JP5316795B2 - Ultrasonic measuring instrument - Google Patents

Description

  The present invention relates to an ultrasonic measuring instrument that measures the flow velocity distribution of a fluid to be measured using ultrasonic waves, and in particular, reduces the amount of calculation of correlation calculation by the reflection correlation measurement method, shortens the calculation time, and measures up to a large flow velocity. The present invention relates to an ultrasonic measuring instrument that can be used.

  2. Description of the Related Art As a measuring instrument used for flow control in a chemical plant or the like, an ultrasonic measuring instrument that measures a flow velocity distribution and a flow rate of a fluid to be measured is known. Some ultrasonic measuring instruments use a reflection correlation measurement method in which a correlation calculation is performed on an ultrasonic signal reflected by an ultrasonic reflector to obtain a flow velocity distribution and a flow rate (see Patent Document 1). An ultrasonic measuring instrument based on this reflection correlation measurement method will be described with reference to the block diagram of FIG.

  In FIG. 4, a fluid to be measured FLD (liquid, gas, gas, etc.) flows through the measurement tube 2 in the direction of the arrow (from left to right). The ultrasonic measuring instrument 1 that measures the flow velocity distribution of the fluid FLD to be measured includes an ultrasonic transducer 10, a switching circuit 20, a switching control means 30, a transmitting circuit 40, a receiving circuit 50, an A / D conversion circuit 60, and a correlation calculating means 70. , A flow velocity distribution calculating means 80 and a flow rate calculating means 90 are provided.

  The ultrasonic transducer 10 is provided on the outer periphery of the measuring tube 2 and has a function of emitting and receiving ultrasonic waves. Its external terminal is connected to one end C of the switching circuit 20. The switching circuit 20 includes one end C and the other ends S and R that are switched and connected to the one end C by a switching control signal from the switching control means 30.

  After receiving the trigger control signal from the switching control unit 30, the transmission circuit 40 outputs a signal serving as a trigger for emitting ultrasonic waves from the ultrasonic transducer 10 to the other end S of the switching circuit 20. The receiving circuit 50 receives the ultrasonic signal received by the ultrasonic transducer 10 from the other end R of the switching circuit 20 and amplifies this signal.

  The A / D conversion circuit 60 receives the amplified ultrasonic signal from the reception circuit 50 and converts it into a digital signal. The correlation calculation means 70 receives a digital signal from the A / D conversion circuit 60 and performs a correlation calculation.

  The flow velocity distribution calculation means 80 receives the correlation calculation value from the correlation calculation means 70 and calculates the flow velocity distribution. The flow rate calculation means 90 receives the flow velocity constituting the flow velocity distribution from the flow velocity distribution calculation means 80, calculates the flow rate of the fluid to be measured FLD, outputs it to an external device (not shown), and displays means (not shown) as necessary. To display.

  Hereinafter, the flow velocity distribution measurement operation by the reflection correlation measurement method will be described. The switching control means 30 outputs a switching control signal to the switching circuit 20 in order to connect one end C and the other end S of the switching circuit 20. The switching circuit 20 connects the one end C and the other end S by a switching control signal. Thereafter, the switching control means 30 outputs a trigger control signal to the transmission circuit 40.

  The transmission circuit 40 outputs a signal serving as a trigger for emitting ultrasonic waves from the ultrasonic transducer 10 to the other end S of the switching circuit 20 in accordance with the trigger control signal. This trigger signal is input to the ultrasonic transducer 10 via the other end S and one end C of the switching circuit 20.

  Then, in preparation for receiving an ultrasonic signal to be described later, the switching control means 30 outputs a switching control signal for connecting one end C and the other end R of the switching circuit 20 to the switching circuit 20. The switching circuit 20 connects one end C and the other end R by a switching control signal.

  The ultrasonic transducer 10 emits an ultrasonic signal CT to the fluid to be measured FLD by a trigger signal. The ultrasonic signal CT incident on the fluid to be measured FLD is reflected by the ultrasonic reflector PT such as bubbles and fine particles in the fluid to be measured FLD.

  Note that the path of the ultrasonic signal CT (one-dot chain line) and the path of the extension line (dotted line) are taken as a measurement line ML.

