Can a vibration pen detect missing grease in a bearing?
Velocity can read fine while acceleration is high. If acceleration falls after regreasing, that points to lubrication. A pen gives evidence, not a grease measurement.
A field observation
A common pattern on routine rounds with a handheld vibration pen: the overall velocity reading is inside the acceptable limit, but the acceleration reading is high. The bearing is regreased, the point is measured again, and acceleration drops. That response supports a lubrication cause, and it shows why an acceptable velocity reading does not describe the whole bearing.
Why velocity and acceleration tell different stories
| Reading | What it mainly reflects | What it can miss |
|---|---|---|
| Velocity | General machine vibration: unbalance, misalignment, looseness | Small high-frequency activity from the bearing surfaces |
| Acceleration | Higher-frequency activity linked to impacts and surface interaction | It does not say by itself what caused the rise |
How poor lubrication raises acceleration
When the lubricant film is too thin or missing, the rolling surfaces touch more often and the high-frequency activity rises. Relubrication restores the film, and the reading can fall. This is a response seen in practice, not a rule that holds every time.
What else can raise acceleration
- Bearing damage such as spalling or indentations
- Contamination in the lubricant
- Too much grease, which causes churning and heat
- A different sensor position, contact pressure or instrument setting
- Noise from a nearby gear, coupling or other machine
So, can a pen detect missing grease?
It can give evidence of a possible lubrication problem. It does not measure how much grease is in the bearing or how thick the oil film is. The value comes from the comparison, not from one reading.
How to make the comparison meaningful
- Measure at the same point, with the same instrument and settings, and the same contact pressure.
- Compare readings at similar speed and load.
- Check the lubrication history: when it was last greased, how much and with what.
- Look at other condition indicators, such as temperature, sound and trend.
- Record the reading before and after relubrication, and again after the grease has spread through the bearing.
Reading the result
| After regreasing | What it suggests | Next step |
|---|---|---|
| Acceleration falls and stays down | Lubrication was a likely cause. The diagnosis is strengthened. | Review the interval and quantity, and add the bearing to the lubrication plan. |
| Falls briefly, then rises again | The lubricant is not lasting, or damage has started. | Shorten the check interval, review the lubricant and take a spectrum or envelope reading. |
| No change | Lubrication is probably not the main cause. | Do not keep adding grease. Look for damage, contamination or another source. |
Where this fits in the programme
Lubrication calculations give a starting plan for quantity and interval. Vibration and ultrasound readings show how the bearing is behaving in service. Trained interpretation connects the two, and a pen is a screening tool that tells you where to look more closely.