Ultrasonic measuring apparatus

Abstract

To provide an ultrasonic measuring device capable of reducing a measurement error due to a temperature influence by suppressing a change in transmission / reception characteristics of an ultrasonic signal due to a temperature change.SOLUTION: An ultrasonic measurement apparatus 100 for measuring a fluid by transmitting an ultrasonic signal into a pipe P through which the fluid flows and receiving the ultrasonic signal that has passed through the fluid includes an ultrasonic transducer 1 that transmits and receives the ultrasonic signal, a voltage application unit 4 that applies a high-frequency voltage to the ultrasonic transducer 1 to generate the ultrasonic signal and transmits and receives ultrasonic vibration through an acoustic emission surface 1s, and a pair of ultrasonic transducers and a pair of matching members 2 that are held apart from each other along a longitudinal direction. A casing having a box-shaped main body member 31 that opens in one direction orthogonal to a longitudinal direction, a plate-shaped lid member 32 that covers an opening of the main body member, and a lock mechanism that locks a movement of the lid member in a state where the opening of the main body member is covered, The voltage application unit 4 applies a high-frequency voltage having a frequency other than an integral multiple of the resonance frequency of the ultrasonic transducer 1 to the ultrasonic transducer 1.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an ultrasonic measurement device. [Background technology]

[0002] Conventionally, a known ultrasonic measurement device includes a pair of ultrasonic vibrators (piezoelectric elements) spaced apart along a pipe through which a fluid to be measured flows, and measures the flow rate based on the difference in propagation time between the two ultrasonic signals by alternately transmitting and receiving ultrasonic signals from the ultrasonic vibrators (see, for example, Patent Document 1). In such an ultrasonic measurement device, a high-frequency voltage is applied to the ultrasonic vibrators to drive them and generate high-frequency signals. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-048471 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the characteristics (e.g., phase characteristics, impedance characteristics, capacitance characteristics, etc.) of the piezoelectric elements used in ultrasonic vibrators can change depending on the temperature. When the characteristics of the ultrasonic vibrator change, the oscillation characteristics and reception characteristics of the ultrasonic signal also change, which poses a problem that it becomes difficult to accurately measure the flow rate of the measurement target in situations where the temperature of the measurement target flowing through the pipe or the temperature of the surrounding environment changes.

[0005] The present invention has been made to solve the above-mentioned problems, and its main object is to provide an ultrasonic measurement device that can suppress changes in the reception and transmission characteristics of ultrasonic signals due to temperature changes and reduce measurement errors due to temperature effects. [Means for solving the problem]

[0006] To solve the above problems, the inventors focused on the frequency of the high-frequency voltage applied to the ultrasonic vibrator. It is common knowledge that an ultrasonic measurement device typically generates an ultrasonic signal with a high vibration intensity, and applies a high-frequency voltage to the ultrasonic vibrator that matches its resonant frequency, so that a high voltage value can be obtained from the ultrasonic signal on the receiving side, enabling highly stable flow rate measurement. After extensive research, the inventors discovered that the characteristics of an ultrasonic vibrator, which is a piezoelectric element, are particularly affected by temperature when the frequency of the applied high-frequency voltage is the resonant frequency. Further extensive research led the inventors to the idea that the temperature effect is significant not only when the frequency of the applied high-frequency voltage is the resonant frequency, but also when it is an integer multiple of the resonant frequency, and thus conceived the present invention.

[0007] That is, the ultrasonic measuring device according to the present invention transmits an ultrasonic signal into a pipe through which a fluid flows, receives the ultrasonic signal that has passed through the fluid, and measures the fluid. The device comprises an ultrasonic vibrator that transmits and receives the ultrasonic signal, and a voltage application unit that applies a high-frequency voltage to the ultrasonic vibrator to generate an ultrasonic signal, and is characterized in that the voltage application unit applies a high-frequency voltage of a frequency other than an integer multiple of the resonant frequency of the ultrasonic vibrator to the ultrasonic vibrator.

[0008] With this configuration, by setting the frequency of the high-frequency voltage applied to the ultrasonic vibrator to a value other than an integer multiple of the resonant frequency of the ultrasonic vibrator, it is possible to suppress changes in the characteristics of the ultrasonic vibrator, which is a piezoelectric element, due to temperature changes, and reduce measurement errors due to temperature effects.

