The responses of symmetric square and triangular wave pulses have been investigated in planar cells of two ferroelectric liquid crystalline mixtures FLC-6430 and SCE-13 in the SmC* phase. The samples were sandwiched between two parallel polyimide coated substrates. The cells containing SCE-13 and FLC-6430 were considered in the surface stabilised state (p>d) and volume stabilised state (pcd) respectively, (p is the helix pitch and d is the sample thickness). Dynamic processes associated with the helix unwinding and winding by applying bias -10V - 0V- + 10V has been studied. The spontaneous polarisation (P-s), response time (tau(R)) and torsional viscosity (eta) have been evaluated in these materials. Materials in surface stabilised configuration show surface switching while in DHF configuration switching is due to bulk and surface effects.