JP6509644B2 - Piezoelectric sensor - Google Patents

Description

  The present invention relates to a piezoelectric sensor, and in particular, suitably used for a piezoelectric acceleration sensor, a piezoelectric pressure sensor, or the like corresponding to temperature compensation of voltage sensitivity in the entire range from low temperature to high temperature (for example, -50 ° C to 170 ° C). The present invention relates to a piezoelectric sensor that can

  The conventional piezoelectric sensor includes, for example, a piezoelectric element and a charge amplifier electrically connected to the piezoelectric element. Also, the charge amplifier has a feedback capacitor. As the feedback capacitor, a capacitor (hereinafter referred to as "the same material capacitor") which is made of the same material as the piezoelectric element and which is not polarized is used (see Patent Document 1).

Japanese Patent Application Laid-Open No. 05-60643

  However, in the conventional piezoelectric sensor, even if the same material capacitor is used as the feedback capacitor, the change rate of the capacitance of the feedback capacitor becomes larger than the change rate of the charge sensitivity of the piezoelectric element. The voltage sensitivity Sv of the piezoelectric sensor is proportional to the charge sensitivity Sq of the piezoelectric element and inversely proportional to the capacitance Cf of the feedback capacitor (Sv = Sq / Cf). As a result, when the operating temperature changes to the low temperature side or the high temperature side with respect to the reference temperature such as room temperature, there is a problem that the change rate of the voltage sensitivity Sv becomes large.

  Also, even if it is theoretically possible to make the rate of change of the charge sensitivity of the piezoelectric element and the rate of change of the electrostatic capacitance of the feedback capacitor approximately the same, considering that product errors of the piezoelectric element inevitably occur, There is a problem that it is technically and economically difficult to select or manufacture such an ideal feedback capacitor.

  Therefore, the present invention has been made in view of these points, and it is an object of the present invention to provide a piezoelectric sensor capable of easily realizing temperature compensation of voltage sensitivity with high accuracy.

  (1) In order to achieve the above object, the piezoelectric sensor of the present invention has a piezoelectric element and a piezoelectric element and a first feedback capacitor composed of the same material capacitor which is made of the same material as the piezoelectric element and is not polarized. A charge amplifier electrically connected to the piezoelectric element, having a feedback capacitor unit configured by connecting a second feedback capacitor having a capacitance with a temperature change rate smaller than a temperature change rate of charge sensitivity; It is characterized by having.

  As a result, the temperature change rate of the electrostatic capacitance is made larger than the temperature change rate of the charge sensitivity of the piezoelectric element, and the first feedback capacitor and the piezoelectric element have the same tendency as the charge sensitivity of the piezoelectric element with respect to temperature. Since the circuit combining the second feedback capacitor having the capacitance of the temperature change rate smaller than the charge sensitivity temperature change rate is used as the feedback capacitor unit, the temperature change rate of the capacitance of the feedback capacitor unit is a piezoelectric element It can be easily set to a value similar to the rate of change in temperature of charge sensitivity possessed by In addition, the capacitance of the first feedback capacitor and the second feedback capacitor is about 10 to 1000 pF in the relationship with the gain of the charge amplifier, and their respective sizes are small. The size of the capacitor unit also remains small. As a result, the piezoelectric sensor of the present invention can be made comparable in size to the conventional one.

  (2) Further, in the piezoelectric sensor of the present invention, it is preferable that the temperature coefficient of the second feedback capacitor is ± 100 ppm / ° C. or less within the allowable temperature range of the piezoelectric sensor.

  As a result, even if the temperature change rate of the second feedback capacitor is approximated to 0, the temperature change rate of the feedback capacitor unit can be set with an accuracy of about ± 5%, so that the first feedback capacitor and the second feedback capacitor The effort of selecting each capacitance can be greatly reduced.

  (3) Moreover, in the piezoelectric sensor of the present invention, the second feedback capacitor is preferably a ceramic capacitor.

