lgdimaggio/predictive-maintenance-mcp/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 6 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):

These flags are screening only: they name no source and never raise the bearing claim of Step 5.

Decision gate: If Kurtosis < 0 AND Crest Factor < 3, the signal shows no impulsive content. Report "No impulsive content in time-domain screening; the bearing is not assessed by it" and ask whether to continue anyway: the envelope line test of Step 5 can still find lines that screening misses.

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 5.

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.

1. 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)

1. 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 Line Test (Block 3)

The check tests the line at each expected frequency against the local noise floor of one envelope spectrum, then the further lines its kinematics predict. Its result, never your own matching of envelope peaks, decides what may be said about a fault type.

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})

A BSF value is the ball spin frequency: the rolling-element line is tested at twice it (line_frequency_hz).

Report the result in the server's words:

• Name the outcome as returned: no_indication, inconclusive, indicated

or several_types. claim.level, not outcome, decides whether a fault type is named: an indicated outcome can carry a qualified claim.

• outcome_reason and next_step describe the evidence outcome before the

claim: when claim.level is not single_spectrum_evidence, do not relay them to name a fault type or a single element.

• Never report no_indication as "healthy" or "no fault": quote its

overall_assessment verbatim; no_indication is not evidence that the bearing is free of defects.

• Each check's evidence_strength (none, low, moderate, high) grades

lines of one envelope spectrum: it is not a probability. Statistics and harmonics you read elsewhere never raise the claim.

• If a check_bearing_faults result, or a non-null bearing_faults block of

a diagnose_vibration result, has no claim field, the server predates the bearing claim: infer or relay no bearing fault type or bearing assessment from it (its overall_assessment, most_likely_fault, fault_checks, bearing sentence or Bearing recommendations), and tell the user that this bearing guidance needs a server whose check_bearing_faults returns claim. The evidence_strength of such a diagnose_vibration result, and its "Fault evidence strength" sentence, also count the bearing finding, so neither is relayed; results that do not rest on the bearing check, such as the ISO 20816-3 zone and its action, are relayed as usual.

Step 6: 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.

Its overall_diagnosis contains the claim's sentence ("Bearing analysis: ..."), and the "Bearing" entries of its recommendations are the claim's actions: quote them when its bearing_faults block carries a claim. Its evidence_strength (none, weak, moderate, strong) counts the findings of every analysis that ran, the ISO zone among them: it is not a probability and not the strength of a bearing finding.

If a check_bearing_faults result, or a non-null bearing_faults block of a diagnose_vibration result, has no claim field, the server predates the bearing claim: infer or relay no bearing fault type or bearing assessment from it (its overall_assessment, most_likely_fault, fault_checks, bearing sentence or Bearing recommendations), and tell the user that this bearing guidance needs a server whose check_bearing_faults returns claim. The evidence_strength of such a diagnose_vibration result, and its "Fault evidence strength" sentence, also count the bearing finding, so neither is relayed; results that do not rest on the bearing check, such as the ISO 20816-3 zone and its action, are relayed as usual.

Step 7: Report Generation (Block 6)

Call generate_envelope_report(signal_id="<id>", bearing_freqs={"BPFO": 107.4, "BPFI": 162.2}, rpm=1797) 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.

The envelope report's bearing_matches and bearing_assessment are not the bearing evidence: report the claim of check_bearing_faults, and with a server whose check returns no claim, relay neither.

Troubleshooting

The check returns `no_indication`: quote overall_assessment. Do not re-run the check with another tolerance_pct or frequency set to get a different outcome: a repeated check is a new test. Change a declared value (speed, bearing data) only when the user corrects it.

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 the claim names no fault type: the statistics do not identify a source; bearing and non-bearing sources (for example gear mesh or electrical) both remain possible. 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"
• Neither check_bearing_faults nor the bearing block of diagnose_vibration

confirms a bearing defect: never write "confirmed", "damage detected" or "fault present" for a bearing claim, however many indicators agree. If the results do not answer a question (for example whether the bearing is damaged), say that the analysis does not answer it

• 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