RU167569U1 - ULTRASONIC GAS FLOW METER - Google Patents

Abstract

The proposed solution relates to measuring equipment and can be used to measure gas flow in industry and housing and communal services. The device contains a primary flow transducer with two transceiving electro-acoustic transducers, an input switch, an amplifier, an amplitude-time selector, a probe signal shaper, a coarse counter, an interpolation circuit, a subtraction circuit, a dynamic averaging unit, a clock generator, a time interval shaper, and a calculator. Acoustic transducers are connected to the probe signal generator and an amplifier connected to a coarse counter, an interpolation circuit and a subtraction circuit. The time interval former is connected to the input of the probe signal generator and the first input of the coarse counter, the second output is connected to the input of the switch, the third output is connected to the second input of the interpolation circuit, the fourth output is connected to the input of the calculator, the output of which is the output of the device. The clock generator is connected to the shaper of time intervals, inputs of the coarse counter and the interpolation circuit. It contains a window comparator, a measurement switch, and a multi-threshold comparator. The input of the window comparator is connected to the amplifier, and the output is connected to the shaper of time intervals. The first inputs of the measurement switch and multi-threshold comparator are connected to the output of the subtraction circuit. The second input of the multi-threshold comparator is connected to the dynamic averaging unit, the third input of the multi-threshold comparator

Description

The proposed solution relates to measuring equipment and can be used to measure gas flow in industry and housing and communal services.

Known ultrasonic gas meter [1], containing a primary flow transducer, probing signal shaper, analog signal switcher, clock generator, amplifier, measuring counter, digital signal shaper, time chart generating unit, code subtraction circuit, code multiplier, coefficient memory, accumulating adder, code modification scheme, code comparison scheme, comparator and trigger.

The disadvantage of this solution is that maintaining a constant signal level at the output of the receiving sensors is carried out by changing the amplitude of the probing signals, and adjustment is carried out according to the results of evaluating the received signal only at the next measurement step, and the amplitude of the signal at the output of the receiving sensors is indirectly related to the amplitude of the probing signal . It is known that at high flow rates, a significant increase in the fluctuation of the received signal is caused by their scattering by turbulent flow vortices, which in particular relates to gas flows having a low kinematic viscosity. Moreover, changes in the signal amplitude during sounding, both in the flow and against the flow, can be two or more times. At high flow rates, this solution does not allow to quickly monitor the change in the received signal, which can lead to malfunctions and errors in the registration and measurement of signal parameters or to unreasonable adjustments in case of random signal fluctuations.

The closest technical solution is an ultrasonic flow meter [2], which contains a measuring section with transceiver electroacoustic transducers, an input switch, a shaper of a probing signal, an amplifier with automatic gain control (AGC), an amplitude-time selector, a coarse counter, an interpolation circuit, a dynamic averaging unit , a clock generator, a shaper of time intervals and a computer.

The counter works as follows. Measurements are performed in two steps: when sensing downstream and against the flow of the medium being measured. The input switch provides the transmission / reception of signals of the corresponding electro-acoustic transducer (EA) of the primary flow transducer. At the beginning of the measurement cycle, a sensing start signal is supplied to the sensing signal shaper circuit from the first output of the time interval shaper, which controls the formation of the sounding signal, and a sounding resolution signal is supplied to the input switch from the second output of the time interval shaper. At the end of the probe triggering signal, a probe signal is generated at the output of the probe signal generator and, at the same time, the operation of the coarse counter is enabled. The signal passed through the measured medium through the input switch is fed to the input of the amplifier with AGC and, after amplification, is fed to the amplitude-time selector, which contains signal level control comparators. When the oscillation amplitude is exceeded in the received signal of a predetermined threshold level, this oscillation is allocated as a working pulse of the signal. At the moment of the transition of the negative front of the working pulse through zero, the conversion of the time interval to voltage starts. The conversion interval ends at the edge of the reference frequency pulse from the clock generator. The number of reference pulses from the trailing edge of the sounding start signal to the end of the conversion of the time interval into voltage is fixed by the coarse counter as a code of the coarse reference of the time interval. Using the interpolation scheme, the time interval generated by the amplitude-time selector within the frequency period of the reference clock is converted into code. From the output of the interpolation scheme, the code value enters the dynamic averaging block. To reduce the influence of external factors and increase the stability of measurements in the interpolation scheme, the meter is calibrated by the duration of the reference clock period. Codes from the outputs of the dynamic averaging block and the coarse measurement counter are sent to a computer, which generates a signal propagation time code in the measurement channel and calculates the flow parameters. The operation of all nodes of the device is synchronized by the signals from the outputs of the shaper time intervals.

