CN210513276U - Ultrasonic liquid flow measuring system - Google Patents
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- CN210513276U CN210513276U CN201921874259.3U CN201921874259U CN210513276U CN 210513276 U CN210513276 U CN 210513276U CN 201921874259 U CN201921874259 U CN 201921874259U CN 210513276 U CN210513276 U CN 210513276U
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Abstract
The utility model provides an ultrasonic liquid flow measuring system; the device comprises a DSP signal processor, a clock circuit, a transmitting circuit, a receiving circuit, an energy converter, a power circuit, a temperature measuring circuit and a communication circuit; the utility model can effectively eliminate the influence of the change of the fluid temperature on the propagation speed of the ultrasonic wave; the method has the characteristic of non-wetting type, the forward and backward flow propagation time is obtained by adopting the ringing method, the flow of the fluid to be measured can be accurately measured, and the high-precision time difference data reflects that the system has higher measurement accuracy.
Description
Technical Field
The utility model relates to an ultrasonic wave liquid flow measurement system.
Background
With the development of industrial technology, the flow gradually becomes one of three subjects of process industrial measurement, and the other two are temperature and pressure respectively, so that the flow brings infinite convenience to daily life and work of people, the quality of life is improved, and the economic benefit is also improved. At present, flow measurement technology is frequently used in industrial and agricultural water and water resource management, management and transportation of mineral resources such as petroleum and natural gas, and production of chemical raw materials. China is a large population, but because of the characteristics of land, earth, and the like, and water and mineral resources are poor, the high effective use and saving of energy, environmental protection and production efficiency are more and more important in daily life and work. Furthermore, today, both gas and liquid measurement problems are closely related to industrial production, and flow metering is also becoming an increasingly important part of life and production.
In modern industrial production, automation gradually becomes a trend of rapid development of industry and agriculture, however, a measuring instrument and a measuring technology are preconditions for completing industrial automation. In modern industrial fields, meters for measuring fluid flow are generally called flow meters or flowmeters, and play the same role as physical quantity measuring instruments such as temperature, pressure and material level, and play an important role in industrial flow measurement. The flowmeter can effectively measure the fluid flow, and the flow can be regulated and controlled by utilizing the fluid flow, thereby realizing a safe and efficient industrial production environment. The improvement of the quality of life of people pays more and more attention to the improvement of the product quality and the production efficiency, the importance of the flow measurement on the flow industry is gradually highlighted, and meanwhile, the accuracy of the flow measurement is more and more emphasized as the industrial production is gradually scaled.
In recent years, electronic information and microcomputer technology have gradually penetrated the scope of instrumentation, which, on the one hand, has resulted in significant improvements in the measurement function and performance of the flow meters, and, on the other hand, in substantial improvements in the accuracy and reliability of the flow meters. The flow measurement technology is used as a prospective technology for industrial automation development, and the improvement of the performance of the flow meter can bring a good development space for the market, so that the flow measurement technology is very good in development potential in the field of industrial production.
The flowmeter is used as a measuring instrument, which is a key technology for realizing industrial automation, and the improvement of the performance of the flowmeter not only creates good market space, but also promotes the development of other industrial fields. In this context, the research significance of high-performance flowmeters is particularly important.
SUMMERY OF THE UTILITY MODEL
In order to solve the technical problem, the utility model provides an ultrasonic wave liquid flow measurement system.
The utility model discloses a following technical scheme can realize.
The utility model provides an ultrasonic liquid flow measuring system; the device comprises a DSP signal processor, a clock circuit, a transmitting circuit, a receiving circuit, an energy converter, a power circuit, a temperature measuring circuit and a communication circuit;
the clock circuit, the power supply circuit, the temperature measuring circuit and the receiving circuit are respectively connected to the input end of the DSP signal processor, and the transmitting circuit and the transducer are respectively connected to the output end of the DSP signal processor;
the transducer comprises a transducer A and a transducer B, and the transducer A and the transducer B are connected with the DSP signal processor and the receiving circuit through a selection channel.
The DSP signal processor outputs PWM signals by adopting a TMS320F2812 processor of TI company.
