Analysis system

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.

1 . An apparatus for analyzing 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 so as to cause a mechanical vibration; said apparatus including:
 a sensor for monitoring said movable first part so as to generate at least one analogue measurement signal including at least one vibration signal component dependent on said mechanical vibration; wherein said vibration signal component has a repetition frequency which depends on the speed of rotation 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 adapted to generate a digital measurement data sequence in response to said measurement signal (S EA ); said digital measurement data sequence having a first sample rate;   a first digital filter adapted to perform digital filtering of the digital measurement data sequence so as to obtain a filtered measurement signal;   a digital enveloper adapted to generate a first digital signal in response to the filtered measurement signal;   a decimator adapted to perform a decimation of the first digital signal so as to generate a decimated digital signal having a reduced sampling frequency;   an enhancer having an input receiving said decimated digital signal, said enhancer being adapted to generate an output signal sequence in response to said decimated digital signal; and   an analyzer for indicating a machine condition; wherein   said sensor is a resonant Shock Pulse Measurement sensor having a predetermined mechanical resonance frequency so as to achieve an amplification of the mechanical vibration so that the sensor is particularly sensitive to vibrations having a frequency on or near the predetermined mechanical resonance frequency;   
       and wherein
 said first digital filter is a digital band pass filter having a lower cutoff frequency, an upper cutoff frequency and a passband bandwidth between the upper and lower cutoff frequencies, said upper and lower cutoff frequencies of the digital band pass filter being selected so that frequency components of the digital measurement data sequence at the predetermined resonance frequency are in the passband bandwidth; and wherein 
 said decimator is adapted to generate said decimated digital signal in dependence on 
 a signal indicative of said speed of rotation, and 
 a signal indicative of an output sample rate setting signal; wherein said decimator is adapted to generate said decimated digital signal 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 wherein 
 said enhancer is adapted to produce said output signal sequence so that it has repetitive signal components corresponding to said at least one vibration signal component with a second signal-to-noise ratio value which is higher than said first signal-to-noise ratio value, by 
 a) said enhancer being adapted to receive a first plurality of sample values of said decimated digital signal via said input; 
 b) said enhancer being adapted to store the received sample values in an input signal storage portion of a data memory associated with the enhancer; 
 c) said enhancer being adapted to set a variable t to an initial value; 
 d) said enhancer being adapted to calculate an output sample value S MDP (t) for the variable value t by employing the equation: 
 
       
         
           
             
               
                 
                   S 
                   MDP 
                 
                  
                 
                   ( 
                   t 
                   ) 
                 
               
               = 
               
                 
                   ∑ 
                   
                     i 
                     = 
                     1 
                   
                   
                     i 
                     = 
                     CLENGTH 
                   
                 
                  
                 
                   
                     I 
                      
                     
                       ( 
                       i 
                       ) 
                     
                   
                   * 
                   
                     I 
                      
                     
                       ( 
                       
                         i 
                         + 
                         Sstart 
                         + 
                         t 
                       
                       ) 
                     
                   
                 
               
             
           
         
         wherein: 
         S start =O LENGTH , 
         C LENGTH =L*O LENGTH , 
         L is an integer between 1 and 10; and 
         O LENGTH  is a desired number of output sample values; and wherein said first plurality of sample values comprises (L+2)*O LENGTH  sample values; 
         e) said enhancer being adapted to store the resulting output sample value S MDP (t) in an output signal storage portion of the data memory; 
         f) said enhancer being adapted to check the value of variable t, and
 f1) if, in step f), the value of variable t represents a number lower than the desired number of output sample values the enhancer is adapted to increase the value of the variable t, and repeat steps d) and e) and f); and 
 f2) if, in step f), the value of variable t represents a number equal to the desired number of output sample values said output signal sequence is delivered to said analyzer; and 
 
         said analyzer is adapted to indicate a machine condition in response to said output signal sequence. 
       
     
     
         2 . The apparatus according to  claim 1 , wherein
 the resonant Shock Pulse Measurement sensor has a mechanical resonance frequency in a range from a lowest resonance frequency value to a highest resonance frequency value, and   the digital band pass filter is designed to have   a lower cutoff frequency which is lower than the lowest resonance frequency value and   an upper cutoff frequency which is higher than the highest resonance frequency value.   
     
     
         3 . The apparatus according to  claim 1 , wherein
 the Shock Pulse Measurement sensor is designed so that the mechanical resonance frequency is in the range from 28 kHz to 37 kHz.   
     
