An Ex-certified vibration sensor made it possible to monitor a critical motor-pump set installed in a hazardous area. From July 9, 2023, the sensors showed a rise in vibration levels.
The spectrum pointed to bearing wear, and the team scheduled the bearing replacement before the failure stopped the asset.
In this case study, you will see what an Ex-classified area is, how the failure was identified in the telemetry, envelope and cepstrum, and what to check before monitoring assets in these areas.
What is an Ex-classified area?
Ex-classified areas are places where an explosive atmosphere can form. This depends on how the area operates, the materials used or stored there and the type of installation, among other factors.
Dust, vapors and gases are some of the elements that can lead to an Ex classification, in sectors such as mining. These areas are divided into zones, according to how often the explosive atmosphere may be present:
| Explosive atmosphere | Present continuously or for long periods | Likely in normal operation | Unlikely, and only for short periods |
|---|---|---|---|
| Gases and vapors | Zone 0 | Zone 1 | Zone 2 |
| Combustible dust | Zone 20 | Zone 21 | Zone 22 |
Any equipment installed in these zones, sensors included, must carry the Ex marking that matches the zone and the type of atmosphere. Without it, the sensor itself can become an ignition source.
Dynamox’s wireless sensors are Ex-certified, which means they are protected and suitable for safe use in hazardous areas. For this reason, the Dynamox solution could monitor a motor-pump set, a highly critical asset, located in an Ex-classified area.
The asset: a critical motor-pump set in a hazardous area
The monitored asset is a motor-water pump set driven by an explosion-proof motor. In hazardous areas, unplanned stops tend to be more complex, because any intervention requires specific safety procedures.
Detecting a failure early gives the team time to plan the repair.
Monitoring this kind of asset follows the same logic used for other industrial pumps: measuring vibration and temperature continuously to identify changes in the asset’s behavior.
How the bearing failure was detected
The detection followed three steps, each confirming the previous one.
1. Rise in vibration levels in the telemetry
From July 9, 2023, the set showed an increase in vibration levels. The rise appeared in the telemetry (RMS acceleration) and in two other metrics: envelope from 2 kHz to 6.4 kHz, peak-to-peak, and global peak-to-peak acceleration.
2. Envelope spectrum with BSF and harmonics
When analyzing the vibration spectrum, the team identified peaks at 1x the running speed and at the BSF, with harmonics.
BSF (ball spin frequency) is the frequency at which the rolling elements of a bearing spin around their own axis. Peaks at this frequency are typical of defects in the rolling elements.
Envelope analysis isolates the repeated impacts caused by these defects, which makes them visible at an early stage.
3. Cepstrum with rahmonics at 1x RPM
The cepstrum graph also showed the failure and its severity, with rahmonics at 1x RPM clearly visible.
The cepstrum groups families of harmonics into single peaks, called rahmonics. This helps confirm that the harmonics seen in the spectrum come from the same source.
Maintenance action and results
With the failure identified as bearing wear, the team scheduled maintenance to replace the bearing. In the video, you can see and hear the noise of the replaced bearing at each manual rotation.
Monitoring continued after the replacement, and vibration levels dropped. This showed that the action was taken at the right time.
Left unchecked, wear in the rolling elements tends to progress to more severe bearing failures, with risk of a stop in an area where any intervention is more complex.
What to check before monitoring assets in Ex zones
Before installing sensors in a hazardous area, check these points:
- Certification for the zone. The Ex marking must match the zone and the type of atmosphere. The DynaLogger HF+ is certified for Zone 0 and Zone 20.
- Gateway location. If the gateway also stays inside the classified area, it needs its own certification. The DynaGateway LTE Ex is certified for Zone 2 and Zone 22.
- Protection against the environment. Check the IP rating for dust, water and washing conditions.
- Installation procedure. Follow the safety rules of the area for mounting and commissioning.
- Data on the platform. The data must reach the Dynamox Platform, where alerts and diagnoses are generated, so that no one needs to collect it manually in the area.
Read another case of monitoring in a hazardous area: Dynamox solution prevents unexpected screen shutdown in a classified area.
➡️ See more success cases from Dynamox.
Need to monitor assets in hazardous areas? Talk to Dynamox specialists.
FAQ
Yes, as long as they carry the Ex certification for the zone and the type of atmosphere. Dynamox’s DynaLogger HF+ is certified for Zone 0 and Zone 20.
BSF (ball spin frequency) is the frequency at which the rolling elements of a bearing spin around their own axis. Peaks at the BSF and its harmonics indicate defects in the rolling elements.
It isolates the repeated impacts caused by bearing defects from the rest of the vibration signal. This makes small defects visible before they affect the global vibration level.