BLADE TIP TIMING & TIP CLEARANCE MEASUREMENTS
CAPAAB’s CAPACITIVE OFF THE SHELF PRODUCTS THE INNOVATIVE BTT CAPAAB SOLUTION
limitations of single electrode probe principle of the “twin probe” innovative solution example of comparative results BTT / BTC available products by ALAIN BRUERE
BLADE TIP TIMING & TIP CLEARANCE MEASUREMENTS
CAPAAB OFF THE SHELF PRODUCTS Based on capacitive principle OUTPUT LINEAR vs distance (triaxial probe technology) Range : 0 to 20 mm max Bandwidth : from DC to 20 kHz
OUTPUT LINEAR vs capacitance (triaxial & coaxial probe technology) Used with non continues target (like blades) Range : 0 to 5 mm typical Bandwidth : from DC to 250 kHz Standstill probe calibration (no spin rig needed) Remote gain calibration 800 °C max triaxial probes compatible 1300 °C max coaxial probes compatible
BLADE TIP TIMING & TIP CLEARANCE MEASUREMENTS THE INNOVATIVE BTT CAPAAB SOLUTION •
limitations of single electrode probe
BTC voltage
Noise Vpp
LIMITATION DUE TO S/N RATIO
Spatial jitter (mm) = Noise / Slope Slope V/mm
Distance (mm)
Noise = limit given by the conditioner
Slope = how to increase it ? If the bandwidth is reduced (Noise (but …….. proportional BW !) So (Noise / Slope) increases !!!!
SQ Root Bandwidth), the rise time is also reduced
BLADE TIP TIMING & TIP CLEARANCE MEASUREMENTS THE INNOVATIVE BTT CAPAAB SOLUTION •
limitations of single electrode probe LIMITATION DUE TO S/N RATIO
Slope : how to increase it => Smaller probes ?
3 mm probe
2 mm probe
OUTPUT VOLTAGE Vs POSITION 3 mm probe ;2 mm blade thickness ;clearance 1 mm
OUTPUT VOLTAGE Vs POSITION 2 mm probe ;2 mm blade thickness ;clearance 0,7 mm
6000
BTT jitter = noise / slope
OUTPUT VOLTAGE (mV)
5000
4500
OUTPUT VOLTAGE (mV)
= 50 / 1,5 = 33 µm 4000
3000
2000
4000
BTT jitter = noise / slope
3500
= 70 / 1,5 = 45 µm
3000 2500 2000 1500 probe 1000
probe
1000
500
blade
blade
0
0 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1
0
1
2
DISTANCE (mm)
3
4
5
6
7
8
9
10 11 12
-12 -11 -10 -9 -8
-7 -6 -5
-4 -3 -2
-1
0
1
2
3
4
5
6
7
DISTANCE (mm)
Due to fringe effects, the slope is the same …. …. but the noise is higher (more amplification) !
8
9
10 11 12
BLADE TIP TIMING & TIP CLEARANCE MEASUREMENTS THE INNOVATIVE BTT CAPAAB SOLUTION •
limitations of single electrode probe LIMITATION DUE TO S/N RATIO
Noise : how to reduce it => Via bigger probes ?
5 mm probe
5 mm probe OUTPUT VOLTAGE Vs POSITION 5 mm probe ;2 mm blade thickness ;clearance 1,7 mm
OUTPUT VOLTAGE Vs POSITION 5 mm probe ;2 mm blade thickness ;clearance 1 mm
7000
5000
BTT jitter = noise / slope
BTT jitter = noise / slope
10000 OUTPUT VOLTAGE (mV )
OU T P U T V OL T A GE (mV )
6000
12000
= 70 / 1 = 70 µm
4000
3000
2000
= 70 / 2 = 35 µm 8000
6000
4000 probe
probe
2000 1000
blade
blade
0
0 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1
0
1
2
DISTANCE (mm)
3
4
5
6
7
8
9 10 11 12
-12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1
0
1
2
3
4
5
6
7
8
DISTANCE (mm)
Due to blade thickness < probe diameter, when probe diameter increases the output signal increase is not proportional
9 10 11 12
BLADE TIP TIMING & TIP CLEARANCE MEASUREMENTS THE INNOVATIVE BTT CAPAAB SOLUTION •
limitations of single electrode probe
EFFECTS OF CASING VIBRATION
At clearance = 1 mm, if we assume a casing vibration = 20 µm => 0.02 * 4,41 = 88 mV voltage change 88 mV / 1650 mV/mm = 55 µm of BTT Measurement uncertainty
