Shaker system choice depending on testing profile

Question

We operate a testing laboratory for electrical equipment. Sometimes we have to perform mechanical integrity tests. Below you can see the testing impacts requirements. Please give us your recommendations regarding shaker system and vibration control system. 

Test 1: broad band vibration impact within the range of 5 – 20 Hz with vibration acceleration spectral density of 0,96 m2/s3; and within the range of 20 – 500 Hz with vibration acceleration spectral density of  0,96 m2/s3 at the frequency of 20 Hz, and then– 3 dB/oct.

Test 2: sinusoidal vibration, acceleration 4 g, frequency 5 – 80 Hz

Test 3: sinusoidal vibration, acceleration 2 g, frequency 25 Hz during 30 min

Test 4: sinusoidal vibration, acceleration 3 g, frequency up to 15 Hz

Test 5: sinusoidal vibration, acceleration 1 g, frequency 1 – 100 Hz

Test 6: sinusoidal vibration, shift with amplitude 0,76 mm and full sweep of 1,52 mm; impact frequency from 10 up to 55 Hz with a speed of 1 Hz/min (and backwards).

Test 7: sinusoidal vibration, acceleration amplitude 3 g within frequency range of 10 – 100 Hz.

Answer

Testing profile parameters allow to specify the following vibration characteristics limit values:

Frequency range – from 1 up to 500 Hz.

Acceleration– up to 4 g for sinusoidal vibration and  0,9 g for broad band random vibration.

Shift– up to 0,76 mm.

Please, note that at low frequencies (1 – 5 Hz) shaker systems have limitation in displacement; and at high frequencies (over 50 Hz) – limitation in acceleration.

Shaker system accceleration and displacement values of sinusoidal vibration are interrelated in accordance with the following formula:

A[m/s^2] = (2 * pi * F[Hz] ) ^2 * D[mm] / 1000

or approximately: A = D * F^2 / 25

and vice versa D = 25 * A / F^2

Thus, in the case of 1 Hz frequency and maintained accelration value of 1 g the displacement value shall be 250 mm.

At the frequency of 10 Hz and 3 g acceleration the displacement value shall be 7,5 mm.

If we maintain displacement of 0,76 mm at the frequency of  55 Hz the acceleration value will be 9,3 g.

So you will have to calculate profile values for Tests 5, 6 and 7. For operator’s convenience and tests perfomance safety the Software “Sinusoidal vibration” enables calculation of vibration parameters values and checks their compatibility.

Finally, we recommend you to consider shaker system with a displacement value over 75 mm and maximum acceleration over 10 g. In this case you will have to change only one profile (without taking into consideration the tested object weight).