Analysis system

A method for analyzing a condition of a machine having a part rotating with a variable speed of rotation, the method comprising the steps of:

• (I) using an apparatus 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 adapted to sample said analogue electric measurement signal at an initial sampling frequency so as to generate a digital measurement data signal in response to said received analogue electric measurement signal;
• a first decimator for performing a decimation of the digital measurement data signal so as to achieve a first digital signal having a first reduced sampling frequency such that the first reduced sampling frequency is reduced by an integer factor as compared to the initial sampling frequency;
• a second decimator for generating a second digital signal, having a second reduced sampling frequency, in response to said first digital signal, and
• an evaluator for performing a condition analysis function for analysing the condition of the machine dependent on said second digital signal,
• wherein said first decimator has a port for receiving said integer factor;
• wherein said integer factor is settable in dependence on a detected variable speed of rotation,
• 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 a signal indicative of said detected 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 the corresponding speed of rotation of the monitored rotating part, and
• a Finite Impulse Response filter having filter values,
• wherein said fractional decimator is adapted to generate said second digital signal in response to
• said first digital signal,
• said signal indicative of said detected variable speed of rotation, and
• 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
• select a block of data values, and
• to determine a fractional decimation value corresponding to the associated speed of rotation value, and
• wherein said fractional decimator operates to associate said fractional decimation value with the selected block of data values,
• a) said fractional decimator operates to select a block of data values and the associated fractional decimation value, and
• b) 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, by
• b1) said fractional decimator being arranged 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
• b2) said fractional decimator operating to calculate said filter values by means of interpolation such that a filter value Fval for a position Fpos in said Finite Impulse Response filter is
• Fval=A(IFpos)+[A(IFpos+1)−A(IFpos)]*[Fpos−IFpos]
• where A(IFpos) and A(IFpos+1) are values in a reference filter, and the filter position Fpos is a position between these values;
• (II) applying the sensor to a measuring point on the machine;
• and
• (III) generating the machine condition from the evaluator,
• wherein the rotating part has a rotational speed of less than 50 revolutions per minute.

A method for analyzing a condition of a machine having a part rotating with a variable speed of rotation, the method comprising the steps of:

• (I) using an apparatus 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 adapted to sample said analogue electric measurement signal at an initial sampling frequency so as to generate a digital measurement data signal in response to said received analogue electric measurement signal,
• a first decimator for performing a decimation of the digital measurement data signal so as to achieve a first digital signal having a first reduced sampling frequency such that the first reduced sampling frequency is reduced by an integer factor as compared to the initial sampling frequency,
• a second decimator for generating a second digital signal, having a second reduced sampling frequency, in response to said first digital signal, and
• an evaluator for performing a condition analysis function for analysing the condition of the machine dependent on said second digital signal,
• wherein said first decimator has a port for receiving said integer factor;
• wherein said integer factor is settable in dependence on a detected variable speed of rotation,
• 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 a signal indicative of said detected 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 the corresponding speed of rotation of the monitored rotating part, and
• a Finite Impulse Response filter having filter values,
• wherein said fractional decimator is adapted to generate said second digital signal in response to said first digital signal,
• said signal indicative of said detected variable speed of rotation, and
• 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 select a block of data values, and
• to determine a fractional decimation value corresponding to the associated speed of rotation value,
• wherein said fractional decimator operates to associate said fractional decimation value with the selected block of data values, and
• a) said fractional decimator operates to select a block of data values and the associated fractional decimation value, and
• b) 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, by
• b1) said fractional decimator being arranged 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
• b2) said fractional decimator operating to calculate said filter values by means of interpolation such that a filter value Fval for a position Fpos in said Finite Impulse Response filter is:
• Fval=A(IFpos)+[A(IFpos+1)−A(IFpos)]*[Fpos−IFpos]
• where A(IFpos) and A(IFpos+1) are values in a reference filter, and the filter position Fpos is a position between these values;
• (II) applying the sensor to a measuring point on the machine;
• and
• (III) generating the machine condition from the evaluator,
• wherein the rotating part is part of a gear system, and the machine condition is a condition of the gear system.