ac self-field loss measurement system

The accuracy and reproducibility of a self-field ac loss measurement technique for high-temperature superconducting tapes using a digital lock-in amplifier are discussed. The influence of the reference phase setting on the error was calculated and verified experimentally for different degrees of inductive component compensation. We estimated that for precise ac loss measurements of uncompensated specimens it is necessary set the reference phase with the precision on the order of 0.001°. For a compensated sample a phase error of 0.1° is tolerable. The measurement error due to common-mode voltage was studied and its minimization is proposed. A test procedure for common-mode voltage error evaluation was also experimentally verified. Ideas for better performance of the measurement system are proposed.