CN117268483B - An instantaneous flow measurement method suitable for ultrasonic water meters - Google Patents

Abstract

The invention relates to the technical field of flow calculation, and discloses an instantaneous flow metering method suitable for an ultrasonic water meter, which comprises the following steps: measuring the resonance frequency of the water meter, and calculating the difference between the resonance frequency and the excitation frequency; collecting signals received by upstream and downstream transducers of the water meter; extracting an envelope signal to perform three-point correlation calculation and interpolating to calculate the maximum position; performing cross-correlation calculation on the acquired signals; taking a module after FFT of a calculation result; interpolation operation is carried out on the modulus result; calculating peak width ratio and signal to noise ratio of interpolation operation result; calculating a threshold value; and executing the subsequent process according to the comparison result of the peak width ratio and the threshold value. According to the invention, the related calculation range is roughly positioned through the envelope characteristics, so that the calculation efficiency is improved. The threshold value is defined by the frequency difference and the signal to noise ratio, and the frequency domain characteristics of the correlation result of the received signal are adaptively adjusted and calculated, so that the problem that the correlation calculation result and the true value have larger deviation after the signal to noise ratio is reduced due to noise increase, energy converter aging, flow overload and the like is solved, and the accuracy and the operation reliability of the water meter are ensured.

Description

An instantaneous flow measurement method suitable for ultrasonic water meters

Technical field

The present invention relates to the technical field of flow calculation, and in particular to an instantaneous flow measurement method suitable for ultrasonic water meters.

Background technique

Ultrasonic water meters are widely used in civil, industrial and other fields due to their advantages of high measurement accuracy, wide range ratio, and small pressure loss. They calculate the flow rate through the propagation time difference of the ultrasonic signals received by the upstream and downstream transducers. The correlation method calculates the time difference between two signals based on similarity and is insensitive to signal amplitude. It can be used in flow calculation of ultrasonic water meters. However, due to changes in environmental noise, aging of the transducer, flow overload, etc., when the system signal-to-noise ratio decreases, the correlation method calculation time difference will deviate from the true value by ±1 cycle, and there is no effective filtering method to calculate the flow rate. The value will be seriously offset, resulting in large measurement errors.

Contents of the invention

In view of the shortcomings and defects of the existing technology, the present invention provides an instantaneous flow measurement method suitable for ultrasonic water meters, which solves the problem of correlation method calculation time difference after the system signal-to-noise ratio decreases due to changes in environmental noise, aging of the transducer, etc. To solve the problem of large deviation from the true value, the flow rate can be accurately measured to achieve high accuracy and high reliability of ultrasonic water meters.

The object of the present invention can be achieved through the following technical solutions.

An instantaneous flow measurement method suitable for ultrasonic water meters includes the following steps.

S1, measure the resonant frequency of the ultrasonic water meter, and calculate the difference Δf between the resonant frequency and the excitation frequency f ₀ .

S2, collect the signals received by the upstream and downstream transducers of the ultrasonic water meter, recorded as X and Y respectively.

S3: Extract the envelope signals X ₀ and Y ₀ of X and Y respectively, perform three-point correlation calculations, and interpolate to calculate the maximum position P ₀ of the three-point correlation calculation results.

S4, perform cross-correlation calculation on X and Y according to the window width Width and P ₀ .

S5: Perform FFT on the cross-correlation calculation result R _xy and then take the modulus to obtain r _xy .

Interpolate r _xy .

Calculate the peak width ratio PWR and signal-to-noise ratio SNR of the interpolation operation result.

S6, calculate the threshold Thres, the calculation formula is as follows.

;

In the formula, SNR _ideal is the ideal value of signal-to-noise ratio SNR, PWR _ideal is the ideal value of peak width ratio PWR, Δf is the difference between the resonant frequency and the excitation frequency f ₀ , and λ is an adjustable parameter.

S7, compare PWR and Thres, and execute subsequent processes based on the comparison results.

If PWR≤Thres, set the window width to 2 and turn on the signal acquisition optimization function and jump to S2; if PWR≤Thres is satisfied for three consecutive comparisons, terminate this process and issue an alarm.

If PWR>Thres, perform interpolation calculation on R _xy ; obtain the time difference ΔT based on the interpolation calculation result and set the window width to 1; calculate the instantaneous flow rate based on ΔT and perform temperature compensation.

Preferably, the default value of the window width Width is 2, and the ultrasonic water meter signal acquisition optimization function is turned off by default.

Signal acquisition optimization functions include increasing amplifier gain, adding filter functions, and increasing transmit power.

Preferably, the extraction method of the envelope signal in step S3 includes Hilbert transform method and maximum value method.