The disadvantage of this device is that, despite the presence of an amplifier with AGC, incorrect measurements of the propagation time of the probe signal are possible in cases when there is a sharp change in the flow velocity at sufficiently high gas flow velocities or in the presence of interference in the measurement channel. These factors lead to large changes in the amplitude of the received signal or the appearance of false signals, which cannot be promptly taken into account and compensated. Changing the amplitude of the received signal over large limits or the appearance of additional interfering signals leads to the fact that the determination of the working pulse by exceeding the threshold is achieved for different pulses when probing downstream and upstream, or the working pulse cannot be determined at all. In this case, the counter malfunctions or the temporal parameters of the measured flow are distorted and, therefore, the measurement error increases. This circumstance does not allow to ensure the operation of the device with sharp changes in the flow rate, which limits the dynamic range of measurements.

This proposal solves the problem of increasing the noise immunity of flow measurements and providing measurements of rapidly changing flows at ultra-low power consumption.

To solve this problem, an ultrasonic gas flow meter-counter is proposed, containing a primary flow transducer with two transceiver electroacoustic transducers (EAP), an input switch, an amplifier, an amplitude-time selector, a probe signal shaper, a coarse counter, an interpolation circuit, a subtraction circuit, a dynamic block averaging, a clock generator, a shaper of time intervals and a computer, and the inputs / outputs of the transceiving electro-acoustic transducer of the primary flow transducer through the input switch are connected to the output of the probe signal generator and the amplifier input, the output of which is connected to an amplitude-time selector, the output of which is connected to the first inputs of the coarse counter and interpolation circuit, the outputs of which are connected to the inputs of the subtraction circuit, the output of which is connected with the first input of the dynamic averaging unit, in addition, the first output of the shaper of the time intervals is connected to the input of the shaper of the probe signal and the second input coarse counter, the second output is connected to the input of the switch, the third output is connected to the second input of the interpolation circuit, the fourth output is connected to the input of the calculator, the output of which is the output of the device, and the output of the clock generator is connected to the first input of the time slot former, the third inputs of the coarse counter and interpolation schemes. Additionally, the ultrasonic gas flow meter includes a window comparator, a measurement switch and a multi-threshold comparator, the input of the window comparator connected to the output of the amplifier, and the output connected to the second input of the shaper time intervals, the first inputs of the measurement switch and multi-threshold comparator connected to the output of the subtraction circuit, the second input the multi-threshold comparator is connected to the output of the dynamic averaging unit, the third input is connected to the second output of the time interval shaper c, and the first output is connected to the second input of the measurement switch, the output of which is connected to the input of the dynamic averaging unit, the second output of the multi-threshold comparator is connected to the third input of the time interval shaper, and the third output is connected to the second input of the dynamic averaging unit.