The transmitting circuit generates a high-frequency oscillation signal through the multi-stage coupling coil.
The transducer receives the high frequency oscillation signal generated by the transmitting circuit and converts it into ultrasonic pulses.
The receiving circuit receives the ultrasonic pulse, filters and amplifies the ultrasonic pulse, performs zero-crossing comparison on the ultrasonic pulse and outputs the ultrasonic pulse to the DSP signal processor.
The temperature measuring circuit is a four-wire PT100 temperature measuring circuit.
The power supply circuit adopts a TPS767D301 voltage stabilizer to input stable 3.3V voltage for an I/O port and input 1.5-5.5V adjustable voltage for a DSP signal processor system.
The clock circuit forms a system clock through an oscillator and a phase-locked loop PLL.
And the communication circuit adopts an RS-485 interface.
The selection channel is a relay, and the relay outputs high and low levels through an I/O port of the DSP processor to control the on-off of the relay to realize the switching of the channel.
The beneficial effects of the utility model reside in that: the influence of the change of the fluid temperature on the propagation speed of the ultrasonic wave can be effectively eliminated; the method has the characteristic of non-wetting type, the forward and backward flow propagation time is obtained by adopting the ringing method, the flow of the fluid to be measured can be accurately measured, and the high-precision time difference data reflects that the system has higher measurement accuracy.
Drawings
Fig. 1 is a schematic structural diagram of the present invention;
fig. 2 is a schematic diagram of a transmission driving circuit of the present invention;
fig. 3 is a schematic diagram of a receiving circuit of the present invention;
FIG. 4 is a schematic diagram of the DSP control circuit of the present invention;
FIG. 5 is a schematic diagram of the clock circuit of the present invention;
fig. 6 is a schematic diagram of the temperature detection circuit of the present invention;
fig. 7 is a schematic diagram of the signal direction control circuit of the present invention;
FIG. 8 is a schematic diagram of the channel selection circuit of the present invention;
fig. 9 is a schematic diagram of a communication circuit according to the present invention.
Detailed Description
The technical solution of the present invention is further described below, but the scope of the claimed invention is not limited to the described.
An ultrasonic liquid flow measurement system; the device comprises a DSP signal processor, a clock circuit, a transmitting circuit, a receiving circuit, an energy converter, a power circuit, a temperature measuring circuit and a communication circuit;
the clock circuit, the power supply circuit, the temperature measuring circuit and the receiving circuit are respectively connected to the input end of the DSP signal processor, and the transmitting circuit and the transducer are respectively connected to the output end of the DSP signal processor;
the invention adopts a time difference method ultrasonic wave based on a ring sound method to detect the fluid quality, and a design system mainly comprises two parts of ring sound time difference signal acquisition and signal processing and communication between a DSP and an upper computer. The ring tone time difference signal acquisition part mainly takes a DSP as a core to complete the measurement of the transmitting and receiving signals of a transmitting circuit and a receiving circuit and the forward and backward propagation time of ultrasonic waves, and the ring tone time difference signal acquisition part mainly comprises the transmitting circuit, the receiving circuit, a channel selection circuit and the like; the signal processing is mainly completed by the DSP, and finally, the processed collected data is transmitted to the upper computer through the 485 communication interface for further analysis and processing. The structure of the ultrasonic flow measurement system is shown in fig. 1.
The transducer comprises a transducer A and a transducer B, and the transducer A and the transducer B are connected with the DSP signal processor and the receiving circuit through a selection channel.
The control and processing core part of the invention adopts TMS320F2812 processor of TMS320DSP series, which is provided by TI company, the processor has high main frequency, which can make the system run at high speed, and the processor has abundant I/O ports, which is convenient for the user to expand and use the peripheral circuit.
The transmitting circuit generates a high-frequency oscillation signal through the multi-stage coupling coil.
