JP2003014516A - Ultrasonic flow velocity measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flow velocity measuring method capable of accurately specifying a zero cross point of a received wave in a short time. SOLUTION: The measuring method comprises a step for sampling a received wave J in a fixed time period to take a temporary zero cross point Nd0 at which a line segment S1 S1 ' between sample points S1 , S1 ' just before and after a zero cross point Z of the received wave J, obtaining the corresponding relation of the temporary zero cross point N0 to the sample points S1 , S1 '; a step for internally dividing a segment SiSi+1 between adjacent sample points Si, Si+1 according to the corresponding relation of the temporary zero cross point N0 to the sample points S1 , S1 ' to obtain a sine sample value Wi corresponding to the internal division point Ni; a step for converting the sine sample value Wi into a linear sample value Zi to obtain an approximate line ai+b by the least squares method, based on the linear sample value Zi; and a step for specifying the zero cross point of the approximate line ai+b as a zero cross point Z of the received wave (J).

Description

Description: BACKGROUND OF THE INVENTION 1. Field 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. 2. Description of the Related Art Conventionally, when determining the flow rate of a gas or other fluid, the flow rate of the fluid is measured continuously or periodically, and the flow rate is calculated based on this. That is being done. As one of such fluid flow velocity measuring methods, a method using ultrasonic waves is known. FIG. 6 shows the principle of such an ultrasonic flow velocity measuring method.
The description is as follows. In FIG.
(1) is an ultrasonic flow velocity measuring tube through which a fluid such as gas flows. In the ultrasonic flow velocity measuring tube (1), ultrasonic vibrators (2) and (3) are arranged at a predetermined distance upstream and downstream in the flow direction. The ultrasonic vibrators (2) and (3) are driven by a driving pulse from a driving pulse generating circuit (4) to vibrate, generate and transmit ultrasonic waves, and receive transmitted ultrasonic waves. The reception wave (J) when the ultrasonic transducers (3) and (2) vibrate is output from the reception amplification circuit (5). Then, the propagation time until the ultrasonic wave transmitted in the forward direction from the upstream ultrasonic oscillator (2) to the flow is received by the downstream ultrasonic oscillator (3), The difference between the ultrasonic wave transmitted from the downstream ultrasonic oscillator (3) in the opposite direction to the flow and the propagation time until the ultrasonic wave is received by the upstream ultrasonic oscillator (2) is related to the flow velocity. Therefore, the flow velocity of the fluid is measured by determining the difference in the propagation time of the ultrasonic wave by using a clock wave or the like. In FIG. 6, reference numeral (6) denotes a switching circuit for switching the connection between each of the ultrasonic transducers (2) and (3), the drive pulse generating circuit (4) and the receiving amplifier circuit (5). The pulse generating circuit (4) is connected to the upstream ultrasonic oscillator (2), and the downstream ultrasonic oscillator (3) is connected to the receiving amplifier circuit (5) to reduce the propagation time from the upstream to the downstream. After the measurement, the operation of the switching circuit (6) activates the drive pulse generation circuit (4), the downstream ultrasonic oscillator (3), the upstream ultrasonic oscillator (2), and the reception amplifier circuit (5). Are connected so that the propagation time from the downstream side to the upstream side is measured. Generally, the propagation time of an ultrasonic wave is
The zero-cross point Z of the received wave (J) is obtained based on a predetermined zero-cross point Z of the received wave (J) output from the receiving amplifier circuit (5). Conventionally, the zero-cross point Z of the received wave (J) has been specified by the following method. 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 sine waveform sample values Pi 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 sample point immediately before it is αθ, and the sine waveform of the received wave (J) is expressed by the following equation [10]. In this case, the sample value Pi of the sine waveform is converted into a linear sample value Qi by the following equation [11]. Pi = Asin (iα + αθ) [10] Qi = Pi × B (iα + αθ) / Asin (iα + αθ) [11] Qi: Sample value of straight line Pi: Sample value of sine waveform i: Sample number A, B: Coefficient αθ: Approximate line is calculated from the phase difference between the zero-cross point Z of the received wave (J) and the immediately preceding sample point by the least squares method from the sample values Qi of these lines, and the zero-cross point of the approximate line is calculated. It is specified as the zero cross point Z of the received wave (J). However, according to the above method, the above equation [1]
When [1] converts a sine waveform sample value Pi into a straight line sample value Qi, when [theta] is an arbitrary value, (i)
α + αθ) is also an arbitrary value.
