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Research Papers: Gas Turbines: Controls, Diagnostics, and Instrumentation

Influence of Force Field Direction on Pressure Sensors Calibrated at Up to 12,000 g

[+] Author and Article Information
Wieland Uffrecht, Erwin Kaiser

Dresden Institute of Fluid Mechanics, Technische Universität, 01062 Dresden, Germany

J. Eng. Gas Turbines Power 130(6), 061602 (Aug 27, 2008) (8 pages) doi:10.1115/1.2966390 History: Received March 28, 2008; Revised March 28, 2008; Published August 27, 2008

The measurement of pressure within both stationary and rotating frames of reference is a fundamental requirement when studying the flow field through turbomachinery blading. Measurement of pressure within the rotating frame presents a particular challenge, as centrifugal acceleration of the sensor can have a significant impact on sensor calibration, and therefore accuracy of the resulting measurements. In this paper the telemetric calibration of pressure sensors at up to 12,000 g is described, and the impact on calibration of membrane size, sensor body shape, and sensor mounting direction is discussed. The program of work reported in this paper focuses on experimental issues associated with rotating pressure measurement. The combined effect of centrifugal load and pressure on integrally temperature compensated silicon pressure sensors is presented. Experimental results are given that provide insight into the influence of acceleration on pressure readings. Implementation of acceleration into sensor calibration is presented. Supplementary finite element calculations enable impact of sensor body shape to be taken into account during the evaluation of sensor acceleration-to-pressure sensitivity ratio. Different sensors with varied membrane sizes and acceleration force directions are examined and compared.

Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 2

Temperature T over radius r of pressure path, two different temperature and radius spans combined, Cases 1–4, average temperature TA for all cases, and reduced average temperature TA−10 K simulating uncertainty in the known value

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Figure 3

Error over rpm caused by neglected correction for fluid column in force field for the four cases from Fig. 2 for pressure ratio π, see Eq. 7

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Figure 4

Error over rpm caused by correction for the fluid column in the rotating system with constant 10 K to low temperature TA−10 K simulating uncertainty in the known temperature, see Fig. 2 for the four cases and see Eqs. 3,7 for the pressure ratios πT and π

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Figure 5

Error over rpm caused by pressure correction for the fluid column in the rotating system with average temperature TA instead of linear temperature distribution, four cases (see Fig. 2), for pressure ratios πT and π, see Eqs. 3,7

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Figure 6

Sensor element S schematically rotating around the axis RA with sensor radius rS, membrane area AM, and membrane thickness hM

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Figure 7

Calibration test rig, motor M, spindle Sp, air supply A, measurement disk D with pressure sensors to be tested and the telemetry system, pressure measurement hose P, and basement B

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Figure 8

Calibration test rig detail, rotating side Ro, rotating shaft Sh, measurement disk D with rotating radial pressure passage Rp and sensor S, plenum Pl, labyrinth seal L, stationary side St with air supply pipe A, pressure measurement pipe M, and pressure hose toward comparative sensor P

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Figure 9

Relative error of telemetric Sensors A2–A5 for stationary calibration using DPI 515 made by company Druck

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Figure 10

Digital readings of Sensors A2–A5 in digit as supplied by the 8 bit analog to digital converter of the telemetry, centrifugal acceleration acting at sensor radius rS

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Figure 11

Pressure readings pA of Sensors A2–A5 caused by centrifugal acceleration and air column pressure

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Figure 12

Specific membrane mass ρMhM of Sensors A2–A5, linear fit shown for A2, error bars equal one digit uncertainty

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Figure 13

Digital readings of Sensor A2 for different preset calibration pressures from the stationary system

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Figure 14

Specific membrane mass ρMhM of Sensor A2 for different pressures, linear fit for all values >6000 rpm, error bars equal one digit uncertainty

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Figure 15

KPY sensor elements schematically, rotation axis RA for Cases I–III along the dashed-dotted line in the picture plane, sensor radius rS

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Figure 16

Key points of the FEM model for the sensor element

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Figure 17

Displacement at the membrane center over pressure; FEM results for the two fix point selections 2, 12, 13, 3 (bottom) and 1, 2, 12, 13, 3, 4 (bottom and side), see Fig. 1

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Figure 18

Displacement at the membrane center over temperature; FEM results for the two fix point selections 2, 12, 13, 3 (bottom) and 1, 2, 12, 13, 3, 4 (bottom and side), see Fig. 1

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Figure 19

Displacement w0 at the membrane center and acceleration induced pressure pA over acceleration for Case I; FEM results for sensors KPY10 for 10 bars with hM=0.04 mm and KPY2 for 2 bars with hM=0.02 mm

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Figure 20

Displacement at the membrane center over acceleration; FEM results from Case I, same as in Fig. 1, compared with the FEM results from Case III with KPY2 for a 10 deg inclination

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Figure 21

Specific membrane mass over acceleration, experiment, and FEM results, different sensors, but valid as a general calibration parameter for acceleration sensitivity, see Fig. 1

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Figure 1

Sensor (S) location and pressure measurement hole (P) with connecting pipe at different radii r and temperatures T, all rotating around the rotation axis (RA)

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