If the Hilbert transform method is used, the extracted envelope signal needs to be down-sampled, and the down-sampling rate M is the ratio of the sampling rate and the excitation frequency.

Preferably, the three-point correlation calculation formula in step S3 is .

In the formula, R _xy,0 is the three-point correlation calculation result, and N is the signal length of the envelope signal X ₀ and Y ₀ .

Interpolation calculation methods include parabolic interpolation, cosine interpolation, Gaussian interpolation and cubic spline interpolation.

Preferably, the cross-correlation calculation formula in step S4 is .

In the formula, Len is the signal length of the upstream and downstream transducers receiving signals X and Y, and M is the ratio of the sampling rate and the excitation frequency.

Preferably, the peak width ratio PWR calculation formula in step S5 is: .

In the formula, Peak is the peak value calculated after interpolating r _xy , and FHWM is the half-maximum width calculated after interpolating r _xy .

The beneficial technical effect of the present invention is to roughly locate the relevant calculation range through the extracted envelope features and improve the calculation efficiency. Define the threshold with frequency difference and signal-to-noise ratio, and adjust the calculation process adaptively through the frequency domain characteristics of the signal correlation results received by the upstream and downstream transducers to solve system problems caused by increased environmental noise, aging transducers, or traffic overload. After the signal-to-noise ratio is reduced, the correlation method calculation results have a large deviation from the true value, which ensures the accuracy of the ultrasonic water meter and improves the reliability of the ultrasonic water meter operation.

Description of drawings

Figure 1 is an overall flow chart of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention and do not limit the present invention.

Example: As shown in Figure 1, an instantaneous flow measurement method suitable for ultrasonic water meters includes the following steps.

S1, measure the resonant frequency of the ultrasonic water meter, and calculate the difference Δf between the resonant frequency and the excitation frequency f _0. Taking a certain model of ultrasonic water meter as an example, the excitation frequency f ₀ is 2.00 MHz, and the measured resonant frequency is 1.94 MHz. The frequency difference Δf is 0.06MHz.

S2, the sampling rate f _s is 8 MHz, the sampling window is 30 us, and the upstream and downstream transducers of the ultrasonic water meter are collected to receive signals, which are recorded as X and Y respectively, and the signal length is 240.

S3, extract the envelope signals X ₀ and Y ₀ of X and Y respectively. The extraction methods of the envelope signals include the Hilbert transform method and the maximum method. In this embodiment, the Hilbert transform method is used to extract the envelope signals. network, downsampling the envelope output by the Hilbert transform, and the sampling rate M is reduced by 4 times compared with the original sampling rate f _s .

Then perform three related calculations, and the calculation formula is: .

In the formula, It is the three-point correlation calculation result, N is equal to 60, which is the signal length of the envelope signal X ₀ and Y ₀ .

Then, the maximum value position P ₀ of the three-point correlation result is calculated through interpolation. The interpolation calculation method includes parabolic interpolation, cosine interpolation, Gaussian interpolation and cubic spline interpolation. In this embodiment, cosine interpolation is used to calculate the maximum value position of the three-point correlation result. P ₀ is 0.18.

S4, according to the window width Width and P ₀ , perform cross-correlation calculation on the signals X and Y received by the upstream and downstream transducers, and obtain the cross-correlation result R _xy : .

In the formula, is the cross-correlation result of the signals X and Y received by the upstream and downstream transducers; Len is equal _to 240, which is the signal length of the signals X and Y received by the upstream and downstream transducers; P ₀ is equal to _0.18 , which is the envelope signal The maximum position of the result after point correlation; M equals 4, which is the ratio of the sampling rate f _s and the excitation frequency f ₀ ; Width equals 2, which is the window width.

In this example, it is calculated that , since m can only be an integer, the value range is rounded to [- 4, 5].

S5, after performing FFT on the cross-correlation result R _xy , take the modulus to obtain r _xy , and calculate the peak width ratio and signal-to-noise ratio of the interpolation operation result. .

In the formula, Peak is the peak value calculated after interpolating r _xy , and FHWM is the half-maximum width calculated after interpolating r _xy .

In this embodiment, the calculated peak width ratio is 49.19, and the signal-to-noise ratio is the average signal-to-noise ratio of the signals received by the upstream and downstream transducers, which is 38.87 dB.

S6, calculate threshold .

In the formula, SNR _ideal is the ideal value of signal-to-noise ratio SNR, which is related to the design range ratio and accuracy level of the ultrasonic water meter. PWR _ideal is the ideal value of peak width ratio PWR, which is related to the transducer design. Δf is the resonance frequency and excitation The difference between frequency f ₀ and λ is an adjustable parameter. In this embodiment, the ideal value of the signal-to-noise ratio SNR _ideal is 50 dB, and the ideal value of the peak width ratio PWR _ideal is 24.00. According to a certain model of ultrasonic water meter, the value of λ is 0.65, and the calculated threshold Thres is 12.38.

