RU2160887C1 - Ultrasonic flowmeter - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: ultrasonic time-pulse flowmeter has measurement section of pipe-line with two piezoelectric converters fixed on it which are placed in corresponding synchronization rings composed of commutator, amplifier, comparator, OR circuit and first univibrator connected in series. Output of this univibrator is linked to input of second univibrator and via two AND circuits to inputs of first and second formers of sounding pulses correspondingly. Piezoelectric converters are connected to outputs of proper formers of sounding pulses and to proper inputs of commutator whose third input is coupled to second inputs of AND circuits and to output of device of microprocessor control. Third AND circuit, pulse counter, register of sequential approximation, subtracter and digital-to-analog converter connected in series are inserted into flowmeter to adapt operation threshold of comparator to level of received signal. EFFECT: increased operational reliability of flowmeter, enhanced sensitivity of measurement of flow rate of liquid media. 2 dwg

Description

 The invention relates to measuring equipment and can be used to measure the flow of various liquid media.

 Ultrasonic flow meters are known (1-3), which contain a measuring section of a pipeline with two piezoelectric transducers included in the corresponding synchro-rings, consisting of a series-connected commutator (keys or a switch of the direction of radiation), an amplifier-former, I, OR circuits, and a probe pulse shaper ( pulse generator). Known devices also include one-shots, triggers, a time selector, divider counters, a multiplexer-decoder, reversible counters, a subtractor, registers, strobe drivers.

 Ultrasonic flow meters work as follows. Piezoelectric transducers emit and receive ultrasonic pulses that have passed the medium along the stream and against it with the formation of two synchro-rings in one channel. Then, the sync ring periods are quantized by n periods of a special generator, the coincidence in time of the sync ring pulses is excluded, and the flow velocity is calculated from their parameters.

 In case of changes in the operating conditions of the flowmeter of the physicochemical parameters of the measured liquid, the attenuation level changes when an acoustic pulse passes through the measured medium, and the sensitivity of the piezoelectric transducers also changes. As a result, the amplitude of the received pulses can vary over a wide range. This can lead to a breakdown of the autocirculation in the sync ring when the amplitude of the received signal decreases below the threshold level of the driver amplifier, which cannot be chosen sufficiently low, since this will lead to a false response from interfering signals with a large amplitude of the received signals.

 In addition, a wide variation in the amplitude of the received signals leads to a random, non-compensated change in the delay time in the electronic circuits of the amplifier-driver, comparable to the difference in the propagation time of an acoustic pulse in the flow and against at low flow rates (several nanoseconds). This leads to an increase in the error in measuring the flow rate due to a change in the repetition period of the autocirculation pulses by the value of the delay time of the pulses in the electric circuits of the amplifier-former.

 Thus, the disadvantages of the analogues are reduced reliability and increased error in determining the flow rate of the measured liquid.

 The closest analogue of the proposed device is an ultrasonic flowmeter-counter URSV-010M (4). The known device comprises a pipe segment and two piezoelectric transducers fixed to it, connected to a radiation direction switch. The synchro-rings of the flowmeter consist of a series-connected switch of the radiation direction, an amplifier, a pulse shaper, a trigger, a time window shaper, and a powerful pulse shaper. The input of the forced start circuit is connected to the output of the trigger, and the output is connected to the second input of the trigger. The known device also contains the second and third triggers, three pulse counters, a control register, a reference frequency generator and a microprocessor control circuit.

The device operates as follows. After the START trigger pulse is supplied from the microprocessor control circuit, the second and third triggers are reset, and the time window driver is forced to start, which ensures the formation of the first probe pulse using the powerful pulse generator. A probe pulse is fed through a switch of the direction of radiation to one of the piezoelectric transducers. After passing through the measured liquid at the output of another piezoelectric transducer, the signal has the form of a radio pulse. After amplification in the amplifier, the pulse shaper converts it into a packet of pulses, which set the first trigger to the "1" state. According to this signal, the shaper of the time window generates the next triggering pulse. Thus, regeneration of triggering pulses occurs in each cycle of the signal emission along or against the fluid flow. Under the influence of these pulses, the first pulse counter is filled and at the time of its overflow, the measurement cycle in this direction T _n1 (T _n2 ) ends. The value of T _n1 (T _n2 ) is proportional to the propagation time of the signal in the electro-acoustic path T _n1 (T _n2 ):
T _n1 = N • T ₁
where N is the accumulation coefficient of the first counter. Codes proportional to the duration of the flow and against T _n1 and T _n2 are formed in the second and third counters. The resulting codes are read by the microprocessor control circuit, which processes the measurement results and calculates the measured fluid flow:
Q = S _nn • (T _n1 -T _n2 ), m ³ / h,
where S _nn is the conversion coefficient of the flow meter.