  The ultrasonic transducer 10 receives the reflected ultrasonic signal CH (hereinafter referred to as “reflected ultrasonic signal”) and outputs it to one end C of the switching circuit 20. The reflected ultrasonic signal is input to the receiving circuit 50 via one end C and the other end R of the switching circuit 20.

  The reception circuit 50 amplifies the reflected ultrasonic signal, and the A / D conversion circuit 60 receives the amplified reflected ultrasonic signal (analog signal) from the reception circuit 50 and converts it into a digital signal.

  The above ultrasonic signal emission, reception, and A / D conversion are continuously performed at least twice. Here, the description will be made assuming that it is performed twice.

  The correlation calculation by the correlation calculation means 70 will be described with reference to FIG. FIG. 5A shows the waveform of the reflected ultrasonic signal, and FIG. 5B shows a graph of the cross-correlation value with respect to the flow velocity.

  In FIG. 5A, the first reflected ultrasonic signal is a reference reception waveform, and the second reflected ultrasonic signal is a search reception waveform.

  The correlation calculation means 70 shifts the time of the search reception waveform at a predetermined interval on the basis of the reference reception waveform (in FIG. 5A, the search reception waveform is shifted to the left), and the digital value of the reference reception waveform And the cross-correlation value with the digital value of the shifted search reception waveform is calculated.

  The cross-correlation calculation is repeatedly performed by shifting the time a plurality of times, and the shifted time (time difference) when the maximum cross-correlation value is calculated is defined as the flow velocity at a position where the ultrasonic reflector PT is located.

  Then, the correlation calculation means 70 performs a cross-correlation calculation from a flow velocity of zero to a flow velocity VP that can be measured by the ultrasonic measuring instrument 1, and calculates a cross-correlation value for the flow velocity as shown in FIG. FIG. 5B is a graph showing the relationship between the flow velocity and the cross-correlation value at a position where the ultrasonic reflector PT is present.

  In FIG. 5B, the flow velocity of the fluid to be measured FLD actually flowing is a flow velocity at the peak value P2 of the cross-correlation value (hereinafter referred to as “true flow velocity”). On the other hand, the peak value of the cross-correlation value also occurs at P1 and P3 in addition to P2.

  The peak values P1 and P3 generated at other than the true flow velocity are called multimodality generated by the reflection correlation measurement method. Multi-modality occurs when the reference reception waveform and the search reception waveform are sinusoidal and periodic, so that when the time of one cycle is shifted, both waveforms are almost the same and the cross-correlation value increases. .

  Here, the flow velocity interval w (hereinafter referred to as “predetermined flow velocity”) of the peak value caused by the multimodality can be expressed by the following formula (1).

  C is the speed of sound, θ is the angle between the flow direction of the fluid FLD to be measured and the ultrasonic signal CT, t1 is the time interval between two ultrasonic signals emitted from the ultrasonic transducer 10 twice in succession, and f is This is the oscillation frequency of the ultrasonic signal.

  Then, the correlation calculating means 70 determines the flow velocity at the maximum cross-correlation value P2 among the peak values P1 to P3 as the flow velocity at a position where the ultrasonic reflector PT is present. Furthermore, the correlation calculation means 70 performs the same correlation calculation and determines the flow velocity at other positions on the measurement line ML.

  The flow velocity distribution calculation means 80 receives the flow velocity at each position on the measurement line ML determined by the correlation calculation means 70, and calculates the flow velocity distribution on the measurement line ML.

  The flow rate calculation means 90 receives the flow velocity distribution from the flow velocity distribution calculation means 80 and multiplies the flow velocity obtained by averaging the flow velocity constituting the flow velocity distribution by the cross-sectional area in the measurement pipe 2 to calculate the flow rate of the fluid to be measured FLD. To do.

  Patent Document 2 describes that multimodality occurs in an ultrasonic measuring device that calculates such a cross-correlation value.

  In addition to the reflection correlation measurement method, the flow velocity measurement method includes a measurement method based on a propagation time difference. Patent Document 3 describes an ultrasonic measuring device that measures a flow velocity by switching between a reflection correlation measurement method and a propagation time difference measurement method.

