Accelerometer Basics

  Introduction:

3
An accelerometer is an electromechanical device which measures acceleration. A measure is normally in G-forces. One G-force is equivalent to 9.8 meters per second squared. Accelerometer is widely used in many devices such as mobiles, Unmanned Aerial Vehicles, cars etc. They are mainly used for determining tilt by measuring amount of acceleration due to gravity. An accelerometer is basically a transducer that is used to measure the physical or measurable acceleration that is made by an object

Types of accelerometer & their working:

There are mainly two types of accelerometers: Piezoelectric and Capacitive accelerometers. They are described as follows:-

  1. Piezoelectric accelerometers: As the name suggests, they are based on the principle of piezoelectric effect. Piezoelectric effect states that when a force/pressure is applied on quartz crystal then some electric charge will be produced. The rate of charge produced will be proportional to rate of change of force applied as an input.1
  2. Capacitive accelerometers: This type of accelerometer depends on property of capacitors that their capacitance will change by changing the d (distance between plates), A (area) or by introduction of dielectric material between the plates.2

Specifications:

  1. Number of axes – For most projects, two is enough. However, if you want to attempt 3d positioning, you will need a 3 axis accelerometer, or two 2 axis ones mounted at right angles.
  2. Maximum swing – If you only care about measuring tilt using earth’s gravity, a ±1.5g accelerometer will be more than enough. If you are going to use the accelerometer to measure the motion of a robot, ±2g should give you enough headroom to work with. For a project that experiences very sudden starts or stops, you will need one that can handle ±5g or more.
  3. Sensitivity – Generally speaking, the more sensitivity the better. This means that for a given change in acceleration, there will be a larger change in signal. Since larger signal changes are easier to measure, you will get more accurate readings.
  1. Bandwidth – This means the amount of times per second you can take a reliable acceleration reading. For slow moving tilt sensing applications, a bandwidth of 50Hz will probably suffice. If you intend to do vibration measurement, or control a fast moving machine, you will want a bandwidth of several hundred Hz.
  1. Analog/Digital Output – You must take special care in choosing the type of output for the device. Analog output will be in the form of small changing voltages and digital output will be in PWM mode.
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