VELOCITY SENSORS

Operating principle:

The case of the sensor is mounted to the measured object. The magnet of the velocity sensor is suspended on a membrane (spring) which moves through a coil of wire. Due to the vibration, the coil of wire moves through the magnetic field of the permanent magnet and generates (induces) a voltage signal which is proportional to the vibration (velocity).

Application:

Absolute casing vibration
In combination with a trigger measurement: Vector measurement (magnitude and phase)

DISPLACEMENT SENSORS

Operating principle:

The displacement sensor oscillator generates a constant frequency sine wave that passes through an inductive coil, which produces an electromagnetic field in front of the sensor face. When a target metal object comes close to this field, some of the electromagnetic energy is transferred to the target as eddy currents. This transfer of energy reduces the amplitude of the oscillator, which is inversely proportional to the distance of the target metal object being monitored to the face of the sensor.

Applications:

Used on journal-bearing machines
Two sensors are used, at 90º to each other, to determine the position of the shaft (X-/Y-measurement).
Relative shaft vibration, axial vibration, speed/trigger
In combination with a trigger measurement: Vector measurement (magnitude and phase)
Differential Expansion
Rod-drop (on compressors)
Eccentricity

TRANSMITTERS

They simply transfer (“transmit”) a pre-defined specific measurement (e.g. vibration velocity mm/s rms) and measurement range (e.g. 0…20 mm/s rms) to a DCS or PLC via a standardized signal like 4-20 mA, for example.

A transmitter thus “translates” a specific measurement type and range into a signal that a superior controlling system can process.