JP5156918B2 - Ultrasonic density meter - Google Patents

Description

  The present invention relates to an ultrasonic density meter that measures the density of a fluid using ultrasonic waves.

2. Description of the Related Art Conventionally, an ultrasonic flowmeter that measures the volume flow rate of a liquid using ultrasonic waves has been proposed (see, for example, Patent Document 1). Specifically, as shown in FIG. 11, in the ultrasonic flowmeter 60 of Patent Document 1, a pair of ultrasonic transducers 62 and 63 are provided so as to face each other on the upstream side and the downstream side of the pipe 61 through which the liquid W1 flows. Be placed. And the propagation time until the ultrasonic wave emitted from one ultrasonic transducer propagates in the liquid W1 and reaches the other ultrasonic transducer is measured. Specifically, ultrasonic waves are propagated in the forward and reverse directions of the flow of the fluid W1, and the propagation time in the forward direction and the propagation time in the reverse direction are measured. Here, assuming that the ultrasonic wave propagation distance L between the ultrasonic vibrators 62 and 63, the sound velocity C in the fluid W1, and the flow velocity V of the liquid W1, the forward propagation time Td and the reverse propagation time Tu are: Are represented by the following equations (1) and (2), respectively.

That is, when the flow velocity V of the liquid W1 is increased, the propagation time Td of the ultrasonic S ₀ propagated in the forward direction is shortened, the propagation time Tu of ultrasonic S ₀ propagated in the opposite direction becomes longer (see FIG. 12 ). And the propagation time difference ΔT of the ultrasonic waves S ₀ is expressed as the following equation (3).

Here, the flow velocity V of the liquid W1 is negligible compared with the sound velocity C. Therefore, the above equation (3) can be expressed as the following equation (4).

Therefore, the flow velocity V can be obtained by the following equation (5).

  Further, the volume flow rate Q (= SV) of the liquid W1 is obtained by multiplying the flow velocity V by the cross-sectional area S of the pipe 61.

  In addition, an ultrasonic mass flow meter that measures the density of a fluid using ultrasonic waves and obtains the mass flow rate of the fluid by multiplying the density and the volume flow rate has been proposed (for example, see Patent Document 2). .

In the ultrasonic mass flow meter of Patent Document 2, an ultrasonic transmitter / receiver for measuring a volume flow rate is provided in a flow pipe (flow path) through which a fluid flows, and is connected to both ends of a straight pipe portion of a bypass line branched from the flow pipe. An ultrasonic transmitter and an ultrasonic receiver for measuring the density are provided to face each other. A flow rate adjusting valve is provided in the middle of the bypass line. The flow control valve is closed and the flow of the fluid is set so that the fluid flowing through the bypass line is stationary. In this state, ultrasonic waves are propagated from the ultrasonic transmitter into the bypass line fluid. Is received by an ultrasonic receiver. Then, the attenuation amount of the ultrasonic wave propagating in the fluid is measured based on the received signal at the ultrasonic receiver, and the density of the fluid is obtained from the attenuation amount.
JP 2002-162269 A Japanese Patent Laid-Open No. 10-90028

  By the way, for example, in a chemical factory or the like, when adjusting the flow rate of a fluid generated by mixing two or more kinds of liquids, even if the density of the liquid is not uniform and the liquid density is not uniform, The state cannot be reliably detected by the flow rate. In this case, it is necessary to detect the density change of the liquid.

  However, the conventional ultrasonic mass flow meter disclosed in Patent Document 2 cannot obtain an accurate density unless the fluid is made stationary by a bypass line, and the density of the fluid flowing through the flow path is determined in real time. It is difficult to detect with. In addition, even when using a general density meter that does not use ultrasonic waves, it is necessary to measure the density by moving the fluid to the measuring instrument body side, and it is difficult to detect the density of the fluid flowing through the flow path in real time. It is.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an ultrasonic density meter that can quickly measure the density of a fluid flowing through a flow path using ultrasonic waves. .

  In order to solve the above-mentioned problem, the invention described in claim 1 is an ultrasonic density meter that irradiates a fluid flowing through a flow path with ultrasonic waves and obtains the density of the fluid based on the reflected wave. A pair of ultrasonic transducers that are disposed on the outer wall surface of the tube main body constituting the tube, propagate ultrasonic waves in the fluid in a direction orthogonal to the flow, and receive ultrasonic waves reflected by the inner wall surface of the tube main body A sound speed calculating means for obtaining a sound speed of the fluid based on a propagation time and a propagation distance of the ultrasonic wave propagating in the fluid, a signal intensity of the reflected wave received by each ultrasonic transducer, and the tube body Acoustic impedance calculating means for obtaining the acoustic impedance of the fluid based on the acoustic impedance of the fluid, and density calculating means for obtaining the density of the fluid by dividing the acoustic impedance of the fluid by the speed of sound. The ultrasonic densitometer, characterized in that had example as its gist.

  According to the first aspect of the present invention, a pair of ultrasonic vibrators are arranged on the outer wall surface of the tube body constituting the flow path, and each ultrasonic vibrator is orthogonal to the flow in the fluid flowing through the flow path. The ultrasonic wave is propagated in the direction to be transmitted, and the ultrasonic wave reflected by the inner wall surface of the tube main body is received. Then, the sound velocity calculation means obtains the sound velocity of the fluid based on the propagation time and propagation distance of the ultrasonic wave propagating in the fluid. Further, the acoustic impedance calculation means determines the acoustic impedance of the fluid based on the signal intensity of the reflected wave received by each ultrasonic transducer and the acoustic impedance of the tube body. Furthermore, the density of the fluid is obtained by dividing the acoustic impedance of the fluid by the speed of sound by the density calculating means. By configuring the ultrasonic density meter in this way, the density of the fluid can be measured in real time while the fluid is flowing through the flow path in the tube body, so that the density change of the fluid can be detected quickly. be able to.

