Vibration Test Chambers: Shaker Size, Payload and Chamber Fit

Vibration test chambers work best when three things are true: the shaker has enough force for the total moving mass; the table and workroom are big enough to hold the specimen and its fixture; and the climate system can keep the part at the right temperature and humidity. You should pick a shaker that is too small to reach the lip. You can't get air to seal, or get into a chamber that is too small. This guide talks about how the size of the shaker, the weight of the specimen, the size of the specimen, and the fixtures all affect each other. It also shows how published LIB figures relate to these options and ends with a list you can send to any supplier.

Understanding Shaker Size in Vibration Test Chamber Selection

Since the shaker is what makes the system work, every test that comes after it has to be just as big as it is.

What "Size" Actually Means?

There is no one size for a shaker. Its rated force, armature diameter, usable frequency band, and stroke all explain what it is. There is a frequency range of 2 to 4000 Hz on LIB, and the rated force is 1000 kgf. The armature width is φ240 mm. LIB says that its systems could be water- or electricity-based. Do not read one at a time; read them all at once.

Force, Mass and Acceleration

When you multiply the total moving mass by the speed, you get force. The specimen, the fixture, the head expander, and the armature itself are all parts of the moving mass. A shaker can move quickly when the load is light and slowly when the load is heavy. Ask the seller to figure out how fast your biggest setup can go, giving you room for error.

Reading the Rating Table

The table below shows how the numbers that LIB has released answer common questions.

How Payload Capacity Affects Vibration Test Performance?

A lot of purchases go wrong with the payload because the rated figure doesn't tell the whole story.

Rated Load Versus Usable Load

LIB says that the most weight that can be loaded is 500 kg. That number shows how much weight the table can hold, not how fast it can move at full profile level. A part that is close to the load limit doesn't have much force for acceleration, so the test level that can be used goes down. First check the force, and then use the highest load as a structural limit.

Center of Gravity and Overturning Moment

Overturning moments in vibration test chambers are caused by a tall or off-center specimen. These moments load the shaker bearings and change the input. As low and in the middle as the part will allow, place the center of gravity. Since there is no maximum moment in the provided LIB data, you should ask the seller for one.

Effect on Test Accuracy

When there are heavy loads on the shaker-fixture-specimen system, the resonant frequency goes down. This can make the workable band smaller. Closed-loop control fixes the problem by changing the drive signal, but it can't go over the limits of the amplifier and shaker. Control is better when the load is lighter, the fixture is shorter, or the group of specimens is smaller.

Matching Test Specimen Dimensions With Chamber Size

The sample has to fit on the table inside the lab, leaving space for air to flow.

Table Size

There is a 600 x 600 mm head expander and a 600 x 600 mm horizontal slide table on LIB. Testing can be done in both the vertical and horizontal directions. When testing vertically, the head expander gives you a bigger area to set up than just the moving coil. Compare these measurements to the footprint of your specimen, which should include the fixture flanges.

Workroom Clearance

A specimen that touches the walls of the chamber stops airflow and makes it harder to keep the temperature even. Even though LIB calls for a centrifugal fan to make sure air flows evenly, crowded loads can still mess it up. Make sure there is space on all sides and above for the table to move up and down.

Chamber Formats

LIB has basic and unique designs for table, floor-standing, and walk-in types. Small electronics might work well with a small size, but big groups like battery packs or aircraft racks might need a bigger or custom build. The data given doesn't give workroom sizes for each model in the vibration series, so you should ask for drawings.

Fixture Weight and Mounting Requirements for Vibration Testing

It takes the same amount of force and weight as the object to move the anchor.

Weight Budget

The mass of the device is added to the moving mass in vibration test chambers, so a heavy fastener slows down the object. Because they are stiff for their weight, aluminum and magnesium metals are often used. However, the choice you make will rely on the temperature range and your needs. Before you choose the shaker's size, add up the fixture, bolts, and any adapter plates.

Stiffness and Resonance

In the test band, a fixture shouldn't have any resonances. At certain frequencies, a flexible fixture boosts or lowers the input, which means that the part feels a different profile than what the controller says. Problems are found before the real test starts by using accelerometers on the anchor to do a low-level check.

Mounting Fidelity and Thermal Limits

Use the same screws, pressure, and interface to mount the object the same way it is used. Fixture materials must also be able to handle changes in temperature inside the box without coming loose. The LIB specification table lists temperatures from -50 °C to +150 °C. Make sure the design of your fixture and the fasteners you use work with that window.

