Device and method for measuring average molecular weight of mixed gas

Abstract

The invention relates to a device and a method for measuring the average molecular weight of mixed gas, an ultrasonic transducer A and an ultrasonic transducer B are mounted on upstream and downstream pipe walls in the flowing direction of fluid in a pipeline, the ultrasonic transducer A and the ultrasonic transducer B are mounted opposite to the axis of the pipeline and form an included angle theta with the axis of the pipeline, and ultrasonic waves are transmitted according to a linear path. Calculating propagation time when the propagation direction of the ultrasonic waves is the same as the flow velocity of the measured medium and propagation time when the propagation direction of the ultrasonic waves is opposite to the flow velocity of the measured medium, thereby calculating the propagation speed of the ultrasonic waves in the measured medium and calculating the molecular weight; in the ultrasonic echo signal amplification module, a single-end signal is converted into a differential signal, compared with a common amplification mode of converting a single-end signal into a single-end signal, the anti-interference capability of the signal is enhanced, the flow and the molecular weight are measured by using an ultrasonic transducer, and the cost performance is high.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrasonic flow measurement equipment, and in particular to a device and method for measuring the average molecular weight of a mixed gas. Background Art

[0002] When using an ultrasonic flow meter to measure flow, the propagation speed of ultrasonic waves in the medium, that is, the speed of sound, can be measured.

[0003] Gas composition is a major parameter in energy measurement. Currently, gas composition measurement mainly uses chromatography. The chromatograph separates the gas by introducing it into different chromatographic columns, and then uses a detector to detect the concentration of each component. The whole process is a measurement cycle, which may take several minutes. Chromatography has many advantages, such as high separation efficiency, high detection sensitivity, good selectivity, etc., but the price of the chromatograph is expensive and the cost performance is low.

[0004] Ultrasonic measurement has many advantages, such as non-contact measurement, high precision, good stability, etc. It is precisely because of these advantages of ultrasonic measurement that ultrasonic flowmeters are currently being used in more and more flow measurement fields. However, conventional ultrasonic measurement only measures flow and cannot measure molecular weight. The signal during the measurement process is weak, easily disturbed, and has a limited propagation distance, which will cause inaccurate measurement data. Summary of the invention

[0005] The present invention provides a device and method for measuring the average molecular weight of a mixed gas. The method uses temperature, pressure, sound velocity and other signals measured by an ultrasonic flowmeter to indirectly calculate the molecular weight of a measured medium. The device has strong anti-interference ability, low cost and accurate measurement.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A device for measuring the average molecular weight of a mixed gas comprises a DC / DC boost module, a drive signal module, a channel switching control module, an ultrasonic transducer, an ultrasonic echo signal amplifying module, an ultrasonic echo signal filtering processing module and a microprocessor; the ultrasonic transducers are respectively installed on the upstream and downstream pipe walls of the pipeline fluid flow direction, and are installed relative to the pipeline axis, and the angle range between the installation and the pipeline axis is 30-60°; the voltage output pin of the DC / DC boost module is connected to the voltage input end of the drive signal module, the IO pin of the drive signal module is connected to the output pin of the microprocessor, the control output pin of the drive signal module is connected to the input pin of the channel switching control module, the IO pin of the channel switching control module is connected to two ultrasonic transducers, the output pin of the channel switching control module is connected to the input pin of the ultrasonic echo signal amplifying module, the output pin of the ultrasonic echo signal amplifying module is connected to the input pin of the ultrasonic echo signal filtering processing module, and the output pin of the ultrasonic echo signal filtering processing module is connected to the input pin of the microprocessor;

[0008] The input signal of the ultrasonic echo signal amplification module is a single-ended signal, and the output signal is a differential signal. The signal pin is connected to the ultrasonic echo signal filtering and processing module.

[0009] Furthermore, there are one or more channel switching control modules, and the corresponding number is matched according to the logarithm of the ultrasonic transducer.