  According to a second aspect of the present invention, in the first aspect, the tube main body has a pair of inner wall surfaces parallel to the direction in which the fluid flows, and the ultrasonic transducer flows through one inner wall surface. The gist is to propagate ultrasonic waves into the fluid in the passage and receive the ultrasonic waves reflected by the other inner wall surface.

  According to the second aspect of the present invention, the ultrasonic transducer can reliably propagate the ultrasonic wave in the direction orthogonal to the fluid flow, and the reflected wave reflected by each inner wall surface of the flow path can be accurately detected. Can be received.

  According to a third aspect of the present invention, in the second aspect, the pair of ultrasonic transducers are respectively disposed on an outer wall surface on the upstream side and the downstream side of the pipe body, and the inner side is formed between the upstream side and the downstream side. The gist is that the interval between the walls is different.

  According to the invention described in claim 3, since the pair of ultrasonic transducers are arranged so as to be shifted on the upstream and downstream outer wall surfaces, the ultrasonic waves emitted from the ultrasonic transducers interfere with each other. The reflected wave can be reliably received. Also, since the ultrasonic propagation distance is different between the upstream side and the downstream side in the tube body, reflected waves with different signal intensities are received by each ultrasonic transducer when the ultrasonic wave attenuates according to the propagation distance. The And based on the signal intensity of these reflected waves and the acoustic impedance of the tube body, the acoustic impedance of the fluid can be obtained.

  According to a fourth aspect of the present invention, in the second aspect, the pair of ultrasonic transducers are respectively disposed on an outer wall surface on the upstream side and the downstream side of the pipe main body, and the pipe is formed on the upstream side and the downstream side. The main point is that the acoustic impedance of the main body is varied.

  According to the invention described in claim 4, since the pair of ultrasonic transducers are arranged so as to be shifted on the upstream and downstream outer wall surfaces, the ultrasonic waves emitted from the ultrasonic transducers interfere with each other. The reflected wave can be reliably received. In addition, since the acoustic impedance differs between the upstream side and the downstream side of the tube body, the reflected wave with different signal intensity is received by each ultrasonic transducer when the reflectance of the ultrasonic wave changes according to the acoustic impedance. The Then, the acoustic impedance of the fluid can be obtained based on the signal intensity of the reflected wave and each acoustic impedance of the tube body.

  According to a fifth aspect of the present invention, in the second aspect, the tube main body is formed in a rectangular shape, and one ultrasonic transducer of the pair of ultrasonic transducers is a first outer portion of the tube main body. The gist is that the other ultrasonic transducer is disposed on the wall surface and disposed on the second outer wall surface orthogonal to the first outer wall surface.

  According to the invention described in claim 5, since the ultrasonic propagation distance is different between one ultrasonic transducer and the other ultrasonic transducer, the ultrasonic wave is attenuated according to the propagation distance, Reflected waves having different signal intensities are received by each ultrasonic transducer. And based on the signal intensity of these reflected waves and the acoustic impedance of the tube body, the acoustic impedance of the fluid can be obtained. In this case, since it is not necessary to dispose each ultrasonic transducer in the fluid flow direction (upstream or downstream direction), the ultrasonic density meter can be formed compactly.

  As described above in detail, according to the first to fifth aspects of the present invention, an ultrasonic density meter capable of quickly measuring the density of the fluid flowing through the flow path using ultrasonic waves can be provided. .

[First Embodiment]

  DESCRIPTION OF EMBODIMENTS A first embodiment embodying the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an ultrasonic flow meter 1 of the present embodiment. The ultrasonic flowmeter 1 includes a first sensor unit 2 for measuring the volume flow rate of the liquid W1 (for example, a chemical solution for semiconductor cleaning) by an ultrasonic propagation time difference method, and a sound speed and density of the liquid W1. The second sensor unit 3 is provided in the middle of a supply pipe 4 for supplying the liquid W1.

  An adjustment valve 5 for adjusting the flow rate of the liquid W1 is provided on the upstream side of the supply pipe 4, and a controller 6 for changing the opening degree is connected to the adjustment valve 5. In the present embodiment, the measurement value of the volume flow rate or the mass flow rate measured by the ultrasonic flow meter 1 is transmitted to the controller 6, and the controller 6 controls the opening degree of the adjustment valve 5, thereby supplying the supply pipe 4. The flow rate of the flowing liquid W1 is adjusted to be a predetermined flow rate set in advance.

  Hereinafter, a specific configuration of the ultrasonic flowmeter 1 of the present embodiment will be described in detail.

  As shown in FIG. 1, the first sensor unit 2 of the ultrasonic flowmeter 1 is fixed to a pipe 11 bent in a substantially U shape and two corners 11 a and 11 b of the pipe 11. And a pair of ultrasonic transducers 12 and 13 arranged to face each other via 11 straight pipe portions 11c. The pipe 11 of the first sensor unit 2 is formed using a fluororesin (for example, Teflon (registered trademark)) having excellent chemical resistance, and the length of the straight pipe portion 11c is about 10 cm. Moreover, the cross-sectional shape of the flow path formed in this piping 11 is circular, and the aperture is about 10 mm. Thus, by making the cross-sectional shape of a flow path circular, the turbulent flow of the liquid W1 is prevented in the flow path, and the liquid W1 flows smoothly.