How Chamber Fit Influences Vibration Test Accuracy and Stability?

When a chamber fits well, the data is cleaner, and the benefits can be seen in many places.

Airflow and Temperature Uniformity

With PT100 Class A sensors and ±2.5% RH humidity deviation, LIB says that the temperature can change by ±0.5 °C and stay the same within ±2.0 °C. Those numbers are correct for a workroom that is pretty full. Putting sensors on both the part and the air in the box is important because an oversized specimen or a heavy fixture can stop the flow of air.

Sealing at the Shaker Interface

A weak spot for leaks and humidity is often where the shaker hits the chamber. It says that a patented interface sealing system and an air-drying system keep the moisture around it to a minimum. Ask each supplier how the seal works with your table stroke and the different temperatures.

Control Stability

LIB talks about closed-loop control using Bitzer or Bock compressors and RKC or Siemens computers. It has a digital power amplifier, a cooling fan, a digital controller, and sensors. A shaker that is close to its limits is not as stable as one that is running with some room to spare. Select a system that can handle levels higher than the highest one you have planned.

A Practical Checklist for Selecting the Right Chamber Configuration

Build the Brief

Write down the specimen's weight and size, its center of gravity, the mass of the fixture, its axes, the profile type, the temperature and humidity ranges, the dwell times, and the total length of time for vibration test chambers. Because LIB says these can be mixed, add any needs for altitude, pressure, or corrosion. A full brief lets the seller suggest a plan without having to guess.

Ask for Written Figures

Ask each supplier for a table with the following items.

Confirm Support and Site Needs

LIB reports ISO 9001, CE certification, third-party testing by SGS and TUV, a 3-year warranty, lifetime service, 24/7 support, 29 agents and service centers in Malaysia, Canada, the United Kingdom and the United States. Shaker systems also need a strong floor, power supply and a blower with a muffler, where LIB lists 4 kW. Check noise, drainage, and door clearance.

Common Fit Mistakes and How to Avoid Them

Most disappointments can be traced back to a few mistakes that are simple to avoid.

Sizing by Specimen Alone

A lot of the time, buyers only count the specimen's weight and forget to count the fastener, head expander, and armature. This makes a shaker that can't get to the right level. Size by the total mass that is moving.

Ignoring Future Needs

As product lines grow, a chamber bought for the smallest part today might not work on the biggest part next year. The investment is safe because there is a small increase in force, table area, and workroom volume. Oversizing costs more to buy and run, so weigh both risks.

Accepting Unconfirmed Specifications

The ranges of the supplied LIB content are a little different in the overview and the specification table. Before signing off, you should always ask for one confirmed figure in writing and do an acceptance test with a reference load.

Conclusion

When the specimen's shaker force, payload, table size, attachment design, and temperature capabilities are all in agreement, vibration test chambers produce reliable results. Size by total moving mass, leave room for airflow and stroke, check the stiffness of the fixture, and ask for written copies of all important figures. Compare providers based on their service reach, repeatable testing, closing design, and safety features. A chamber that fits the test within a certain range gives consistent results, allows for qualification reviews, and avoids having to redo work, which saves money.

Are you ready to set up your test? LIB Industry makes vibration test chambers and provides turnkey environmental testing solutions. They will look over your samples and standards and send you a clear quote. Write to ellen@lib-industry.com today.

FAQ

How do I know if a shaker is large enough?

Multiply the mass of the specimen, the fastener, the head expander, and the armature by the peak acceleration. Then, compare the result to the rated force, allowing some room for error. Request that the seller check the math.

Does maximum load equal usable test level?

No, the maximum load is the limit of the structure. When making your profile, check the force against the total moving mass separately because heavy loads slow down the speed that can be reached.

Why leave clearance around the specimen?

For even temperature and humidity, air must flow, and there must be room for strokes during vertical testing. Too many loads stop airflow and make control less accurate.

References

1. International Electrotechnical Commission. (2008). IEC 60068-2-6: Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal). IEC, Geneva.

2. International Electrotechnical Commission. (2019). IEC 60068-2-64: Environmental testing – Part 2-64: Tests – Test Fh: Vibration, broadband random and guidance. IEC, Geneva.

3. U.S. Department of Defense. (2019). MIL-STD-810H: Environmental Engineering Considerations and Laboratory Tests.

4. Harris, C. M., & Piersol, A. G. (Eds.). (2002). Harris' Shock and Vibration Handbook (5th ed.). McGraw-Hill, New York.