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Vibration Information for rotating machinery applications.

 

Torsional or Angular Vibration

Saturday, September 01, 2012

Torsional vibration is the angular oscillation of a rotating object such as a drive shaft, caused by fluctuating torsional levels. It is a common occurrence in power transmission systems such as engines and automotive drivetrains.

Torque transmission is rarely “smooth” since the torque in the system usually fluctuates. In an internal combustion (IC) engine , the pistons and connecting rod apply a large torsional force on the crankshaft every time a cylinder fires, causing the crankshaft to twist about its rotational axis. As the power delivery drops off, the crankshaft twists in the opposite direction. This on-and-off power delivery leads to angular oscillations of the crankshaft, known as torsional or angular vibration. Other factors such as changing frictional forces, misalignment, worn or uneven gears, also affect torque and contribute towards torsional vibration.

Measuring torsional vibration requires readings of the angular position of the shaft with respect to time. Precise readings will reveal oscillations of an objects rotational speed, which are proportional to the torsional vibration. Alternatively, you can measure the twist of the object by measuring and comparing the position of two points along the rotational axis. Torsional vibration measurements can be made using lasers, gear tooth sensors, and tachometers.

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