The essential components of a vibration test system are:

Electrodynamic Shaker
Amplifier
Controller
Accelerometer

HOW DOES A VIBRATOR WORK?

In principle, the electrodynamic vibrator operates like a loudspeaker, where the movement of the coil (armature) is produced by an electrical current in the coil, which produces a magnetic field opposing a static magnetic field. The static magnetic field is produced by a permanent magnet in small vibrators and an electromagnet in large vibrators. The electromagnet is a coil of wire which is commonly referred to as the field coil.

HOW TO SIZE AN ELECTRODYNAMIC VIBRATION TEST SYSTEM

1. Determine physical size and weight of the maximum sized unit to be tested (uut) as well as physical size, weight and configuration of any fixtures to be used. Remember to add the weight of the armature.
2. Determine the maximum g sine and grms random required. If shock is required, get the peak g/time duration requirement. For example: 30 g/11msec.
3. Compare the physical size of the maximum uut and or fixture to shaker table diameters available. Select a shaker with an equal diameter to the largest size item to be tested (ideally); do not select a shaker with a table diameter equal to less then one-half of the max of the item.
4. Calculate sine, random and shock forces required using this equation: F=MA, where F = Required Force, M = Total Mass of uut + fixture + armature weight (total mass to accelerated), A = maximum Acceleration required for sine, random or shock.
5. Multiply the calculated values by 1.25 to get the system force ratings needed to meet the application. (The 1.25 gives a safety factor which ensures tests will not exceed 80% of design ratings of a selected system) Compare the system ratings to select the best system for the job.
   
   Other considerations:
   
6. System force capability – can it move the largest envisaged test piece to the maximum envisaged test levels?
7. Main performance characteristics; namely, displacement, velocity and frequency limitations.
8. Payload support capacity – will external help be needed to physically support the payload?
9. Operating environment – will it be used in a laboratory by trained staff, or on the factory floor by untrained workers? Are there any restrictions with cooling services for water cooler equipment – is enough water available, and for air cooled, can the building accommodate the waste heat? There can be several other factors concerning the operational environment.
10. Type of application – is it a general-purpose test facility that must be versatile, or is it a dedicated production test installation?

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