  Searches of the electric dipole moment (EDM) at a pure magnetic ring, like
COSY, encounter strong background coming from magnetic dipole moment (MDM). The
most troubling issue is the MDM spin rotation in the so-called imperfection,
radial and longitudinal, B-fields. To study the systematic effects of the
imperfection fields at COSY we proposed the original method which makes use of
the two static solenoids acting as artificial imperfections. Perturbation of
the spin tune caused by the spin kicks in the solenoids probes the systematic
effect of cumulative spin rotation in the imperfection fields all over the
ring. The spin tune is one of the most precise quantities measured presently at
COSY at $10^{-10}$ level. The method has been successfully tested in September
2014 run at COSY, unravelling strength of spin kicks in the ring's imperfection
fields at the level of $10^{-3} rad$.
