Customers often send us two numbers first: equipment weight and peak shock acceleration. These are enough to estimate shock force, but not enough to select a vibration isolator.

For example, 5 g tells us the peak acceleration, but 5 g / 11 ms gives much more useful information. The additional 11 ms describes the shock pulse duration, which can significantly affect isolator displacement and equipment response.

This is why shock isolator selection at HOAN starts with the load calculation but does not end there.

Basic Shock Load Formula

A simple estimate can be made using:

F = m × a

When acceleration is given in g:

F = m × G × 9.81

Where:

· F = estimated inertial force (N)

· m = equipment mass (kg)

· G = peak shock acceleration (g)

· 9.81 = gravitational acceleration (m/s²)

For a 40 kg unit exposed to a 5 g shock:

F = 40 × 5 × 9.81 = 1,962 N

The estimated peak inertial force is approximately 1.96 kN.

If four isolators carry the equipment equally, the theoretical force is about 490.5 N per isolator.

In an actual installation, however, we rarely assume perfect load distribution without checking the mounting layout and center of gravity.

Why 5 g / 11 ms Is More Useful Than 5 g Alone

Peak acceleration describes only part of a shock event.

Consider:

5 g / 11 ms

Here, 5 g is the peak acceleration and 11 ms is the pulse duration. Change the duration while keeping the same peak g, and the dynamic response can change as well.

This is a common issue in customer inquiries. We may receive the equipment weight and a value such as 5 g, but still need the pulse duration and shock direction before narrowing down an isolator model.

For many HOAN vibration isolators, 30 g / 11 ms is a commonly used shock verification condition. It provides a useful reference during product testing, although the applicable condition still depends on the individual model and application.

5 g / 11 ms vs. 30 g / 11 ms

For the same 40 kg equipment:

Increasing the peak acceleration from 5 g to 30 g increases the simple inertial-force estimate by a factor of six.

That does not mean an isolator should simply be selected with six times the load rating. Its dynamic response must still be considered.

What HOAN Checks After the Calculation

Once the basic shock load has been estimated, our engineers normally look at the actual installation.

Load distribution comes first. An offset center of gravity can place considerably more load on one or two mounts than the theoretical average.

Available travel is also critical. A softer isolator may reduce transmitted acceleration but allow greater movement. If that movement exceeds the available clearance, the equipment may contact surrounding structures or place additional stress on cables and connectors.

Mounting direction matters as well. Compression, shear and other loading directions can produce different responses from the same isolator.

In practice, these factors can eliminate a candidate even when its nominal load capacity appears suitable.

Shock Pulse Shape Also Matters

Common shock test profiles include half-sine, terminal peak sawtooth and trapezoidal pulses.

A specification should therefore include the waveform when it is known, rather than giving only a peak g value.

What We Look for at 30 g / 11 ms

For applications evaluated around 30 g / 11 ms, selecting the isolator with the highest load rating is not necessarily the correct approach.

During an engineering review, HOAN typically checks whether:

· the static load is within the suitable working range;

· sufficient travel is available during shock;

· transmitted acceleration remains acceptable;

· mounting orientation changes the effective response;

· the equipment has adequate surrounding clearance;

· repeated shocks could affect the mounting arrangement.

This is particularly relevant to wire rope isolators. Their shock performance depends not only on load capacity but also on deformation and energy dissipation through the wire rope structure.

A very stiff mount can restrict movement but transmit more acceleration. A softer mount can provide better attenuation but require more travel.

The correct choice has to balance both.

Shock Testing Standards

Different applications may reference different shock test standards.

MIL-STD-810H Method 516.8 covers mechanical shock test methods and is widely referenced when defining shock environments for equipment.

For electrical and electronic equipment installed in road vehicles, ISO 16750-3 addresses mechanical loads including vibration and shock.

These standards help define test conditions, but they should not replace application data. The appropriate shock requirement still depends on where and how the equipment will be installed.

Information Needed for Shock Isolator Selection

For a preliminary HOAN engineering review, the most useful information includes:

· Equipment weight and dimensions

· Center of gravity, if available

· Number and location of isolators

· Peak shock acceleration (g)

· Pulse duration (ms)

· Pulse waveform

· Shock direction

· Available displacement

· Mounting orientation

· Operating environment

· Installation drawing or STEP file

A drawing is particularly useful when the center of gravity or mounting points are not symmetrical.

From Shock Load to the Right Isolator

The formula F = m × a gives a useful first estimate, but it cannot identify the correct vibration isolator on its own.

In practical HOAN selection work, peak g, pulse duration, load distribution, available travel and mounting direction are reviewed together.

This avoids two common problems: choosing an isolator that is too stiff and transmits excessive acceleration, or choosing one that is too soft and allows more movement than the installation can accommodate.

FAQ

Is 30 g / 11 ms the same as 30 g?

No. 30 g describes peak acceleration, while 11 ms describes the pulse duration. Both are important when evaluating shock response.

Is 30 g / 11 ms used for all HOAN isolators?

No. It is a commonly used shock verification condition for many HOAN vibration isolators, but actual test conditions and performance depend on the model and application.

Can equipment weight and peak g determine the isolator model?

They provide an initial load estimate. Pulse duration, mounting direction, center of gravity, allowable movement and installation layout should also be reviewed.

Is a higher load rating better for shock isolation?

Not necessarily. A higher-capacity isolator may be stiffer and could transmit more acceleration to the protected equipment.

Need Help Selecting a Vibration Isolator?

Send HOAN your equipment weight, shock acceleration, pulse duration, mounting drawing and available displacement. These parameters allow our engineers to narrow down suitable isolator models before prototype testing or final validation.