JP4889882B2 - Ultrasonic flow velocity measurement method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic flow velocity measuring method for measuring the flow velocity of a gas or other fluid using ultrasonic waves.
[0002]
[Background Art and Problems to be Solved by the Invention]
Conventionally, when determining the flow rate of a gas or other fluid, first, the flow rate of the fluid is measured continuously or periodically, and the flow rate is calculated based on this measurement. A method using ultrasonic waves is known as one of the fluid flow velocity measurement methods.
[0003]
The principle of this ultrasonic flow velocity measuring method will be described with reference to FIG. In FIG. 6, (1) is an ultrasonic flow velocity measuring tube through which a fluid such as a gas flows. In this ultrasonic flow velocity measuring tube (1), ultrasonic transducers (2) and (3) are arranged at a predetermined distance on the upstream side and the downstream side in the flow direction. The ultrasonic transducers (2) and (3) are driven by drive pulses from the drive pulse generation circuit (4) to vibrate, generate and transmit ultrasonic waves, and receive transmitted ultrasonic waves. The received wave (J) when the ultrasonic transducers (3) and (2) vibrate are output from the reception amplification circuit (5).
[0004]
Then, the propagation time until the ultrasonic wave transmitted in the forward direction from the upstream ultrasonic transducer (2) is received by the downstream ultrasonic transducer (3), and the downstream side The difference from the propagation time until the ultrasonic wave transmitted from the ultrasonic transducer (3) in the opposite direction to the flow is received by the upstream ultrasonic transducer (2) is related to the flow velocity. The flow velocity of the fluid is measured by obtaining the difference in propagation time of the ultrasonic waves by using a clock wave or the like.
[0005]
In FIG. 6, (6) is a switching circuit for switching the connection between the ultrasonic transducers (2), (3), the drive pulse generation circuit (4), and the reception amplification circuit (5). First, the drive pulse generation circuit After connecting the upstream ultrasonic transducer (2) and the downstream ultrasonic transducer (3) to the reception amplification circuit (5) and measuring the propagation time from the upstream side to the downstream side, The operation of the switching circuit (6) connects the drive pulse generation circuit (4) to the downstream ultrasonic transducer (3), and the upstream ultrasonic transducer (2) to the reception amplification circuit (5). Thus, the propagation time from the downstream side to the upstream side is measured.
[0006]
By the way, in general, the propagation time of an ultrasonic wave is obtained based on a predetermined zero-cross point Z of the received wave (J) output from the reception amplifier circuit (5). Conventionally, the zero-cross point of the received wave (J) is used. Z was specified by the following method.
[0007]
That is, first, the received wave (J) is sampled at a constant period, the sample values Pi (voltage values) are treated as sine waveforms, and the sample values Pi of the sine waveforms are converted into linear sample values Qi. For example, as shown in FIG. 7, the phase difference between the zero cross point Z of the received wave (J) and the immediately preceding sample point is αθ, and the sine waveform of the received wave (J) is expressed by the following equation [10]. In this case, the sine waveform sample value Pi is converted into a linear sample value Qi by the following equation [11].
Pi = Asin (iα + αθ) [10]
Qi = Pi * B (i [alpha] + [alpha] [theta]) / Asin (i [alpha] + [alpha] [theta]) [11]
Qi: linear sample value Pi: sine waveform sample value i: sample number A, B: coefficient αθ: phase difference between the zero cross point Z of the received wave (J) and the immediately preceding sample point, and sample values of those lines An approximate straight line is calculated from Qi by the least square method, and the zero cross point of the approximate straight line is specified as the zero cross point Z of the received wave (J).
[0008]
However, in the above method, when the sample value Pi of the sine waveform is converted into the linear sample value Qi by the above equation [11], when θ is an arbitrary value, (iα + αθ) is also an arbitrary value. The calculation process of sin (iα + αθ) by a microcomputer or the like is complicated, and there is a problem that it takes time to specify the zero-cross point Z of the received wave (J).
[0009]
The present invention has been made in view of the above-described problem, and it is possible to specify a zero-cross point of a received wave with high accuracy in a short time, and in turn, an ultrasonic flow velocity measurement method capable of rapid and highly accurate flow velocity measurement. The purpose is to provide.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention converts the sample value Vi of the received wave (J) into a straight line sample value as it is when obtaining an approximate straight line for specifying the zero-cross point Z of the received wave (J). Instead, the line segment SiSi + 1 connecting the sample points Si and Si + 1 of the received wave (J) is internally divided, and the sine sample value Wi corresponding to the internal division point Ni is converted into a linear sample value Zi. It is.
