Short answer: a wobulator is a quick functional check of a probe channel at one speed. A shaker with a reference accelerometer gives a traceable displacement you can set and sweep across frequency, so it is the better choice when you need documented dynamic calibration.
Static vs dynamic checks
A proximity probe system (probe, extension cable and driver) converts gap to a DC voltage. A typical industrial system has a scale factor of 200 mV/mil (7.87 V/mm) when calibrated to its intended target material, commonly AISI 4140 steel.
- Static calibration steps the gap with a micrometer fixture and records the voltage, to check scale factor and linearity across the range.
- Dynamic calibration moves the target sinusoidally and checks that the monitor reads the right vibration in mils or µm peak-to-peak. It proves the channel responds correctly to real vibration, including the monitor’s filters and scaling.
Both matter. Most kits do the static check the same way; the choice is in how you do the dynamic one.
How a wobulator works
A wobulator is a motor-driven spindle carrying a target disc set slightly off square, so its face moves toward and away from the probe once per revolution. Probe test kits such as the Bently Nevada TK-3 pair a wobulator with a static micrometer fixture.
Strengths
Simple, compact and familiar. It’s good for confirming a channel responds and its scaling is roughly right.
Limits
Frequency is tied to motor speed, and the displacement depends on where the probe sits over the tilted disc, so the amplitude has to be set up by measuring the probe’s own output rather than an independent reference. That makes the result hard to make traceable, and you can’t sweep frequency to check filters.
How shaker calibration works
The probe is held in a fixed bracket, gapped to its mid-range, above a target of the right material mounted on the shaker. The shaker’s reference accelerometer measures the motion and its closed-loop control holds the displacement you set. Because that reference is calibrated to ISO/IEC 17025, the dynamic result is traceable.
Strengths
You choose the frequency and displacement, sweep across the band, test at alarm levels, and record a documented result. The same shaker also calibrates your accelerometers and velocity sensors.
Limits
At low frequencies displacement is limited by stroke; at high frequencies large displacements need very high acceleration. Check that your test points fit, using the calculator below.
The AT2040 with the proximity probe calibration kit vibrates the target, powers the probe driver (−24 V) and reads gap voltage and vibration together. See how to calibrate a proximity probe in the field.
Side-by-side comparison
| Wobulator | Portable shaker | |
|---|---|---|
| Displacement reference | Set up from the probe’s own output | Independent, calibrated reference accelerometer |
| Traceability | Hard to document | ISO/IEC 17025 traceable reference |
| Frequency | Tied to motor speed | Set and swept, for example 5 Hz upward |
| Amplitude control | Depends on probe position over the disc | Set directly in mils or µm pk-pk |
| Filter and scaling check | One point | Multiple frequencies and levels |
| Other sensors | Proximity probes only | Also accelerometers, velocity sensors, transmitters |
| Best for | Quick functional checks | Documented dynamic calibration |
Displacement calculator
Convert a probe test point
Enter a frequency and displacement to see the matching velocity and acceleration, and whether it fits a bare Gen 2 Agate shaker.
FAQ
What is a wobulator?
A motor-driven spindle with a target disc mounted slightly off square, so the disc face moves toward and away from a proximity probe once per revolution. It provides a quick dynamic check of a probe channel.
Can you calibrate a proximity probe on a shaker?
Yes. Mount a target of the right material on the shaker, hold the probe in a fixed bracket at its mid-range gap, and set the displacement using the shaker’s reference accelerometer. The result is traceable and can be repeated at several frequencies.
Why does target material matter?
Eddy-current probes are calibrated for a specific material, commonly AISI 4140 steel. A different shaft material changes the scale factor, so test against the material the probe will see in service.
What is the typical proximity probe scale factor?
Many industrial systems use 200 mV/mil (7.87 V/mm) when calibrated to their intended target material. Check your system’s specification.
Do I still need a static calibration?
Yes. The static gap-versus-voltage check confirms scale factor and linearity; the dynamic check confirms the channel reads vibration correctly. Use both.
Related: How to choose a portable vibration calibrator · Testing Bently Nevada negative-voltage sensors