S7, compare PWR and Thres, and execute subsequent processes based on the comparison results.

If PWR≤Thres, set the window width to 2 and turn on the signal acquisition optimization function, then jump to S2. First increase the amplifier gain and transmit power, and then re-acquire. The collected signals received by the upstream and downstream transducers will be filtered first, and then Execute steps S3~S7; if three consecutive collections meet PWR≤Thres, the process will be terminated and an alarm will be issued.

If the peak width ratio > the threshold, R _xy is interpolated, and finally the time difference ΔT is obtained and the window width is set to 1; the instantaneous flow rate is calculated based on ΔT and temperature compensation is performed.

The default value of window width Width is 2, and the ultrasonic water meter signal acquisition optimization function is turned off by default; the ultrasonic water meter signal acquisition optimization function includes increasing the amplifier gain, adding filter functions, and increasing transmit power.

The above embodiments are illustrative of specific implementations of the present invention, rather than limitations of the present invention. Those skilled in the relevant technical fields can also make various transformations and changes without departing from the spirit and scope of the present invention. Corresponding equivalent technical solutions, therefore all equivalent technical solutions should be included in the patent protection scope of the present invention.

Claims (6)

1. An instantaneous flow measurement method suitable for ultrasonic water meters, which is characterized in that it includes the following steps: S1, measure the resonant frequency of the ultrasonic water meter, and calculate the difference Δf between the resonant frequency and the excitation frequency f ₀ ; S2, collect the signals received by the upstream and downstream transducers of the ultrasonic water meter, recorded as X and Y respectively; S3, extract the envelope signals X ₀ and Y ₀ of X and Y respectively, perform three-point correlation calculations, and interpolate to calculate the maximum position P ₀ of the three-point correlation calculation results; S4, perform cross-correlation calculation on X and Y according to the window width Width and P ₀ ; S5, perform FFT on the cross-correlation calculation result R _xy and then take the modulus to obtain r _xy ; Perform interpolation operations on r _xy ; Calculate the peak width ratio PWR and signal-to-noise ratio SNR of the interpolation operation result; S6, calculate the threshold Thres, the calculation formula is as follows: ; In the formula, SNR _ideal is the ideal value of signal-to-noise ratio SNR, PWR _ideal is the ideal value of peak width ratio PWR, Δf is the difference between the resonant frequency and the excitation frequency f ₀ , and λ is an adjustable parameter; S7, compare PWR and Thres, and execute subsequent processes based on the comparison results: If PWR≤Thres, set the window width to 2 and turn on the signal acquisition optimization function and then jump to S2; if three consecutive comparisons satisfy PWR≤Thres, terminate this process and issue an alarm; If PWR>Thres, perform interpolation calculation on R _xy ; obtain the time difference ΔT based on the interpolation calculation result and set the window width to 1; calculate the instantaneous flow rate based on ΔT and perform temperature compensation. 2. An instantaneous flow measurement method suitable for ultrasonic water meters according to claim 1, characterized in that the default value of the window width Width is 2, and the ultrasonic water meter signal acquisition optimization function is turned off by default; Signal acquisition optimization functions include increasing amplifier gain, adding filter functions, and increasing transmit power. 3. An instantaneous flow measurement method suitable for ultrasonic water meters according to claim 1, characterized in that the extraction method of the envelope signal in step S3 includes Hilbert transform method and maximum value method; If the Hilbert transform method is used, the extracted envelope signal needs to be down-sampled, and the down-sampling rate M is the ratio of the sampling rate and the excitation frequency. 4. An instantaneous flow measurement method suitable for ultrasonic water meters according to claim 1, characterized in that the three-point correlation calculation formula in step S3 is: ; In the formula, R _xy,0 is the three-point correlation calculation result, and N is the signal length of the envelope signal X ₀ and Y ₀ ; Interpolation calculation methods include parabolic interpolation, cosine interpolation, Gaussian interpolation and cubic spline interpolation. 5. An instantaneous flow measurement method suitable for ultrasonic water meters according to claim 1, characterized in that the cross-correlation calculation formula in step S4 is: ; In the formula, Len is the signal length of the upstream and downstream transducers receiving signals X and Y, and M is the ratio of the sampling rate and the excitation frequency. 6. An instantaneous flow measurement method suitable for ultrasonic water meters according to claim 1, characterized in that the peak width ratio PWR calculation formula in step S5 is: ; In the formula, Peak is the peak value calculated after interpolating r _xy , and FHWM is the half-maximum width calculated after interpolating r _xy .