APPLICATION NOTE TURBINE BLADE TIP MEASUREMENTS

Transcription

1 Philtec APPLICATION NOTE Aug TURBINE BLADE TIP MEASUREMENTS 4 mm mm mm 44 mm Two turbine blade samples are shown here:. One blade p measures mm wide x 44 mm long with rough ground surface. One blade p measures mm wide x 4 mm long with dark surface A Philtec model RC99 sensor, designed for blade p measurements, has an ac ve fiber area x.54 mm. 3.8 The sensor was fixtured above the target blades and mounted on a linear stage table..54 The stage moved the sensor across the face of the blades as data was recorded. Fiber Optic Detail Model RC99 DIRECTION OF TRAVEL RC99 Turbine Blade

2 CALIBRATION OF SENSOR The RC99 operates over a mil (5 mm) range with a sensitivity of 3 mv/mil (. mv/μm) when calibrated to a diffuse (dull) reflective target. SETTING OF SENSOR GAP FOR BLADE SCANS The RC99 gap to the target blades was set to ~ volts, in the middle of its linear range, at a gap of ~5 mils (~.3 mm). Two outputs were recorded from the sensor:. The SNR Voltage, which is a measure of the signal strength returned from the target. The Distance Voltage, which was converted to Distance using the Y = mx + b formula where m =.37 and b =.37 volts as shown on the calibration chart.

3 RESULTS - mm Blade The active fiber area for the RC99 is mm, which means that the sensor can be fully over the blade tip for a distance not greater than mm. The SNR voltage rises when the blade comes into the sensor s view. The DISTANCE voltage also rises but there are edge effects due to light refraction off the edges of the blade. We calculate the standard deviation of the distance data for stage travel distances of 7-9 mils, where we are certain the probe is totally over the blade tip and there are no edge effects. Sensor Blade STD DEV = 77 μm (3 mils). PHILTEC Model RC99 SCAN ACROSS ROUGH GROUND TURBINE BLADE mm Blade SNR, Volts PHILTEC Model RC99 SCAN ACROSS ROUGH GROUND TURBINE BLADE mm Blade DISTANCE TO BLADE, mm STD DEV = 77 μm From mm

4 RESULTS - mm Blade The active fiber area for the RC99 is mm, which means that the sensor can be fully over the blade tip for a distance not greater than mm on this narrow blade. The SNR voltage rises when the blade comes into the sensor s view. The DISTANCE voltage also rises but there are edge effects due to light refraction off the edges of the blade. We calculate the standard deviation of the distance data between the stage travel distances of.7 -. mm, where we are certain the probe is totally over the blade tip and edge effects are avoided. STD DEV = 9 μm (.75 mils). Sensor Blade PHILTEC Model RC99 SCAN ACROSS SMOOTH DARK TURBINE BLADE mm Blade Width Volts SNR PHILTEC Model RC99 SCAN ACROSS SMOOTH DARK TURBINE BLADE mm Blade Width. DISTANCE TO BLADE, mm STD DEV = 9 μm From.7 -. mm

5 ADDITIONAL SCAN - FRONT SURFACE MIRROR To check the electronic resolution of the sensor, we scanned along a front surface mirror. We calculated the standard deviation of the distance data over the same range of stage travel as was used for the mm blade (3 mm). STD DEV = μm (.4 mils). Note: The mirror was not vacuum chucked to the stage. STD DEV would be even smaller if the mirror was parallel to the stage table. Volts SNR PHILTEC Model RC99-BC, s/n 5 SCAN ACROSS Mirror PHILTEC Model RC99-BC, s/n 5 SCAN ACROSS Mirror DISTANCE TO TARGET, mm STD DEV = μm From 4-7 mm

6 ADDITIONAL SCAN - Diffuse Reflector Next we scanned along a anodized aluminum plate. We calculated the standard deviation of the distance data over the same range of stage travel as was used for the mm blade (3 mm). STD DEV = 4 μm (.9 mils). Volts SNR PHILTEC Model RC99-BC, s/n 5 SCAN ACROSS Diffuse Aluminum PHILTEC Model RC99-BC, s/n 5 SCAN ACROSS Diffuse Aluminum.7 DISTANCE TO TARGET, mm STD DEV = 4 μm From 4-7 mm