[0010] Furthermore, the receiving end of the ultrasonic echo signal amplifying module is connected to the output end of the channel switching control module, and a TVS diode, a series inductor and a capacitor are connected to the ground on the connection circuit.

[0011] A method for measuring the average molecular weight of a mixed gas comprises the following steps:

[0012] S1. Ultrasonic transducers A and B are installed on the upstream and downstream walls of the pipeline fluid flow direction. Each transducer can be used to transmit ultrasonic signals and to receive ultrasonic signals.

[0013] S2, ultrasonic transducer A and ultrasonic transducer B are installed relative to the axis of the pipeline, forming an angle θ with the axis of the pipeline. The ultrasonic wave propagates along a straight path. The propagation distance of the ultrasonic wave is P. Then the propagation speed of the ultrasonic signal in the measured medium is:

[0014]

[0015] Where c is the speed of sound, i.e. the propagation speed of the ultrasonic signal in the measured medium;

[0016] t AB is the forward propagation time of ultrasonic wave;

[0017] t BA is the reverse propagation time of ultrasonic wave;

[0018] p is the sound path, i.e. the straight-line distance between two ultrasonic transducers;

[0019] S3. Calculate molecular weight:

[0020]

[0021] Wherein, M is the molecular weight of the gas medium being measured;

[0022] k is the adiabatic index of the gas;

[0023] R is the molar gas constant;

[0024] T is the temperature of the measured medium, that is, the thermodynamic temperature value.

[0025] Furthermore, the forward propagation time of the ultrasonic wave, that is, the propagation time when the propagation direction of the ultrasonic wave is in the same direction as the flow velocity of the measured medium:

[0026]

[0027] Where v is the flow velocity of the measured medium in the pipeline.

[0028] Furthermore, the reverse propagation time of the ultrasonic wave is the propagation time in the direction opposite to the flow velocity of the measured medium:

[0029]

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1) In the hardware ultrasonic echo signal amplification module, the method of converting the single-ended signal into a differential signal enhances the signal's anti-interference ability compared with the ordinary single-ended signal to single-ended signal amplification method;

[0032] 2) In the channel switching control module, the number of channels can be increased or decreased according to actual conditions to meet different needs;

[0033] 3) Molecular weight is measured only by using ultrasonic transducers, flow is compensated by temperature and pressure, and then the speed of sound is used to measure not only flow but also molecular weight. This is very cost-effective compared to other molecular weight measurement devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural block diagram of the device described in the present invention.

[0035] Figure 2It is a schematic diagram of the positions of the ultrasonic transducer A and the ultrasonic transducer B described in the present invention.

[0036] Figure 3 This is a wiring diagram of the DC / DC boost module of the present invention.

[0037] Figure 4 This is a wiring diagram of the drive signal module of the present invention.

[0038] Figure 5 It is a wiring diagram of the channel switching control module of the present invention.

[0039] Figure 6 This is a wiring diagram of the ultrasonic echo signal amplification module of the present invention.

[0040] Figure 7 It is a wiring diagram of the ultrasonic echo signal filtering processing module of the present invention.

[0041] In the figure: 1. Ultrasonic transducer A 2. Ultrasonic transducer B DETAILED DESCRIPTION

[0042] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings:

[0043] See Figure 1 The present invention discloses a device for measuring the average molecular weight of a mixed gas, comprising a DC / DC boost module, a drive signal module, a channel switching control module, an ultrasonic transducer, an ultrasonic echo signal amplification module, an ultrasonic echo signal filtering and processing module, and a microprocessor; the ultrasonic transducers are respectively installed on the upstream and downstream pipe walls of the pipeline fluid flow direction, and are installed relative to the pipeline axis, and the angle range between the installation and the pipeline axis is 30 to 60 degrees.

[0044] See Figure 3 The DC / DC boost module provides a higher voltage level for the ultrasonic drive signal. The input VCC+10V signal is boosted to VH_OUT through the U12 chip. The DC / DC boost module pin VH_OUT is connected to the drive signal module voltage input terminal VH_OUT.

