5 of the temperature of the coil 2 at 0 deg.C, 30 deg.C, 60 deg.C, 90 deg.C, 120 deg.C. As can be seen from the graphs of fig. 5, when neither temperature correction nor linearization processing is performed, the output signal level changes nonlinearly according to the size of the gap with the object to be measured, and the input/output characteristics of the displacement sensor change according to the temperature of the coil 2.

Fig. 6 and 7 are diagrams showing characteristics of the displacement sensor 1 according to the present embodiment including the signal characteristic improving unit 8, and fig. 8 and 9 are diagrams showing characteristics of the displacement sensor 1 according to a comparative example not including the signal characteristic improving unit. Fig. 6 and 8 show the input-output characteristics of the displacement sensor 1, and fig. 7 and 9 show the relationship between the temperature and the output signal level of the displacement sensor 1. The abscissa of fig. 6 and 8 represents the gap (mm) with the object to be measured, and the ordinate represents the output signal level of the displacement sensor 1. The abscissa of fig. 7 and 9 represents the temperature (° c) of the coil 2, and the ordinate represents the output signal level of the displacement sensor 1. The gap is larger on the right side of the horizontal axis of fig. 6 and 8, the temperature is higher on the right side of the horizontal axis of fig. 7 and 9, and the output signal level is higher on the upper side of the vertical axis of fig. 6 to 9.

FIGS. 6 and 8 depict graphs w 6-w 9 at 0 deg.C, 40 deg.C, 80 deg.C and 120 deg.C. In the case where the signal characteristic improving section 8 is not provided, as shown in fig. 8, the linearity is deteriorated as the temperature is higher, and the output signal level is decreased as the gap is larger. In contrast, when the signal characteristic improving section 8 is provided, as shown in fig. 6, it is possible to maintain good linearity regardless of the temperature and the gap. That is, by providing the signal characteristic improving section 8, the output of the linearizer 5 with respect to the displacement of the object to be measured, that is, the gap between the objects to be measured becomes substantially the same straight line regardless of the temperature. In the case where neither the signal characteristic improving section 8 nor the linearizer 5 is provided, the input/output characteristic of the displacement sensor differs depending on the temperature and exhibits a nonlinear characteristic as shown in fig. 5, but by providing the linearizer 5, the input/output characteristic is linearized as shown in fig. 6 and 8, and by providing the signal characteristic improving section 8, the input/output characteristic of the displacement sensor no longer has a temperature dependency as shown in fig. 6.

In addition, fig. 7 and 9 depict graphs w10 to w15 showing the relationship between the temperature of the coil 2 and the output level of the linearizer 5 with respect to a plurality of gaps. Graphs w 10-w 15 are arranged in order of decreasing gap. In the case where the signal characteristic improving section 8 is not provided, as shown in fig. 9, the output level of the linearizer 5 decreases as the temperature increases. This means that the sensitivity of the displacement sensor 1 decreases the higher the temperature. In addition, although not shown in fig. 9, when the temperature becomes gradually lower, the output level of the linearizer 5 drops once it reaches a peak. Therefore, when the temperature is too low, the sensitivity of the displacement sensor 1 also tends to decrease. In contrast, when the signal characteristic improving section 8 is provided, the output level of the linearizer 5 is substantially constant even if the temperature is changed, as shown in fig. 7. This means that the sensitivity of the displacement sensor 1 is substantially fixed, i.e. independent of temperature and independent of the gap.

The present inventors prepared graphs of fig. 8 and 9 by using the displacement sensor 1 as a reference while changing the temperature of the coil 2 and the gap between the coil and the object to be measured. After that, the gain of the variable gain amplifier 11 was variously changed, and an optimum gain was found in the graphs shown in fig. 6 and 7. Then, the relative relationship between the temperature and the gain is stored in the correlation storage unit 13, so that when the temperature of the coil 2 is input, the optimum gain corresponding to the temperature can be easily and quickly retrieved.

As described above, in the first embodiment, since the signal characteristic improving section 8 is provided in the signal path between the rectifier 4 and the linearizer 5, it is possible to output a signal having a better linearity and no temperature dependency than when the linearity improving process is performed on the internal signal of the oscillator 3 or the output signal of the oscillator 3.

