Converting Acceleration at 1x to Displacment

[Coryman]

Folks, 

This ought to be an easy one for someone on this blog.  

Finishing up adding all of the balance programs to MotorVibe and the phase answers were not looking right.  This was due to some narrowband filtering around 1x, which ALWAYS shifts phase.  So, we are calculating the phase from the acceleration fft and tach signal and then flipping the phase 180 degrees.  Displacement is 180 degrees out of phase with Acceleration.

Yes, I know it doesn't matter and you can balance in accleration as well as displacment, but mils are units field personnel are more comfortable with.

Here’s the question:

The formula in English units to convert acceleration (g's) to displacment (inches) is as follows – D = (19.57g/f^2)

D – Displacement in inches pk to pk

G – 386.2 inch/sec^2

F – 1x in Hertz

Multiply answer by 1000 to get mils pk to pk

Works fine every time but in order to feel real warm and fuzzy about it, where does that constant come from?

[Jay14159265]

what issue are you having with LabVIEW? 

[dsb@NI]

386.2 (in / g) * 2 (in pk-pk / in pk) / (2*pi (rad/s / Hz))^2 = 19.565 

So the mystery constant includes the conversion from g pk to inch pk-pk and the conversion from frequency in Hz to frequency in rad/s.

To really build confidence in your code, remove the magic constant and handle the conversions explicitly. To really, really build confidence in your code, add a unit test!