Machine Vibration Monitors

Compare MACHINE VIBRATION MONITORS. Machine vibration monitoring tools are vital for the early sensing of machine vibration. The machine vibration transducers and vibration meters listed here are state of the art. The measuring instruments are for amplitude and simple harmonic sensing. To do more advanced type of analysis requires training and may need more advanced instrumentation.

Compare VIBRATION METERS that monitor vibration in rotating machinery. Vibration can be sensed with portable meters or with multiple vibration probes attached to multi-channel vibration analyzers. Which measuring system to use depends on the complexity of the process to be measured, the most likely cause of excessive vibration, and the degree of process downtime and its effect on the overall manufacturing process

 

Vibration is the displacements of a rotary element either axially, radially or tangentially. The vibration can be measured as the amount of displacement peak to peak) in inches or mm. It can also be measured as velocity (max inches or mm per sec) or acceleration as peak g's. (g is gravity and unit value is 32 ft/sec²).

When measuring vibration, values of good, fair and bad performance have to be known. ISO 2372 and 10816 are the best reference at this time. MIL specs and some industry standards address specific applications.

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 For these reasons, the velocity sensor has been replaced by the accelerometer in most applications.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 piezo electric crystal that is clamped with a spring loaded mass. When the piezo electric 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).