Electric Motor Vibration Checker (ISO 10816)

Per ISO 10816, up to 1.12 mm/s RMS is new-machine condition (zone A) and up to 2.8 mm/s is acceptable for unrestricted long-term operation (zone B). Between 2.8 and 7.1 mm/s the machine should be scheduled for corrective maintenance (zone C), and above 7.1 mm/s vibration is severe enough to cause damage (zone D).

An electrical source. Vibration at exactly 2× line frequency (100 Hz on 50 Hz supply) that dies instantly at switch-off points to air-gap eccentricity, unbalanced phases or stator issues, not bearings or balance. A current-spectrum check or a motor circuit analysis confirms it.

On the drive-end bearing housing, horizontal, with an axial reading at the same bearing — as close to the bearing as possible, on stiff metal (never on covers or guards). Take horizontal, vertical and axial readings if you can; use the highest for the ISO grade and always re-measure at the same spot, load and speed.

The usual suspects are rotor imbalance, coupling misalignment, soft foot, bearing defects and electrical faults (broken rotor bars, eccentric air gap). A frequency spectrum tells them apart: imbalance shows at 1× running speed, misalignment at 2×, bearing defects at non-synchronous frequencies, and looseness as a raised noise floor with harmonics.

Velocity in mm/s RMS, 10–1,000 Hz. ISO 10816 zone tables are defined on broadband RMS velocity because it weights low- and high-frequency faults evenly for general machines. Acceleration (g) suits high-frequency bearing analysis and displacement (µm) suits low-speed machines, but neither maps onto these zone boundaries.