The design of the method of time difference ultrasonic flowmeter scale

Abstract: the method of time difference ultrasonic flowmeter scale design information produced by excellent flow meter, flow meter manufacturer to offer you the quotation. In recent years, due to its non-contact ultrasonic flowmeter, unaffected by fluid physical and chemical properties of features are widely used. For time difference ultrasonic flowmeter, accurate measurement of ultrasonic transmission time is the key to improve the accuracy of measurement, and in the current. More flow meter manufacturers choose model price quote you are welcome to inquire, here is a method of time difference ultrasonic flowmeter scale details the design of the article. In recent years, due to its non-contact ultrasonic flowmeter, unaffected by fluid physical and chemical properties of features are widely used. For time difference ultrasonic flowmeter, accurate measurement of ultrasonic transmission time is the key to improve the accuracy of measurement, and in the current when the chip measurement precision has reached the ps level, on the basis of to improve the measurement precision of the key lies in the accurate judgment of ultrasonic wave arrival times. The waveform of ultrasonic signal to accurately judge the time of arrival of the ultrasonic is particularly critical. In this condition this paper designed a method of time difference ultrasonic flowmeter, and introduces its hardware realization circuit design. 1 principle of measuring the time difference method is based on the ultrasonic transmission time of downstream and upstream in the fluid and the relationship between the flow velocity of body to find the method of flow velocity. Its essence is the ultrasonic velocity in fluid under the influence of fluid flow, measured in the downstream and upstream of time will be different, so the time difference can be calculated according to the measured fluid velocity and fluid flow can be calculated, too. Its principle diagram is shown in figure 1: current transducer and downstream Angle relative to the pipe axis installation for & theta; , the pipe diameter D, two transducer linear distance L, fluid velocity v. Figure 1 time difference method, the working principle of the ultrasonic flowmeter measurement, flow transducer and the downstream transducer emit ultrasonic alternately as receiving and end. C and ultrasonic transmission speed c0 is the actual sound velocity component of the fluid in the channel direction vcosθ And: c0 = c± vcosθ （ 1) At this point, the suitable current travel time as follows: ( 2) By type available on reflux time difference is: ( 3) Due to general zui ultrasonic flowmeter can flow speed at 10 m/s, and the sound velocity in the fluid is about 1500 m/s, is far greater than the fluid velocity, so can get suitable reflux time difference approximation is: ( 4) Accordingly, the fluid flow rate formula can be expressed as follows: ( 5) （ 6) By type ( 5) Know the measure precision of the ultrasonic transmission time along the upstream directly affect the velocity measurement accuracy and measuring range. 2 the system hardware design system hardware structure diagram as shown in figure 2. Figure 2 system the system hardware mainly includes the hardware structure of the power supply module, signal transceiver module, a signal processing module, timing chip measurement module, MSP430F1612 microprocessor module and system data acquisition module. The following simple introduce several important module circuit design. 2. 1 signal processing module circuit design as shown in figure 2 the system hardware structure, the signal processing module includes primary amplifier, secondary controllable gain amplifier, bandpass filter, half-wave rectifier and threshold is five links. Including amplifier and bandpass filter are chosen operational amplifier OPA2725 to build, half-wave rectifier circuit is composed of diodes and resistors, secondary controllable gain amplifier by the voltage-controlled gain amplifier VCA822, these four link circuit is simple, so the article mainly introduces the specific structure of the threshold value comparison circuit. Threshold comparison circuit as shown in figure 3, choose the Ana - comparator LogDevices AD8611 chip, a company's propagation delay to 4 ns. When the input signal amplitude is higher than the reference electricity at ordinary times, output QA, output level electricity at ordinary times, when the input signal amplitude is lower than the reference output QA output low level. Therefore, for the ultrasonic signal to be processed received signal input port, plus a reference level, then it can output the square wave signal after a series of comparison. The square wave signal along the rising or falling time is the arrival time of ultrasonic signal. Needed for the comparator reference level provided by the threshold circuit. Threshold circuit formed by instrumentation amplifier and op-amp combination, instrumentation amplifier for high precision instrumentation amplifier IN114, for its gain, the op-amp for high-speed op-amp OPA2604, op-amp will IN114 output voltage to follow the way of feedback to IN114 reference voltage. Figure 3 threshold comparison circuit 2. 2 clock chip measurement module circuit design of square wave signal is obtained by the signal processing module after signal contains the system needs to record time, accurately record the time point for the microprocessor do further analysis, judgment and calculation is the key part of the flow measurement system. So you must select a high measuring accuracy, fast response timing chip. This article selects the high precision time measuring TDC - chip GP2 to realize timing, TDC - GP2 with high-speed pulse generator, stop signal can make and clock control and the function module makes it can satisfy the requirement of the ultrasonic flowmeter to measure various aspects. Due to the TDC - is needed here GP2 time to measure the edge of the square wave signals, including the rising and falling, so you need two pieces of TDC - time chip GP2 to realize the measurement of time, a TDC - GP2 along the trigger is set to rise, another is set to drop along the trigger, the square wave signals were measured before three rise along the time and the first three fall along the time. The application circuit design as shown in figure 4. Figure 4 above timing measurement circuit chip is all there is in this article, you are welcome to inquire me factory flowmeter selection, quotation, etc.

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