There is a problem that the calculation process of in (iα + αθ) becomes complicated, and it takes time to specify the zero-cross point Z of the received wave (J). SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and is capable of accurately specifying a zero-cross point of a received wave in a short time, and thus, capable of quickly and highly accurately measuring a flow velocity. The purpose is to provide a method for measuring flow velocity. In order to achieve the above object, the present invention provides a method for determining an approximate straight line for specifying a zero-cross point Z of a received wave (J). Instead of directly converting the sample value Vi to a straight line sample value, a line segment SiSi + 1 connecting each sample point Si and Si + 1 of the received wave (J) is internally divided, and a sign corresponding to the subdivision point Ni is obtained. The sample value Wi is converted into a linear sample value Zi. That is, according to the present invention, the ultrasonic vibrators 2, 3 are arranged on the upstream side and the downstream side of the measuring fluid flowing through the ultrasonic flow velocity measuring tube 1, respectively. While generating and transmitting the ultrasonic waves, the transmitted ultrasonic waves are mutually received, the propagation time of the ultrasonic waves is obtained based on the zero cross point Z of the received waves (J), and the difference between the propagation times of the ultrasonic waves is calculated. In the ultrasonic flow velocity measuring method for measuring the flow velocity based on the above, a step of sampling the received wave (J) at a constant period, and a zero cross point Z of the received wave (J)
Line segment S1S1 'connecting sample points S1 and S1' immediately before and after
A point at which the zero crossing is performed is defined as a temporary zero crossing point N0, and a step of determining the correspondence between the sample points S1 and S1 'and the temporary zero crossing point N0; and according to the correspondence between the sample points S1 and S1' and the temporary zero crossing point N0, A step of internally dividing a line segment SiSi + 1 connecting the adjacent sample points Si and Si + 1 to obtain a sine sample value Wi corresponding to the internally divided point Ni; and converting the sine sample value Wi into a linear sample value Zi. Converting, obtaining an approximate straight line ai + b by the least square method based on the straight line sample value Zi, and specifying a zero cross point of the approximate straight line ai + b as a zero cross point Z of the received wave (J). It is characterized by having. According to this, the sine sampling value Wi is a voltage value for each sampling period Ts based on the temporary zero cross point Z, and the waveform constituted by the sine sampling values Wi does not include the phase difference αθ. Since the signal has a sine waveform, 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, so that a quick and accurate flow velocity measurement can be performed. FIG. 1 shows an ultrasonic flow velocity measuring device for carrying out the present invention. In FIG. 1, (1) is an ultrasonic flow velocity measuring tube, (2) and (3) are ultrasonic vibrators arranged at a predetermined distance upstream and downstream in a flow direction, and (4) is a driving pulse. A pulse generating circuit that generates a signal; (5) a receiving amplifier circuit that outputs a received wave (J) when ultrasonic waves are received by the ultrasonic transducers (2) and (3);
(6) is a switching circuit for switching the connection between the ultrasonic transducers (2) and (3), the pulse generating circuit (4) and the receiving amplifier circuit (5), which are the same as those shown in FIG. (7) A central processing unit (hereinafter referred to as a CPU) for performing various processes, a read / write memory (RAM) as needed, and a read-only memory (RO)
M), and is connected to the pulse generation circuit (4), the reception amplification circuit (5), and the switching circuit (6), respectively. The microcomputer (7) causes the ultrasonic vibrators (2) and (3) to generate and transmit ultrasonic waves. After the ultrasonic waves are received by the ultrasonic vibrators (3) and (2), the microcomputer (7) will be described later. Receive amplifier circuit by receiving wave zero crossing specification processing (5)
The zero-cross point Z of the received wave (J) output from is specified as the ultrasonic reception timing. Then, the propagation times of the ultrasonic waves in the forward and reverse directions are measured based on 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. Hereinafter, the received wave zero-cross identification processing will be specifically described. In this embodiment, the zero-cross point (Z) of the third wave (W3) of the received wave (J) is specified as the ultrasonic reception timing. This received wave zero-crossing specifying process includes a first step to a sixth step. In the first step, as shown in FIG. 2A, the zero-cross point (Z) of the received wave (J) is determined. ) Is sampled at a constant period Ts. In this embodiment, the sample points before the zero cross point (Z) of the received wave (J) are defined as S1, S2,.
