To complete a sine vibration test according to the specifications, the capabilities of the vibration test table are divided into three categories: vibration functional indicators, technical indicators and auxiliary technical indicators.
1)Functional indicators
It refers to the functions required by the vibration table to complete the sinusoidal vibration, as shown below:
a) Fixed frequency vibration: implement sinusoidal vibration at a certain fixed frequency.
b) Vibration dwell: usually refers to the vibration implemented at the resonant frequency point of the product. When the resonant frequency point of the product drifts, the vibration control system can automatically track the change of the resonant frequency and always “reside” at the resonance of the product. vibrate at frequency.
c) Sweeping frequency vibration: Sweeping frequency vibration refers to a vibration test in which the frequency of vibration changes with time according to a certain pattern during the vibration test. Sweep vibration is divided into linear sweep and logarithmic sweep.
d) Beat frequency vibration:Beat frequency vibration uses a sine wave signal with a lower vibration frequency to modulate another sine wave signal with a higher vibration frequency. Mathematically it can be understood as the product of two sinusoidal vibrations of different frequencies, namely:
x(t)=x0sin(ωt)xsin(ωt/m)
In the formula: x0–amplitude of sinusoidal vibration, cm;
ω–circular frequency of sinusoidal vibration, rad/s;
m–The modulation magnification, that is, the ratio of the modulation frequency to the basic signal frequency.
2) Technical indicators
Technical indicators refer to the basic performance parameters of the shaking table, as follows:
a) Exciting force: the force transmitted by the vibration table to the test specimen. The maximum force (N; kN) usually given is divided into sinusoidal force and random force values;
b) Vibration amplitude: refers to the macro motion parameters of the vibrating table. Including the maximum displacement or represented by peak-to-peak displacement and maximum stroke (cm), maximum speed (m/s), maximum no-load acceleration (m/s2; g=9.81m/s2);
c) Load capacity: Maximum inertial mass that the vibrating table can bear (kg):
d) Frequency range: the lowest to the highest frequency value at which the vibration table can work (Hz);
e) Frequency sweep rate: the rate at which the vibration table implements linear frequency sweep or logarithmic frequency sweep (Hz/min; oct/min).
A frequency sweep whose ratio of frequency change to frequency sweep elapsed time is equal to a constant m is a linear frequency sweep:
m=(fh -f1)/Δt
In the formula: m–linear sweep rate, Hz/min;
f1–Start frequency of linear sweep, Hz;
fh–termination frequency of linear sweep, Hz.
Δt–the time elapsed from the start frequency f1 frequency sweep to the end frequency fh
In a logarithmic frequency sweep, the ratio of the logarithmic value of the frequency change to time is a constant. Logarithmic sweep rate is usually expressed as the number of octaves swept(oct) per unit time.
The rated performance of sinusoidal vibration is usually expressed in terms of the maximum value (peak value), but it can also be expressed in terms of the root mean square value, with the peak value being 1.414 times the root mean square value. Since the square of the root mean square value of the current flowing through the moving coil of the electric vibrating table multiplied by the impedance of the moving coil is the total heat generation of the moving coil, the root mean square value is an important parameter in the structural design of the electric vibrating table and the calculation of cooling air volume and cooling temperature.
For auxiliary technical indicators, please check out Part-2