Modelling Fluid Loss Faults in an Industrial Pressure Sensor

Abstract

The efficient operation of industrial processes requires the timely and accurate diagnosis of faults in process equipment, particularly sensors, as acting on faulty measurement data can result in inefficient or dangerous operation. A common fault mode in industrial pressure sensors is mechanical damage resulting in the leakage of the internal oil (used to transmit external pressure to the sensing element) and the development of an air pocket within the device. In previous work, we have experimentally determined the faulty measurement characteristics of a commercial pressure sensor, where the sensor manufacturer has provided modified sensors with calibrated degrees of oil loss. The current paper develops a mathematical model of this tensoresistive pressure sensor, which describes and explains the impact that oil loss, and hence the presence of an air pocket, has on the static measurement response.

Development of a Wireless Pressure Transmitter with Diagnostics

“…This in turn may result in loss of the silicone oil used to transmit the external pressure to the internal transducers, causing measurement error. Earlier research by the current authors, including a companion paper at this conference [23][24][25][26][27]), has examined aspects of this fault mode, including the development of mathematical models of its physical behaviour, predicting the signal characteristics of the fault, developing proposed diagnostic techniques, and carrying out experimental work on sensors with calibrated levels of oil loss, in order to provide verification of the proposed diagnostic techniques.…”

“…Our companion paper at this conference [25], provides a review of the various types of pressure sensors conventionally used in industrial practice, and considers the main fault modes of the particular technology investigated here, the tensoresistive pressure sensor. Of these various faults, the loss of fill liquid is described in detail, and a mathematical model is developed to describe the expected measurement behavior of the sensor, with simulation results illustrating the results.…”

“…Of these various faults, the loss of fill liquid is described in detail, and a mathematical model is developed to describe the expected measurement behavior of the sensor, with simulation results illustrating the results. Figure (1), taken from [25], shows a simplified depiction of the pressure transducer structure, and illustrates the liquid loss fault. Essentially, the pressure sensor consists of an external, relatively soft plate, called the membrane, which is exposed to Fig.…”

“…1. A schematic view of the cross-section of the tenso-resistive pressure transducer (from [25]). the pressure source from the industrial process.…”

“…The transmission of the external pressure at the membrane to the plate is achieved via an incompressible liquid, typically silicone oil, which fills the channel between the two plates. Where the oil-loss fault occurs, for example as a result of damage to the external membrane, this results in air or other gas forming in the liquid channel; in [25], for simplicity, this is modelled as a thin film of air. The presence of this air interferes with the pressure transmission between the two plates.…”