Design and optimisation of NiTi pressure gauge

This paper describes construction of a NiTi pressure gauge for possible application mostly in an automotive. The aim of our work is to present different data of an electrical properties of the pressure gauge. These data are strongly dependent on several input variables - for example the mechanical stress and the temperature of surrounding environment. Next aim of this paper is to describe development of the software which was designed for optimisation of the sensor shape. This is necessary to reach expected force range, to ensure that maximal allowed strain would not be exceeded and to come up with an optimal solution of compensation of sensors resistance temperature drift and nonlinearities. NiTi wires are very thermal dependent, but they shows also several useful properties including large recoverable strains, higher sensitivity and smaller time constants then other strain gauges, for example foil ones. NiTi wires also provides linear dependence between resistance and strain, however split by the start of austenite-martensite transformation. Our proposed compensation is realised by thermally compensated quarter bridge with combination of a look-up tables. Look-up tables were realised by measuring system which was equipped by independent thermometer to be able to choose appropriate characteristic and to judge on its limitations. Acquired data shows that quarter bridge cannot be used by itself, namely when subzero temperatures might be reached. This is caused due to material properties of NiTi wires which affects maximal recoverable stress of the wire and this stress is dependent on temperature. We did many measurements of thermal characteristics, stress-strain and resistance-strain characteristics. These measured data were used for software development. The used model allowed us to skip some of the model creation processes and the result - final model - has been validated by real measurement.