Japanese Patent No. 36669580 JP 2002-243514 A JP 2005-181268 A

  However, since the correlation calculation means 70 performs the cross-correlation calculation over a wide range from the flow velocity zero to the measurable flow velocity VP, there is a problem that the calculation amount and calculation time become large.

  Further, the cross-correlation value decreases as the flow rate increases. For this reason, when the flow rate is large, the cross-correlation value of the true flow rate becomes small, and thus there is a problem that the correlation calculation means 70 cannot determine an accurate flow rate and it is difficult to measure up to a large flow rate.

  The present invention relates to an ultrasonic measuring instrument that measures the flow velocity distribution of a fluid to be measured using ultrasonic waves, and in particular, reduces the amount of calculation of correlation calculation by the reflection correlation measurement method, shortens the calculation time, and measures up to a large flow velocity. It is to provide an ultrasonic measuring device that can be used.

In order to achieve such an object, the invention of claim 1
A plurality of ultrasonic signals incident on the fluid to be measured flowing through the measurement tube are reflected by the ultrasonic reflector, and the flow velocity distribution of the fluid to be measured is measured based on the reflected plurality of ultrasonic signals. In the ultrasonic measuring instrument that measures the average flow velocity of the fluid under measurement based on the propagation time until the ultrasonic signal incident on the fluid under measurement from the sound wave transmitting unit reaches the ultrasonic wave receiver,
Correlation calculating means for calculating a cross-correlation value of the plurality of ultrasonic signals reflected at at least one position in the measuring tube within a flow velocity range based on a predetermined flow velocity according to the frequency of the ultrasonic signals;
A comparison flow velocity calculating means for calculating a comparison flow velocity to be compared with an average flow velocity measured based on the propagation time using a correlation maximum flow velocity at which the cross-correlation value is maximized and an offset flow velocity based on the predetermined flow velocity;
When the comparison flow velocity calculated by the comparison flow velocity calculation means is within a predetermined range with respect to the average flow velocity, the measured flow rate is based on the correlation maximum flow velocity and the offset flow velocity at each position in the measurement tube. A flow velocity distribution calculating means for calculating a flow velocity distribution of the fluid;
It is provided with.
The invention of claim 2 is the invention of claim 1,
The comparison flow velocity calculation means uses a flow velocity obtained by multiplying the predetermined flow velocity by a predetermined value as the offset flow velocity.
The invention of claim 3 is the invention of claim 2,
The predetermined value is an integer.
The invention of claim 4 is the invention according to any one of claims 1 to 3,
The comparison flow velocity calculation means calculates the comparison flow velocity by adding the offset flow velocity to the correlation maximum flow velocity,
The flow velocity distribution calculating means calculates the flow velocity distribution based on a flow velocity obtained by adding the offset flow velocity to the correlation maximum flow velocity at each position in the measurement tube.
It is characterized by that.
The invention according to claim 5 is the invention according to any one of claims 1 to 4,
The correlation calculation means calculates a cross-correlation value of the plurality of ultrasonic signals reflected at a central position in the measurement tube.
The invention of claim 6 is the invention according to any one of claims 1 to 5,
The flow velocity range used in the correlation calculation means is a flow velocity range obtained by multiplying the predetermined flow velocity by a value between 0.75 and 1.

  According to the present invention, in the ultrasonic measuring instrument that measures the flow velocity distribution of the fluid to be measured using ultrasonic waves, the correlation calculation means performs the cross-correlation calculation within the flow velocity range based on the predetermined flow velocity. The calculation amount can be reduced and the calculation time can be shortened.

  Further, the comparison flow velocity calculation means calculates the comparison flow velocity using the correlation maximum flow velocity and the offset flow velocity, and when the comparison flow velocity is within a predetermined range with respect to the average flow velocity, the flow velocity distribution calculation means is arranged at each position in the measurement tube. The flow velocity distribution is calculated based on the correlation maximum flow velocity and the offset flow velocity at. Thereby, it is possible to measure up to a large flow rate.

