The present paper gives a systematic way to refine specifications of
hybrid control systems written in DC (Duration Calculus) into their
automata models. The iteration DC formulas are introduced together
with rules for transforming, refining DC formulas into the forms that
describe the systems in more details. Then, the plant automata derived
from DC formulas are defined, which allow the designers to derive a
specification of control automata more easily. A necessary and
sufficient condition for a plant automaton and a requirement to have a
control automaton is given. Some simple examples are presented to
illustrate the method.