Accelerometer Lab Report

III. ACCELEROMETER AND ITS WORKING PRINCIPLE

A. Working of Accelerometer Sensor

Accelerometer sensor is used to measure the acceleration. Acceleration is the amount of force we need to move each unit of mass. Newton’s second law of motion relates the force, mass and acceleration through this equation:

F=ma

F=Force m=mass a= acceleration due to gravity

Fig. 2 Accelerometer schematic diagram

This Newton’s equation is the theory behind accelerometers. The sensing element essentially is a proof mass (also known as seismic mass). The proof mass is attached to a spring of stiffness k which in turn connected to its casing. Further, a dash pot is also included in a system to provide desirable

Mechanical ones have something like a mass attached to a spring suspended inside an outer casing. When it is subjected to linear acceleration, the casing moves off immediately leaving behind the mass and spring stretches with a force that corresponds to the acceleration. The distance the spring stretches can be used to measure the force and the acceleration in the variety of different ways. Fig.2.1 (a) Mechanical Accelerometer

The basic concept of mechanical accelerometer (from fig. 2.1(a)): as the gray accelerometer box moves from side to side, the mass (which is a red blob) is left behind and the spring connecting it to the box (red zigzag) soon pulls it back into the position and, as it moves, it draws a trace (blue line) on the paper. Fig.2.1 (b) Capacitive Accelerometer

Alternative designs of accelerometers measure force not by making a pen trace on paper but by generating electrical or magnetic signals. Capacitors can be used in accelerometers to measure force in a similar way as that of mechanical ones: if a moving mass alters the distance between two metal plates, measuring the change in their capacitance gives a measurement of the force that’s acting on it. The broad concept of capacitor based accelerometer can be understood from the above figure (Fig.2.1 (b)). In some accelerometers piezoelectric crystals such as quartz do the clever work. There is a crystal attached to a mass, so when the

The sensing element essentially is a proof mass (also known as seismic mass). The proof mass is attached to a spring of stiffness k which in turn connected to its casing. Further, a dash pot is also included in a system to provide desirable damping effect; otherwise system might oscillate at its natural frequency. When the system is subjected to linear acceleration, a force equaling to mass times the acceleration acts on the proof-mass. This causes the mass to deflect; the deflection is sensed by a suitable means and is converted into an equivalent electrical signal.

B. Types of Accelerometer Sensors

There are different types of accelerometers. Mechanical ones have something like a mass attached to a spring suspended inside an outer casing. When it is subjected to linear acceleration, the casing moves off immediately leaving behind the mass and spring stretches with a force that corresponds to the acceleration. The distance the spring stretches can be used to measure the force and the acceleration in the variety of different ways. Fig.2.1 (a) Mechanical