JP2014081269A - Pressure measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for measuring pressure of liquid.SOLUTION: A pressure measuring device for measuring pressure of liquid of a measuring object includes: a passage having passage resistance; a liquid housing chamber of a predetermined volume which communicates with one end of the passage; pressure change means for changing pressure of the liquid housing chamber; a measurement part which measures behavior of pressure in the liquid housing chamber associated with operation of the pressure change means in a state where liquid is housed in the passage and the liquid housing chamber; and an acquisition part which acquires pressure based on the behavior of pressure.

Description

  The present invention relates to a technique for measuring the pressure of a liquid.

  Conventionally, as a technique for measuring the pressure of a liquid, for example, the technique of Patent Document 1 below is known. Patent Document 1 describes a technique for measuring pressure based on a CI value (equivalent series resistance) of a tuning fork type piezoelectric vibrator.

JP 2010-85377 A

  However, in the pressure measurement technique of Patent Document 1, the CI value greatly depends on the physical property of the tuning fork type piezoelectric vibrator. Therefore, in order to accurately measure pressure, it is necessary to control the shape and size of the tuning fork vibrator with high accuracy and to accurately grasp and control the electrical characteristics of the tuning fork vibrator during manufacturing. There has been a problem that a very high accuracy is required. In addition, it has been pointed out that there is a need for frequent calibration even when used. Since the behavior of the tuning fork type piezoelectric vibrator also fluctuates due to the influence of dust in the air, there has been a problem that a precise structure is required and the use environment is limited. These problems are common problems in general techniques for measuring the pressure of a liquid. In addition, in an apparatus for measuring the pressure of a liquid, there has been a demand for downsizing, cost reduction, resource saving, ease of manufacture, improvement in usability, and the like.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms.

(1) According to one aspect of the present invention, a pressure measuring device that measures the pressure of a liquid to be measured is provided. The pressure measuring apparatus includes: a flow path having flow path resistance; a liquid storage chamber having a predetermined volume communicating with one end of the flow path; pressure changing means for changing the pressure of the liquid storage chamber; A measuring unit that measures the behavior of pressure in the liquid storage chamber in accordance with the operation of the pressure changing means in a state in which the liquid is stored in the liquid storage chamber; and obtains the pressure of the liquid based on the behavior of the pressure And an acquisition unit. According to this pressure measuring device, since the pressure of the liquid is measured based on the behavior of the pressure of the liquid generated by the pressure change by the pressure changing means, the structural limitation necessary when directly measuring the pressure is avoided, The structure can be simplified. The behavior of pressure may be obtained indirectly from various parameters relating to the liquid, such as the flow rate, flow rate, and mobility of the liquid.

(2) In the pressure measuring device according to the aspect described above, the behavior of the pressure is a period from when the liquid in the liquid storage chamber reaches a predetermined pressure due to the change in the pressure until the next predetermined pressure is reached. It is good also as what is. According to this pressure measuring device, the pressure is measured by measuring the period from when the liquid in the liquid storage chamber reaches a predetermined pressure until the next predetermined pressure is reached. The pressure of the liquid can be measured.

(3) In the pressure measuring device according to the above aspect, the pressure changing unit may include a piezoelectric element, and may change the pressure of the liquid storage chamber by a strain force of the piezoelectric element. According to this pressure measuring device, the change in pressure can be electrically controlled.

(4) In the pressure measuring device according to the above aspect, the piezoelectric element is further distorted by a pressure change in the liquid storage chamber; the measuring unit measures the pressure behavior based on the distortion of the piezoelectric element. Also good. According to this pressure measuring device, the change in the pressure of the liquid in the liquid storage chamber and the measurement of the behavior of the pressure can be performed by the same piezoelectric element.

  A plurality of constituent elements of each aspect of the present invention described above are not indispensable, and some or all of the effects described in the present specification are to be solved to solve part or all of the above-described problems. In order to achieve the above, it is possible to appropriately change, delete, replace with another new component, and partially delete the limited contents of some of the plurality of components. In order to solve part or all of the above-described problems or to achieve part or all of the effects described in this specification, technical features included in one embodiment of the present invention described above. A part or all of the technical features included in the other aspects of the present invention described above may be combined to form an independent form of the present invention. Moreover, according to such a form, it is possible to solve at least one of various problems such as downsizing of the apparatus, cost reduction, resource saving, ease of manufacture, and improvement in usability.

