CN111220816B - Time Difference Ultrasonic Velocity Measurement Method Using Frequency Hopping Signal - Google Patents

Abstract

The invention discloses a time difference type ultrasonic flow velocity measuring method adopting frequency hopping signals, which comprises the following steps: the first transducer and the second transducer transmit ultrasonic signals comprising a plurality of signal segments in turn, and different signal segments have different signal frequencies; the second transducer receives the ultrasonic signals transmitted by the first transducer, detects boundary points, namely frequency hopping points, of different signal segments, and determines the receiving time of the ultrasonic signals according to the time of the frequency hopping points and the duration of each signal segment; the first transducer receives the ultrasonic signals transmitted by the second transducer, detects boundary points, namely frequency hopping points, of different signal segments, and determines the receiving time of the ultrasonic signals according to the time of the frequency hopping points and the duration of each signal segment; comparing the receiving time of the ultrasonic signals and calculating the time difference; and calculating the flow velocity of the fluid according to the time difference by adopting a time difference method. The method has the advantages of high measurement precision, high flow velocity measurement stability, strong anti-interference capability and good environmental adaptability.

Description

Time Difference Ultrasonic Velocity Measurement Method Using Frequency Hopping Signal

technical field

The invention belongs to the field of fluid flow velocity measurement, and in particular relates to a time difference ultrasonic flow velocity measurement method using a frequency hopping signal.

Background technique

The time difference method is used to measure the average velocity of the river (channel) end face. When the sound wave propagates in the fluid, the propagation speed is different due to the different flow direction of the fluid. The velocity of fluid flow, the principle is shown in Figure 1.

The existing ultrasonic flow meter mainly uses the method of single-frequency pulse signal amplitude detection to measure the sound wave propagation time, and the detection method is shown in FIG. 2 . The receiving circuit at both ends of the river (channel) detects the amplitude of the received single-frequency pulse signal, and compares it with the threshold value. The time when the threshold value is higher is the time of signal reception, and the time difference from the time of signal transmission is the sound wave propagation time. The measurement accuracy of the acoustic wave propagation time is greatly affected by the consistency of the amplitudes of the two received signals, and the requirements for the consistency of the transducer parameters and equipment allocation are relatively high, which reduces the production efficiency and increases the production cost. The amplitude of the underwater acoustic signal is greatly affected by factors such as water surface, bottom reflection and foreign object occlusion, which requires higher installation environment of the equipment, which increases the installation difficulty and reduces the environmental adaptability of the equipment.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the above problems and provide a time difference ultrasonic flow velocity measurement method using frequency hopping signals. The ultrasonic signal used for measurement includes a plurality of signal segments, and different signal segments have mutually different signal frequencies. The demarcation point is the frequency hopping point. When receiving ultrasonic signals, the ultrasonic receiving time is determined by detecting the frequency hopping point and the duration of each signal segment, which reduces the requirements for the consistency of signal amplitude, the consistency of transducer parameters and equipment allocation, and improves the flow rate. Measurement stability and environmental adaptability.

The technical scheme of the present invention is to use a time-difference ultrasonic flow velocity measurement method of frequency hopping signals. A first transducer and a second transducer are arranged at intervals on both side walls of the fluid channel. The connection between the two lines and the flow direction of the fluid form a certain angle. The first transducer and the second transducer transmit the same two ultrasonic signals in turn, and receive the ultrasonic signals transmitted by the other party to determine the receiving time difference of the two ultrasonic signals. The measurement method includes the following steps,

Step 1: The first transducer and the second transducer alternately transmit ultrasonic signals including multiple signal segments, and different signal segments have different signal frequencies;

Step 2: the second transducer receives the ultrasonic signal transmitted by the first transducer, detects the boundary point of different signal segments, that is, the frequency hopping point, and determines the receiving time of the ultrasonic signal according to the time of the frequency hopping point and the duration of each signal segment;

Step 3: the first transducer receives the ultrasonic signal transmitted by the second transducer, detects the boundary point of different signal segments, that is, the frequency hopping point, and determines the receiving time of the ultrasonic signal according to the time of the frequency hopping point and the duration of each signal segment;

Step 4: compare the receiving moments of the ultrasonic signals in Step 2 and Step 3, and calculate the time difference;

Step 5: Using the time difference method, according to the time difference in step 4, calculate the flow rate of the fluid.

Further, in step 2 or step 3, before the detection of the boundary points of different signal segments, smooth filtering is performed on the received ultrasonic signals.

Further, the ultrasonic signal is a sine wave signal.

Further, in step 2 or step 3, the described detection of the demarcation points of different signal segments, search for all peak points and trough points of the ultrasonic signal, calculate each sine wave signal cycle by the peak point or the trough point, and determine the difference according to the signal cycle. The demarcation point of the signal segment, that is, the frequency hopping point.

Preferably, the different signal segments contain the same number of signal periods.

