JP7368728B2 - Physical quantity measuring device - Google Patents

Description

The present invention relates to a physical quantity measuring device, and particularly relates to a technique for improving resolution near an arbitrarily set measurement point when measuring physical quantities of an object to be measured, such as distance to the object, displacement, pressure, etc.

Generally, with a sensor having a coil excited by an alternating current signal, it is difficult to improve the resolution of measured values over the entire measurement range.

For example, the LVDT (Linear Variable Differential Transformer) sensor described in Patent Document 1 is a differential transformer type displacement sensor that has a primary coil excited by an alternating current signal and two secondary coils.

An amplifier is introduced into the circuit of this LVDT sensor, and by adjusting the magnification (gain) of the amplifier, the resolution of the subsequent A/D (Analog to Digital) converter is utilized to the maximum. That is, the gain of the amplifier is adjusted so that the maximum value of the sensor output falls within the maximum input range of the A/D converter.

Japanese Patent Application Publication No. 2004-156459

The invention described in Patent Document 1 can improve the "resolution" near the zero point (measurement point where the input AC signal level is 0V) which is the mechanical reference point of the LVDT sensor, but it is possible to improve the "resolution" near the zero point (measurement point where the input AC signal level is 0V), but There is a problem in that it is not possible to improve the "resolution" in the vicinity.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a physical quantity measuring device that can improve resolution near arbitrarily set measurement points.

In order to achieve the above object, a physical quantity measuring device according to a first aspect of the present invention includes an AC signal source that generates an AC signal of a first amplitude, an AC signal generated from the AC signal source, and a measurement target. a sensor unit that outputs a detection signal according to a physical quantity for an object; a compensation unit that receives an AC signal, amplifies the AC signal using a first gain for setting a zero point, and provides a phase shift for setting a zero point; , a first subtraction unit that subtracts the output signal of the compensation unit from the detection signal of the sensor unit, and a first signal processing unit including a first rectification circuit and a first amplifier, the difference signal being output from the first subtraction unit. a first signal processing section that rectifies and amplifies the output signal with a second gain; a second rectifier circuit that rectifies the output signal output from the compensation section; A DC constant voltage generation section that generates a first DC constant voltage signal, a second subtraction section that subtracts the first DC constant voltage signal from the output signal of the second rectifier circuit, and a subtraction signal output from the second subtraction section. The device includes a second amplifier that amplifies with a second gain, and an adder that adds the output signal of the first amplifier and the output signal of the second amplifier.

According to the first aspect of the present invention, the output signal of the compensation unit that amplifies the AC signal by the first gain for zero point setting and provides a phase shift for zero point setting is subtracted from the detection signal of the sensor unit. do. As a result, when the sensor section outputs a detection signal at an arbitrary measurement point whose resolution is desired to be improved (hereinafter referred to as a "virtual zero point"), a difference signal is obtained by subtracting the output signal of the compensation section from the detection signal. becomes a signal of almost 0 level.

The difference signal is then amplified by the second gain by the first signal processing section, but since it becomes a signal of almost 0 level at the "virtual zero point", it is possible to increase the second gain, and the "virtual zero point" is amplified by the second gain. The resolution near the zero point can be improved. Additionally, if the amplification of the AC signal changes due to the influence of temperature, etc., the detection signal of the sensor unit will change proportionally, but even if the amplitude of the AC signal changes, the difference signal at the "virtual zero point" will always be zero. Therefore, it is possible to suppress a reduction in measurement accuracy near the "virtual zero point".

On the other hand, by rectifying the output signal output from the compensation section in the second rectifier circuit and then adding the output signal of the second amplifier that is amplified with the second gain to the output signal of the first signal processing section, Even if the amplitude and phase of the output signal of the compensator are different from the output signal of the sensor at the "virtual zero point", the effect will be canceled and the measurement accuracy and resolution near the "virtual zero point" will be affected. You can prevent it from happening.

Further, the output signal output from the second amplifier is a first DC constant voltage signal from the DC constant voltage generator (a first DC constant voltage signal proportional to the product of the voltage signal indicating the first amplitude of the AC signal and the first gain). Since the voltage signal obtained by amplifying the constant voltage signal) with the second gain is subtracted, it becomes zero when the measurement point is the "virtual zero point", thereby making it possible to set the "zero point".

In the physical quantity measuring device according to a second aspect of the present invention, in the first aspect, the first signal processing section rectifies the difference signal with the first rectifier circuit, and amplifies the rectified rectified signal with a second gain using the first amplifier. Alternatively, it is preferable that the difference signal is amplified with a second gain by a first amplifier, and the amplified signal is rectified by a first rectifier circuit.

The first signal processing section may rectify the difference signal output from the subtraction section and then amplify it using the second gain, or amplify the difference signal output from the subtraction section using the second gain and then rectify it. However, the former is preferable. This is because the signal input to the first amplifier can be made smaller.

