Ultrasonic Bearing Readings Log Worksheet
Ultrasound is one of the cheapest condition monitoring techniques, but the value is in the trend. This log stores the baseline next to each reading and calculates the rise, so the technician and the planner can see at a glance which bearings need grease and which need a closer look.
| Date | Asset | Bearing or point | Sensor frequency (kHz) | Baseline (dBuV) | Reading (dBuV) | Rise over baseline | Condition | Note | |
|---|---|---|---|---|---|---|---|---|---|
2 | |||||||||
12 | |||||||||
13 | |||||||||
2 |
A common rule of thumb is that about 8 dB over baseline suggests the onset of lubrication need, and 16 dB or more points to early failure, but baselines must be taken on the same sensor, same spot and same settings. Treat these as starting points and set your own limits.
Route ultrasound findings into maintenance tasks
Optional review of how readings and lubrication actions could be tracked in your ERP.
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How to use the log
Take a baseline when the bearing is known to be healthy and correctly lubricated, using the same sensor frequency, same gain setting and same contact point each time. Enter the baseline once per point and the current reading on every route. The rise is calculated automatically. Choose a condition and note what you did, for example the number of grease strokes. Export to Excel to filter by asset and graph the rise by date.
Reading the rise
Ultrasound reports the high frequency sound generated by friction and impacts. A bearing that is starving for lubricant gets noisier, so the dB level climbs. Many practitioners treat a 8 dB rise as the point to lubricate and 12 to 16 dB or more as a sign of a developing defect, then confirm with vibration. Because the scale is logarithmic, each 6 dB is roughly a doubling of amplitude.
- Never grease more than the quantity calculated for the bearing
- Recheck after lubrication to confirm the level falls
- A level that stays high after greasing needs inspection, not more grease
Other uses of the same log
The same sheet works for compressed air and steam trap surveys. Replace the bearing column with a leak or trap ID and log the reading and the repair. For electrical inspection, ultrasound can detect corona and tracking in switchgear, where the reading is a relative indicator rather than a numeric limit.
Common mistakes
Frequent errors are changing the sensor or gain between visits, pressing with a different force, taking the baseline from a bearing already in distress and comparing readings across different bearing sizes and speeds. Slow-speed bearings need special handling, check your instrument guidance.
Frequently Asked Questions
What is a baseline reading?
It is the level measured on a healthy, properly lubricated bearing using the same instrument, frequency and gain. Everything afterwards is judged by how far it rises above that baseline. Without a baseline, a single dB number is hard to interpret.
Which sensor frequency should I use?
Many bearing surveys use around 40 kHz, which is the common default on airborne and contact ultrasound instruments. Whatever you use, log it per row and keep it constant for each point.
Can ultrasound replace vibration analysis?
They complement each other. Ultrasound often detects lubrication problems and very early defects, while vibration spectra help identify unbalance, misalignment and the type of bearing fault. Many programs use both.
How often should I walk the route?
Monthly is typical for important rotating equipment, with weekly checks on assets with known issues. Set the interval from the criticality and the P-F interval of your failure modes.
Netray can help turn ultrasound route results into lubrication tasks inside your ERP or CMMS.
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