Vibration analyzers and machine diagnostics

Vibration analyzers and machine diagnostic instruments are advanced devices that combine data acquisition, real-time FFT spectral analysis, in-place dynamic balancing, modal analysis and historical measurement management for the predictive maintenance and advanced diagnosis of rotating machinery and mechanical components. Unlike simple portable vibration meters, which give overall parameters (RMS, peak), spectral analyzers identify the specific components of the vibration spectrum and correlate them with the characteristic frequencies of bearing faults, unbalance, misalignment, gear defects and pump cavitation.

FFT analysis

The analyzer performs an FFT (Fast Fourier Transform) of the time-domain vibration signal, converting it into a frequency spectrum. Spectral resolution depends on the number of FFT lines (typically 400, 800, 1600 or 3200 lines) and on the analysis bandwidth (up to 10-25 kHz for industrial analyzers). The displayed spectrum highlights the vibration peaks at the various frequencies; the operator (or expert software) identifies the characteristic frequencies of specific faults: 1× RPM for unbalance, 2× RPM for misalignment, bearing frequencies calculated from the geometry, gear mesh frequencies GMF, and blade frequencies for fans (number of blades × RPM). Diagnosis rests on comparing the measured spectrum with reference “healthy machine” spectra.

Dynamic balancing

One advanced function of these analyzers is in-place dynamic balancing: by measuring the amplitude and phase of the 1× RPM vibration, the instrument calculates the position and size of the correction masses to be fitted to the rotor in order to bring the unbalance below acceptable thresholds (ISO 1940-1, quality grade G = 1, 2.5 or 6.3 depending on the type of machine). Balancing can be carried out in one, two or more planes, on rigid or flexible rotors. The procedure involves preliminary measurements, fitting a trial mass, influence measurements and calculation of the correction mass. Typical applications are industrial fans, transmission shafts, electric motors, spindles and rotating components in general.

Advanced bearing analysis

Early diagnosis of rolling bearing faults is one of the most widespread applications of vibration diagnostics. The characteristic bearing frequencies (BPFO – Ball Pass Frequency Outer, BPFI – Ball Pass Frequency Inner, BSF – Ball Spin Frequency, FTF – Fundamental Train Frequency) can be calculated from the bearing geometry (raceway diameter, ball diameter, number of balls, contact angle) and from the rotation speed. Peaks appearing at these frequencies indicate localized defects on the outer race, the inner race, the balls or the cage. Envelope analysis or high-frequency demodulation functions are particularly effective at detecting incipient defects.

Software and data management

Dedicated vibration analysis software manages: programmed data collector routes (sequences of measurement points across every machine in the plant, walked at a fixed interval); a historical measurement database for trend analysis; automatic diagnostic algorithms (artificial intelligence for identifying fault patterns); automatic machine status reports with intervention priorities; alerting when critical thresholds are exceeded; integration with CMMS (Computerized Maintenance Management System) for automatic work scheduling; and cloud computing for remote access and the management of distributed sites.

Reference standards

The main standards are: ISO 10816 (severity, parts 1-7); ISO 13373 (condition-based maintenance through vibration); ISO 18436 (qualification of personnel in vibration analysis, levels 1-4 – increasingly required by structured industries); ISO 7919 (rotating shafts); ISO 1940-1 (balance quality of rigid rotors); IEC 60034 (for electric motors). Analyzers are calibrated with calibrated shakers and precision signal generators, certified to ISO 17025.

Selection criteria

The choice of vibration analyzer takes into account: FFT capability (number of lines, analysis bandwidth); advanced functions (balancing, envelope analysis, order tracking for variable-speed machines); ergonomics for field use (interface, battery life); integration with the company’s CMMS software; compliance with the ISO standards; the supplier’s training service (qualification of personnel in vibration analysis); and the investment involved in structured predictive maintenance programs.