Indikon, a world leading manufacturer and supplier of vibration monitoring equipment, offers a full line of high resolution seismic pickups (providing direct displacement outputs at very low noise levels) and various solid state accelerometers and velocity transducers.
Displacement Pickups - These vibration transducers incorporate a spring-mass system with eddy-current damping using a frictionless pivot, which allows resolutions down to the micro inch range.
This pivot is a flexure that serves as the 'spring', and a moment arm attached to the pivot serves as the 'mass'. At frequencies above 50 Hz, the mass remains fixed in space and becomes an inertial reference.
A transducer within the pickup senses the motion of the mounting base relative to the inertial reference and converts it into a proportional signal.
Appropriate damping results in a frequency response flat down to 10 Hz. Note that the pickup senses in only one direction, which is perpendicular to the mounting base.
The damping is done through eddy-currents generated by a metal flag moving between the poles of a magnet.
Unlike other velocity transducers that use a viscous fluid or gel for damping, the Indikon pickup is not as dependent upon temperature for performance and reliability.
Note that the proportional signal being generated by the transducer is a direct function of the vibration amplitude of the machine relative to a fixed point in space.
Therefore it allows it to measure absolute dislacement even in low-speed machinery such as cooling towers, forced draft fans and induced draft fans which is the key to its application.
Note that using a proximity probe, for instance, to detect vibration displacement would yield results after damage to bearings had already occurred, because it measures shaft vibration relative to the housing.
|
Seismic Displacement Pickups may operate in temperatures up to 300?F, when used in conjunction with a probe driver model 590 or 4-20mA transmitter such as the XT101 and are available in different mountings to capture the direction of the vibration.
Accelerometers - These piezo-electric devices are used in the measurement of force derived from vibration as detected in machine casings, bearing caps and/or pedestals.
Accelerometers are best suited to obtain a great frequency response and are useful in detecting blade passing or gear mesh problems in turbines, compressors and gearboxes.
Acceleration is defined as the time rate of change of velocity and its unit of measure is gravity defined by the letter 'g'.
Acceleration is most practical where actual mechanical failure is present and accelerometers, being small, are optimum for usage in smaller machine structures.
Charge-coupled accelerometers are available for temperatures up to 1200?F (i.e. gas combustion turbines).
Those built with charge amplifiers are available for temperatures up to 300?F.
Velocity Transducers - The original mechanical transducers had a spring-mass/moving coil system and now have been replaced with a solid state type.
The new transducers are piezo-electric device with built-in intergrating electronics that converts the acceleration signal to a velocity signal. Usually have a +/-5% frequency range and may go down to 3Hz and up to 2500 Hz.
Their temperature range is limited to 250?F and are used for high moisture applications (with water-proof connections) such as water circulating pumps and in applications where mounting space is limited.
|
Digital Torquemeter and