It is an example of the block diagram of the ultrasonic measuring device to which this invention is applied. It is an example of the flowchart figure of the arithmetic processing of the ultrasonic measuring device to which this invention is applied. It is an example of the graph showing the correlation maximum flow velocity and flow velocity distribution in each position in a measurement tube. It is an example of the block diagram of the ultrasonic measuring device shown by background art. (A) is a waveform diagram of a reflected ultrasonic signal, and (b) is an example of a graph of a cross-correlation value with respect to a flow velocity.

  This embodiment will be described with reference to FIG. FIG. 1 is a configuration diagram of an ultrasonic measuring device 100 to which the present invention is applied.

  In FIG. 1, an ultrasonic flowmeter 100 includes an ultrasonic transducer 10, a switching circuit 20, a switching control means 30, a transmission circuit 40, a receiving circuit 50, an A / D conversion circuit 60, a flow rate calculation means 90, and a predetermined flow velocity calculation means 210. , Correlation calculation means 220, comparative flow velocity calculation means 230 having correlation maximum flow velocity calculation means 231 and offset flow velocity calculation means 232, flow velocity distribution calculation means 240, propagation time calculation means 250, average flow velocity calculation means 260, storage means 300 and super A sonic transducer 400 is provided.

  In addition, the same component as FIG. 4 is attached | subjected the same code | symbol, and the description is abbreviate | omitted.

  The ultrasonic transducer 400 is provided on the outer periphery of the measuring tube 2 at a position facing the ultrasonic transducer 10 and has a function of receiving and emitting ultrasonic waves, and its external terminal is connected to one end T of the switching circuit 20. The

  When there is no ultrasonic reflector PT, the ultrasonic transducer 400 receives an ultrasonic signal emitted from the ultrasonic transducer 10 and traveling along the measurement line ML (hereinafter referred to as “transmission ultrasonic signal”). Also, the ultrasonic signal emitted from the ultrasonic transducer 400 is received by the ultrasonic transducer 10.

  The predetermined flow velocity calculation means 210 receives the sound velocity C, the incident angle θ of the ultrasonic signal, the time interval t1 of the ultrasonic signal, and the oscillation frequency f of the ultrasonic signal from the storage means 300, and the predetermined flow velocity w by the above equation (1). Is output to the correlation calculation means 220 and the comparison flow velocity calculation means 230.

  The correlation calculation means 220 receives the predetermined flow velocity w and the reflected ultrasonic signal digitally converted by the A / D conversion circuit 60, performs the cross-correlation calculation within the flow velocity range R in which the cross-correlation calculation is executed, and the cross-correlation value Is output to the comparison flow velocity calculation means 230.

  The correlation maximum flow velocity calculation means 231 in the comparison flow velocity calculation means 230 receives the cross-correlation value, and calculates a flow velocity Vm (hereinafter referred to as “correlation maximum flow velocity”) at the maximum cross-correlation value.

  The offset flow velocity calculation means 232 in the comparison flow velocity calculation means 230 receives the predetermined flow velocity w and calculates the offset flow velocity VS.

  Then, the comparison flow velocity calculation means 230 calculates a comparison flow velocity VC for comparison with an average flow velocity VT (described later) from the correlation maximum flow velocity Vm and the offset flow velocity VS, and outputs it to the flow velocity distribution calculation means 240.

  Further, the propagation time calculation means 250 receives the transmission ultrasonic signal digitally converted by the A / D conversion circuit 60 and then outputs the ultrasonic signal from the time when the ultrasonic transducer 10 is emitted until the time when the ultrasonic transducer 400 is received. The propagation time is calculated and output to the average flow velocity calculation means 260.

  The average flow velocity calculation means 260 calculates the average flow velocity VT of the fluid to be measured FLD from the received propagation time and outputs it to the flow velocity distribution calculation means 240.

  Then, the flow velocity distribution calculating means 240, if the comparative flow velocity VC is within the predetermined range TH with respect to the average flow velocity VT, the correlation maximum flow velocity Vmx obtained from the reflected ultrasonic signal at other positions of the measurement line ML, Received from the correlation maximum flow velocity calculation means 231, calculates the flow velocity distribution at each position, and outputs it to the flow rate calculation means 90.

