Apparatus and a method for analysing the vibration of a machine having a rotating part

A method for detecting an operating condition of a machine including a bearing associated with a shaft that rotates at a speed of rotation, the method comprising the steps of:

• generating, by way of a vibration sensor applied to the machine, an analogue measurement signal responsive to mechanical vibration emanating from the bearing during rotation of the shaft,
• sampling, by way of an analogue-to-digital converter, said analogue measurement signal at a first sample rate;
• generating, from said sampling, a digital measurement data signal having said first sample rate;
• enveloping said digital measurement data signal, thereby generating an enveloped digital signal;
• decimating said enveloped digital signal, thereby generating a decimated enveloped digital signal such that said decimated enveloped digital signal has a reduced sample rate which is lower than said first sample rate;
• said decimated enveloped digital signal including a first vibration signal signature dependent on said mechanical vibration, wherein the first vibration signal signature includes a first repetition frequency, said decimated enveloped digital signal including noise as well as said first vibration signal signature so that said decimated enveloped digital signal has a first signal-to-noise ratio value in respect of said first vibration signal signature;
• autocorrelating, in the time domain, a first number of input sample values of said decimated enveloped digital signal, said autocorrelation being performed at a lag, wherein said lag corresponds to a certain number of input sample values, said certain number being a predetermined integer value smaller than said first number value;
• generating, from said autocorrelation, an autocorrelated enveloped signal sequence including a second number of autocorrelated sample values so that said autocorrelated enveloped signal sequence has a first repetitive signal component corresponding to said first vibration signal signature, said autocorrelated enveloped signal sequence having a second signal-to-noise ratio value in respect of said first repetitive signal component, said second signal-to-noise ratio value being higher than said first signal-to-noise ratio value;
• said second number being a positive integer;
• wherein an autocorrelated sample value is based on a third number of input signal products;
• said third number being a positive integer;
• setting the first number to a value equal to an integer IL or to a value higher than the integer IL, wherein
• IL=OLENGTH*L+SSTART+OLENGTH,
• wherein
• OLENGTH is an integer equal to said second number value;
• L is a Signal-to-Noise Ratio improver value;
• and
• SSTART is said certain number;
• and
• detecting an operating condition of the machine based on the autocorrelated enveloped signal sequence.

A non-transitory computer-readable medium on which is stored a computer program for detecting an operating condition of a machine including a bearing associated with a shaft that rotates at a speed of rotation, the computer program comprising computer readable code means which, when said computer program is run on a computer, causes the computer to perform the steps of:

• receiving a digital measurement data signal responsive to mechanical vibration emanating from the bearing during rotation of the shaft, said digital measurement data signal having a first sample rate;
• enveloping said digital measurement data signal, thereby generating an enveloped digital signal;
• decimating said enveloped digital signal, thereby generating a decimated enveloped digital signal such that said decimated enveloped digital signal has a reduced sample rate which is lower than said first sample rate;
• autocorrelating, in the time domain, a first number of input sample values of said decimated enveloped digital signal, said autocorrelation being performed at a lag, wherein said lag corresponds to a certain number of input sample values, said certain number being a predetermined integer value smaller than said first number value;
• setting the first number to a value equal to an integer IL or to a value higher than the integer IL, wherein
• IL=OLENGTH*L+SSTART+OLENGTH
• wherein
• OLENGTH is an integer equal to said second number value;
• L is a Signal-to-Noise Ratio improver value;
• and
• SSTART is said certain number;
• and
• detecting an operating condition of the machine based on the autocorrelation.