[0009] It is preferable that the ultrasonic measurement device measures the fluid by receiving an ultrasonic signal that has been reflected one or more times within the pipe. With this configuration, the ultrasonic signal can be reflected one or more times, thereby making it possible to extend the propagation path and improve the resolution. On the other hand, changes in the characteristics of the ultrasonic vibrator can affect the refraction angle when the ultrasonic signal enters the fluid and the reflection angle within the pipe, so the impact of changes in the characteristics of the ultrasonic vibrator is greater in embodiments in which the ultrasonic signal is reflected one or more times. Furthermore, changes in the characteristics of the ultrasonic vibrator can also cause changes in signal strength, so in configurations in which the propagation path is longer due to the ultrasonic signal being reflected one or more times, the influence of changes in signal strength due to changes in the characteristics of the ultrasonic vibrator is more likely to be felt. Therefore, in embodiments in which the ultrasonic signal is reflected one or more times, the effect of the present invention, which is achieved by suppressing changes in the characteristics of the ultrasonic vibrator, is even more pronounced.

[0010] Furthermore, it is preferable that the ultrasonic measurement device includes a plurality of ultrasonic vibrators that transmit and receive ultrasonic signals to and from each other, and that the plurality of ultrasonic vibrators have the same resonance frequency and are made of the same material. In this way, by using multiple ultrasonic transducers with the same resonant frequency and material, the difference in the characteristic changes of each ultrasonic transducer due to temperature changes can be reduced, and the deterioration of measurement accuracy due to temperature effects can be suppressed.

[0011] Furthermore, a specific embodiment that can reduce the influence of temperature changes is one in which the voltage application unit applies to the ultrasonic vibrator a high-frequency voltage having a frequency such that the phase characteristic of the ultrasonic vibrator falls within a range of -90° to -45°. In this case, it is preferable that the voltage application unit applies to the ultrasonic vibrator a high-frequency voltage having a frequency such that the change in the phase characteristic of the ultrasonic vibrator due to temperature changes is 1.0° / °C or less, preferably 0.5° / °C or less. The phase characteristics of an ultrasonic transducer correlate with its frequency, and changes in frequency affect the directivity of the ultrasonic signal, which can affect the changes in the refraction angle and reflection angle mentioned above. Therefore, by reducing the change in the phase characteristics due to temperature changes, the change in the frequency of the ultrasonic transducer due to temperature changes can be reduced, suppressing changes in the refraction angle and reflection angle, and further reducing measurement errors due to temperature effects.

[0012] Another specific embodiment that can reduce the effects of temperature changes is one in which the voltage application unit applies to the ultrasonic vibrator a high-frequency voltage of a frequency that causes the change in impedance characteristics of the ultrasonic vibrator due to temperature changes to be 1.5% / °C or less, preferably 0.5% / °C or less.

[0013] Another specific embodiment that can reduce the effects of temperature changes is one in which the voltage application unit applies to the ultrasonic vibrator a high-frequency voltage of a frequency that causes the change in capacitance characteristics of the ultrasonic vibrator due to temperature changes to be 5.0 pF / °C or less, preferably 1.5 pF / °C or less.

[0014] The impedance characteristics and capacitance of an ultrasonic transducer correlate with the intensity of the ultrasonic signal it generates, which can lead to measurement errors. Specifically, changes in intensity affect the stability of the measurement reading (causing it to fluctuate), and the fluctuation in the measurement reading itself is a direct cause of measurement errors. Furthermore, fluctuations in the measurement reading also affect the adjustment of the zero point, resulting in measurement errors due to a shift in the zero point. Therefore, by minimizing the changes in impedance characteristics and capacitance due to temperature changes, the change in ultrasonic signal intensity due to temperature changes can be minimized, further reducing measurement errors due to temperature effects.

[0015] An example of an embodiment in which the effects of the present invention are particularly pronounced is a clamp-on type ultrasonic measuring device that further includes an alignment member that is interposed between the ultrasonic vibrator and the piping and transmits ultrasonic vibrations, and is attached to the outer peripheral surface of the piping when in use. By making the ultrasonic measuring device a clamp-on type in this way, the ultrasonic measuring device can be easily attached to the piping. On the other hand, clamp-on types often have a casing that is divided into a cover member and a main body member, with a pair of ultrasonic vibrators mounted on the main body member. In other words, clamp-on type ultrasonic measurement devices are often configured so that the ultrasonic signal is reflected more than once. In this case, the effects of changes in the characteristics of the ultrasonic vibrator, as described above, become more pronounced. Therefore, the effect of the present invention becomes even more pronounced in the clamp-on type. [Effects of the Invention]

