ANALYSIS SYSTEM

• US 20110301872A1
• Filed: 12/22/2009
• Published: 12/08/2011
• Est. Priority Date: 12/22/2008
• Status: Active Grant

• Current Assignee: S.P.M. Instrument AB
• Original Assignee: S.P.M. Instrument AB
• Inventors: Hedin, Lars-Olov Elis
• Granted Patent: US 9,304,033 B2
• Time in Patent Office: Days
• US Class Current: 702/34
• CPC Class Codes: G01H 1/003 of rotating machines G01H1/10 takes precedence
• CPC Class Codes: G01M 13/021 Gearings
• CPC Class Codes: G01M 13/028 Acoustic or vibration analysis
• CPC Class Codes: G01M 13/045 Acoustic or vibration analysis

Abstract

Method for analyzing the condition of a machine having a slowly rotating part, includes:

• • rotating a rotatable part at a rotational speed of less than 50 rpm;
  • generating an analogue electric measurement signal dependent on mechanical vibrations emanating from rotation of a shaft using a sensor having mechanical characteristics causing it to resonate at a certain resonance frequency;
  • sampling the analogue measurement signal at a sampling frequency to generate a digital measurement data sequence in response to the received analogue measurement data;
  • digitally filtering the digital measurement data sequence to obtain a filtered measurement signal and achieve a signal having a bandwidth between an upper and a lower frequency which is lower than the certain resonance frequency and the upper frequency being higher than the certain resonance frequency;
  • generating a digitally enveloped signal in response to the filtered measurement signal by digitally rectifying the filtered measurement signal, and by digital low pass filtering of the rectified filtered measurement signal to generate the digitally enveloped signal;
  • performing a condition analysis function for analysing the condition of the machine dependent on the digitally enveloped signal.

Claims

1. An apparatus for analysing the condition of a machine having a first part which is rotationally movable at a speed of rotation in relation to a second machine part;

said apparatus including;

a Shock Pulse Measurement sensor for monitoring said movable part so as to generate at least one analogue measurement signal including at least one vibration signal component dependent on a vibration movement of said rotationally movable part;

wherein said vibration signal component has a repetition frequency (f_D) which depends on the speed of rotation (f_ROT) of said first part;

said measurement signal including noise as well as said vibration signal component so that said measurement signal has a first signal-to-noise ratio value in respect of said vibration signal component;

an A/D-converter (40,44) for generating a digital measurement data sequence (S_MD) in response to said measurement signal;

said digital measurement data sequence (S_MD) having a first sample rate (f_S);

a first digital filter (240) for performing digital filtering of the digital measurement data sequence (S_MD) so as to obtain a filtered measurement signal (S_F);

an envelopper for generating a first digital signal (S_ENV, S_MDP) in response to the filtered measurement signal (S_F);

a decimator for performing a decimation of the first digital signal (S_ENV, S_MDP) so as to achieve a decimated digital signal (S_RED) having a reduced sampling frequency (f_SR1, f_SR2);

said decimator (470, 470A, 470B) having

a first input for receiving said first digital signal (S_ENV, S_MDP); and

a second input for receiving a signal indicative of said variable speed of rotation (f_ROT);

a third input for receiving a signal indicative of an output sample rate setting signal;

said decimator (470, 470A, 470B) being adapted to generate said decimated digital signal (S_RED) in dependence on

said first digital signal (S_MD, S_ENV),

said signal indicative of said speed of rotation (f_ROT), and

said signal indicative of an output sample rate setting signal;

wherein said decimator (470, 470A, 470B) is adapted to generate said decimated digital signal (S_RED) such that the number of sample values per revolution of said rotating part is kept at a substantially constant value when said speed of rotation varies; and

an enhancer (320) having an input for receiving said decimated digital signal (S_RED);

said enhancer being adapted to produce an output signal sequence (O) having repetitive signal components corresponding to said at least one vibration signal component so that said output signal sequence (O) has a second signal-to-noise ratio value in respect of said vibration signal component;

said second signal-to-noise ratio value being higher than said first signal-to-noise ratio value; and

an analyzer (105;

290;

290T;

294, 290F) for indicating a machine condition dependent on said vibration movement of said rotationally movable part in response to said output signal sequence (O).

2. The apparatus according to claim 1, wherein

Said first digital filter (240) is a high pass filter having a cut-off frequency.

3. The apparatus according to claim 2, wherein

Said Shock Pulse Measurement sensor (10) is resonant having a mechanical resonance frequency value (f_RMU);

the cut-off frequency f_LC of the high pass filter 240 is selected to a value lower than the mechanical resonance frequency value (f_RMU) of the resonant Shock Pulse Measurement sensor (10).

4. The apparatus according to claim 1, wherein

the enveloper (250) comprises a digital rectifier (270), and wherein

said decimator (310) is coupled to receive the signal to be decimated from an output of said rectifier (270);

and wherein

said decimator (310) which includes low pass filtering.

5. The apparatus according to claim 1, wherein

the decimator includes an integer decimator (310) adapted to perform decimation by an integer M;

wherein

the value M is automatically set in dependence on said speed of rotation (f_ROT);

6. The apparatus according to claim 1, wherein

the integer decimator includes plural Low Pass Finite Impulse Response Filters.

