Question 1

What is vibration displacement?

Accepted Answer

Vibration displacement is the total distance a vibrating object moves from its rest position. It is typically measured in micrometers (μm) and can be expressed as peak (0-peak, the maximum excursion from center) or peak-to-peak (the full range of motion). Displacement is most useful for evaluating low-frequency vibration below about 10 Hz.

Question 2

What is the difference between peak and peak-to-peak displacement?

Accepted Answer

Peak displacement (0-peak) measures the maximum excursion from the center rest position in one direction. Peak-to-peak displacement measures the total range of motion — from the maximum positive to the maximum negative excursion. For sinusoidal vibration, peak-to-peak is exactly twice the peak value. Peak-to-peak is the more commonly specified parameter for displacement measurements.

Question 3

How do you convert vibration velocity to displacement?

Accepted Answer

To convert velocity (mm/s RMS) to displacement (μm peak-to-peak), use the formula: d_pp = v_RMS × √2 × 1000 / (π × f), where f is the frequency in Hz. The √2 factor converts RMS to peak, and dividing by (π × f) is the integration from velocity to displacement. The factor 1000 converts mm to μm.

Question 4

What is the relationship between displacement, velocity, and acceleration?

Accepted Answer

For sinusoidal vibration, displacement, velocity, and acceleration are mathematically related through frequency. Velocity is the time derivative of displacement (v = 2πf × d), and acceleration is the time derivative of velocity (a = 2πf × v). This means higher frequencies amplify acceleration relative to displacement, which is why displacement measurements are preferred at low frequencies and acceleration at high frequencies.

Question 5

When should I use displacement instead of velocity for vibration monitoring?

Accepted Answer

Displacement is most useful for low-frequency vibration monitoring, typically below 10 Hz (600 RPM). At low frequencies, velocity and acceleration values become very small even when displacement is significant. Large slow-speed machines like paper mill rolls, cooling tower fans, and reciprocating compressors often require displacement-based monitoring. Velocity (mm/s RMS) is preferred for general machinery in the 10–1000 Hz range, while acceleration is best above 1000 Hz.

參數	符號	單位	最佳範圍
位移	d	μm (mils)	低頻 < 10 Hz
速度	v	mm/s (in/s)	10 – 1000 Hz
加速度	a	m/s² (g)	> 1000 Hz

振動位移計算器

結果

位移 (峰峰值)

位移 (0-峰值)

加速度 (峰值)

實務範例

振動參數 — 快速參考