Vibration sensor placement guide
Where to put the accelerometer — which bearings, which directions, and which mount — so the reading is worth trending. The conventions, not a vendor pitch.
Each axis reveals a different fault family.
| Direction | Orientation | What it reveals |
|---|---|---|
| Horizontal (H) | Radial, perpendicular to the shaft, in the running plane | Imbalance, looseness, and most general radial faults — usually the highest radial reading. |
| Vertical (V) | Radial, perpendicular to the shaft, vertical | Structural and mounting weakness; comparing H vs V exposes soft foot and looseness. |
| Axial (A) | Parallel to the shaft centreline | Misalignment and bent-shaft faults; thrust-bearing condition — the direction angular faults show up first. |
The mount sets the frequency ceiling — and what you can detect.
Early bearing defects live in high-frequency content. A weak mount quietly removes exactly the band you need. Match the method to the job; figures are approximate and depend on the sensor and surface.
| Mount | Practical upper limit | Use it for |
|---|---|---|
| Stud / permanent | ≥ 10 kHz (widest) | Permanent points and any high-frequency bearing work. The reference standard — drill, tap, and spot-face once. |
| Adhesive pad | Several kHz to ~10 kHz | Semi-permanent points where drilling is not allowed; performance depends on the adhesive and a flat, clean surface. |
| Flat magnet | To a few kHz (resonance 5-10 kHz) | Repeatable route measurements on flat, clean steel. Good general-purpose mount. |
| Two-pole magnet | Lower (resonance 3-7 kHz) | Curved surfaces such as motor housings; trades some high-frequency response for grip. |
| Handheld probe | ≈ 1 kHz or less | Quick screening only. Not repeatable enough for trending and blind to bearing-frequency content. |
Six steps to points worth trending.
- 01
Identify every bearing on the train — both ends of the motor and both ends of each driven machine.
- 02
At each bearing, plan three measurement points: horizontal, vertical, and axial.
- 03
Place the sensor on the bearing housing, in the load zone, as close to the bearing centreline as the structure allows — not on covers, fan guards, or sheet metal.
- 04
Choose the mount for the job: stud for permanent high-frequency points, magnet for repeatable routes, probe only for screening.
- 05
Mark and label each point so the same location is measured every time — repeatability is what makes the trend meaningful.
- 06
Record the operating state with every reading; compare against the ISO 20816 severity zones for the machine class.
Questions teams ask about sensor placement
Where should I mount a vibration sensor on a motor?
On the bearing housing, in the load zone, as close to the bearing centreline as the structure allows — at both the drive end and non-drive end. Avoid fan covers, terminal boxes, and sheet-metal guards, which add their own resonances and hide the bearing signal. Take horizontal, vertical, and axial readings at each bearing.
Why measure in three directions?
Each direction reveals different faults. Horizontal radial readings are usually highest and expose imbalance and looseness; vertical readings expose mounting and structural weakness; axial readings are where misalignment, bent shafts, and thrust-bearing problems appear first. One direction alone leaves blind spots.
Does the mounting method affect what I can detect?
Significantly. A stud mount preserves response above 10 kHz; a flat magnet typically falls to a few kHz with a mounted resonance around 5-10 kHz; a two-pole magnet on a curved surface is lower still; a handheld probe is accurate only to about 1 kHz. Early bearing defects live in high-frequency content, so a weak mount can hide exactly the fault you are trying to catch.
How many measurement points does a machine need?
As a baseline, three directions at every bearing on the train. A simple motor-pump set has four bearings, so twelve points; larger trains scale from there. The right number is driven by criticality and access — instrument the bearings whose failure carries real consequence, consistently, rather than scattering points thinly across everything.