[0045] See Figure 4The driving signal module provides an excitation pulse signal for the ultrasonic transducer. Theoretically, the larger the amplitude of the excitation pulse signal, the longer the transmission distance of the ultrasonic signal generated by the transducer. The enable pin PWM_CS of the driving signal module is connected to the PWM_CS pin of the microprocessor to control whether the driving signal module outputs the driving signal. The driving signal pin of the driving signal module is connected to the pin PWM_SIG of the microprocessor that generates a low-voltage driving pulse signal. The driving module converts the low-voltage driving pulse signal PWM_SIG into a high-voltage driving pulse signal TX_SIG with an amplitude of VH_OUT through the U11 chip. The signal output pin TX_SIG of the driving signal module is connected to the TX_SIG pin of the channel switching control module.

[0046] See Figure 5 The channel switching control module controls the switching of different ultrasonic channels and the switching of the transceiver transmitting and receiving directions of the same channel transducer. P5 is an ultrasonic transducer terminal. Two ultrasonic transducers are connected to the P5 terminal. Each ultrasonic transducer has two wires, a signal wire and a ground wire. The TX_CH1_SIG_AB pin and the TX_CH1_SIG_BA pin are the signal wire pins of the two transducers respectively. The function of the circuit is the channel switching controlled by the microprocessor. The control pin CTRL_CH1_A2B of the microprocessor controls the enable so that the drive pin TX_SIG is connected to the ultrasonic transducer pin TX_CH1_SIG_AB, and the TX_CH1_SIG_BA pin is connected to the pin USS_RCV. In this way, the ultrasonic transducer connected to the pin TX_CH1_SIG_AB is used as a transmitting ultrasonic transducer, and the ultrasonic transducer connected to the pin TX_CH1_SIG_BA is used as a receiving transducer to receive the transmitting ultrasonic transducer. The ultrasonic signal emitted by the transmitting transducer, the pin USS_RCV is connected to the ultrasonic echo signal amplification module; when the control pin CTRL_CH1_SIG_B2A of the microprocessor sends an enable signal, the driving pin TX_SIG is connected to the ultrasonic transducer pin TX_CH1_SIG_BA, and the TX_CH1_SIG_AB pin is connected to the pin USS_RCV, so that the ultrasonic transducer connected to the pin TX_CH1_SIG_BA is used as a transmitting ultrasonic transducer, and the ultrasonic transducer connected to the pin TX_CH1_SIG_AB is used as a receiving transducer to receive the ultrasonic signal emitted by the transmitting transducer, and the pin USS_RCV is connected to the ultrasonic echo signal amplification module; a channel switching control module can only connect two transducers, and multiple channel switching modules can be used to connect multiple ultrasonic transducers, such as realizing 4 channels (8 transducers), etc. The use of multiple channels can improve the accuracy of measurement data.

[0047] The ultrasonic transducer is a device that generates ultrasonic signals. When an excitation pulse signal is applied to the ultrasonic transducer, the ultrasonic transducer transmits an ultrasonic signal. The transmitted ultrasonic signal is received by a receiving transducer installed on the same channel. The same ultrasonic transducer is used as both a transmitting transducer and a receiving transducer.

[0048] See Figure 6 Due to factors such as scattering and absorption of ultrasonic waves during propagation, the signals actually received by the receiving transducer are relatively small and weak, so it is generally necessary to amplify the received signals. The USS_RECV of the ultrasonic echo signal amplification module is connected to the echo signal pin of the ultrasonic transducer. After the signal is processed by the chip U16 of the module, the weak ultrasonic signal is amplified. The output signal after amplification is a differential signal with pins VGA_VOL and VGA_VOH. The differential signal is connected to the V GA_VOL and VGA_VOH pins; the U16 adopts the AD8331ARQZ model chip, and the INH pin of U16 is connected in series with the capacitor C61 and the inductor L9, and then connected to the resistor R16 and the TVS diode respectively. The connection between the resistor R16 and the TVS diode is connected to the channel switching control module, so as to ensure the continuity of the ultrasonic signal input by the ultrasonic echo signal amplification module; in the ultrasonic echo signal amplification module, the input single-ended signal is converted into a differential signal through the amplification module, which greatly enhances the anti-interference ability and also filters out some interference signals.