  Thus, the temperature coefficient of the ceramic capacitor as the second feedback capacitor is ± about 30 ppm / ° C. Therefore, even if the temperature change rate is made close to 0, the temperature change rate of the feedback capacitor unit is accurate to about ± 2%. Since it is possible to set, it is possible to greatly reduce the effort of selecting each capacitance of the first feedback capacitor and the second feedback capacitor. In addition, commercially available ceramic capacitors are easily available, and can increase the degree of freedom of selection of the second feedback capacitor. In addition, since the second feedback capacitor is a ceramic capacitor having excellent heat resistance, the piezoelectric sensor can be used at a higher temperature than before.

  (4) Further, in the piezoelectric sensor of the present invention, preferably, the feedback capacitor unit is configured by connecting the first feedback capacitor and the second feedback capacitor in parallel.

  Thus, the capacitance Cf of the feedback capacitor unit becomes a value (Cf = Cf1 + Cf2) obtained by adding the capacitance Cf1 of the first feedback capacitor and the capacitance Cf2 of the second feedback capacitor. It can facilitate the calculation of its capacitance at the time of design. In addition, the capacitance of the first feedback capacitor used in parallel connection is smaller than the capacitance of the first feedback capacitor used in series connection, and the size of the first feedback capacitor is correspondingly smaller, so the piezoelectric sensor Can be miniaturized.

  According to the piezoelectric sensor of the present invention, it is easy to set the temperature change rate of the capacitance of the feedback capacitor unit to a value similar to the temperature change rate of the charge sensitivity of the piezoelectric element. The temperature compensation can be realized with high accuracy and easily.

It is an equivalent circuit diagram showing an example of the piezoelectric sensor which connected in parallel the 1st feedback capacitor of this embodiment, and the 2nd feedback capacitor. It is an equivalent circuit diagram showing an example of the piezoelectric sensor which connected in series the 1st feedback capacitor of this embodiment, and the 2nd feedback capacitor. It is a graph which shows the temperature change rate of the piezoelectric sensor which connected in parallel the 1st feedback capacitor of this embodiment, and the 2nd feedback capacitor. It is a graph which shows the temperature change rate of the piezoelectric sensor which connected in series the 1st feedback capacitor of this embodiment, and the 2nd feedback capacitor.

  Hereinafter, the piezoelectric sensor of the present embodiment will be described using the drawings.

[1] Configuration of Piezoelectric Sensor 1 FIG. 1 is an equivalent circuit diagram showing an example of a piezoelectric sensor in which a first feedback capacitor and a second feedback capacitor of the present embodiment are connected in parallel. FIG. 2 is an equivalent circuit diagram showing an example of a piezoelectric sensor in which the first feedback capacitor and the second feedback capacitor of the present embodiment are connected in series.

  The piezoelectric sensor of the present embodiment assumes, for example, a sensor that converts acceleration or force into a low impedance electrical signal, such as a piezoelectric acceleration sensor incorporating a charge amplifier (preamplifier) or a piezoelectric pressure sensor. Also, the piezoelectric sensor is, for example, a piezoelectric acceleration sensor incorporating a feedback capacitor, a piezoelectric pressure sensor, etc., a sensor corresponding to temperature compensation of voltage sensitivity in the entire range from low temperature to high temperature (eg -50.degree. C. to 170.degree. C.) Is assumed.

  Therefore, as shown in FIG. 1 or FIG. 2, the piezoelectric sensor 1 of the present embodiment includes the piezoelectric element 10 and the charge amplifier 20.

(1) Piezoelectric element 10
The piezoelectric element 10 is an element that produces a piezoelectric effect that generates an electric charge (a high impedance electrical signal) when receiving a force. The piezoelectric element 10 of the present embodiment has an electrode on a desired surface. Also, the electrode and the charge amplifier 20 are electrically connected. As a material of the piezoelectric element, for example, lead zirconate titanate (PZT) or quartz is used. Nickel (Ni), gold (Au) or the like is used as a material of the electrode.

