KR100559139B1 - Ultrasonic wave flow meter using correlation - Google Patents

Abstract

An ultrasonic flow meter using cross-correlation is disclosed. The ultrasonic flowmeter using the cross-correlation of the present invention comprises: a first phase comparator for performing phase comparison between a received signal and a transmitted signal; A first low pass filter for low passing the phase comparison output; An integrator for integrating the output signal of the phase comparator; A second phase comparator for performing phase comparison between an output signal of the compensation circuit itself and a transmission signal; A second low pass filter for low passing the phase comparison output; And a voltage controlled oscillator configured to receive a signal obtained by adding the signal output from the integrator and the output value of the second low pass filter to generate and output a signal following the transmission signal. According to the present invention, not only are less affected by the type, pressure, etc. of the measurement target fluid, it is possible to measure the flow rate in real time with excellent reproducibility and precise values. In addition, since it is attached to the outside of the pipe (clamp on type), it is possible to measure the flow rate without disassembling the pipe in the field, so it has excellent mobility and applicability.

Cross-correlation, Ultrasonic, Flowmeter

Description

Ultrasonic wave flow meter using correlation             

1 is a view illustrating a concept of a conventional phase demodulation detection method;

2 is a view illustrating a concept of a phase demodulation detection method using a conventional bubble detector,

3 is a control circuit block diagram schematically showing the configuration of the ultrasonic flow measurement apparatus using cross-correlation;

4 is a diagram illustrating a concept of a phase demodulation detection method using a double PLL according to the present invention.

Explanation of symbols on the main parts of the drawings

10, 10 ': generator 20, 20': amplifier

30: sensor A 30 ': sensor B

40: pipe 50: sensor C

50 ': sensor D 60, 60': amplifier

70, 70 ': demodulator 80: cross-correlator

The present invention relates to an ultrasonic flowmeter using cross-correlation, and in particular, by taking a cross-correlation of the turbulent noise input through a sensor installed at a certain interval outside the pipe, it is excellent in reproducibility and can measure real-time flow rate with precise values. It relates to an ultrasonic flowmeter using.

Flow measurement is very important for handling oil, gas, water and sewage, and chemical fluids. Accuracy, reliability, reproducibility, and scalability are very important factors, and various types of flowmeters are used depending on the purpose of use and environment.

Ultrasonic signals used in cross-correlation ultrasonic flowmeters are used for transmitting and receiving high frequency signals of several MHz (1 MHz to 10 MHz), and the signals are turbulent in the form of phase modulation as they pass through the fluid. Obtain information. As a method of detecting a phase modulation signal generated while passing through turbulence, a phase detector is detected using a phase detector, and then a low pass filter (LPF) is used to filter the normal phase modulation signal. There is no problem with demodulation. In general, the phase detection circuit uses a phase locked loop (PLL). However, phase modulation in ultrasonic flowmeters is not only caused by turbulence, but also by bubbles or suspended matter in the fluid. In general, the magnitude of phase modulation by turbulence is not so large as about ± 10 °, but bubbles and suspended matter in the fluid may cause rapid and continuous phase modulation of more than ± 90 ° depending on the type. Therefore, in this case, a normal phase demodulation cannot be performed using only a phase detection circuit and a low pass filter. Therefore, a method for solving this problem is required.

1 is a diagram illustrating a concept of a conventional phase demodulation detection method. Referring to FIG. 1, the phase demodulation detection method is a phase demodulation detection method through a phase comparator 120. The input of the phase comparator 120 is a transmission signal S _T (t) 100 and a reception signal ( S _R (t), 110). The phase comparator 120 compares the phase difference of these two signals. If there is no phase difference between the two signals using an XOR logic circuit, the output of the phase comparator 120 becomes “0”, and the larger the phase difference, the wider the pulse width and the demodulated signal S _D (t) 140. Is output. The low pass filter (LPF) 130 serves to remove high frequency components. Therefore, as the phase difference increases, the magnitude of the DC voltage output from the low pass filter LPF 130 becomes larger. Therefore, a problem arises in that the output is saturated with a large continuous change and the phase change due to turbulence cannot be detected.

