Chiller Compressor Vibration Monitor

Per ISO 10816, up to 1.4 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 4.5 mm/s the machine should be scheduled for corrective maintenance (zone C), and above 4.5 mm/s vibration is severe enough to cause damage (zone D).

On screw machines, slide-valve positions create resonance bands at certain part-loads; on centrifugals, low load brings incipient surge. Both show as load-dependent vibration with healthy bearings. Map readings vs load percentage, avoid sustained running in the worst band, and have controls stage chillers around it.

On the compressor casing over the motor and at the bearing locations the OEM specifies — 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 impeller fouling (centrifugal), worn slide-valve mechanisms (screw), motor bearing wear, refrigerant flooding/liquid carry-over and mount deterioration. 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.