7. The apparatus according to claim 1, wherein

each FIR Filter is settable to a desired degree of decimation.

8. The apparatus according to claim 1, wherein

the integer decimator includes a bank of different FIR filters such that plural filters among said bank of filters may be combined to achieve a desired total decimation M.

9. The apparatus according to claim 1, wherein

the bank of FIR filters includes more than three filters.

10. The apparatus according to claim 1, wherein

An output (312) of said integer Decimator (310) is coupled to an input of a fractional decimator (470) and to a terminal of a selector (460);

said selector having another terminal;

said another terminal being coupled to an output of said fractional decimator (470); and

a third terminal of said selector (460) being coupled to the input of said enhancer (320).

11. The apparatus according to claim 1, further comprising a parameter controller (930);

said parameter controller being adapted to cooperate with a user interface (102, 104, 106) for setting control parameters of said apparatus so as to adapt functionality (94, 310, 470, 320, 294) dependent on user input via said interface;

wherein said apparatus is adapted to request setting information via said user interface (102, 104, 106).

12. The apparatus according to claim 11, wherein

said requested information includes information indicative of a frequency range to be monitored for detection of said signature (S_D) having said repetition frequency (f_D).

13. The apparatus according to claim 11, wherein

said requested information includes information indicative of a highest repetition frequency (f_D) of interest.

14. The apparatus according to claim 11, wherein

said requested information includes information indicative of a desired degree of improvement of the second signal-to-noise ratio value.

15. The apparatus according to claim 11, wherein

said requested information includes information indicative of a desired frequency resolution for a Fast Fourier Transform.

16. The apparatus according to claim 11, wherein

said requested information includes information indicative of a setting to have the arrangement (920) keep repeating the measurement with a certain repetition period (T_PM).

17. The apparatus according to claim 11, wherein

the arrangement (920) is adapted to provide a warning indication via the user interface (102,106) if the user entered repetition period value (T_PM) is shorter or about the same as the expected duration of measurements (T_M)

18. A method for analysing the condition of a machine having a slowly rotating part, comprising:

rotating a rotatable part at a rotational speed (f_ROT) of less than 50 revolutions per minute;

generating an analogue electric measurement signal (S_EA) dependent on mechanical vibrations emanating from rotation of said shaft using a sensor having mechanical characteristics causing it to resonate at a certain resonance frequency (f_R);

sampling said analogue measurement signal at a sampling frequency (f_S) so as to generate a digital measurement data sequence (S_MD) in response to said received analogue measurement data;

performing digital filtering (240) of the digital measurement data sequence (S_MD) so as to obtain a filtered measurement signal (S_PBMD) so as to achieve a signal having a bandwidth between an upper and a lower frequency;

said lower frequency (f_LC) being lower than the certain resonance frequency (f_R) and said upper frequency (f_UC) being higher than the certain resonance frequency (f_R);

generating a digitally enveloped signal (S_ENV, S_MDP) in response to the filtered measurement signal (S_PBMD) by digitally rectifying said filtered measurement signal, and by digital low pass filtering of the rectified filtered measurement signal so as to generate said digitally enveloped signal (S_ENV, S_MDP);

performing a condition analysis function (F1, F2, Fn) for analysing the condition of the machine dependent on said digitally enveloped signal (S_ENV, S_MDP).

19. The method according to claim 18, wherein

said sampling frequency (f_S) is controlled to depend on the rotational speed (f_ROT) of said rotating a shaft so that the number of samples per revolution of the rotating shaft is substantially independent of shaft speed variations.

20. A computer program for causing a computer to analyse the condition of a machine having a slowly rotating part, the computer program comprising:

computer readable code means which, when run on a computer, causes the computer to sample an analogue measurement signal at a sampling frequency (f_S) so as to generate a digital measurement data sequence (S_MD) in response to received analogue measurement data;

computer readable code means which, when run on a computer, causes the computer to perform digital filtering (240) of the digital measurement data sequence (S_MD) so as to obtain a filtered measurement signal (S_PBMD) so as to achieve a signal having a bandwidth between an upper and a lower frequency;

said lower frequency (f_LC) being lower than the certain resonance frequency (f_R) and said upper frequency (f_UC) being higher than the certain resonance frequency (f_R);

computer readable code means which, when run on a computer, causes the computer to generate a digitally enveloped signal (S_ENV, S_MDP) in response to the filtered measurement signal (S_PBMD) by digitally rectifying said filtered measurement signal, and by digital low pass filtering of the rectified filtered measurement signal so as to generate said digitally enveloped signal (S_ENV, S_MDP);

computer readable code means which, when run on a computer, causes the computer to perform a condition analysis function (F1, F2, Fn) for analysing the condition of the machine dependent on said digitally enveloped signal (S_ENV, S_MDP).

21. A computer program product comprising

a computer readable medium;

and

a computer program according to claim 20,

said computer program being recorded on said computer readable medium.

22. The computer program product according to claim 21, wherein said computer readable medium comprises a memory chip.