Understanding Cascade Plots

Devices

Portable balancer & Vibration analyzer Balanset-1A

$2,364.82 Izvorna cijena bila je: $2,364.82.$1,915.80Trenutna cijena je: $1,915.80.

Parts

Vibration sensor

$107.76 Izvorna cijena bila je: $107.76.$71.84Trenutna cijena je: $71.84.

Parts

Optical Sensor (Laser Tachometer)

$148.47 Izvorna cijena bila je: $148.47.$83.82Trenutna cijena je: $83.82.

Devices

Balanset-4

$8,145.74

Parts

Magnetic Stand Insize-60-kgf

$55.08

Parts

Reflective tape

$11.97

Devices

Dynamic balancer “Balanset-1A” OEM

$2,077.45 Izvorna cijena bila je: $2,077.45.$1,676.33Trenutna cijena je: $1,676.33.

Definition: What is a Cascade Plot?

Cascade plot (also called waterfall plot, 3D spectrum, or spectral map) is a three-dimensional graphical display that shows how vibration frequency spectra change over time, speed, or another variable. The plot has frequency on the X-axis, time or speed on the Y-axis, and vibration amplitude on the Z-axis (typically shown as height and/or color intensity). Multiple spectra are stacked behind each other like cascading waterfalls, creating a 3D visualization that reveals patterns invisible in individual 2D spectra.

Cascade plots are particularly powerful for rotor dynamics analysis (identifying critical speeds during startup/coastdown) and for monitoring fault progression over time (watching bearing defect frequencies emerge and grow). They are also known as waterfall plots, with the terms used interchangeably.

Cascade Plot Construction

Axes and Dimensions

• X-Axis (Horizontal): Frequency (Hz, CPM, or orders)
• Y-Axis (Depth): Time, speed, or parameter being varied
• Z-Axis (Vertical/Color): Vibration amplitude
• Perspective: Typically viewed from front-top angle for clarity

Types Based on Y-Axis Variable

Speed-Based Cascade (Startup/Coastdown)

• Y-axis represents rotational speed (RPM)
• Generated during startup or coastdown
• Most common for critical speed identification
• Speed typically increases from front to back

Time-Based Cascade

• Y-axis represents calendar time
• Shows fault development over days, weeks, months
• Useful for monitoring progressive failures
• Recent measurements at back, old at front

Load-Based Cascade

• Y-axis represents load or power
• Shows how vibration changes with loading
• Useful for variable-load equipment
• Identifies load-dependent phenomena

Reading and Interpreting Cascade Plots

Key Features to Identify

Speed-Tracking Components

• Appear as diagonal lines (frequency increases/decreases with speed)
• 1× Line: Straight diagonal from origin (unbalance)
• 2× Line: Steeper diagonal (misalignment)
• Higher Orders: Even steeper diagonals

Fixed-Frequency Components

• Appear as vertical lines (constant frequency regardless of speed)
• Natural Frequencies: Vertical features at critical speeds
• Electrical Frequencies: 2× line frequency (120/100 Hz) appears vertical
• External Vibration: Constant frequencies from nearby equipment

Critical Speed Identification

• Where diagonal 1× line crosses vertical natural frequency feature
• Shows as “mountain peak” at intersection
• Amplitude maximum at critical speed
• Resonance amplification visible

Applications

Critical Speed Analysis

• Identify all critical speeds in operating range
• Verify separation margins from operating speed
• Assess damping from peak sharpness
• Compare experimental to predicted critical speeds
• Most common use in commissioning and troubleshooting

Bearing Defect Monitoring

• Time-based cascade showing bearing frequency emergence
• Watch BPFO, BPFI, BSF peaks grow over time
• Harmonic development indicates progression
• Predict failure timeline from growth rate

Order Analysis

• Frequency axis in orders (multiples of running speed) rather than Hz
• Speed-synchronous components appear as vertical lines
• Non-synchronous components appear diagonal
• Useful for variable-speed equipment

Fault Development Visualization

• Watch new frequency peaks emerge
• See existing peaks grow in amplitude
• Observe harmonic development
• Visualize sideband emergence

Creating Effective Cascade Plots

Data Collection

• Sufficient Slices: Minimum 10-20 spectra for clear visualization
• Consistent Increment: Even spacing in Y-axis variable
• Adequate Resolution: Frequency resolution sufficient to identify peaks
• Full Range: Cover complete operating range or trending period

Display Settings

• Amplitude Scale: Linear or logarithmic based on data range
• Color Map: Choose colors enhancing feature visibility
• Perspective Angle: Adjust for clarity (typically 20-30° elevation)
• Peak Retention: Some software shows peak envelope for clarity

Advantages and Limitations

Advantages

• Visualizes multidimensional data in understandable format
• Reveals patterns invisible in 2D plots
• Distinguishes speed-dependent from speed-independent components
• Comprehensive view of dynamic behavior
• Excellent for presentations and reports

Limitations

• Can be cluttered if too many components present
• Requires experience to interpret correctly
• Detail can be obscured in 3D view
• Difficult to extract precise numerical values
• Complements but doesn’t replace 2D analysis

Cascade plots are powerful visualization tools that add the dimension of time or speed to frequency analysis, revealing dynamic patterns and progressions that would be missed in static spectral views. Mastering cascade plot interpretation—recognizing diagonal vs. vertical features, identifying critical speed intersections, and tracking fault progression—is essential for advanced vibration analysis and rotor dynamics assessment.

---

← Back to Main Index