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.
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.