CN103471668B - The circuit of ultrasonic time of flight is measured in a kind of excitation of boosted voltage step by step - Google Patents

Abstract

The invention relates to a circuit for step-by-step voltage excitation and measurement of ultrasonic transit time. The circuit excites the ultrasonic sensor with three voltage square waves of different intensities, and based on this, locates the characteristic point of the waveform peak and calculates the transit time of the waveform. The circuit composition of the present invention includes: the first multiplex (4) is used to select and construct the excitation signal among four alternative voltages, the excitation signal is sent to the sending sensor through the second multiplex (5), and the echo The signal is imported into the post-processing circuit; the waveform feature point determination circuit (6) determines the position of the first zero-crossing point after each peak value according to the corresponding relationship between the excitation and the echo peak value, and obtains the transit time difference. The present invention uses the corresponding relationship between excitation and received wave peaks to determine the characteristic points. In order to avoid misalignment of the received wave peaks due to external interference, step voltage excitation is used to increase the voltage difference of the peaks and increase the tolerance of anti-interference.

Description

A Step-by-Step Voltage Excitation Circuit for Measuring Ultrasonic Transit Time

technical field

The invention relates to a circuit for measuring the transit time of ultrasonic waves, in particular to a circuit for gradually increasing voltage excitation to measure the transit time of ultrasonic waves.

Background technique

The transit-time ultrasonic flowmeter relies on detecting the modulation effect of the flowing medium on the ultrasonic signal, and obtains the transit time of the sound wave on the fixed-length channel, thereby deriving the flow velocity data of the medium. At present, ultrasonic flowmeters usually judge the transit time by identifying specific mark points on the waveform, so the judgment of specific mark points on the waveform has become the key technology of time difference ultrasonic flowmeters.

In the prior art, when sending out ultrasonic signals, the main methods adopted include:

1. Use equal-amplitude square wave sequence excitation, and set the threshold value. When the signal replication exceeds the threshold value, the zero-crossing positions of several subsequent waveforms are used as the characteristic positions. This method has certain difficulties in the application of gas transit-time flowmeters. When the flow stability is poor, its amplitude may vary in different time periods, resulting in the threshold being unable to be located on the same waveform, resulting in characteristic points cross-period misjudgment. As shown in Figure 2 and Figure 4.

2. Use equal-amplitude square wave excitation with frequency coding, and detect the frequency change in the received waveform, and determine the waveform feature points through the corresponding relationship with the excitation code, as shown in Figure 3 and Figure 5. This method is often used on radar, but it has certain problems when used on ultrasonic sensors. The ultrasonic sensor can obtain the best output at its resonant frequency point, but it is inevitable to deviate from its resonant frequency point when using coded transmission. When the ultrasonic sensor works less than the resonant frequency, the current leads the voltage to reflect the capacitive, and the circuit shows the inductive when the work is greater than the resonant frequency. In actual work, it will be difficult for the received waveform to have an ideal coding effect, and there are obvious transition frequency components in the waveform, and the feature points are also very prone to cycle misjudgment.

Contents of the invention

The purpose of the present invention is to solve the problem of high error rate and complex algorithm in the determination of ultrasonic zero-crossing point in the prior art, and to design a step-by-step voltage excitation method, which uses the signal amplitude to mark the corresponding relationship of the waveform and determine the ultrasonic wave. over time. The technical solution adopted is: a step-by-step voltage excitation circuit for measuring the ultrasonic transit time, which is used for the primary instrument of the flowmeter composed of the flowmeter casing and two ultrasonic sensors, including: the first multi-channel selection A passer, which generates step-by-step voltage excitation signals; a second multiplexer, through which the excitation and reception signals are switched between the two ultrasonic sensors; waveform feature point determination The circuit inputs the excitation signal and the receiving signal, and uses the highest peak value of the waveform to determine the corresponding relationship between the two, and subtracts it at the first crossing zero moment after that as the transit time; the transit time filter output will The result input by the waveform feature point determination circuit is output after being smoothed and filtered.

Further, 1.8~3.3V is used to start the vibration of the ultrasonic sensor.

Further, 5V voltage is used for excitation.

Further, the working voltage is 20-24V.

Further, the signal to excite the ultrasonic sensor has a square wave sequence of four voltages.

The beneficial effect of the patent of the present invention is that the amplitude is used as the basis for judging the positioning point of the waveform, which avoids the problem of easy misjudgment of the zero-crossing point in other technologies. And by widening the gap between the maximum excitation voltage and other voltages, the tolerance of signal amplitude changes caused by flow is increased, and the stability of judging feature points is increased.

During the working process, this circuit constructs a square wave sequence with gradually increasing voltage amplitude, so as to determine the corresponding relationship between the excitation and the receiving waveform at the peak value. This working principle can effectively avoid the The corresponding error problem that may exist in finding the corresponding relationship between the equal-amplitude square wave sequence and the sine wave sequence.