[0011]
That is, according to the present invention, the ultrasonic transducers 2 and 3 are arranged on the upstream side and the downstream side of the measurement fluid flowing through the ultrasonic flow velocity measuring tube 1, respectively, and ultrasonic waves are transmitted from the ultrasonic transducers 2 and 3 to each other. Generated and transmitted, mutually received transmitted ultrasonic waves, obtained ultrasonic propagation time with reference to the zero-cross point Z of the received waves (J), and flow velocity based on the difference between the ultrasonic propagation times In the ultrasonic flow velocity measuring method for measuring the received wave (J), a line segment S1S1 connecting the step of sampling the received wave (J) at a constant period and the sample points S1, S1 'immediately before and after the zero cross point Z of the received wave (J). The point at which 'is zero-crossed is set as a temporary zero-cross point N0, the step of obtaining the correspondence between the sample points S1, S1' and the temporary zero-cross point N0, and the correspondence between the sample points S1, S1 'and the temporary zero-cross point N0 , Next to each other Sample points Si, and internally dividing the line segment SiSi + 1 connecting the Si + 1, corresponding to the internal division point Ni, the value of every sampling period Ts relative to the temporary zero-crossing point Z, be regarded as sine wave determining a sign sample value Wi that can, converting the sine sample value Wi to linear sample values Zi, a step of obtaining an approximate line ai + b by the least square method based on the linear sample values Zi, the approximate straight line specifying a zero cross point of ai + b as a zero cross point Z of the received wave (J).
[0012]
According to this, the sine sampling value Wi is a voltage value for each sampling period Ts with the provisional zero cross point Z as a reference, and the waveform constituted by these sine sampling values Wi is a sine waveform that does not include the phase difference αθ. Therefore, the processing by the microcomputer or the like when converting the sine sampling value Wi into the linear sample value Zi is simplified. For this reason, the zero-cross point Z of the received wave (J) can be specified with high accuracy in a short processing time, and as a result, the flow velocity can be measured quickly and with high accuracy.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an ultrasonic flow velocity measuring apparatus for carrying out the present invention. In FIG. 1, (1) is an ultrasonic flow velocity measuring tube, (2) and (3) are ultrasonic transducers arranged at a predetermined distance upstream and downstream in the flow direction, and (4) is a drive pulse. A pulse generation circuit to be generated, (5) a reception amplification circuit that outputs a reception wave (J) when ultrasonic waves are received by the ultrasonic transducers (2) and (3), and (6) an ultrasonic transducer (2 ) (3), a switching circuit for switching the connection between the pulse generation circuit (4) and the reception amplifier circuit (5), which are the same as those shown in FIG.
[0014]
(7) is a microcomputer (hereinafter referred to as a microcomputer) having a central processing unit (hereinafter referred to as a CPU) that performs various processes, an occasional write / read memory (RAM), and a read-only memory (ROM). The pulse generation circuit (4), the reception amplification circuit (5), and the switching circuit (6) are connected to each other.
[0015]
The microcomputer (7) generates and transmits ultrasonic waves from the ultrasonic transducers (2) and (3), and after the ultrasonic waves are received by the ultrasonic transducers (3) and (2), the received wave zero cross described later. The zero cross point Z of the received wave (J) output from the reception amplifier circuit (5) is specified as the ultrasonic reception timing by the specifying process. Then, the propagation time of the ultrasonic waves in the forward direction and the reverse direction is measured with reference to the zero cross point Z, and the flow velocity of the fluid is obtained based on the difference between the propagation times of the ultrasonic waves.
[0016]
The received wave zero cross specifying process will be specifically described below. In this embodiment, the zero cross point (Z) of the third wave (W3) of the received wave (J) is specified as the ultrasonic wave reception timing.
[0017]
This received wave zero cross specifying process includes the first step to the sixth step. First, in the first step, as shown in FIG. 2A, the received wave (J) is near the zero cross point (Z). The voltage value is sampled at a constant period Ts. In this embodiment, sample points before the zero cross point (Z) of the received wave (J) are S1, S2,..., Sn, and their sample values are V1, V2,. In addition, the sample points after the zero cross point (Z) of the received wave (J) are S1 ′, S2 ′,..., Sn ′, and their sample values are V1 ′, V2 ′,. 'And.