 The disadvantage of the prototype, as well as analogues, is the low reliability and increased error in determining the flow rate of the measured liquid due to the presence of a fixed threshold for the operation of the pulse shaper. At a fixed threshold of operation, autocirculation of pulses is disrupted, and the delay time in the electronic circuits of the pulse shaper changes when the amplitude of the received pulses varies over a wide range, which increases the measurement error.

 The objective of the present invention is the creation of an ultrasonic flow meter, in which by adapting the threshold of the comparator to the level of the received signal, the reliability and accuracy of the measurement of fluid flow are increased.

 The problem is solved in that in an ultrasonic flow meter containing a measuring section of the pipeline with a calibrated cross-section and two reversible conjugated piezoelectric transducers fixed on it, included in the corresponding synchro rings, consisting of a series-connected switch, amplifier, comparator, OR circuit, and the first one-shot, the output of which is connected with the input of the second one-shot, as well as through two AND circuits with the inputs of the first and second formers probing the pulse, respectively c, and the piezoelectric transducers are connected to the outputs of the corresponding probing pulse shapers and the corresponding inputs of the switch, the third input of which is connected to the second inputs of the AND circuit and the output of the microprocessor control device, the second output of which is connected to the second input of the OR circuit, and the input is connected to the output of the second one-shot and the second input of the comparator, the third AND circuit is connected in series, a pulse counter, a sequential approximation register, a subtractor and a digital channel the burn converter, the output of which is connected to the third input of the comparator, the input of the third circuit And connected to the output of the pulse counter, the second input of the circuit And connected to the output of the second one-shot, and the second input of the counter connected to the second input of the sequential approximation register and the second output of the microprocessor control device, the third output of which is connected to the third input of the sequential approximation register, the second output of which is connected to the second input of the microprocessor control device, fourth the outputs of which are connected to the second inputs of the subtractor.

 The drawing shows: figure 1 is a block diagram of the proposed flow meter; FIG. 2 - timing diagrams of signals at points in the flowmeter circuit.

 The ultrasonic flow meter contains a measuring section of the pipeline 1 with a calibrated cross-section and two reversible conjugated piezoelectric transducers 2 and 3 fixed on it, included in the corresponding synchro rings, consisting of a series-connected switch 4, amplifier 5, comparator 6, circuit OR 7 and the first one-shot 8. Output the first one-shot 8 is connected to the input of the second one-shot 9, as well as the inputs of the two circuits And 10 and 11, the outputs of which are connected to the inputs of the first 12 and second 13 f probers of probing pulses. Piezoelectric transducers 2 and 3 are connected to the outputs of the corresponding probing pulse generators 12 and 13 and the corresponding inputs of the switch 4, the third input of which is connected to the second inputs of the circuits And 10 and 11, as well as the output of the microprocessor control 14. The second output of the microprocessor control 14 is connected to the second input of the OR circuit 7, and the input of the device 14 is connected to the output of the second one-shot 9 and the second input of the comparator 6.

 To adapt the threshold of the comparator 6 to the level of the received signal, the flow meter contains a third AND 15 circuit connected in series, a pulse counter 16, a sequential approximation register 17, a subtractor 18 and a digital-to-analog converter 19, the output of which is connected to the third input of the comparator 6. The input of the third circuit And 15 connected to the output of the pulse counter 16, and the second input of the circuit And 15 is connected to the output of the second one-shot 9. The second input of the pulse counter 16 is connected to the second input of the serial register 17 and the second output of the microprocessor control device 14, the third output of which is connected to the third input of the sequential approximation register 17. The second output of the sequential approximation register 17 is connected to the second input of the microprocessor control device 14, the fourth outputs of which are connected to the second inputs of the subtracting device 18.

 Switch 4 is an analog signal multiplexer with a digital control input and is designed to connect a receiving piezoelectric transducer 2 or 3, depending on the direction of radiation of the probe pulse to the input of amplifier 5.

 The amplifier 5 is a logarithmic amplifier and is designed to reduce the dynamic range of the received signal at the input of the comparator 6.

