Modelling, characterisation and design optimisation of an ironless inductive position sensor

Abstract

Safety critical systems such as particle accelerators and nuclear plants strongly depend on the sensors that control the system. The Large Hadron Collider (LHC) found at the European Organisation for Nuclear Research (CERN) depends on a collimation system to control the beam. The jaw position with respect to the beam of particles is measured with linear position sensors. The traditional transducer used for this task is the Linear Variable Differential Transformer (LVDT) while a newer transducer called the Ironless Inductive Position Sensor (I2PS) is taking up the LVDT’s place, in areas characterised with magnetic interference. An electrical metrological characterisation of the transducer, with long cables, is first presented. The frequency response of the sensor is conducted to assess the I2PS sensitivity at different frequencies with different cable lengths. Moreover, a set of experimental results are performed to assess the I2PS’s sensitivity to cable capacitance change. Comparison with a commercial off-the-shelf LVDT is presented, knowing that this was required to gain a better understanding. A novel SPICE simulation that models the I2PS sensor and its electronics is consequently developed. Furthermore, a countermeasure circuit is presented to eliminate the effects of cable capacitance. A detailed thermal analysis is then presented which characterises the impact of ambient temperature change on the sensor. This study itself becomes an important step in developing changes and defining guidelines, which optimise the stability of the I2PS. A number of modifications to the sensor are proposed to reduce the drift, making the sensor more robust. Nevertheless, not all solutions lead to sensor immunisation, given the unavoidable design of the transducer. Furthermore, a detailed study of operating multiple I2PS in close proximity at the same frequency is presented. Finally, this work also identifies the optimisation parameters and constants required when manually designing an I2PS. Consequently, it presents an automated design procedure, which when powered by a multi-objective optimisation algorithm, it automatically produces an I2PS, tailor made to the user’s specifications, very quickly by a user with minimal training. The research provided in this thesis presents a more thorough characterisation of the thermal and electrical behaviour of the transducer. This is accomplished by taking into consideration typical and infrequent circumstances of the operation of the LHC collimator system.