GENERAL NOTES ON SINE RATINGS

Sine ratings are more easily understood. The peak sinusoidal force is measured using test loads which are specified in the Companys Quality Standard test procedures. For systems up to 22.24 kN (2267 kgf 5000 lbf), loads are usually about twice the armature mass. For the larger machines heavier loads are used to demonstrate the off-set load capability of the armature guidance system and the pneumatic suspension system.

Transformer coupling

Velocity and Displacement Limits

Some systems use transformer coupling for optimum sine and/or random ratings. For sine operation the voltage tap is normally chosen to give maximum system thrust for a given amplifier size. This results in a finite velocity limit. For applications requiring higher velocity limits than those shown, it is sometimes possible to use the coupling transformer (when supplied) as an alternative voltage supply. If the drive voltage is higher, the velocity can be increased pro-rata, but the thrust must be reduced pro rata.

The maximum continuous velocity limit is 2m/s peak for all LDS vibration generators unless specified otherwise.

Transformer coupled systems sometimes have a displacement range lower than the maximum for the machine. This is because the transformer limits the low frequency drive voltage to the vibration generator.

Low frequency limitations

Direct amplifier/vibration generator coupling is now available for a wide range of systems giving full displacement at very low frequencies. It is still usual, however, to limit the low frequency response of the amplifiers to prevent unwanted dc off-set voltages in the control signal driving the vibration generator. For this reason direct coupled systems are not normally specified below 5 Hz. A simple modification can be used to extend the operating frequency of direct coupled systems down to 1 Hz or below. However the latest range of amplifiers ( SPAK ) are all dc coupled and include an integral armature centre positioning system.

High frequency limitations

The upper frequency for most vibration systems is limited by the vibration generator. In practical terms an approximate guide to frequency range at full force can be calculated by taking the first armature resonance and multiplying by a factor of 1.3. This will apply for small mass loads. For larger loads using fixtures the operating frequency range will depend mainly on the design of the fixture.

Maximum acceleration 'gn' limitations

The (maximum. sine) acceleration (gn) figures quoted in the tables are the maximum permitted levels for the system with an unloaded vibration generator table. This limitation can be for one or both of the following reasons.

  1. The maximum permitted level for the particular system vibration generator. This level is typically 100 gn peak (but can be lower) and will usually not provide the full rated force performance of the system.

  2. The maximum permitted level that will not exceed the full force rating of the system. This will usually be a system with a smaller amplifier rating than that required to drive the vibration generator to its full force rating.

In both cases it may not be possible to achieve the maximum quoted gn peak level over the full frequency range of the system under light or unloaded conditions, due to the high frequency voltage requirement of the vibration generator just prior to the fundamental armature resonance being beyond the capability of the amplifier.

SUMMARY

  1. Check the maximum force required assuming that the armature, load and fixture are mass loads.

  2. Check that the specified velocity and displacement levels meet the test requirements.

  3. Velocity limits can sometimes be increased by using an alternative voltage tap which may be available on a matching transformer. Thrust will, however, need to be de-rated pro-rata.

Introduction  General notes on Random Ratings  General notes on Shock Ratings  Sine Test Worked Example  Random Test Worked Example  V830-335 SPA10K Specification

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