FIG. 2 is a diagram illustrating a concept of a phase demodulation detection method using a conventional bubble detector. Referring to FIG. 2, two types of inputs of the phase comparator 220 are the same as those of FIG. 1, but two types of the transmission signals S _T (t) and 200 and the reception signals S _R (t) and 210. The difference is that the received signal S _R (t) 210 passes through a bubble detector 250. If the input of the float detector 250 suddenly changes, there are bubbles or floats, so a signal such as a transmission signal S _T (t) 200 is input to the input of the PLL 220. That is, the output voltage and the final output voltage S _D (t) 240 of the PLL 220 are initialized to “0” for a predetermined time. After a certain time, the demodulation signal is detected through phase comparison as a normal transmission / reception signal.

As described above, when a large phase change in a fluid causes a sudden change in phase, the input is detected and the input is reset, and the signal is not received until the phase change is normally recovered. I'm using the method. In the case of a sudden change in phase out of the normal phase change range, the duty of the output to the phase comparator becomes large, so that the output of the low pass filter 230 will increase rapidly. Therefore, in order to limit the output of the low pass filter 230 within a certain operating range, it is necessary to add the float detector circuit 250 so that the phase modulation detection signal is always limited within a certain range.

However, the demodulator using the float detector 250 is not only a disadvantage that the demodulation signal S _D (t) 240 is generated for a predetermined time when bubbles or floats are present, as well as a phase due to a slowly changing temperature change (Temperature Drift). The amount of change could not be detected, causing a phase demodulation error.

Accordingly, an object of the present invention is to provide an ultrasonic flowmeter using cross-correlation which can measure real-time flow rate with high reproducibility and precise values by taking a cross-correlation of turbulent noise input through a sensor installed at a certain interval outside the pipe. have.

Ultrasonic flowmeter using the cross-correlation of the present invention for achieving the above object of the present invention, the signal generator for generating an ultrasonic signal having a predetermined frequency; A first amplifier for amplifying the ultrasonic signal; A transmission sensor for transmitting a transmission signal corresponding to the amplified ultrasonic signal; A reception sensor configured to receive a reception signal generated after the transmission signal passes through the fluid in the pipe; A second amplifier for amplifying the received signal to a predetermined magnitude; And a demodulator for demodulating the amplified signal, wherein the ultrasonic flow meters are each disposed at a predetermined interval outside the pipe, and receive a signal output from the demodulators of the respective ultrasonic flow meters to measure a time delay to measure a flow rate. And a first phase comparator configured to perform phase comparison between the received signal and the transmitted signal for measuring a flow rate. A first low pass filter for low passing the phase comparison output; An integrator for integrating the output signal of the phase comparator; And a cross-correlator consisting of a compensation circuit for compensating for rapid and continuous phase changes and slowly changing temperature changes caused by bubbles or suspended solids. In this case, the compensation circuit may include a second phase comparator for performing phase comparison between an output signal of the compensation circuit itself and a transmission signal; A second low pass filter for low passing the phase comparison output; And a voltage controlled oscillator configured to receive a signal obtained by adding the signal output from the integrator and the output value of the second low pass filter to generate and output a signal following the transmission signal.

Flow measurement technology using cross-correlation is a measure of the moving speed of turbulent noise signals caused by fluid flow at two points in a pipe, and correlates the time that fluid is transferred from upstream to downstream. It is a technique to measure using. The flow rate can be measured when the diameter of the tube is known from the velocity measurement of the fluid.

Ultrasonic flowmeters using such cross-correlation are less affected by the type and pressure of the fluid to be measured, unlike flowmeters using mechanical or other ultrasonic methods (Transit, Doppler). And with excellent reproducibility, it is possible to measure flow rate in real time with precise value. In addition, unlike the wet type that installs the ultrasonic sensor inside the pipe, it is possible to attach the outside to the clamp on type so that the flow rate can be measured without disassembling the pipe in the field. good.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the present invention.

3 is a control circuit block diagram schematically showing the configuration of the ultrasonic flow rate measuring apparatus using cross-correlation. As described above, the cross-correlation method uses a phenomenon in which an ultrasonic signal is phase-modulated by a turbulent noise signal generated when a fluid in a pipe flows. In other words, if the ultrasonic sensor is installed at a certain distance from two points outside the pipe, the signal received from each sensor will have a similar phase modulation characteristic with only time delay. It is assumed here that the turbulent noise in the fluid does not change while the fluid passes between the upstream and downstream sensors. Thus, cross-correlation of these two signals allows us to measure the time it takes to pass between the two sensors and calculate the flow rate.