  Note that the present invention can be realized in various modes. For example, it can be realized in the form of a pressure gauge, a water pressure gauge, a water depth gauge, a pressure measurement system, a pressure measurement method, and the like.

1 is an explanatory diagram for explaining a measurement system 10. FIG. 3 is a block diagram illustrating a configuration of a drive circuit 50. FIG. It is explanatory drawing which illustrated pressure signal Vp and detection signal DS. It is an actual measurement result showing the relationship between the negative pressure period T and the pressure in the container 20. It is explanatory drawing which shows the aspect of the pressure measuring apparatus as the modification 2.

A. First embodiment:
(A1) System configuration:
FIG. 1 is an explanatory diagram for explaining a measurement system 10 using a pressure measurement device 30 as a first embodiment of the present invention. The pressure measuring device 30 is a device that measures the pressure of the liquid. The measurement system 10 includes a container 20 that stores a liquid Lq to be measured, and a pressure measurement device 30. In the present embodiment, the liquid Lq accommodated in the container 20 is water. A predetermined pressure is maintained inside the container 20.

  The pressure measuring device 30 includes a housing 32, a flow path 34, a diaphragm 36, a piezoelectric element 38, and a drive circuit 50. The housing 32 has a pump chamber 40 inside. The pump chamber 40 is formed by the inner wall of the housing 32 and the diaphragm 36. The flow path 34 is connected to the container 20 and communicates the pump chamber 40 and the container 20. Therefore, the flow path 34 and the pump chamber 40 are filled with the liquid Lq to be measured (water in this embodiment). The pump chamber 40 may be provided with an air vent hole with a lid for extracting air existing in the pump chamber 40 from before the measurement in order to fill the liquid Lq. In this embodiment, the container 20 and the housing | casing 32 are comprised with the very hard member. For example, stainless steel can be employed.

  The piezoelectric element 38 has one end fixed to the diaphragm 36 and the other end fixed to the inner wall of the housing 32. In the present embodiment, a stacked piezoelectric element is used as the piezoelectric element 38. The present invention is not limited to this, and a monomorph or bimorph piezoelectric element may be employed. The piezoelectric element 38 is connected to the drive circuit 50 and expands by a drive signal (power) applied from the drive circuit 50. The piezoelectric element 38 indirectly pressurizes and depressurizes the water in the pump chamber 40 by pushing and pulling the diaphragm 36 by the strain force due to expansion and changing the volume of the pump chamber 40. The diaphragm 36 and the piezoelectric element 38 correspond to the pressure changing means described in the claims.

  The drive circuit 50 applies a drive signal to the piezoelectric element 38 and detects a change in the internal pressure of the pump chamber 40. Specifically, when the pressure in the pump chamber 40 changes, a force is applied to the piezoelectric element 38 via the diaphragm 36. The piezoelectric element 38 generates a voltage due to the piezoelectric effect. The drive circuit 50 detects a change in the internal pressure of the pump chamber 40 by detecting the voltage generated by the piezoelectric element 38. Note that the “internal pressure” of the pump chamber 40 in this description is a relative internal pressure that is not defined by a reference pressure. As will be described later, the drive circuit 50 measures the absolute pressure of the water to be measured based on the change in the internal pressure of the pump chamber 40 detected under a predetermined condition.

  FIG. 2 is a block diagram illustrating the configuration of the drive circuit 50. The drive circuit 50 includes a control unit 52 that outputs the drive waveform signal Vin, an amplification circuit 54 that amplifies the drive waveform signal Vin with an amplification factor G and outputs the drive signal Vout, and a pressure that detects the internal pressure of the pump chamber 40. The detection part 60, the comparison part 56 which compares the detected internal pressure with a predetermined threshold value, and the display part 70 are provided. The pressure detection unit 60 includes a current detection circuit 62 that detects the drive current of the piezoelectric element 38, an integration circuit 64 that integrates the detected drive current, and a subtraction that outputs a difference between the output of the integration circuit 64 and the drive waveform signal Vin. A circuit 66 is provided.