[0018]
In the second step, as shown in FIG. 2B, the point where the line segment S1S1 'connecting the sample points S1, S1' immediately before and after the zero cross point Z of the received wave (J) zero crosses is the temporary zero cross point. Let N0 be the correspondence between the sample points S1, S1 'and the provisional zero cross point N0.
[0019]
In this embodiment, as shown in the following formula [1], first, a time Tm from the sample point S1 to the temporary zero cross point N0 is obtained based on the sample values V1 and V1 ′, and further, the following formula [2] As shown in FIG. 5, the internal division ratio θ of the line segment S1S1 ′ at the temporary zero cross point N0 is obtained based on the time Tm and the sampling period Ts. The internal division ratio θ represents the correspondence between the sample points S1 and S1 ′ and the temporary zero cross point Z.
Tm = Ts × V1 / (V1 + V1 ′) [1]
θ = Tm / Ts [2]
Tm: Time from sample point S1 to provisional zero cross point N0: Sampling period V1: Sampling value V1 ′ immediately before zero cross point Z of received wave (J): Sampling value θ immediately after zero cross point Z of received wave (J): Internal division ratio Ts: Sampling period In the third step, as shown in FIG. 2 (c), each adjacent sample point Si, Si according to the correspondence between the sample points S1, S1 'and the provisional zero cross point Z. A line segment SiSi + 1 connecting +1 is internally divided, and a sine sample value Wi corresponding to the internal dividing point Ni is obtained.
[0020]
In this embodiment, the correspondence between the sample points S1, S1 ′ and the temporary zero cross point N0 is expressed by the internal division ratio θ of the line segment S1S1 ′ by the temporary zero cross point N0. Then, line segments Si and Si + 1 connecting adjacent sample points Si and Si + 1 are internally divided by the internal division ratio θ, and a sine sample value Wi corresponding to the internal division point Ni is obtained. Further, as shown in the following equation [4], the sine sample value Wi ′ is also obtained in the same manner as described above.
Wi = θVi + (1−θ) Vi + 1 [3]
Wi ′ = θVi ′ + (1−θ) Vi + 1 ′... [4]
These sine sampling values Wi and Wi ′ are voltage values for each sampling period Ts with the provisional zero cross point Z as a reference, and the sampling period Ts is also very short. For this reason, the waveform constituted by the sine sampling values Wi and Wi ′ can be regarded as a sine waveform that does not include the phase difference αθ.
[0021]
In this embodiment, the correspondence between the sample points S1, S1 ′ and the temporary zero cross point N0 is expressed by the internal division ratio θ of the line segment S1S1 ′ by the temporary zero cross point N0. Then, line segments Si and Si + 1 connecting adjacent sample points Si and Si + 1 are internally divided by the internal division ratio θ, and a sine sample value Wi corresponding to the internal division point Ni is obtained. Further, as shown in the following equation [4], the sine sample value Wi ′ is also obtained in the same manner as described above.
Wi = θVi + (1−θ) Vi + 1 ... [3]
Wi ′ = θVi ′ + (1−θ) Vi + 1 ′... [4]
These sine sampling values Wi and Wi ′ are voltage values for each sampling period Ts with the provisional zero cross point Z as a reference, and the sampling period Ts is also very short. For this reason, the waveform constituted by the sine sampling values Wi and Wi ′ can be regarded as a sine waveform that does not include the phase difference αθ.
[0022]
In the fifth step, an approximate straight line ai + b is obtained by the least square method based on the straight line sample values Zi and Zi ′. Since this least square method is known, its description is omitted.
[0023]
In the sixth step, as shown in FIG. 3, the zero cross point of the approximate straight line ai + b is specified as the zero cross point Z of the received wave.
[0024]
In this embodiment, as shown in the following equation [7], a time ratio θz with respect to the sampling period Ts from the sample point S1 to the zero cross point of the approximate straight line ai + b is obtained, and further, as shown in the following equation [8]. Based on the time ratio θz, a time Tmz from the sample point S1 to the zero cross point of the approximate straight line ai + b is obtained.