  In addition, when the piezoelectric sensor 1 of the present embodiment is a piezoelectric acceleration sensor, the piezoelectric element 10 may be, for example, a fixing material such as a screw or an adhesive between the base serving as the main body of the piezoelectric acceleration sensor and the weight. It is fixed using. Then, when the piezoelectric acceleration sensor receives acceleration, a force generated on the weight due to the acceleration is applied to the piezoelectric element 10, and charge is generated in the piezoelectric element 10.

(2) Charge amplifier 20
The charge amplifier 20 is an amplifier that outputs a voltage proportional to the charge obtained from the piezoelectric element 10. The charge amplifier 20 is composed of a feedback capacitor unit 30, which is a feedback capacitance that determines the amplification factor of the output voltage, and an operational amplifier or a transistor. The charge amplifier 20 is incorporated in the piezoelectric sensor 1. This is because when the charge amplifier 20 is not built in the piezoelectric sensor 1, the stray capacitance of the external connection cable that connects the piezoelectric sensor 1 and the external charge amplifier causes output from the piezoelectric element 10. This is to eliminate the occurrence of noise in the electrical signal.

(3) Feedback capacitor unit 30
The feedback capacitor unit 30 serves as a temperature compensating capacitor. Therefore, it is preferable that the feedback capacitor unit 30 be disposed near the piezoelectric element 10 in the piezoelectric sensor 1 so as to have a temperature environment similar to that of the piezoelectric element 10.

  The feedback capacitor unit 30 also has a first feedback capacitor 31 and a second feedback capacitor 32. The first feedback capacitor 31 and the second feedback capacitor 32 may be connected either in parallel as shown in FIG. 1 or in series as shown in FIG. 2 from the viewpoint of temperature compensation. On the other hand, from the viewpoint of the design easiness of the feedback capacitor unit 30, as a connection method of the first feedback capacitor 31 and the second feedback capacitor 32, a parallel connection as shown in FIG. 1 is preferable.

(3-1) First feedback capacitor 31
The first feedback capacitor 31 has a capacitance with a temperature change rate larger than that of the charge sensitivity of the piezoelectric element 10.

  The first feedback capacitor 31 is preferably a capacitor made of the same material as the piezoelectric element 10 and not polarized.

  In addition, the first feedback capacitor 31 may be configured of one capacitor, or may be configured of two or more combined capacitors.

(3-2) Second feedback capacitor 32
The second feedback capacitor 32 has a capacitance with a temperature change rate smaller than the temperature change rate of the charge sensitivity of the piezoelectric element 10.

  The temperature coefficient of the second feedback capacitor 32 is preferably ± 100 ppm / ° C. or less within the allowable temperature range of the piezoelectric sensor 1. In this way, the temperature change rate of the feedback capacitor unit 30 can be set with high accuracy within the range of about ± 5%. Furthermore, the second feedback capacitor 32 is preferably a ceramic capacitor having a temperature coefficient of ± 30 ppm / ° C. or less. In this way, the temperature change rate of the feedback capacitor unit 30 can be set with high accuracy within a range of about ± 2%.

  Further, the second feedback capacitor 32 may be configured by one capacitor, or may be configured by two or more composite capacitors.

(3-3) Design Principle of Feedback Capacitor Unit 30 (3-3-1) Basic Principle of Temperature Compensation Equation 1 is the voltage sensitivity Svo of the charge amplifier 20 at a reference temperature of 20 degrees and that of the piezoelectric element 10 at a reference temperature of 20 degrees. Charge sensitivity Sqo and capacitance Cfo of feedback capacitor unit 30 at a reference temperature of 20 degrees, voltage sensitivity Sv of charge amplifier 20 at an arbitrary temperature, charge sensitivity Sq of piezoelectric element 10 at an arbitrary temperature, and feedback capacitor unit 30 at an arbitrary temperature The relationship of the capacitance Cf of The rate of temperature change z (t-20) of Sv, the rate of temperature change y (t-20) of Sq or the rate of temperature change x (t-20) of Cf are based on the temperature change rates of Svo, Sqo or Cfo It is calculated.

