Shock Pulse Transducers – Detect Bearing Damage Early

  1. Overview

Shock Pulse transducers are specifically designed for early bearing damage detection.

They are five to seven times more sensitive than conventional vibration transducers and can detect very early-stage bearing defects.

  1. Construction

A Shock Pulse transducer consists of:

  • Brass reference mass
  • Piezoelectric crystal
  • Base plate

  1. Operating Principle

3.1 Resonance

The brass reference mass is mechanically and electrically tuned to 32 kHz, similar to how a tuning fork responds at its resonant frequency.

When a shock wave reaches the transducer:

  • The reference mass begins a dampened oscillation at 32 kHz.
  • The oscillation is proportional to the energy of the shock wave.

3.2 Signal Generation

  • The oscillating reference mass compresses the piezoelectric crystal.
  • The crystal produces a voltage proportional to the oscillation.
  • The peak amplitude of the signal is directly related to the impact velocity.

Since impact velocity depends on shaft speed, higher rotational speed generally produces higher shock amplitude.

  1. Signal Processing

The raw signal is processed as follows:

  1. A band-pass filter removes frequencies below and above 32 kHz.
  2. The signal is modulated on a carrier frequency.
  3. The carrier frequency is then:
    • Demodulated
    • Rectified
    • Enveloped

Result

The final enveloped signal profile contains information about:

  • Strong impacts
  • Weak impacts

This profile is used to evaluate bearing condition.

  1. dBi and dBn Calculation

Two programmable parameters are required to calculate the dBi (decibel initial) value, which is then used to generate the normalized dBn scale (Green / Yellow / Red condition scale):

  • Shaft rotational speed (RPM)
  • Bearing inside diameter

Because shock amplitude is a function of impact velocity, and impact velocity depends on shaft speed, RPM is a critical input parameter.

  1. Normalized Scale

The normalized (dBn) scale allows comparison between different bearings and operating conditions by compensating for speed and bearing size.

This enables consistent condition evaluation using a standardized Green / Yellow / Red indication system.

Measurement Location – Shock Pulse Method

Measurement location remains important when using the Shock Pulse Method (SPM).

  • Shock pulses are omnidirectional, unlike some vibration measurements that depend on direction.
  • Select measurement points that follow the mass path directly to the bearing for best signal transmission.
  • Minimize material interfaces, joints, and other sources of interference between the bearing and the measurement point.

Proper measurement location improves signal quality and diagnostic accuracy.