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

This study presents a new 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 validated and used on a large-scale NbTi superconducting dipole magnet detector during the cooling, excitation, and quench tests. The strains measured using the ESCB were also compared with those measured using a traditional half-active compensation bridge. The observations showed that the ESCB method can overcome the interference of the temperature gradient and electromagnetic field of long wires during both cooling and electromagnetic excitation processes. In addition to the abrupt strain signal appearing when a quench occurred, high amplitudes occurring at high frequencies were observed at the onset of a quench based on the strain spectra analysis. Thus, the strain spectra are expected to provide a novel means for early quench warning.