  The flow rate calculation means 90 calculates the flow rate of the fluid to be measured FLD from the flow velocity distribution, outputs it to an external device (not shown), and displays it on a display means (not shown) as necessary.

  Hereinafter, the flow velocity distribution measuring operation in this embodiment will be described with reference to FIG. FIG. 2 is a flowchart showing a flow rate distribution measurement calculation.

  First, in order to perform correlation calculation by the reflection correlation measurement method, the A / D conversion circuit 60 obtains a reflected ultrasonic signal at the position of the ultrasonic reflector PT by the switching operation of the switching circuit 20 as described above.

  In step S10 of FIG. 2, the correlation calculation means 220 multiplies the predetermined flow velocity w by a constant K to calculate a flow velocity range R in which cross-correlation calculation is performed. In order to simplify the description, K is assumed to be 1 here.

  In step S20, as described with reference to FIG. 5A, the correlation calculation unit 220 shifts the time of the search reception waveform at a predetermined interval on the basis of the reference reception waveform and shifts it from the digital value of the reference reception waveform. The cross-correlation value with the digital value of the received search waveform is calculated.

  By performing this cross-correlation calculation within the flow velocity range R, the correlation calculation means 220 calculates a cross-correlation value for the flow velocity within the flow velocity range R as shown in FIG. That is, the correlation calculation means 220 does not perform the cross-correlation calculation up to a flow velocity (for example, a measurable flow velocity VP) larger than the flow velocity range R.

  In step S30 of FIG. 2, the correlation maximum flow velocity calculation means 231 sets the predetermined value n to zero.

  In step S40, the correlation maximum flow velocity calculation means 231 calculates the correlation maximum flow velocity Vm. Specifically, in FIG. 5B, the correlation maximum flow velocity Vm is a flow velocity at P1, which is the maximum cross-correlation value within the flow velocity range R.

  Next, the average flow velocity VT of the fluid to be measured FLD is calculated by the measurement method based on the propagation time using the transmitted ultrasonic signal.

  In step S50 of FIG. 2, the switching control means 30 connects the terminals S and C of the switching circuit 20 and the terminals R and T. Thereafter, the transmitted ultrasonic signal emitted from the ultrasonic transducer 10 (ultrasonic transmitter) and received by the ultrasonic transducer 400 (ultrasonic receiver) is received via the terminals T and R of the switching circuit 20. Input to the circuit 50.

  The propagation time calculation means 250 transmits the ultrasonic signal propagation time from the transmission ultrasonic signal digitally converted by the A / D conversion circuit 60 to the reception time of the ultrasonic transducer 400 from the time when the ultrasonic transducer 10 is received (first time). (Propagation time) is calculated.

  Further, the switching control means 30 connects the terminals S and T of the switching circuit 20 and also connects the terminals R and C. Thereafter, the transmitted ultrasonic signal emitted from the ultrasonic transducer 400 (ultrasonic transmitter) and received by the ultrasonic transducer 10 (ultrasonic receiver) is received via the terminals C and R of the switching circuit 20 through the receiving circuit. 50.

  The propagation time calculation means 250 transmits the ultrasonic signal propagation time from the transmission ultrasonic signal digitally converted by the A / D conversion circuit 60 to the reception time of the ultrasonic transducer 10 (second time). (Propagation time) is calculated.

  That is, the first propagation time is the propagation time when the ultrasonic signal is advanced from the upstream side to the downstream side of the fluid to be measured FLD, and the second propagation time is from the downstream side to the upstream side of the fluid to be measured FLD. It is a propagation time when an ultrasonic signal is advanced toward the head.

  Then, the average flow velocity calculating means 260 calculates the average flow velocity VT using the propagation time difference between the first propagation time and the second propagation time and the sound velocity C. Note that the flow velocity obtained by the propagation time difference measurement method is an average flow velocity, and the flow velocity distribution at each position in the measurement tube cannot be obtained.

  Next, in step S60, the offset flow velocity calculation means 232 calculates the offset flow velocity VS by multiplying the predetermined flow velocity w by a predetermined value n. At this time, since the predetermined value n is zero, the offset flow velocity VS is zero (VS = 0).

