GENERAL NOTES ON SHOCK RATINGS

Shock (bump) ratings are specified using HALF SINE waveforms. System ratings are summarised on System Performance data sheets which indicate the following limitations.

1. System Peak Force Level.

2. Peak Acceleration Level.

3. Peak Velocity Level.

4. Peak Acceleration/Pulse Duration boundary limits which have been calculated for LDS vibration generators with a peak to peak displacement range of 51 mm. The assumption is also made that pre-pulse and post-pulse acceleration levels will not exceed 10% of the specified shock (bump) test level.

General

In most cases for a given system size, the peak shock (bump) force rating will be approximately the same as the equivalent system sine rating. The peak velocity limit will also be very close to the system sine velocity limit. It follows that peak force (current) and velocity (voltage) can only be varied by using alternative transformer taps when these are available.

The vibration generator shock (bump) peak force can be rated up to two (2) times the sine peak force provided that the amplifier has sufficient power to supply the required current (force) and voltage (velocity) required by the test waveforms. Again, an alternative transformer tap may help to optimise the shock force rating for a particular waveform which has a low velocity requirement.

To rate any vibration generator to have a shock (bump) force rating of twice the sine rating a larger amplifier will normally be required.

As a rough guide, if it is not required to increase the shock velocity limit, it will be necessary to double the amplifier size to achieve a shock force rating two (2) times the peak sine force rating.

It is important to note that vibrator body motion will occur as the test load increases. For most shock (bump) tests it is possible to lock-out the vibration generator isolation system so that the vibrator can be thus considered to be mounted on a rigid trunnion.

Caution: Locking the isolation system is not recommended for normal sine or random testing.

A shock (bump) performance table can be provided on request for any system.