     
         4 . The apparatus according to  claim 1 , wherein
 the Shock Pulse Measurement sensor is designed so that the mechanical resonance frequency is in the range from 30 kHz to 35 kHz.   
     
     
         5 . The apparatus according to  claim 1 , wherein
 the envelopper includes a digital rectifier and a low pass filter.   
     
     
         6 . The apparatus according to  claim 1 , wherein
 the envelopper includes a digital rectifier; and the decimator includes a low pass filter function.   
     
     
         7 . 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.   
     
     
         8 . The apparatus according to  claim 1 , wherein
 the integer decimator includes plural Low Pass Finite Impulse Response Filters.   
     
     
         9 . A method for analyzing a condition of a first machine part that is rotationally movable at a speed of rotation in relation to a second machine part so as to cause a mechanical vibration, the method comprising steps of:
 (I) providing an apparatus comprising:   a sensor for monitoring said movable first part so as to generate at least one analogue measurement signal including at least one vibration signal component dependent on said mechanical vibration; wherein said vibration signal component has a repetition frequency which depends on the speed of rotation 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 adapted to generate a digital measurement data sequence in response to said measurement signal (S EA ); said digital measurement data sequence having a first sample rate;   a first digital filter adapted to perform digital filtering of the digital measurement data sequence so as to obtain a filtered measurement signal;   a digital envelopper adapted to generate a first digital signal in response to the filtered measurement signal;   a decimator adapted to perform a decimation of the first digital signal so as to generate a decimated digital signal having a reduced sampling frequency;   an enhancer having an input receiving said decimated digital signal, said enhancer being adapted to generate an output signal sequence in response to said decimated digital signal; and   an analyzer for indicating a machine condition; wherein   said sensor is a resonant Shock Pulse Measurement sensor having a predetermined mechanical resonance frequency so as to achieve an amplification of the mechanical vibration so that the sensor is particularly sensitive to vibrations having a frequency on or near the predetermined mechanical resonance frequency; and wherein   said first digital filter is a digital band pass filter having a lower cutoff frequency, an upper cutoff frequency and a passband bandwidth between the upper and lower cutoff frequencies, said upper and lower cutoff frequencies of the digital band pass filter being selected so that frequency components of the digital measurement data sequence at the predetermined resonance frequency are in the passband bandwidth; and wherein   said decimator is adapted to generate said decimated digital signal in dependence on   a signal indicative of said speed of rotation, and   a signal indicative of an output sample rate setting signal; wherein said decimator is adapted to generate said decimated digital signal 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 wherein   said enhancer is adapted to produce said output signal sequence so that it has repetitive signal components corresponding to said at least one vibration signal component with a second signal-to-noise ratio value which is higher than said first signal-to-noise ratio value, by   a) said enhancer being adapted to receive a first plurality of sample values of said decimated digital signal via said input;   b) said enhancer being adapted to store the received sample values in an input signal storage portion of a data memory associated with the enhancer;   c) said enhancer being adapted to set a variable t to an initial value;   d) said enhancer being adapted to calculate an output sample value S MDP (t) for the variable value t by employing the equation:   
       
         
           
             
               
                 
                   S 
                   MDP 
                 
                  
                 
                   ( 
                   t 
                   ) 
                 
               
               = 
               
                 
                   ∑ 
                   
                     i 
                     = 
                     1 
                   
                   
                     i 
                     = 
                     CLENGTH 
                   
                 
                  
                 
                   
                     I 
                      
                     
                       ( 
                       i 
                       ) 
                     
                   
                   * 
                   
                     I 
                      
                     
                       ( 
                       
                         i 
                         + 
                         Sstart 
                         + 
                         t 
                       
                       ) 
                     
                   
                 
               
             
           
         
         wherein: 
         S start =O LENGTH , 
         C LENGTH =L*O LENGTH , 
         L is an integer between 1 and 10; and 
         O LENGTH  is a desired number of output sample values; and wherein 
         said first plurality of sample values comprises (L+2)*O LENGTH  sample values; 
         e) said enhancer being adapted to store the resulting output sample value S MDP (t) in an output signal storage portion of the data memory; 
         f) said enhancer being adapted to check the value of variable t, and
 f1) if, in step f), the value of variable t represents a number lower than the desired number of output sample values the enhancer is adapted to increase the value of the variable t, and repeat steps d) and e) and f); and 
 f2) if, in step f), the value of variable t represents a number equal to the desired number of output sample values said output signal sequence is delivered to said analyzer; and 
 
         said analyzer is adapted to indicate a machine condition in response to said output signal sequence; and 
         (II) applying the sensor to a measuring point on the machine; and 
         (III) generating the machine condition from the analyzer; 
         wherein the first machine part has a rotational speed of less than 50 revolutions per minute in relation to said second machine part. 
       