The transmission driving circuit is shown in the schematic diagram of FIG. 2, and the 200kHz PWM signal generated by the DSP is directly transmitted to the triode Q1Base of (2) driving a switching transistor Q1On and off. Switch triode Q1On and off, directly controlling the boosting middle period T1The primary coil is turned on and off to generate a 200kHz coupling signal, and the coupling signal is coupled to the secondary coil, so that the secondary coil generates a 200kHz high-voltage oscillation signal to drive an ultrasonic transducer (referred to as a probe herein and the same applies hereinafter) P1 to send an ultrasonic pulse.
The transducer receives the high frequency oscillation signal generated by the transmitting circuit and converts it into ultrasonic pulses.
The receiving circuit receives the ultrasonic pulse, filters and amplifies the ultrasonic pulse, performs zero-crossing comparison on the ultrasonic pulse and outputs the ultrasonic pulse to the DSP signal processor.
The transducer is driven by the transmitting driving circuit to emit ultrasonic pulse signals, the signals are transmitted through a fluid medium to reach a receiving end of the transducer to be received, in the process, due to the fact that the fluid contains a lot of impurities and bubbles, the signal quality can be affected to be greatly attenuated, and the receiving end of the transducer is quite unfavorable for receiving the signals. In order to enable the receiving transducer to receive high-precision ultrasonic signals, it is necessary to process the signals using a receiving circuit so that the receiving transducer receives a precise amplified signal. The receiving circuit in the design mainly comprises a preamplification circuit, a band-pass filter circuit and a zero-crossing detection circuit, and a schematic diagram of the receiving circuit is shown in figure 3. Considering that the signal received by the receiving transducer is very small, and may be only about a few mV, the design adopts the pre-amplifier circuit to amplify the received signal, and the signal processed by the amplifier circuit is output to the next stage for filtering.
Because the receiving circuit only needs to detect the first edge signal of the receiving signal of the transducer, the design of the amplifying circuit has no high requirement on the amplifying quality of the signal, and only needs to amplify the receiving signal and then transmit the signal to the next stage processing circuit, so that a common emitter amplifying circuit is adopted as a pre-amplifying circuit. As shown in FIG. 3, the signal received by the transducer is filtered by the capacitor c through the DC signal, and then passes through the transistor Q3The amplifier is amplified and then passes through a capacitor C5And filtering the direct current signal again, and finally sending the direct current signal to a next-stage processing circuit for band-pass filtering.
Since the frequency of the signal received by the transducer is about 40kHz, the center frequency of the band-pass filter is preferably set to about 40kHz, so that the signal components near the center frequency can be amplified to the maximum extent, and the signals outside the center frequency can be attenuated greatly. The design selects an active second-order band-pass filter, the prototype of the filter is shown in figure 3, R1And C1Forming a low-pass network allowing low-frequency signals to pass, R2And C2Forming a high-pass network for allowing high-frequency signals to pass through, connecting the high-pass network and the high-frequency signals in series to form a passive band-pass filter circuit, and connecting a voltage discharge to the tail end of the band-pass filter circuitThe amplifier is isolated with the load in the band-pass filter shop for the three has constituteed active second order band-pass filter circuit, and voltage amplifier can realize enlargiing to the signal of filtering out simultaneously. Regulating R1、C1And R2、C2The value of the parameter(s) may adjust the center frequency of the band pass filter circuit.
From the Laplace transform, the S-domain equation set for the circuits of FIGS. 3-7 can be derived, where matching of capacitances and simplification of the equations are facilitated, let C be1＝C2Then, there is:
the circuit transfer function can be solved from the above equation set as:
the center frequency is given by the formula (3.2):
considering that the center frequency of the bandpass filter is about 40kHz, the parameters R1-2 k Ω, R2-350 Ω, R3-240 k Ω, and C are taken1＝C2The frequency response curves of the circuit are shown in fig. 3-8, and the filtering results are shown in fig. 3-9, 470 pF.
The key point of the fluid quality measurement in the invention is to measure the forward and backward flow time of sound wave in the fluid, so that accurately capturing the ultrasonic receiving signal is a crucial step for improving the accuracy of the system. It can be known from the design of the transmitting circuit that the frequency of the transmitted ultrasonic signal is relatively stable, and therefore the shape of the signal waveform is also relatively stable, but the waveform of the received signal is deformed to some extent due to the propagation of the ultrasonic wave and the medium factor, and this distorted signal cannot be detected by the threshold setting, that is, a fixed time that is not affected by the waveform shape change needs to be found to receive the signal. Therefore, a zero-crossing comparison circuit is adopted to check the arrival time of the received signal, the threshold voltage is set through the resistance value in the adjusting circuit, and the arrival point of the ultrasonic wave received signal is checked.