The problem is solved by introducing a window comparator, a measurement switch and a multi-threshold comparator into the ultrasonic flowmeter. The presence of a window comparator allows, by changing the amplitude of the probing signal, to maintain the level of the received signal within a given working window. The multi-threshold comparator monitors the result of the deviation of the measured time intervals along and against the flow from their average values. The deviation in each direction is compared with the set thresholds and, based on the results of the comparison, further operations are carried out with the measurements obtained. With large excesses, deviations in only one direction, which corresponds to measurements taken at different working pulses when sensing along the flow and against the flow or when switching to measurements on a different pulse, block the passage of measurements through the measurement switch and their further participation in the calculations. Deviations that exceed a certain average level and have a different sign form control signals to the time interval shaper to change (increase) the measurement frequency and to the dynamic averaging unit to reduce the constant averaging of parameters depending on the rate of change of flow rate, which increases the accuracy of measurement of rapidly changing flows. The presence of a measurement control mechanism increases the noise immunity of the measurements and their reliability. The mechanism of adaptive change in the measurement frequency and constant averaging ensures high accuracy in measuring rapidly varying flows while maintaining a low overall energy consumption level, which is especially important for household gas meters that must operate without replacing the battery during the entire calibration interval.

The essence of the proposed solution is illustrated by a block diagram of an ultrasonic flow meter-counter (Fig. 1).

The ultrasonic flow meter-counter contains a primary flow transducer 1 with a set of electro-acoustic transducers (EAP) (EAP1 and EAP2), an input switch 2, an amplifier 3, an amplitude-time selector 4, a probe signal shaper 5, a window comparator 6, a coarse counter 7, a circuit 8 interpolation, a subtraction circuit 9, a dynamic averaging block 10, a clock generator 11, a shaper 12 time intervals, a calculator 13, a measurement switch 14 and a multi-threshold comparator 15. The inputs / outputs of the receiving-emitting electric of the EAP1 and EAP2 converters of the primary flow rate converter 1 through the input switch 2 are connected to the output of the probe signal generator 5 and the input of the amplifier 3, the output of the amplifier is connected to the amplitude-time selector 4 and the input of the window comparator 6, and the output of the amplitude-time selector is connected to the first inputs coarse counter 7 and interpolation circuit 8, the outputs of which are connected to the inputs of the subtraction circuit 9. The first output of the shaper 12 time intervals is connected to the input of the shaper probing signal 5 and the second input of the coarse counter 7, the second output of the shaper 12 is connected to the second input of the switch 2, the third output of the shaper 12 is connected to the second input of the interpolation circuit 8, the fourth output is connected to the first input of the calculator 13, the second input of which is connected to the output of the dynamic block averaging 10, and the output of which is the output of the device. The output of the clock generator 11 is connected to the first input of the shaper 12 time intervals, the third inputs of the counter coarse reference 7 and the interpolation circuit 8, and the output of the window comparator 6 is connected to the second input of the shaper 12 time intervals. The first inputs of the measurement switch 14 and the multi-threshold comparator 15 are connected to the output of the subtraction circuit 9, the second input of the multi-threshold comparator 15 is connected to the output of the dynamic averaging unit 10, the third input is connected to the second output of the time interval shaper 12, and the first output is connected to the second input of the measurement switch 14 the output of which is connected to the input of the dynamic averaging unit 10. The second output of the multi-threshold comparator 13 is connected to the third input of the shaper 12 time intervals, and the third output one with a second input of the dynamic averaging unit 10.

The operation of the ultrasonic flowmeter-counter consists of 2 measurement cycles, which correspond to two directions of ultrasonic sensing (along the flow of the measured medium and against the flow). The flow rate v is determined by the difference in the propagation times of the signal along the stream T ₁ and against the stream T ₂ .

The measured time interval when sensing the stream T ₁ can be represented as

When probing against the stream, the time interval T ₂ is

where L is the path length of the ultrasonic signal in the stream;

L ₀ is the path length of the ultrasonic signal in a stationary medium;

C is the propagation velocity of ultrasound in a stationary medium;

v is the flow rate;

t ₁ - constant delay, not associated with the propagation of ultrasound in the medium when sensing downstream;

t ₂ - constant delay, not associated with the propagation of ultrasound in the medium, when sensing against the stream;

α is the angle between the direction of flow and the direction of propagation of the ultrasonic signal.