[0049] See Figure 7 Since the propagation path of ultrasound is not an ideal environment, due to the influence of various factors, the received ultrasonic echo signal will inevitably be mixed with some interference signals. It is necessary to filter these signals and send the processed signals to the microprocessor for signal acquisition and other processing. The differential signal after amplification by the ultrasonic echo signal amplification module is filtered by the ultrasonic echo signal filtering processing module and then connected to the microprocessor at the REV_BAUD_A pin. The microprocessor collects and processes the signal to calculate information such as the speed of sound.

[0050] The microprocessor is the core part of the sound velocity calculation, which controls each part of the sound velocity measurement module. When calculating the sound velocity inside the flow meter, the forward and reverse propagation time needs to be calculated according to the formula. The calculation of this propagation time is also obtained through relevant filtering, averaging and other algorithms. The propagation speed of ultrasonic waves in each gas medium is different, and each has its theoretical value. The actual sound velocity value set calculated is taken as the final sound velocity value through the data processing algorithm. Of course, the measured value of the sound velocity is also related to the environmental conditions, such as temperature and pressure. Therefore, temperature and pressure compensation is required under specific conditions.

[0051] A method for measuring the average molecular weight of a mixed gas comprises the following steps:

[0052] S1. The ultrasonic signal propagates between the two transducers of the flow meter. Figure 2 The time difference method calculates the sound velocity by measuring the propagation time of the ultrasonic signal in the medium in the downstream and upstream directions, and then calculates the flow rate by the sound velocity; ultrasonic transducer A1 and ultrasonic transducer B2 are installed upstream and downstream of the pipeline fluid flow, and each transducer can be used as both a transmitter and a receiver of ultrasonic signals.

[0053] S2, ultrasonic transducer A1 and ultrasonic transducer B2 are installed relative to the axis of the pipeline, forming an angle θ with the axis of the pipeline. The ultrasonic wave propagates along a straight path. The propagation distance of the ultrasonic wave is Figure 1 P shown; The propagation time calculation formula for the forward propagation of ultrasound, that is, the propagation direction of the ultrasound is in the same direction as the flow velocity of the measured medium:

[0054]

[0055] Wherein, c is the speed of sound, i.e., the propagation speed of the ultrasonic signal in the measured medium;

[0056] t AB is the forward propagation time of ultrasonic wave;

[0057] t BA is the reverse propagation time of ultrasonic wave;

[0058] p is the sound path, i.e. the straight-line distance between two ultrasonic transducers;

[0059] v is the flow velocity of the measured medium in the pipeline.

[0060] S3. The reverse propagation of ultrasound, that is, the propagation time calculation formula when the direction of ultrasound propagation is opposite to the flow velocity of the measured medium:

[0061]

[0062] The above ultrasonic forward and reverse propagation time calculation formula can be obtained:

[0063]

[0064] In formula (7), p is a constant, t AB and t BA It can be directly calculated by collecting ultrasonic echo signals, so that the propagation speed of ultrasonic waves in the medium can be obtained by formula (7).

[0065] S3. Calculate molecular weight:

[0066]

[0067] Wherein, M is the molecular weight of the gas medium being measured;

[0068] k is the adiabatic index of the gas;

[0069] R is the molar gas constant;

[0070] T is the temperature of the measured medium (thermodynamic temperature value);

[0071] c is the propagation speed of ultrasonic wave in the measured medium.

[0072] Among the parameters in formula (8), the gas adiabatic index and molar gas constant can be obtained by looking up the table, and the medium temperature and sound velocity can be obtained by the ultrasonic flow meter, which are also the necessary parameters for the ultrasonic flow meter to calculate the flow rate.