  The drive circuit 50 detects the pressure signal Vp indicating the internal pressure of the pump chamber 40 as follows. The controller 52 outputs a drive waveform signal Vin. The drive waveform signal Vin is amplified by the amplifier circuit 54 and applied to the piezoelectric element 38 as the drive signal Vout. At this time, the drive current Iout corresponding to the drive signal Vout flows into the piezoelectric element 38. A current detection resistor r is connected to the other end of the piezoelectric element 38. The other end of the resistor r is grounded. The current detection circuit 62 converts the potential difference between the resistance r terminals caused by the drive current Iout into a current signal Vi by dividing by the resistance value of the resistance r, and inputs the current signal Vi to the integration circuit 64. The integration circuit 64 integrates the input current signal Vi with an integrator, and outputs a charge signal Vq that is a value corresponding to the amount of charge stored in the piezoelectric element 38.

  The drive current Iout (current signal Vi) flowing through the piezoelectric element 38 is proportional to the displacement speed of the piezoelectric element 38. Therefore, the amount of charge (charge signal Vq) stored in the piezoelectric element 38 is proportional to the displacement of the piezoelectric element 38. In a state where the piezoelectric element 38 can freely expand and contract, the displacement of the piezoelectric element 38 is substantially proportional to the drive signal. On the other hand, when the internal pressure changes in the pump chamber 40, the piezoelectric element 38 receives a change in pressure through the diaphragm 36. At this time, since the piezoelectric element 38 expands and contracts (changes in displacement) in proportion to the change in the received pressure, the displacement of the piezoelectric element 38 when the pressure change in the pump chamber 40 is received and the original displacement of the piezoelectric element 38. (The difference from when no pressure is received) is proportional to the pressure received by the piezoelectric element 38 (the internal pressure of the pump chamber 40).

  The pressure detection unit 60 divides the charge signal Vq obtained by the integrator of the integration circuit 64 by the equivalent capacitance c of the piezoelectric element 38 and the amplification factor G of the amplification circuit 54 to obtain the voltage signal Vx. The pressure detection unit 60 calculates the difference between the voltage signal Vx corresponding to the actual displacement of the piezoelectric element 38 and the drive waveform signal Vin by the subtraction circuit 66, so that the pressure corresponding to the relative internal pressure of the pump chamber 40 is obtained. The signal Vp is acquired.

  The pressure detection unit 60 inputs the acquired pressure signal Vp to the comparison unit 56. The comparison unit 56 generates a binarized detection signal DS by comparing with a predetermined threshold value and inputs the detection signal DS to the control unit 52. The control unit 52 includes a lookup table LUT. The control unit 52 acquires the water pressure based on the input detection signal DS and the lookup table LUT. And the acquired pressure value is displayed on the display part 70 so that a user can visually recognize. A method for acquiring the pressure based on the lookup table LUT and the detection signal DS will be described later.

(A2) Pressure vibration:
FIG. 3 is an explanatory diagram illustrating the pressure signal Vp obtained by the pressure detection unit 60 and the detection signal DS obtained by the comparison unit 56 when the drive signal Vout is applied to the piezoelectric element 38. FIG. 3A shows the drive signal Vout applied to the piezoelectric element 38. FIG. 3B shows the pressure signal Vp obtained by the pressure detector 60. FIG. 3C shows the detection signal DS obtained by the comparison unit 56.

  As shown in FIG. 3A, in the present embodiment, one pulse of Vin is output from the control unit 52, and the drive signal Vout is applied to the piezoelectric element 38. The piezoelectric element 38 expands when the voltage (drive voltage) of the drive signal Vout increases, and pressurizes the liquid in the pump chamber 40 via the diaphragm 36. As a result, as shown in FIG. 3B, the voltage of the drive signal Vout rises, and the internal pressure of the pump chamber 40 increases rapidly. While the drive voltage is maintained at the maximum voltage, the displacement of the piezoelectric element 38 does not change. For this reason, a pressure difference arises between the liquid of the pump chamber 40 and the liquid of the container 20, and a liquid flows out into the container 20 from the pump chamber 40 (refer FIG. 1). The internal pressure of the pump chamber 40 decreases as the liquid flows out into the container 20. At this time, an inertia force acts on the liquid passing through the flow path 34 due to the inertance of the flow path 34, and the liquid continues to flow from the pump chamber 40 to the container 20. As a result, the internal pressure of the pump chamber 40 becomes a negative pressure. The inertance will be described in detail later.

