FI95837C - Procedure for measuring vibration - Google Patents

Description

95837

METHOD OF MEASUREMENT OF VIBRATIONS FÖRFARANDE FÖR MÄTNING AV VTBRATIONEN

The present invention relates to a method for measuring oscillations, in which the signal from the sensor is processed, derivatized and integrated with respect to time using electrical or mechanical devices. The purpose is to form a weighted sum of the rms values of generalized time derivatives of different degrees and generalized time integrals when their degree is different from the integer, i.e., conventional time derivatives and time integrals are excluded.

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Traditionally, measurements of oscillations have been limited to x, x, x, i.e. the use of rms or maximum values of displacement speed and acceleration [1]. Acceleration time derivative x'has been used to study a better signal-to-noise ratio [2]. A method is also known [3] weighted rms values, which also include the first time derivative of the acceleration, the weighted rms values of the conventional time derivatives x 1 of the higher-degree displacement, where n is an integer, and the weighted rms values obtained by integrating the displacement induced by the desired times is an integer, that is, it is a normal integration. In addition, the patent application [4] discloses a method in which the signal is also formed into weighted maximum values of a time derivative of any degree different from the transition, velocity, acceleration or its first time derivative, and weighted maximum values obtained by a time integral of any degree.

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A disadvantage of the known rms measurements is that they lead to a completely erroneous result when measurements have to be made in frequency ranges where the permissible vibration levels [5] of the machines are not constant for any conventional 2 95837 time derivative or any conventional time integral. The scope of application of maximum value measurements, in turn, is limited to the measurement of impact phenomena, which leads to erroneous results when assessing the condition of machines in the case of harmonic or random oscillations. The new solution to this problem is characterized by what appears from the characterizing part of claim 5.

The invention will now be described in detail with reference to the figures, in which

Figure 1 shows some of the vibration intensity evaluation curves used in industry [5], 1, 2, 3, 4 are the displacement curves, 5, 6, 7, 8 are the speed curves and 9, 10, 11, 12 are the acceleration intensity evaluation curves, where the intensity of the oscillation is on the vertical axis and the frequency is on the horizontal axis.

Fig. 2 13 shows a sensor from which the signal is fed to a measuring device 14 which performs signal processing.

3 4 (4 5129421

Fig. 3 15 shows an xv ′ ′ curve plotted on a logantine scale between 4 x 10 Hz and 10 Hz, corresponding to a part of the curve 12 according to Fig. 1 in said frequency range.

This part of the curve is marked 16.

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The method according to the invention is based on the realization that although none of the conventional time derivatives or time integrals of a transition is constant in a frequency range, one of the generalized time derivatives or generalized time integrals of the transition may still be constant in that frequency range. Using this information, the evaluation of the vibration intensity 25 is decisively facilitated and at the same time, as will be readily appreciated by one skilled in the art, simple rms measurements can be applied to evaluate the vibration intensity.

The component x / ° ^ of the spectrum of the generalized derivative x ^ is obtained from the expression «

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3 95837 x, (a) = (2πίί) αχ ,, (1) where χ, is the i-th component of the transition spectrum, fj is its frequency and the real number a> 0. Correspondingly, the spectral component x / a of the generalized time integral x ^ a is obtained from 5

Ia, ^ xi = (Γ-r) xi. (2)

The fact that the transition spectrum was used as a starting point above is by no means a limiting factor. In principle, it would have been equally possible to start from the signals given by the speed or acceleration sensor, in which case the starting point would have been the speed or acceleration spectrum, respectively.

10 The rms values of generalized time derivatives or generalized time integrals can be determined, either directly using analog circuits or with the aid of frequency analysis. The following is a review of the principles of the invention in the light of a practical example.

If it is desired to make acceleration measurements according to curve 12 in Figure 1 in the frequency range 3 4 2 15 4 x 10 Hz - 10 Hz, then it is observed that the acceleration values in G (= 9.80665 m / s) that are allowed decrease by 1 G -> 10 "1 G i.e. one to one tenth, and the acceleration levels at different frequencies are not equivalent in terms of the degree of hazard in the frequency range 3 3 in question. Thus, the value of 3 4 (4) (5) 20 jerks according to curve 12 is not constant between 4 x 10 Hz and 10 Hz, and the corresponding situation is at x and x.