Given that t ₁ ≈t ₂ = t ₀ , and, denoting Δt = t ₂ -t ₁ and 2⋅t ₀ = t ₁ + t ₂ , after the conversion we obtain the expression for the flow rate

where T _p = T ₂ -T ₁ ,

T _c = T ₁ + T ₂ ,

In = L + L ₀ - the geometric base of the device.

Volumetric flow rate is calculated by the formula

where D is the diameter of the flow section.

Volume V _{0 is} calculated on an accrual basis in accordance with the expression

where T _IZ is the interval between measurements.

To perform all necessary measurements and obtain flow and volume values, each measurement step includes five time intervals:

- sounding interval l ₁ - the formation of the control pulse by the shaper of the sounding signal and the sounding pulse;

- measuring interval l ₂ - measuring the propagation time of the probe signal in the primary flow transducer.

- calibration interval l ₃ - measurement of the duration of the period of the reference frequency.

- measurement processing interval l ₄ - formation of the resulting value of the measured time interval and selection of measurements.

- calculation interval l ₅ - calculation of the values of the measured parameters: flow rate and volume of the measured medium.

It should be noted that the first four measurement intervals are performed in each measurement step, while the calculation interval is added only after the second measurement step of the time intervals to calculate the gas flow rate and volume in accordance with the expressions (3), (4) and (5 )

Depending on the measurement cycle, from the first output of the shaper 12 time intervals, a control signal is received at the input switch 2, which provides the transmission / reception of signals to / from the corresponding EAP.

In each measure, the following procedures are performed:

At the beginning of the first interval (l ₁ ), a sensing trigger signal is supplied to the circuit of the probe signal generator 5 from the first output of the driver 12 time intervals, which controls the trigger and the amplitude of the probe driver, and an enable signal is supplied to the input switch 2 from the second output of the driver 12 sensing. The switched EAP is determined by the number of the working cycle in the measurement cycle. In the flow sensing cycle by the probe enable signal 12, the output of the probe signal generator 5 through the public key of the input switch 2 is connected to the electroacoustic transducer EAP1 of the primary flow transducer 1. The second EAP2 is bypassed to reduce the mutual influence of the channels. At the end of the probe start signal, the probe signal generator 5 generates a probe signal, and the coarse counter 7 starts counting the pulses of the clock generator 11. At the end of the probe signal, the probe permission signal is removed.

In the second interval (I ₂ ), the EAP2 of the primary flow converter 1 through the input switch 2 is connected to the input of the amplifier 3 through the reception permission signal received from the first output of the shaper 12 time intervals 3. The sounding signal passed through the measured medium and amplified by the amplifier 3 is fed to the amplitude time selector 4, which contains signal level control comparators. If the oscillation amplitude is exceeded in the received signal of a given threshold level, this oscillation is selected as the working pulse of the signal. The working pulse of the signal is supplied to the window comparator 6, which contains two comparators: a comparator of the upper border of the window and a comparator of the lower border of the window, and two event counters associated with them: the attenuation counter and the gain counter. When the signal amplitude goes beyond the control window, the corresponding counter counts the number of events. The signal from the comparator output of the upper window boundary is fed to the counting input of the attenuation counter and to the reset input of the gain counter. The signal from the output of the comparator of the lower boundary of the window enters the counting input of the gain meter and the reset input of the attenuation counter. The overflow signals of the counters are fed to the shaper 12 time intervals, which increases or decreases the duration of the control signal supplied to the shaper 5 of the probe signal, increasing or decreasing, thus, the amplitude of the probe signal. The presence of counters of the number of events provides amplitude control only with a steady change in the received signal and does not lead to a chaotic reaction to random signal fluctuations.

