eNotes: Mechatronics and Controls

13.5 VELOCITY

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This can be measured with dedicated sensors.

We may also differential the output of a position sensor to find a velocity

13.5.1 Velocity Pickups

Output voltage is proportional to velocity (V/(cm/s))

These devices have low natural frequencies, and are used for signals with higher frequencies.

well suited to measuring severe vibrations, but it may be affected by noise from AC sources.

because signals are velocity, some form of integration must be done, making these devices bulky, and somewhat inaccurate

There are two common methods for mounting velocity pickups,

- Magnetic mounts allow fast and easy mounting, but the magnetic mount acts as a slight spring mass isolator, limiting the frequency range.

- Stud mounted transducers have a thin layer of silicone grease to improve contact

13.5.2 Tachometers

These devices measure the angular velocity of a rotating shaft.

One way is to connect a DC generator (motor). The faster the shaft turns, the higher the voltage.

Another technique uses a magnet with a pickup coil. As the magnet passes the coil a pulse is generated. The pulse magnitude and frequency are proportional to speed.