In the physical quantity measuring device according to the third aspect of the present invention, in the first aspect or the second aspect, the output signal of the sensor section has the same frequency as the AC signal, and the amplitude changes depending on the physical quantity with respect to the object to be measured. , and is a signal whose phase changes.

In the physical quantity measuring device according to the fourth aspect of the present invention, in the third aspect, the first gain for zero point setting is determined by the sensor unit when the first amplitude of the AC signal and the physical quantity of the object to be measured are preset physical quantities. The phase shift for zero point setting is the ratio of the amplitude of the detection signal output from the sensor unit to the amplitude of the detection signal output from the sensor unit, and the phase shift for zero point setting is the phase difference between the detection signal output from the sensor unit and the AC signal when the physical quantity of the measurement object is a preset physical quantity. Preferably, there is a deviation.

In the physical quantity measuring device according to the fifth aspect of the present invention, in the fourth aspect, it is preferable that the compensation section includes a resistor and a capacitor selected according to the first gain and the phase shift. By selecting a resistor and a capacitor according to the first gain and phase shift, a "virtual zero point" can be set.

In a physical quantity measuring device according to a sixth aspect of the present invention, in any one of the first to fifth aspects, the AC signal source includes an oscillator that generates a reference signal having the frequency of the AC signal, and amplifies the reference signal; a variable amplifier that generates an AC signal; a third rectifier circuit that rectifies the AC signal output from the variable amplifier and outputs a DC voltage signal indicating the amplitude of the AC signal; and a second DC constant voltage corresponding to the first amplitude. A DC constant voltage source that outputs a signal, and a gain adjustment section that adjusts the gain of the variable amplifier so as to make the difference voltage zero based on the voltage difference between the second DC constant voltage signal and the DC voltage signal. is preferred. This makes it possible to stabilize the amplitude of the AC signal oscillated from the oscillator, and to prevent a problem in which the sensor output varies in proportion to fluctuations in the amplitude of the AC signal.

In the physical quantity measuring device according to the seventh aspect of the present invention, in the sixth aspect, the DC constant voltage generation section inputs the second DC constant voltage signal from the DC constant voltage source, and converts the second DC constant voltage signal into the first gain. It is preferable to generate a first DC constant voltage signal proportional to . The DC constant voltage generation section amplifies the second DC constant voltage signal for controlling the amplitude of the AC signal and generates the first DC constant voltage signal. can be linked to each other, further improving measurement accuracy (reducing errors due to differences between both signals).

In the physical quantity measuring device according to an eighth aspect of the present invention, in any one of the first to seventh aspects, the sensor section has a detection coil to which an AC signal generated from an AC signal source is applied, and the sensor unit has a single-end Preferably, the sensor outputs a detection signal based on an operation. The present invention is particularly effective for a sensor unit that operates in a single-end manner and cannot set a zero point in the detection signal itself.

In a physical quantity measuring device according to a ninth aspect of the present invention, in any one of the first to seventh aspects, the sensor section includes a primary coil to which an AC signal generated from an AC signal source is applied, and two secondary coils. It is preferable that the sensor is a differential transformer type displacement sensor that includes a coil and a magnetic core connected to a probe that moves in contact with the object to be measured, and that outputs a detection signal corresponding to the displacement of the probe. In the case of a differential transformer type displacement sensor, the sensor output can be adjusted to zero at the zero point, which is the mechanical reference point. You can set a virtual zero point.

According to the present invention, resolution near an arbitrarily set measurement point (virtual zero point) can be improved.

FIG. 1 is a configuration diagram showing an embodiment of a physical quantity measuring device according to the present invention. FIG. 2(A) is a schematic diagram showing an example of the sensor section shown in FIG. 1, and FIG. 2(B) is a diagram showing the positional relationship between the eddy current sensor and the object to be measured. FIG. 3 is a waveform diagram showing a detection signal that changes depending on the distance to the object to be measured. FIG. 4 is a circuit diagram showing an example of the complex compensation circuit shown in FIG. 1. FIG. 5 is a waveform diagram showing an outline of signals output from each part of the physical quantity measuring device. FIG. 6 is a configuration diagram showing a preferred embodiment of the oscillation section and DC constant voltage generation section shown in FIG. FIG. 7 is a schematic diagram showing another example of the sensor section shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a physical quantity measuring device according to the present invention will be described below with reference to the accompanying drawings.

[Configuration of physical quantity measuring device]
FIG. 1 is a configuration diagram showing an embodiment of a physical quantity measuring device according to the present invention.

The physical quantity measuring device 1 of this embodiment includes an AC signal source 10, a sensor section 20, a complex compensation circuit 30 functioning as a compensation section, a first subtraction section 40, a first signal processing section 50, a second signal processing section 60, and It is composed of an adding section 90.

