Abstract: Differential-output current loops (B-dot probes) were designed and calibrated to derive inner-MITL current in the PTS facility. The B-dots upper limiting frequency was 51.7 MHz in frequency response experiments, which was satisfactory for current measurement in our experiments. The B-dots were calibrated using a radial transmission line that was driven by an azimuthally symmetric current pulse. And then the B-dots were calibrated using a radial transmission line with a post-hole convolute feeding structure. The result indicates that the sensitivity of B-dots are consistent in the two calibration systems. The interference test and experiments with variable peak currents were performed to focus on B-dot linearity, and insulation, pressure exerted by magnetic fields, energy absorbing and related temperature rise of B-dot were analyzed in order to assess the validity of B-dot calibration. The results imply that the B-dots are valid for several mega-ampere current measurements. Also, it shows that outer-MITL current and inner-MITL current are self-consistent in PTS experiment.