A transit case uses isolating mounts to protect electronic payloads from vibration. These mounts are chosen with a natural frequency of vibration significantly different from the expected excitation frequency. This helps ensure the minimum of vibration is transmitted to the payload. However, there are challenges:
- Often the excitation frequency is either not known or a wide range of excitation frequencies and amplitudes should be anticipated.
- Natural frequency numbers for vibration mounts are usually derived from static testing. Under dynamic real-world conditions, resonance may happen at other frequencies.
For these reasons, when the payload cannot be risked, the safest course of action is to perform physical tests.
Simulating the real-world
The adjacent video shows a test of vibration attenuation performance. Here a transit case is mounted on a shaker table which can be driven through a range of frequencies and amplitudes. The payload is secured in the case and instrumented with accelerometers hooked to a data acquisition system.
In the video, two jars of water are used to demonstrate vibration attenuation. In the one mounted on the case, the water is clearly agitated while that on the payload shows very little disturbance. Clearly the isolating mounts are doing their job, protecting the case contents from damaging vibration.
Verify the attenuation provided
Vibration, especially if sustained, as happens during air transportation, can be very damaging to electronics. Unless appropriate protection is provided there is a risk of mission-critical equipment being rendered inoperable, possibly with expensive consequences.
A high-quality transit case uses elastomeric or wire rope isolators to attenuate vibration. However, these must be selected carefully with regard to the external vibration frequency to avoid resonance transmitting vibration to the payload. Specification sheets will provide some guidance. However, when protection cannot be left to chance the best approach is to perform physical testing.