The schematic diagram of the zero-crossing detection circuit is shown in fig. 3, and an envelope signal processed by the two-stage band-pass filter circuit is processed by the capacitor C3Isolating DC component, the AC signal continues to pass through the capacitor C8And filtering to remove high-frequency components in the signals, wherein low-frequency alternating current components in the signals continuously pass through each resistor and each triode. Using a resistor R in the circuit7And a resistance R12The voltage division principle of the zero-crossing trigger is used for adjusting the threshold voltage of the zero-crossing trigger. When the voltage at the point A is more than 0.7V, the triode Q2When the OUTPUT is turned on, the OUTPUT jumps from a high level to a low level, and then the jump signal is transmitted to the DSP, and the DSP performs an interrupt process.
The DSP timing interrupt is specifically realized as follows: the signal sent by the transmitting transducer is a periodic signal, the type of the signal is similar to a sine wave, and the sine wave signal is output as a square wave signal after passing through a zero-crossing comparison circuit. When the DSP detects the rising edge of the square wave signal, it triggers a DSP interrupt response. And after the interruption response is started, the DSP timer starts to count time, when the rising edge is detected again, the interruption response stops counting time, and then the interruption response program is closed. Thus the time from transmitting to receiving the transducer can be directly obtained. If the time of one period is too short, the counting number can be set in the DSP, and the timing is stopped when the specified period number is reached.
According to the invention, a four-wire system Pt100 temperature measurement method is adopted, and the balance bridge circuit is designed, so that errors caused by a resistance outgoing line to a flow measurement result can be eliminated, and the measurement accuracy of the system is greatly improved.
The four-wire temperature measuring circuit is designed as shown in FIG. 6, and uses a constant current source I as a driving power supply, r1、 r2、r3And r4Is a sensor resistor, and the four resistors are substantially equal in value. Since the power supply I is a constant power supply, and r1、r4The resistance remains unchanged, so that the platinum resistor RtThe pressure difference between the two ends is kept unchanged; this is achieved byIn addition, since AIN1 and AIN2 are high impedance input terminals, r is a high impedance input terminal2And r3The shunt to the branch can be basically ignored, so that the platinum resistor R can be obtainedtThe voltage difference between the two ends is I (R)t+ Δ R), it can be seen that this design method can completely eliminate the lead resistance R2And r3The resulting error, so the temperature measurement circuit in this design adopts a four-wire system circuit.
Because the TMS320F2812DSP digital processor has the characteristic of low power consumption, and the DSP core and the I/O port are independent of each other and supply power, specifically, if the operating voltage of the core chip is 1.8V and the operating voltage of the I/O port is 3.3V, a power supply of 1.8V needs to be increased on one hand and a power supply of 3.3V needs to be provided on the other hand when the power supply circuit is designed. In addition, considering the safe use of the DSP controller, when supplying power, we need to supply power to the DSP core first and then to supply power to the I/O port, so that the design of the power supply circuit becomes more complex. Based on the reasons, a TPS767D301 voltage stabilizer is adopted in the design, the voltage stabilizer is a low-dropout voltage regulator specially designed by TI company aiming at a TMS320F2812DSP controller chip and a special power supply system thereof, and the regulator has two-way output function and very stable working characteristics. The voltage stabilizer is characterized in that: when a 5V stabilized voltage power supply is provided, two voltage branches can be generated in the circuit, one voltage branch outputs a stabilized voltage of 3.3V, and the other voltage branch outputs an adjustable stabilized voltage in a range of 1.5-5.5V. The change of the adjustable voltage can be adjusted by changing the size of the external resistor, and the adjustable voltage can be expressed as
Wherein Vref＝1.18V，R1、R2For external variable resistance, consider the pass resistance R1、R2The current of (2) is not too large, and is usually around 40 μ A, so R1、R2The resistance value of (3) is not suitable to be too large or too small, and R2 is selected to be 30k omega in the design.
