TYPES OF ACCELEROMETER

L.D. COLLEGE OF ENGINEERING SUBJECT : EXPERIMENTAL TECHNIQUES AND INSTRUMENTATION IN AUTOMOBILE

M.E. (I.C./AUTO) 2nd SEM.

PREPARED BY : NEJAL PATEL (140280711012)ACCELERATION AND VIBRATION MEASUREMENTACCELERATIONIt is derived from either displacement or velocityIn this method acceleration is measured indirectly. But today accelerometer is available to measure the acceleration of vehicle for direct measurement.

VIBRATIONMajor parameter in vibration measurements are displacement ,velocity and acceleration. The peaks values of these quantities should be known.Today a device called vibrometer is used to measure natural frequency directly from vehicle.

TYPES OF ACCELEROMETER1.Potentiometric Type Accelerometer

The seismic mass is attached to the wiper arm of resistance potentiometer. The relative motion of mass and frame is sensed either in change in resistance or change in voltage output.Major drawback is limited resolution and lower natural frequency(less than 100 Hz).

2.LVDT(Linear Voltage Differential Transformer) Accelerometer.

The primary and secondary windings are used in LVDT. The core acts as a mass. The reeds are attached to the housing which is subjected to the vibration.The secondary winding gives the AC output voltage whose magnitude depends upon the amplitude of vibration.ADVANTAGES-smaller mass and higher frequencybetter resolutioncontactless device

3.STRAIN GUAGE ACCELEROMETERMass is mounted on cantilever beam. Strain gauge is mounted on each side of beam and damping is provided with completely filling the housing with viscous fluid.The output of strain gauge is connected to Wheatstone bridge circuit whose output indicates the relative displacement of mass with respect to frame.

4.PIEZO ELECTIC ACCELEROMETERThe piezoelectric crystal is spring loaded with mass in contact with the crystal. When subjected to acceleration the mass stresses the crystal with the force F=ma resulting with voltage generated across the crystal.The force generated is proportional to acceleration.

5.VARIABLE RELUCTANCE ACCELEROMETERIn this accelerometer the mass is permanent magnet.Output voltage is obtained from the coil surrounding the magnet.Movement of mass induces the voltage in coil which is proportional to the acceleration.Used for the measurement of frequency less than 100 Hz

VIBRATION MEASUREMENTVIBRATION- If the displacement time variation is continuous form with some degree of repetitive nature it is called a vibration.SHOCK-If the action is of single event form a transient with the motion decaying before further action takes place referred as a shock.

NATURE OF VIBRATIONMost vibrations are sinusoidal displacement from the mean position.The displacement is given by X=XmSintBy differentiation we can get velocity as well as acceleration.

VIBROMETERVibrating Wedge When the amplitude of the motion is greater than 1mm Vibrating wedge is used.

Amplitude is given byXm=Atan/2This device does not give any information about waveform of the motion.

Cantilever beam as frequency measurement

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