Strain measurement method based on external symmetrical compensation bridge composed of strain gauges with four-wire configuration for a large- scale NbTi superconducting dipole magnet detector

In this study, we present a strain measurement method based on an external symmetrical compensation bridge (ESCB) composed of strain gauges with a four-wire configuration. Unlike the traditional strain measurement methods, this method includes two features: first, utilising the four-wire configuration to eliminate measurement errors that occur due to large space-varying thermal and field imbalances of long signal wires during operation, and second, utilising two independent quarter-active sub-bridges with a four-wire configuration composed of ESCB to eliminate the errors that occur due to the large time-varying cryogenic temperature and magnetic field. This method was used on a large-scale NbTi superconducting dipole magnet detector during the cooling, excitation, and quench tests. The strains measured using the ESCB were compared with those measured using a traditional half-active compensation bridge. The results indicated that the new method can accurately detect the strain features of a large-scale superconducting magnet. In addition, using the proposed method, spectrum analysis of strain measurements was implemented during excitation, quench onset, and post-quench. A larger amplitude at a higher frequency was clearly observed at the onset of a quench than that observed during excitation and post-quench. Thus, the dynamic strain characteristics of a superconducting magnet structure could be a candidate for predicting the quench.