Vibration Frequency Analysis

What Is Vibration Frequency?

Vibration frequency is the number of vibration cycles per second. It is measured in Hertz (Hz).

Basic Formula

[
\text{Frequency (Hz)} = \frac{\text{RPM}}{60}
]

Where:

• RPM = Rotational speed (revolutions per minute)
• Hz = Cycles per second

Example

If a machine runs at 1800 RPM:

[
\text{Frequency} = \frac{1800}{60} = 30 \text{ Hz}
]

This is called the fundamental frequency (1×).

Why Vibration Frequency Analysis Is Important

Vibration frequency analysis is widely used in:

• Predictive maintenance
• Condition monitoring
• Fault diagnosis
• Machine health monitoring
• Structural engineering
• Automotive and aerospace industries
• Power plants and manufacturing

Key Benefits

• Early fault detection
• Reduced downtime
• Lower maintenance cost
• Improved safety
• Longer equipment life

Core Components of Vibration Frequency Analysis

Modern vibration analysis involves multiple frequency types. Your calculator calculates all major frequencies used in real-world diagnostics.

1) Fundamental Frequency (1× RPM)

The fundamental frequency is the base vibration frequency of a rotating machine.

[
f_{1×} = \frac{\text{RPM}}{60}
]

This frequency is usually linked to:

• Rotor imbalance
• Shaft rotation
• Basic mechanical motion

2) Electrical Frequency

Electrical frequency depends on the number of motor poles.

[
f_{electrical} = f_{1×} \times \text{Pole Multiplier}
]

Typical pole multipliers:

Poles	Multiplier
2	1.0
4	0.5
6	0.333
8	0.25
10	0.2

Electrical frequency is useful for detecting:

• Motor electrical faults
• Magnetic imbalance
• Power supply issues

3) Harmonic Frequencies (n×)

Harmonics are multiples of the fundamental frequency.

[
f_{harmonic} = f_{1×} \times n
]

Where:

• n = harmonic order (1, 2, 3, 4, 5…)

Examples:

• 2× frequency → misalignment
• 3× frequency → looseness
• Higher harmonics → structural resonance or faults

4) Gear Mesh Frequency (GMF)

Gear mesh frequency occurs when gear teeth engage.

[
f_{gear} = f_{1×} \times \text{Gear Ratio}
]

Gear mesh frequency helps identify:

• Gear wear
• Tooth damage
• Backlash
• Gear misalignment

5) Blade Pass Frequency (BPF)

Blade pass frequency occurs in fans, turbines, and impellers.

[
f_{blade} = f_{1×} \times \text{Number of Blades}
]

Blade pass frequency indicates:

• Blade defects
• Flow turbulence
• Aerodynamic issues
• Fan imbalance

6) Bearing Frequencies

Bearings generate specific frequencies when defects occur.

Your calculator computes four key bearing frequencies:

(a) BPFO – Ball Pass Frequency Outer Race

[
BPFO = f_{1×} \times \text{BPFO Factor}
]

Indicates defects on the outer race.

(b) BPFI – Ball Pass Frequency Inner Race

[
BPFI = f_{1×} \times \text{BPFI Factor}
]

Indicates defects on the inner race.

(c) BSF – Ball Spin Frequency

[
BSF = f_{1×} \times \text{BSF Factor}
]

Indicates rolling element defects.

(d) FTF – Fundamental Train Frequency

[
FTF = f_{1×} \times \text{FTF Factor}
]

Indicates cage or retainer defects.

Bearing Type Influence

Different bearing types have different frequency factors:

• Ball bearings
• Deep groove ball bearings
• Cylindrical roller bearings
• Tapered roller bearings
• Angular contact bearings

This is why your calculator allows bearing selection.

How Vibration Frequency Analysis Works in Practice

Step 1: Measure RPM

Measure the machine rotational speed.

Step 2: Convert RPM to Frequency

Use the formula:

[
f = \frac{RPM}{60}
]

Step 3: Calculate Key Frequencies

• Fundamental frequency
• Electrical frequency
• Harmonics
• Gear mesh frequency
• Blade pass frequency
• Bearing defect frequencies

Step 4: Compare with Measured Data

Compare calculated frequencies with vibration spectrum data from sensors.

Step 5: Identify Faults

If measured peaks match calculated frequencies, faults can be identified.

Common Faults Detected by Frequency Analysis

Frequency Pattern	Possible Fault
1× RPM peak	Imbalance
2× RPM peak	Misalignment
Multiple harmonics	Looseness
Gear mesh frequency	Gear damage
BPFO/BPFI peaks	Bearing defects
Blade pass frequency	Fan blade issues
Electrical frequency	Motor faults

Example Calculation (Real Case)

Assume:

• RPM = 1800
• Poles = 4
• Gear ratio = 2.5
• Blades = 12
• Harmonic = 3

Step 1: Fundamental Frequency

[
f_{1×} = \frac{1800}{60} = 30 \text{ Hz}
]

Step 2: Electrical Frequency

[
f_{electrical} = 30 \times 0.5 = 15 \text{ Hz}
]

Step 3: Gear Mesh Frequency

[
f_{gear} = 30 \times 2.5 = 75 \text{ Hz}
]

Step 4: Blade Pass Frequency

[
f_{blade} = 30 \times 12 = 360 \text{ Hz}
]

Step 5: Harmonic Frequency

[
f_{harmonic} = 30 \times 3 = 90 \text{ Hz}
]

These values help engineers interpret vibration spectra.

Applications of Vibration Frequency Analysis

Industrial Machines

• Motors
• Pumps
• Compressors
• Gearboxes

Energy Sector

• Turbines
• Generators
• Windmills

Automotive Industry

• Engines
• Transmissions
• Bearings

Structural Engineering

• Bridges
• Buildings
• Towers

Aerospace

• Aircraft engines
• Rotating components

Advantages of Using a Vibration Frequency Calculator

A vibration frequency calculator simplifies complex calculations.

Key Advantages

• Fast and accurate results
• Multiple frequency outputs
• Fault prediction support
• User-friendly analysis
• Engineering decision support

Your calculator provides:

• Fundamental frequency
• Electrical frequency
• Gear mesh frequency
• Bearing frequencies
• Blade pass frequency
• Harmonic frequency

This makes it a complete vibration analysis tool.

Limitations of Vibration Frequency Analysis

Although powerful, vibration analysis has limitations:

• Results are theoretical
• Real conditions may vary
• Noise can affect measurements
• Load and environment influence vibrations

Therefore, calculated values should always be verified with actual sensor data.

Best Practices for Accurate Analysis

• Use calibrated sensors
• Measure RPM accurately
• Analyze multiple harmonics
• Compare trends over time
• Combine vibration analysis with temperature and acoustic data