.., Sn and their sampled values are V1, V2,.
, Vn, and the sample points after the zero cross point (Z) of the received wave (J) are S1 ', S2',.
n 'and their sample values are V1', V2 ',.
, Vn '. In the second step, as shown in FIG. 2B, the point at which the line segment S1S1 'connecting the sampling points S1 and S1' immediately before and after the zero-cross point Z of the received wave (J) crosses the zero-cross point. A temporary zero-cross point N0 is set, and the sample point S1,
The correspondence between S1 'and the temporary zero cross point N0 is determined. In this embodiment, as shown in the following equation [1], first, a time Tm from the sample point S1 to the temporary zero crossing point N0 is obtained based on the sample values V1 and V1 '. As shown in [2], based on the time Tm and the sampling period Ts, the temporary zero cross point N0
To determine the internal division ratio θ of the line segment S1S1 ′. The internal division ratio θ indicates 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 Ts from sample point S1 to temporary zero crossing point N0 Ts: Sampling cycle V1: Received wave (J )): Sampling value V1 ′ immediately before the zero-cross point Z: sampling value θ immediately after the zero-cross point Z of the received wave (J): internal division ratio Ts: sampling cycle In the third step, as shown in FIG. According to the correspondence between the sample points S1 and S1 'and the temporary zero cross point Z, a line segment Si connecting the adjacent sample points Si and Si + 1.
Si + 1 is internally divided, and a sine sample value Wi corresponding to the internally divided point Ni is obtained. In this embodiment, the sample points S1,
Since the correspondence between S1 'and the temporary zero-crossing point N0 is represented by the internal division ratio θ of the line segment S1S1' by the temporary zero-crossing point N0, as shown in the following equation [3], each adjacent sample point Si, Si The line segments Si and Si + 1 connecting +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 obtained in the same manner as described above. Wi = [theta] Vi + (1- [theta]) Vi + 1 ... [3] Wi '= [theta] Vi' + (1- [theta]) Vi + 1 '... [4] These sine sampling values Wi and Wi' are the temporary zero cross points Z. , And the sampling period Ts is very short. Therefore, the waveform composed of the sine sampling values Wi and Wi ′ can be regarded as a sine waveform that does not include the phase difference αθ. In the fourth step, as shown in the following equations [5] and [6], the sine sample values Wi and Wi 'are converted into linear sample values Zi and Zi'. Zi = (isinα / siniα) × Wi (5) Zi ′ = (isinα / siniα) × Wi ′ (6) Thus, the sine sample values Wi and Wi ′ are converted to the linear sample values Zi and Zi. When converting to ′, the processing by the microcomputer is simplified because it is divided by siniα that does not include the phase difference θα as in the related art. Note that the above equation [5]
The reason why [6] is multiplied by isin α is to make a straight line such that the sine sample values W1 and W1 ′ coincide with the straight line sample values Z1 and Z1 ′. In the fifth step, an approximate straight line ai is obtained by the least square method based on the straight line sample values Zi and Zi '.
+ B is obtained. Since the least squares method is known, its description is omitted. In the sixth step, as shown in FIG.
