# Interpretation of Accelerometer Measurements

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1. Apr 16, 2015

### ClapClap

I have performed an impact test on different football shin guards to assess their performance. I am however confused with the readings measured by the accelerometer I have used. The sensor was attached to a striking mass of 4.3 kg which was dropped at different heights.
The graph I have attached shows the data collected by the accelerometer (y-axis) versus the time (x-axis) for an impact test at drop height of 20 cm.
Can anyone help me understand how to read this data? (i assume the graph looks messy because they weight 'bounced off' the shin guard a few times).
How can I use this data to assess guards performance?

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2. Apr 16, 2015

### FactChecker

The data will be difficult to use. Starting at time=0, you would expect it to instantly drop to zero as free fall begins. It slopes down linearly over a 10'th of a second. That is hard to explain. Then, when it first hits, the measurements are limited at about 32000. That is a serious problem. It makes it impossible to know how high it really went. I think you need an accelerometer with a wider range.

3. Apr 17, 2015

### ClapClap

The accelerometer I used had a range of 2g. So you suggest 3g?
The physical impact begins when the acceleration hits the x-axis right? Does the pick of the graph represent the maximum indentation of the striking mass on the shin guard?

4. Apr 17, 2015

### FactChecker

It's hard to guess how high the acceleration might get. 3g might not be enough either. I think it is safe to assume that the deepest indent came from the impact with the maximum acceleration. You might get an estimate of the maximum acceleration by calculating how much acceleration would go from the falling speed to 0.0 in the distance of the deepest indent.

5. Apr 17, 2015

### ClapClap

What falling speed? The one from the peak or the initial one?

So, the physical impact between the two bodies occurs between time 154 to 198 yea? Say i consider the data recorded from 154 to the peak, if i integrate it once I would get the velocity vs time graph, and if i integrate that again I would get the deflection vs time graph right? So from there I'd be able to estimate the maximum deflection of the striking mass?

How can I estimate the impact force? Initially I thought of finding the g-force and then converting it into Newtons, but I am not sure if that is the impact force on the sin guard..

Sorry for so many questions, I have my viva presentation of my honorous project in a couple of days and I've been trying to figure out my results for ages without success