  The pump chamber 40 sucks liquid from the container 20 when the internal pressure becomes negative. Accordingly, the liquid flows from the container 20 into the pump chamber 40. Also in this case, the liquid continues to flow from the container 20 to the pump chamber 40 by the inertial force based on the inertance of the flow path as described above. Therefore, as shown in FIG. 3B, the internal pressure of the pump chamber 40 increases. Thus, the internal pressure of the pump chamber 40 is vibrated by the inertia force caused by the inertance of the flow path 34. As can be seen from FIG. 3B, the vibration of the internal pressure of the pump chamber 40 has a predetermined period.

  Here, as shown in FIG. 3B, a wave of pressure vibration consisting of one rise and fall of the internal pressure of the pump chamber 40 accompanying application of the drive signal Vout to the piezoelectric element 38 is referred to as a first wave. Call. The waves of pressure oscillation following the first wave are called as the second wave, the third wave, the fourth wave, and so on. As shown in FIG. 3C, the detection signal DS is a signal corresponding to the pressure vibration wave (first wave, second wave, etc.) of the pump chamber 40. The pulse of the detection signal DS corresponding to each pressure vibration is called as a first pulse, a second pulse,.

  As shown in FIG. 3C, when the second pulse is detected following the first pulse of the detection signal DS, the length of the period from when the first pulse is generated until the second pulse is generated. Has information on the pressure at which the liquid feed pump 100 pumps the liquid. More specifically, it has information regarding the pressure in the container 20. The second wave of the pressure signal Vp is generated when the liquid flowing from the pump chamber 40 toward the container 20 in the flow path 34 is pulled back to the pump chamber 40 due to the pressure difference between the pump chamber 40 and the container 20. Therefore, when the pressure difference between the pump chamber 40 and the container 20 increases, the force with which the pump chamber 40 pulls back the liquid Lq in the container 20 increases, so the second wave is generated earlier, and as a result, the second signal in the detection signal DS is increased. Two pulses occur as early as possible.

  As can be seen from FIG. 3 (b), the pressure in the pump chamber 40 is generally negative from the first wave to the second wave. In addition, since the liquid Lq does not enter or leave the pump chamber 40 other than communicating with the container 20, the pressure in the pump chamber 40 does not fluctuate greatly during the period until the second wave is generated. Therefore, the pressure difference between the container 20 and the pump chamber 40 in the period from the end of the first wave to the generation of the second wave (hereinafter also referred to as the negative pressure period T) is mainly the pressure in the container 20. Is determined. Specifically, the negative pressure period T decreases as the pressure in the container 20 increases. In other words, it can be said that the shorter the negative pressure period T, the higher the pressure in the container 20. Further, it has been confirmed from the experiment that the time from the generation of the first wave to the end, that is, the pulse width of the first pulse does not depend on the pressure in the pump chamber 40 and hardly changes.

  Next, it is shown by actual measurement that the negative pressure period in the pump chamber 40 depends on the pressure of the container 20. Specifically, the negative pressure period is shortened as the pressure in the container 20 increases. FIG. 4 is an actual measurement result showing a relationship between the negative pressure period T from the first pulse to the second pulse and the pressure in the container 20. The horizontal axis of the graph of FIG. 4 is the negative pressure period T, and the vertical axis is the pressure of the container 20. In this experiment, the pressure in the container 20 is measured by a pressure gauge provided separately. As shown in FIG. 4, it can be seen that the negative pressure period T decreases as the pressure in the container 20 increases. That is, by detecting the negative pressure period T, the pressure of the liquid to be measured (the container 20 in this embodiment) can be detected.

(A3) Pressure measurement:
The pressure measuring device 30 stores a lookup table LUT corresponding to the above-described graph of FIG. 4 in the control unit 52 (see FIG. 2). That is, the control unit 52 includes a lookup table LUT that associates each value of the negative pressure period T with a value based on actual measurement of the pressure to be measured. When actually measuring the pressure of the liquid to be measured, the control unit 52 applies a one-pulse drive signal Vout to the piezoelectric element 38 to generate and detect a pressure oscillation in the pump chamber 40. A negative pressure period T is extracted from the detection signal DS. Then, the acquired negative pressure period T is input to the lookup table LUT. The control unit 52 acquires the pressure value output from the lookup table LUT corresponding to the negative pressure period T.