As shown in FIG. 2, the second sensor unit 3 is connected to the pipe 15 (pipe body) connected to the downstream side of the first sensor unit 2, and the upstream and downstream outer wall surfaces of the pipe 15. A pair of ultrasonic transducers 16 and 17 are provided. The pipe 15 of the second sensor unit 3 is also formed using a fluororesin (for example, Teflon (trade name)) having excellent chemical resistance. The pipe 15 the cross-sectional shape of the formed are flow paths within denote squares, ultrasonic S ₀ emitted from each of the ultrasonic transducers 16 and 17, a direction parallel to a pair of inner wall surfaces 15a of the flow of liquid W1, It is incident at an angle that intersects perpendicularly to 15b. In the pipe 15, the interval between the inner wall surfaces 15 a and 15 b is different between the upstream side and the downstream side where the pair of ultrasonic transducers 16 and 17 are provided. Specifically, the upstream side of the inner wall surface 15a, distance _{d 1} and 15b has a inner wall surface 15a, 15b 2 times the distance of the spacing _{d 2} of the downstream side. Further, the thickness of the side wall of the pipe 15 provided with the pair of ultrasonic transducers 16 and 17 is equal on the upstream side and the downstream side.

  In the ultrasonic flow meter 1, a control device 20 is electrically connected to the ultrasonic transducers 12 and 13 of the first sensor unit 2 and the ultrasonic transducers 16 and 17 of the second sensor unit 3. . In the present embodiment, an ultrasonic density meter is configured by the second sensor unit 3 and the control device 20.

  FIG. 3 is a block diagram showing an electrical configuration of the ultrasonic flowmeter 1. As shown in FIG. 3, the control device 20 includes a CPU 21, a first signal processing circuit 22, a second signal processing circuit 23, a memory 24, an input device 25, a display device 26, and a data output circuit 27.

  The first signal processing circuit 22 includes a switching circuit 31, a pulse generation circuit 32, a reception circuit 33, a detection circuit 34, and an A / D conversion circuit 35.

  The switching circuit 31 connects the upstream ultrasonic transducer 12 of the pair of ultrasonic transducers 12 and 13 to the pulse generation circuit 32 and connects the downstream ultrasonic transducer 13 to the reception circuit 33. 1 and a second connection position for connecting the ultrasonic transducer 13 on the downstream side to the pulse generation circuit 32 and the second connection position for connecting the ultrasonic transducer 12 on the upstream side to the reception circuit 33. ing. The connection position in the switching circuit 31 is controlled by a switching signal output from the CPU 21.

  The pulse generation circuit 32 operates in response to a control signal from the CPU 32 and outputs drive pulses for driving the ultrasonic transducers 12 and 13. This drive pulse is supplied to the ultrasonic transducers 12 and 13 via the switching circuit 31. Here, for example, when the switching circuit 31 is switched to the first connection position, a drive pulse is supplied to the ultrasonic transducer 12 on the upstream side, and the ultrasonic transducer 12 vibrates, so that a predetermined frequency (specifically, Specifically, an ultrasonic wave having a frequency of 1 MHz is output. The ultrasonic wave propagates in the liquid W1 of the pipe 11 in the positive direction of the flow of the liquid W1 and is received by the ultrasonic transducer 13 on the downstream side. Conversely, when the switching circuit 31 is switched to the second connection position, a drive pulse is supplied to the ultrasonic transducer 13 on the downstream side, and the ultrasonic transducer 13 vibrates, thereby causing a predetermined frequency. An ultrasonic wave (specifically, a frequency of 1 MHz) is output. Then, the ultrasonic wave propagates in the liquid W1 of the pipe 11 in the direction opposite to the flow of the liquid W1, and is received by the ultrasonic transducer 12 on the upstream side.

  The reception circuit 33 includes a signal amplification circuit (not shown), amplifies the ultrasonic signals received by the ultrasonic transducers 12 and 13, and then outputs them to the detection circuit 34. The detection circuit 34 includes a gate circuit (not shown), extracts an ultrasonic signal for one pulse from the received signal, and outputs it to the A / D conversion circuit 35. The A / D conversion circuit 35 A / D converts an ultrasonic signal that is an analog signal into a digital signal. The CPU 21 takes in the ultrasonic signal after this A / D conversion and temporarily stores it in the memory 24.

  The second signal processing circuit 23 includes a switching circuit 41, a pulse generation circuit 42, a reception circuit 43, a detection circuit 44, an A / D conversion circuit 45, and a timer 46.

  The switching circuit 41 includes a first switch unit 41a and a second switch unit 41b. In the first switch unit 41a, either the upstream ultrasonic transducer 16 or the downstream ultrasonic transducer 17 is connected. The connection position is switched, and the second switch unit 41 b switches the connection position to either the pulse generation circuit 42 or the reception circuit 43. The connection position in the switching circuit 41 is also controlled by a switching signal output from the CPU 21.

  The pulse generation circuit 42 operates in response to a control signal from the CPU 21 and outputs drive pulses for driving the ultrasonic transducers 16 and 17. The drive pulse is output, for example, every 500 ms, and is alternately supplied to the upstream ultrasonic transducer 16 and the downstream ultrasonic transducer 17 via the switching circuit 41. Then, the ultrasonic transducers 16 and 17 are vibrated by the drive pulse, whereby ultrasonic waves having a predetermined frequency (specifically, a frequency of 1 MHz) are output.

As shown in FIG. 2, the ultrasonic wave S ₀ output from each of the ultrasonic transducers 16 and 17 propagates through the side wall of the pipe 15 to the liquid W1 that flows inside the pipe 15. At this time, a portion of the ultrasonic S _0, together with reflected at the boundary surface between the pipe 15 and the liquid W1 (one inner wall surface 15a of the flow path), propagates partially through the liquid W1. In addition, some of the ultrasonic S ₀ propagating liquid W1 is reflected by the boundary surface between the liquid W1 and pipe 15 (the other of the inner wall surface 15b of the flow path). Here, on the upstream side, the reflected wave S ₀₁ reflected by one inner wall surface 15 a and the reflected wave S ₁₁ reflected by the other inner wall surface 15 b are received by the ultrasonic transducer 16 and converted into an electronic signal. Further, on the downstream side, and one reflected wave S ₁₂ reflected by the reflection wave S ₀₂ and the other inner wall surface 15b that is reflected by the inner wall surface 15a of are received by the ultrasonic transducer 17 and converted into an electronic signal. The signals of these reflected waves S ₀₁ , S ₁₁ , S ₀₂ , S ₁₂ are supplied to the receiving circuit 43 via the switching circuit 41.

