RU2180435C2 - Method determining parameters of vibrations of rotating rotor - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: invention refers to determination of parameters of vibrations of rotating rotor of predominantly high-speed centrifuge, parameters of centrifuge and defects in its units. In correspondence with method frequency, amplitude and form of vibrations are found from frequency spectrum of transmitter, for instance, speed transmitter by values of side bands caused by modulation of basic signal with frequency of vibrations of rotor. Method is characterized by simplified technology of determination of amplitudes and form of vibrations of rotor of centrifuge. EFFECT: increased measurement sensitivity. 2 cl, 3 cl

Description

 The invention relates to the field of technology for measuring oscillations of a rotating rotor (precession, axial, etc.).

 When the rotor rotates, its regular vibrations can occur, which in some cases lead to damage to the machines. The appearance of fluctuations can reflect both certain operating modes and defects of individual nodes. In this regard, especially in high-speed centrifuges, there is a need to register rotor vibrations.

 This problem can be solved by installing special displacement sensors, vibrations [1]. Typically, the parameters of the centrifuges are chosen such that in the operating range of the operating parameters, the oscillations with the rotational speed caused by the imbalance are minimal and other vibrations are absent, and there is no need for continuous monitoring in these centrifuges. Therefore, the installation of separate sensors on such centrifuges, leading to additional costs, is impractical. In addition, the design of the sensors can be quite complicated due to the need to work in aggressive environments, vacuum, at elevated temperatures, etc.

 The closest technical solution to the proposed one is the solution [2]. According to this decision, at least one vibration sensor is installed in the centrifuge, and it is considered advantageous to install the sensor outside the working chamber, i.e., on the housing. During centrifuge operation, a frequency analysis of the signal of this sensor is carried out. The spectrum of the signal of the vibration sensor will contain harmonics with the rotational speed and frequencies of other vibrations of the centrifuge. Separate harmonic vibrations are isolated from the spectrum and the intensity (amplitude) of the centrifuge vibrations is determined from them.

 The technical solution [2] has several disadvantages. Firstly, it is necessary to install an additional vibration sensor, which leads to additional costs. Secondly, only harmonics with frequencies of selected harmonic oscillations are considered in the spectrum, which does not allow determining the type of oscillations and in most cases has low sensitivity. Thirdly, the sensor is located practically outside the working chamber and captures the vibrations of the housing transmitted to it by the rotor through the supports. In this case, the amplitudes of the harmonics with the oscillation frequencies, although it is related to the intensity of the rotor vibrations, however, this relationship is significantly affected by the support, the state of which can change during operation.

 If the vibration sensor is optional, then practically every centrifuge has a rotation speed sensor. The most widely used are pulsed tachometers of angular velocity, the basis of which are various proximity sensors or optical sensors [1]. For the operation of these sensors, it is required that one or more marks with sharp changes in magnetic or optical properties be in motion on a rotating body. Most of the real designs of such sensors are sensitive to changes in the distance between their rotating and stationary parts, which leads to the appearance of modulation of the main sensor signal, the frequency of which is determined by the speed of rotation and the number of marks. In the presence of rotor oscillations, the signal is modulated by the oscillation frequency, and the modulation level is related to the oscillation amplitude.

 It is known that in the spectrum of a signal modulated in amplitude or phase, symmetrical sidebands are present at the distances of the modulating frequency near the fundamental frequency, while the amplitude-phase modulation with the same frequency is accompanied by the symmetry of the sidebands [3].

 The technical problem solved by the claimed invention is to simplify the technology for determining the amplitudes and type of vibrations of the centrifuge rotor while increasing the sensitivity of the measurements.

The problem is solved in that in the known method for determining the frequency and intensity of oscillations of a centrifuge, which includes receiving a signal from an oscillation sensor and a frequency spectral analysis of this signal to determine the intensity of oscillations, the frequency components associated with amplitude and phase modulation having different character for different types of oscillations of the rotor, by measuring the amplitudes of the fundamental harmonic with frequency Ω and side bands with frequencies Ω- ω _i , Ω + ω _i (left, right side bands), where ω _i is the frequency of the i-th mode of oscillation.

 The levels and nature of the modulation depend on the types and designs of sensors, but in all cases, side bands that are uniquely associated with vibration parameters will be observed in the spectra near the fundamental frequency, and this relationship can be established experimentally or theoretically from considering the motion pattern of the vibrating rotating part of the rotor relative to the non-rotating sensor.