 The probes pulse generators 12 and 13 are key amplifiers and are designed to amplify the probe pulses and match with the input of the piezoelectric transducers 2 and 3.

 The microprocessor control device 14 is a single-chip computer and is intended to control the modes of operation of the flow meter and calculate the parameters of the measured fluid.

 The subtractor 18 includes, for example, EXCLUSIVE OR circuits and adders, and is designed to subtract from the output code of the sequential approximation register 17 the code from the fourth output of the microprocessor control device 14.

 The remaining elements of the scheme are well known and have no features.

 According to the principle of operation, the flow meter refers to time-pulsed ultrasonic flow meters, its operation is based on measuring the difference in the transit times of short probe pulses of ultrasonic vibrations in the direction of movement of the fluid flow in the pipeline and against it. The probe pulses are excited by primary piezoelectric transducers mounted on a pipeline with a measured flow rate.

 According to the method of organizing sounding of a fluid flow by ultrasonic pulses, the flow meter relates to alternating-circuit auto-circulation flow meters. A feature of the flowmeter is the alternate functioning of two synchro-rings. The synchro-rings are formed by a receiving-amplifying path covered by delayed feedback through the electro-acoustic path (piezoelectric transducer 2 — liquid — piezoelectric transducer 3).

где T₁, T₂ - полное время распространения зондирующих импульсов, соответственно против потока и по потоку жидкости;
L - расстояние между излучателями;
C - скорость распространения ультразвуковых колебаний в неподвижной жидкости;
V - скорость жидкости, усредненная вдоль ультразвукового луча;
ΔL/C время прохождения зондирующих импульсов не измерительных участков синхроколец, включающее и время задержки в электронных цепях расходомера.The movement of fluid in the pipeline leads to a change in the total propagation time of ultrasonic signals between piezoelectric transducers: the propagation time decreases along the fluid flow, and increases against the flow. The flowmeter, through alternating radiation into the moving fluid of ultrasonic vibrations and their reception, measures the propagation times of the probe pulses along and against the fluid flow:

where T ₁ , T ₂ - the total propagation time of the probe pulses, respectively, against the flow and the fluid flow;
L is the distance between the emitters;
C is the propagation velocity of ultrasonic vibrations in a stationary fluid;
V is the fluid velocity averaged along the ultrasound beam;
ΔL / C is the transit time of the probe pulses of non-measuring sections of the synchro ring, including the delay time in the electronic circuits of the flowmeter.

где Q - измеряемый расход жидкости;
K₁ - гидродинамический коэффициент;

D - внутренний диаметр трубопровода.Then the flowmeter calculates the difference and flow rate,

where Q is the measured fluid flow rate;
K ₁ is the hydrodynamic coefficient;

D is the inner diameter of the pipeline.

 Ultrasonic flowmeter operates as follows.

 The device operates in two modes: "Calibration" and "Measurement". In the "Calibration" mode, the sensitivity threshold of the comparator 6 is adapted to the level of the received signal. This is followed by the “Measurement” mode, in which the total propagation time of N pulses in the electro-acoustic path is measured.

 In the "Calibration" mode, the microprocessor control device 14 at its first output generates a radiation direction command, for example, a log. "0", which enters the third input of the switch 4 and the second inputs of circuits I 10 and 11, a flow meter is prepared for radiation and reception of probe pulses against the flow. In this case, the one-shot 8 through the circuit And 11 is connected to the input of the shaper of the probe pulses 13, and the piezoelectric transducer 2 through the switch 4 is connected to the input of the amplifier 5.

 Timing diagrams of the flowmeter operation in the Calibration mode are presented in FIG. 2, a-d.

After that, the microprocessor control device 14 at its second and third outputs generates, respectively, triggering signals (Fig. 2, b) and calibration (Fig. 2, a), and the triggering signal is fed to the reset input of the pulse counter 16, the clock input of the sequential approximation register 17 and the second input of the OR circuit 7, and the calibration signal is fed to the start input of the sequential approximation register 17. Based on these signals, the pulse counter 16 is reset and the conversion cycle of the sequential approximation register 17 starts, while ode MSB Q _n low level voltage appears on all others - high level. At the fourth output, the microprocessor control device 14 generates a zero code, which is fed to the second input of the subtracting device 18. Thus, the output code of the sequential approximation register 17 through the subtracting device 18 goes to the input of the digital-analog converter 19, which generates the corresponding analog voltage supplied to threshold input of the comparator 6. This voltage at the first conversion step is equal to half the range of the signal at the output of the amplifier 5.

