Bearing Monitoring on Auxiliary Motor Drives | Bently Nevada — KEG TRK

On industrial sites, auxiliary motors number in the hundreds — pumps, fans, conveyors, agitators. Rolling bearings are the #1 cause of unplanned removal. Most 4–200 kW units never get spectral analysis — only walkdowns and “still noisy, still running.”

The reliability engineer’s job is to cover at least the critical subset with a method that catches bearing defects at P-F stages 3–4, not at cage failure. For direct vibration on the motor bearing housing, Bently Nevada — 330400, 200150, Orbit DCM and route SCOUT — delivers measurable results without shaft-mounted sensors.

Why auxiliary motors are a separate class

• High RPM (1500/3000 sync) — convenient for bearing diagnostics;
• Standardised layout — repeatable DE/NDE mounting;
• Limited budget — not every motor gets a 3500 rack;
• High count — scalable strategy: online on critical, route on the rest.

Current signature methods help fleet screening, but NDE bearing defects on a pump or axial overload on a fan often appear earlier in motor housing vibration. For motor–load trains with mechanical coupling, vibration on the motor remains mandatory.

Bearing fault frequencies

In acceleration or velocity spectra look for:

• BPFO — outer race
• BPFI — inner race
• BSF — rolling element
• FTF — cage

Early stages need envelope demodulation in SCOUT or System 1. Classic sign — BPFO harmonics with ±1x sidebands.

→ How to read FFT spectra · For electrical screening of the same motors, see Artesis e-MCM.

Mounting: DE and NDE

• DE — coupling side, load path from pump or gearbox;
• NDE — fan end, sensitive to misalignment axial load.

Minimum: one radial sensor on DE. Critical assets: DE + NDE, H + V on DE.

Parameter	330400	200150
Type	General IEPE	High-frequency IEPE
Use	15–250 kW standard motors	Small high-speed, envelope
Mount	Stud, magnet (route)	Same

Three programme levels

Level A — SCOUT route (whole fleet)

Monthly walkdown; overall level + spectrum on alarm; 100% coverage over time.

Level B — Orbit DCM on critical 20–30%

Non-redundant pumps, ID/FD fans, single-drive conveyors; alarm → SCOUT confirmation.

Level C — CMMS integration

Auto work order on alarm; close after bearing change and new baseline.

Typical mistakes

1. Over-greasing — raises temperature and vibration; see overheated bearings.
2. Misalignment after repair — 2x rise before BPFO; fix alignment, not just bearing.
3. Bracket resonance — mount only on bearing housing.

P-F stages on the motor DE

Stage	Vibration on DE
1–2	Usually invisible
3	Weak BPFO/BPFI in envelope — target
4	Broadband noise, high RMS

Goal: catch stage 3 with 4–12 weeks lead time. RMS alone is not enough.

VFD motors

Variable speed moves BPFO/BPFI along the axis — record RPM in SCOUT, use order tracking in System 1, or broadband alarm + manual spectrum on Orbit DCM.

KPIs

• Coverage — % critical motors measured on schedule
• Lead time — first BPFO to repair (target >14 days)
• False alarm rate — target <15%
• Prevented failures — documented per quarter

Scaling 200+ motors

1. Q1 — inventory, SCOUT route, baselines.
2. Q2 — Orbit DCM on class A assets.
3. Q3–4 — expand DCM, CMMS, KPIs.

Typical KZ metals/mining mix: 40% pumps, 30% fans/conveyors, 20% agitators/mills. Start with non-redundant pumps and boiler fans.

Combine methods

Vibration on the motor housing complements thermography, current analysis and ultrasound — it does not replace them. Optimal non-redundant pump: Orbit DCM + terminal thermography + SCOUT on the fleet. When temperature is normal but vibration rises, prioritise mechanical shaft defects.

After a confirmed BPFO alarm

1. Reduce load or switch to spare.
2. Order bearing from motor nameplate.
3. Replace in planned 4–8 h window.
4. Align coupling if needed.
5. New baseline in Orbit DCM.
6. Check at 48 h and 168 h.

Skipping step 5 causes repeat failure in 3–6 months from uncorrected misalignment.

Summary

SCOUT for wide coverage, Orbit DCM with 330400 on critical nodes — spectral BPFO/BPFI gives 2–3 months warning with regular analysis. KEG TRK helps design the programme for your motor fleet.

Contact KEG TRK