где А_В - амплитуда осевых колебаний; С - определяемая конструкцией датчика постоянная; U₁ - значение первой пары боковых полос; М_В - коэффициент амплитудной модуляции при осевом смещении; U₀ - значение основной гармоники,
- для круговых движений

где А_к - амплитуда прецессионных движений; U_п, U_л - значение правой и левой пары боковых полос; М_к, К_к - коэффициенты амплитудной и фазовой модуляций при радиальном смещении.For electromagnetic sensors with variable magnetic resistance of the type shown in figure 1, when a variable electromotive force is created in the coil 1 due to the rotation of the inductor 2 connected to the rotor in the field of the permanent magnet 3, in the case of axial vibrations, the amplitudes of the left and right side bands are equal to in the case of circular (precession) movements - significantly different. Depending on which of the side bands in the pair (right or left) is greater, the direction of precession movements is determined. At large amplitudes of oscillations, several pairs of side bands are observed. The amplitude of the rotor, within the linear dependence of the modulation levels on the amplitude of the oscillations, is determined by:
- for axial vibrations

where And _In - the amplitude of the axial vibrations; C is a constant determined by the design of the sensor; U ₁ - the value of the first pair of side bands; M _B is the coefficient of amplitude modulation at axial displacement; U ₀ - the value of the fundamental harmonic,
- for circular movements

where And _to - the amplitude of the precession movements; U _p , U _l - the value of the right and left pair of side bands; M _to , To _to - the coefficients of the amplitude and phase modulations at a radial displacement.

Figure 2 shows the signal spectrum of the speed sensor of a centrifuge with a rotor that performs axial vibrations and precession movements in the direction of its rotation. The presence of vertical vibrations is seen from a pair of side strips with the same amplitudes U ₁ , and the presence of precession in the direction of rotation of the rotor is seen from a pair of side strips with amplitudes U _p , U _l , where U _p > U _l .

Figure 3 shows the signal spectrum of the speed sensor of a centrifuge with a rotor performing precession movements. The presence of phase modulation leads to the fact that in spectra of the type of FIG. 3, the amplitude of at least one band in the first pair of side bands U _p or U _{l is} greater than the harmonic amplitude U _ω with an oscillation frequency ω. In the case of Fig. 3, where the amplitudes of the harmonics are shown on a logarithmic scale and the value of U _{ω is} indicated by a dashed line, U _{p is} greater than U _{ω by} ~ 8 times, which indicates the same increase in the sensitivity of the proposed method.

 Thus, by considering the centrifuge sensors in the signal spectrum, for example speed sensors, caused by the modulation of the signal with the oscillation frequency of the sideband centrifuge near the fundamental, the technology for determining the amplitudes of the centrifuge oscillations improves, and it becomes possible to determine the type of oscillations while increasing the measurement sensitivity.

Sources of information
1. J. Ash. Sensors of measuring systems. M.: Mir, 1992.

 2. The patent of Germany N 4327291, CL B 04 B 11/04, 1993.

 3. A. Ango. Mathematics for electrical and radio engineers. M .: Nauka, 1965.

Claims (3)

1. The method of determining the oscillation parameters of a rotating centrifuge rotor from the frequency spectrum of a sensor signal, for example a rotation speed sensor, characterized in that the spectrum of the sensor signal measures the harmonics amplitudes with a fundamental frequency Ω and side bands with frequencies Ω-n • ω _i , Ω + n • ω _i , where ω _i is the frequency of the ith oscillation mode, n is a positive integer, in relation to the harmonics amplitudes with frequencies Ω-n • ω _i , Ω + n • ω _i identify the oscillation mode and calculate the same harmonics amplitudes the amplitude of the rotor. 2. The method according to p. 1, characterized in that for the electromagnetic type sensors, when a variable electromotive force is created in the coil due to the rotation of the inductor connected to the rotor in a magnetic field, a signal spectrum is obtained, the sideband values are measured, and if the values in each pair are equal side bands identify the oscillations as axial, calculate the amplitude, according to the formula

where A _B is the amplitude of the axial vibrations of the rotor;
C is a constant determined by the design of the sensor;
U ₁ - the amplitude of the harmonics in the first pair of side bands;
M _B - coefficient of amplitude modulation with axial displacement of the rotor;
U ₀ - the value of the main multiple of the rotor speed, harmonic. 3. The method according to p. 1, characterized in that for the electromagnetic type sensors, when an alternating electromotive force is created in the coil due to rotation of the inductor connected to the rotor in a magnetic field, a signal spectrum is obtained, the amplitudes of the side bands are measured and, with significant differences in the amplitudes of the left and the right components in the pairs of side strips identify the oscillations as precession movements in the direction coinciding or opposite to the direction of rotation of the rotor, and calculate the amplitude of the oscillations of the rotor according to the formula

where A _K is the amplitude of the precession movements of the rotor;
U _P , U _L - the amplitudes of the right and left harmonics in the first pair of side bands;
M _K , K _K are the coefficients of the amplitude and phase modulations with a radial displacement of the rotor;
U ₀ - the amplitude of the main multiple of the rotor speed, harmonic.

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