  Electric dipole moment of the proton can be searched in an electric storage
ring by measuring the spin precession rate of the proton beam on the vertical
plane. In the ideal case, the spin precession comes from the coupling between
the electric field and the electric dipole moment. In a realistic scenario, the
magnetic field becomes a major systematic error source as it couples with the
magnetic dipole moment in a similar way. The beam can see the magnetic field in
various configurations which include direction, time dependence, etc. For
instance, geometric phase effect is observed when the beam sees the field at
different directions and phases periodically. We have simulated the effect of
the magnetic field in the major independent scenarios and found consistent
results with the analytical estimations regarding the static magnetic field
cases. We have set a limit for the magnetic field in each scenario and proposed
solutions to avoid systematic errors from magnetic fields.