The AC signal source 10 oscillates an AC signal a with an amplitude (first amplitude) V ₀ and outputs it to the sensor section 20 and the complex compensation circuit 30, respectively.

The sensor unit 20 receives an AC signal a from the AC signal source 10 and outputs a detection signal b corresponding to a physical quantity of the object to be measured.

<Example of sensor part>
FIG. 2(A) is a schematic diagram showing an example of the sensor section 20 shown in FIG. 1, and FIG. 2(B) is a diagram showing the positional relationship between the eddy current sensor 20-1 and the measurement target 24. be.

The sensor section shown in FIG. 2A is an eddy current sensor 20-1, and has a detection coil 22 to which an AC signal a is applied from an AC signal source 10. The detection coil 22 can be considered as a series circuit of an impedance 22A and a resistance 22B. In FIG. 2, 22C and 22D are additional impedances of the detection coil 22 viewed from the AC signal source 10 side.

An alternating current signal a with an amplitude V ₀ is supplied from the alternating current signal source 10 to the detection coil 22 through an additional impedance 22C, and an alternating magnetic field is generated from the detection coil 22. When there is a measurement object 24 made of a metal material within this alternating magnetic field, an eddy current flows on the surface of the measurement object 24 in a direction perpendicular to the passage of magnetic flux due to electromagnetic induction, and the impedance 22A of the detection coil 22 changes. The magnitude of the eddy current changes depending on the distance x between the detection coil 22 and the measurement object 24.

Due to this phenomenon, the eddy current sensor 20-1 outputs a detection signal b whose amplitude changes depending on the distance x from the object to be measured 24.

FIG. 3 is a waveform diagram showing a detection signal that changes depending on the distance x from the measurement object 24.

As shown in FIG. 3, the detection signal output from the eddy current sensor 20-1 changes in amplitude depending on the distance x from the object to be measured 24, and a phase shift occurs.

An example of improving the detection sensitivity of the eddy current sensor 20-1 is to adjust 22C and 22D so that the longer the distance x is, the larger the amplitude of the detection signal is. In the case of this adjustment, generally speaking, the longer the distance x is, the larger the phase shift (phase lead) becomes.

Note that the detection sensitivity of the eddy current sensor 20-1 may be improved by other means, and even if the relationship between the distance x and the amplitude of the detection signal or the manner in which the phase shift occurs exhibits different behavior, The technology described in this specification is of course effective.

Here, the complex ratio between the AC signal a applied to the detection coil 22 and the detection signal of the eddy current sensor 20-1 (hereinafter referred to as "sensor gain") is the difference between the eddy current sensor 20-1 and the measurement target. It is determined by the distance x from the object 24. Note that among the behaviors of the sensor gain, behaviors that are independent of the distance x are considered as error factors.

Furthermore, the eddy current sensor 20-1 is a single-end operated sensor that cannot set a zero point in the detection signal itself output by the eddy current sensor 20-1, and has a complex impedance-like response to the AC signal a. do.

Returning to FIG. 1, the complex compensation circuit 30 inputs the AC signal a from the AC signal source 10, amplifies the AC signal a by a first gain P for setting the zero point, and adjusts the phase shift ( θ) (hereinafter, outputting an AC signal in which the input AC signal is multiplied by a real number and whose phase is shifted is also referred to as ``complex response'').

That is, the complex compensation circuit 30 sets the sensor gain at an arbitrary measurement point (virtual zero point) whose resolution is desired to be improved as the first gain (P) for zero point setting, and calculates the phase shift with respect to the AC signal a at the virtual zero point. is the phase shift (θ) for zero point setting, the AC signal a is amplified by the first gain (P), and the phase shift (θ) is applied to the amplified AC signal a.

Thereby, the complex compensation circuit 30 makes its output signal c (V ₁ in the figure) coincide with the detection signal b of the sensor unit 20 at the virtual zero point.

FIG. 4 is a circuit diagram showing an example of the complex compensation circuit 30 shown in FIG. 1.

As shown in FIG. 4, the complex compensation circuit 30 can be composed of impedance elements (resistors, capacitors, and inductors) 31 to 34 and an amplification element (op-amp) 35. The impedance elements 31 to 34 are appropriately selected depending on the first gain (P) and phase shift (θ).

Note that the impedance elements 31 to 34 are not limited to resistors, capacitors, and inductors, and other elements may be used as long as the complex compensation circuit 30 has a complex response. Further, the amplification element 35 is not limited to an operational amplifier, and other elements may be used as long as the complex compensation circuit 30 has a complex response. Furthermore, the circuit configuration of the complex compensation circuit 30 may be a configuration other than the circuit shown in FIG. 4 as long as the complex compensation circuit 30 has a complex response.

