  For cosmic microwave background (CMB) polarization observations, calibration
of detector polarization angles is essential. We have developed a fully remote
controlled calibration system with a sparse wire grid that reflects linearly
polarized light along the wire direction. The new feature is a
remote-controlled system for regular calibration, which has not been possible
in sparse wire grid calibrators in past experiments. The remote control can be
achieved by two electric linear actuators that load or unload the sparse wire
grid into a position centered on the optical axis of a telescope between the
calibration time and CMB observation. Furthermore, the sparse wire grid can be
rotated by a motor. A rotary encoder and a gravity sensor are installed on the
sparse wire grid to monitor the wire direction. They allow us to achieve
detector angle calibration with expected systematic error of $0.08^{\circ}$.
The calibration system will be installed in small-aperture telescopes at Simons
Observatory.