If the generalized derivative x ^ = χ (4 · 512942) ^ is used, then its values remain constant 3 4 in the whole frequency range 4x10 Hz - 10 Hz, when the acceleration values decrease according to the curve 12 4 95837 G -> 0.1 G. This can be seen from the following calculations, x ^ = χ (4512942) ^ oa 1.119613773 x 1012 m / s corresponding to the acceleration values in vertical row A calculated at 500 Hz intervals and fully consistent with the acceleration values in vertical row B as determined analytically by curve 12.

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A B

Hz 1012 m / s m / s2 m / s2 4000 1.119613773 9.80665 9.80665 4500 "7.294195 7.294195 10 5000” 5.59747 5.59747 5500 ”4.40529 4.40529 6000” 3.54008 3.54008 6500 ”2.89507 2.89507 7000” 2.40315 2.40315 15 7500 ”2.040 ”1.47532 1.47532 9000” 1.27793 1.27793 9500 ”1.11558 1.11558 20 10000” 0.980665 0.980665 (4 512942)

Figure 3 shows an x-curve, i.e. curve 15, and a part of curve 12 3 4 according to Figure 1, i.e. curve 16, between 4x10 Hz and 10 Hz using a logarithmic scale. Faults; · For hazards, curves 15 and 16 contain the same information. A significant advantage of the curve 15 at 15 is that its values do not depend on the frequency, whereby the interpretation of the intensity of the oscillations is decisively facilitated and simple measurements of the rms value of χ (4.512942) ^ can be used. In an analogous way, the need for χΙα can be demonstrated when estimating the intensity of the oscillation.

li 95837 s

When the sum of the weighted rms values of the transition time derivatives x 1 and the transition time integrals χΙα, where a can be any positive non-integer real value, is formed, one numerical value is obtained that can be used to estimate the condition of machines in the frequency ranges with any of the conventional the time integrals are not constant with respect to the degree of hazard of the faults, but are so with respect to the generalized time derivatives x ^ and the generalized time integrals x ^ a. Weighting factors can be determined experimentally or by calculation. They make the rms values obtained with different measurement parameters more common in terms of the degree of hazard of the faults.

95837 6

REFERENCE PUBLICATIONS - ANFÖRDA PUBLIKATIONER

1. LAHDELMA S., Methods and measuring devices for vibration monitoring. Helsinki 1988. Insi-nöörijäijestojen Koulutukeskus, Publication 83-88, Systematic use and condition monitoring. 7 s.

2. SMITH, J.D., Vibration monitoring of bearings at low speeds. Tribology international 15 (June 1982) 3, pp. 139-144.

3. Pat. SF. 91327. Method for measuring the intensity of vibrations. Insinööritoimisto Mitsol Oy, Finland. (Sulo Lahdelma). App. 922395, 26.05.1992. (28.02.1994). 15 p.

4. Patent Application No. 944590.

5. BOYCE, MP., How to achieve online availability of centrifugal compressors. Chemical Engineering 85 (June 5 1978) 13, pp. 115-127.

6. VDI2056 Inurteilungsmasstäbe fur mechanische Schwingungen von Maschinen. VDI-RICHTLINEN, October 1964. 12 p.

7. ISO 2372 Mechanical vibration of machines with operating speeds from 10 to 200 rev / s-Basis for specifying evalution standards. International Standard, First edition-1974-11-01.

9 s.

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Claims (1)

95837 CLAIMS A method for measuring oscillations, in which a signal from a sensor (13) is processed, derivatized and integrated with time using electrical (14) or mechanical devices to obtain weighted rms values of varying degrees, characterized in that the signal is transformed into , with a degree different from the integer, weighted rms values. • «95837 For the purpose of vibration, for which the signal is provided by a commercial device (13) without the use of a single derivative and with an integral part of the electronic (M) or mechanical apparatus for a stand-by type of effect , känne-t ecknat därav, att av signalen bildas viktade efFektvärden av förskjutningens allmänna tidsderivator och av förskjutninges allmänna tidsintegraler, vilkas grad är olik än et heltat. 1 11 ·