Auto-Calibrating Fast Digital Integrator for Magnetic-Field Measurement

Abstract

The trajectory of particle beams in the large hadron collider (LHC) of CERN depends on the magnetic field in the LHC. The magnets in the LHC are tested and characterised to study the field quality, strength, direction etc. The field strength is measured in realtime using a digital integrator with an analog acquisition system. This analog front end suffers from offset and gain errors due to manufacturing and non-manufacturing variations resulting in measurement errors. Inaccuracies and drawbacks related to magnetic measurements at best decrease the performance of the integrator and at worst result in loss of beam. This thesis work aims to design an integrator with real-time calibration to identify and correct such systematic errors. The calibration involves determining coil attenuation using ratiometric method, designing potentiometer interface for DAC and implementing best-fit line to correct gain and offset errors of ADC. The calibration system conditions the signal before the start of integration and is critical for the integrator’s accuracy. Results show that the calibration system ensures a high degree of accuracy, limiting the output variation to 2.17 least-significant bits (LSB). This sytem, when coupled with trapezoidal integrator, registered an average accuracy of 1.74 LSB, an order of three improvement in comparison to the previous version of the integrator.