The reception circuit 43 includes a signal amplification circuit (not shown), amplifies the reflected waves S ₀₁ , S ₁₁ , S ₀₂ , and S ₁₂ received by the ultrasonic transducers 16 and 17, and then outputs the amplified signals to the detection circuit 44. . The detection circuit 44 is a circuit for detecting the reflected waves S ₀₁ , S ₁₁ , S ₀₂ , S ₁₂ of the ultrasonic waves reflected by the inner wall surfaces 15a, 15b in the pipe 15, and is not shown in the figure. Etc. Specifically, the detection circuit 44 extracts the reflected waves _{S 01, S 11, S 02} , S 12 by the gate circuit corresponding to the signal intensity of each reflected wave _{S 01, S 11, S 02} , S 12 The voltage signal is output to the A / D conversion circuit 45. The A / D conversion circuit 45 A / D converts a voltage signal, which is an analog signal, into a digital signal, and the CPU 21 takes in the voltage signal after the A / D conversion, and each reflected wave S ₀₁ , S ₁₁ , S _02. , S ₁₂ , and stored in the memory 24. Further, the detection circuit 44 detects the timing at which the signals of the reflected waves S ₀₁ , S ₁₁ , S ₀₂ and S ₁₂ exceed a predetermined threshold voltage by the comparison circuit, and notifies the timer 46 of the detection signal.

The timer 46 measures the propagation time of the ultrasonic wave S ₀ based on the detection signal output from the detection circuit 44 and outputs data corresponding to the time. The propagation time data is stored in the memory 24 by the CPU 21.

  The CPU 21 executes a control program using the memory 24 and controls the entire apparatus in an integrated manner. The control program includes a program for calculating sound speed, density, volume flow rate, and mass flow rate, a program for displaying the measured values, and the like. The program executed by the CPU 21 may be a program stored in a storage medium such as a memory card or a program downloaded via a communication medium, and is read into the memory 24 and used at the time of execution.

  The display device 26 is, for example, a liquid crystal display, and is used for displaying measured values of sound speed, density, volume flow rate, and mass flow rate. The input device 25 includes various operation buttons and is used for starting / ending measurement, setting a display mode, and the like. The data output circuit 27 includes an interface for data output (for example, a port such as RS232), and transfers data relating to the measured volume flow rate or mass flow rate to the controller 6.

  Next, a specific method for calculating the speed of sound C in the liquid W1 in the present embodiment will be described.

First, in the second sensor unit 3, the ultrasonic wave S ₀ is output from the ultrasonic transducer 16 on the upstream side. Pipe 15 for liquid W1 and acoustic impedance made of a fluororesin is different, the pair of inner wall surfaces 15a, 15b ultrasound _{S 0} in (the boundary surface between the liquid W1) is reflected respectively. Then, the ultrasonic wave propagation time T1 (= t2−t1) is acquired from the reception times t1 and t2 of the reflected waves S ₀₁ and S ₁₁ (see FIG. 4). Specifically, as shown in FIG. 4, the detection signal from the detection circuit 44 is received at the reception times t1 and t2 of the reflected waves S ₀₁ and S ₁₁ (timing when the waveform signal exceeds a predetermined threshold voltage). Is output. In the timer 46, the time from the received reflected waves S ₀₁ based on the detection signal to the reflected wave S ₁₁ is received is measured, the measured value is acquired as the propagation time T1. Here, since the propagation distance of the ultrasonic wave S ₀ is twice the distance d ₁ (width of the flow path) between the inner wall surfaces 15a and 15b, the propagation distance 2d ₁ is propagated as shown in the following equation (6). By dividing by time T1, the speed of sound C in the liquid W1 is obtained.

Also, the sound velocity C in the liquid W1 can be obtained in the same manner by using the ultrasonic transducer 17 on the downstream side. It should be noted that in this case, the propagation distance of the ultrasonic wave becomes 2d _2.

  Next, a method for calculating the acoustic impedance and density of the liquid W1 will be described.

In the second sensor unit 3, an ultrasound _{S 0} emitted from each of the ultrasonic transducers 16, 17 is partially reflected at the boundary surface between the pipe 15 and the liquid W1 (the inner wall surface 15a, 15b) ( (See FIG. 2).

The signal intensities of the reflected waves S ₀₁ , S ₁₁ , S ₀₂ , and S _{12 on} the inner wall surfaces 15a and 15b have the following relationships (7) and (8).

Here, α is the attenuation constant of the liquid W1, Z ₀ is the acoustic impedance of the fluororesin constituting the pipe 15, and Z _f is the acoustic impedance of the liquid W1.

These formula (7) and (8), it is possible to obtain the reflected waves _{S 01, S 11, S 02} , the acoustic impedance _{Z f} of the liquid W1 based on the signal strength and the acoustic impedance _{Z 0} of the _{S 12} .

Then, the density ρ of the liquid W1 is obtained by the following equation (9) based on the acoustic impedance _Zf and the sound velocity C.

  Next, a specific method for calculating the volume flow rate and the mass flow rate in the present embodiment will be described.

