PowerPoint Presentation

SKF GroupOctobe04, 2010 SKF Group Slide 2

Eddy current Probes - Technology

SKF Group2 SKF GroupOctobe04, 2010 SKF Group Slide 3 Shaft Relative MotionProbe #2Probe #1CLLCGeometric Centerof BearingTilt PadBearingEddy ProbesRelative Shaft VibrationMeasures Gap-ve Volts outputDC componentAC componentShaft materialProbe track7.87mV/m200mV/Mil

SKF Group3 SKF GroupOctobe04, 2010 SKF Group Slide 4 Eddy Probe TheoryElectric FieldShaft/TargetGapEddy Current orProximity ProbeSensitive Calibration:Magnetic PropertiesElectrical PropertiesShaft Physical Properties SKF Group4 SKF GroupOctobe04, 2010 SKF Group Slide 5

Probe - Extension Cable DriverProbe & extension use coaxial cable5m, 9m or 10m system lengths All components are electrically matchedProbe driver performs linearisation

Any change in system length or target material will affect the linearity/calibration.CABLESKFCMSS665GND-24VGNDSIG-24VEXTENSIONPROBEDRIVERFIELDWIRINGComponents of an ECP System SKF Group5Eddy Probe System Components

The eddy probe system consists of: Pickup Extension cable Driver Field wiring The driver/extension cable/probe are a matched system and cannot be changed in any way without affecting the systems calibration. The field wiring, consisting of a 3-wire twisted, shielded cable (Belden # 8770), connects each driver to the monitoring system.The eddy probe system operates on the proximity theory where a high frequency RF signal is generated by the driver when -24 VDC is provided. This signal is passed down the extension cable, the probe cable to the wire coil at the probe tip. As the signal is passed through the wire coil, a cone shaped electo-magnetic field is radiated. As this EM field penetrates the rotor shaft, eddy currents are created on the surface of the shaft. As these eddy currents are created, a signal loss is created and the driver converts this loss into a negative DC output voltage. When the gap between the shaft and the probe tip decreases, more eddy currents are created, and a larger signal loss is sensed by the driver, which sends a proportionately larger negative DC voltage to the monitor. As the shaft vibrates, the gap varies proportionately, and a varying negative DC voltage is passed to the monitor (which resembles an AC signal). Thus, the relative gap between the shaft and the probe is available as the DC signal and the vibration is available as the AC signal. SKF GroupOctobe04, 2010 SKF Group Slide 6 TSI Shaft EccentricityMeasurement of shaft bow at slow roll speedUses ECP, displaced from bearing locationDMx provides, per rev, peak & peak to peak displacement measurement

Per rev mode can be enabled/disabled, has low speed disengage thresholdLack or loss of T1 (rpm < threshold) - conventional detection resumes.

SKF Group6 SKF GroupOctobe04, 2010 SKF Group Slide 7 TSI SMAXVisualised by a shaft orbit derived from an orthogonal XY ECP pairSMAX : maximum displacement from 0May differ from X peak or Y peakX & Y peak dependent on Tx location SMAX independent of transducer locationApproximate methods can be usedSome may under-estimate SMAXDMx uses resultant value of X & YThis will only ever over-estimate SMAXMaximum error 40%.

SKF Group7 SKF GroupOctobe04, 2010 SKF Group Slide 8

TSI Differential ExpansionPrimary purpose to guard against rub between rotor & casingLong Range single ECP Standard Thrust applicationDual axial ECP, Complementary modeMeasurement range approaches 2x single ECP

SKF Group8 SKF GroupOctobe04, 2010 SKF Group Slide 9 TSI - Differential Expansion

Sensitivity of sensor S1 and S2 is 1000mV/mm.

Sensor S1 and sensor S2 will be connected to a pair of channels, in this example, to channel 1 and channel 2.

The collar is closest to sensor S1 when no expansion and closest to sensor S2 at maximum expansion.

In this example, channel 1 has the target positive direction set as "Active / Normal (away from probe)".

S1 is selected to be the sensor that decides when to switch over to S2 depending on the crossover voltage. SKF Group9 SKF GroupOctobe04, 2010 SKF Group Slide 10

TSI Differential ExpansionPrimary purpose to guard against rub between rotor & casingDual ECP, Ramp differential modeSingle rampOr dual ramp concave or convex modesTypically 9.5 to 14.50 ramp angleMeasurement range around 5x-6x single ECPDMx makes axial & radial displacements available.

SKF Group10 SKF GroupOctobe04, 2010 SKF Group Slide 11 Eliminate periodic inspections that require Machine shutdown and disassembly Provide real time trend of rider ring wear.

CMSS 65/68 seriesEddy Probe SystemRod Drop SKF Group11The most popular method of determining when to rotate or replace the rings is Rod Drop Monitoring. The measurement is made with an Eddy Current Probe, mounted in a vertical direction, directly viewing the rod. The preferred installation would have a probe bracket adapted to the packing gland plate, mounted internal to the distance piece. As an alternate solution, some users have used the CMCP801 probe housing, providing for an external adjustment of the probe gap. As the Eddy Probe field will penetrate the rod surface approximately 15 mils, it is important that the observed rod be homogenous in nature and free of any surface irregularities. The Eddy Probe system is interfaced to a CMCP545 Position Monitor to measure the probes DC output (Probe Gap). By trending the DC Gap voltages from the eddy probe, it is possible to measure the average horizontal running position of the piston rod. The CMCP545 provides two levels of alarm, corresponding Alert and Danger relays and a 4-20 mA output proportional to the DC Gap voltage. SKF GroupOctobe04, 2010 SKF Group Slide 12 Rod Drop

SKF Group12The most popular method of determining when to rotate or replace the rings is Rod Drop Monitoring. The measurement is made with an Eddy Current Probe, mounted in a vertical direction, directly viewing the rod. The preferred installation would have a probe bracket adapted to the packing gland plate, mounted internal to the distance piece. As an alternate solution, some users have used the CMCP801 probe housing, providing for an external adjustment of the probe gap. As the Eddy Probe field will penetrate the rod surface approximately 15 mils, it is important that the observed rod be homogenous in nature and free of any surface irregularities. The Eddy Probe system is interfaced to a CMCP545 Position Monitor to measure the probes DC output (Probe Gap). By trending the DC Gap voltages from the eddy probe, it is possible to measure the average horizontal running position of the piston rod. The CMCP545 provides two levels of alarm, corresponding Alert and Danger relays and a 4-20 mA output proportional to the DC Gap voltage. SKF Group SKF Group

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