[0073] The ultrasonic flowmeter based on the time difference method needs to measure the forward and reverse propagation time and the time difference when calculating the flow rate. The speed of sound is calculated by the propagation time parameter, and then the flow rate is calculated. The molecular weight can be calculated by the relationship between the speed of sound and the molecular weight (Formula (8)). This is a very cost-effective method for measuring molecular weight, and the molecular weight can be used to verify the gas composition.

[0074] The above embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the above embodiments. The methods used in the above embodiments are conventional methods unless otherwise specified.

Claims

1. A device for measuring the average molecular weight of a mixed gas, characterized in that: It includes a DC / DC boost module, a drive signal module, a channel switching control module, an ultrasonic transducer, an ultrasonic echo signal amplifying module, an ultrasonic echo signal filtering processing module and a microprocessor; the ultrasonic transducers are respectively installed on the upstream and downstream pipe walls of the pipeline fluid flow direction, and are installed relative to the pipeline axis, and the angle range between them and the pipeline axis is 30-60°; the voltage output pin of the DC / DC boost module is connected to the voltage input end of the drive signal module, the IO pin of the drive signal module is connected to the output pin of the microprocessor, the control output pin of the drive signal module is connected to the input pin of the channel switching control module, the IO pin of the channel switching control module is connected to two ultrasonic transducers, the output pin of the channel switching control module is connected to the input pin of the ultrasonic echo signal amplifying module, the output pin of the ultrasonic echo signal amplifying module is connected to the input pin of the ultrasonic echo signal filtering processing module, and the output pin of the ultrasonic echo signal filtering processing module is connected to the input pin of the microprocessor; The input signal of the ultrasonic echo signal amplification module is a single-ended signal, and the output signal is a differential signal. The signal pin is connected to the ultrasonic echo signal filtering and processing module.

2. A device for measuring the average molecular weight of a mixed gas according to claim 1, characterized in that: There are one or more channel switching control modules, and the corresponding number is matched according to the logarithm of the ultrasonic transducer.

3. The device for measuring the average molecular weight of a mixed gas according to claim 1, characterized in that: The receiving end of the ultrasonic echo signal amplifying module is connected to the output end of the channel switching control module, and a TVS diode, a series inductor and a capacitor are connected to the ground on the connection circuit.

4. The method for measuring the average molecular weight of a mixed gas according to any one of claims 1 to 3, characterized in that: The steps include: S1. Ultrasonic transducers A and B are installed on the upstream and downstream walls of the pipeline fluid flow direction. Each ultrasonic transducer can be used as both a transmitter and a receiver of ultrasonic signals. S2, ultrasonic transducer A and ultrasonic transducer B are installed relative to the axis of the pipeline, forming an angle θ with the axis of the pipeline. The ultrasonic wave propagates along a straight path. The propagation distance of the ultrasonic wave is P. Then the propagation speed of the ultrasonic signal in the measured medium is: Wherein, c is the speed of sound, i.e., the propagation speed of the ultrasonic signal in the measured medium; t AB is the forward propagation time of ultrasonic wave; t BA is the reverse propagation time of ultrasonic wave; p is the sound path, i.e. the straight-line distance between two ultrasonic transducers; S3. Calculate molecular weight: Wherein, M is the molecular weight of the gas medium being measured; k is the adiabatic index of the gas; R is the molar gas constant; T is the temperature of the measured medium, that is, the thermodynamic temperature value.

5. The method for measuring the average molecular weight of a mixed gas according to claim 1, characterized in that: The forward propagation time of the ultrasonic wave is the propagation time when the propagation direction of the ultrasonic wave is in the same direction as the flow velocity of the measured medium: Where v is the flow velocity of the measured medium in the pipeline.

6. The method for measuring the average molecular weight of a mixed gas according to claim 1, characterized in that: The reverse propagation time of the ultrasonic wave is the propagation time in the opposite direction of the flow velocity of the measured medium:

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