  In the present embodiment, first, in the pair of ultrasonic transducers 12 and 13 of the first sensor unit 2, for example, every 250 μs, with one predetermined pattern in the order of forward direction, reverse direction, reverse direction, and forward direction. The ultrasonic wave is transmitted from the ultrasonic vibrator and the ultrasonic waves propagated in the liquid W1 are received by the other ultrasonic vibrator. At this time, the ultrasonic signals converted into electric signals by the ultrasonic transducers 12 and 13 are further passed through the switching circuit 31, the receiving circuit 33, the detection circuit 34, and the A / D conversion circuit 35 in the first signal processing circuit 22. Then, after being converted into a digital signal, it is stored in the memory 24 as an ultrasonic waveform signal. In the present embodiment, the waveform signals for four pulses acquired by transmitting and receiving the predetermined pattern of ultrasonic waves described above are stored in the memory 24 as a data lump for obtaining the flow rate of the liquid W1.

  Then, the correlation function of the waveform signal is calculated by comparing the waveform signals of the ultrasonic waves. Specifically, for example, the waveform signal of the first pulse transmitted / received first is compared with the waveform signal of the second pulse transmitted / received next, and a correlation function based on the first pulse is obtained. In addition, the waveform signal of the first pulse and the waveform signal of the third pulse are compared to obtain a correlation function based on the first pulse. Further, the waveform signal of the first pulse and the waveform signal of the fourth pulse are compared to obtain a correlation function based on the first pulse. Similarly, the second pulse waveform signal and the third pulse waveform signal are compared to obtain a correlation function based on the second pulse, and the second pulse waveform signal and the fourth pulse waveform signal are compared. To obtain a correlation function based on the second pulse. Further, the third pulse waveform signal and the fourth pulse waveform signal are compared to obtain a correlation function based on the third pulse.

  Here, when a foreign substance such as a bubble is included in the liquid W1 flowing through the pipe 11, since the ultrasonic wave is irregularly reflected by the foreign substance, each received ultrasonic wave has a different waveform. In this case, the correlation value of the correlation function obtained from each waveform signal is considerably smaller than 1. On the other hand, when bubbles are not included in the liquid W1, the waveforms of the ultrasonic waves are similar, and the correlation value of the correlation function is a value close to 1 (for example, 0.97). Therefore, in this embodiment, when the correlation value of the correlation function is a value close to 1 (for example, 0.9 or more), it is determined that the waveform signal is effective for measurement. Then, an ultrasonic propagation time difference is obtained based on the waveform signal determined to be valid.

  In the present embodiment, both the first pulse ultrasonic wave and the fourth pulse ultrasonic wave propagate in the liquid W1 in the positive direction. Therefore, as shown in FIG. 5, the correlation function f1 obtained by comparing the waveform signals of these ultrasonic waves has a temporal deviation of zero. In contrast, the ultrasonic waves of the first pulse and the ultrasonic waves of the second pulse propagate in the forward direction and the reverse direction. For this reason, the correlation function f2 obtained by comparing these ultrasonic waveform signals causes a deviation of the ultrasonic propagation time difference ΔT when compared with the correlation function f1. Therefore, in the present embodiment, the ultrasonic propagation time difference ΔT is obtained based on the time when the correlation value of the correlation function f2 becomes maximum.

  Then, the flow velocity V of the fluid W1 is obtained by substituting the sound velocity C in the liquid W1 obtained by the equation (6) and the propagation time difference ΔT into the equation (5). Further, the volume flow rate Q (= SV) of the liquid W1 is obtained by multiplying the flow velocity V by the cross-sectional area S of the pipe 11.

  In the actual flow rate measurement, the flow of the liquid W1 is disturbed in the two corner portions 11a and 11b of the pipe 11. Further, in the pipe 11, the flow of the liquid W <b> 1 is faster at the center portion than at the side wall side. Therefore, a more accurate volume flow rate Q is calculated by performing a correction calculation in consideration of the flow velocity distribution of the liquid W1. Furthermore, the mass flow rate M (= ρQ) is obtained by multiplying the density ρ obtained by the above equation (9) and the volume flow rate Q.

  Next, in the present embodiment, a processing example for measuring the density ρ of the liquid W1 will be described with reference to the flowchart of FIG. 6 is started when an operator operates a start button provided on the input device 25.

First, the CPU 21 operates the pulse generation circuit 42 of the second signal processing circuit 23 to output a drive pulse every 500 ms, for example, and switches the connection position of the switching circuit 41 so that the upstream side in the second sensor unit 3 is switched. Drive pulses are sequentially supplied to the ultrasonic transducer 16 and the downstream ultrasonic transducer 17 (step 100). Thereby, the ultrasonic _{S 0} from the ultrasonic transducer 16, 17 is illuminated, the inner wall surface 15a of the flow path, the reflected wave _S 01 reflected by _{15b, S 11, S 02,} S 12 electric signals Is extracted by the detection circuit 44. Then, the CPU 21 takes in the data converted by the A / D conversion circuit 45 and stores it in the memory 24 as data of the signal intensity of the reflected waves S ₀₁ , S ₁₁ , S ₀₂ , S ₁₂ . At this time, the ultrasonic wave propagation time T1 is measured by the timer 46 based on the reception timing of the reflected waves S ₀₁ and S ₁₁ , and the data of the propagation time T 1 is stored in the memory 24.

Then, CPU 21 of the sound velocity calculation means, based on the propagation distance 2d ₁ and the propagation time T1 of the ultrasonic wave, it obtains the sound velocity C of the liquid W1 (step 110). Further, the CPU 21 as the acoustic impedance calculating means, based on the signal intensity of each reflected wave S ₀₁ , S ₁₁ , S ₀₂ , S ₁₂ and the acoustic impedance Z _{0 of the} pipe 15 (fluororesin), the acoustic impedance of the liquid W1. _Zf is obtained (step 120). Furthermore, CPU 21 of the density calculating means calculates the density of the liquid W1 [rho by dividing the acoustic impedance _{Z f} of the liquid W1 at the speed of sound C (step 130).