More specifically, when the dc signal rectified by the rectifier 4 is multiplied by the gain by the variable gain amplifier 11, the gain is optimized according to the temperature around the coil 2, and therefore the linearity of the displacement sensor 1 can be improved without complicating the structure.

(second embodiment)

The second embodiment described below performs the linearity improvement processing inside the linearizer 5.

Fig. 10 is a block diagram showing a schematic configuration of the displacement sensor 1 according to the second embodiment. The displacement sensor 1 in fig. 10 includes the same coil 2, oscillator 3, rectifier 4, output amplifier 6, and temperature measuring instrument 7 as in fig. 1, but the internal configuration of the linearizer 5 is different from that in fig. 1. In the displacement sensor 1 of fig. 10, the variable gain amplifier 11 is not an essential component, and is therefore omitted from fig. 10. As will be described later, the displacement sensor 1 of fig. 10 may be provided with a variable gain amplifier 11.

The linearizer 5 of fig. 10 has a signal characteristic improving section 8 inside it. The signal characteristic improving section 8 of fig. 10 corrects the input/output characteristic of the linearizer 5 in accordance with the temperature around the coil 2. That is, the signal characteristic improving section 8 corrects the input/output characteristic of the linearizer 5 to improve the linearity of the input/output characteristic of the linearizer 5. More specifically, the signal characteristic improving section 8 performs level conversion on the output of the rectifier 4 based on a polygonal line function in which the input/output characteristic changes at a reference signal level that differs according to the temperature around the coil 2, and outputs the converted output.

Here, the polygonal line function is a function obtained by connecting a plurality of line segments having different slopes. In this specification, the connection point of each line segment is referred to as a polyline point. The reference signal level refers to each polyline point of the polyline function. The position of the broken line point changes in accordance with the temperature of the periphery of the coil 2. And respectively setting fold line functions according to the temperature, wherein each fold line function is provided with a plurality of fold line points, and every two adjacent fold line points are connected by line segments with different slopes.

Fig. 11 is a diagram showing a polygonal line function of the signal characteristic improving section 8 in the linearizer 5. The horizontal axis of fig. 11 represents the input signal of the linearizer 5, and the vertical axis represents the output signal. The input signal level is shown to be higher on the right side of the horizontal axis, and the output signal level is shown to be higher on the upper side of the vertical axis.

FIG. 11 illustrates 3 polyline functions w 16-w 18. The broken-line function w16 shows that the sensitivity of the coil 2 is not changed, the broken-line function w17 shows that the sensitivity is decreased by 10%, and the broken-line function w18 shows that the sensitivity is decreased by 20%. The black circles in fig. 11 are broken line points as reference signal levels. The polygonal line functions w16 to w18 change the overall slope by changing the polygonal line points. The broken line point differs depending on the sensitivity of the coil 2, that is, the temperature of the coil 2, and therefore the input-output characteristics of the linearizer 5 differ depending on the temperature. When the output of the rectifier 4 is input to the linearizer 5, the input signal is level-converted and output in a polygonal line function corresponding to the temperature of the coil 2. Fig. 11 illustrates 3 kinds of polygonal line functions different in temperature, i.e., sensitivity, but there are actually a large number of polygonal line functions corresponding to a large number of temperatures.

From the positions of the respective polygonal-line points on the respective polygonal-line functions of fig. 11, it is understood that the polygonal-line points are shifted to the left side when the sensitivity is lowered as the temperature becomes higher. This means that the lower the sensitivity becomes, the linearity improvement processing is performed from a smaller input signal level. At each polyline point, the slope of the polyline function changes. In addition, the slope of the line segment connecting between 2 adjacent polygonal line points is set to be the same even if the temperature changes. For example, a line segment connecting the polyline point p1 and the polyline point p4, a line segment connecting the polyline point p2 and the polyline point p5, and a line segment connecting the polyline point p3 and the polyline point p6 all have the same slope. Further, these slopes may be different from each other. In addition, instead of the straight line approximation, a curve approximation may be performed to further improve the linearity.

Fig. 12 to 14 are graphs each showing the characteristics of the linearizer 5 at different sensitivities. Fig. 12 shows the characteristic when the sensitivity of the coil 2 is not changed, fig. 13 shows the characteristic when the sensitivity of the coil 2 is decreased by 10%, and fig. 14 shows the characteristic when the sensitivity of the coil 2 is decreased by 20%. In fig. 12 to 14, the horizontal axis represents the gap (mm) with the object to be measured, and the vertical axis represents the voltage (V) or the linearity (%).

