Campbell Diagram Tool

The Campbell Diagram Tool is a standalone Windows application for rotating machinery noise and vibration (NVH) analysis. It builds a frequency × RPM color map (Campbell diagram) from OROS NVGate data — either from raw time-domain signals or from pre-computed waterfall results — and overlays order lines and resonance markers to identify critical speeds.

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What is a Campbell Diagram?

A Campbell diagram plots vibration amplitude as a function of both frequency (Y-axis) and rotation speed (X-axis, in RPM). The color intensity represents the amplitude level (in dB or linear units).

Two families of features are visible at a glance:

Feature	Appearance on the plot	Physical meaning
Order lines	Diagonal straight lines rising from lower-left to upper-right	Harmonic excitations that rotate with the shaft (1X = imbalance, 2X = misalignment, nX = gear mesh, blade pass…)
Structural resonances	Horizontal bright bands at fixed frequency	Natural frequencies of the structure, independent of rotation speed
Critical speeds	Intersection of an order line and a resonance band	Operating speed where a harmonic excitation drives a structural mode → high vibration risk

Understanding the difference with a classic waterfall:

• A waterfall shows spectra stacked over time or speed
• A Campbell diagram adds the diagonal order lines that immediately reveal which peaks are rotation-driven and which are structural resonances.

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Getting Started

Launching the application

Double-click Campbell_Diagram.exe. No installation is required; all dependencies are bundled.

The application opens on the Data tab showing your NVGate project tree.

Setting the database path

By default the tool looks for NVGate projects in C:\OROS\NVGate data\Projects. To change it:

1. Click the … button next to the path field at the top of the Data tab.
2. Browse to your NVGate database folder.
3. The project tree refreshes automatically.

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Data Tab

File:Campbell data tab.png

Data tab — project tree (left) and measurement settings (right)

Project tree

Projects are listed alphabetically in a collapsible tree. Click the arrow ▶ next to a project name to expand it and see its measurements.

Each measurement shows an icon indicating what data is available:

Icon	Meaning
▶	Raw time-domain signals (.ors/.orm)
◈	Pre-computed waterfall (Result.res)
▶◈	Both available

Click a measurement to select it. The right panel shows the available channels and a summary.

Choosing the data source

Two modes are available via radio buttons:

Raw signals (.ors/.orm)

This is the metrologically rigorous method. The tool reads raw vibration samples and a tacho signal, then computes one independent FFT per RPM bin (no speed-smearing).

Required settings:

Setting	Description	Recommended
Vibration channel	The acceleration, velocity or displacement channel to analyse	The main vibration sensor
Tacho channel	The tachometer pulse channel	Any channel named "Tacho", "Ref", "RPM"… (auto-detected if possible)
PPR	Pulses per revolution of the tacho encoder	1 for a single-pulse encoder
FFT lines	Frequency resolution: 400 to 6400 lines	1600 lines (good balance)
RPM bin size	Width of each RPM slice	50 RPM (reduce for finer RPM resolution)
RPM min/max	Limit the analysis to a speed range	Leave at 0/120 000 for full range

Optional tacho settings (advanced):

Setting	Default	Notes
Threshold	Auto (signal midpoint)	Override for noisy tacho signals
Hysteresis	5 %	Schmitt-trigger band — increase if false triggers occur
Edge	Rising	Use Falling if your encoder pulses are inverted

NVGate waterfall (.res)

Loads a pre-computed waterfall directly from the Result.res file produced by NVGate. This is faster but uses the STFT windows already computed by NVGate (speed-smearing may affect amplitude accuracy at high sweep rates and high orders).

Required settings:

Setting	Description
Waterfall channel	Select the vibration channel from the .res file
RPM reference	The tacho reference used to build the RPM axis (auto-selected to Tacho by priority)

Computing the diagram

Click ⚙ Compute Campbell Diagram (or Load Waterfall from Result.res in .res mode).

A progress bar appears at the bottom right. The computation runs in a background thread — the interface stays responsive.

When complete, the tool switches automatically to the Campbell Map tab.

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Campbell Map Tab

File:Campbell map tab.png

Campbell Map tab — diagram with order lines and resonance markers

The Campbell Map tab displays the diagram and all display controls in a scrollable right panel.

Use the ← Back to Data / Compute button at the top of the right panel to return without losing your current diagram.