  Thereafter, the CPU 21 determines whether or not to continue the density ρ measurement process (step 140). Specifically, the CPU 21 determines whether or not the end button of the input device 25 is operated. When the end button is not operated, the CPU 21 returns to the process of step 100 and performs the processes of steps 100 to 140. Again. And when the end button of the input device 25 is operated, CPU21 complete | finishes the process of FIG.

  Next, in the present embodiment, a processing example for measuring the mass flow rate M of the liquid W1 will be described with reference to the flowchart of FIG. The process of FIG. 7 is executed after the sound speed C and the density ρ of the liquid W1 are measured by the process of FIG.

  First, the CPU 21 operates the pulse generation circuit 32 of the first signal processing circuit 22 to output a drive pulse every 250 μs, and switches the connection position of the switching circuit 31, and the ultrasonic transducer 12 on the upstream side and the downstream side. Drive pulses are sequentially supplied to the ultrasonic transducer 13 on the side (step 200). Thereby, in each ultrasonic transducer | vibrator 12, 13, an ultrasonic wave is transmitted / received by the predetermined pattern which becomes a forward direction, a reverse direction, a reverse direction, and the order of a forward direction. The ultrasonic signals received by the ultrasonic transducers 12 and 13 are converted into digital signals through the switching circuit 31, the reception circuit 33, the detection circuit 34, and the A / D conversion circuit 35 in the first signal processing circuit 22. Converted. The CPU 21 sequentially takes in the ultrasonic signals after the A / D conversion and stores them in the memory 24 as ultrasonic waveform signals. Here, the waveform signals for the four pulses of the predetermined pattern described above are stored in the memory 24.

  Thereafter, the CPU 21 reads the waveform signals of the respective ultrasonic waves, compares the waveform signals, and calculates a correlation function (step 210). Then, the CPU 21 determines whether or not the waveform signal is effective for measurement based on the correlation value of the correlation function of the waveform signal (step 220). Specifically, when the correlation value of the correlation function is a predetermined threshold value (for example, 0.9) or more, the CPU 21 determines that the waveform signal is effective for measurement, and stores the waveform signal data in the memory. Leave to 24. On the other hand, when it is smaller than the predetermined threshold, at least one of the compared waveform signals is a waveform signal that is invalid for measurement. In this case, the CPU 21 specifies a waveform signal that is invalid for measurement by using a correlation function obtained by comparison with another waveform signal, and deletes the waveform signal data from the memory 24. Then, in the four-pulse ultrasonic wave, it is determined that both the waveform signals of the first pulse and the fourth pulse in the forward direction or the waveform signals of the second pulse and the third pulse in the reverse direction are invalid waveform signals. In such a case, it is determined that there is foreign matter in the liquid, and the CPU 21 displays that fact on the display device 26 (step 230). Thereafter, the CPU 21 returns to the process of step 200 and performs transmission / reception of ultrasonic waves in a predetermined pattern again.

  On the other hand, it is determined that at least one of the waveform signals of the first pulse and the fourth pulse in the forward direction is valid, and at least one of the waveform signals of the second pulse and the third pulse in the reverse direction is determined to be valid. In this case, the CPU 21 obtains a propagation time difference ΔT between the ultrasonic wave propagated in the forward direction and the ultrasonic wave propagated in the reverse direction based on the correlation function of the waveform signal determined to be valid (step 240).

  Further, the CPU 21 obtains the flow velocity V of the liquid W1 by performing a calculation corresponding to the equation (5) using the sound velocity C obtained in the process of FIG. The volume flow rate Q of the liquid W1 is obtained by multiplying by the cross-sectional area S (step 250). Further, the CPU 21 obtains the mass flow rate M by multiplying the volume flow rate Q and the density ρ (step 260).

  Thereafter, the CPU 21 displays the measured value of the mass flow rate M on the display device 26 (step 270). Then, the CPU 21 determines whether or not to continue the flow rate measurement process (step 280). Specifically, the CPU 21 determines whether or not the end button of the input device 25 is operated. If the end button is not operated, the CPU 21 returns to the process of step 200 and performs the processes of step 200 to step 280. Again. Then, when the end button of the input device 25 is operated, the CPU 21 ends the process of FIG.

  Therefore, according to the present embodiment, the following effects can be obtained.

  (1) In the case of the present embodiment, in the second sensor unit 3, the density ρ of the liquid W1 can be measured in real time in a state where the liquid W1 is flowed through the flow path of the pipe 15. A density change can be detected quickly. Further, the mass flow rate M can be calculated based on the density ρ, and the controller 6 controls the opening degree of the adjustment valve 5 according to the calculated value, whereby the flow rate of the liquid W1 flowing through the supply pipe 4 is further increased. It can be adjusted accurately.

(2) In the case of the present embodiment, since the pair of ultrasonic transducers 16 and 17 are arranged to be shifted upstream and downstream, the ultrasonic waves emitted from the ultrasonic transducers 16 and 17 interfere with each other. Therefore, the reflected waves S ₀₁ , S ₁₁ , S ₀₂ and S ₁₂ can be reliably received. Moreover, since the propagation distance of the ultrasonic waves is different between the upstream side and the downstream side of the pipe 15, the reflected waves S ₀₁ , S ₁₁ , S ₀₂ and S ₁₂ are received by the ultrasonic transducers 16 and 17. Therefore, by using the above equations (7) and (8), based on the signal intensity of these reflected waves S ₀₁ , S ₁₁ , S ₀₂ and S ₁₂ and the acoustic impedance Z _{0 of the} pipe 15, the acoustic of the liquid W 1 is obtained. it can be determined impedance _{Z f.}

