Metrological Characterization of the LHC Collimators Positioning Survey System

This thesis work deals with the analysis the two abovementioned problems of characterizing the LVDT magnetic interference, and the metrological characterization of the PRS.
In the first four chapters, we illustrate the state of art on: the Large Hadron Collider (LHC), the Collimator System, the Linear Variable Differential Transformer (LVDT) and the Position Survey System (PRS).
In chapter 5 we analyze the magnetic interferences on the LVDT. The goal is to describe the interaction between the LVDT reading and an external stationary magnetic field providing a figure of the LVDT sensibility to external magnetic fields of different directions.
As first step of this work, a test bench that generates the external magnetic field, acquires contemporaneously the LVDT secondary voltages and measures the magnetic flux density that interferes with the LVDT has been developed.
Resistive magnets have been used to generate a dipolar magnetic field before longitudinal (i.e. direct along the axis of the LVDT) and after transversal. In addition, in order to reproduce the same effects experienced in the LHC tunnel, not uniform magnetic fields have been taken into account. These have been generated by a current wire close to the LVDT and placed in different orientations (orthogonal, parallel to the LVDT axis).The magnetic interference has been characterized evaluating the LVDT position error as function of external magnetic field intensity, the LVDT excitation voltage and the LVDT core position. Where the relation between the position error and the external magnetic field was linear, a sensibility coefficient has been evaluated.
In chapter 6 we analyze the thermal effects. A complete metrological characterization of the PRS system has been carried. LVDTs have been connected via a 500 m long cable to the system to reproduce the working condition in the tunnel. The system reading accuracy as well as the stability over long time (24 h) has been evaluated and compared with a reading solution based on standard multimeters. Thermal cycles have been applied to the LVDT conditioning electronic used in order to study the thermal stability of the solution adopted. The same cycles have been applied only on the LVDTs to evaluate the thermal sensitivity of the sensors.