  Thereafter, the control unit 52 displays the acquired pressure value on the display unit 70 so as to be visible to the user. The control unit 52 may include a lookup table LUT for various liquids such as water, predetermined oil, and predetermined organic solvent. For each liquid, this can be realized by measuring the correlation between the negative pressure period T and the pressure of the liquid to be measured and generating a lookup table.

  Next, the inertance used in the description of this embodiment will be described. Inertance is a characteristic value of a flow path. Specifically, it shows the ease of fluid flow when the fluid in the channel is about to flow due to the pressure applied to one end of the channel. For example, a flow path having a cross-sectional area of S and a length of L is filled with a density fluid (liquid in this embodiment), and pressure P (pressure difference at both ends) is applied to one end of the flow path. Shall. A P × S force acts on the fluid in the flow path. As a result, the liquid in the flow channel flows out. If the acceleration of the fluid is a, the equation of motion of the following equation (1) is established.

  When the volume flow rate flowing through the flow path is Q and the flow velocity of the fluid flowing through the flow path is v, the following expressions (2) and (3) are obtained.

  The following equation (4) can be obtained from the equations (2) and (3).

  Equation (4) represents that, if the same pressure P is applied, dQ / dt increases (that is, the flow velocity changes greatly) as (ρ × L / S) decreases. This (ρ × L / S) is a value called inertance. The inertance has been described above.

  As described above, the pressure measuring device 30 can measure the pressure of the liquid to be measured using the pressure vibration between the container 20 and the pump chamber 40. Therefore, in the pressure measurement device 30, a drive signal is applied to the piezoelectric element 38 to generate pressure vibration between the pump chamber 40 and the container 20, and a change in the internal pressure (relative pressure) of the pump chamber 40 is acquired. If possible, the pressure (absolute pressure) of the liquid to be measured can be measured. Accordingly, calibration of the piezoelectric element is not required. Moreover, pressure measurement can be performed with a simple structure. As a result, when measuring pressure, it is possible to have a highly durable configuration that is not easily affected by external changes of the pressure measuring device 30, such as external pride or temperature changes. Therefore, since pressure measurement is possible even in a relatively poor measurement environment, it is possible to provide a pressure gauge that is optimal for industrial use. For example, industrial tanks for storing liquids and piping as industrial liquid flow paths are usually provided with through holes for inserting thermometers and through holes for draining. By connecting the flow path 34 of the pressure measuring device 30 to such a through hole, it is possible to measure the pressure in the tank or the pipe. Further, in the present embodiment, the pressure of the pump chamber 40 and the measurement of the internal pressure of the pump chamber 40 are performed by one piezoelectric element 38, so that the structure is compared with the case where each is performed by separate elements and devices. Simplification, size reduction, and cost reduction can be realized.

  As a correspondence relationship with the claims, the pump chamber 40 corresponds to the liquid storage chamber described in the claims. The diaphragm 36 and the piezoelectric element 38 correspond to the pressure changing means described in the claims. The pressure oscillation of the liquid corresponds to the pressure behavior described in the claims. The piezoelectric element 38 and the drive circuit 50 correspond to the measurement unit described in the claims. The drive circuit 50 (control unit 52) corresponds to the acquisition unit described in the claims.

B. Variations:
The present invention is not limited to the above-described embodiments and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.
(B1) Modification 1:
In the above embodiment, the pressure of the water stored in the container 20 is measured, but the liquid to be measured is not limited to being stored in a sealed container, but is stored in a pipe or an open container. It may be. Even in such a case, the pressure measuring device 30 can measure the pressure of the liquid.

(B2) Modification 2:
The aspect of the pressure measuring device 30 is not limited to the aspect shown in FIG. 1, and various aspects can be adopted. FIG. 5 is an explanatory view showing an aspect of a pressure measuring device as a second modification. As shown in the drawing, the tip of the flow path 34 has a sharp shape, and the container 20 is pierced and used. In the container 20 in which the liquid Lq to be measured is accommodated, an insertion portion 22 is provided to pierce the flow path 34 and communicate with the inside of the container 20. The insertion portion 22 is made of a thick rubber member. The hole of the insertion portion 22 formed after the flow path 34 is pulled out is closed by the elastic force of the rubber member.