(3) In the case of the present embodiment, the second signal processing circuit 23 common to the upstream ultrasonic transducer 16 and the downstream ultrasonic transducer 17 in the second sensor unit 3 is provided, and the ultrasonic transducer The reflected waves S ₀₁ and S ₁₁ received at 16 and the reflected waves S ₀₂ and S ₁₂ received at the ultrasonic transducer 17 are acquired using the same second signal processing circuit 23. In this case, errors caused by circuit elements can be suppressed as compared with the case where separate signal processing circuits are provided for the ultrasonic transducers 16 and 17. As a result, the signal intensities of the reflected waves S ₀₁ , S ₁₁ , S ₀₂ and S ₁₂ can be obtained more accurately, and the measurement accuracy of the density ρ and the mass flow rate M of the liquid W1 can be improved.
[Second Embodiment]

  Next, a second embodiment embodying the present invention will be described. The present embodiment is different from the first embodiment in that the configuration of the pipe 15 in the second sensor unit 3 is changed. In the ultrasonic flowmeter 1 of the present embodiment, the configuration other than the second sensor unit 3 (such as the electrical configuration of the first sensor unit 2 and the control device 20) is the same as that of the first embodiment. is there.

Specifically, as shown in FIG. 8, the pipe 15 (pipe body) of the second sensor unit 3 in the present embodiment is formed of pipe members 51 and 52 having different acoustic impedances on the upstream side and the downstream side. Has been. Further, the interval d ₁ (width of the flow path) between the inner wall surfaces 15a and 15b in the pipe 15 is formed equal on the upstream side and the downstream side.

In this case, if the acoustic impedance of the upstream piping member 51 is Z ₀₁ and the acoustic impedance of the downstream piping member 52 is Z ₀₂ , the reflected waves S ₀₁ , S ₁₁ , S ₀₂ , S _12, the following equation (10), holds the relationship (11).

Then, these equations (10) and (11), reflected waves _{S 01,} S _11, S _02, based on the signal strength of the _{S 12} and the acoustic impedance _{Z 01, Z 02,} the acoustic impedance Z of a liquid W1 _f can be obtained. Furthermore, the sound velocity C of the liquid W1 can be determined in the same manner as the first embodiment, it is possible to determine the density of the liquid W1 [rho by its sound velocity C and the acoustic impedance Z _f.
[Third Embodiment]

  Next, a third embodiment embodying the present invention will be described. This embodiment is also different from the first embodiment in that the configuration of the pipe 15 in the second sensor unit 3 is changed. In the ultrasonic flowmeter 1 of the present embodiment, other configurations (such as the first sensor unit 2 and the electrical configuration of the control device 20) are the same as those of the first embodiment.

Specifically, as shown in FIG. 9, the pipe 15 (pipe body) of the second sensor unit 3 in the present embodiment is formed in a rectangular shape, and one ultrasonic transducer 16 is the first one. The other ultrasonic transducer 17 is disposed on a second outer wall surface 15f orthogonal to the first outer wall surface 15e. Further, the side wall where the pair of ultrasonic transducers 16 and 17 are arranged in the pipe 15 is equal, and the flow path formed in the pipe 15 has a horizontal width d ₁ (of the inner wall surfaces 15a and 15b). The distance) is twice the vertical width d ₂ (the distance between the inner wall surfaces 15c and 15d). In addition, in the piping 15 of FIG. 9, the liquid W1 flows in the depth direction from the near side of the page.

Thus case where the second sensor unit 3, a reflected wave _S 01 reflected by the inner wall surfaces _{15a, 15b, 15c, 15d,} S 11, S 02, S 12 is the above equation (7), (8) The relationship holds. Therefore, also in this embodiment, as in the first embodiment, it is possible to obtain the acoustic impedance Z _f of the liquid W1, furthermore, it is possible to obtain the density ρ and mass flow rate M of the liquid W1. Further, unlike the first embodiment, the ultrasonic transducers 16 and 17 do not need to be shifted in the flow direction (upstream side or downstream side) of the liquid W1, so the ultrasonic flowmeter 1 can be formed compactly.

  In addition, you may change each embodiment of this invention as follows.

In the second embodiment, the upstream side and the downstream side of the pipe 15 in the second sensor unit 3 are formed by the pipe members 51 and 52 having different acoustic impedances Z ₀₁ and Z ₀₂ . As shown in FIG. 10, a part of the inner wall surface 15 b serving as an ultrasonic reflection surface may be formed by a plate member 55 having a different acoustic impedance from the pipe 15. Even when the second sensor unit 3 is formed in this way, the acoustic impedance of the liquid W1 flowing through the pipe 15 is based on the signal strength of the reflected waves S ₀₁ , S ₁₁ , S ₀₂ , S _{12 on} the inner wall surfaces 15a, 15b. it is possible to obtain the Z _f.

  In each of the above embodiments, the correlation function of the waveform signal is obtained and the waveform signal effective for measurement is determined based on the correlation value. However, the present invention is not limited to this. For example, when measuring a liquid that does not contain bubbles, a highly reliable waveform signal can be reliably acquired, so there is no need to calculate a correlation function, and the propagation time difference is calculated using the acquired waveform signal as it is. May be.

In each of the above embodiments, the measurement value of the mass flow rate M is displayed on the display device 26. However, other measurement values such as the density ρ may be displayed. Specifically, for example, a display mode is set in advance by a button operation of the input device 25, the CPU 21 determines the display mode, and the measurement values displayed on the display device 26 are the volume flow rate Q and the mass flow rate M. , the density [rho, may be configured to switch to one of the acoustic impedance Z _f. If comprised in this way, it will become possible to confirm the state of the liquid W1 more strictly.