  In step S70, the comparison flow velocity calculation unit 230 calculates the comparison flow velocity VC by adding the offset flow velocity VS to the correlation maximum flow velocity Vm obtained in step S40. At this time, since the offset flow velocity VS is zero, the comparison flow velocity VC is equal to the correlation maximum flow velocity Vm (VC = Vm).

  In step S80, the flow velocity distribution calculating means 240 determines whether or not the absolute value of the difference between the comparative flow velocity VC and the average flow velocity VT obtained in step S50 is smaller than a predetermined range TH. For example, the value of the flow velocity measurement accuracy of the ultrasonic measuring instrument 100 can be used as the predetermined range TH.

  Here, the average flow velocity VT is equal to or close to the true flow velocity. Therefore, if the difference between the comparison flow velocity VC and the average flow velocity VT is within the flow velocity measurement accuracy, the comparison flow velocity VC is also equal to or close to the true flow velocity.

  As described above, in FIG. 5B, the true flow velocity is the flow velocity (Vm + w) at the peak value P2 of the cross-correlation value, and the average flow velocity VT is also substantially equal to this flow velocity. Since the absolute value of the difference between the average flow velocity VT and the average flow velocity VT is approximately the predetermined flow velocity w (> flow velocity measurement accuracy), the process proceeds to step S90 (“No” in step S80). In step S90, 1 is added to the predetermined value n, so that n = 1.

  Returning to step S60, the offset flow velocity VS is calculated again, and the offset flow velocity VS becomes the predetermined flow velocity w (VS = w).

  In step S70, the comparison flow velocity VC is calculated, and the comparison flow velocity VC is a value obtained by adding the predetermined flow velocity w to the maximum correlation flow velocity Vm (VC = Vm + w).

  In step S80, since the comparison flow velocity VC is equal to or close to the average flow velocity VT, the absolute value of the difference between the comparison flow velocity VC and the average flow velocity VT is within the flow velocity measurement accuracy, and the process proceeds to step S100. ("Yes" in step S80).

  In step S100, the correlation maximum flow velocity Vmx is calculated by the correlation calculation means 220 and the correlation maximum flow velocity calculation means 231 from the reflected ultrasonic signal reflected by the ultrasonic reflector PT at each position x of the measurement line ML.

  Thereafter, the flow velocity distribution calculation means 240 calculates the flow velocity distribution Vx by adding the correlation maximum flow velocity Vmx at each position x to the offset flow velocity VS (= w) that satisfies the condition of step S80.

  In step S110, the flow rate calculation unit 90 calculates the flow rate of the fluid to be measured FLD by multiplying the flow rate obtained by averaging the flow rates constituting the flow rate distribution by the cross-sectional area in the measurement tube 2.

  Next, the flow from the correlation maximum flow velocity calculation in step S40 to the flow velocity distribution calculation in step S100 will be described visually with reference to FIG. FIG. 3 is a graph showing the correlation maximum flow velocity and the flow velocity distribution at the position x on the measurement line ML in the measurement tube 2. Note that the flow velocity values are plotted from the tube inner wall on the ultrasonic transducer 10 side on the horizontal axis to the tube inner wall on the ultrasonic transducer 400 side.

  In FIG. 3, when the ultrasonic reflector PT exists at the center position CS on the measurement line ML, the correlation maximum flow velocity Vm at this position is calculated in step S40 of FIG.

  As described above, when the offset flow velocity VS = w and the comparison flow velocity VC = Vm + w, in step S80, the absolute value of the difference between the comparison flow velocity VC and the average flow velocity VT is within the flow velocity measurement accuracy.

  This will be described with reference to FIG. 3. A value obtained by adding the offset flow velocity VS (= predetermined flow rate w) to the maximum correlation flow velocity Vm at the center position CS is represented by a dotted circle as a comparative flow velocity VC.

  Since the comparison flow velocity VC is within the predetermined range TH with respect to the average flow velocity VT, the condition of step S80 is satisfied.

  Next, in step S100, the flow velocity distribution Vx at each position x on the measurement line ML is calculated.

