• Condmaster Ruby Software Add-On SPM Spectrum for verify source of high shock pulse readings
• SPM Spectrum measuring technique complements SPM dBm/dBc and LR/HR techniques
• First Measures shock amplitude by shock pulse measurement with the dBm/dBc or the LR/HR
• Second measurement produces a time record that is subjected to a Fast Fourier Transform (FFT)
• Preset patterns in Condmaster Ruby matched against bearing symptoms for proof of signal origination

The SPM Spectrum measuring technique is a complement to the SPM dBm/dBc and LR/HR techniques. The purpose of SPM Spectrum is to verify the source of high shock pulse readings. Shocks generated by damaged bearings will typically have an occurrence pattern matching the ball pass frequency over the rotating race. Shocks from e.g. damaged gears have different patterns, while random shocks from disturbance sources normally do not coincide with the pattern of the machine element of interest.

The resonance frequency of the SPM shock pulse transducer, calibrated to 32 kHz, constitutes the ideal carrier wave for transients caused by shocks. The output of this transducer is the same type of demodulated signal produced by ' enveloping', with this important difference: both frequency and amplitude response of the SPM transducer are precisely tuned, so there is no need to find uncertain and shifting machine resonances to get a signal. The measuring system measures the shock amplitude by a shock pulse measurement with the dBm/dBc or the LR/HR method. The results are the bearing condition data, evaluated in green-yellow-red. The second measurement produces a time record that is subjected to a Fast Fourier Transform (FFT). The resulting spectrum is used mostly for pattern recognition. Spectrum line amplitudes are influenced by too many factors to be reliable condition indicators, so all condition evaluation is based on the dBm or the HR values.

One unit for amplitude in an SPM spectrum is SD (Shock Distribution unit), where each spectrum is scaled so that the total RMS value of all spectrum lines = 100 SD = the RMS value of the time record. The alternative is SL (Shock Level unit), the RMS value of the frequency component in decibels. Alert levels are manually set for each symptom to show evaluated results in green - yellow - red. Various types of spectra can be produced.

*Pattern recognition demands precise data on the bearing and exact measurement of the rpm. The rpm should preferably be measured, not preset. The factors that define the bearing frequencies are obtained from the bearing catalog in Condmaster by stating the ISO bearing number.

The frequency patterns of bearings are preset in Cond master Ruby. Linking the symptom group 'Bearing' to the measuring point allows the user to highlight a bearing pattern by selecting its name. Other symptoms may be added when appropriate, e.g. for gear mesh patterns. Finding a clear match of a bearing symptom in the spectrum is proof that the measured signal originates from the bearing.