134624360 Bently Nevada Vibration

Check Resistance Sensor Vibration Probe Bently Nevada A. According

the manual book normal resistance sensor probe plus extension cable is : 7Ω – 11Ω (depending total length of cable)

isconnect !ield "ire to the #$% terminal o! the proximitor and remove miniature co&axial extension cable connector !rom proximitor' (nsure !emale connector on proximitor and male connector on extension cable are clean' )easure the resistance bet"een the outer *not the armor braid i! !itted+ conductor and the inner conductor o! the extension cable as this !igure:

B. ,! resistance is out o! limits disconect the miniature co&axial connection bet"een probe and extension cable' (nsure !emale connector on extension cable and male connector on probe are clean' )easure the resistance bet"een the outer conductor and the inner conductor o! the probe'

C. ,!

the resistance is out o! limits replace probe "ith a compatible item' ,! resistance is "ithin limits replace extension cable "ith compatible item

Machine Vibration Measurement - Vibration Sensors Sensors Sensors used to measure measure vibration come in three three basic basic types: types: displacem displacement, ent, velocity, and accelerat acceleration. ion. Displa Displacem cement ent sensor sensors s measur measure e change changes s in dis distan tance ce betwe between en a machin machine’s e’s rotati rotating ng elemen elementt and its stationary housing (frame). Displacement sensors come in the form of a probe that threads into a hole drille drilled d and tapped tapped in the machine machine’s ’s frame, frame, just above above the surface surface of a rotati rotating ng shaft. shaft. eloci elocity ty and acceleration sensors, by contrast, measure the velocity or acceleration of whatever element the sensor is attached to, which is usually some e!ternal part of the machine frame".

# design of displacement sensor manufactured by the $ently%&evada corporation uses electromagnetic eddy current technology to sense the distance between the probe tip and the rotating machine shaft. 'he sensor itself is an encapsulated coil of wire, energied with high%freuency alternating current (#*). 'he magnetic field produced by the coil induces eddy currents in the metal shaft of the machine, as though the metal piece were a short%circuited secondary coil of a transformer (with the probe’s coil as the transformer primary winding). 'he closer the shaft moves toward the sensor tip, the tighter the magnetic coupling between the shaft and the sensor coil, and the stronger the eddy currents.  'he high%freuency oscillator circuit providing the sensor coil’s e!citation signal becomes loaded by the induced eddy currents. 'herefore, the oscillator’s load becomes a direct indication of how close the probe tip is to the metal shaft. 'his is not unli+e the operation of a metal detector: measuring the pro!imity of a wire coil to any metal object by the degree of loading caused by eddy current induction. n the $ently%&evada design, the oscillator circuit providing sensor coil e!citation is called a pro!imitor.  'he pro!imitor module is powered by an e!ternal D* power source, and drives the sensor coil through a coa!ial cable. -ro!imity to the metal shaft is represented by a D* voltage output from the pro!imitor module, with // millivolts per mil (" mil 0 "1"/// inch) of motion being the standard calibration.

Since the pro!imitor’s output voltage is a direct representation of distance between the probe’s tip and the shaft’s surface, a 2uiet3 signal (no vibration) will be a pure D* voltage. 'he probe is adjusted by a technician such that this uiescent voltage will lie between the pro!imitor’s output voltage range limits. #ny vibration of the shaft will cause the pro!imitor’s output voltage to vary in precise step. # shaft vibration of 4.56 7, for instance, will cause the pro!imitor output signal to be a 4.56 7 waveform superimposed on the D* 2bias3 voltage set by the initial probe1shaft gap. #n oscilloscope connected to this output signal will show a direct representation of shaft vibration, as measured in the a!is of the probe. n fact, any electronic test euipment capable of analying the voltage signal output by the pro!imitor may be used to analye the machine’s vibration: oscilloscopes, spectrum analyers, pea+%indicating voltmeters, 89S%indicating voltmeters, etc. t is customary to arrange a set of three displacement probes at the end of a machine shaft to measure vibration: two radial probes and one a!ial (or thrust) probe. 'he purpose of this tria!ial probe configuration is to measure shaft vibration (and1or shaft displacement) in all three dimensions:

-hotographs of a $ently%&evada displacement sensor (sensing a!ial vibration on a 2ring3 style air compressor) and two pro!imitor modules are shown here:

t is also common to see one phase reference probe installed on the machine shaft, positioned in such a way that it detects the periodic passing of a +eyway or other irregular feature on the shaft. 'he 2+eyphasor3 signal will consist of one large pulse per revolution:

 'he purpose of a +eyphasor signal is two%fold: to provide a reference point in the machine’s rotation to correlate other vibration signals against, and to provide a simple means of measuring shaft speed. 'he location in time of the pulse represents shaft position, while the freuency of that pulse signal represents shaft speed. or instance, if one of the radial displacement sensors indicates a high vibration at the same freuency as the shaft rotation (i.e. the shaft is bowed in one direction, li+e a banana spinning on its long a!is), the phase shift between the vibration’s sinusoidal pea+ and the phase reference pulse will indicate to maintenance machinists where the machine is out of balance. 'his is not unli+e automatic tire%balancing machines designed to measure imbalance in automobile tire and wheel assemblies: the machine must have some way of indicating to the human operator where a balancing weight should be placed, not just how far out of balance the tire is. n the case of machine vibration monitoring euipment, the +eyphasor signal and one of the a!ial displacement signals may be simultaneously plotted on a dual%trace oscilloscope for the purposes of determining the position of the imbalance on the machine shaft.

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rom the perspective of measurement, it would be ideal to affi! a velocimeter or accelerometer sensor directly to the rotating element of the machine, but this leads to the problem of electrically connecting the (now rotating;) sensor to stationary analysis euipment.