RU2526586C2 - Controlled medium pressure measurement - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: invention relates to active nondestructive control and can be used for controlled medium pressure measurement. Proposed method comprises pressure oscillation signal measurement by transducer, conversion of signals via ADC and registration of received digital signals. Note here that signal is transmitted to ADC to generate digital signal in dimensionless units while conversion in pressure dimension is executed by two U-like pressure gages tuned to measure maximum pressure by one arm and minimum pressure by another arm. In case maximum pressure is measured check valve transmits fluid level difference towards atmosphere and suppress towards measured medium. In case minimum pressure is measured, it transmits towards measured fluid and suppresses towards atmosphere. Software of computer converts sound change digital signal into pressure in dimensionless units and dimensionless units in dimension of pressure or velocity.

EFFECT: accurate and comprehensive measurement.

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Description

The invention relates to measuring technique and active non-destructive testing and can be used to measure the pressure of a controlled environment. The developed method can be used to detect defects in the operation of energy devices operating on the basis of vibrational (pulsating, detonation) combustion of fuel used in energy and transport.

The method includes measuring the nature of the vibrational component of the pressure change over time for the energy device, allows you to work out the start-stop mode, start-up mode, long-term operation and shutdown of the power device, transient conditions when the main ones change (resonance frequency, fuel and air consumption and composition) and additional ( fuel pressure, temperature of the working medium) of the parameters of the energy device, makes it possible to register and process the measurement results, to compare frequency characteristics teristics at different points of the working device space, to evaluate the presence of defects in their work.

A known method of measuring the pressure of the medium [GOST 2405-88. Manometers, vacuum gauges, manovacuum gauges, head gauges, gravimeters and weight gauges. General specifications]. Atmospheric pressure P _atm acts on one end of a U-shaped tube, partially filled with a working fluid. The other end of the tube is connected using various kinds of supply devices to the region of the measured pressure P _meas. At P _meas > P _{atm, the} liquid located in the part of the supplied measured pressure will be displaced into the part connected to the atmosphere. As a result, between the liquid levels located in different parts of the U-shaped tube, a liquid column is formed whose height is the measured overpressure. However, this method is acceptable for determining the amplitude of the oscillation of the medium; the nature of the change in the pressure of the medium with it is impossible to determine.

A known method of measuring pressure (see RF patent 2349886, class G01L 9/08), which consists in placing a pressure sensor in the test medium, placing a temperature sensor on the pressure sensor, recording the output signals of the pressure sensor and temperature sensor. These signals determine the pressure of the medium, form mechanical vibrations in the medium under study with a frequency greater than the possible frequency of oscillations of the working pressure of the medium, and an alternating signal with the frequency of the specified mechanical vibrations is isolated from the output signal of the sensor. Using this signal and the output signals of the sensor and temperature sensor, the diagnostic functions are determined, by the deviation of which from the nominal value, the error of pressure measurement is judged.

The disadvantages of the existing method are the complexity of calibration and binding of the measurement units by the sensor to pressure units, while the sensor is not acoustically isolated from the environment, which leads to the dependence of the measurement on any noise.

The closest method to the claimed invention is a method for measuring blood pressure (see RF patent 2158107, class A61B 5/02, 2000), when the compressor pumps air into the cuff until the pressure reaches a known value greater than the maximum pressure in the patient, and then through the decompression valve begins to reduce the pressure in the cuff, during which the signals of the pressure fluctuations in the cuff from the pressure sensor enter the decision block. The microprocessor receives these signals through an analog-to-digital converter. All these signals, in addition, are recorded by a multi-channel recorder.

A disadvantage of the known system is the low noise immunity of measurements, especially in conditions of uneven and intense fluctuations in the pressure of the medium, that is, precisely when pressure measurements are of great practical interest.

When starting the boiler, internal combustion engine or their transient modes, the pressure measurement form is distorted in time, which can lead to incorrect measurement and technical conclusion about the operability of the power facility. The disadvantage is the functional insufficiency of the method, which consists in a limited range of the studied objects.

The aim of the invention is to increase the accuracy and information content of pressure measurement methods, creating the possibility of measuring and predicting the operation of the system in non-stationary conditions of vibrational combustion, assessing the presence of defects in the operation of energy devices.