Description of drawings

Fig. 1 is a schematic diagram of circuit composition structure of the present invention;

Fig. 2 is the schematic diagram that utilizes the square wave sequence of equal amplitude and fixed frequency to excite the sensor in the prior art;

Fig. 3 is the schematic diagram that utilizes the square wave sequence of equal-amplitude frequency coding to excite the sensor in the prior art;

FIG. 4 is a schematic diagram of determining waveform feature points using a single threshold method in the prior art;

5 is a schematic diagram of determining waveform feature points using frequency changes in waveforms in the prior art;

Fig. 6 is a schematic diagram of comparing waveforms of the step-by-step voltage excitation signal and the received signal.

The meanings of the reference signs in the figure are: 1-flow meter housing; 2, 3-ultrasonic sensor; 4-first multiplexer; 5-second multiplexer; 6-waveform feature point determination circuit ; 7 - Transit time filter outputter.

detailed description

The present invention will be further described below in conjunction with accompanying drawing.

The step-by-step step-up voltage excitation circuit for measuring ultrasonic transit time of the present invention constructs a three-stage square wave sequence with step-by-step increase in voltage amplitude, and at the same time widens the excitation voltage difference between stages as much as possible. In the received signal, there will also be a corresponding amplitude difference, so that this parameter can be used as a mark of the waveform corresponding to the excitation signal to realize the measurement of the transit time. In order to realize the above logical relationship, the circuit system is provided with: the first multi-way gate 4, which is used to construct a square wave sequence whose voltage amplitude increases step by step; the second multi-way gate 5, which separates the excitation voltage and the received signal between two Two ultrasonic sensors are switched to realize the downstream and reverse flow test; the waveform feature point determination circuit 6 needs to input the excitation signal and the receiving signal, and use the highest peak value of the waveform to determine the corresponding relationship between the two, and then on the first one after that. The time of crossing the zero point is subtracted as the transit time; the transit time filter outputter 7 smoothes and filters the result input by the waveform characteristic point determination circuit 6 to realize the output.

The circuit structure of the step-by-step voltage excitation measurement ultrasonic transit time of the present invention is shown in Figure 1, the flow meter housing 1 and the ultrasonic sensors 2, 3 constitute the primary meter of the flow meter; the circuit part of the present invention includes: a first multiple The gate 4 generates step-by-step voltage excitation signals; the excitation and reception signals are switched between the two ultrasonic sensors 2 and 3 through the second multiplexer 5, so as to achieve the purpose of downstream and countercurrent measurement; the waveform The feature point determination circuit 6 needs to input the excitation signal and the receiving signal, and use the highest peak value of the waveform to determine the corresponding relationship between the two, and subtract it as the transit time at the first crossing zero moment after that; The time filter output unit 7 smoothes and filters the result input by the waveform characteristic point determination circuit 6, and then outputs it. The signal waveforms of each key part are shown in Figure 6.

In the implementation, the alternative voltages are respectively designed as: 1.8~3.3V. This small voltage excitation is for the start-up of the ultrasonic sensor, and then 5V voltage is used for excitation. The final working voltage is 20~24V voltage to generate a peak voltage mark. The above voltages exist in conventional ultrasonic flowmeter circuits, and the difference between the peak voltage and other voltages is maximized to obtain a better peak marking effect. In Figure 6, we can clearly see the waveform correspondence between the excitation voltage and the received signal. After the peak value appears, cross the zero-crossing position on the first one after that, and calculate the transit time as the corresponding point of the signal. The subsequent receiving waveform is free oscillation of the sensor, no longer receiving.

The present invention uses step-by-step voltage excitation, and judges feature points according to the highest amplitude corresponding relationship between the received wave and the excitation waveform. The advantage of the present invention is to use very obvious amplitude changes to determine the corresponding point. At the same time, in order to avoid the signal amplitude changes caused by flow fluctuations, the maximum excitation voltage and other voltage values are separated by a large gap, and the flow causes signal amplitude changes. Tolerance, increase the stability of judging feature points.

Claims (5)

1. A circuit for step-by-step voltage excitation measurement of ultrasonic transit time, which is used for the flowmeter housing (1) and two ultrasonic sensors (2, 3) to form a primary instrument of the flowmeter, including: the first multi-channel A strobe (4), which generates a step-by-step voltage excitation signal, wherein the voltage excitation signal is a square wave sequence; a second multiplexer (5), implemented by the second multiplexer (5) Switching between the excitation and reception signals between the two ultrasonic sensors (2, 3); the waveform feature point determination circuit (6) inputs the excitation signal and the reception signal, and uses the highest peak value of the waveform to determine the corresponding relationship between the two , and subtract it as the transit time at the time of crossing the zero point on the first waveform thereafter; after the transit time filter outputter (7) smoothes and filters the input result of the waveform feature point determination circuit (6), it realizes output. 2. The step-by-step boost voltage excitation circuit for measuring ultrasonic transit time according to claim 1, characterized in that: 1.8-3.3V is used to make the ultrasonic sensor vibrate. 3. The step-by-step voltage excitation circuit for measuring ultrasonic transit time according to claim 1, characterized in that: 5V voltage excitation is used. 4. The step-by-step boost voltage excitation circuit for measuring ultrasonic transit time according to claim 1, characterized in that: the working voltage is 20-24V. 5. The step-by-step boost voltage excitation circuit for measuring ultrasonic transit time according to claim 1, characterized in that: the signal for exciting the ultrasonic sensor has a square wave sequence of four voltages.