Fig. 12 to 14 show an input signal waveform w19 of the linearizer 5, an ideal output signal waveform w20 of the linearizer 5, an output signal waveform w21 of the linearizer 5 according to the present embodiment, and a waveform w22 indicating linearity in each gap. That is, the waveform w22 shows the difference between the ideal output signal waveform w20 and the output signal waveform w21 linearized by the linearizer 5, and the smaller the variation in the difference over the entire region of the gap, the better the linearization by the linearizer 5.

The ideal output signal waveform w20 is a linear waveform. The positions of the valleys of the waveform w22 indicating linearity are broken line points. Ideally, the waveform w22 changes uniformly up and down with respect to the reference line L1 extending in the level direction intersecting the waveform w 22. In fig. 12 showing that the sensitivity is not changed, the characteristic of the actual output signal waveform w21 of the linearizer 5 is closest to the ideal output signal waveform w20, as compared with fig. 13 and 14 in which the sensitivity is decreased.

When the sensitivity is decreased by 10%, the broken line point is shifted to a lower input signal level than when the sensitivity is not changed. In addition, when the sensitivity is decreased by 20%, the broken line point is shifted to a lower input signal level than when the sensitivity is decreased by 10%. Thus, even when the sensitivity is lowered, the actual output signal waveform w21 of the linearizer 5 can be brought close to the ideal output signal waveform w 20.

Fig. 15 is a circuit diagram of a specific example of the linearizer 5 having the characteristics of fig. 11 to 14. The linearizer 5 shown in fig. 15 includes operational amplifiers OP1 to OP6, resistors R1 to R18, and diodes D1 to D6.

The non-inverting input terminals of the operational amplifiers OP1 to OP6 are grounded. The output of the rectifier 4 is input to the inverting input terminal of the operational amplifier OP1 via a resistor R1. A resistor R2 is connected between the output terminal and the inverting input terminal of the operational amplifier OP 1. The operational amplifier OP1 inverts and outputs the output of the rectifier 4.

The output signals of the operational amplifiers OP1 are input to inverting input terminals of the operational amplifiers OP2 to OP4 via resistors R3 to R5, respectively. The reference signals V1 to V3 are input to inverting input terminals of the operational amplifiers OP2 to OP4 via resistors R6 to R8, respectively. The reference signals V1 to V3 are signals at broken line points in fig. 11. For example, the signal levels of the broken line points p1, p4, and p7 on the waveform w16 are input as the reference signals V1 to V3. The inverting input terminals of the operational amplifiers OP2 to OP4 are connected to the anodes of the diodes D1 to D3, respectively, and the output terminals of the operational amplifiers OP2 to OP4 are connected to the cathodes of the diodes D1 to D3, respectively. The cathodes of the diodes D1 to D3 and the output terminals of the operational amplifiers OP2 to OP4 are connected to the anodes of the diodes D4 to D6, respectively. Resistors R9 to R11 are connected between the cathodes of the diodes D4 to D6 and the anodes of the diodes D1 to D3, respectively. Cathodes of the diodes D4 to D6 are connected to the inverting input terminal of the operational amplifier OP5 via resistors R12 to R14, respectively. A resistor R15 is connected between the inverting input terminal and the output terminal of the operational amplifier OP 5. A resistor R16 is connected between the output terminal of the operational amplifier OP5 and the inverting input terminal of the operational amplifier OP 6. A resistor R17 is connected between the inverting input terminal of the operational amplifier OP6 and the output terminal of the operational amplifier OP 1. A resistor R18 is connected between the inverting input terminal and the output terminal OUT of the operational amplifier OP 6. Next, the resistances of the resistors R12 to R14 are R1, R2, and R3, respectively, and the resistances of the other resistors R1 to R11 and R15 to R18 are R.

When the input signal input to the linearizer 5 of fig. 15 is set to Vin, the output voltage of the operational amplifier OP1 is-Vin. When the input signal Vin is equal to or less than the reference signal V1 at V3> V2> V1, the cathode voltages of the diodes D4 to D6 are all 0V, and therefore the output of the operational amplifier OP5 is also 0V, and the output of the operational amplifier OP6 is an inverted signal of the operational amplifier OP 1. That is, Vout becomes Vin.

