Very large values from accelerometer

[jyuan]

Hello,

I did a small impact test in the lab, and recorded the acceleration. But I got very large peak numbers, like 300g, which is unreasonable. My vi has been checked by many people, seems like no problem. Does anyone have the idea why I got such big numbers?

Thanks.

Yuan

[johnsold]

Yuan,

Why do you think the values you reported in your other thread are unreasonable? 200-300 g does not seem out of line for impact of one steel object against another.

What are the sizes and shapes of the objects involved? How is the accelerometer attached to the object? What is the range of motion and speed of the objects before impact? Is there any damping?

Lynn

[billko]

Also, the material(s) of the objects.

[Yamaeda]

If an object falls at 1m/s and is stopped over 1mm (little deformation):

s=v*t

v=a*t

v=a*s/v

a=v^2/s

a=1^2/0.001=1000m/s ~100g

So, how much deformation does two metal balls or two marble balls display when impacting?

It is good food for thought, as a rubber casing, adding just a couple of millimeters will do a lot for the G forces!

/Y

[jyuan]

Hi,

Sorry for the delay. The speed of  the impactor is about 305in/s, and the impact duration is about 0.1s. The acceleration should be much less than 200g. In vi, I set the minimum and maxmium value as -250g and 250g, which are the measurement limits of the PCB accelerometer I used. This morning, I changed the range to -20g-20g, I got much smaller peak values, like from -25g to 25g. Then I found that every time when I tried to change the input range, my results changed accrodingly, the peak values are pretty much around the input range. Apparently, this is also not what I want. I was wondering why this happened?

Thanks.

Yuan

[lvABC]

Can you double check your sensitivity and sensitivity units?
If you don’t have correct sensitivity value that would make big difference.
Hope it helps!

-lvABC

[lvABC]

Can you double check your sensitivity and sensitivity units?
If you don’t have correct sensitivity value that would make big difference.
Hope it helps!

-lvABC

[Henrik_Volkers]

It would be helpful if you describe your hardware, DAQ , (signal-conditioner with setting) , sensor

and please post a link to the spec-sheet of the sensor and (if you have) the individual sensitivity (cal) value(s) of your sensor. (in metric if possible 😉 )

Now read the input voltage at a high sample rate (you can use one of the example vi's ) . If you have a pulse in the diagram hit edit-make current values default, save as a new vi and post that vi.

[jyuan]

Yes, I double checked the sensitivity and the unit

[jyuan]

Hi, Henrik,

The hardwire I am using is NI SCXI-1001, the module for accelerometer is SCXI 1531. I use DAQmx 14.1 version, the accelerometer is 353B01 from PCB.

The following link is the sepc-sheet of the accelerometer: http://www.pcb.com/Products.aspx?m=353B01, the individual sensitivity of the sensor  is 19.25 mV/g (1.963 mV/m/s^2). I set the sample rate as 10k HZ.

Please check out the attached vi.

Thanks.

Yuan