Specifically, if the complex voltage signals in signals a and c are Va and Vc, respectively, and the complex impedances of impedance elements 31 to 34 are Z31 to Z34, respectively, then the complex amplification factor Vc/Va of this circuit is expressed by the following formula,
[Number 1]
Vc/Va={Z32・(Z33+Z34)}/{(Z31+Z32)・Z33}
becomes. The impedance elements 31 to 34 may be selected so that the absolute value of the right side is P and the deflection angle is θ.

Note that a complex voltage signal represents the voltage state of an AC signal having the same frequency as the AC signal source 10 with a single complex value, and the absolute value of the complex value matches the amplitude of the voltage signal. The argument angle of the value is a quantity expressed by the leading phase from the signal of the AC signal source 10.

Further, it is assumed that the complex impedance of each impedance element is a complex impedance value when a current of the same frequency as the AC signal source 10 is passed.

Here, the output signal c output from the complex compensation circuit 30 does not have to be made to completely match the detection signal b of the sensor unit 20 at the virtual zero point, but may be slightly shifted.

Since the constants of commonly available inexpensive resistors and capacitors are discrete and have large tolerances, it is difficult to accurately create a phase difference between input and output signals.

Further, it is not easy to always keep the phase of the output signal constant with respect to the input signal for the following reasons.

(1) The constants of commonly available inexpensive resistors and capacitors change due to changes in ambient temperature, etc.

(2) Even if the frequency of AC signal a changes, the relationship between the amplitude and phase of the input and output signals will change.

(3) The complex amplification factor also changes depending on the performance (temperature characteristics, linearity, etc.) of the amplifier element and circuit configuration of the amplifier circuit.

However, the output signal c output from the complex compensation circuit 30 does not need to completely match the detection signal b of the sensor section 20 at the virtual zero point, as will be described later. It can be constructed by appropriately selecting inexpensive resistors and capacitors that are on the market, and a simple circuit construction like the circuit 30 can be used.
Ru.

Returning to FIG. 1, the first subtraction unit 40 receives the detection signal b from the sensor unit 20 and the output signal c from the complex compensation circuit 30, and the first subtraction unit 40 receives the detection signal b from the detection signal b. The output signal c is subtracted, and the difference signal d is output to the first signal processing section 50.

Note that when the sensor unit 20 outputs the detection signal b at the virtual zero point, the difference signal d (V ₂ in the figure) becomes zero. This is because the output signal c (V ₁ in the figure) output from the complex compensation circuit 30 is generated to match the detection signal b at the virtual zero point. Furthermore, in this example, the signal level becoming zero due to addition and subtraction etc. includes the case where the signal level becomes almost zero.

The first signal processing section 50 includes a first rectifier circuit 52 and a first amplifier 54.

The first rectifier circuit 52 rectifies the difference signal d output from the first subtractor 40. The first rectifier circuit 52 is preferably a circuit that responds linearly, and is preferably a synchronous rectifier circuit that performs a switching operation depending on the polarity (zero-crossing point) of the input signal, for example. Since the difference signal d becomes a signal of approximately 0 level at the "virtual zero point," the rectified signal e also becomes a signal of approximately 0 level at the "virtual zero point."

The first amplifier 54 amplifies the rectified signal e output from the first rectifier circuit 52 using the second gain (A) of the first amplifier 54. Since the rectified signal e becomes a signal of approximately 0 level at the "virtual zero point", the second gain (A) can be increased, and the resolution near the "virtual zero point" can be improved.

The second signal processing section 60 includes a second rectifying circuit 62, a DC constant voltage generating section 64, a second subtracting section 66, and a second amplifier 68.

The second rectifier circuit 62 has the same configuration as the first rectifier circuit 52, and the second amplifier 68 has the same configuration as the first amplifier 54.

The second rectifier circuit 62 rectifies the signal c output from the complex compensation circuit 30. The level of the signal c is determined by the configuration of the complex compensation circuit 30, but strictly speaking, there may be a slight deviation from the ideal value depending on the impedance element and amplification element used in the circuit 30, and the performance of the circuit configuration, and there may be slight fluctuations. occurs.

The DC constant voltage generator 64 is configured to output a first DC constant voltage signal h assuming that the complex compensation circuit 30 outputs an ideal signal. Note that "constant voltage signal assuming ideal signal output" here includes a constant voltage signal that is almost the same as "constant voltage signal assuming ideal signal output". shall be held.

From the above, the rectified signal g becomes a signal slightly shifted from the first DC constant voltage signal h output from the DC constant voltage generation section 64.

The rectified signal g is input to the positive input of the second subtractor 66, and the first constant DC voltage h is input to the negative input. That is, the second subtractor 66 outputs a difference signal obtained by subtracting the first DC constant voltage h from the rectified signal g.