The zero cross point of the approximate straight line ai + b is specified as the zero cross point Z of the received wave. In this embodiment, as shown in the following equation [7], the time ratio θz from the sampling point S1 to the zero cross point of the approximate straight line ai + b with respect to the sampling cycle Ts is obtained. As shown, the time Tmz from the sample point S1 to the zero cross point of the approximate straight line ai + b is obtained based on the time ratio θz. [7] Tmz = [theta] zTs = ([theta] -b / a) Ts [8] [theta] z: The sampling period from the sample point S1 to the zero cross point Z of the approximate straight line ai + b. Time ratio to Ts: Internal division ratio a, b: Coefficient Tmz: Time from sample point S1 to zero crossing point Z of approximate straight line ai + b Ts: Sampling cycle Next, ultrasonic flow velocity measurement using the above ultrasonic flow velocity measuring device The method will be described with reference to the flowchart shown in FIG. In the following description and drawings, “step” is abbreviated as “S”. First, in S1, the microcomputer (7) generates a driving pulse from the driving pulse generating circuit (4) and applies the driving pulse to the ultrasonic vibrator (2) to thereby generate the ultrasonic vibrator ( Transmit the ultrasonic wave from 2). In S2, the ultrasonic wave transmitted from the ultrasonic vibrator (2) is received by the ultrasonic vibrator (3), and a reception wave is output from the reception amplifier circuit (5). In step S3, the microcomputer (7) executes the reception wave zero-cross identification processing described later to execute the reception amplification circuit (7).
The zero-crossing point Z of three waves (J3) of the received waves (J) output from is specified as the ultrasonic arrival timing. At 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) by using the clock wave as the ultrasonic wave propagation time. In S5, it is determined whether or not the propagation time of the ultrasonic wave in the reverse direction has been measured. If the propagation time of the ultrasonic wave in the reverse direction has not been measured (NO in S5), the driving pulse is determined in S6. The generation circuit (4) and the downstream ultrasonic vibrator (3), and the upstream ultrasonic vibrator (2) and the reception amplifier circuit (5) are switched so as to be connected, and the above-described S1 to S4 The processing measures the propagation time of the ultrasonic wave in the reverse direction. On the other hand, when the propagation time of the ultrasonic wave in the reverse direction is measured (YE in S15)
S), proceed to S7. 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 backward 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) (6) V: flow velocity of fluid L: length of measuring tube t1: propagation time of forward ultrasonic wave t2: reverse direction FIG. 5 is a flowchart showing a subroutine of the received wave zero-crossing specifying process (the process of S3 in FIG. 4). First, in S31, as shown in FIG. 2A, a voltage value near the zero cross point (Z) of the received wave (J) is sampled at a constant period Ts. In step S32, as shown in FIG. 2B, the point at which 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 the temporary zero-cross point. N0 is set, and the correspondence between the sample points S1 and S1 'and the temporary zero-crossing point N0 is determined. In step S33, as shown in FIG. 2C, a line segment SiSi connecting the adjacent sample points Si and Si + 1 according to the correspondence between the sample points S1 and S1 'and the temporary zero cross point Z. +1 is internally divided to obtain a sine sample value Wi corresponding to the internally divided point Ni. These sine sampling values W
i and Wi 'are voltage values for each sampling period Ts with reference to the temporary zero cross point Z, and the sampling period Ts is also very short. Therefore, the waveform composed of the sine sampling values Wi and Wi ′ can be regarded as a sine waveform that does not include the phase difference αθ. In S34, as shown in the above equations [5] and [6], the sine sample values Wi and Wi 'are converted into linear sample values Zi and Zi'. As described above, when the sine sample values Wi and Wi ′ are converted into the linear sample values Zi and Zi ′, the conventional method does not include the phase difference θα.
