What to check on a Online Vibration Monitor.
An online vibration monitoring system permanently mounts accelerometers or velocity sensors on critical machinery — main engine, propulsion shafting, turbochargers, large pumps and compressors — and feeds their signal continuously to a monitoring unit rather than relying on a technician walking round with a portable collector. The difference from portable monitoring is not accuracy but coverage in time: a permanent system catches a fast-developing fault, such as a turbocharger bearing failing over a few hours, that a monthly or quarterly round would only find after the fact.
What this type is
An online vibration monitoring system permanently mounts accelerometers or velocity sensors on critical machinery — main engine, propulsion shafting, turbochargers, large pumps and compressors — and feeds their signal continuously to a monitoring unit rather than relying on a technician walking round with a portable collector. The difference from portable monitoring is not accuracy but coverage in time: a permanent system catches a fast-developing fault, such as a turbocharger bearing failing over a few hours, that a monthly or quarterly round would only find after the fact.
Main components
- Sensors — accelerometers for high-frequency bearing and gear defects, velocity transducers for lower-frequency unbalance and misalignment, sometimes proximity probes for shaft displacement on fluid-film bearings.
- Signal conditioning / data acquisition unit — converts raw sensor signal into usable spectra and trend values, often mounted local to the machine.
- Monitoring processor — runs the alarm logic, stores trend history, and in many installations feeds the vessel's alarm and monitoring system directly.
- Software/HMI — displays spectra, waterfall plots and trend charts, and lets an engineer set alarm thresholds per machine and per measurement point.
Selection and sizing
Sizing is driven by how many measurement points the machinery needs, not by a single monitor size. A main engine may need points on each main bearing and the turbocharger; a shaft line needs axial and radial coverage at the thrust and line bearings. Sensor frequency range must match the fault types expected — gear mesh and bearing defects generate high-frequency content that a low-bandwidth sensor will miss entirely.
| Machine | Typical points | Primary concern |
|---|---|---|
| Main engine bearings | 1 per bearing | Unbalance, misalignment, bearing wear |
| Turbocharger | 1-2 radial | Bearing degradation, blade fouling |
| Shaft line | Thrust + line bearings | Axial movement, alignment drift |
Regulations and class
Class societies offer machinery condition monitoring notations (schemes vary by society) that permit extended survey intervals on machinery covered by an approved online monitoring system, in place of some fixed-interval opening-up inspections. Qualifying for the notation requires the monitoring scope, alarm limits and data retention to meet the society's rules, and the system's calibration record is checked at survey.
Typical faults
- Sensor cable damaged by heat or chafe near the engine, producing a flat-lined or noisy signal that is mistaken for a healthy machine.
- Alarm thresholds left at factory default rather than set for the specific machine's baseline, causing either nuisance alarms or missed trends.
- Sensor mounting loosened by vibration over time, shifting the measured frequency response and invalidating trend comparisons.
- Software left unmonitored — the system logs data correctly but no one reviews the trend until an alarm finally trips.
What to look for in a supplier
- Sensor frequency range matched to the specific fault types on the machinery in question, not a generic industrial sensor.
- Compatibility with the vessel's existing alarm and monitoring system, or a clear standalone alternative.
- Support for the class society's condition monitoring notation if that is the vessel's goal.
- Local technical support able to help set realistic alarm baselines, not just supply hardware.
A trend line is only as good as its baseline — record a full spectrum on newly installed or overhauled machinery while it is known to be healthy, or every later alarm threshold is a guess.