Preferably, the frequencies of the different signal segments of the ultrasonic signal are 204 kHz, 210 kHz, 205 kHz, 209 kHz, 206 kHz, 208 kHz, and 207 kHz in sequence.

Compared with the prior art, the beneficial effects of the present invention:

1) The method of the present invention has high measurement accuracy, good real-time performance, high flow velocity measurement stability, strong anti-interference ability, and good environmental adaptability;

2) The frequency hopping point is easy to detect. Compared with the amplitude comparison method, the requirements for the consistency of transducer parameters and equipment allocation are low, which improves the production efficiency and reduces the production cost;

3) The ultrasonic signal contains multiple signal segments and frequency hopping points. Each frequency hopping point can be used as a reference point for the receiving time to determine the ultrasonic receiving time. Even if the received ultrasonic signal is partially distorted, it will not affect the accurate measurement of the propagation time difference. .

Description of drawings

The present invention will be further described below with reference to the accompanying drawings and embodiments.

Fig. 1 is the principle schematic diagram of the time difference ultrasonic flow velocity measurement method;

Fig. 2 is a schematic diagram of single-frequency pulse signal amplitude detection;

Fig. 3 is the waveform diagram of the first ultrasonic wave signal of the embodiment;

Fig. 4 is the waveform diagram of the second ultrasonic wave signal of the embodiment;

In the figure, T1 is the signal period of the first signal segment, T2 is the signal period of the second signal segment, T3 is the signal period of the third signal segment, Td1 is the signal duration from the first frequency hopping point to the receiving time, and Td2 is the second frequency hopping point to The signal duration at the reception time, _t10 is the reception time of the first ultrasonic signal, _t11 is the time of the first frequency hopping point of the first ultrasonic signal, and _t12 is the time of the second frequency hopping point of the first ultrasonic signal , t ₂₀ is the receiving time of the second ultrasonic signal, t ₂₁ is the time of the first frequency hopping point of the second ultrasonic signal, and t ₂₂ is the time of the second frequency hopping of the second ultrasonic signal.

Detailed ways

As shown in Figure 1, the time difference ultrasonic flow velocity measurement method of the frequency hopping signal is adopted, and the first transducer and the second transducer are arranged at intervals on both sides of the river, and the connection line between the first transducer and the second transducer is arranged. Form a certain angle with the flow direction of the river water. The first transducer and the second transducer transmit the same 2-channel sinusoidal ultrasonic signals in turn, and receive the ultrasonic signals transmitted by the other party to determine the receiving time difference of the 2-channel ultrasonic signals. Measurement method Include the following steps,

Step 1: The first transducer and the second transducer alternately transmit ultrasonic signals including 7 signal segments, and different signal segments have different signal frequencies;

Step 2: The second transducer receives the first ultrasonic signal transmitted by the first transducer, performs smooth filtering, and detects the demarcation point of different signal segments, that is, the frequency hopping point. According to the time of the frequency hopping point and the duration of each signal segment Determine the receiving time of the ultrasonic signal, as shown in Figure 3;

Step 2.1: Receive the ultrasonic signal transmitted by the first transducer, and perform smooth filtering;

Step 2.2: Find all the crest points and trough points of the received ultrasonic signal, calculate the period of each sine wave signal through the crest point or the trough point, and determine the demarcation point of different signal segments according to the signal period, that is, the frequency hopping point;

Step 2.3: Select one of the frequency hopping points, such as the first frequency hopping point as the reference point of the receiving time, calculate the receiving time t ₁₀ of the first ultrasonic signal, t ₁₀ =t ₁₁ -Td1;

Step 3: The first transducer receives the second ultrasonic signal transmitted by the second transducer, performs smooth filtering, and detects the demarcation point of different signal segments, that is, the frequency hopping point, according to the time of the frequency hopping point and the duration of each signal segment. Determine the receiving time of the ultrasonic signal, as shown in Figure 4;

Step 3.1: Receive the second ultrasonic signal transmitted by the second transducer, and perform smooth filtering;

Step 3.2: Find all the crest points and trough points of the received ultrasonic signal, calculate the period of each sine wave signal through the crest point or the trough point, and determine the demarcation point of different signal segments according to the signal period, that is, the frequency hopping point;

Step 3.3: Select one of the frequency hopping points, such as the second frequency hopping point as the reference point of the receiving time, calculate the receiving time t ₂₀ of the second ultrasonic signal, t ₂₀ =t ₂₁ -Td2;

Step 4: compare the receiving time of the ultrasonic signal in step 2 and step 3, calculate the time difference, time difference Δt=t ₂₀ -t ₁₀ ;

Step 5: Using the time difference method, according to the time difference Δt in step 4, calculate the flow rate of the river water.

The frequencies of the seven signal segments of the ultrasonic signal are 204kHz, 210kHz, 205kHz, 209kHz, 206kHz, 208kHz, and 207kHz in sequence.

As shown in Fig. 1, the time difference method is based on the time difference Δt of the ultrasonic signal transmitted by the opposite transducer at the same time.