The division by niα simplifies the processing by the microcomputer. In S35, the linear sample values Zi, Z
An approximate straight line ai + b is obtained by the least squares method based on i ′. At 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. As described above, when obtaining the approximate straight line for specifying the zero-cross point Z of the received wave (J), the sample value Vi of the received wave (J) is not directly converted to a linear sample value, (J) each sample point Si,
The sine sample value Wi corresponding to the subdivision point Ni of the line segment SiSi + 1 connecting Si + 1 is converted into a linear sample value Zi. The sine sampling value Wi is a voltage value for each sampling period Ts based on the temporary zero-crossing point Z, and a waveform composed of the sine sampling values Wi is a sine waveform that does not include the phase difference αθ. 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-crossing point Z of the received wave (J) can be specified with high accuracy in a short processing time, so that a quick and highly accurate flow velocity measurement becomes possible. According to the present invention, when obtaining an approximate straight line for specifying the zero-cross point Z of the received wave (J),
The sample value Vi of the received wave (J) is not directly converted to a linear sample value, but corresponds to the subdivision point Ni of the line segment SiSi + 1 connecting the sample points Si and Si + 1 of the received wave (J). The sine sample value Wi is converted to a linear sample value Zi.
The sine sampling value Wi is a voltage value for each sampling period Ts based on the temporary zero-crossing point Z, and a waveform composed of the sine sampling values Wi is a sine waveform that does not include the phase difference αθ. 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-crossing point Z of the received wave (J) can be specified with high accuracy in a short processing time, so that a quick and highly accurate flow velocity measurement becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of an ultrasonic flow velocity measuring device for performing an ultrasonic flow velocity measuring method according to an embodiment of the present invention. FIG. 2 is a diagram showing a state from sampling of a received wave to obtaining a linear sample value. FIG. 3 is a diagram showing a relationship between an approximate straight line and a line segment connecting sample points. FIG. 4 is a flowchart showing the operation of the ultrasonic flow velocity measuring device of FIG. FIG. 5 is a flowchart showing a subroutine of a received wave specifying process of FIG. 4; FIG. 6 is a schematic diagram of a configuration of a conventional ultrasonic flow velocity measuring device. FIG. 7 is a diagram showing a state in which a sample value of a received wave is converted into a linear sample value. [Description of Signs] 1 ... Ultrasonic flow velocity measuring tube 2, 3 ... Ultrasonic vibrator 4 ... Drive pulse generating circuit 5 ... Receiving amplifying circuit 6 ... Switching circuit 7 ... Microcomputer

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Kazuo Eshita             Kansai gas             Data Corporation (72) Inventor Tetsuya Yasuda             10 Kansai Gasme, Kagidacho, Chudo-ji, Shimogyo-ku, Kyoto             Data Corporation (72) Inventor Naohiro Tadazu             Kansai gas             Data Corporation F term (reference) 2F035 DA14 DA22 DA23

Claims (1)

Claims: 1. Ultrasonic vibrators 2, 3 are arranged on the upstream side and downstream side of a measurement fluid flowing through an ultrasonic flow velocity measuring tube 1, respectively. While generating and transmitting ultrasonic waves to each other, mutually receiving the transmitted ultrasonic waves,
An ultrasonic flow velocity measuring method for determining a propagation time of an ultrasonic wave based on a zero-cross point Z of the received waves (J) and measuring a flow velocity based on a difference between the propagation times of the ultrasonic waves. Is sampled at a constant period. A point at which 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. , S1 '
Calculating a correspondence relationship between the sample points S1 and S1 'and the provisional zero cross point N0, and forming a line segment SiSi + 1 connecting the adjacent sample points Si and Si + 1 according to the correspondence relationship between the sample points S1 and S1' and the provisional zero cross point N0. Subdividing and obtaining a sine sample value Wi corresponding to the subdivision point Ni; converting the sine sample value Wi into a linear sample value Zi; approximating by a least square method based on the linear sample value Zi An ultrasonic flow velocity measuring method, comprising: determining a straight line ai + b; and identifying a zero cross point of the approximate straight line ai + b as a zero cross point Z of the received wave (J).