As described above, since the rectified signal g is a signal slightly deviated from the first DC constant voltage h, the difference signal h becomes a signal of approximately 0 level.

The second amplifier 68 amplifies the difference signal i output from the second subtractor 66 by a second gain (A). Since the difference signal i is a signal at approximately 0 level, the second gain (A) can be increased. That is, the gain of the second signal processing section 60 can be the same as the gain of the first signal processing section 50.

The result f of the first signal processing section 50 and the result j of the second signal processing section 60 are each input to the addition section 90. That is, a signal obtained by adding the result f and the result h is output as the signal k to the output of the adder.

Note that the first signal processing unit 50 of this example rectifies the input difference signal d with the first rectifier circuit 52, and amplifies the rectified rectified signal e with the second gain (A) using the first amplifier 54. The input difference signal d may be amplified by the first amplifier 54 with a second gain (A), and the amplified signal may be rectified by the first rectifier circuit 52.

Further, the DC constant voltage generation unit 64 can generate the first DC constant voltage signal h using the voltage signal indicating the amplitude V ₀ and the first gain (P), but is not limited to this, and the complex compensation Any device may be used as long as it generates an output signal assuming that the circuit 30 outputs an ideal signal. In addition, in this example, the explanation is given on the assumption that the amplitude of the input signal and the DC voltage of the output signal are equal in the first rectifier circuit 52 and the second rectifier circuit 62 for the sake of simplicity. By setting the sensitivity of each circuit (constant DC voltage generating section 64), it is not necessary to equalize the amplitude of the input signal and the DC voltage of the output signal.

When the output signal c (V ₁ in the figure) of the complex compensation circuit 30 is rectified, it becomes the same voltage signal as the DC constant voltage generator 64, so the difference signal i output from the second subtractor 66 and this The signal j (V ₃ in the figure) multiplied by A becomes zero. However, the actual _V3 is not held at zero, but takes a value near zero. For example, the amplitude (V ₀ ×P) of the output signal c output from the complex compensation circuit 30 may vary due to changes in ambient temperature, etc., but in this case, a signal j corresponding to the variation will be output. Become.

The adder 90 adds the output signal f output from the first signal processor 50 and the output signal j output from the second signal processor 60, and uses the addition result as the measurement signal k by the physical quantity measuring device 1. Output.

Now, focusing on the output signal c output from the complex compensation circuit 30, this output signal c is inverted and rectified and amplified by the first signal processing unit 50 in one system, and is directly transmitted to the first signal processing unit 50 in the other system. After being rectified and amplified by the second signal processing section 60, the output signal of the first signal processing section 50 and the output signal of the second signal processing section 60 are added. Therefore, the influence of the output signal c is canceled in the measurement signal k output from the adder 90.

Thereby, as described above, the output signal c output from the complex compensation circuit 30 does not have to completely match the detection signal b of the sensor section 20 at the virtual zero point.

Further, the first constant DC voltage signal h output from the constant DC voltage generating section 64 acts so that the measurement signal k at the virtual zero point becomes zero.

From the above, at any circuit point of the physical quantity measuring device 1, even if the second gain (A) of the first amplifier 54 is larger than the conventional maximum settable gain, the dynamic range (analog signal variation In addition, by increasing the second gain (A) of the first amplifier 54, the resolution near the virtual zero point can be improved.

FIG. 5 is a waveform diagram showing an overview of signals output from each part of the physical quantity measuring device 1.

In addition, in FIG. 5, FIGS. 5(A) to 5(K) respectively show the signals a to k in FIG. The dotted line indicates the case where the measurement target 24 is located at a distance farther than the distance of the virtual zero point.

First, the waveforms of signals at each part in the case of a virtual zero point will be explained.

FIG. 5A is a waveform diagram showing an excitation AC signal a generated from the AC signal source 10. In FIG.

The solid line in FIG. 5(B) indicates the detection signal b of the sensor unit 20 when the measurement target 24 is at a distance from the virtual zero point. In this case, the detection signal b of the sensor unit 20 has a smaller amplitude and is out of phase than the AC signal a.

FIG. 5C is a waveform diagram showing the output signal c output from the complex compensation circuit 30. The output signal c of the complex compensation circuit 30 matches the detection signal b shown by the solid line in FIG. 5(B) by adjusting the gain and phase with respect to the AC signal a.

FIG. 5(D) is a waveform diagram showing the difference signal d output from the first subtractor 40. The difference signal d shown by the solid line in FIG. 5(D) is a difference signal between the detection signal b and the output signal c at the virtual zero point, and is therefore zero.

FIGS. 5E and 5F are waveform diagrams showing the output signal e of the first rectifier circuit 52 which rectified the difference signal d, and the output signal f of the first amplifier 54 which amplified the signal, respectively. As shown by the solid lines in FIGS. 5(E) and 5(F), the output signal e of the first rectifier circuit 52 which rectified the zero difference signal d and the output signal f of the first amplifier 54 which amplified the same are respectively It is zero.