[0016] According to the present invention as described above, it is possible to provide an ultrasonic measurement device that can suppress changes in the transmission and reception characteristics of ultrasonic signals due to temperature changes and reduce measurement errors due to temperature effects. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram showing the overall configuration of an ultrasonic measurement device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram schematically showing the internal configuration of the ultrasonic measurement device according to the embodiment. [Figure 3] 1A is a perspective view showing the configuration of the alignment member of the embodiment, FIG. 1B is a plan view seen from the tube axis direction, and FIG. 1C is a plan view seen from a direction perpendicular to the tube axis direction. [Figure 4] FIG. 2 is a diagram showing the ultrasonic measurement device of the embodiment with the casing open. [Figure 5] 6 is a graph illustrating the effect of the ultrasonic measurement device according to the embodiment. [Figure 6] 6 is a graph illustrating the effect of the ultrasonic measurement device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] An ultrasonic measurement device 100 according to one embodiment of the present invention will be described below with reference to the drawings.

[0019] The ultrasonic measurement device 100 of this embodiment is a so-called clamp-on type ultrasonic flowmeter that is attached to the outer peripheral surface of a pipe P through which a fluid such as a liquid or gas flows and measures the flow rate of the fluid flowing through the pipe P.

[0020] 1 and 2, the ultrasonic measuring device 100 comprises a plurality of (here, a pair of) ultrasonic vibrators 1 arranged at a distance along the axial direction of the pipe P to which the device is attached (or the direction in which the fluid flows), a pair of matching members 2 interposed between each ultrasonic vibrator 1 and the pipe P to transmit ultrasonic vibrations, a casing 3 that houses and holds the ultrasonic vibrators 1 and the matching members 2 and is configured to be detachably attached to the pipe P, and a voltage application unit 4 that applies a high-frequency voltage to each ultrasonic vibrator 1 to drive it and generate an ultrasonic signal. The ultrasonic measuring device 100 is a so-called propagation time type that alternately transmits and receives ultrasonic signals using the pair of ultrasonic vibrators 1 and measures the flow rate based on the difference in propagation time between the two ultrasonic signals. Each unit will be described below.

[0021] The ultrasonic transducer 1 transmits and receives ultrasonic vibrations through, for example, a substantially circular acoustic emission surface 1s, and is configured using, for example, a piezoelectric element made of PZT (lead zirconate titanate). The ultrasonic transducers 1 of this embodiment are arranged one on the upstream side and one on the downstream side along the axial direction of the pipe P, and are arranged in a positional relationship such that ultrasonic vibrations emitted from one ultrasonic transducer 1 and reflected one or more times within the pipe P (for example, by the pipe wall) are received by the other ultrasonic transducer 1. More specifically, the pair of ultrasonic transducers 1 are arranged at approximately the same positions in the circumferential direction of the pipe P when viewed from the axial direction, but this is not limited to this. The pair of ultrasonic transducers 1 are identical and have the same resonance frequency Fr.

[0022] The matching members 2 are provided to reduce the difference in acoustic impedance between the ultrasonic transducer 1 and the piping P, thereby enabling efficient transmission of ultrasonic vibrations. A pair of matching members 2 is provided corresponding to each ultrasonic transducer 1, and transmits ultrasonic signals transmitted from the ultrasonic transducer 1 to the piping P, and also transmits ultrasonic signals from the piping P to the ultrasonic transducer 1. The matching members 2 are installed on an installation surface 3s set on the inner surface of the casing 3.

[0023] Specifically, as shown in FIG. 3 , the matching member 2 has a rectangular columnar shape, with its column axis (height direction) perpendicular to the pipe axis direction of the piping P. The matching member 2 is a resin-molded product entirely made of an elastic material (elastically deformable material) such as a silicone-based resin, and is configured as a single component. The matching member 2 has a contact surface 22s that elastically deforms to come into close contact with the surface of the piping P and thereby transmits ultrasonic vibrations to and from the piping P, a transducer mounting surface 23 that is attached so that the acoustic emission surface 1s of the ultrasonic transducer 1 is in surface contact with the contact surface 22s and transmits ultrasonic vibrations to and from the ultrasonic transducer 1, and an installation surface 25 that contacts the installation surface 3s of the casing 3. In the matching member 2 of this embodiment, the contact surface 22s is formed so as to be convex toward the piping P, but this is not limited thereto. The contact surface 22s may be formed so as to be concave toward the piping P, or may simply be flat.

