In the field of industrial product transportation packaging verification, electromagnetic shakers are widely used to simulate the vibration environment during road, rail or sea transportation. The core purpose of testing is to assess the ability of products and packaging to withstand dynamic stresses, so as to detect potential structural defects or inadequate packaging protection in advance. The test is mainly divided into two modes: sweep frequency test and fixed frequency test, and there are significant differences between the two in principle, application scenarios and execution standards. The correct selection of the test mode is directly related to the accuracy of the test results and the value of engineering guidance.
The difference between the principle of swept frequency and fixed frequency
Sweep frequency testing refers to the test process in which the vibration frequency changes continuously over time according to a certain law (such as linear or logarithmic law) within a set frequency range. The aim is to find the resonant frequency points of the product and evaluate the response of the product in a broadband random vibration environment. The frequency change process can be described by the formula: f(t) = fstart + (fend - fstart) × (t/T), where fstartis the starting frequency, fendFor the termination frequency, T is the total time of the sweep frequency, and t is the current time.
Fixed-frequency testing is a continuous application of vibration for a specified period of time at one or more fixed frequency points. This test is mainly used to assess the fatigue strength and long-term stability of the product under a known and specific vibration environment (such as the power frequency of some rotating machinery).
Reference Standards
| Test type | Typical standards and core objectives |
| Sweep Frequency Test | ASTM D999, ISTA Series Standard: Used to find resonance points for packaging or products and to evaluate resonance residency. |
| Fixed frequency test | GB/T 4857.7, ISO 2247: Used to assess the durability of a product at a specific frequency (e.g., natural frequency of a means of transport). |
| Sweep Frequency Test | MIL-STD-810G Method 514.6: For Identification of Structural Vulnerabilities and Functional Inspection. |
| Fixed frequency test | Enterprise internal control standards: often used for quality consistency inspection at known product sensitive frequencies. |
Select the test type based on the test objective
The choice between swept and fixed frequency should not be based on subjective experience, but strictly based on the test objectives and the stage of the product life cycle. Here are the key considerations for decision-making:
| Select the situation for the sweep testing | Select the case of the fixed-frequency test |
| In the early stage of product design, its resonance characteristics are unknown. | The vibration characteristics of the product are known, and batch quality sampling is required. |
| It is necessary to comprehensively evaluate the dynamic response of the product over a wide frequency band. | Simulate a known, single, fixed vibration source environment. |
| Verify that the packaging effectively isolates and attenuates resonance. | Perform a long fatigue life test. |
| Meets the requirements of transportation simulation standards such as ISTA. | Comply with the requirements of certain specific national standards or industry standards. |
Common misconceptions
A common misconception is to blindly choose swept frequency testing as simply understood as "more comprehensive". In fact, if the vibration frequency of the product transportation environment is relatively fixed (such as near a certain engine), the use of fixed frequency testing can more realistically simulate working conditions and is more efficient. Conversely, if the fixed frequency test is carried out without knowing the dynamic characteristics of the product, the key resonance frequency point may be completely missed, resulting in the test being invalid.
Operational suggestions: First, check the product circulation environment data or relevant transportation standards (such as ISTA, ASTM, GB series) to clarify the test types and parameters recommended by the standards. Secondly, for new products, it is recommended to conduct a sweep frequency test to identify the resonance point, and then decide whether to perform a residence (fixed frequency) test at the resonance point according to the situation. Finally, the vibration value (displacement, acceleration), test duration and other parameters are strictly controlled according to the standard to ensure the reproducibility and comparability of the test.
Summary
Sweep frequency test and fixed frequency test are two complementary methods in the simulation transportation test of electromagnetic shaker table. The sweep frequency focuses on exploration and identification, and the fixed frequency focuses on assessment and verification. Understanding the differences in principle, closely focusing on the purpose of testing and following accepted technical standards is the fundamental prerequisite for ensuring that the test is scientific and effective, and provides a reliable basis for product design and packaging improvement. Any arbitrary choice that deviates from specific standards and test objectives may make the test work lose its due engineering value.
References
ASTM D999 Standard Method for Vibration Testing of Packaging Containers
ISTA Transport Packaging Test Series Standards
GB/T 4857.7 Basic tests for transport packaging parts - Part 7: Test methods for sinusoidal constant frequency vibration
MIL-STD-810G Environmental Engineering Considerations and Laboratory Testing
ISO 2247 Packaging - Complete Transport Packaging - Constant Frequency Vibration Test