 As mentioned above, the start pulse from the second output of the microprocessor control device 14 through the OR 7 circuit is fed to the input of a single-shot 8, which generates a short pulse coming through the And 11 circuit to the input of the probe pulse shaper 13. The latter generates a powerful pulse received at the input of the piezoelectric transducer 3, which converts an electrical signal into an acoustic signal and emits it into a measured liquid. The piezoelectric transducer 2 receives an acoustic signal, converts it into an electric signal, which through the switch 4 is fed to the input of the amplifier 5. The received signal has the form of a radio pulse. The amplified signal is fed to the input of the comparator 6, where it is compared with the threshold level set by the digital-to-analog converter 19. If the amplitude of the signal of the threshold level is exceeded, a pulse appears at the output of the comparator 6, which, through the OR 7 circuit, is fed to the input of the one-shot 8, forming a short pulse, which again through the circuit And 11 enters the input of the shaper of the probe pulses 13 and the process of auto-circulation in the synchro ring continues.

 At the same time, a short pulse from the output of the single vibrator 8 is fed to the input of the single vibrator 9, which generates a strobe signal with a duration not exceeding the propagation time of the signal in the measured liquid (Fig. 2, c). This signal is fed to the ban input of the comparator 6 and prohibits its operation after the passage of the first half-wave of the input radio pulse, which is necessary to protect against interference.

 The strobe signal from the output of the one-shot 9 through the And 15 circuit also goes to the clock input of the pulse counter 16. Under the influence of these pulses, the counter 16 is filled and at the time of its overflow an output signal is generated - log "1", which is fed to the input of the serial data of register 17 and the first input of the circuit And 15, prohibiting the further passage of strobe pulses to the input of the counter 16.

 If the threshold initially set at the output of the digital-analog converter 19 exceeds the amplitude of the signal at the input of the comparator 6, then the auto-circulation process does not occur in the sync ring and, therefore, the strobe pulses at the output of the single-vibrator 9 are not generated, the counter 16 remains blank and its output signal is also not generated.

After the time required to completely fill the counter 16, the microprocessor control device 14 generates at its second output the next trigger signal. By this signal, the counter 16 is reset, and by the input of the serial data of the register 17, the output signal of the counter 16 is written to the high order, depending on whether the counter 16 has been filled or not. In addition, a low level voltage appears at the output of the subsequent high order bit Q _{n-1 of} register 17, and a high level voltage remains at all subsequent low order bits. Thus, the threshold voltage at the input of the comparator 6 is changed.

The start pulse through the OR 7 circuit also arrives at the single-vibrator 8 and the process of auto-circulation of pulses in the sync ring resumes, but already with a new threshold voltage at the input of the comparator 6. Then the flowmeter works as described above and as a result, the code value in the discharge Q _{n is} set in register 17 _-1 .

 Similarly, according to the well-known principle of operation of the sequential approximation register, the code values are set in all other low-order bits of the register 17, and the total number of clock cycles of the start pulses is equal to the number of bits of the register 17. At the end of the conversion cycle, a negative voltage drop is formed at the second output of the register 17 (Fig. 2, g) received at the second input of the microprocessor control device 14. Based on this signal, the microprocessor control device 14 generates a code at the fourth output, post Payuschie the second input of subtractor 18 which subtracts from the output register 17. The output code code subtractor 18 is converted to a digital to analog converter 19 into an analog voltage and is supplied to the threshold input of comparator 6.

 Thus, a code corresponding to the signal amplitude at the input of the comparator 6 is generated in the sequential approximation register 17, and the threshold voltage generated by the digital-to-analog converter 19 is obviously less than the signal amplitude under the operating conditions actually existing at the moment by the amount of noise immunity, i.e. the threshold level is adapted to the actual amplitude of the input signal. This leads to the impossibility of disrupting the auto-circulation process when the physico-chemical parameters of the measured liquid change under operating conditions of the flowmeter and, consequently, the level of the received signal changes, which increases the reliability of the device. In addition, adjusting the response threshold to the amplitude of the received signal allows you to make the delay time in the electronic circuits of the comparator a constant value that does not depend on the amplitude of the received signal, which increases the accuracy of the flow meter.

 This is followed by the "Measurement" mode, in which the total propagation time of N pulses in the electro-acoustic path is measured when the pulses are emitted in the same direction as the "Calibration" mode.

