point plot

i have simulated distribution electric field, and in potential i put as fucntion of cosine (V*cos(2*pi*f*t)). and i want to visualize the result in graph especially in specific point in volume. and i have tried to put graph it trough put the coordinat (x, y and z). but view of the graph in straigh line not cosine curve. it's properly cosine graph, isn't it? i was confused to set the parameter so i could get the desirable result. what should i do? and i use the depedent time in solve parameter. could you help me?

thank before
kind regards