  As shown in Equation 1, the voltage sensitivity Sv of the charge amplifier 20 is proportional to the charge sensitivity Sq of the piezoelectric element 10 and inversely proportional to the capacitance Cf of the feedback capacitor unit 30, regardless of the operating temperature of the piezoelectric sensor 1 (Sv = Sq / Cf).

  Equation 2 shows the temperature change rate z (t−20) of the voltage sensitivity Sv of the charge amplifier 20 based on Equation 1.

  As shown in Equation 2, the temperature change rate z (t-20) of the voltage sensitivity Sv of the charge amplifier 20 increases with the increase of the temperature change rate y (t-20) of the charge sensitivity Sq of the piezoelectric element The temperature change rate z (t−20) of the voltage sensitivity Sv of the charge amplifier 20 decreases with the increase of the temperature change rate x (t−20) of the capacitance Cf of the capacitor unit 30 (formula: z (t−) 20) = (1 + y (t-20)) / (1 + x (t-20))-1). For example, when the temperature change rate y (t-20) of the charge sensitivity Sq of the piezoelectric element 10 and the temperature change rate x (t-20) of the capacitance Cf of the feedback capacitor unit 30 are the same (y (t-20) = X (t-20), the temperature change rate z (t-20) of the voltage sensitivity Sv of the charge amplifier 20 becomes 0 (formula: z (t-20) = 0). However, as described above, even if the same material capacitor is used as the feedback capacitor, the change rate of the electrostatic capacitance Cf becomes larger than the change rate of the charge sensitivity Sq of the piezoelectric element 10 only with the same material capacitor.

  Therefore, in the case of performing temperature compensation on the piezoelectric sensor 1 of the present embodiment, for example, the following conditions are required.

  (A) The temperature change rate x (t-20) with Cf and the temperature change rate y (t-20) with Sq are the same.

  (B) The absolute value of x (t-20) is larger than the absolute value of y (t-20).

  (C) x (t-20) and y (t-20) have a proportional relationship or an approximate relationship with each other.

  When the above conditions (A) to (C) are satisfied, even if the operating temperature of the piezoelectric sensor 1 changes, the “voltage change rate of the voltage sensitivity Sv of the charge amplifier 20 if z (t−20) ≒ 0” means “voltage Since the sensitivity Sv is constant, temperature compensation can be performed on the piezoelectric sensor 1.

(3-3-2) Design Principle of Feedback Capacitor Unit 30 Formula 3 shows the respective capacitances Cf1 and Cf2 of the first feedback capacitor 31 and the second feedback capacitor 32 constituting the feedback capacitor unit 30, and the reference temperature of 20 degrees. The relationship between the capacitances Cf1o and Cf2o of the first feedback capacitor 31 and the second feedback capacitor 32 in FIG. The temperature change rate x1 (t-20) of Cf1 or the temperature change rate x2 (t-20) of Cf2 is calculated based on the temperature change rates of Cf1o or Cf2o.

  In the feedback capacitor unit 30, the first feedback capacitor 31 and the second feedback capacitor 32 are connected in parallel or in series as described above. Further, since the feedback capacitor unit 30 is a composite capacitor including the first feedback capacitor 31 and the second feedback capacitor 32, the capacitances Cf and Cf0 of the feedback capacitor unit 30 are the capacitance Cf1 of the first feedback capacitor 31. And the capacitance Cf2 of the second feedback capacitor 32.

