How to Choose the Right Electrodynamic Vibration Test System?

Selecting the ideal electrodynamic vibration test system for your specific needs is a critical decision that impacts the accuracy and effectiveness of your product testing. At Dongguan Precision Test Equipment Co., Ltd., we understand that navigating the various options can be complex. Our priority is to ensure you choose a system that perfectly aligns with your test requirements.

The type, size, and power level of the vibration shaker are fundamentally determined by the demands of your testing protocols. If you're new to vibration testing or uncertain about your options, we strongly encourage you to consult with our experienced engineers early in the selection process. Seeking our advice upfront can help you avoid potential pitfalls, as several interconnected factors can influence our recommendations. These key considerations include:

1) Determining Shaker Sizing: Applying the Laws of Motion

The cornerstone of selecting the appropriate shaker lies in understanding Newton’s second law of motion:

Force = Mass x Acceleration (F=MA)

Our electrodynamic vibration systems have output force ratings specified in three key scenarios:

• Sine Force: Expressed as kgf (kilonewtons) peak.
• Random Force: Expressed as kgf (kilonewtons) RMS (Root Mean Square).
• Shock Force: Expressed as kgf (kilonewtons) peak.

Applying Newton’s Law in Shaker Selection:

To assess the suitability of a particular vibration test system, consider the following aspects in relation to Newton's Law:

• Force Requirement (kgf): A practical estimation of the required sine force can be calculated using the following formula:

  F = Moving MASS (Specimen Mass + Fixture Mass + Armature Mass) x G (Desired Acceleration) x 1.30 (Safety Factor)

  The 1.30 safety factor accounts for potential resonances and other dynamic effects.

• Maximum Displacement: Ensure the shaker's maximum displacement capability meets or exceeds the displacement demands of your test specification, particularly at lower frequencies.

• Maximum Velocity: Verify that the shaker's maximum velocity rating is sufficient for the velocity requirements of your test profile, especially during frequency sweeps.

• Maximum Test Frequency: The shaker's usable frequency range must extend to the maximum frequency specified in your test protocol.

2) Specimen Specifics: Understanding Your Test Article

To accurately recommend a system, we require detailed information about your test specimen:

• Specimen Description: A brief description of the product or component being tested.
• Specimen Test Mass: The weight of the item to be tested.
• Specimen Dimensions: The physical size and shape of the test article.
• Specimen Center of Gravity (CG): The location of the specimen's center of mass, crucial for proper fixturing and load distribution.
• Specimen Mounting Considerations: How the specimen will be attached to the fixture (e.g., bolt pattern, number of mounting points).

3) Fixture Specifics: The Interface to Your Specimen

The test fixture plays a critical role in transmitting the vibration to the specimen and can significantly impact the overall test quality and introduce resonances. Consider these factors when choosing a shaker system:

• Fixture Existence: Do you already have suitable fixtures, or will new ones need to be designed and fabricated?
• Approximate Fixture Dimensions: Provide estimated dimensions (length, width, height) if existing fixtures are not available.
• Approximate Fixture Mass: Estimate the weight of the fixture if existing data is unavailable.
• Mounting Issues: Are there any specific mounting constraints, such as bolt patterns or sizes, that need to be accommodated by the shaker or head expander?
• Need for a Head Expander: Will a head expander be necessary to accommodate the size or mounting requirements of your specimen and fixture?

4) Test Specifications (F=ma): Defining the Excitation

The maximum acceleration required for your F=MA calculation is directly derived from your test specification:

• Sine Vibration: Maximum acceleration in G-peak.
• Random Vibration: Maximum acceleration in G-RMS.
• Classical Shock Pulses: Maximum acceleration in G-peak.

Our operators also need to be aware of the system’s maximum displacement and maximum velocity limits to ensure the test profile remains within the shaker's operational envelope.

5) Evaluating the Test Specifications: Understanding the Waveform

The type of vibration waveform specified in your test protocol is a key determinant of the required shaker system and its control capabilities:

• Sine: A single-frequency oscillation.
• Random: A complex waveform consisting of a spectrum of frequencies applied simultaneously.
• Classical Shock: A transient pulse with a defined shape (e.g., half-sine, sawtooth, trapezoidal).
• SRS Shock (Shock Response Spectrum): A method of characterizing the potential damage of a shock event on systems with multiple resonances.
• Mixed Mode: Combining different waveform types, such as Sine on Random or Random on Random, to simulate complex real-world environments.

6) Understanding Random Vibration: Power Spectral Density

Our random vibration rating is determined following the guidelines of ISO 5344. This standard specifies a flat power spectral density (PSD) spectrum with a load mass on the armature typically three to four times the armature's own mass. This approach helps ensure a degree of consistency in ratings across different manufacturers.

Utilizing a non-resonant armature for a mass load of three to four times its own weight can, however, reduce the resonant frequency of the vibrator armature under test to typically less than 2000 Hz. This allows our vibration test system to efficiently deliver energy at higher frequencies within that usable range.

7) Effects of Resonance: Accounting for Structural Dynamics

It's crucial to remember that every mechanical structure, including your test specimen and fixture, possesses natural resonant frequencies. At these frequencies, the structure can exhibit significant amplification of the applied vibration, leading to increased power absorption by the test system. This phenomenon must be carefully considered during the estimation process.

The force rating provided by our shaker manufacturer is the force capability at the armature surface. When you attach test systems with associated fixtures, head expanders, and slip tables, these additional masses and their inherent resonances can act as force absorbers and potentially overdrive the shaker if not properly accounted for.

In a professional testing environment, installing a monitoring accelerometer directly on the armature surface can provide valuable insight into the "true force" being achieved and help optimize your test setup.

Partnering with Dongguan Precision for Your Vibration Testing Needs:

Choosing the right electrodynamic vibration test system requires a thorough understanding of your specific test requirements, specimen characteristics, and fixturing considerations. By carefully evaluating these factors and collaborating with our experienced engineers, you can ensure you select a system that delivers accurate, reliable, and efficient vibration testing for your products. Contact Dongguan Precision today to discuss your application and let us guide you towards the ideal vibration testing solution.