  Explaining this with reference to FIG. 3, the correlation maximum flow velocity Vmx is calculated from the reflected ultrasonic signals reflected by the ultrasonic reflector PT at the central positions CL and CR at the left and right of the central position CS on the measurement line ML. . A value obtained by adding the offset flow velocity VS (= predetermined flow velocity w) to the maximum correlation flow velocity Vmx is represented by a dotted circle as a flow velocity distribution Vx.

  By performing this calculation at each position on the measurement line ML, a flow velocity distribution Vx made up of a collection of dotted circles is obtained as shown in FIG.

  According to the present embodiment, the correlation calculation means 220 performs the cross-correlation calculation within the flow velocity range R and does not need to perform the cross-correlation calculation up to the measurable flow velocity VP larger than the flow velocity range R. The calculation time can be shortened.

  Further, the comparison flow velocity calculation means 230 adds the correlation maximum flow velocity Vm and the offset flow velocity VS to obtain the comparison flow velocity VC, and the flow velocity distribution calculation means 240 determines the absolute value of the difference between the comparison flow velocity VC and the average flow velocity VT. When within the range TH, the flow velocity distribution Vx is obtained by adding the correlation maximum flow velocity Vmx and the offset flow velocity VS at each position x on the measurement line ML. As a result, even if the true flow rate becomes large (for example, close to the measurable flow rate VP), the flow velocity distribution Vx can be obtained by adding the offset flow velocity VS, and measurement is possible up to a large flow velocity. .

  Further, the offset flow velocity VS is obtained from the reflected ultrasonic signal at the center position CS on the measurement line ML shown in FIG. 3, and further, from the reflected ultrasonic signals at the center positions CL and CR on the measurement line ML. The offset flow velocity VS may be obtained.

  In this case, as the offset flow velocity VS satisfying the condition of step S80 in FIG. 2, three offset flow VSs obtained from the reflected ultrasonic signals at the center position CS and the center positions CL and CR on the measurement line ML are obtained. .

  Therefore, in step S100, the flow velocity distribution calculating means 240 averages the three offset flow velocity VS and adds the correlation maximum flow velocity Vmx at each position x to the offset average flow velocity to obtain the flow velocity distribution Vx. it can.

  In this way, by calculating the offset average flow velocity from the reflected ultrasonic signals at a plurality of positions, for example, even when noise is superimposed on one reflected ultrasonic signal, the noise is removed by averaging. A stable offset average flow velocity can be obtained, and a stable and accurate flow velocity distribution Vx can be obtained.

  Furthermore, the flow velocity at the center position CS, the center positions CR, and CL on the measurement line ML is more stable than the flow velocity near the pipe inner wall because there is no friction with the pipe inner wall. Therefore, by obtaining the offset flow velocity VS from the reflected ultrasonic signals at the center position CS, the center positions CR, and CL on the measurement line ML, a stable offset flow velocity VS is obtained, and a stable and accurate flow velocity distribution Vx is obtained. be able to.

  Further, as shown in FIG. 5B, the flow velocity range R needs to be a range including the peak value P1. For this reason, it is preferable that the flow velocity range R is a value that includes the flow velocity Vm at the peak value P1 and is not much larger than Vm. This is because if the value is too large, the amount of cross-correlation calculation increases.

  Therefore, the value of the constant K is preferably a value capable of obtaining such a flow velocity range R, and for example, a value between 0.75 and 1 can be used.

  Further, the predetermined value n is not limited to an integer. For example, an accurate flow velocity distribution Vx can be obtained by a value close to an integer such as 0, 0.95, and 1.95. As explained in the example, it is preferably an integer (0, 1, 2, etc.).

  The reason is as follows. Due to the multimodality, peaks of cross-correlation values appear at intervals of a predetermined flow rate w, and the true flow rate is a value close to the flow rate at any peak value. In the description of this embodiment, as shown in FIG. 5B, the peak values are P1, P2, and P3, and the true flow velocity is a value close to the flow velocity at P2 (= Vm + w).

