Bearing failure rarely occurs suddenly. Weeks before a failure, measurable changes occur in the vibration behavior of the bearing, pump, or motor—long before an operator hears or feels anything. Vibration analysis reveals precisely these changes.
ISO 20816 provides the basis for vibration analysis, with four zones ranging from A to D. For Class II machines, the limit values are 1.4, 2.8, and 4.5 millimeters per second (root mean square). However, the trend is crucial: imbalance is evident between 1 and 100 hertz, while incipient bearing damage only becomes apparent above 5 kilohertz and only with Envelope Analysis.
The Standard as a Starting Point
The basis for the evaluation is provided by the ISO 20816 standard, the successor to the older ISO 10816, which applies to machines ranging from 15 kilowatts to 50 megawatts (fabrico.io, 2026). It classifies vibration levels into four zones, from A to D, ranging from as-new condition to damage requiring immediate action. For Class II machines, the limit values are 1.4, 2.8, and 4.5 millimeters per second RMS (ISO 20816-3 via fabrico.io, 2026).
higher is the failure risk for Class II bearings above 7.1 millimeters per second RMS vibration velocity.
UNITEC, 2026
What Vibration Analysis Reveals
Not every error manifests itself in the same frequency range. Therefore, those who measure only the total rms value often overlook precisely those errors that become apparent earliest.
| Fault Pattern | Frequency range | Measurement Methods |
|---|---|---|
| Imbalance | 1 to 100 hertz | RMS value of vibration velocity |
| Alignment error | low-frequency range, axially prominent | Combined radial and axial measurement |
| Early-stage bearing damage | above 5 kilohertz | Spectral and Envelope Analysis |
| Short impacts in the bearing | high-frequency, pulsed | Crest factor |
Bearing damage requires high-frequency measurement with spectral and envelope analysis to distinguish the characteristic pattern of incipient damage from normal operating noise (ICS Schneider, 2026). Modern IO-Link sensors provide several parameters simultaneously for this purpose, including the root mean square (RMS) and peak values of velocity, the RMS value of acceleration, the crest factor, and temperature (autosen, 2026). The crest factor is particularly revealing because it detects short, sharp spikes—which are typical of incipient bearing damage—even before the root mean square value changes significantly.
Why a Threshold Value Alone Is Not Enough
Threshold values are helpful, but they are no substitute for monitoring trends over time. A value that remains stable at 3 millimeters per second over several months is less concerning than a value that jumps from 1 to 3 millimeters per second within a week, even if both values are still below the critical threshold. The trend often tells us more than the current value.
Sensor installation for vibration analysis without modifying the machine
In most cases, a vibration sensor can be mounted externally on the bearing housing or motor housing without opening the machine or interfering with its control system. It is important to ensure a secure, vibration-resistant connection between the sensor and the component, such as via a threaded hole or an adhesive mount. While a loose magnetic mount can provide initial indications, it distorts the measurement at higher frequencies and is more suitable for an initial assessment than for continuous operation.
The position of the sensor plays a key role in determining the accuracy of the measurement. The most meaningful measurement points are those as close as possible to the bearing location, in the direction of the expected force. For an electric motor, this usually means a measurement on the bearing shield in the radial direction, supplemented by an axial measurement if alignment errors could also be a factor.
A realistic rollout begins with the machines whose downtime has already proven costly. Only once stable operation of the sensors and data analysis has been achieved on those machines is it worthwhile to expand to less critical units.
Fixed installation or mobile measurement
The choice between permanently installed sensors and mobile measurements depends on the criticality of the machine. Permanently installed sensors provide continuous data and detect rapid changes, such as in machines that would halt all production in the event of a malfunction. Mobile measurements using a handheld device are often sufficient for machines that change more slowly or whose failure is manageable.
A hybrid approach is common in practice. The most critical units are equipped with fixed sensors that provide continuous monitoring, while the rest are inspected using mobile equipment at regular intervals. How often a mobile inspection is necessary depends on the wear characteristics of the respective machine. A pump in continuous operation wears out faster than an emergency power generator that is rarely used. This prioritization follows the same logic as the data chain from the Sensor for the Dashboard.
Which units require fixed sensors?Tell us which three of your machines are the most critical. We'll tell you which parameters should be measured on them and where mobile measurement is sufficient.
Frequently Asked Questions
Should sensors be permanently installed or used on a mobile basis?
That depends on the criticality of the machine. Permanently installed sensors are suitable for equipment whose failure would immediately halt production, because they continuously monitor changes. For less critical machines, mobile measurements taken at fixed intervals are often sufficient.
How much does a measurement point for vibration analysis cost?
The cost depends on the type of sensor, the number of measurement axes, and the connection to an evaluation system. A simple IO-Link sensor for a single measurement point costs in the low three-digit range, plus installation, cabling or wireless connectivity, and integration into the software.
Is the ISO 20816 standard sufficient as the sole alarm threshold?
It provides a good starting point, but it is no substitute for a machine-specific analysis. A more sensible approach is to combine the standard value as a rough guideline with individual monitoring that can detect even minor but rapid changes in the specific machine.
The Next Step
torck develops its own plant monitoring systems with in-house teams in Maxhütte-Haidhof, Vienna, and Rabat, who also bring experience from OT-IT integration projects in existing plants. For vibration analysis, this means a seamless process—from sensor selection to dashboard analysis—all from a single source. You can schedule an initial consultation via our page at Plant Monitoring.
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