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Displacement type Accelerometer

As in the case of normal navigation systems, The Inertial Navigation system is not dependent on the external fields or forces. In place of that, an Inertial Navigation system always keeps on tracking its location by precise measurement of the acceleration and its rotary motion it is sensing. The acceleration is measured with the help of accelerometer and the rotary motion (rotation) is measured with the help of Gyroscopes. This is why it has the advantage that it can be useful even in those secluded regions where the navaids which are ground based are unavailable. Displacement type accelerometer is also one of the kind of Inertial Navigation system.

The Inertial navigation system obtain its location primarily from the motion/rotation at the gate. And thus, with reference to its primary location, it senses/calculates the acceleration and rotary motion. This acceleration and rotary motion is further integrated to obtain speed and direction. And so, by this procedure, the location is tracked continuously.

With increase of service life, the system attains minor errors (like positional error, speed error) due to generation of minute imprecisions. Here, We are going to discuss the basic displacement type accelerometer. The measuring principle of the Displacement type accelerometer follows the “Principle of Inertia“. The principle of Inertia states that a body in motion or rest continue to be in motion or rest untill unless an external force is applied on it.

Working principle of Displacement type accelerometerIt is the inertia of a mass which moves the mass in opposite direction when an external force (F) acts on it under an acceleration.

Composition :

This system usually consists a pendulum (marked as P) which suspends with the help of a Flexible Blade (marked as L). The logic behind suspending the pendulum with a flexible blade is that it reduces its strains during the motion. in order to minimize the strains involved in the movement. The pendulum is kept in equilibrium with the help of two magnets (permanent type).

Compositin of Displacement type accelerometerWhen the base moves, its shifting of position is detected with the help of a Capacitor based pick off unit (marked as C). This pick off unit consists of 02 in no capacitors (C1,C2) connected in Wheatstone bridge layout. Just to ensure that the pendulum reaches its equilibrium position, the pendulum is also provided with a torque motor within it only.

Circuit diagram of displacement type accelerometerwhen an external force is applied to the system, it experiences an acceleration. Due to this acceleration, the value of C1 & C2 changes and so an error current is produced due to the potential difference. If we measure this error current, we can calculate acceleration as well. In addition, The error current is also used to drive the torque motor (in the pendulum) to move back the pendulum to its original position.

Block diagram of Displacement type accelerometer

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