The power supply circuit adopts a TPS767D301 voltage stabilizer to input stable 3.3V voltage for an I/O port and input 1.5-5.5V adjustable voltage for a DSP signal processor system.
The X1 and X2 pins of the TMS320F2812DSP controller chip are externally connected with a crystal oscillator, the oscillation frequency of the externally connected crystal oscillator is 30MHz, then the phase-locked loop PLL and the oscillator simultaneously act on the oscillation circuit to form a system clock, and the system clock is sent to the CPU, namely the system clock is CLKIN. When the system is powered on, the system clock is controlled by the external crystal oscillator and the internal phase-locked loop PLL, so the system clock sysclk may be expressed as equation (3.4):
as can be seen from equation (3.4), when the PLL is disabled, the system clock is the clock of the external crystal oscillator, and the PLL disable, bypass, or enable is changed by the high/low level of the XPLLDIS pin, and the circuit of the pin will jump during the power-on reset of the system, which is represented by: if the XPLLDIS pin is high, PLL is enabled, otherwise, the PLL is disabled. As discussed in the previous analysis, if the XPLLDIS pin is high at the time of system power-on reset, the PLL is enabled, but if GPIODIV is 0, the PLL is in a bypass state, and the system clock sysclk is one-half of the external crystal oscillator frequency; if the XPLLDIS pin is high at power-on reset of the system, and GPIODIV is not 0 at this time, the PLL is enabled. Considering that GPIODIV has a 4-bit strobe signal, the theoretical value can reach 1111, but in practice the maximum value used is 10, and the maximum possible off-chip crystal oscillator frequency is 30MHz, so the clock frequency of the system is set to 150 MHz. In the design, the frequency of the off-chip crystal oscillator selects 30MHz, and when the system is reset and powered on, the XPLLDIS pin is set to be at high level, so that the PLL is in an enabling state, and therefore the system clock frequency of the circuit is 150 MHz.
And the communication circuit adopts an RS-485 interface.
The ultrasonic flowmeter outputs high and low levels through an I/O port of the DSP processor, and controls the switching of the channel selection switch, so that the transducer alternately transmits and receives ultrasonic signals. Considering that the control of the analog channel switch is simpler and no electric interference exists during operation, the relay is adopted in the design to carry out switching control on the analog signal. In addition, because the power used by the relay is equal to the power supply power in the circuit, the 24V power supply relay of the OMRON company is selected and used in the design, and two double-pole double-throw switches and two-way switch channels in the relay are used. In the flow measurement process, the reception and transmission of the ultrasonic signal are realized by controlling the on-off of the relay by outputting high and low levels through the I/O port of the DSP processor, and the specific implementation is as shown in fig. 7: when the output of the I/O port is low level, a certain voltage drop exists at two ends of the relay, the relay processes a normally open state, so that the contact points 1 and 4 are respectively gated on the pins 2 and 5, a received signal is transmitted by the switch line 1, and a sent signal is transmitted by the switch line 2. Fig. 8 is a schematic diagram of the switch channel selection transducer, when the output of the I/O port is low, the relay is in "normally open" state, so that switches 1 and 2 are both attracted, so that switch route No. 1 corresponds to transducer P1, switch route No. 2 corresponds to transducer P2, and from previous analysis, transducer P1 receives ultrasonic signals, and transducer P2 transmits ultrasonic signals.
RS-485 is a typical serial communication standard that defines the use of voltage, impedance in the circuit, but does not require the use of software protocols. The operating characteristics of RS-485 are briefly described as follows:
(1) + (2-6) V represents a logical "1", and- (2-6) V represents a logical "0";
(2) the transmission rate is at most 10Mb per second;
(3) the RS-485 interface has a combined packaging structure of a balanced driving type and a differential receiving type, and has strong capacity of resisting external signal interference;
(4) data transmission distances are long, typically up to three or four thousand feet;
(5) at least 128 transceivers can be connected to the bus by using a master-slave communication mode.