     
     
         10 . A method for analyzing a condition of a first machine part that is rotationally movable at a speed of rotation in relation to a second machine part so as to cause a mechanical vibration, the method comprising steps of:
 (I) providing an apparatus comprising:   a sensor for monitoring said movable first part so as to generate at least one analogue measurement signal including at least one vibration signal component dependent on said mechanical vibration; wherein said vibration signal component has a repetition frequency which depends on the speed of rotation 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 adapted to generate a digital measurement data sequence in response to said measurement signal; said digital measurement data sequence having a first sample rate;   a first digital filter adapted to perform digital filtering of the digital measurement data sequence so as to obtain a filtered measurement signal;   a digital envelopper adapted to generate a first digital signal in response to the filtered measurement signal;   a decimator adapted to perform a decimation of the first digital signal so as to generate a decimated digital signal having a reduced sampling frequency;   an enhancer having an input receiving said decimated digital signal, said enhancer being adapted to generate an output signal sequence in response to said decimated digital signal; and   an analyzer for indicating a machine condition; wherein   said sensor is a resonant Shock Pulse Measurement sensor having a predetermined mechanical resonance frequency so as to achieve an amplification of the mechanical vibration so that the sensor is particularly sensitive to vibrations having a frequency on or near the predetermined mechanical resonance frequency; and wherein   said first digital filter is a high pass filter having a cut-off frequency selected to a value lower than the predetermined mechanical resonance frequency;   and wherein   said decimator is adapted to generate said decimated digital signal in dependence on   a signal indicative of said speed of rotation, and   a signal indicative of an output sample rate setting signal; wherein said decimator is adapted to generate said decimated digital signal 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 wherein   said enhancer is adapted to produce said output signal sequence so that it has repetitive signal components corresponding to said at least one vibration signal component with a second signal-to-noise ratio value which is higher than said first signal-to-noise ratio value, by   a) said enhancer being adapted to receive a first plurality of sample values of said decimated digital signal via said input;   b) said enhancer being adapted to store the received sample values in an input signal storage portion of a data memory associated with the enhancer;   c) said enhancer being adapted to set a variable t to an initial value;   d) said enhancer being adapted to calculate an output sample value S MDP (t) for the variable value t by employing the equation:   
       
         
           
             
               
                 
                   S 
                   MDP 
                 
                  
                 
                   ( 
                   t 
                   ) 
                 
               
               = 
               
                 
                   ∑ 
                   
                     i 
                     = 
                     1 
                   
                   
                     i 
                     = 
                     CLENGTH 
                   
                 
                  
                 
                   
                     I 
                      
                     
                       ( 
                       i 
                       ) 
                     
                   
                   * 
                   
                     I 
                      
                     
                       ( 
                       
                         i 
                         + 
                         Sstart 
                         + 
                         t 
                       
                       ) 
                     
                   
                 
               
             
           
         
         wherein: 
         S start =O LENGTH , 
         C LENGTH =L*O LENGTH , 
         L is an integer between 1 and 10; and 
         O LENGTH  is a desired number of output sample values; and wherein 
         said first plurality of sample values comprises (L+2)*O LENGTH  sample values; 
         e) said enhancer being adapted to store the resulting output sample value S MDP (t) in an output signal storage portion of the data memory; 
         f) said enhancer being adapted to check the value of the variable t, and
 f1) if, in step f), the value of the variable t represents a number lower than the desired number of output sample values the enhancer is adapted to increase the value of the variable t, and repeat steps d) and e) and f); and 
 f2) if, in step f), the value of the variable t represents a number equal to the desired number of output sample values said output signal sequence is delivered to said analyzer; and wherein 
 
         said analyzer is adapted to indicate a machine condition in response to said output signal sequence; and 
         (II) applying the sensor to a measuring point on the machine; and 
         (III) generating the machine condition from the analyzer; 
         wherein the first machine part has a rotational speed of less than 50 revolutions per minute in relation to said second machine part.