# B G force and rate of deceleration

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1. Oct 30, 2016

### lawrence fickett

gee i am not worthy of being here with you guys but i must know is an accelerometer's negative output due to the braking of a motor vehicle directly proportional to the the rate of deceleration of the motor vehicle and can this be predicted using a derivative function? And if I were to plot the negative g's how would the deceleration rate plot compare.

Sorry to bother you'se with such a trivial question, but I've been researching this and can't seem to get a definitive answer. I am preparing a patent using the above and dont want to make a claim that can't be proven.

Many Thanks

2. Oct 30, 2016

### FactChecker

Assuming that you have already converted the accelerometer output signal to engineering units of g's, it should be directly related to the rate of deceleration. 1g = 9.80665 m/s2.

3. Oct 31, 2016

### Staff: Mentor

Not exactly proportional, but the better (and usually more expensive) the accelerometer is, the closer to that ideal it will be. There will be a data sheet or other specification for the particular model that you're working with. It will include the details for that particular model, including (most likely) a plot of the output signal as a function of the actual negative acceleration.

If you haven't already, you might try googling for "accelerometer specifications".

4. Oct 31, 2016

### CWatters

You would hope so.

As Nugatory said, not all accelerometers are perfect. Not all are designed to measure negative acceleration (eg deceleration) as well as positive. You would hope the designer picked one that was suitable.

5. Oct 31, 2016

### CWatters

I suppose we should also check that the accelerometer is mounted on the car body and not something loose inside the car like a box of tissues or a passenger.

Likewise an accelerometer mounted on the wheels (measuring angular acceleration) could be used to calculate the linear acceleration/deceleration but only if the wheels aren't skidding.