7 ADDITIONAL SCANS - Surface Roughness Samples Next we scanned mm along several surface roughness specimen surfaces. We calculated the standard deviations of the distance data over the same range of stage travel as was used for the mm blade (3 mm). Volts SNR PHILTEC Model RC99-BC, s/n 5 SCAN ACROSS 3.μm RaTurned Surface PHILTEC Model RC99-BC, s/n 5 SCAN ACROSS 3.μm RaTurned Surface DISTANCE TO TARGET, mm STD DEV = 66 μm From 4-7 mm

8 ADDITIONAL SCANS - Surface Roughness Samples - Summary This table shows all of the test results using the model RC99. SENSOR Sample Surface (Ra) STD DEV, μm STD DEV, mils RC99 Mirror (Specular)..4 RC99 Dull (Diffuse) 4.9 RC99.5 μm Lapped 48.9 RC99. μm Lapped 53. RC99.5 μm Ground 4.6 RC99. μm Ground 54. RC99.6 μm Ground RC99 3. μm Turned 66.6 RC99 mm Blade 9.75 RC99 mm Blade DISCUSSION The model RC99 sensor uses a long narrow fiberoptic bundle to achieve 5 mm range on a narrow turbine blade. The scan results show that excellent accuracy is achievable with specular (smooth) targets only. The small thin blade was smooth enough to produce a standard deviation of 9 μm. The large blade has a rough grind with the grain going parallel to the long axis of the blade tip. The degree of scattering of light rays from that grain pattern are similar to those observed from the surface roughness specimens with.6 and 3. μm Ra. 3.8 Fiber Optic Detail Model RC99.54 The model RC sensor uses a mm diameter round fiberoptic bundle. It s downside is that it has a small.3 mm operating range, therefore needs to be positioned very close to the targets; ~.4 mm vs. ~ mm for the RC99. Because it is so small and round, the sensor tip orientation can be rotated into a most favorable position to minimize standard deviations..8 mm O.D. ØC Side-by-Side Fiberoptics In Sensor Tip Fiber Optic Detail Model RC 8

9 CALIBRATION OF SENSOR The RC operates over a 5 mil (.3 mm) range, with a sensitivity of 49 mv/mil (5.9 mv/μm), when calibrated to a diffuse (dull) reflective target. 5. PHILTEC Model RC Serial No. 7 Calibration To Diffuse Aluminum 7/3/ Volts SENSITIVITY = 49. mv/mil Linear Range ± % = mils Noise VDC (DC- KHz) = 3. mv pk-pk Y Intercept = -.57 Volts Gap, mils 9

10 ADDITIONAL SCANS - RC Sensor The two turbine blade tips were scanned with the RC fiberoptics oriented parallel to - and perpendicular to - the long axis of the blades. Perpendicular orientation had better performance. With the mm blade: = μm, = 8 μm STD DEV.8 PHILTEC RC SCAN ACROSS mm Blade RC Parallel To Blade Fiberoptics Parallel To Blade Fiberoptics Perpendicular To Blade DISTANCE TO TARGET, mm STD DEV = 8 μm From - 5 mm PHILTEC Model RC SCAN ACROSS mm Blade RC Perpendicular To Blade.8 DISTANCE TO TARGET, mm STD DEV = μm From - 5 mm

11 ADDITIONAL SCANS - RC Sensor The two turbine blade tips were scanned with the RC fiberoptics oriented parallel to - and perpendicular to - the long axis of the blades. Perpendicular orientation had better performance. With the mm blade: = μm, = 49 μm STD DEV.8 PHILTEC RC SCAN ACROSS mm Blade RC Parallel To Blade.7 DISTANCE TO TARGET, mils STD DEV = 49 μm From. -.7 mm PHILTEC RC SCAN ACROSS mm Blade RC Perpendicular To Blade DISTANCE TO TARGET, mm STD DEV = μm From mm

12 RESULTS - ALL SCANS This table shows all of the test results. SENSOR Sample Surface (Ra) STD DEV, μm STD DEV, mils RC99 Mirror (Specular)..4 RC99 Dull (Diffuse) 4.9 RC99.5 μm Lapped 48.9 RC99. μm Lapped 53. RC99.5 μm Ground 4.6 RC99. μm Ground 54. RC99.6 μm Ground RC99 3. μm Turned 66.6 RC99 mm Blade 9.75 RC99 mm Blade RC Para mm Blade 8. RC Perp mm Blade.8 RC Para mm Blade 45.8 RC Perp mm Blade 5. DISCUSSION PHILTEC Fiberoptic Sensors for the Measurement of Distance, Displacement and Vibration