CALIBRATION CURVE WITH target 2 mm thick centered
OUTPUT VOLTAGE Vs POSITION 3 mm probe ;2 mm blade thickness ;clearance 1 mm
CONDITIONNING UNIT MC1000B 201 / 06 / 002 / PROBE S1CW / 19 6000
Slope =-4.41 V/mm
10 8
5000
BTT jitter = noise / slope = 50 / 1,5 = 33 µm
OUTPUT VOLTAGE (mV)
O U T P U T V O L T A G E (V )
12
6 4
4000
3000
2000
2
probe
1000
0
blade
0
0,5
1
1,5
2
2,5
3
3,5
0 -12 -11 -10 -9
Distance (mm)
-8
-7
-6
-5 -4
-3
-2
-1
0
1
2
3
4
DISTANCE (mm)
Slope 1650mV/mm
Tip timing measurement improvement ? => twin probe solution
5
6
7
8
9
10 11 12
BLADE TIP TIMING & TIP CLEARANCE MEASUREMENTS THE INNOVATIVE BTT CAPAAB SOLUTION •
principle of the “twin probe” innovative solution CAPACITIVE probe with 2 half A & B identical parts
Blades rotation
A + B => B T C signal
A signal
Axial shift
B signal
blade
Conditioner A - B => B T T signal
SCHEMATIC TOP VIEW
Insensitive to casing vibration
BLADE TIP TIMING & TIP CLEARANCE MEASUREMENTS THE INNOVATIVE BTT CAPAAB SOLUTION •
example of comparative results Improvement of the S/ N ratio Single electrode vs twin electrode probe comparision 15
4
slope = 4 / 0,2 = 20
3,5 10 3 5
2,5
Volt
1,5 -5
Volt
2
0
1 0,5
-10
slope = 28/0,05 = 560
0 -15 -0,5 -20
-1 -0,5
-0,4
-0,3
-0,2
-0,1
0
0,1
0,2
0,3
0,4
0,5
Time (arbitrary units)
In this example, improvement of the NOISE / SLOPE ratio get with the “twin probe” compared to single electrode is about 5 = (560/ 20 * 5/28) = slope ratio * noise ratio
BLADE TIP TIMING & TIP CLEARANCE MEASUREMENTS THE INNOVATIVE BTT CAPAAB SOLUTION •
example of comparative results Processing from Clearance Output
(amplitude blade vibration vs RPM) Processing from Tip timing Output
In this example, the improvement with “twin probe” = 28.5 / 4.39 = 6.5 Processing thanks to
software
BLADE TIP TIMING & TIP CLEARANCE MEASUREMENTS THE INNOVATIVE BTT CAPAAB SOLUTION •
example of comparative results Signal from optical probe = Noise approx. 8x10-5 mm
(amplitude blade vibration vs RPM) CAPAAB Capacitive Probe (BTC OUTPUT) = Noise approx = 3x Optical
Other Cap Probe – Noise = 20x Optical
BLADE TIP TIMING & TIP CLEARANCE MEASUREMENTS THE INNOVATIVE BTT CAPAAB SOLUTION •
BTT / BTC available products
CAP 1000a : for triaxial probes ; 3U module CAP 1000b : for triaxial probes ; stand alone CAP 1800a : for pseudo triaxial probes ; 3U module CAP 1800b : for pseudo triaxial probes ; stand alone CAP 1802b : for twin coaxial probes BTC / BTT OUTPUT; stand alone
NO ADJUSTMENT NEEDED FULL AUTOMATIC BALANCE
BLADE TIP TIMING & TIP CLEARANCE MEASUREMENTS THE INNOVATIVE BTT CAPAAB SOLUTION •
example of BTT / BTC complete solution
8 CHANNELS 12
bits DIGITIZING UNIT
TWIN PROBES (up to 16)
BTC DISPLAY
CLEARANCE
TIME
V
TIME
CAP 1802 CONDITIONERS
PC + BTT DISPLAY PC
UP TO 16 CHANNELS PER SYSTEM
BLADE TIP TIMING & TIP CLEARANCE MEASUREMENTS THE INNOVATIVE BTT CAPAAB SOLUTION •
SUMMARY
The advantage of the “twin probe” concept has been clearly established with the results obtained with a signal simulator / real vibration induced and the use of suitable data processing Manufacturing the twin sensor is more difficult than the simple sensor but on the other hand it involves well-known processes The “twin probe” technique can be applied to various sensors diameters => Hence its uses ranges from aero engines to grounded power engines. Last but not least, the Blade Tip Clearance signal is available simultaneously with BTT
