Vibration Test/Combined Climatic (Temperature/Humidity) and Dynamic (Vibration/Shock) Test
- Test summary/features
Today's ever smaller electronic devices and more diverse operating and installation environments are making devices increasingly vulnerable to direct effects from vibrations, and electrical device vibration testing has grown in importance as a result. Combined-environment testing combines vibrations with various environmental stresses such as a low-temperature environment, high-temperature environment or high-temperature/humidity environment. It is a type of testing that recreates environments that more closely approximate actual operating environments.
While individual environmental factors also need to be tested independently when evaluating the quality of parts or devices used in environments prone to vibrations and temperature/humidity stresses, the application of mutually interacting environmental factors simultaneously can result in the generation of mutually induced failures, making quality evaluations in combined environments an important type of testing.
- Test equipment
The test equipment available ranges from standard temperature chambers (temperature range of -70 to +150°C; humidity range of 20 to 98% RH), to high-performance temperature chambers enabling temperature variation at a rate of 5°C /minute (between -55 and +100°C), and vibration generators applying vibratory forces ranging from 10 to 20 kN.
The maximum acceleration and maximum amplitude that can be tested vary according to the test frequency and mounting weight. Along with the vibration test conditions, specify information such as the weights of the test samples and jigs when requesting testing. ESPEC can also design the vibration jigs needed to secure test samples.
- Equipment particulars
- Combined Environmental Test System, Vibration Test System (installed at Utsunomiya, Toyota and Kobe Test Centers)
|Temperature and Humidity Chamber|
|Temperature/humidity ranges||-70 to +150°C/20 to 95%rh||-70 to +150°C/30 to 98%rh|
|Vibration Test System|
|Frequency range||3 to 2000Hz||3 to 2000Hz||5 to 2000Hz|
|Installation location||Kobe||Toyota||Utsunomiya, Kobe|
- Vibration Test Systems
While vibration testing is one of the common types of a laboratory testing service ESPEC provides, the test equipment and conditions tend to vary, so clients often have questions.
This page provides a concise explanation of terms related to vibration testing and vibration generators.
- Vibration test system structure
Depending on how they generate vibrations, vibration test systems can be classed into mechanical types, hydraulic types and electrodynamic types.
Electrodynamic types are the best-suited types for satisfying the test conditions needed for vibration testing of electronic parts.
An electrodynamic vibration tester has drive coils integrated with a vibration table, and inserted in the centers of excitation coils.
When a DC current is applied to the excitation coils (which are in the magnetic path), magnetic fluxes are generated in the arrow directions shown here, and a DC magnetic field forms in the vacant space, intersecting the lines of the drive coils at right angles.
Applying a AC current to the drive coils causes the vibration table to generate vibrations in accordance with Fleming's left-hand rule.
The principle is the same as the principle used for speaker operation.
The characteristic features of electrodynamic vibration testers are that they enable generation of arbitrary vibration quantities with arbitrary waveforms by controlling the current applied to the drive coils, and can generate a wide frequency range and high vibration acceleration values. To perform vibration testing, an acceleration sensor is mounted on the vibration table. A current corresponding to the desired acceleration is applied to the drive coils and controlled, to generate vibrations satisfying the test condition.
- Types of vibration testing
- Sine wave vibration testing
- Fixed-frequency vibration testing: Vibrations are applied with a specified constant vibration frequency, acceleration or amplitude.
- Sweep vibration testing: Upper and lower vibration frequency limits are set, and the frequency is varied (swept) at a fixed rate of variation over this frequency range. Vibration intensity is specified using acceleration or amplitude values corresponding to the frequency.
- Resonance testing: Upper and lower vibration frequency limits are set, and the frequency is varied (swept) at a fixed rate of variation over this frequency range. The acceleration generated in the test sample relative to the vibrations applied is measured as the frequency is swept, to search for resonance and determine the resonance frequency.
Since this type of testing is performed to measure the vibration response, a smaller (slower) rate of frequency change and lower acceleration are usually used than are used for durability testing.
- Random vibration testing
Multiple sets of vibrations of specified frequency ranges are applied simultaneously. Since vibrations of multiple frequencies are superimposed, vibrations with irregular waveforms result. The test conditions are specified by the frequency band and acceleration spectrum density.
Vibration testing conditions usually specify the sequential application of vibrations in three directions: forward/backward, up/down and right/left. But since most vibration generators only generate vibrations in the up/down direction, the vibrations in the forward/backward and left/right directions need to be reproduced using the jig used to secure the test sample.
- Sine wave vibration testing
- Vibration testing terminology
Vibration intensity in vibration testing is expressed in terms of vibration frequency f, displacement (amplitude) D, or acceleration A.
Vibration frequency f (Hz): The number of cyclical movements a vibrating object makes per second. The time for a single cycle is called the period (T). Vibration frequency (f) = 1/T.
Displacement (amplitude) D (m): The distance the vibrating object moves over one vibration cycle. Can also be expressed in microns (µm) or millimeters (mm).
Displacement (amplitude) can refer to the total back-and-forward distance over one cycle (total amplitude or double amplitude) or the distance in one direction only (half amplitude), so care is needed.
Acceleration (m/s2): Indicates how much the velocity (V) changes per unit time. The SI unit used to express acceleration is meters per second per second (m/s2), but it can also be expressed in the non-SI unit G.
These attributes are related by the formula below.
A = （2πf）2 × D (D: half amplitude)
As shown by this formula, the same acceleration can result in different amplitude if the frequency value is different.
When acceleration is kept constant and frequency is increased during sweep vibration testing, amplitude falls as frequency rises.
Similarly, when amplitude is kept constant and frequency is increased, acceleration rises as frequency rises.
Ignoring these relationships when planning vibration conditions can result in transient vibrations being applied to the test sample, or conditions of excessively small vibrations.
When specifying vibration conditions for testing, amplitude is usually kept constant in the low frequency range, and acceleration is kept constant once a certain frequency value has been exceeded.