  Here, as shown in Equation 3, the capacitance Cf1 of the first feedback capacitor 31 and the capacitance Cf2 of the second feedback capacitor 32 of the first feedback capacitor 31 and the second feedback capacitor 32 at a reference temperature of 20 degrees. It depends on the respective capacitances Cf1o and Cf2o, and their temperature change rates x1 (t-20) and x2 (t-20). That is, by adjusting Cf1o, Cf2o, x1 (t-20) and x2 (t-20), it is possible to obtain a temperature change rate x (t-20) which is desired or close to that in the feedback capacitor unit 30.

(3-3-3) Feedback capacitor unit 30 in parallel connection
FIG. 3 is a graph showing the temperature change rate in the piezoelectric sensor 1 in which the first feedback capacitor 31 and the second feedback capacitor 32 of this embodiment are connected in parallel.

  As shown in FIG. 3, the temperature change rate y (t-20) at the charge sensitivity Sq of the piezoelectric element 10 rises substantially in proportion to the temperature rise, assuming that the temperature change rate at the reference temperature of 20 ° C is 0. Do.

  Further, the first feedback capacitor 31 and the capacitance Cf1 thereof are selected or created so as to satisfy the conditions (A) to (C) or to approach the conditions. In such a case, as shown in FIG. 3, when the temperature change rate at the reference temperature of 20 ° C. is 0, the temperature rise rate x (t−20 of capacitance Cf1 of the first feedback capacitor 31) with respect to the temperature rise. ) Rises almost proportionally. Further, since the first feedback capacitor 31 is a capacitor made of the same material, it is easy to obtain a graph of temperature characteristics as shown in FIG.

  When the feedback capacitor unit 30 is only the first feedback capacitor 31, as shown in FIG. 3, the temperature of the voltage sensitivity Sv of the charge amplifier 20 with respect to the temperature rise when each temperature change rate at the reference temperature of 20.degree. The rate of change z (t-20) falls almost proportionally.

  Then, as described above, in order to approach the voltage sensitivity Sv = constant, “the temperature change rate z (t−20) チ ャ ー ジ 0 of the voltage sensitivity Sv of the charge amplifier 20”, that is, “the capacitance of the feedback capacitor unit 30 The temperature change rate of Cf x (t-20) 変 化 the temperature change rate of charge sensitivity Sq of the piezoelectric element 10 y (t-20) ".

  Therefore, in the feedback capacitor unit 30, the first feedback capacitor 31 and the second feedback capacitor 32 are connected in parallel.

  Here, Equation 4 is based on Equations 1 to 3, and it is possible to adjust the capacitance Cf of the feedback capacitor unit 30 in parallel by using adjustable Cf1o, Cf2o, x1 (t-20) and x2 (t-20). The calculation formula which calculates temperature change rate x (t-20) is shown.

  As shown in Equation 4, the capacitance Cf1 of the first feedback capacitor 31 having the temperature change rate x1 (t-20) larger than the charge sensitivity Sq is reduced, and the temperature change rate x2 (t-20) smaller than the charge sensitivity Sq is It is possible to keep the capacitance Cf of the feedback capacitor unit 30 substantially constant while increasing the capacitance Cf2 of the second feedback capacitor 32 having the same.

  That is, when the first feedback capacitor 31 and the second feedback capacitor 32 are connected in parallel in the feedback capacitor unit 30, by adjusting Cf1o, Cf2o, x1 (t-20) and x2 (t-20), "feedback capacitor unit The temperature change rate x (t-20) of the capacitance Cf of 30 ≒ the temperature change rate y (t-20) of the charge sensitivity Sq of the piezoelectric element 10 "can be obtained. The temperature change rate z (t-20) of the voltage sensitivity Sv of the above can be approximated to zero.

  Since the first feedback capacitor 31 is a capacitor made of the same material, the temperature characteristics of x (t-20) and y (t-20) have the same tendency with respect to the reference temperature (20 ° C), as shown in FIG. In addition, the temperature change rate can be significantly reduced in the case where there is the second feedback capacitor 32 (= with temperature compensation) as compared with the case without the second feedback capacitor 32 (= without temperature compensation).

