# Vibration measurement of rotating blade

In a vibration measurement of a rotating blade, I have the following information. The vibration signal is measured using an ICP accelerometer which has the following specification

• Measurement range: 50g
• Sensitivity: 100 mV/g
• max output voltage: ±5V
• Broadband resolution: 100e-6g

The variance of the acquired signal is

$$var_{aq} = var_{acl} + var_{adc} + var_{sig} \approx 6.2e-4 g$$

• $$var_{acl}$$ = variance of noise in the accelerometer
• $$var_{adc}$$ = variance of the ADC noise (quantization, jitter)
• $$var_{sig}$$ = variance of the vibration acceleration of the blade.

Assuming that $$var_{acl} \approx \sqrt{\text{broadband noise of accelerometer}} = 1e-8 \text{g_rms}$$.

From the specification sheet of the ADC, for the used input gain of 30db and sampling frequency = 51.2Hz, the $$var_{adc} = 1e-12 \text{V_rms}$$

Can anyone please help, how can I calculate the variance of vibration acceleration of the blade $$var_{sig}$$?

• Hi, welcome to Engineering. If I understand correctly your question can be reduced to "How can I convert $var_{adc}$ units ($V_{rms}$) to $g_{rms}$ which are compatible with the rest of the quantities. " – NMech Dec 11 '20 at 6:47
• Yes that would be one thing to conver the Vrms to grms. Do i need to consider any other factors or it is just straight forward substituition into the summation equation and calculate the unknown – Elvir Peco Dec 11 '20 at 21:27