Experimental strain analysis of the high pressure strain gauge pressuretransducer and verification by using a finite element method

Abstract

The finite element method (FEM) was used in this study for theanalysis of the strain distribution of a strain gauge pressure transducer forhydrostatic pressure measurements up to 150 MPa. The pressure transducer, whichwe investigated, on the basis of `thick-walled cylindrical vessel' theory hasa free steel active element. Pressure is applied to the inside and both openends of this active element. The symmetrical shape of the transducer and allthe design parameters of the active element were selected in such a way as toensure that a symmetrical stress and strain distribution was obtained even atthe maximum working pressure of the transducer. The FEM analysis was conductedby investigating one half of the element in three dimensions. This paperpresents the FEM output strain values for the area where the strain gaugeswere bonded. The validity of those values was established by comparing themwith the results obtained from the strain gauge measurements. The relativedifference between the two sets of values determined to be lower than 13% ofthe full scale. The two kinds of measuring elements were made of two differentmaterials; AISI 4340 steel and Invar steel, which work in the hydraulic gaugepressure ranges of up to 150 and 100 MPa respectively. The transducers werecalibrated using piston pressure balance. The metrological specifications of atotal of eight specimens were evaluated. Although the scope of the study isonly an application of the FEM, this evaluation also suggests that this typeof transducer can be used with an estimated uncertainty of up to 0.1% of thefull scale. However, this uncertainty can be improved by a small modificationin design, to reduce the reproducibility and hysteresis errors of the device,which are the main parameters in the evaluation of the uncertainty. Theresults presented in this paper will be helpful for practical static pressuremeasurements as well as for the appropriate design of this kind of pressuretransducer using the FEM.