An Electrodynamic Vibration System and an audio system are somewhat similar in the basic principle. In an Electrodynamic Vibration System the Electrodynamic Shaker works like the speakers of an audio system. The Vibration Controller generates the signal that is feed to a Power Amplifier much like an MP3 Player of an audio system. The Power Amplifier’s outputs is proportional to the input signal by a fixed gain. This output of the Power Amplifier matches the input impedance of the speaker in an audio system and Electrodynamic Shaker in an Electrodynamic Vibration System. The main purpose of speaker in an audio system is to drives the diaphragm to create sound whereas the main purpose of Electrodynamic Shaker in an Electrodynamic Vibration System is to create the vibration itself.
The one big difference between the two is that in an Electrodynamic Vibration System, a sensor is placed on the armature of the Electrodynamic Shaker to sense the acceleration and provide a negative feedback to the Vibration Controller so that it may control the vibrations to meet the required test parameters.
The basic formula behind any Electrodynamic Vibration System is Force = Mass × Acceleration.
- The unit of Force is ‘Newton’ (N) as per SI and ‘kgf’ as per Gravitational Units
- The unit of Acceleration is ‘m/s²’as per SI and ‘g’ as per Gravitational Units
- The unit of Mass is ‘kg’ as per SI and Gravitational Units
An acceleration of 9.8 m/s² is 1 g. To make the math easy this value of 9.8 m/s² is sometimes referred as 10 m/s². If we have a mass of 10 kg and acceleration is 10 m/s² or 1 g, then we get a force of 100 N if we consider acceleration in m/s² and 10 kgf if we consider acceleration in g. Hence, we say that 10 N = 1 kgf.
In the real world, vibration is a noise with infinite degree of freedom, but in a laboratory, this noise has to be made meaningful. We therefore break down vibration to Acceleration (m/s²), Velocity (m/s) and Displacement (m) at a single or multiple Frequency (Hz). From these values we recreate the vibration in a controlled manner while monitoring the response of the Unit under Test (UUT).
- For given Frequency and Acceleration, Velocity(v) is derived by
- For given Frequency and Acceleration, Displacement(d) is derived by
- For given Frequency and Velocity, Acceleration(g) is derived by
- For given Frequency and Velocity, Displacement(d) is derived by
- For given Frequency and Displacement, Acceleration(g) is derived by
- For given Frequency and Displacement, Velocity(v) is derived by
Major Sub Systems of an Electrodynamic Vibration System are:
An Electrodynamic Shaker converts electrical energy from the Power Amplifier to mechanical vibrations using the principles of electromagnetism as described by Maxwell’s Right Hand Rule and Fleming’s Left Hand Rule.
A Power Amplifier is a Class-D – Full Bridge – Switching Amplifier which multiplies the voltage output of the Vibration Controller by a fixed gain, with great efficiency and high current capability, as required by the Electrodynamic Shaker.
A Head Expander is bolted to the Armature head for increasing the platform size in the vertical orientation for testing in Z axis. A Head Expander can be Non-Guided or Guided of Square or Circular shape
Horizontal Slip Table
A Horizontal Slip Table is a frictionless platform used for vibration testing in X and Y axis. The Electrodynamic Shaker turns from its vertical orientation to a horizontal orientation to couple with a Horizontal Slip Table.
A Vibration Controller allows the user to create a test profile on a PC and generates a signal in real time to match the test profile. An Accelerometer on the Electrodynamic Shaker provides feedback to keep the system under closed-loop control.