Deutsches Zentrum für Luft- und Raumfahrt (DLR) has released a technical brief on holistic condition monitoring for predictive maintenance, recasting machinery health assessment as a synchronized multi-physics measurement problem rather than a single-instrument routine. The publication signals how aerospace-grade sensing architectures are migrating into industrial maintenance programs that previously relied on a single accelerometer per asset.

What does "holistic" change in a vibration analyzer?

Conventional predictive maintenance programs lean on envelope analysis of IEPE accelerometer data and on spectral kurtosis methods applied to bearing and gear signatures. The holistic framework layers additional modalities on this baseline: acoustic emission sensors for incipient crack-front detection in slow-speed components, infrared thermography for stator and brushgear hot-spot identification, and motor current signature analysis (MCSA) for rotor-bar and air-gap fault isolation. Each modality carries its own bandwidth requirement that the data acquisition system must accommodate simultaneously.

How do the bandwidths stack up?

Vibration accelerometers typically span 0.5 Hz to 10 kHz for bearing defect work, with bandwidths extending to 30 kHz or 50 kHz for gearbox analysis. Acoustic emission sensors operate from roughly 20 kHz to 1 MHz to capture transient crack-tip emissions. Infrared thermography frames run at 30 Hz to 60 Hz thermal sampling, while MCSA channels demand analog bandwidth above the inverter switching frequency — often 100 kHz or more on modern variable-frequency drives. A synchronized acquisition system must therefore bridge a sampling-rate range that exceeds four orders of magnitude within one timing domain.

What does the measurement chain look like?

A representative holistic chain pairs:

• IEPE accelerometers feeding constant-current signal conditioners
• differential acoustic emission preamps with 40 dB gain stages and selectable bandpass filtering
• type K or PT100 RTD strings through 24-bit resistance-temperature digitizers
• Hall-effect or current transformers on the motor feed, anti-alias filtered to the inverter switching frequency

Sampling rates commonly run at 25.6 kSa/s to 51.2 kSa/s for vibration, 1 MSa/s or higher for acoustic emission, 1 Sa/s to 10 Sa/s for thermal, and 10 kSa/s to 100 kSa/s for motor current. Data reduction happens at the edge. Feature extraction — RMS, crest factor, kurtosis, spectral entropy, wavelet packet energy — runs on a local processor before compressed statistics enter the historian, avoiding the bandwidth penalty of streaming raw waveforms from a 64-channel node.

Where does calibration fit?

Each chain carries its own traceability story. Accelerometers require shock calibration against a back-to-back reference per ISO 16063-21. Acoustic emission sensors rely on pencil-lead-break reciprocity verification, since absolute AE amplitude rarely reaches a national-standard trace. Thermography demands blackbody-source calibration against a target of known emissivity. The DLR framing pushes the metrologist toward system-level calibration: not one sensor at a time but the chain as a whole, synchronized through a known fault-injection event such as a seeded bearing defect on a test rig or a controlled stator short.

Does this change procurement and compliance?

For operators, the practical question becomes integration rather than sensor selection. A maintenance program that buys the best accelerometer available but streams its data through a proprietary analytics platform cannot easily fold in acoustic emission or thermography later. Open data formats, synchronized timestamping, and documented feature-extraction firmware become purchasing criteria as consequential as bandwidth or noise floor.

For regulators, the brief touches the boundary between operational monitoring and continuing airworthiness. In civil aviation, condition-based maintenance feeds directly into EASA Part-M and FAA Part 121 maintenance program requirements. A framework that documents multi-sensor data provenance and timestamps across modalities produces audit trails more defensible than a handwritten logbook entry.

The adoption question the publication raises is whether holistic monitoring belongs on the maintenance schedule, on the type certificate, or both at once. The answer for industrial users with no regulatory anchor is largely commercial: programs that can correlate a thermal excursion with a shaft event and an electrical signature gain earlier warning than any single channel allows, and that earlier warning translates into hours of avoided downtime. For aerospace operators, the choice narrows to which authority will accept the multi-sensor record as equivalent to a prescribed inspection interval.