FIG. 5(G) is a waveform diagram showing the output signal g of the second rectifier circuit 62 which rectified the signal c shown in FIG. 5(C).

FIG. 5(H) is a waveform diagram showing the first DC constant voltage signal h generated from the DC constant voltage generator 64. This first DC constant voltage signal h matches the output signal g of the second rectifier circuit 62 shown in FIG. 5(G).

FIG. 5(I) is a waveform diagram showing the difference signal i output from the second subtractor 66. The second subtraction unit 66 subtracts the first DC constant voltage signal h from the rectified signal of the output signal of the complex compensation circuit 30 (the signal obtained by multiplying the amplitude V ₀ by P by the first gain (P)). The difference signal i is zero.

FIG. 5(J) is a waveform diagram showing the output signal j of the second amplifier 68 which amplifies the signal i shown in FIG. 5(I) by the second gain (A). Since it is a signal obtained by amplifying the difference signal i which is zero, the output signal j is zero.

FIG. 5(K) is a waveform diagram showing the measurement signal k output from the adder 90. In the case of the virtual zero point, the measurement signal k output from the adding section 90 is such that the output signal f of the first signal processing section 50 shown by the solid line in FIG. 5(F) is zero, and the measurement signal k is shown as shown in FIG. Since the output signal j of the second signal processing section 60 is also zero, the measurement signal k indicating the result of these additions is also zero.

That is, when the measurement object 24 is located at a distance from the virtual zero point, the signal level of the measurement signal k becomes zero.

Next, a case will be described in which the measurement target object 24 is located at a distance farther than the distance of the virtual zero point.

When the sensor unit 20 is the eddy current sensor 20-1 shown in FIG. In addition, a phase shift occurs. When the measurement target 24 is located at a distance farther than the distance to the virtual zero point, the amplitude of the detection signal b shown by the dotted line in FIG. 5(B) is larger than the amplitude when the distance to the virtual zero point is shown by the solid line. and the phase advances.

The difference signal d output from the first subtractor 40 changes in accordance with the change in the detection signal b, and the difference signal d becomes as shown by the dotted line in FIG. 5(D).

A signal e obtained by rectifying the difference signal d shown by the dotted line in FIG. 5(D) and a signal f amplified by the second gain (A) are as shown by the dotted lines in FIG. 5(E) and (F), respectively. become.

The measurement signal k shown by the dotted line in FIG. 5(K) is the output signal f of the first signal processing section 50 shown by the dotted line in FIG. 5(F) and the output signal of the second signal processing section 60 shown in FIG. 5(J). However, since the signal j is zero, the measurement signal k becomes a signal equivalent to the output signal f of the first rectifier circuit 52 shown by the dotted line in FIG. 5(F).

That is, when the measurement object 24 changes to a different distance from the distance of the virtual zero point, the measurement signal k is rectified by the first rectifier circuit 52, and the amount of change in the detection signal b corresponding to the change is rectified by the first rectifier circuit 52. 54, the signal is outputted as a measurement signal k multiplied by A. In particular, since the signal e obtained by rectifying the variation of the detection signal b from the virtual zero point is input to the first amplifier 54, the second gain (A) in the first amplifier 54 can be increased. The resolution of the measurement signal k when measuring the distance near the virtual zero point can be improved.

<Embodiment of AC signal source and DC constant voltage generator>
FIG. 6 is a configuration diagram showing a preferred embodiment of the AC signal source 10 and the DC constant voltage generator 64 shown in FIG.

The AC signal source 10 shown in FIG. It is composed of a voltage source 15 and an amplifier 18.

The oscillator 11 oscillates a reference signal having the frequency of an alternating current signal, and outputs it to the negative input of a variable amplifier 12 made up of an operational amplifier. The variable amplifier 12 amplifies the reference signal and outputs it as an alternating current signal, and an analog photocoupler 12A is provided in its negative feedback circuit. Since the resistance of the negative feedback circuit changes depending on the magnitude of the current flowing through the analog photocoupler 12A, the gain of the variable amplifier 12 for amplifying the reference signal changes depending on the magnitude of the current flowing through the analog photocoupler 12A. and functions as a variable amplifier.

Specifically, when the current flowing through the analog photocoupler 12A increases, the resistance of the negative feedback circuit decreases, and the gain of the variable amplifier 12 also decreases; conversely, when the current flowing through the analog photocoupler 12A decreases, the negative feedback circuit decreases. The resistance of the variable amplifier 12 increases, and the gain of the variable amplifier 12 also increases.