To this end, as shown in Figure 3, the ultrasonic flow rate measuring device is installed at a predetermined interval outside the pipe 40, respectively. These ultrasonic flow measurement devices are respectively a signal generator 10, 10 ', an amplifier 20, 20', a sensor A 30, a sensor B 30 ', a pipe 40, a sensor C 50, a sensor. D (50 '), amplifiers (60, 60'), demodulators (70, 70 '), and cross-correlator (80).

In this manner, the signal generator 10, 10 'generates a signal of several MHz and transmits an ultrasonic signal from the transmission sensors 30, 30' through the amplifiers 20, 20 '. The signal passing through the fluid in the pipe 40 is received through the receiving sensors 50 and 50 ', and then amplified to a size suitable for signal processing through the amplifiers 60 and 60'. Thereafter, the ultrasonic signals modulated by the flow of the fluid are demodulated through the demodulators 70 and 70 '. The demodulated signal measures the time delay between the two sensors via the cross-correlator 80 to measure the flow rate and the flow rate. In addition, it is a clamp on type method that attaches the ultrasonic sensors 30, 30 ', 50, 50' to the outside of the pipe, and there is no need to touch the pipe when the sensor is installed. The advantage is that accurate and reliable flow rates can be measured without this. In general, the cross-correlation method enables real-time flow measurement with an error of within ± 1% without being calibrated by the flow standard system regardless of the fluid type.

On the other hand, the cross-correlation ultrasonic flowmeter of the present invention by installing an ultrasonic sensor in the pipe to pass the ultrasonic signal of 1MHz or more through the pipe flowing the fluid to process the received signal to measure the flow rate. The emitted ultrasonic signal is phase modulated (PM) by turbulence generated in the flow of the fluid as it passes through the pipe. Since the phase modulated signal is proportional to the flow velocity, the phase velocity of the transmitted / received signal is obtained to calculate the flow velocity. It is very important to accurately detect the amount of modulation. Here, assuming that the flow of the fluid is constant and there are no bubbles or large floats (foreign matters, etc.) in the fluid, phase demodulation through phase comparison will be able to detect the correct flow rate.

However, in actual fluids, large floats such as bubbles or foreign matters are often present. When ultrasonic waves meet bubbles or floats, ultrasonic signals are blocked or scattered. At this time, the amount of phase change of the ultrasonic signal received is very large compared to the phase modulation generally occurs due to turbulent noise. Therefore, the output of the phase detection circuit generates a large error in the presence of bubbles or floats, which may not only reduce the accuracy of the flow measurement system but also affect stability.

Therefore, in order to measure accurately and stably even if bubbles or floats exist, a detection method that can minimize the phase error caused by bubbles or floats is required. This can be solved through the following process of FIG. 4.

4 is a diagram illustrating a concept of a phase demodulation detection method using a double PLL according to the present invention. 4, the ultrasonic flowmeter using the cross-correlation of the present invention, the phase comparators (PD-1, 320) for performing the phase comparison of the received signal 300 and the transmission signal 310, and the low-pass phase comparison output The low pass filter 330 to pass through, the integrator 350 to integrate the output signals of the phase comparators PD-1 and 320, and the rapid and continuous phase change and the slowly changing temperature change caused by bubbles or suspended matter Compensation circuit 400 for compensating.

The compensation circuit 400 includes phase comparators PD-2 and 430 for performing phase comparison with the output signal and the transmission signal 310 of the compensation circuit 400 itself, and a low pass filter for low-passing the phase comparison output. 420 and a voltage control for generating and outputting a signal following the transmission signal 310 by receiving a signal obtained by adding the signal output from the integrator 350 and the output value of the low pass filter 420. It consists of a Voltage Controlled Oscillator (VCO).

The ultrasonic flowmeter using the cross-correlation of the present invention configured as described above is made as follows.

In the normal case in which no bubbles or floats exist, the output signal of the final demodulated signal 340 is obtained through the low pass filter 330 after passing the transmission signal 310 and the reception signal 300 through the phase comparator 320. At this time, the output of the VCO 410 is the same signal is output without the same phase noise as the transmission signal. However, the transmission signal and the phase may be different.

