How to convert acceleration value to decibel dB?

[yirmidokuz]

Dear all,

I measure the acceleration of the collision of the inner parts as an outcome of the noise vibration, with the sensitive acceleration sensors.

How can I convert the acceleration value of 90 m/s^2 to decibel value?

Thanks in advance.

 

[BrianE22]

You would need some reference level to compare it to. Maybe there's a common one for the industry you are involved with.

 

[Tmoose]

Here is one fairly common reference used for vibration measurements.

I am not certain if frequency information is required, or not.

 

[Strong]

Acceleration Level
dB (La) = 20 lg (a/ao) dB re 1 µm/s2.
Acceleration Reference Level (ao) = 1 μm/s2 ≡ 0 dB (also defined in ISO 1683) *
An increase or decrease in acceleration of 20 dB = a factor of 10
An increase or decrease in acceleration of 40 dB = a factor of 100
An increase or decrease in acceleration of 60 dB = a factor of 1000 etc.
(Vibratory) Acceleration Level Definition.
IEC 801-22-09, logarithm of the ratio of a given (vibratory) acceleration to the reference acceleration. Acceleration level in decibels is 20 times the logarithm to the base ten of the ratio.
● Note 1 unless otherwise specified, the reference acceleration is 1 μm/s2 *
● Note 2 unless otherwise specified, the accelerations are understood to be expressed in RMS values.
* ISO 1683 also states 'in connection with structure-borne sound, a vibratory acceleration reference value of 10 μm/s2 is also in use'

From <

http://www.acoustic-glossary.co.uk/definitions-a.htm>

Walt

 

[yirmidokuz]

Thanks!

But it is kind of complex equation to interpret.

dB (La) = 20 lg (a/ao) dB re 1 µm/s2.

For example what is "re" in the equation above?

I get the decibel values at the LHS of equation when I plug the values for a 6 m/s^2 and a0 = 10µm/s2, as 115 dB?

 

[271828]

A dB value must have a reference. "a" is higher than what?

 

[yirmidokuz]

@271828

a0 = 10µm/s2 is ref. value, than 0dB -> 10µm/s2.

In this case, how you calculate the dB ?

 

[271828]

I don't understand the question. We would need the acceleration, a, to calculate the measured acceleration in dB. We're trying to represent the measured acceleration relative to the reference.

For example, if the reference acceleration, ao, is 10 um/s2 and the measured acceleration, a, is 15 um/s2, then the measured acceleration, expressed in decibels, is 20*log(15/10) = 3.52 dB.

As an aside, in my work, I rarely find that it makes sense to use dB. For typical accelerations and velocities, it just causes confusion. Aside from people not indicating the reference, 10*log(a/ao) is sometimes used, so you need to say which equation you're using.

 

[Strong]

In your above equation "a" is the acceleration value in linear units and "ao" is the Reference Value (abbreviated Re).
My old HP 20S calculator gives 115.56 dB Referenced to 10.0 µm/s2, and 135.56 dB Referenced to 1.0 µm/s2 for an acceleration value of 6.0 m/s^2. As you can see the dB value depends on your choice of Reference Value (Re). A factor of 10x is equal to 20-dB.

Walt