| texaslabrat |
2009-09-15 17:19 |
Re: N900 Specifications
Quote:
Originally Posted by sljonson
(Post 327286)
No, not necessarily g-force. Any acceleration will be measure. These devices will work anywhere even deep space with no gravity. They work because certain crystals can generate small electrical current if the crystalline structure inside are stressed (i.e. deformed). That is if you grab a crystal and squeeze it in you fingers it will generate an electrical current.
Now for the way it works in an accelerometer, think back you basic physics. More specify Newton's 1st law. (paraphrased) An object at rest tends to stays at rest...unless acted upon an outside force. The crystal is mounted in an accelerometer normally at rest. Now when the device it's mounted in moves, a certain amount of force is exerted on the crystal. The crystal wants to stay still, but it's mounting points are pressing against the crystal which will deform the structure of the crystal. Just like squeezing the crystal in your fingers.
And the key is that the crystals inside the accelerometer is that they only measure movement along a certain direction (aka vector in science speak). So you mount 2 (or 3) crystals so you can measure the up/down and left/right movements.
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The term "g-force" is a colloquialism that is generally used to describe acceleration forces felt from an observer's frame of reference...not just the "g" (9.81 m/s^2 vector pointed at earth's center) imposed by the earth's gravity.
Also, the accelerometers used in applications like this utilize changes in the resistive or capacitive properties, not the measurement of a current (voltage). The resistance and capcitance changes are steady-state depending on the strain (hence stress, hence force, hence acceleration) similar to old-school strain gauges.
Voltage creation by piezoelectric devices is dependent on *rate of change* and is far less useful in this use case since you not only have to measure instantaneous voltage but have to keep a history to make that measurement useful. Contrast with a pizeoresistive or capacitive element where the instantaneous measurement of the resistance/capacitance corresponds directly to the acceleration at that very moment without need to consider the history of change to make that calculation.
Perhaps a pedantic correction..but it is worth noting IMHO. |
