Vibration shaker sizing is not an isolated decision; it is an interdependent calculation chain where every link impacts the next:
Core Concept: Manufacturer ratings (including ASLI TEST's) for rated thrust exclude the mass of the payload and custom fixtures. Always budget a 20% to 30% force safety margin. Neglecting this means the system will fail to reach target acceleration once real-world expanders are bolted on.
Step 1: Size the Table to the Specimen
The footprint of your test object dictates the minimum size of the table. A standard aerospace and automotive rule of thumb is:
This ensures the specimen does not overhang the table edges, which would introduce structural flexing and cause edge-to-center amplitude deviations exceeding ±3%.
The Headboard Tax: Adding large vertical expanders or slip tables increases moving mass significantly and lowers the upper frequency limit. For example, an ASLI TEST bare armature rated up to 2500Hz may see its practical limit drop to 1500Hz once fitted with a wide expander.
Material Properties: Aluminum vs. Magnesium
| Material | Density | Specific Stiffness | Cost Profile | ASLI TEST Recommended Use Case |
|---|---|---|---|---|
| Aluminum 6061-T6 | ≈2.7 g/cm³ | Good | Cost-Effective | Standard industrial profiles; general purpose testing. |
| Magnesium Alloys | ≈1.8 g/cm³ | Excellent | Premium | High-frequency profiles; large head expanders where weight reduction is mandatory. |
Step 2: Calculate Required Force (Thrust)
The foundational calculation uses Newton's Second Law, adjusted for environmental testing environments:
- mtotal = Specimen Mass + Fixture Mass + Table/Expander Mass + Armature Mass (from ASLI TEST datasheet)
- a = Target Acceleration (in g or m/s²)
- Safety Factor = 1.2 to 1.3 (ASLI TEST highly recommends 1.3 for high-frequency profiles)
Total Moving Mass = 50kg (Specimen) + 15kg (Fixture) + 25kg (ASLI TEST Expander) + 12kg (Armature) = 102 kg
F = 102 kg × 10g × 1.3 = 1326 kgf (~13 kN)
➔ Recommended selection: An ASLI TEST system rated at ≥ 1400 kgf (14 kN) force.
Common Error: Many operators multiply just the specimen weight by the target acceleration. This undercalculates the demand by 30% to 50% because it treats fixtures and the copper armature coil as weightless. ASLI TEST provides complimentary calculations to clear up these discrepancies.
Step 3: Map the Performance Curve
Every ASLI TEST electrodynamic shaker is bound by a Performance Curve divided into three discrete physical regions:
| Region | Frequency Range | Limiting Physical Factor |
|---|---|---|
| Low Freq | Typically below 50Hz | Displacement (Peak-to-Peak Stroke limit) |
| Mid Freq | Approx. 50 to 300Hz | Velocity (Power amplifier voltage cap) |
| High Freq | Above 300Hz | Force/Acceleration (Armature current/mass limits) |
Note: Performance curves are mapped under "Bare Armature" conditions. Adding loads shifts these envelopes downward.
The High-Frequency Trap: Table Expansion vs. Response
Per ISO 5344, the maximum usable high-frequency limit of a shaker system is constrained by its first major axial resonance frequency. Bulky, wide expansion tables shift this resonance point directly into lower frequencies.
If your test profile calls for 2000Hz, but an oversized expander drops the system's combined resonance point down to 1200Hz, any data collected at 2000Hz will be unusable due to massive cross-axis distortion and phase delays.
ASLI TEST 7-Step Sizing Matrix
- Log physical dimensions & weight of the largest intended test article.
- Define testing profiles (g level, frequency band, random/sine profiles, standards like MIL-STD or ISO).
- Sum total moving mass (Specimen + custom fixture designs + expander head + armature).
- Run the force equation using a 1.3 margin multiplier.
- Select structural material: Aluminum for standard setups, Magnesium for critical high-frequency projects.
- Plot against ASLI TEST Performance Curves to secure velocity and stroke clearance.
- Verify resonance frequencies to guarantee cross-axis metrics remain clean at your highest testing octaves.