Choosing the Right Vibration Sensor: Proximitor vs. Velocity vs. Accelerometer
April 2026 · 7 min read
Not all vibration sensors are interchangeable. Choosing the wrong sensor type for your application leads to missed faults, false alarms, or premature sensor failure. Here's a practical comparison to help you make the right call.
The Three Sensor Types
| Parameter | Proximitor (Eddy Current) | Velocity Sensor | Accelerometer (IEPE) |
|---|---|---|---|
| Measures | Displacement (mils/μm) | Velocity (mm/s, in/s) | Acceleration (g) |
| Frequency Range | DC–2,000 Hz | 4–1,000 Hz | 0.5–20,000 Hz |
| Best For | Shaft vibration, thrust position, Keyphasor | Casing vibration per ISO 10816 | Gearbox, bearing fault detection |
| Typical Cost | $800–$2,000 | $350–$800 | $500–$1,500 |
| Power Required | -24 VDC from monitor | Self-generating (none) | +24 VDC / 4 mA IEPE |
| Contact? | Non-contact | Contact (mounted) | Contact (mounted) |
When to Use a Proximitor (Bently Nevada 3300/3500 Series)
Eddy-current proximity probes are the gold standard for shaft-relative measurements on fluid-film bearing machines. They measure displacement directly — shaft movement relative to the bearing housing. Use Proximitors when you need:
- Shaft vibration orbits (X-Y probes at each bearing)
- Axial thrust position monitoring
- Keyphasor (once-per-rev reference)
- Differential expansion on steam turbines
Limitation: Probes must be mounted in a rigid bracket with precise gap setting. The target surface must be conductive (steel) and free of plating, rust, or surface irregularities larger than the probe tip diameter.
When to Use a Velocity Sensor (EPRO PR9268, Metrix)
Electrodynamic velocity sensors are the simplest to install — mount on the bearing housing, connect two wires, done. No power supply needed. They output a voltage proportional to casing vibration velocity, which directly corresponds to ISO 10816 severity zones. Best for:
- Pumps, fans, and motors (600–6,000 RPM)
- Bearing housing vibration trending
- Brownfield installations where adding power supplies isn't practical
Limitation: Frequency range tops out at 1 kHz — can't detect early-stage bearing faults (which manifest above 2 kHz). Not suitable for gearboxes or high-speed machines above 6,000 RPM.