The AC signal output from the variable amplifier 12 is added to the third rectifier circuit 14 , and the third rectifier circuit 14 rectifies the input AC signal and inputs the rectified DC voltage signal to the negative input of the subtraction unit 16 . Output to. It is assumed that the third rectifier circuit 14 of this example outputs a DC voltage signal indicating the amplitude of the input AC signal.

A DC constant voltage signal (second DC constant voltage signal) of voltage V ₀ is applied from the DC constant voltage source 15 to the positive input of the subtraction unit 16 . The second DC constant voltage signal of voltage V ₀ is a reference voltage signal set corresponding to the desired amplitude V ₀ (first amplitude) of the AC signal generated via the variable amplifier 12.

The subtraction unit 16 subtracts the output signal (DC voltage signal) of the third rectifier circuit 14 from the second DC constant voltage signal. The subtracted differential voltage signal is applied to the negative input of the operational amplifier 17 via the input resistance. The operational amplifier 17 inverts and amplifies the input differential voltage signal and outputs it to the analog photocoupler 12A. Note that a capacitor is placed in the negative feedback of the operational amplifier 17, and the operational amplifier 17 behaves as an integrating circuit (integral value x -1), so if a negative voltage is input to V4, the output of the operational amplifier 17 will be If the voltage continues to increase and a positive voltage is input to V4, the output of the operational amplifier 17 continues to decrease.

The current flowing through the analog photocoupler 12A decreases as the output voltage of the operational amplifier 17 decreases, and the gain of the variable amplifier 12 increases, and increases as the output voltage of the operational amplifier 17 increases, and the gain of the variable amplifier 12 decreases.

Therefore, the subtraction section 16 and the operational amplifier 17 function as a gain adjustment section that adjusts the gain of the variable amplifier 12, and the circuit constituted by the third rectifier circuit 14, the subtraction section 16, and the operational amplifier 17 outputs the output from the subtraction section 16. It functions as a feedback circuit that adjusts the gain of the variable amplifier 12 so that (V ₄ ) is always zero. As a result, the amplitude of the AC signal output from the variable amplifier 12 is maintained at the voltage V ₀ of the second DC constant voltage signal from the DC constant voltage source 15 .

According to the AC signal source 10 shown in FIG. 6, even if the amplitude of the reference signal output from the oscillator 11 fluctuates due to ambient temperature or the like, it is possible to stably output an AC signal with an amplitude _V0 .

Further, the amplification factor B of the amplifier 18 constituting the DC constant voltage generating section 64 is such that the amplifier 18 outputs the same (or almost the same) signal as the output signal when the complex compensation circuit 30 outputs an ideal signal. Decide to output. Specifically, the amplification factor B is determined to have the following value.

B=P×A×cosθ
_The AC signal source 10 and the DC constant voltage generator ₆₄ shown in FIG. Since the first DC constant voltage signal (V ₀ ×P × cos θ) is output, the measurement signal generated using these signals has higher measurement accuracy.

<Other examples of sensor section>
FIG. 7 is a schematic diagram showing another example of the sensor section 20 shown in FIG. 1.

The sensor section shown in FIG. 7 is a differential transformer type displacement sensor 20-2.

This differential transformer type displacement sensor 20-2 includes a primary coil 25 to which an AC signal generated from an AC signal source 10 is applied, and two secondary coils 26A and 26B connected in series with opposite polarities. It has a magnetic core 28 connected to a measuring stylus 27 that moves in contact with the object to be measured, and outputs a detection signal corresponding to the displacement of the measuring stylus 27.

In the differential transformer type displacement sensor 20-2, when the primary coil 25 is excited by an AC signal, a differential output proportional to the position of the magnetic core 28 (gauge head 27) is generated from the two secondary coils 26A and 26B. A signal is induced and output as a detection signal.

As shown in FIG. 7, when the magnetic core 28 is located at the center of the two secondary coils 26A, 26B, the mutual inductance of the two secondary coils 26A, 26B with respect to the primary coil 25 is equal; Since the output voltages of 26B are also equal and the phases are 180° different from each other, the detection signal becomes zero.

Therefore, in the differential transformer type displacement sensor 20-2, the point where the detection signal becomes zero (ie, the state where the probe 27 is not in contact with the object to be measured) is generally set as the zero point.

However, if the differential transformer type displacement sensor 20-2 is used as the sensor section of the physical quantity measuring device 1 shown in FIG. It can be set as a virtual zero point, and the resolution around the virtual zero point can be improved.

[others]
The signals output from each part of the physical quantity measuring device 1 of this embodiment are analog signals, but the analog signal is not limited to this, but the analog signal is converted to a digital signal by an A/D converter, and some processing of the physical quantity measuring device is performed. may be digitally processed. For example, an A/D converter is placed after the first signal processing section 50 and the second signal processing section 60, and these A/D converters sample the two systems at the same timing, and the subsequent processing is performed using software or hardware. Signal processing can be digitally processed.