 Timing diagrams of the flowmeter operation in the "Measurement" mode are presented in FIG. 2, d.

 In this mode, the microprocessor control device 14 at the second output generates a trigger signal that arrives through the OR 7 circuit at the input of the single-shot 8, which generates short pulses of a given duration (Fig. 2, h). The pulses from the output of the one-shot 8 through the circuit And 11 are fed to the probe pulse shaper 13, which generates a powerful pulse of a given shape (Fig. 2, e), which is transmitted to the transmitting transducer 3. The input signal received by the piezoelectric transducer 2 through the switch 4 and the amplifier 5 is fed to the input of the comparator 6 (Fig. 2, e), where it is compared with the threshold level set earlier in the "Calibration" mode. At the output of the comparator 6, pulses are formed that exceed the amplitude of the input signal over the threshold value (Fig. 2g), which, through the OR 7 circuit, are fed to the input of a single-vibrator 8 and the process of auto-circulation of pulses in the sync ring begins.

At the same time, a short pulse from the output of the one-shot 8 goes to the input of the one-shot 9, which generates a strobe signal (Fig. 2, and), which goes to the inhibit input of the comparator 6 and prohibits its operation after the first half-wave of the input radio pulse passes, which increases the noise immunity of the flowmeter. The signal from the output of the one-shot 9 also arrives at the first input of the microprocessor control device 14, which measures the propagation time of a packet of N probe pulses against the flow: T _n1 = N • T ₁ .

 After that, the flowmeter enters the “Calibration” mode, and then the “Measurement” mode when the sounding pulses are emitted from the measured fluid flow. For this, the microprocessor control device 14 generates at the first output a command for directing radiation along the stream (log. "1"), which in this case connects the single-shot 8 through the I 10 circuit to the input of the probe pulse generator 12, and the piezoelectric transducer 3 is connected via the switch 4 to the input of the amplifier 5, preparing a flowmeter for radiation and reception of probe pulses along the flow of the measured liquid. Then the flowmeter in the "Calibration" and "Measurement" modes works similarly to that described above when probing pulses are emitted against the flow.

As a result, the microprocessor control device 14 measures the propagation time of a packet of N probe pulses along the flow of the measured liquid: T _n2 = N • T ₂
After measuring the propagation time against the flow T _n1 and the flow T _n2 , the microprocessor control device 14 processes the measurement results and calculates the measured time intervals in both directions of fluid flow according to the above formula. Then the process of calibration and measurement of the propagation time of the probe pulses in both directions is repeated, etc.

 Thus, the ultrasonic flow meter provides high reliability and measurement of fluid flow with a small error in case of changes in the operating conditions of the physico-chemical parameters of the measured fluid and the sensitivity of the piezoelectric transducers.

LITERATURE
1. Auth. St. USSR N 1364882, G 01 F 1/66, publ. 1988 year

 2. RF patent N 2018089, G 01 F 1/66, publ. 1994

 3. RF patent N 2085858, G 01 F 1/66, publ. 1997 year

 4. Ultrasonic flowmeter-counter URSV-010M "Takeoff RS" B 35.30-00.00m

Claims (1)

 An ultrasonic flow meter containing a measuring section of a pipeline with a calibrated cross section and fixed on it by two reversible conjugated piezoelectric transducers included in the corresponding synchro rings, consisting of a series-connected switch, amplifier, comparator, OR circuit, and a first one-shot, the output of which is connected to the input of the second one-shot, and also through two AND circuits with inputs of the first and second probes of probes, respectively, and the piezoelectric pre Browsers are connected to the outputs of the corresponding probing pulse generators and the corresponding inputs of the switch, the third input of which is connected to the second inputs of the AND circuit and the output of the microprocessor control device, the second output of which is connected to the second input of the OR circuit, and the input is connected to the output of the second one-shot and the second input of the comparator, characterized in that a third AND circuit, a pulse counter, a sequential approximation register, a subtractor and a digital channel are introduced in series the burn converter, the output of which is connected to the third input of the comparator, the input of the third circuit And connected to the output of the pulse counter, the second input of the circuit And to the output of the second one-shot, and the second input of the pulse counter to the second input of the sequential approximation register and the second output of the microprocessor control device the third output of which is connected to the third input of the sequential approximation register, the second output of which is connected to the second input of the microprocessor control device, the fourth outputs whose odes are connected to the second inputs of the subtractor.

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