The RS-485 has the characteristics of high transmission rate, long data transmission distance, strong anti-interference capability, multi-site capability and the like, so that the RS-485 becomes a preferred protocol for serial communication in industrial control.
Considering that the RS-485 has the good characteristics and the bidirectional half-duplex lifting point, the RS-485-based communication design is used in the design, and the flow acquisition data is sent to the upper computer for data analysis, precision calibration and reliability verification. A circuit diagram of RS-485 communication hardware design is shown in fig. 9, and 3 6N137 optoelectronic isolation chips are used to achieve complete electrical isolation between input signals and output signals. The data transmit pin TX and the data receive pin RX of the TMS320F2812 controller chip and the control signal pin DE of the controller chip are connected to the D, R pin of SN65LBC184D through 3 chips 6N137 chips. The control signal pin DE of the DSP controller chip controls the transmission direction of data: when the DE pin is at a high level, the transmitter is activated, the receiver is deactivated, and the DSP can transmit data to the RS 485; when the DE pin is low, the receiver is enabled, the transmitter is disabled, and the DSP can receive the data byte from RS 485. The SN65LBC184D chip has two simple modes of operation, known as receive and transmit states, but at a certain time the chip can only be in one of the modes of operation.
Claims (10)
1. An ultrasonic liquid flow measurement system characterized by: the device comprises a DSP signal processor, a clock circuit, a transmitting circuit, a receiving circuit, an energy converter, a power circuit, a temperature measuring circuit and a communication circuit;
the clock circuit, the power supply circuit, the temperature measuring circuit and the receiving circuit are respectively connected to the input end of the DSP signal processor, and the transmitting circuit and the transducer are respectively connected to the output end of the DSP signal processor;
the transducer comprises a transducer A and a transducer B, and the transducer A and the transducer B are connected with the DSP signal processor and the receiving circuit through a selection channel.
2. An ultrasonic liquid flow measurement system according to claim 1, wherein: the DSP signal processor outputs PWM signals by adopting a TMS320F2812 processor of TI company.
3. An ultrasonic liquid flow measurement system according to claim 1, wherein: the transmitting circuit generates a high-frequency oscillation signal through the multi-stage coupling coil.
4. An ultrasonic liquid flow measurement system according to claim 1, wherein: the transducer receives the high frequency oscillation signal generated by the transmitting circuit and converts it into ultrasonic pulses.
5. An ultrasonic liquid flow measurement system according to claim 1, wherein: the receiving circuit receives the ultrasonic pulse, filters and amplifies the ultrasonic pulse, performs zero-crossing comparison on the ultrasonic pulse and outputs the ultrasonic pulse to the DSP signal processor.
6. An ultrasonic liquid flow measurement system according to claim 1, wherein: the temperature measuring circuit is a four-wire PT100 temperature measuring circuit.
7. An ultrasonic liquid flow measurement system according to claim 1, wherein: the power supply circuit adopts a TPS767D301 voltage stabilizer to input stable 3.3V voltage for an I/O port and input 1.5-5.5V adjustable voltage for a DSP signal processor system.
8. An ultrasonic liquid flow measurement system according to claim 1, wherein: the clock circuit forms a system clock through an oscillator and a phase-locked loop PLL.
9. An ultrasonic liquid flow measurement system according to claim 1, wherein: and the communication circuit adopts an RS-485 interface.
10. An ultrasonic liquid flow measurement system according to claim 1, wherein: the selection channel is a relay, and the relay outputs high and low levels through an I/O port of the DSP processor to control the on-off of the relay to realize the switching of the channel.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113504307A (en) * | 2021-09-10 | 2021-10-15 | 西南石油大学 | Multi-frequency core sound velocity measuring device |
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| CN113504307A (en) * | 2021-09-10 | 2021-10-15 | 西南石油大学 | Multi-frequency core sound velocity measuring device |
| CN113504307B (en) * | 2021-09-10 | 2021-12-21 | 西南石油大学 | Multi-frequency core sound velocity measuring device |
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Granted publication date: 20200512 |