Vibration Transducers

Compare VIBRATION TRANSDUCERS that sense the vibration of rotating machines. A vibration transducer senses vibration via internal magnet vibration which sends a transducer signal to a measuring instrument. The transducer is actuated by a vibration sensor.  The sensors used by vibration transducers to detect uncontrolled motion (vibration) in rotating machinery come in two types: velocity sensors and accelerometers.

A velocity sensor contains a coil of wire in proximity to a permanent magnet which is suspended by a set of springs. When exposed to vibration, the magnet moves in the direction of the vibration. This induces a voltage in the wire coil. The voltage output of the sensor is proportional to the magnitude and speed of motion of the vibration. The sensor does not need a power supply. The springs that support the magnet provide a force which is temperature dependent. This makes the signal out of the sensor temperature dependent. Also, the wire coil and magnet structure is large and heavy. For these reasons, the velocity sensor has been replaced by the accelerometer in most applications.

The accelerometer uses a piezoelectric crystal that is clamped with a spring loaded mass. When the piezoelectric crystal is subjected to a force, a charge is developed at its surfaces. The accelerometers contain a preamplifier, but require external power excitation to generate a current signal. Velocity sensors do not require the external excitation. The operating temperature is important for the housing materials as well as the mounting of the crystal. The speed response of the sensing structure has to be considered. It is expressed in either Hertz (cycles per second) or CPM (counts per minute) where 60 CPM equals 1 Hertz. Sensitivity is measured as millivolts (mV) per ips (inches per second) or mV per unit gravity g (g = 32 ft/sec2).

Both of the above types of sensors can be used to determine displacement, velocity or acceleration of a vibrating signal