ROTEC KNOWLEDGE

Torsional Vibration Testing

Torsional vibration testing turns a suspected problem — unexplained noise, a fatigue crack, an unexpected NVH complaint — into hard data. This page explains what a torsional vibration test involves, what a typical test setup looks like, and how to get one done.

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What Torsional Vibration Testing Involves

A torsional vibration test captures how a shaft's rotational speed fluctuates across its full operating range — typically during a run-up test, where speed is swept from idle to maximum RPM while the measurement system records rotational speed variations continuously. Zooming into any short window of that run-up reveals the underlying oscillation: rapid speed fluctuations riding on top of the overall RPM trend, generated by torque pulses from combustion, gear meshing, or other rotating sources.

The goal of the test is to capture this behaviour with enough resolution and speed range coverage to identify:

Which torsional orders are present and how strong they are
Whether any order crosses a structural natural frequency (a resonance risk)
How amplitude changes with speed and load
Whether observed behaviour matches predictions from design or simulation

Typical Test Setup

A torsional vibration test system typically combines:

A speed sensor (magnetic pickup, optical encoder, or incremental encoder) mounted on the shaft — crankshaft, camshaft, turbine shaft, or gearbox input/output shaft, depending on the application
Sensor electronics to condition and clean the raw signal
A high-resolution measurement device, using speed input boards operating in the gigahertz range to achieve very fine angular resolution regardless of sensor tooth count
Analysis software to process the angle-domain data into orders, spectra, and diagnostic diagrams

For applications with additional dynamic requirements — such as valvetrain behaviour on fired engines — the same measurement philosophy extends to fast analogue channels (multi-megahertz sampling) alongside the speed reference, enabling synchronised analysis of multiple fast-moving components in a single test.

What You Get From a Torsional Vibration Test

A well-run test delivers more than a single number — it produces a set of diagnostic views engineers can act on directly:

Waterfall diagrams, showing how amplitude evolves across orders and speed
Contour diagrams, giving a fast visual overview of problem orders
Campbell diagrams, revealing where order lines cross natural frequencies — the classic signature of a resonance risk
Quantified seating, lift-off, or dynamic behaviour data for valvetrain-specific tests

These results feed directly into design decisions: adding or tuning dampers, revising gear or valvetrain geometry, or comparing the results with agreed technical assessment criteria.

Industries and Applications We Test

Industries and applications

Automotive and commercial-vehicle engines
Motorsport drivetrains
Marine and stationary diesel engines
Steam and gas turbines
Electric-vehicle drivetrains
Wind turbine gearboxes

Why test with ROTEC

Why Test With ROTEC

ROTEC's single-source approach covers the entire measurement chain — sensors, signal conditioning, high-resolution data acquisition, and post-processing analysis software — backed by decades of engineering experience across racing, road, and heavy-duty applications. That combination is what turns raw speed data into a reliable diagnosis, not just a chart.

Questions and answers

What does torsional vibration testing investigate?

Speed fluctuations and vibration amplitudes across the agreed speed and load range. The assessment can examine orders, indications of resonance and differences between operating points.

Which results can a test provide?

Depending on the test brief, outputs include order, waterfall, contour or Campbell diagrams and a technical assessment. Measurement scope and assessment criteria are agreed for the application.

Can ROTEC help with the test setup?

ROTEC ENGINEERING supports measurement-point design and sensor installation through to measurement, analysis and presentation of the results.

Discuss your measurement project

Discuss your measurement task, operating conditions and suitable analysis with ROTEC.