Δt=t ₂ -t ₁ (1)

V _p =V cosα (4)

Where L is the distance between the first transducer and the second transducer, C is the speed of sound in the fluid, V is the fluid velocity, α is the installation angle of the transducer relative to the fluid channel, and V _p is the fluid velocity along the The velocity component in the direction of the transducer, t ₁ is the propagation time of the ultrasonic signal from transducer A to transducer B, and t ₂ is the propagation time of the ultrasonic signal from transducer B to transducer A;

Combining formula (1)(2)(3)(4), we can get

Since the fluid velocity is much smaller than the sound velocity in the fluid, that is, V<<C, it can be obtained from formula (5)

After transformation, we can get

In step 5, the flow velocity of the water flow can be calculated by using the formula (6).

The specific details of the time difference method refer to the international standard ISO6416-1992: Ultrasonic (acoustic) wave method for flow measurement.

In the embodiment, the frequency hopping points of the received sinusoidal ultrasonic signal, such as the first frequency hopping point and the second frequency hopping point, are easy to detect, and compared with the method of amplitude comparison, the requirements for the consistency of transducer parameters and equipment allocation are low. , improve production efficiency and reduce production costs; multiple frequency hopping points of ultrasonic signals can be used as reference points for receiving time to determine ultrasonic receiving time, adding effective data samples, and comparing multiple frequency hopping points can also judge the signal transmission process. Whether there is distortion or interruption due to interference factors.

Claims (5)

1. The time difference ultrasonic flow velocity measurement method of frequency hopping signal is adopted, and the first transducer and the second transducer are arranged at intervals on both side walls of the fluid channel, and the connecting lines of the first transducer and the second transducer and The flow direction of the fluid forms an included angle, the first transducer and the second transducer transmit the same two ultrasonic signals in turn, and receive the ultrasonic signals transmitted by the other party to determine the receiving time difference of the two ultrasonic signals, which is characterized in that it includes the following steps, Step 1: The first transducer and the second transducer alternately transmit ultrasonic signals including multiple signal segments, and different signal segments have different signal frequencies; Step 2: the second transducer receives the ultrasonic signal transmitted by the first transducer, detects the boundary point of different signal segments, that is, the frequency hopping point, and determines the receiving time of the ultrasonic signal according to the time of the frequency hopping point and the duration of each signal segment; Step 3: the first transducer receives the ultrasonic signal transmitted by the second transducer, detects the boundary point of different signal segments, that is, the frequency hopping point, and determines the receiving time of the ultrasonic signal according to the time of the frequency hopping point and the duration of each signal segment; Step 4: compare the receiving moments of the ultrasonic signals in Step 2 and Step 3, and calculate the time difference; Step 5: Using the time difference method, according to the time difference in step 4, calculate the flow rate of the fluid; In step 2 or step 3, the demarcation points of different signal segments are detected, and all the peak points and trough points of the ultrasonic signal are searched, and each sine wave signal period is calculated by the peak points or trough points, and the signal period of different signal segments is determined according to the signal period. Demarcation point, namely frequency hopping point; In step 2, the second transducer receives the receiving time t ₁₀ of the first ultrasonic signal transmitted by the first transducer, t ₁₀ =t ₁₁ -Td1=t ₁₂ -Td2; Wherein t ₁₁ is the moment of the first frequency hopping point of the first ultrasonic signal, t ₁₂ is the moment of the second frequency hopping point of the first ultrasonic signal, Td1 is the signal duration from the first frequency hopping point to the receiving time, and Td2 is The signal duration from the second frequency hopping point to the receiving moment; In step 3, the receiving time t ₂₀ at which the first transducer receives the second ultrasonic signal transmitted by the second transducer, t ₂₀ =t ₂₁ -Td1=t ₂₂ -Td2; Wherein t ₂₁ is the moment of the first frequency hopping point of the second ultrasonic signal, and t ₂₂ is the moment of the second frequency hopping point of the second ultrasonic signal; time difference Δt=t ₂₀ -t ₁₀ ; Using the time difference method, according to the time difference Δt, the flow velocity of the river water is calculated. 2. The time-difference ultrasonic flow velocity measurement method using frequency hopping signal according to claim 1, is characterized in that, in step 2 or step 3, before the described detection of the demarcation point of different signal segments, the received ultrasonic signal is smoothed filter. 3 . The time-difference ultrasonic flow velocity measurement method using a frequency hopping signal according to claim 2 , wherein the ultrasonic signal is a sine wave signal. 4 . 4 . The time-difference ultrasonic flow velocity measurement method using a frequency hopping signal according to claim 1 , wherein different signal segments contain the same number of signal periods. 5 . 5. the time-difference ultrasonic flow velocity measuring method using frequency hopping signal according to any one of claims 1-4, is characterized in that, the frequency of different signal segments of ultrasonic signal is successively 204kHz, 210kHz, 205kHz, 209kHz, 206kHz, 208kHz, 207kHz.

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