Portable vibration meters

Portable vibration meters are instruments for measuring vibration on rotating machinery (motors, fans, pumps, compressors, gearboxes, turbines) and on mechanical structures. They are used for predictive maintenance, preventive diagnostics, safety checks, acceptance of new machines and balancing verification. They measure vibration acceleration (m/s² or g), velocity (mm/s) and displacement (µm) simultaneously, with statistical analysis and on-screen display. They use sensors (piezoelectric accelerometers) attached to the machine by magnetic contact, by a screw mount or with a hand-held probe.

Piezoelectric accelerometers

A piezoelectric accelerometer consists of a seismic mass resting on a piezoelectric crystal (quartz, PZT ceramic, synthetic materials): the acceleration of the structure it is mounted on exerts a force on the mass, which the crystal converts into a proportional electric charge. The signal is amplified and displayed. The typical characteristics are: sensitivity 100 mV/g (standard models) or 500-1000 mV/g (high-sensitivity models for low vibration levels); range 0.5-10,000 g; passband 0.5-10,000 Hz; operating temperature -40 °C / +120 °C (standard versions), up to +250 °C for high-temperature applications.

Vibration parameters

The standard parameters for evaluating vibration are: RMS acceleration (for high-frequency analysis, an indicator of bearing and gear damage); RMS velocity in mm/s (the vibration severity parameter for rotating machinery, standardized in ISO 10816); peak-to-peak displacement in µm (for low-speed machines and unbalance problems); crest factor (the peak/RMS ratio – an indicator of shocks such as the impacts of a faulty rolling element); and FFT spectral analysis (decomposition of the signal into frequencies for diagnosing specific faults). Advanced models measure in several directions at once (3 axes) and average over extended periods to reduce noise.

Fault diagnosis

FFT spectral analysis makes it possible to diagnose specific faults: rotating unbalance (a peak at 1× the rotation frequency); misalignment (peaks at 1× and 2× the rotation frequency, possibly with axial components); mechanical looseness (components at multiples of 1× with sidebands); rolling bearing defects (the characteristic BPFO/BPFI/BSF/FTF frequencies calculated from the bearing geometry); gear defects (gear mesh frequencies GMF = number of teeth × shaft speed); pump cavitation (random broadband noise). A thorough knowledge of the characteristic frequencies is essential to the diagnosis.

Applications

The industrial applications are: predictive maintenance of rotating machinery (reducing unplanned downtime, scheduling work before failure); acceptance testing of new machines (verifying conformity with the manufacturer’s specifications); periodic fleet surveys (collecting data on every machine in the plant for historical analysis and drift detection); dynamic rotor balancing (together with balancing machines); safety checks on cranes, lifts and industrial equipment; verification of dampers and anti-vibration mounts; and structural vibration analysis of buildings, bridges and infrastructure.

Reference standards

The main standards are: ISO 10816 (Mechanical vibration – Evaluation of machine vibration by measurements on non-rotating parts, parts 1-7 specific to machine types); ISO 7919 (vibration of rotating shafts); ISO 13373 (condition-based maintenance with vibration analysis); ISO 18434 (thermography for maintenance); ISO 1940-1 (balance quality of rigid rotors). Accelerometers are calibrated periodically on ISO 17025 calibrated shakers, typically once a year.

Selection criteria

The choice of vibration meter depends on: the application (simple periodic checks → single-axis models displaying the basic quantities; advanced diagnostics → models with built-in FFT and spectral analysis); the frequency range required (which varies with the type of machine); sensor sensitivity (high sensitivity for low levels on large machines); datalogging and archiving functions for historical analysis; integration with PC software for advanced analysis and fleet management; and compliance with the applicable ISO standards.