  In the case where the second feedback capacitor 32 is a ceramic capacitor, there is no problem in terms of products even if it is calculated as x2 (t-20) = 0 by using a commercially available product having a temperature coefficient of about 30 ppm or less. As a result, when setting the temperature change rate x (t-20) of the capacitance Cf of the feedback capacitor unit 30, the variables can be reduced to three of Cf1o, Cf2o and x1 (t-20).

(3-3-4) Feedback capacitor unit 30 in series connection
FIG. 4 is a graph showing the temperature change rate in the piezoelectric sensor 1 in which the first feedback capacitor 31 and the second feedback capacitor 32 of the present embodiment are connected in series.

  Further, equation 5 shows the temperature of capacitance Cf of feedback capacitor unit 30 in series using adjustable Cf1 o, Cf2 o, x1 (t-20) and x2 (t-20) based on equations 1 to 3 The calculation formula which calculates change rate x (t-20) is shown.

  The feedback capacitor unit 30 at the time of series connection is, as shown in FIG. 4 and the equation 5, similarly to the feedback capacitor unit 30 at the time of parallel connection described above, Cf1o, Cf2o, x1 (t-20) and x2 (t-20) The temperature change rate x (t-20) of the capacitance Cft of the feedback capacitor unit 30? The temperature change rate y (t-20) of the charge sensitivity Sq of the piezoelectric element 10 "can be adjusted by adjusting. Therefore, the temperature change rate zt of the voltage sensitivity Svt of the charge amplifier 20 with respect to temperature change can be approximated to zero.

  Further, as described above, since the first feedback capacitor 31 is a capacitor made of the same material, the temperature characteristics of x (t-20) and y (t-20) tend to be similar to the reference temperature (20 ° C.). Therefore, as shown in FIG. 4, compared with no second feedback capacitor 32 (= no temperature compensation), the temperature change rate can be significantly reduced when there is a second feedback capacitor 32 (= with temperature compensation). it can.

  In the case where the second feedback capacitor 32 is a ceramic capacitor, there is no problem in terms of products even if it is calculated as x2 (t-20) = 0 by using a commercially available product having a temperature coefficient of about 30 ppm or less. As a result, when setting the temperature change rate x (t-20) of the capacitance Cf of the feedback capacitor unit 30, the variables can be reduced to three of Cf1o, Cf2o and x1 (t-20). In particular, the calculation of the combined capacitance in series connection is more complicated than the calculation of combined capacitance in parallel connection. Therefore, a reduction of one variable can facilitate the design of the feedback capacitor.

[2] Effects Next, the effects of the piezoelectric sensor 1 of the present embodiment will be described.

  (1) The piezoelectric sensor 1 according to the present embodiment includes the piezoelectric element 10 and the charge sensitivity of the first feedback capacitor 31 and the piezoelectric element 10 which are made of the same material as the piezoelectric element 10 and made of the same material capacitor which is not polarized. And a feedback capacitor unit 30 configured to be connected to a second feedback capacitor 32 having a capacitance with a temperature change rate smaller than the temperature change rate, and the charge amplifier 20 electrically connected to the piezoelectric element 10 And are characterized.

  Thereby, the temperature change rate of the electrostatic capacitance is made larger than the temperature change rate of the charge sensitivity of the piezoelectric element, and the first feedback capacitor 31 and the piezoelectric have a tendency similar to the charge sensitivity of the piezoelectric element 10 with respect to temperature. Since the circuit combining the second feedback capacitor 32 having the capacitance of temperature change rate smaller than the temperature change rate of charge sensitivity of the element is used as the feedback capacitor unit 30, the temperature of the capacitance of the feedback capacitor unit 30 is The rate of change can be easily set to a value similar to the rate of change in temperature of the charge sensitivity that the piezoelectric element 10 has. In addition, the capacitance of the first feedback capacitor 31 and the second feedback capacitor 32 of about 10 to 1000 pF is sufficient from the relationship with the gain of the charge amplifier 20, and their respective sizes are small. The size of the combined feedback capacitor unit 30 also remains small. As a result, the size of the piezoelectric sensor 1 of the present embodiment can be made comparable to that of the prior art.