θz = θ−b / a [7]
Tmz = θzTs = (θ−b / a) Ts [8]
θz: Time ratio with respect to the sampling period Ts from the sample point S1 to the zero cross point Z of the approximate line ai + b θ: Internal ratio a, b: Coefficient Tmz: Time from the sample point S1 to the zero cross point Z of the approximate line ai + b Ts: Sampling period Next, an ultrasonic flow velocity measuring method using the ultrasonic flow velocity measuring apparatus will be described with reference to the flowchart shown in FIG. In the following description and drawings, “step” is abbreviated as “S”.
[0025]
First, in S1, the microcomputer (7) generates a drive pulse from the drive pulse generation circuit (4) and applies the drive pulse to the ultrasonic vibrator (2), thereby causing the ultrasonic vibrator (2) to generate a drive pulse. Send an ultrasonic wave.
[0026]
In S2, the ultrasonic wave transmitted from the ultrasonic transducer (2) is received by the ultrasonic transducer (3), and the received wave is output from the reception amplification circuit (5).
[0027]
In S3, the microcomputer (7) uses the zero-cross point Z of the three waves (J3) of the received wave (J) output from the reception amplifier circuit (7) by the later-described received wave zero-cross specifying process as the ultrasonic wave arrival timing. Identify.
[0028]
In S4, the microcomputer (7) measures the time from the time when the ultrasonic wave is transmitted to the time when the ultrasonic wave is received (ultrasonic arrival timing) using the clock wave as the ultrasonic wave propagation time.
[0029]
In S5, it is determined whether or not the propagation time of the ultrasonic wave in the reverse direction is measured. If the propagation time of the ultrasonic wave in the reverse direction is not measured (NO in S5), the drive pulse generation circuit ( 4) and the downstream ultrasonic transducer (3), and the upstream ultrasonic transducer (2) and the reception amplification circuit (5) are switched so as to be connected, and the reverse is performed by the processing of S1 to S4 described above. Measure the ultrasonic propagation time in the direction. On the other hand, when the propagation time of the ultrasonic wave in the reverse direction is measured ( YES in S5 ), the process proceeds to S7.
[0030]
In S7, the flow velocity of the fluid is obtained based on the difference between the propagation times of the ultrasonic waves in the forward direction and the reverse direction, and the process returns. In this embodiment, the flow velocity of the fluid is obtained by the following equation [9].
V = L / 2 × (t2−t1) / (t1 × t2)... [9]
V: Fluid flow velocity L: Measurement tube length t1: Forward ultrasonic wave propagation time t2: Reverse ultrasonic wave propagation time FIG. 5 shows a received wave zero cross identification process (the process of S3 in FIG. 4). It is a flowchart which shows a subroutine.
[0031]
First, in S31, as shown in FIG. 2A, the voltage value near the zero cross point (Z) of the received wave (J) is sampled at a constant period Ts.
[0032]
In S32, as shown in FIG. 2 (b), the point where the line segment S1S1 'connecting the sample points S1, S1' immediately before and after the zero cross point Z of the received wave (J) zero crosses is set as a temporary zero cross point N0. The correspondence between the sample points S1, S1 ′ and the temporary zero cross point N0 is obtained.
[0033]
In S33, as shown in FIG. 2C, a line segment SiSi + 1 connecting the adjacent sample points Si and Si + 1 is determined in accordance with the correspondence between the sample points S1 and S1 ′ and the temporary zero cross point Z. Internal division is performed, and a sine sample value Wi corresponding to the internal division point Ni is obtained. These sine sampling values Wi and Wi ′ are voltage values for each sampling period Ts with the provisional zero cross point Z as a reference, and the sampling period Ts is also very short. For this reason, the waveform constituted by the sine sampling values Wi and Wi ′ can be regarded as a sine waveform that does not include the phase difference αθ.
[0034]
In S34, the sine sample values Wi and Wi ′ are converted into linear sample values Zi and Zi ′ as shown in the above equations [5] and [6]. In this way, when the sine sample values Wi and Wi ′ are converted into the linear sample values Zi and Zi ′, the division by siniα that does not include the phase difference θα as in the prior art is performed, so that the processing by the microcomputer is simplified.
[0035]
In S35, an approximate straight line ai + b is obtained by the least square method based on the straight line sample values Zi and Zi ′.