When the input signal Vin is V1< Vin ≦ V2, a voltage of (Vin-V1) appears only at the cathode of the diode D4 due to a current flowing through the resistor R18, and thus Vout ═ Vin + (Vin-V1) R/R1 is obtained.

When the input signal Vin is V2< Vin ≦ V3, the voltage appearing at the cathode of the diode D4 (Vin-V1) and the voltage appearing at the cathode of the diode D5 (Vin-V2) are added by R1 and R2 to obtain Vout ═ Vin + (Vin-V1) R/R1+ (Vin-V2) R/R2.

When the input signal Vin is V3< Vin, the voltage appearing at the cathode of the diode D4 (Vin-V1), the voltage appearing at the cathode of the diode D5 (Vin-V2), and the voltage appearing at the cathode of the diode D6 (Vin-V3) are added by R1, R2, and R3 to obtain Vout ═ Vin + (Vin-V1) R/R1+ (Vin-V2) R/R2+ (Vin-V3) R/R3.

Further, the specific circuit configuration of the linearizer 5 is not limited to the configuration shown in fig. 15. For example, fig. 16 is a circuit diagram of the linearizer 5 according to one modification. The linearizer 5 shown in fig. 16 includes operational amplifiers OP7 to OP11, resistors R21 to R27, transistors Q1 to Q3, and diodes D7 to D9.

The non-inverting input terminals of the operational amplifiers OP7 and OP11 are grounded. The output of the rectifier 4 is input to the inverting input terminal of the operational amplifier OP7 via a resistor R21. A resistor R22 is connected between the output terminal and the inverting input terminal of the operational amplifier OP 7. The operational amplifier OP7 inverts and outputs the output of the rectifier 4.

The reference signals V1 to V3 are input to the noninverting input terminals of the operational amplifiers OP8 to OP10, respectively. The output of the rectifier 4 is input to inverting input terminals of the operational amplifiers OP8 to OP10 via resistors R23 to R25. The output signals of the operational amplifiers OP8 to OP10 are input to the bases of the transistors Q1 to Q3 and the anodes of the diodes D7 to D9, respectively. Cathodes of the diodes D7 to D9 are connected to inverting input terminals of the operational amplifiers OP8 to OP10 and emitters of the transistors Q1 to Q3, respectively. Collectors of the transistors Q1 to Q3 are connected to an inverting input terminal of the operational amplifier OP 7. The output terminal of the operational amplifier OP7 is connected to the inverting input terminal of the operational amplifier OP11 via a resistor R26. A resistor R27 is connected between the output terminal and the inverting input terminal of the operational amplifier OP 11.

Like the linearizer 5 of fig. 15, the signal level of the output signal Vout of the linearizer 5 of fig. 16 also changes depending on the magnitude relationship between the input signal Vin and the reference signals V1 to V3.

Fig. 11 shows an example in which the position of the broken line point of the broken line function of the linearizer 5 is changed in accordance with the temperature of the coil 2, but the slope of the line segment between the broken line points may be changed in accordance with the temperature of the coil 2 without changing the position of the broken line point. Fig. 17 is a diagram showing polyline functions w23 to w25 according to a modification. Unlike fig. 11, the polygonal-line functions w23 to w25 in fig. 17 do not change the positions of the polygonal-line points even if the temperature of the coil 2 changes, but the slopes of the line segments between the polygonal-line points change according to the temperature. The signal characteristic improving section 8 in the linearizer 5 may convert the level of the output of the rectifier 4 based on a polygonal line function as shown in fig. 17 and output the converted output. This enables the linearity improvement processing to be performed to the same extent as in the case of using the polygonal line function of fig. 11.

In the second embodiment, the signal characteristic improving section 8 is provided inside the linearizer 5, and outputs a signal obtained by level-converting the output of the rectifier 4 based on a polygonal line function according to the temperature of the coil 2. Therefore, the linearity of the linearizer 5 can be maintained even if the coil 2 is left at a high temperature.

(third embodiment)

The third embodiment is obtained by combining the first embodiment with the second embodiment.