When the negative front of the working pulse passes through zero, the end of the measured time interval is fixed. When this starts the interpolation circuit 8, which measures the time interval in the range from the fixed end of the measured time interval to the front of the pulse of the reference frequency of the clock generator 11. On the same front of the pulse of the reference frequency stops the counter 7 coarse reference, the counter code 7 is fixed as the coarse reference value time interval.

On the third time interval (I ₃ ) calibration of the time interval meter is carried out, i.e. the period of the reference frequency of the clock generator is measured 11. To determine the code of the period of the reference frequency, the calibration is performed in two cycles: in the first cycle, from the third output of the shaper 12 time intervals, a calibration signal with a duration equal to (n + 1) periods of the reference cycle is supplied to the interpolation circuit 8 , in the second step - the duration of n periods (n≥1). The code period of the reference frequency K ₀ is

where K _cl1 is the code for the duration of the first calibration step,

K _cl2 is the code for the duration of the second calibration clock.

The calibration code is supplied to interpolation circuit 8 to obtain a code for the value of the interpolation part of the measured time interval in accordance with the expression

where K _IZ is the measured value of the code of the interpolation interval,

K _IN - normalized code value.

In the fourth interval (I ₄ ), the codes from the outputs of the coarse counter 7 and interpolation circuit 8 are fed to the subtraction circuit 9, where the code for the resulting value of the time interval is generated, 7) in accordance with the expression

where T ₀ - period of the frequency of the reference oscillator in μs,

N is the number of periods calculated by the coarse counter.

The value of the propagation time code through the measurement switch 14 enters the dynamic averaging unit 10, where the measured values of the propagation time are averaged with the set averaging constant.

In the multi-threshold comparator 15, codes for the deviation of the measured value from its average value in the direction determined by the signal from the second output of the time interval shaper are generated by the time interval measured value code coming from the subtraction circuit 9 and the average time interval code from the dynamic averaging block 10 .

The deviation codes for each sounding direction are compared with the specified three threshold values: upper, middle and lower.

If the upper threshold is exceeded in only one direction, which corresponds to the reception of the interfering signal, the signal from the first output of the multi-threshold comparator 15 blocks the passage of measurements through the measurement switch 14 and their further participation in the flow measurement, which ensures the noise immunity of the measurement circuit and the reliability of the measurement results.

Deviations that exceed a certain average threshold level and have a different sign from the second output of the multi-threshold comparator 15 generate control signals in the shaper of time intervals 12 to increase the measurement frequency of rapidly changing flows.

Exceeding the deviations of different signs of the lower threshold level leads to the formation of a signal from the third output of the comparator 15 into the dynamic averaging unit 10 to reduce the constant averaging of flow parameters.

An increase in the measurement frequency and a decrease in the constant averaging provide an increase in the tuning rate and an increase in the accuracy of flow measurements. With a steady flow, the deviations of the current measurements from the average value become small, below the lowest threshold level, and the meter switches to measurements with a low frequency, which significantly reduces power consumption.

In the fifth interval (I ₅ ), the calculator 13 calculates the flow characteristics in accordance with the expressions (3), (4) and (5). The operation of the calculator 13 is synchronized by the signals from the output of the shaper 12 time intervals.

The operation of the flow meter-counter is controlled by the shaper 12 time intervals. The shaper 12 time intervals for the input reference clock pulses generates the number of the time interval and the number of the cycle in the measurement cycle, as well as control signals and averaging code.

The two-channel input switch 2 contains four keys per channel: a probe enable key, a receive enable key, a probe bypass key, and a receive bypass key.