[0024] The casing 3 is elongated, for example, in the shape of a rectangular parallelepiped, and is attached to the pipe P so that its longitudinal direction coincides with the axial direction of the pipe P. Specifically, as shown in Fig. 4, the casing 3 holds the pair of ultrasonic vibrators 1 and the pair of matching members 2 spaced apart along the longitudinal direction, and includes a box-shaped main body member 31 that opens in one direction perpendicular to the longitudinal direction, a plate-shaped lid member 32 that covers the opening of the main body member 31, and a locking mechanism 33 that locks the movement of the lid member 32 with the opening of the main body member 31 covered. The casing 3 is configured to be attached to the pipe P by sandwiching the pipe P between the main body member 31 and the lid member 32 and gripping its outer circumferential surface. The main body member 31 holds the ultrasonic vibrator 1 and the matching member 2 so that the contact surface 22s of the matching member 2 faces the back surface of the cover member 32, and when the piping P is sandwiched between the main body member 31 and the cover member 32, the piping P is pressed against the contact surface 22s of the matching member 2, causing the contact surface 22s to elastically deform.

[0025] The voltage application unit 4 applies a high-frequency voltage of a predetermined frequency Fp to the ultrasonic transducer 1. Specifically, the voltage application unit 4 includes a signal generator that generates a voltage signal of an arbitrary frequency Fp, and an output unit that outputs the generated voltage signal to the ultrasonic transducer 1.

[0026] Thus, in the ultrasonic measurement device 100 of this embodiment, the voltage application unit 4 is configured to apply a high-frequency voltage of a frequency Fp other than an integer multiple of the resonance frequency Fr of the ultrasonic transducer 1 to the ultrasonic transducer 1 (i.e., Fp≠n×Fr, n is an integer equal to or greater than 1). Under these conditions, the voltage application unit 4 further sets the frequency Fp of the high-frequency voltage so that the phase characteristic, impedance characteristic, and capacitance characteristic of the ultrasonic transducer 1 satisfy the following conditions:

[0027] (Phase characteristics) The phase characteristic of the ultrasonic vibrator 1 indicates the resonance characteristic of the ultrasonic vibrator. In the voltage application unit 4 of this embodiment, the frequency Fp of the high-frequency voltage to be applied is set so that the phase characteristic of the ultrasonic vibrator 1 is in the range of -90° or more and -45° or less.

[0028] More specifically, the voltage application unit 4 sets the frequency Fp of the high-frequency voltage to be applied so that the change in phase characteristics of the ultrasonic transducer 1 due to temperature change is 1.0° / °C or less, preferably 0.5° / °C or less. The "temperature change" refers to a temperature change in the vicinity of the temperature of the fluid flowing through the pipe P to which the ultrasonic measurement device 100 is attached, and is, for example, a temperature change in the temperature range of 20°C to 30°C, but is not limited to this.

[0029] (Impedance characteristics) The impedance characteristics of the ultrasonic transducer 1 indicate the electrical resistance to the frequency Fp of the applied high-frequency voltage. In the voltage application unit 4 of this embodiment, the frequency Fp of the applied high-frequency voltage is set so that the change in the impedance characteristics of the ultrasonic transducer due to temperature change is 1.5% / °C or less, preferably 0.5% / °C or less. The "temperature change" here is as described above.

[0030] (Capacitance characteristics) Furthermore, in the voltage application unit 4 of this embodiment, the frequency Fp of the high frequency voltage to be applied is set so that the change in the capacitance characteristics of the ultrasonic transducer 1 due to temperature change is 5.0 pF / °C or less, preferably 1.5 pF / °C or less. The "temperature change" here is as described above.

[0031] According to the ultrasonic measurement device 100 of this embodiment configured as described above, the frequency Fp of the high-frequency voltage applied to the ultrasonic vibrator 1 is set to a value other than an integer multiple of the resonance frequency Fr of the ultrasonic vibrator 1, and the amounts of change in the phase characteristics, impedance characteristics, and capacitance characteristics of the ultrasonic vibrator 1 due to temperature change are set to be within a predetermined range, thereby suppressing changes in the characteristics of the ultrasonic vibrator 1, which is a piezoelectric element, due to temperature change and reducing measurement errors due to temperature effects.

[0032] Graphs illustrating the effects of the ultrasonic measurement device 100 of this embodiment are shown in FIGS.

[0033] 5 and 6 are graphs plotting flow rate values ​​output from the ultrasonic measuring device 100 while changing the ambient temperature after attaching the ultrasonic measuring device 100 to a pipe through which no fluid is flowing (i.e., a pipe with zero flow rate). In Fig. 5, a high-frequency voltage having the same frequency as the resonant frequency was applied to the ultrasonic vibrator 1, and in Fig. 6, a high-frequency voltage having a frequency Fp other than an integer multiple of the resonant frequency was applied to the ultrasonic vibrator 1.