Fig. 18 is a block diagram showing a schematic configuration of the displacement sensor 1 according to the third embodiment. The displacement sensor 1 in fig. 18 includes the same variable gain amplifier 11 and gain adjustment unit 12 as in fig. 2, and the same linearizer 5 as in fig. 10.

In the displacement sensor 1 of fig. 18, the gain adjustment unit 12 adjusts the gain of the variable gain amplifier 11 in accordance with the temperature of the coil 2. The linearizer 5, which is input to the output of the variable gain amplifier 11, has a signal characteristic improving section 8 that corrects the input-output characteristic of the linearizer 5 according to the temperature of the coil 2, and the signal characteristic improving section 8 corrects the input-output characteristic of the linearizer 5 to improve the linearity of the input-output characteristic of the linearizer 5.

In the displacement sensor 1 of fig. 18, after the gain of the variable gain amplifier 11 is adjusted by the gain adjustment unit 12, the linearity improvement processing of the input/output characteristics is performed by the linearizer 5, and therefore the linearity of the linearizer 5 is further improved.

In the first to third embodiments described above, the displacement sensor 1 can appropriately perform the linearity-improving process even if the temperature around the coil 2 changes. When the coil 2 has a core, the sensitivity of the coil 2 is improved, but the core is a magnetic body and its permeability is reduced at high temperature, and thus the coil cannot perform its original function. Therefore, when the displacement sensor 1 is used at a high temperature, the coreless coil 2 is often used. The displacement sensor 1 according to the first to third embodiments can be applied to both the cored coil 2 and the coreless coil 2, and the linearity of the displacement signal with respect to the displacement can be improved by the above-described method.

In the first to third embodiments described above, the temperature measuring instrument 7 measures the temperature around the coil 2, and based on the measured temperature, linearization processing of the displacement signal with respect to the displacement of the object to be measured is performed. In the displacement sensor 1 according to the first to third embodiments, the components other than the coil 2 are often mounted on a common substrate, and only the coil 2 is often disposed at a position distant from the substrate. In this case, there is a possibility that a temperature difference between the temperature around the coil 2 and the temperature of the substrate becomes large. In particular, when the temperature of the object to be measured becomes high, such as exceeding several hundreds of degrees celsius, or when the displacement of the valve of the engine is detected, the temperature difference between the temperature around the coil 2 and the temperature around the substrate tends to increase. As described above, the impedance of the coil 2 changes according to the temperature of the coil 2, but the electrical characteristics of the circuit elements in the substrate also change according to the temperature of the substrate, and affect the signal level of the displacement signal.

Therefore, when there is a possibility that the temperature around the coil 2 and the temperature around the substrate are different from each other, a substrate temperature measuring instrument for measuring the temperature around the substrate may be provided in addition to the temperature measuring instrument 7 for measuring the temperature around the coil 2.

In this case, in the first to third embodiments, the linearity improving process is performed in consideration of not only the temperature around the coil 2 measured by the temperature measuring instrument 7 but also the temperature around the substrate measured by the substrate temperature measuring instrument. Thus, a displacement signal corresponding to the displacement of the object to be measured can be generated based on the temperature of the periphery of the coil 2 and the temperature of the periphery of the substrate, and the linearity of the displacement signal with respect to the displacement can be further improved even if the temperatures of the coil 2 and the substrate change and even if the displacement of the object to be measured changes.

At least a part of the processing of the gain adjustment section 12 and the linearizer 5 described above may be performed by software. For example, a program for executing the processing of the gain adjustment section 12 and the linearizer 5 may be executed by using a signal processing processor or the like.

The technical ideas of the above-described embodiments can be summarized as the following (1) to (12).

(1) A displacement sensor is provided with:

and a signal characteristic improving unit that is disposed on a path from the output terminal of the rectifier to the output terminal of the signal converter, acquires a temperature around the coil, and improves the output characteristic of the signal converter by increasing a correction value at a higher temperature than at a lower temperature based on the temperature.

(2) The displacement sensor according to (1),

the signal converter is a linearizer that is,

the signal characteristic improving section includes:

(3) The displacement sensor according to (2),

the variable gain amplifier has an analog multiplier or a multiplying type D/A converter for generating a signal obtained by multiplying the output of the rectifier by the gain,

(4) The displacement sensor according to (2) or (3),

further comprises a correlation storage unit for storing a correlation between the temperature around the coil and the gain adjusted by the gain adjustment unit,

(5) The displacement sensor according to (1),

the signal converter is a linearizer that is,

(6) The displacement sensor according to (5),

the signal characteristic improving section corrects the input-output characteristic of the linearizer to improve the linearity of the input-output characteristic of the linearizer.

