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Method and apparatus for analysing the condition of a machine having a rotating part

  • US 8,762,104 B2
  • Filed: 12/22/2009
  • Issued: 06/24/2014
  • Est. Priority Date: 12/22/2008
  • Status: Active Grant
First Claim
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1. An apparatus for analysing the condition of a machine having a part rotating with a variable speed of rotation, comprising:

  • a first sensor adapted to generate an analogue electric measurement signal dependent on mechanical vibrations emanating from rotation of said part;

    an analogue-to-digital converter for sampling said analogue electric measurement signal at a sampling frequency so as to generate a digital measurement data signal in response to said analogue electric measurement signal, said digital measurement data signal having a first Signal-to-Noise-Ratio level;

    a digital filter for filtering said digital measurement data signal so as to produce a filtered digital measurement data signal;

    a digital enveloper for generating a digital envelope signal in response to said filtered digital measurement data signal;

    a decimator for performing a decimation of the digital envelope signal so as to achieve a decimated digital signal having a reduced sampling frequency dependent on a signal indicative of said variable speed of rotation, said decimator comprisinga first decimator adapted to reduce the sampling rate of the digital envelope signal by an integer factor so as to achieve a first digital signal having a first reduced sampling frequency, anda second decimator adapted to generate said decimated digital signal such that it has a second reduced sampling frequency in response to said first digital signal,wherein said second decimator is a fractional decimator having;

    a first input for receiving said first digital signal as a sequence of data values,a second input for receiving said signal indicative of said variable speed of rotation associated with said part,a third input for receiving a signal indicative of an output sample rate setting signal,a memory adapted to receive and store the data values as well as information indicative of said variable speed of rotation of the monitored rotating part,a Finite Impulse Response filter having filter values,said fractional decimator being adapted to generate said second digital signal in response to i) said first digital signal, ii) said signal indicative of said variable speed of rotation, and iii) said signal indicative of an output sample rate setting signal,wherein said fractional decimator operates to record said data values in said memory, and associate each data value with a speed of rotation value,wherein said memory is adapted to store each data value so that it is associated with a value indicative of the speed of rotation of the monitored part at the time of detection of the sensor signal value corresponding to the data value,wherein said fractional decimator operates to analyze the recorded speed of rotation values, and divide the recorded data values into blocks of data dependent on the speed of rotation values so as to generate a number of blocks of data values, each block of data values being associated with a speed of rotation value,wherein said fractional decimator operates to i) select a block of data values, and ii) determine a fractional decimation value corresponding to the associated speed of rotation value,wherein said fractional decimator is adapted to generate said fractional decimation value dependent on said speed of rotation value,wherein said fractional decimator operates to associate said fractional decimation value with the selected block of data values,wherein said fractional decimator operates to select a block of data values and the associated fractional decimation value,wherein said fractional decimator operates to generate a block of output values in response to the selected block of input values and the associated fractional decimation value such that the number of sample values per revolution of said rotating part is kept at a substantially constant value, generating the block of output values including said fractional decimator operating to adapt said Finite Impulse Response filter in response to said fractional value and to generate said block of output values corresponding to that associated fractional decimation value; and

    an enhancer having an input for receiving said decimated digital signal, said enhancer being adapted to receive a first plurality of sample values, wherein said decimated digital signal represents mechanical vibrations emanating from rotation of said part for a duration of time,said enhancer being adapted to perform discrete autocorrelation of the decimated digital signal so as to produce an output signal sequence in the time domain wherein repetitive signal amplitude components are amplified in relation to stochastic signal components; and

    an evaluator for performing a condition analysis function for analysing the condition of the machine, said evaluator being adapted to perform said condition analysis function dependent on said output signal sequence.

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