The PD-1 320 detects a phase difference between the received signal and the signal generated by the VCO 410. On the other hand, if a large change in phase occurs due to the presence of air bubbles or suspended solids, the VCO 410 is controlled by adding the average of the PD-1 320 output and the PD-2 430 output by phase comparison. Create a signal that follows the signal. At this time, the generated signal is the same as the input transmission signal 310, but the phase is different, the phase is the same as the phase amount changed by the bubble or suspended matter. Therefore, the output of the phase comparator PD-1 320 that detects the phase of the received signal 300 cancels the phase change caused by bubbles or suspended matter, and only the phase change caused by the turbulence generated by the flow of fluid is used. It is detected at 1 (320).

This operation is similarly performed with respect to the phase change (Drift) due to the temperature change, so that only the phase due to the turbulence is stably detected by the phase comparator PD-1 (320).

Therefore, it is possible to stably operate continuously by solving the problem of stopping the operation by the reset of the existing circuit and the problem of reliability and accuracy, and also eliminating the phase change caused by temperature.

As such, the difference between the conventional single PLL phase detection circuit and the ultrasonic flowmeter using the cross-correlation of the present invention can be summarized as follows.

The integrator 350 used in the present invention has a very large time constant so as not to respond to rapid changes due to turbulence. In a general PLL circuit, when an integrator with a very large time constant is inserted into a feedback circuit, the VCO output frequency is corrected at the integrator. If it changes at a speed less than a few, it cannot respond, but this appears as phase noise, which makes phase detection by turbulence to be detected in the present invention impossible. If the time constant of the integrator is increased to suppress phase noise, even the phase change caused by the turbulence is followed by the PLL circuit to cancel.

However, in the present invention, the output of the integrator 350 is added to the independent PLL including the PD-2 430, the LPF 420, and the VCO 410, so that the output of the VCO 410 has a constant phase difference without phase noise. Only the presence of a signal is made, and the phase comparator PD-1 320 detects the phase of the input signal 300 based on this, and thus, the fine phase difference is also detected by the phase comparator PD-1 320.

As described above, the ultrasonic flowmeter using the cross-correlation according to the present invention, unlike conventional flowmeters using mechanical or other ultrasonic methods (Transit, Doppler) is less affected by the type, pressure, etc. of the fluid to be measured. In addition, the reproducibility is excellent and real-time flow rate measurement is possible with precise values. And unlike the built-in type (Wet Type) that installs the ultrasonic sensor inside the pipe, it is possible to attach the outside (Clamp On Type) to attach the outside, so it is possible to measure the flow rate without disassembling the pipe in the field so that mobility and applicability very good. The present invention is not limited to the above-described embodiments, and it will be apparent that many modifications are possible by those skilled in the art within the technical spirit of the present invention.

Claims (4)

A signal generator for generating an ultrasonic signal having a predetermined frequency; A first amplifier for amplifying the ultrasonic signal; A transmission sensor for transmitting a transmission signal corresponding to the amplified ultrasonic signal; A reception sensor configured to receive a reception signal generated after the transmission signal passes through the fluid in the pipe; A second amplifier for amplifying the received signal to a predetermined magnitude; And an demodulator for demodulating the amplified signal. The ultrasonic flowmeters are each disposed at a predetermined interval outside the pipe, Measuring the time delay by receiving the signal output from the demodulator of each ultrasonic flow meter to measure the flow rate and flow rate A first phase comparator configured to perform phase comparison between the received signal and the transmitted signal; A first low pass filter for low passing the phase comparison output; An integrator for integrating the output signal of the phase comparator; And An ultrasonic flowmeter using cross-correlation further comprising a cross-correlation circuit configured to compensate for rapid and continuous phase changes and slowly changing temperature changes caused by bubbles or suspended matter. delete The method of claim 1, wherein the compensation circuit, A second phase comparator for performing phase comparison between an output signal of the compensation circuit itself and a transmission signal; A second low pass filter for low passing the phase comparison output; And And a voltage controlled oscillator configured to receive a signal obtained by adding the signal output from the integrator and the output value of the second low pass filter to generate and output a signal following the transmission signal. . A first phase comparator for performing phase comparison between the received signal and the transmitted signal; A first low pass filter for low passing the phase comparison output; An integrator for integrating the output signal of the phase comparator; A second phase comparator for performing phase comparison between an output signal of the compensation circuit itself and a transmission signal; A second low pass filter for low passing the phase comparison output; And And a voltage controlled oscillator configured to receive a signal obtained by adding the signal output from the integrator and the output value of the second low pass filter to generate and output a signal following the transmission signal. .

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