Design of Ultrasonic Flow Meter with Time Difference Method

Abstract: The design information of the time difference ultrasonic flowmeter is provided by the excellent flowmeter and flowmeter manufacturers. In recent years, ultrasonic flowmeters have been widely used due to their non-contact and unaffected by the physical and chemical properties of fluids. For the time difference ultrasonic flowmeter, accurate measurement of ultrasonic propagation time is the key to improve the measurement accuracy, and at present. More flowmeter manufacturers select models and price quotations. You are welcome to inquire. The following is the design article details of the time difference ultrasonic flowmeter. In recent years, ultrasonic flowmeters have been widely used due to their non-contact and unaffected by the physical and chemical properties of fluids. For the time difference ultrasonic flowmeter, accurate measurement of the ultrasonic propagation time is the key to improving the measurement accuracy. On the basis that the current time measurement chip accuracy has reached the ps level, the key to improving the time measurement accuracy is to accurately judge the ultrasonic wave. the moment the shape arrives. The waveform of the ultrasonic signal is particularly critical for accurately judging the arrival time of the ultrasonic wave. Under this premise, this paper designs a time difference ultrasonic flowmeter, and introduces the design idea of ​​its hardware implementation circuit. 1 Measurement principle The time difference method is a method to find the flow velocity according to the relationship between the propagation time difference between the forward and reverse flow of ultrasonic waves in the fluid and the flow velocity of the measured fluid. The essence is that the propagation speed of ultrasonic waves in the fluid is affected by the flow of the fluid, and the measured time will be different in the forward flow and the reverse flow. fluid flow. The schematic diagram is shown in Figure 1: the installation angle of the countercurrent transducer and the downstream transducer relative to the axis of the pipeline isθ, the pipe diameter is D, the linear distance between the two transducers is L, and the fluid velocity is v. Fig. 1 The working principle of the time difference ultrasonic flowmeter When measuring, the countercurrent transducer and the downstream transducer are alternately used as the receiving and transmitting ultrasonic ends. The actual propagation velocity c0 of the ultrasonic wave is the sound velocity c and the velocity component vcos of the fluid in the direction of the channelθSum: c0=c±vcosθ (1) At this time, the propagation time of forward and reverse flow is: (2) From the above formula, the time difference between forward and reverse flow can be obtained as: (3) Since the maximum measurable flow velocity of the general ultrasonic flowmeter is about 10m/s, and the sound propagation speed in the fluid It is about 1500m/s, which is much larger than the fluid velocity, so the time difference between the forward and reverse flow can be approximated as: (4) Correspondingly, the fluid flow velocity and flow formula can be expressed as follows: (5) (6) It can be seen from the formula (5) that the ultrasonic wave is forward and reverse flow The measurement accuracy of the propagation time directly affects the measurement accuracy and measurement range of the flow velocity. 2 System Hardware Design The system hardware structure diagram is shown in Figure 2. Figure 2 System hardware structure diagram The system hardware mainly includes power supply module, signal transceiver module, signal processing module, timing chip measurement module, MSP430F1612 microprocessor module and system data acquisition module. The circuit design of several important modules is briefly introduced below. 2.1 The circuit design of the signal processing module As shown in the hardware structure diagram of the system in Figure 2, the signal processing module includes five links: first-stage amplification, second-stage controllable gain amplification, band-pass filtering, half-wave rectification and threshold comparison. Among them, the first-stage amplification and band-pass filtering are built with the operational amplifier OPA2725. The half-wave rectifier circuit is composed of diodes and resistors. The second-stage controllable gain amplifier is realized by the voltage-controlled gain amplifier VCA822. These four link circuits are compared It is simple, so the following mainly introduces the specific structure of the threshold comparison circuit. The threshold comparison circuit is shown in Figure 3, among which the comparator selects AD8611 chip of Ana-logDevices Company, and its propagation delay is 4ns. When the amplitude of the input signal is higher than the reference level, the output terminal QA outputs a high level, and when the amplitude of the input signal is lower than the reference level, the output terminal QA outputs a low level. Therefore, by connecting the ultrasonic signal to be processed to the signal input port and adding a reference level, a series of compared square wave signals can be output. The rising edge and falling edge time of the square wave signal is the arrival time of the ultrasonic signal. The reference level required by the comparator is provided by the threshold circuit. The threshold circuit is formed by a combination of an instrumentation amplifier and an operational amplifier. The instrumentation amplifier is a high-precision instrumentation amplifier IN114 with a gain of . Figure 3. Threshold comparison circuit 2.2 Timing chip measurement module circuit design The square wave signal obtained after passing through the signal processing module includes the time signal that the system needs to record, and these time points are accurately recorded and provided to the microprocessor for further analysis, judgment and analysis. Calculations are a critical part of system flow measurement. Therefore, a timing chip with high measurement accuracy and fast response speed must be selected. In this paper, the high-precision time measurement chip TDC-GP2 is selected to realize timing. TDC-GP2 has functions such as high-speed pulse generator, stop signal enable and clock control. These functional modules make it meet various requirements of ultrasonic flowmeter measurement. Since TDC-GP2 is needed here to measure the edge moment of the square wave signal, including rising and falling edges, two time chips TDC-GP2 are needed to measure the time. One TDC-GP2 is set to trigger on the rising edge, and the other is set For falling edge triggering, measure the first three rising edge moments and the first three falling edge moments of the square wave signal respectively. Its application circuit design is shown in Figure 4. Figure 4 Timing chip measurement circuit The above is the whole content of this article. You are welcome to inquire about the flowmeter selection and quotation of our factory. 'Design of Time Difference Ultrasonic Flow Meter'

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