  (2) Further, in the piezoelectric sensor 1 of the present embodiment, the temperature coefficient of the second feedback capacitor 32 is preferably ± 100 ppm / ° C. or less within the range of the allowable use temperature of the piezoelectric sensor 1.

  As a result, even if the temperature change rate of the second feedback capacitor 32 is approximated to 0, the temperature change rate of the feedback capacitor unit 30 can be set with an accuracy of about ± 5%. The effort of selecting each capacitance of the feedback capacitor 32 can be greatly reduced.

  (3) Further, in the piezoelectric sensor 1 of the present embodiment, the second feedback capacitor 32 is preferably a ceramic capacitor.

  Thereby, since the temperature coefficient of the ceramic capacitor as the second feedback capacitor 32 is ± about 30 ppm / ° C., the temperature change rate of the feedback capacitor unit 30 is about ± 2% even if the temperature change rate is approximated to 0. Since the accuracy can be set, the labor for selecting the respective capacitances of the first feedback capacitor 31 and the second feedback capacitor 32 can be greatly reduced. In addition, commercially available ceramic capacitors are easily available, and the degree of freedom of selection of the second feedback capacitor 32 can be enhanced. In addition, since the second feedback capacitor 32 is a ceramic capacitor having excellent heat resistance, the piezoelectric sensor 1 can be used at a temperature higher than that of the related art.

  (4) Further, in the piezoelectric sensor 1 of the present embodiment, it is preferable that the feedback capacitor unit 30 be configured by connecting the first feedback capacitor 31 and the second feedback capacitor 32 in parallel.

  As a result, the capacitance Cf of the feedback capacitor unit 30 becomes a value (Cf = Cf1 + Cf2) obtained by adding the capacitance Cf1 of the first feedback capacitor 31 and the capacitance Cf2 of the second feedback capacitor 32. At the time of design of the feedback capacitor unit 30, calculation of its capacitance can be facilitated. Further, the capacitance of the first feedback capacitor 31 used in parallel connection is smaller than the capacitance of the first feedback capacitor 31 used in series connection, and the size of the first feedback capacitor 31 is correspondingly smaller. The piezoelectric sensor 1 can be miniaturized.

  That is, according to the piezoelectric sensor 1 of the present embodiment, it is easy to set the temperature change rate of the capacitance of the feedback capacitor unit 30 to a value similar to the temperature change rate of the charge sensitivity of the piezoelectric element 10. Accordingly, temperature compensation of voltage sensitivity can be realized with high accuracy and easily.

  The present invention is not limited to the above-described embodiment and the like, and various modifications can be made as needed.

DESCRIPTION OF SYMBOLS 1 piezoelectric sensor 10 piezoelectric element 20 charge amplifier 30 feedback capacitor unit 31 1st feedback capacitor 32 2nd feedback capacitor

Claims (4)

A piezoelectric element,
A second feedback capacitor composed of the same material as the piezoelectric element and made of the same material capacitor which is not polarized, and a capacitance having a temperature change rate smaller than the temperature change rate of the charge sensitivity of the piezoelectric element A charge amplifier electrically connected to the piezoelectric element, having a feedback capacitor unit configured by connecting a capacitor;
A piezoelectric sensor comprising: The piezoelectric sensor according to claim 1, wherein a temperature coefficient of the second feedback capacitor is ± 100 ppm / ° C. or less within a range of a use allowable temperature of the piezoelectric sensor. The piezoelectric sensor according to claim 2, wherein the second feedback capacitor is a ceramic capacitor. The piezoelectric according to any one of claims 1 to 3, wherein the feedback capacitor unit is configured by connecting the first feedback capacitor and the second feedback capacitor in parallel. Sensor.