Display Options

Option	Description	Tips
Colormap	Color palette for the amplitude intensity	jet (classic), hot, plasma, turbo
Scale	dB (logarithmic) or Linear	dB strongly recommended — compresses the dynamic range
dB min / dB max	Color axis limits	Narrow the range (e.g. −40 to 0 dB) to increase contrast on weak features
Freq min / Freq max	Frequency range displayed	Auto-set to the data's full band on first load; preserved on recompute
Peak threshold	Show Campbell dots within N dB of the loudest peak	−40 dB shows strong peaks; −80 dB shows more (noisier)
Marker size	Maximum circle size for the loudest peaks (pt²)	400 pt² default (Onosokki DS-3000 style)
Circle lower / upper	Linear amplitude limits for dot sizing	Leave blank for automatic scaling
Spectrogram background	Show the color-map waterfall behind the Campbell dots	Useful to see the full amplitude field
Apply Display	Redraw with current settings	Colormap changes apply immediately; other settings need Apply

Order Lines

Check or uncheck orders to overlay the corresponding harmonic lines on the diagram. Each order nX corresponds to the line f = n × RPM / 60.

Available orders: 0.5X, 1X, 1.5X, 2X, 2.5X, 3X, 4X, 5X, 6X, 7X, 8X, 9X, 10X, 12X, 15X, 20X.

Auto Marker (beta)

Click ⚡ Detect Orders & Resonances to automatically:

1. Select active order lines — the tool samples the amplitude along each order's frequency track across all RPM slices and checks the orders that carry the most energy (above 15 % of the strongest order).
2. Add resonance marker candidates — the tool averages the amplitude over all RPM slices to get a mean spectrum, then picks the top 5 peaks. A sub-bin parabolic interpolation gives accurate frequency estimates. Existing auto-markers are replaced each time.

Review the result and delete false positives with the − Remove button.

Resonance Markers

Resonance markers draw a horizontal dashed line at a fixed frequency — useful to visualise where a structural mode intersects the order lines (critical speed).

• + Add — opens a dialog to enter the frequency (Hz) and a label. The label appears on the plot with a coloured background.
• − Remove — select a row in the table then click Remove.
• Right-click on the plot — opens a context menu pre-filled with the cursor frequency for fast placement.

Markers persist across display changes (Apply Display, zoom, color change) but are cleared when a new diagram is computed.

Cursor

Move the mouse over the plot to see the current RPM, frequency, and amplitude in the status bar at the bottom of the window.

Export

Button	Output
PNG	High-resolution (200 dpi) image of the current diagram, including order lines and markers
CSV	Full amplitude matrix: rows = RPM bins, columns = frequency bins

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Interpretation Guide

Reading the diagram

1. Look for diagonal bright streaks aligned with order lines → strong harmonic excitations from the rotor.
2. Look for horizontal bright bands → structural resonances of the machine or test bench.
3. The intersections (where a diagonal crosses a horizontal band) are the critical speeds — operating RPMs to avoid for extended periods.

Adjusting the display for clarity

• If the diagram looks flat (all one colour), narrow the dB range (e.g. set dB min to −30 instead of −60).
• If weak features are invisible, widen the dB range or switch to Linear scale.
• Enable Spectrogram background to see the full spectral energy distribution.
• Reduce Peak threshold (less negative) to show only the strongest peaks; increase it (more negative) to reveal faint features.

Metrological note on waterfall source

When using raw signals, the tool applies the rigorous RPM-bin method: one independent FFT per RPM bin, driven by the tacho. This eliminates speed-smearing and gives accurate amplitudes at all orders.

When using a pre-computed waterfall (.res), the STFT windows are fixed in time. At sweep rates above ~50 RPM/s and for orders higher than 5×, some amplitude underestimation and peak broadening may occur. For resonance location (critical speed identification), this is generally acceptable. For amplitude-critical measurements (API acceptance tests, ISO compliance), prefer raw signals with a tacho.

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Technical Reference

Supported NVGate file types

File	Description
.orm	JSON metadata for one recorded channel (sampling rate, unit, name…)
.ors	Raw float32 little-endian samples in SI units
Result.res	Pre-computed NVGate results (waterfall, spectra…) — read via the OROS orostk library

Keyboard shortcuts

Key	Action
Mouse move	Update cursor (RPM, freq, amplitude)
Right-click on plot	Add resonance marker at cursor frequency
Scrollbar (right panel)	Access all display settings when in full-screen mode

System requirements

	Minimum	Recommended
OS	Windows 10	Windows 10/11 64-bit
RAM	2 GB	4 GB
Disk	600 MB free	1 GB free
Display	1280 × 720	1920 × 1080 or dual monitor

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See Also

• NVGate SOA and CBT techniques
• NVGate Tachometer — centred averaging
• OROS Multi-function FFT Spectrum Analyzer

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Campbell Diagram Tool — OROS NVGate · Last updated 2026