[0036]
In S36, as shown in FIG. 3, the zero cross point of the approximate straight line ai + b is specified as the zero cross point Z of the received wave, and the process returns.
[0037]
As described above, when the approximate straight line for specifying the zero-cross point Z of the received wave (J) is obtained, the sample value Vi of the received wave (J) is not directly converted into the linear sample value, but the received wave (J). The sine sample value Wi corresponding to the internal division point Ni of the line segment SiSi + 1 connecting the respective sample points Si and Si + 1 is converted into a linear sample value Zi. The sine sampling value Wi is a voltage value for each sampling period Ts with the provisional zero-cross point Z as a reference, and the waveform constituted by these sine sampling values Wi is a sine waveform that does not include the phase difference αθ. The processing by the microcomputer or the like when converting the sine sampling value Wi into the linear sample value Zi is simplified. For this reason. The zero cross point Z of the received wave (J) can be specified with high accuracy in a short processing time, and as a result, the flow velocity can be measured quickly and with high accuracy.
[0038]
【Effect of the invention】
According to the present invention, when the approximate straight line for specifying the zero-cross point Z of the received wave (J) is obtained, the sample value Vi of the received wave (J) is not directly converted into the linear sample value, but the received wave ( J) The sine sample value Wi corresponding to the internal dividing point Ni of the line segment SiSi + 1 connecting the sample points Si and Si + 1 is converted into a linear sample value Zi. The sine sampling value Wi is a voltage value for each sampling period Ts with the provisional zero-cross point Z as a reference, and the waveform constituted by these sine sampling values Wi is a sine waveform that does not include the phase difference αθ. The processing by the microcomputer or the like when converting the sine sampling value Wi into the linear sample value Zi is simplified. For this reason. The zero cross point Z of the received wave (J) can be specified with high accuracy in a short processing time, and as a result, the flow velocity can be measured quickly and with high accuracy.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an ultrasonic flow velocity measuring apparatus for carrying out an ultrasonic flow velocity measuring method according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a state from when a received wave is sampled until a linear sample value is obtained.
FIG. 3 is a diagram illustrating a relationship between an approximate straight line and a line segment connecting sample points.
4 is a flowchart showing the operation of the ultrasonic flow velocity measuring apparatus of FIG.
5 is a flowchart showing a subroutine of received wave specifying processing of FIG. 4;
FIG. 6 is a schematic configuration diagram of a conventional ultrasonic flow velocity measuring apparatus.
FIG. 7 is a diagram illustrating a state in which a sample value of a received wave is converted into a linear sample value.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Ultrasonic flow velocity measuring tube 2, 3 ... Ultrasonic vibrator 4 ... Drive pulse generation circuit 5 ... Reception amplification circuit 6 ... Switching circuit 7 ... Microcomputer

Claims (1)

Ultrasonic transducers 2 and 3 are respectively arranged on the upstream side and the downstream side of the measurement fluid flowing through the ultrasonic flow velocity measuring tube 1, and generate and transmit ultrasonic waves from the ultrasonic transducers 2 and 3. Ultrasonic waves that receive the received ultrasonic waves from each other, determine the ultrasonic wave propagation time based on the zero-cross point Z of the received waves (J), and measure the flow velocity based on the difference in the ultrasonic wave propagation times In the measurement method,
Sampling the received wave (J) at a constant period;
A point where the line segment S1S1 'connecting the sample points S1 and S1' immediately before and after the zero cross point Z of the received wave (J) crosses zero is defined as a temporary zero cross point N0, and the sample points S1, S1 'and the temporary zero cross point N0 A step of finding a correspondence relationship;
In accordance with the correspondence between the sample points S1, S1 ′ and the temporary zero cross point N0, a line segment SiSi + 1 connecting the adjacent sample points Si, Si + 1 is internally divided, corresponding to the internal dividing point Ni , Obtaining a sine sample value Wi that is a value for each sampling period Ts with reference to the provisional zero cross point Z and can be regarded as a sine waveform ;
Converting the sine sample value Wi into a linear sample value Zi;
Obtaining an approximate straight line ai + b by a least square method based on the straight line sample value Zi;
Identifying a zero cross point of the approximate straight line ai + b as a zero cross point Z of the received wave (J);
An ultrasonic flow velocity measuring method comprising:

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