The advantages of the proposed solution in comparison with analogues are as follows:

1. The ability to measure process parameters at high ambient temperatures in the heat-stressed zone of the energy device (over 700 ° C).

2. The acoustic isolation of the conversion system of the mechanical signal into analog, which increases the measurement accuracy at the lowest pressure amplitudes and reduces the measurement time.

3. When testing an energy device for analysis, not only the values of the maximum, average and minimum pressure of the working medium are displayed, but also the dynamics of the pressure change over a specified period of time, which allows us to evaluate the reliability of the measurement in the presence of any errors and, in cases where interference led to an erroneous measurement, do not take into account the obtained values; to reconfigure the amplitude of the oscillations for the obtained pressure change curve without changing the overall picture of the process (if the amplitude is adjusted to the required value); evaluate the relationship of oscillations at various points in the working path of the energy device; evaluate the influence of secondary parameters of the working process on the pressure in the combustion chamber of the device (for example, the influence of the configuration of the working space).

This goal is achieved by the fact that the pressure of the medium at least one measuring point along the impulse tube is perceived by a mechanical-electric transducer located in a thermally sound-insulated acoustic capacitance, in which mechanical vibration is converted into an electrical signal by an electronic circuit consisting of an emf and a resistance source, while the signal is transmitted to an analog-to-digital conversion device, where a digital signal is generated in dimensionless units, the translation of which exists with the help of two U-shaped pressure gauges configured so that one of them measures the maximum pressure, and the second - the minimum, while the check valve in the case of measuring the maximum pressure passes the difference in liquid levels towards the atmosphere and blocks towards the medium being measured; in the case of measuring the minimum pressure - passes in the direction of the measured liquid and blocks in the direction of the atmosphere; using the software environment of the computer computing unit, the digital signal of sound change to pressure is converted in dimensionless units, as well as the conversion from dimensionless units to pressure dimensions is used to measure and predict the operation of the energy system under unsteady conditions of vibration combustion, to assess the presence of defects in the operation of energy devices.

For clarity, figure 1 shows a diagram of a pressure measurement, figure 2 shows the results of the study using the proposed method and comparison with a known method of measuring pressure.

Figure 1 schematically shows a measuring device consisting of a heat and sound insulated housing 1, in which an acoustic container 2 is placed, a pulse tube 3 connected at one end to an acoustic capacity, and thermal and sound insulation 4 filling the free space of the housing 1. A mechanical container is placed in the acoustic container 2 an electric converter, in particular a carbon microphone 5, included in an electric circuit consisting of an emf source 6 and a resistance 7. The signal output is connected by an analog-to-digital conversion device and registration 8.

The scheme for measuring the nature of pressure fluctuations consists of an attached pulse tube 3 to the measurement object 9, a contact tube 10 installed in the sleeve 11 and fixed in it using heat and sound insulating material 12.

The oscillation amplitude measuring circuit consists of two U-shaped pressure gauges 13 for measuring the pressure of the medium, connected by a pulse tube 3 with a non-return valve 14, installed so that to measure the minimum pressure P _min it is placed in the direction of the pressure gauge 13, and to measure the maximum pressure P _max placed in the opposite direction. Here P _meas - the measured pressure of the medium, P _at - atmospheric pressure.

A device for implementing the proposed method works as follows. Depending on the test task, at least one measurement point is selected at which the pressure of the medium will be measured. In the measurement object 9, a sleeve 11 is preliminarily arranged, in which the contact tube 10 is fixed. In order to avoid thermal and noise impacts on the measurement system, heat and sound insulating material 12. The contact tube 10 is connected on one side to the pulse tube 3 and the other is placed in the measurement object 9 so way to interact with the environment. Calibration of a system for measuring the amplitude of pressure fluctuations is performed using standard methods and instrumentation (not shown conditionally).

When the measurement object 9 is operating, the pressure of the medium through the impulse tube 3 is perceived by the mechanical-electric converter 5, while external environmental noise is suppressed by thermal and sound insulation 4. In the converter 5, the received sound signal is converted by an electric circuit consisting of an EMF source 6 and resistance 7 to an analog one a signal transmitted to an analog-to-digital conversion device 8, in particular a PC sound card, where a digital signal is generated, which is, in particular, a periodic process from changes in sound in dimensionless units over time.