  In each of the above embodiments, the common control device 20 is used for the first sensor unit 2 and the second sensor unit 3. However, the control units may be provided separately in the sensor units 2 and 3. In this case, the density ρ of the liquid W1 detected by the second sensor unit 3 may be displayed on a display device different from the mass flow rate M of the liquid W1 detected by the first sensor unit 2.

In each of the embodiments described above, the common second signal processing circuit 23 is provided in each of the ultrasonic transducers 16 and 17 of the second sensor unit 3, but a separate signal processing circuit is provided in each of the ultrasonic transducers 16 and 17. May be provided. In this way, the reflected wave _S 01 by the signal processing _circuit, S _11, S _02, the _{S 12} can be quickly acquired.

  In each of the above embodiments, the second sensor unit 3 is provided on the supply pipe 4 on the downstream side of the first sensor unit 2, but the second sensor unit 3 may be provided on the upstream side of the first sensor unit 2. .

In the above first embodiment, the second sensor part 3 of the pipe 15, the inner wall surface 15a on the upstream side, the inner wall surface 15a distance _{d 1} is the downstream side of 15b, so that wider than the spacing _{d 2} of 15b are formed, the upstream side of the inner wall surface 15a on the contrary, the inner wall surface 15a distance d ₁ is the downstream side of 15b, may be formed to be narrower than the spacing d ₂ of 15b.

  In each of the above embodiments, the density ρ of the liquid W1 is measured. However, in addition to the liquid W1, for example, the density ρ of a fluid such as high-pressure gas may be measured.

  Next, in addition to the technical ideas described in the claims, the technical ideas grasped by the respective embodiments described above are listed below.

  (1) The ultrasonic density meter according to any one of claims 1 to 5, wherein the side walls of the tube main body on which the pair of ultrasonic transducers are arranged have the same thickness.

  (2) The ultrasonic density meter according to any one of claims 1 to 5, wherein the tube body is formed of a resin material having excellent chemical resistance.

  (3) The ultrasonic density meter according to claim 4, wherein the upstream side and the downstream side of the tube main body are formed of piping members having different acoustic impedances.

  (4) The ultrasonic density meter according to claim 4, wherein a part of an inner wall surface which is a reflection surface of the ultrasonic wave in the tube main body is formed of a plate member having an acoustic impedance different from that of the tube main body. .

  (5) The ultrasonic density meter according to any one of claims 1 to 5, further comprising a detection circuit for extracting a waveform signal of the ultrasonic wave reflected by the inner wall surface.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows the ultrasonic flowmeter of 1st Embodiment which actualized this invention. Sectional drawing which shows schematic structure of the 2nd sensor part in 1st Embodiment. The block diagram which shows the electrical constitution of an ultrasonic flowmeter. The timing chart which shows the reception time and propagation time of each reflected wave. Explanatory drawing which shows the correlation function of a waveform signal. The flowchart which shows the process example for calculating the density of a liquid. The flowchart which shows the process example for calculating the mass flow rate of a liquid. Sectional drawing which shows schematic structure of the 2nd sensor part in 2nd Embodiment. Sectional drawing which shows schematic structure of the 2nd sensor part in 3rd Embodiment. Sectional drawing which shows schematic structure of the 2nd sensor part in embodiment of another example. The schematic block diagram which shows the conventional ultrasonic flowmeter. The timing chart which shows the propagation time and propagation time difference of an ultrasonic wave.

Explanation of symbols

2 ... 2nd sensor part which comprises an ultrasonic density meter 15 ... Piping 15a, 15b, 15c, 15d ... Inner wall surface 15e ... 1st outer wall surface 15f ... 2nd outer wall surface 16, 17 ... Ultrasonic Vibrator 20 ... Control device constituting ultrasonic density meter 21 ... Sound velocity calculation means wave, acoustic impedance calculation means, CPU as density calculation means

Claims (5)

An ultrasonic density meter that irradiates a fluid flowing through a flow path with ultrasonic waves and obtains the density of the fluid based on the reflected waves,
A pair of ultrasonic waves that are disposed on the outer wall surface of the tube main body constituting the flow path, propagate ultrasonic waves in the fluid in a direction orthogonal to the flow, and receive ultrasonic waves reflected by the inner wall surface of the tube main body. A sound wave oscillator,
A sound velocity calculating means for obtaining a sound velocity of the fluid based on a propagation time and a propagation distance of the ultrasonic wave propagating in the fluid;
Based on the signal intensity of the reflected wave received by each of the ultrasonic transducers and the acoustic impedance of the tube body, acoustic impedance calculation means for obtaining the acoustic impedance of the fluid;
An ultrasonic density meter comprising: density calculating means for determining the density of the fluid by dividing the acoustic impedance of the fluid by the speed of sound.   The tube main body has a pair of inner wall surfaces parallel to the fluid flow direction, and the ultrasonic transducer propagates ultrasonic waves into the fluid in the flow path through one inner wall surface, and the other The ultrasonic density meter according to claim 1, wherein the ultrasonic density meter receives the ultrasonic wave reflected by the inner wall surface.   The pair of ultrasonic transducers are respectively disposed on an outer wall surface on an upstream side and a downstream side in the pipe body, and the interval between the inner wall surfaces is different between the upstream side and the downstream side. 2. The ultrasonic density meter according to 2.   The pair of ultrasonic transducers are respectively disposed on an outer wall surface on an upstream side and a downstream side in the tube body, and the acoustic impedance of the tube body is made different between the upstream side and the downstream side. Item 3. The ultrasonic density meter according to Item 2.   The tube main body is formed in a rectangular shape, and one ultrasonic transducer of the pair of ultrasonic transducers is disposed on a first outer wall surface of the tube main body, and the other ultrasonic transducer is The ultrasonic density meter according to claim 2, wherein the ultrasonic density meter is disposed on a second outer wall surface orthogonal to the first outer wall surface.

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