In the shaper 5 of the probing signal to generate the amplitude of the pulse exceeding the supply voltage of the circuit, energy is accumulated in the inductance when a direct current flows through it. The probe signal generator 5 comprises an energy storage choke L, a voltage doubling circuit, and a charging current switch. When the sensing start signal is applied, the energy storage throttle is connected to the voltage doubling circuit via a closed charging current switch. When the key is opened, through which the current was passed, the inductor current generates a probe pulse. The duration of the probe pulse is determined by the frequency of the resonant circuit formed by the inductance of the inductor and the capacitance of the EA, and its amplitude is determined by the duration of the current flowing through the inductance. The resonance frequency of the circuit is chosen equal to the frequency of the mechanical resonance of the EAP. The voltage doubling circuit serves to increase the efficiency of the circuit and the possibility of generating probing signals of large amplitude, several times higher than the supply voltage of the meter battery (voltage 3.0 ... 3.6 V).

The amplitude-time selector 4 includes two level comparators: a comparator of the threshold of the working oscillation and a comparator of the received signal. Comparators provide the selection of the operating oscillations from the received signal and the fixation of its temporary position to control the coarse reference circuit 7 and the interpolation circuit 8.

The interpolation circuit 8 serves to determine the exact value of the signal propagation time by measuring a part within the clock frequency period in accordance with formula (8). The beginning of the measurement interval is set by the reception fixation comparator of the amplitude-time selector 4 for the transition through zero of the trailing edge of the working pulse, and the end of the interval is set by the working front of the clock pulse. The value of the time interval is converted into a voltage value using a time-voltage converter, and then into a code by an analog-to-digital converter. To ensure that measurements are independent of the time-code conversion characteristics, the interpolation scheme on the calibration interval determines the code of the clock period.

Block 10 dynamic averaging is a drive with a variable constant accumulation. The accumulation constant is adjusted by the multi-threshold comparator 15 depending on the dynamics of the flow.

The multi-threshold comparator 15 includes a code difference calculator, upper, middle, and lower level comparators, a status register, and an analyzer, which is three schemes for matching codes of certain bits of the status register. According to the measurement results, depending on the deviation of the measured values from their average values recorded in the bits of the state register of the comparator 15, control outputs for blocks 14, 12 and 10 are generated at its outputs, which provide, respectively, the selection of reliable measurements, a change in the measurement frequency and the selection of an appropriate degree averaging.

Information sources:

1. Eurasian patent No. 014208, IPC G01F 1/66, published October 29, 2010.

2. RB patent for utility model No. 5266, IPC G01F 1/66, published June 30, 2009 (prototype).

Claims (1)

An ultrasonic gas flow meter containing a primary flow transducer with two transceiver electroacoustic transducers, an input switch, an amplifier, an amplitude-time selector, a probe signal shaper, a coarse counter, an interpolation circuit, a subtraction circuit, a dynamic averaging block, a clock generator, a time interval shaper and a calculator, the inputs / outputs of the transceiving electro-acoustic transducers of the primary flow transducer through the inputs the new switch is connected to the output of the probe of the probe signal and the input of the amplifier, the output of which is connected via the amplitude-time selector to the first inputs of the coarse counter and the interpolation circuit, the outputs of which are connected to the inputs of the subtraction circuit, in addition, the first output of the shaper of time intervals is connected to the input of the probe of the probe signal and the second input of the coarse counter, the second output is connected to the input of the switch, the third output is connected to the second input of the interpolation circuit, the fourth you One is connected to the input of the calculator, the output of which is the output of the device, and the output of the clock generator is connected to the first input of the time slot generator, the third inputs of the coarse counter and the interpolation circuit, characterized in that it further comprises a window comparator, a measurement switch and a multi-threshold comparator, the input of the window comparator is connected to the output of the amplifier, and the output is connected to the second input of the shaper time intervals, the first inputs of the measurement switch and multi-threshold about the comparator are connected to the output of the subtraction circuit, the second input of the multi-threshold comparator is connected to the output of the dynamic averaging unit, the third input of the multi-threshold comparator is connected to the second output of the time interval generator, the first output is connected to the second input of the measurement switch, the output of which is connected to the input of the dynamic averaging unit, the second the output of the multi-threshold comparator is connected to the third input of the shaper of time intervals, and the third output is connected to the second input of the dynamic unit averaging th.

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