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

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 SiO_x (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.