Reading a Random Vibration PSD: What the Control Loop Delivered

A shaker reproduces an input, not an environment. The test is only as representative as the profile you load and the fixture through which the specimen receives it, and both are decisions made long before the machine is switched on.

Applying that to a real purchase is easier when the equipment comes from a supplier that builds rather than assembles. Simulated Transportation Vibration Table is a typical example of a machine where the specification sheet is only half the story, because the fabrication and commissioning route determines how the numbers behave in service.

What to verify before you specify

1. Sine sweeps find resonances, random profiles reproduce stress

A sine sweep identifies natural frequencies and weak points, while a random profile with the correct PSD represents the cumulative fatigue of a real route. They answer different questions and are often both needed.

2. Force capability must match the fixture mass

The rated force on the table is not the usable force. The fixture, adapter and specimen all consume dynamic force, and the remaining margin determines the achievable excitation level.

3. The fixture is part of the measurement chain

A fixture that is too heavy reduces usable force, and a fixture that resonates introduces its own peaks into the result. Aluminium fixtures are common for good reasons.

4. Control strategy must cover the band of interest

A control strategy designed for one range can behave badly at the edges, and resonance control during a sweep needs the controller to be able to hold level as the specimen stiffness changes.

5. Axis selection follows the real failure mode

Vertical, horizontal and combined tests are not interchangeable. The axis sequence should be derived from the orientation the product actually experiences in transport and use.

6. Monitor for damage during the run

Fixtures crack, specimens loosen and adapters deform. A camera or accelerometer on the fixture catches this before it corrupts the data of a long run.

Mistakes that show up in the acceptance report

• Sizing the table on rated force without accounting for fixture mass.
• Using a heavy steel fixture where an aluminium one would do.
• Running a random profile without recording the PSD actually delivered.
• Ignoring fixture resonance until the data shows unexplained peaks.

Why the engineer who specified the chamber should visit the factory

Specification is a negotiation between what a process needs and what a machine can do, and both sides of it are better understood in person.

A walk through the production floor shows how a chamber is actually built, and a surprising number of specification disputes dissolve once the fabricator and the user have seen the same weld.

The engineering team that draws the chamber, the technicians that assemble it and the engineers that commission it work in the same organisation, so a question asked at the design stage gets a direct answer instead of a filtered one.

On-site commissioning is where the acceptance data is produced on the installed machine rather than on the factory data, which is the difference between a certificate and a verified result.

• In-house Manufacturing: Every machine is engineered, welded, assembled and tested under one roof. Two production plants control tolerances from raw sheet steel to final calibration.
• OEM & ODM Engineering: Drawings, PLC logic, instrumentation and chamber geometry are developed in-house, so non-standard chamber sizes and test profiles ship without external dependencies.
• Full In-House Calibration: Temperature, humidity, pressure and load cells are calibrated on our own accredited benches before shipment, with certificates issued per unit.
• QC at Every Stage: IQC, IPQC and OQC gates sit between material intake, welding, assembly and dispatch. Nothing leaves the line without a signed inspection record.

How the equipment is produced

The production route below is the one every HAOEN machine follows. It is listed because the steps a manufacturer controls are the steps that determine whether your laboratory receives a machine that performs as specified on the day it is commissioned, and still performs two years later.

1. Engineering Drawing — Chamber geometry, load frame, airflow and instrumentation are modelled and reviewed before any steel is cut.
2. Material Intake — Sheet metal, compressors, sensors and electrical parts pass incoming inspection against incoming QC checkpoints.
3. Cutting & Bending — CNC cutting and press braking form the chamber body, liner and door frame to millimetre drawings.
4. Welding & Forming — TIG and robot welding seal the chamber, followed by stress relief and surface treatment.
5. Assembly & Wiring — Refrigeration, electrical cabinets, sensors and control panels are installed and wired to the schematic.
6. Debugging & Calibration — Commissioning runs temperature, humidity, vibration and load profiles; data is logged per unit.
7. Packing & Documents — Crating, manuals, certificates and the QC file are completed and sealed for dispatch.
8. Delivery & Support — Shipment tracking, on-site installation and operator training are arranged with local partners.

Equipment referenced in this guide

• Simulated Transportation Vibration Table — Vibration Shaker Table System, manufactured in-house with per-unit calibration.
• Simulated Transportation VibrationTable — Vibration Shaker Table System, manufactured in-house with per-unit calibration.
• Simulated Transportation VibrationTable — Vibration Shaker Table System, manufactured in-house with per-unit calibration.

Conclusion

Specification is where a procurement process starts, but it is not where the result is decided. The variables that separate a repeatable test from an arguable one are the ones the manufacturer controls: the geometry of the chamber, the tightness of the weld, the stability of the control loop and the discipline of the calibration bench. Those are the variables worth asking about, because they are the ones that will still be there when the instrument is three years old and a colleague asks why the new machine and the old one give different numbers on the same specimen.

If you have a specification in front of you that has a profile, a volume and a tolerance, send it over. Our engineers will respond with a configuration, a lead time and the specific items in the manufacturing route that will affect your result.