The measurement of the amplitude of the pressure fluctuations using two U-shaped pressure gauges 13, configured so that one of them is configured to measure the maximum pressure, and the second to measure the minimum. The pressure of the medium is transmitted through the impulse tube 3 to the working fluid of the pressure gauge 13, which is exposed to atmospheric pressure from the side of its open part, causing the fluid level to change depending on whether the pressure is higher, measured or atmospheric. Valve 14 in the case of measuring the maximum pressure passes the differential level of the liquid in the direction of the atmosphere and blocks in the direction of the medium being measured; in the case of measuring the minimum pressure - vice versa: it passes towards the measured liquid and blocks towards the atmosphere.

Using software environments of a computer computing unit (not shown conditionally), the digital signal of the sound change into pressure is converted in dimensionless units, as well as the conversion from dimensionless units to pressure dimensions.

By processing the data of the analog-to-digital conversion device 8 and the pressure gauges 13 on a computer, it is possible to obtain the frequency-pulse nature of the propagation of thermoacoustic oscillations in P-τ coordinates.

For example, the known formula [Knorre, G.F. Theory of furnace processes / G.F.Knorre, K.M. Arefiev, A.G. Bloch. - M .: Energia, 1966. - 491 pp., Ill.] For the transfer function, which is the ratio of pressure fluctuations P at the inlet and outlet of the channel both along its length along the x coordinate and in time along the τ coordinate. This is a complex function that depends on the phase velocity ω of the propagation of pressure waves and the damping coefficient k.

$$p\left(x,\tau \right)=-c_z\rho \Delta P_{\upsilon }\cos \left(\omega \tau +\frac{\pi }{2}\right)e^{\omega kx}.\left(\mathrm{one}\right)$$

Here, to characterize the wave periodic process, a general trigonometric harmonic function is introduced, where ΔP _υ is the pressure change during thermoacoustic oscillations of the medium. To determine the magnitude of the pressure change during thermoacoustic vibrations of the medium (as a result of vibrational combustion), one can use the rad of the following equations (2) - (5), where c _z is the speed of sound in the medium under consideration, ρ is the density of the medium.

The speed of sound in the test medium (in m / s) is determined by equation (2):

$$c_z=\sqrt{\frac{\gamma \cdot R\cdot T_g}{M}},\left(2\right)$$

where γ is the adiabatic index of the medium;

R is the universal gas constant;

T _g is the temperature of the medium;

M is the molar mass of the medium.

The increase in pressure from the sound wave (in Pa) can be determined based on equation (3):

$$\Delta P_z=9800\left(\rho \cdot c_z\cdot {\tau }_g\right),\left(3\right)$$

where τ _g is the cycle time.

The velocity of the medium in the sound wave (in m / s) is determined as follows:

$$\upsilon =\frac{\Delta P_z}{\rho \cdot c_z}.\left(\mathrm{four}\right)$$

The increase in medium pressure (in Pa) can be calculated by equation (5):

$$\Delta P_{\upsilon }=9800\left(\rho \cdot \upsilon \cdot {\tau }_g\right),\left(5\right)$$

The velocity of the medium (in m / s) can be determined from the relation (6):

$$\upsilon \left(x,\tau \right)=\upsilon \sin \left(\omega \tau \right)e^{\omega kx}.\left(6\right)$$

An example of the implementation of the proposed method is given for studying the frequency-pulse nature of the propagation of thermoacoustic oscillations in an operating pulsed combustion boiler of the PV type based on the Helmholtz resonator under the following conditions:

1. The pressure in the gas pipe is 102 kPa;

2. Pressure in the air pipe - 100 kPa (atmospheric pressure);

3. Fuel consumption - 3 6 m ³ / h;

4. The water temperature at the inlet to the boiler is 44 ° C;

5. The temperature of the water leaving the boiler is 50 ° C;

6. The coefficient of excess air - 1.25;

7. The resonant frequency is 33 Hz;

8. The flue gas adiabat index γ is 1.4.

Research was carried out in three stages.