  As shown in the figure, the pressure measuring device 30 includes a display unit 70 and various operation buttons 72 such as a start button for starting measurement and an operation button for instructing recording of a measurement value. The display unit 70 displays the measured pressure value so as to be visible to the user. By setting the pressure measuring device 30 to such an aspect, the user can easily measure the pressure of the liquid Lq contained in the container 20.

(B3) Modification 3:
In the above embodiment, the piezoelectric element 38 causes pressure vibration and the internal pressure (relative pressure) of the pump chamber 40 is measured. However, separate piezoelectric elements may be used. That is, the pressure measuring device 30 may separately include a piezoelectric element as a pressure difference generation unit and a piezoelectric element as a measurement unit. In the above embodiment, the piezoelectric element is employed as the pressure difference generating unit. However, an element capable of generating a pressure difference between the pump chamber 40 and the container 20, such as a magnetostrictive element instead of the piezoelectric element, An apparatus may be used. Since the magnetostrictive element has a large displacement due to the strain, it is possible to generate a larger pressure vibration. Even if it does in this way, the effect similar to the said embodiment can be acquired.

(B4) Modification 4:
In the above embodiment, the liquid pressure is acquired from the negative pressure period T using the lookup table LUT. However, the pressure may be acquired by other methods. For example, a predetermined function indicating the correlation between the negative pressure period T and the pressure shown in the graph of FIG. 4 may be used. This can be realized by the controller 52 calculating the liquid pressure by substituting the negative pressure period T into a predetermined function.

(B5) Modification 5:
In the above embodiment, water is used as the liquid. However, the present invention is not limited to this, and various liquids such as a predetermined oil (for example, silicon oil) and a predetermined organic solvent (for example, alcohol) can be used. . In this case, the control unit 52 can be realized by providing a lookup table LUT for various liquids such as a predetermined oil and a predetermined organic solvent in addition to water.

(B6) Modification 6:
In the above embodiment, the piezoelectric element 38 and the diaphragm 36 are employed as the pressure changing means. However, the present invention is not limited to this, and various configurations that can change the pressure of the pump chamber 40 can be employed. For example, the pressure in the pump chamber 40 may be changed by injecting liquid into the pump chamber 40 from the outside. In addition, a laser emitting unit may be provided in the pump chamber 40, and bubbles may be generated by irradiating the water in the pump chamber 40 with a laser, and the pressure may be changed by the bubbles. Even if it does in this way, the effect similar to the said embodiment can be acquired.

DESCRIPTION OF SYMBOLS 10 ... Measurement system 20 ... Container 22 ... Insertion part 30 ... Pressure measuring device 32 ... Case 34 ... Flow path 36 ... Diaphragm 38 ... Piezoelectric element 40 ... Pump chamber 50 ... Drive circuit 52 ... Control part 54 ... Amplification circuit 56 ... Comparison Reference numeral 60: Pressure detection unit 62: Current detection circuit 64: Integration circuit 66 ... Subtraction circuit 70 ... Display unit 72 ... Operation button 100 ... Liquid feed pump Lq ... Liquid LUT ... Look-up table

Claims (4)

A pressure measuring device for measuring the pressure of a liquid to be measured,
A channel having channel resistance;
A liquid storage chamber having a predetermined volume communicating with one end of the flow path;
Pressure changing means for changing the pressure of the liquid storage chamber;
A measurement unit that measures the behavior of pressure in the liquid storage chamber in accordance with the operation of the pressure changing unit in a state where the liquid is stored in the flow path and the liquid storage chamber;
An acquisition unit that acquires the pressure of the liquid based on the behavior of the pressure. The pressure measuring device according to claim 1,
The pressure behavior is a period from when the liquid in the liquid storage chamber reaches a predetermined pressure due to the change in the pressure until the next predetermined pressure is reached. The pressure measuring device according to claim 1 or 2,
The pressure measuring device includes a piezoelectric element, and changes the pressure of the liquid storage chamber by a distortion force of the piezoelectric element. The pressure measuring device according to claim 3,
The piezoelectric element is further distorted by a pressure change in the liquid storage chamber,
The said measurement part measures the behavior of the said pressure based on distortion of the said piezoelectric element Pressure measuring apparatus.

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