Bearing Diagnosis

Bearing Fault Diagnosis

Evidence-based bearing fault detection using vibration signals. Orchestrate MCP tools in a precise diagnostic sequence (ISO 13374 blocks 1-4) with decision gates at each step. This workflow supports the judgment of a qualified vibration engineer — it never replaces it.

Prerequisite: The predictive-maintenance-mcp MCP server must be connected.

Never infer a fault from a signal id or filename — "OuterRaceFault" in an id is not evidence. Base every conclusion exclusively on tool outputs.

Workflow

Step 1 — Signal Discovery (ISO 13374 Block 1)

Call list_signals(scope="memory") to check which signal_ids are already loaded, or list_signals(scope="disk") to browse loadable files under the data/signals/ directory. If the target signal is not loaded, load it:

Call load_signal(filepath="real_train/OuterRaceFault_1.csv", signal_unit="g")

• The returned signal_id (derived from the relative path, e.g. real_train_OuterRaceFault_1) is the single handle for every later call.
• For raw binary files (.bin/.raw/.dat), also declare sample_format and sampling_rate (or provide a companion <stem>_metadata.json) — see the signal-management skill.
• Declare signal_unit ("g", "m/s2", "mm/s", or "m/s") if you know it — the ISO severity verdict in Step 7 is REFUSED without a declared unit. Units are never guessed. Ask the user; do not invent one.
• Verify with get_signal_info(signal_id="<id>"): sampling rate, duration, declared unit, and any companion metadata (rpm, reference frequencies).

If the sampling rate is missing, STOP and ask the user — do not guess.

Step 2 — Statistical Screening (Block 2)

Call analyze_statistics(signal_id="<id>").

Evaluate screening flags (excess kurtosis, Fisher convention):

Decision gate: If Kurtosis < 0 AND Crest Factor < 3, the signal shows no impulsive content. Report "No bearing fault indicators in time-domain screening" and ask whether to continue anyway — envelope analysis can still reveal early faults.

Step 3 — Spectral Analysis (Block 2)

Call analyze_fft(signal_id="<id>").

Identify:

• Dominant frequencies and their harmonics
• Shaft frequency (1x RPM) and multiples
• Broadband energy increase

If the operating speed is unknown, ask the user for the RPM — it is required for Steps 4 and 6.

Step 4 — Bearing Characteristic Frequencies

Establish the expected BPFO/BPFI/BSF/FTF frequencies by ONE of these routes:

1. Catalog: search_bearing_catalog(bearing_id="6205") — returns verified geometry with its source citation, plus per-RPM fault frequency multipliers.
2. Explicit geometry (bearing not in catalog): calculate_bearing_characteristic_frequencies(num_balls=9, ball_diameter_mm=7.94, pitch_diameter_mm=39.04, contact_angle_deg=0.0, rpm=1797)
3. Machine manual: extract_manual_specs(file_name="pump_manual.pdf") to pull the bearing designation from documentation, then route 1.

If the bearing is not in the catalog and no geometry is available, ask the user. Never fabricate geometry or frequencies.

Expected frequencies:

• BPFO — Ball Pass Frequency, Outer race (canonical fault: outer_race)
• BPFI — Ball Pass Frequency, Inner race (canonical fault: inner_race)
• BSF — Ball Spin Frequency (canonical fault: ball)
• FTF — Fundamental Train Frequency, cage (canonical fault: cage)

Step 5 — Envelope Analysis (Block 2, primary evidence)

Call analyze_envelope(signal_id="<id>", filter_low=500, filter_high=5000).

• Default demodulation band 500-5000 Hz suits general bearing analysis.
• If Step 3 found a structural resonance, center the band around it.
• The band must stay below Nyquist — an invalid band is an explicit error, never a silent clamp.

Step 6 — Evidence Matching (Block 3)

Compare envelope peaks against the expected frequencies systematically:

Call check_bearing_faults(signal_id="<id>", rpm=1797, bearing_id="6205")

or, when frequencies came from geometry or the user:

Call check_bearing_faults(signal_id="<id>", rpm=1797, frequencies={"BPFO": 107.4, "BPFI": 162.2})

Evidence strength language:

• Strong evidence: peak + harmonics + corroborating statistics
• Possible / consistent with: peak present but missing corroboration
• Inconclusive: insufficient evidence — say so plainly

Step 7 — ISO Severity (Block 4)

Call assess_severity(signal_id="<id>", machine_group=2, support_type="rigid")

• machine_group: 1 (large, >300 kW) or 2 (medium, 15-300 kW). Confirm with the user; pass machine_power_kw if known (< 15 kW is out of ISO scope and is refused).
• Report the zone (A/B/C/D) and RMS velocity in mm/s.
• If the verdict is refused because no unit is declared, re-load with load_signal(filepath="<file>", signal_unit="g", overwrite=True) after confirming the unit with the user.
• Severity is machine-level context, NOT bearing-specific evidence.

One-call alternative: diagnose_vibration(signal_id="<id>", rpm=1797, bearing_id="6205", machine_group=2, support_type="rigid") runs FFT + PSD + STFT + bearing checks + ISO severity in one pass and degrades to a structured ISO refusal (reason + remedy) when the unit is undeclared.

Step 8 — Report Generation (Block 6)

Call generate_envelope_report(signal_id="<id>", bearing_freqs={"BPFO": 107.4, "BPFI": 162.2}) and generate_fft_report(signal_id="<id>", rpm=1797). Optionally generate_diagnostic_report_docx(signal_id="<id>", sections={"summary": "..."}) for a Word document. Report the returned file paths to the user.

Troubleshooting

No peaks in envelope spectrum — Wrong demodulation band or signal too short. Try a different band within Nyquist (e.g. filter_low=1000, filter_high=4000) guided by the FFT resonances.

Unknown bearing type — Ask for the designation (e.g. "6205") and call search_bearing_catalog(bearing_id="6205"). If it is not in the catalog, the result says so with a suggestion — ask the user for geometry; never invent it.

Kurtosis high but no envelope peaks — Impulses may come from a non-bearing source (gear mesh, electrical). Suggest the gear-diagnosis skill or check for line-frequency harmonics.

ISO verdict refused — The signal has no declared unit. Confirm the unit with the user and re-load with load_signal(filepath="<file>", signal_unit="mm/s", overwrite=True).

Important Notes

• Always use cautious diagnostic language: "consistent with", "possible fault"
• Never claim a definitive fault without multiple corroborating indicators
• This skill augments and accelerates expert judgment; the final maintenance decision rests with a qualified engineer
• All processing happens locally — raw signal data never leaves the machine