(7) The displacement sensor according to (6),

the signal characteristic improving unit converts the level of the output of the rectifier based on a polygonal function that changes the input/output characteristic at a reference signal level that differs according to the temperature measured by the temperature measuring unit, and outputs the converted output.

(8) The displacement sensor according to (7),

(9) The displacement sensor according to (6),

the signal characteristic improving unit converts the level of the output of the rectifier based on a polygonal function whose slope changes in accordance with the temperature measured by the temperature measuring unit at a reference signal level, and outputs the converted output.

(10) The displacement sensor according to any one of (2) to (9), further comprising:

wherein the signal characteristic improving section improves the characteristic of the output of the signal converter based on the temperature of the coil measured by the temperature measuring instrument and the temperature of the substrate measured by the substrate temperature measuring instrument.

(11) The displacement sensor according to any one of (1) to (10),

further comprising a self-excited oscillation circuit which performs an oscillation operation using the impedance of the coil and outputs an oscillation signal,

(12) The displacement sensor according to any one of (1) to (11),

the coil is either a coreless coil or a cored coil.

The embodiments of the present invention are not limited to the above-described embodiments, and include various modifications that can be conceived by those skilled in the art, and the effects of the present invention are not limited to the above-described ones. That is, various additions, modifications, and deletions can be made without departing from the concept and spirit of the present invention derived from the contents and equivalents defined in the claims.

Claims

1. A displacement sensor is provided with:

a signal converter for outputting a voltage or a current converted into a displacement of the object to be measured based on an output of the rectifier from an output terminal;

a signal characteristic improving unit that is disposed on a path from an output terminal of the rectifier to an output terminal of the signal converter, acquires a temperature around the coil, and improves a characteristic of an output of the signal converter by increasing a correction value at a high temperature as compared with a correction value at a low temperature based on the temperature; and

a temperature measuring device that measures a temperature around the coil,

wherein the signal converter is a linearizer,

the signal characteristic improving section includes:

a gain adjustment section that adjusts the gain based on the temperature measured by the temperature measurer to improve linearity of the output of the linearizer with respect to the displacement,

the displacement sensor further includes a correlation storage unit that stores a correlation between the temperature around the coil and the gain adjusted by the gain adjustment unit,

2. Displacement sensor according to claim 1,

3. The displacement sensor according to claim 1 or 2, further comprising:

4. Displacement sensor according to claim 1 or 2,

5. Displacement sensor according to claim 1 or 2,

the coil is either a coreless coil or a cored coil.

6. A displacement sensor is provided with:

a temperature measuring device that measures a temperature around the coil,

wherein the signal converter is a linearizer,

the signal characteristic improving section corrects the input-output characteristic of the linearizer according to the temperature measured by the temperature measurer to improve the linearity of the input-output characteristic of the linearizer, and level-converts and outputs the output of the rectifier based on a polygonal line function,

wherein the polygonal function is a function in which input/output characteristics change at reference signal levels that differ according to a difference in temperature measured by the temperature measuring device.

7. Displacement sensor according to claim 6,

8. The displacement sensor according to claim 6 or 7, further comprising:

9. Displacement sensor according to claim 6 or 7,

10. Displacement sensor according to claim 6 or 7,

the coil is either a coreless coil or a cored coil.

11. A displacement sensor is provided with:

a signal characteristic improving unit that is disposed on a path from an output terminal of the rectifier to an output terminal of the signal converter, acquires a temperature around the coil, and improves a characteristic of an output of the signal converter by increasing a correction value at a high temperature as compared with a correction value at a low temperature based on the temperature; and a temperature measuring device that measures a temperature around the coil,

wherein the signal converter is a linearizer,

wherein the polygonal function is a function in which a slope changes at a reference signal level in accordance with the temperature measured by the temperature measurer.

12. The displacement sensor according to claim 11, further comprising:

13. Displacement sensor according to claim 11,

14. Displacement sensor according to claim 11,

the coil is either a coreless coil or a cored coil.