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Research Papers: Elastohydrodynamic Lubrication

Influence of Electrical Parameters of a Thin-Layer Sensor on the Accuracy of Pressure Measurement in an EHD Contact

[+] Author and Article Information
Adam Wilczek

 Faculty of Mechanical Engineering, Technical University of Radom, ul. Krasickiego 54, 26-600 Radom, Polandadam.wilczek@pr.radom.pl

J. Tribol 133(3), 031504 (Jul 28, 2011) (8 pages) doi:10.1115/1.4004345 History: Received March 14, 2011; Revised May 29, 2011; Accepted June 06, 2011; Published July 28, 2011; Online July 28, 2011

This paper presents a model study of inductive, capacitive, and piezoelectric effects on the accuracy of pressure measurements in an EHD contact. Circuit and mathematical models of a thin-layer sensor and a measurement system were developed. It has been assumed that isolation layers of the sensor, deposited as SiOx (1 ≤ x ≤ 2) layers, have piezoelectric properties. The circuit model of the sensor contains a resistance, an electric capacitance, an inductance of a sensor’s circuit, and an ideal current source representing piezoelectric properties of isolating layers of the sensor. The circuit model of the measurement system forms a full measuring bridge with the thin-layer sensor in one of its branches. A derived equation for output voltage of the measurement bridge was used as a mathematical model of the measurement system. The investigations show that at inappropriate electric parameters of the measurement system, inappropriate shape of the sensor’s transducer and short transition time of the sensor through the contact zone, the capacitive, and piezoelectric effects have a significant impact on the accuracy of pressure measurement in the EHD contact. The transducer with an active part located along its connection edges (asymmetric transducer) and a transducer with the active part located in the middle of connections width (symmetric transducer) was tested. It was shown that in the case of the symmetric transducer, the pressure measurement signal change caused by the capacitive and piezoelectric effects, is much smaller than in the case of the asymmetric transducer.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

EHD line contact and its characteristic quantities

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Figure 2

Design of a thin-layer sensor: (a) sensor in the two-disk system, (b) symmetric transducer, (c) asymmetric transducer, and (d) cross section of the sensor

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Figure 3

Circuit models of the thin-layer sensor: (a) expanded model and (b) and (c) simplified equivalent models

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Figure 4

Model for the calculation of electrical capacitance and loading of transducer layer

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Figure 5

Circuit model of the measurement system

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Figure 6

Influence of basic capacitance Co on the measurement accuracy (dC/dt = 0, dz  = 0, tH  = 30 μs): (a) voltage supply (Uo  = const) and (b) current supply (Io  = const). 1—noneffected signal course; 2—Co  = 1000 pF; 3—Co  = 3000 pF.

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Figure 7

Influence of variable capacitance component Ch on the measurement accuracy (Co  = 1 pF, dz  = 0, tH  = 30 μs): 1—noneffected signal course; 2—hm  = 1 μm; 3—hm  = 2 μm

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Figure 12

Influence of the piezoelectric effect of the measurement signal in the case of the symmetric transducer (l1 /2b = 0.037): (a) dz  = 5 × 10−14 C/N, (b) dz  = 3 × 10−12 C/N; 1—noneffected signal course; 2—effected signal course, 3—signal courses at Uo  = 0

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Figure 8

Influence of piezoelectric phenomenon on the measurement accuracy (Co  = 1 pF, dC/dt = 0, tH  = 30 μs): 1—noneffected signal course; 2, 4—dz  = 2.5·10−14 C/N; 3, 5—dz  = 5 × 10−14 C/N; 4, 5—signal courses at Uo  = 0

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Figure 9

Cumulative influence of capacitance and piezoelectric phenomenon (tH – 30 μs): 1—noneffected signal course; 2, 4—Co  = 1000 pF, hm  = 2 μm, dz  = 2.5 × 10−14 C/N; 3, 5—Co  = 3000 pF, hm  = 1 μm, dz  = 5 × 10−14 C/N; 4, 5—signal courses at Uo  = 0

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Figure 10

Distortion of measurement signal with artificially accelerated piezoelectric current (l1 /2b = 0.037, iz  = f(ttps ), tps  = 3 μs, dz  = 5 × 10−14 C/N): 1—noneffected signal course; 2—effected signal course, 3—signal courses at Uo  = 0

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Figure 11

Signal courses resulting from the piezoelectric phenomenon (l1 /2b = 0.037): 1—noneffected signal course; 2—signal course from the active part of the transducer, 3—signal course from connections of the transducer; 2, 3—signal courses at Uo  = 0

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