Initial excitation impulse frequency, min⁻¹	Forced excitation impulse frequency, min⁻¹
Initial excitation impulse frequency, min⁻¹	120	150	180	200	210	220	230	240
60	yes	yes	yes	no	no	no	no	no
120		yes	yes	no	no	no	no	no
150			yes	yes	yes	no	no	no
180				yes	yes	yes	*	no
200					yes	yes	*	*
210						yes	*	*
220							yes	*
230								yes