1.5.1 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
• 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.