Further, the sensor section 20 is not limited to the eddy current sensor 20-1 and the differential transformer type displacement sensor 20-2, but may be any sensor as long as it has a complex response.

Furthermore, it goes without saying that the present invention is not limited to the embodiments described above, and that various modifications can be made without departing from the spirit of the present invention.

1 Physical quantity measuring device 10 AC signal source 11 Oscillator 12 Variable amplifier 12A Analog photocoupler 14 Third rectifier circuit 15 DC constant voltage source 16 Subtraction section 17, 35 Operational amplifier 18 Amplifier 20 Sensor section 20-1 Eddy current sensor 20-2 Displacement sensor 22 Detection coil 22A Impedance 22B Resistance 22C, 22D Additional impedance 24 Measurement object 25 Primary coil 26A Secondary coil 26B Secondary coil 27 Measuring element 28 Magnetic core 30 Complex compensation circuits 31 to 34 Impedance element 40 First subtraction section 50 First Signal processing section 52 First rectification circuit 54 First amplifier 60 Second signal processing section 62 Second rectification circuit 64 DC constant voltage generation section 66 Second subtraction section 68 Second amplifier 90 Addition section

Claims (9)

an AC signal source that generates an AC signal with a first amplitude;
a sensor unit that receives an AC signal generated from the AC signal source and outputs a detection signal according to a physical quantity of the object to be measured;
a compensation unit that inputs the AC signal, amplifies the AC signal by a first gain for setting a zero point, and provides a phase shift for setting the zero point;
a first subtraction unit that subtracts the output signal of the compensation unit from the detection signal of the sensor unit;
a first signal processing section including a first rectification circuit and a first amplifier, the first signal processing section rectifying and amplifying the difference signal output from the first subtraction section using a second gain;
a second rectifier circuit that rectifies the output signal output from the compensation section;
a DC constant voltage generator that generates a first DC constant voltage signal proportional to the product of the first amplitude and the first gain;
a second subtraction unit that subtracts the first DC constant voltage signal from the output signal of the second rectifier circuit;
a second amplifier that amplifies the difference signal output from the second subtraction section with a second gain;
an adder that adds the output signal of the first amplifier and the output signal of the second amplifier;
A physical quantity measuring device equipped with The first signal processing section rectifies the difference signal by the first rectifier circuit, amplifies the rectified rectified signal by the first amplifier with a second gain, or amplifies the difference signal by the first amplifier with a second gain. amplifying with a gain of 2 and rectifying the amplified signal by the first rectifier circuit;
The physical quantity measuring device according to claim 1. The output signal of the sensor unit has the same frequency as the alternating current signal, and is a signal whose amplitude changes and phase changes depending on the physical quantity with respect to the object to be measured.
The physical quantity measuring device according to claim 1 or 2. The first gain for setting the zero point is a ratio between the first amplitude of the AC signal and the amplitude of the detection signal output from the sensor unit when the physical quantity of the measurement object is a preset physical quantity,
The phase shift for zero point setting is a phase shift between the detection signal output from the sensor unit and the alternating current signal when the physical quantity of the measurement object is a preset physical quantity.
The physical quantity measuring device according to claim 3. The physical quantity measuring device according to claim 4, wherein the compensation section includes a resistor and a capacitor selected according to the first gain and the phase shift. The AC signal source is
an oscillator that generates a reference signal having a frequency of the alternating current signal;
a variable amplifier that amplifies the reference signal and generates the alternating current signal;
a third rectifier circuit that rectifies the AC signal output from the variable amplifier and outputs a DC voltage signal indicating the amplitude of the AC signal;
a DC constant voltage source that outputs a second DC constant voltage signal corresponding to the first amplitude;
a gain adjustment unit that adjusts the gain of the variable amplifier so as to make the difference voltage zero based on the difference voltage between the second DC constant voltage signal and the DC voltage signal;
The physical quantity measuring device according to any one of claims 1 to 5, comprising: The DC constant voltage generator receives the second DC constant voltage signal from the DC constant voltage source and generates the first DC constant voltage signal in which the second DC constant voltage signal is proportional to the first gain. ,
The physical quantity measuring device according to claim 6. The sensor unit is a sensor that has a detection coil to which an AC signal generated from the AC signal source is applied, and outputs the detection signal by single-ended operation.
The physical quantity measuring device according to any one of claims 1 to 7. The sensor section includes a primary coil to which an alternating current signal generated from the alternating current signal source is applied, two secondary coils, and a magnetic core connected to a measuring tip that moves in contact with the object to be measured. and a differential transformer type displacement sensor that outputs the detection signal corresponding to the displacement of the measuring head,
The physical quantity measuring device according to any one of claims 1 to 7.

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