  The correlation maximum flow velocity Vm is a flow velocity at the peak value (P1) that appears first. When the predetermined value n is 1 (integer), the offset flow velocity VS is w. Since the comparison flow velocity VC (= Vm + w) obtained by adding the correlation maximum flow velocity Vm and the offset flow velocity VS is substantially equal to the average flow velocity VT and the true flow velocity, the flow velocity distribution Vx obtained using this offset flow velocity VS is also more This is because it is an accurate value.

  Moreover, although the start point of the flow velocity range R for performing the cross-correlation calculation has been described as zero flow velocity, it is not limited to this, and the flow velocity range R is a start point at which any peak value (P1, P2, P3, etc.) can be included. I just need it. If the starting point of the flow velocity range R is larger than the true flow velocity, the offset flow velocity VS is obtained by setting the predetermined value n to a negative value.

  The flow rate calculation means 90, the predetermined flow rate calculation means 210, the correlation calculation means 220, the comparison flow velocity calculation means 230, the correlation maximum flow velocity calculation means 231, the offset flow velocity calculation means 232, the flow velocity distribution calculation means 240, the propagation time calculation means 250, and the average The flow velocity calculation means 260 is executed by a processor such as a DSP 200 (digital signal processor) according to a predetermined program, and may be realized by a logic circuit.

  In addition, this invention is not limited to the above-mentioned Example, In the range which does not deviate from the essence, many change and deformation | transformation are included. Moreover, combinations other than the combination of each means mentioned above can be included.

90 Flow rate calculation unit 100 Ultrasonic measuring device 210 Predetermined flow rate calculation unit 220 Correlation calculation unit 230 Comparison flow rate calculation unit 231 Correlation maximum flow rate calculation unit 232 Offset flow rate calculation unit 240 Flow rate distribution calculation unit 250 Propagation time calculation unit 260 Average flow rate calculation unit 300 Storage means 400 Ultrasonic transducer

Claims (6)

A plurality of ultrasonic signals incident on the fluid to be measured flowing through the measurement tube are reflected by the ultrasonic reflector, and the flow velocity distribution of the fluid to be measured is measured based on the reflected plurality of ultrasonic signals. In the ultrasonic measuring instrument that measures the average flow velocity of the fluid under measurement based on the propagation time until the ultrasonic signal incident on the fluid under measurement from the sound wave transmitting unit reaches the ultrasonic wave receiver,
Correlation calculating means for calculating a cross-correlation value of the plurality of ultrasonic signals reflected at at least one position in the measuring tube within a flow velocity range based on a predetermined flow velocity according to the frequency of the ultrasonic signals;
A comparison flow velocity calculating means for calculating a comparison flow velocity to be compared with an average flow velocity measured based on the propagation time using a correlation maximum flow velocity at which the cross-correlation value is maximized and an offset flow velocity based on the predetermined flow velocity;
When the comparison flow velocity calculated by the comparison flow velocity calculation means is within a predetermined range with respect to the average flow velocity, the measured flow rate is based on the correlation maximum flow velocity and the offset flow velocity at each position in the measurement tube. A flow velocity distribution calculating means for calculating a flow velocity distribution of the fluid;
An ultrasonic measuring instrument comprising:   2. The ultrasonic measuring instrument according to claim 1, wherein the comparison flow velocity calculation means uses a flow velocity obtained by multiplying the predetermined flow velocity by a predetermined value as the offset flow velocity.   The ultrasonic measuring apparatus according to claim 2, wherein the predetermined value is an integer. The comparison flow velocity calculation means calculates the comparison flow velocity by adding the offset flow velocity to the correlation maximum flow velocity,
The flow velocity distribution calculating means calculates the flow velocity distribution based on a flow velocity obtained by adding the offset flow velocity to the correlation maximum flow velocity at each position in the measurement tube.
The ultrasonic measuring instrument according to any one of claims 1 to 3, wherein   The ultrasonic wave according to any one of claims 1 to 4, wherein the correlation calculation unit calculates a cross-correlation value of the plurality of ultrasonic signals reflected at a central position in the measurement tube. Measuring instrument.   The flow velocity range used by the correlation calculation means is a flow velocity range obtained by multiplying the predetermined flow velocity by a value between 0.75 and 1; Sound wave measuring instrument.