compressor — vibration_health (accelerometer-bearing)

Physics

A rotary-screw or reciprocating compressor’s drive motor and shaft bearings radiate mechanical vibration energy whose broadband velocity RMS (10-1000 Hz, per ISO 20816-3) tracks overall mechanical health, while narrowband content at 1x/2x running speed and at bearing defect frequencies (BPFO/BPFI/BSF/FTF) points to imbalance, misalignment, or developing bearing wear specifically. Large industrial compressors (motor nameplate above roughly 300 kW) fall in ISO 20816-3 group 1, which is why this recipe defaults to iso_group=group1 (a smaller compressor should instead use the pump/group2 defaults as its closer fit). An accelerometer on the motor or compressor bearing housing is sampled well above 2x the highest bearing-defect frequency of interest, which at a typical 1800-3600 RPM (30-60 Hz) running speed and bearing defect multipliers of roughly 3-10x running speed stays under 1 kHz, so a 4000 Hz acquisition rate gives ample Nyquist margin; the edge node then reduces this to 1 Hz velocity-RMS and order-amplitude features plus a periodic spectrum snapshot, rather than streaming raw waveform continuously.

Sensor

Spec: piezoelectric accelerometer, IEPE/4-20mA output, 0.5-10 kHz bandwidth, stud or magnetic mount
Signal: scalar (mm/s), range n/a

Example parts

ifm electronic VSA001 vibration sensor with integrated velocity RMS and acceleration output
SKF CMSS 2200 industrial IEPE accelerometer (100 mV/g, top-exit connector)
Pepperl+Fuchs VIS-M18-AI-KH1 M18 vibration sensor (acceleration/velocity 4-20 mA output)

Mounting

Stud-mount the accelerometer on the compressor motor’s or airend’s outboard bearing housing, radially, on a flat unpainted machined surface close to the bearing, following the manufacturer’s torque spec for the stud. Avoid mounting on sheet-metal guarding or any panel that is not rigidly part of the bearing housing structure, since a flexible mounting surface attenuates the high-frequency bearing-defect signal.

Wiring

2-wire shielded IEPE cable to a dedicated vibration input module on the edge box (or a 4-20 mA analog input for a current-loop variant); route separately from compressor motor power and any VFD cabling to avoid electrical noise on the high-frequency signal, and strain-relieve the cable away from the drive belt/coupling guard.

Validation

with the compressor running under normal load, compare the detector’s reported velocity-RMS against a handheld calibrated vibration meter at the same bearing-housing point, and confirm the nameplate rated power against the iso_group default configured

Expected: detector velocity-RMS within +/-10% of the handheld meter reading; if the nameplate rated power is below 300 kW, iso_group should be reconfigured to group2 before the zone comparison is considered valid

Safety notes

de-energize and lock out the compressor and its motor starter (LOTO) before mounting a stud-type sensor on the bearing housing
compressors store pressurized air/gas in the system even after motor lockout; verify the discharge line and receiver are isolated or vented per the site’s energy-isolation procedure before working near the airend
let the housing cool before touching it after a run; the bearing housing on a loaded compressor can reach burn-hazard surface temperatures

Cost

150–700 USD, difficulty 3/5, ~35 min install downtime.