[0034] As shown in Figure 5, when a high-frequency voltage with the same frequency as the resonant frequency is applied to the ultrasonic vibrator 1, changes in ambient temperature cause a large deviation in the flow rate value. On the other hand, as shown in Figure 6, when a high-frequency voltage with a frequency other than an integer multiple of the resonant frequency is applied to the ultrasonic vibrator 1, deviations in the flow rate value caused by changes in ambient temperature can be significantly reduced.

[0035] The present invention is not limited to the above-described embodiment. For example, in the above embodiment, the voltage application unit 4 sets the frequency Fp of the high-frequency voltage so that the phase characteristics, impedance characteristics, and capacitance characteristics of the ultrasonic transducer 1 satisfy various conditions, but this is not limited to this. The effects of the present invention can be achieved as long as the voltage application unit 4 is configured to apply to the ultrasonic transducer 1 a high-frequency voltage with a frequency Fp other than an integer multiple of the resonance frequency Fr of the ultrasonic transducer 1.

[0036] In another embodiment, the voltage application unit 4 may set the frequency Fp of the high frequency voltage so as to satisfy the conditions of some of the phase characteristics, impedance characteristics, and capacitance characteristics of the ultrasonic transducer 1.

[0037] The ultrasonic measurement device 100 in the above embodiment is a clamp-on type that is attached to the outer peripheral surface of the pipe P when in use, but is not limited to this. The ultrasonic measurement device 100 in other embodiments does not have to be a clamp-on type.

[0038] Furthermore, although the ultrasonic measurement device 100 in the above embodiment includes a pair of ultrasonic transducers, this is not limiting. The ultrasonic measurement device 100 in other embodiments may include only one ultrasonic transducer, and transmit and receive ultrasonic signals using this single ultrasonic transducer.

[0039] Furthermore, although the ultrasonic measurement device 100 in the above embodiment is an ultrasonic flowmeter that measures the flow rate of a fluid flowing through the pipe P, this is not limiting. The ultrasonic measurement device 100 in another embodiment may be an ultrasonic concentration meter that measures the concentration of a fluid flowing through the pipe P.

[0040] In addition, various modifications and combinations of the embodiments may be made as long as they do not go against the spirit of the present invention. [Explanation of symbols]

[0041] 100 Ultrasonic measuring device 1. Ultrasonic vibrator 2. Alignment member 3 Casing 4. Voltage application section P...Piping

Claims

1. A device that transmits an ultrasonic signal into a pipe through which a fluid flows and receives the ultrasonic signal that has passed through the fluid to measure the fluid, an ultrasonic transducer for transmitting and / or receiving the ultrasonic signal; a voltage application unit that applies a high-frequency voltage to the ultrasonic vibrator to generate an ultrasonic signal, The voltage application unit applies a high-frequency voltage having a frequency other than an integer multiple of the resonant frequency of the ultrasonic transducer to the ultrasonic transducer.

2. 2. The ultrasonic measuring device according to claim 1, wherein the fluid is measured by receiving an ultrasonic signal that has been reflected one or more times within the pipe.

3. a plurality of the ultrasonic transducers that transmit and receive ultrasonic signals to and from each other; 3. The ultrasonic measuring device according to claim 1, wherein the plurality of ultrasonic transducers have the same resonance frequency.

4. 4. The ultrasonic measuring device according to claim 1, wherein the voltage application unit applies to the ultrasonic transducer a high-frequency voltage having a frequency such that the phase characteristic of the ultrasonic transducer is in the range of -90° or more and -45° or less.

5. 5. The ultrasonic measuring device according to claim 4, wherein the voltage application unit applies to the ultrasonic vibrator a high-frequency voltage having a frequency such that a change in the phase characteristics of the ultrasonic vibrator due to a temperature change is 1.0° / °C or less, preferably 0.5° / °C or less.

6. An ultrasonic measuring device according to any one of claims 1 to 5, wherein the voltage application unit applies to the ultrasonic vibrator a high-frequency voltage having a frequency such that a change in impedance characteristics of the ultrasonic vibrator due to temperature change is 1.5% / °C or less, preferably 0.5% / °C or less.

7. The ultrasonic measuring device according to any one of claims 1 to 6, wherein the voltage application unit applies to the ultrasonic vibrator a high-frequency voltage having a frequency such that the change in capacitance characteristics of the ultrasonic vibrator due to temperature change is 5.0 pF / °C or less, preferably 1.5 pF / °C or less.

8. The ultrasonic measuring device according to any one of claims 1 to 7, further comprising an alignment member interposed between the ultrasonic vibrator and the piping to transmit ultrasonic vibrations, and being a clamp-on type device that is attached to the outer peripheral surface of the piping.

Images