1. Obtaining an analog signal with its conversion to digital using a sound computer editor.

2. Mathematical processing of an audio signal in a batch process.

3. Determination of the amplitudes of the oscillations.

At the first stage, using the SOUND RECORDING program built into Windows, an audio signal was received from the signal converter of the 5-sided microphone and recorded as a file with the * .wav extension. Preparation for mathematical processing of the sound file was made using the sound program Sound Forge 4.5. Mathematical processing of the sound file was performed using the MathCAD 11 Enterprise Edition program and the additional Signal Processing package, designed to process audio signals. The signal was read from the sound file, obtaining complete information about it, and plotting the original signal graph. Further, to switch from voltage dimensions to pressure dimensions, the signal was calibrated using a U-shaped pressure gauge.

For comparison, the data on the pressure amplitude are correlated with the results of similar experiments by Korean researchers [Keel, S.I. A Study of the Operating Characteristics of a Helmholtz-type Pulsating Combustor / S.I. Keel, Hyun Dong Shin // Institute of Energy. V. 64, 99. -1991] for the Helmholtz chamber with an aerodynamic valve - PCS (Pulsating Combustion System). The results of two experiments are tabulated.

Table Value PCS PV-400 Maximum amplitude, kPa 113.8 111.1 Minimum amplitude, kPa 93.1 91.5

Figure 2 presents the results of studies of frequency characteristics by the method [Keel, S.I. A Study of the Operating Characteristics of a Helmholtz-type Pulsating Combustor / S.I. Keel, Hyun Dong Shin // Institute of Energy. V. 64, 99. - 1991] and the proposed method. Here, poses A.I and A.2 are fragments of pressure fluctuations in the PCS and PV-400 boiler, respectively, B.1 and B.2 are one cycle of the vibrational combustion process of the PCS and PV-400 boiler, respectively. Due to the fact that the studies were carried out on two boilers of the same principle of operation by different methods of measuring pressure, it is clear that the data obtained by the first method carry large noise interference, which is reflected in the processing of each cycle of the periodic process of pressure fluctuation. These interferences affect both the magnitudes of the pressure fluctuation amplitudes and the nature of the pressure change over time, and the measurement error will affect the test result of the boiler and subsequent measures to increase its efficiency.

Based on the results of an experimental study using this method, the process of changing the pressure in the path of the pulsating combustion boiler has become possible to present in the form of a diagram with a description of the processes occurring in this case (Fig. 2). Here: AB — pressure increase in the process of combustion of a fuel-air mixture; VA - the process of cooling flue gases; C-F - the process of natural gas intake through a gas pulsating valve; D-E - the process of air intake through an air-pulsating valve; AA - time 1 cycle (determined by the acoustic properties of the resonator).

Claims (2)

1. A method of measuring the pressure of a controlled medium, including measuring signals of pressure fluctuations in the object of study by means of a sensor, converting signals through an analog-to-digital converter and registering the received digital signals, characterized in that the pressure of the medium at least at one point of measurement through the impulse tube is perceived mechanically -electric transducer located in a heat and sound insulated acoustic container in which mechanical vibration is converted into an electrical signal an electronic circuit consisting of a source of EMF and resistance, the signal is transmitted to an analog-to-digital conversion device, where a digital signal is generated in dimensionless units, whose pressure dimension is converted using two U-shaped pressure gauges configured so that one of them measures the maximum pressure, and the second - the minimum, while the check valve in the case of measuring the maximum pressure passes the differential level of the liquid toward the atmosphere and blocks towards the medium being measured; in the case of measuring the minimum pressure - passes in the direction of the measured liquid and blocks in the direction of the atmosphere; using the software environments of the computing unit of the computer, the digital signal of the sound change into pressure is converted in dimensionless units, as well as the conversion from dimensionless units to pressure dimensions is based on the rule:

,
τ is the cycle time;
c is the speed of sound;
ρ is the density of the medium;
P is the pressure;
ω is the phase velocity;
k is the attenuation coefficient. 2. The method according to claim 1, characterized in that the computing unit is configured to determine the speed of the medium based on the rule:
υ (x, τ) = υ sin (ωτ) e ^ωkx ,
υ is the speed of movement in the sound wave.

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