The expected answers were:
(a)(i) An open-loop control system is one in which control action does not utilize
information concerning the output state.
(ii) A closed-loop control system utilizes feedback information on the output state for
the initiation and sustenance of control action.
(b)(i) Error detector – compares feedback information with set reference level to
determine nature of desired control action.
(ii) Power amplifier – amplifies the ‘error signal’ and its output feeds the motor.
(iii) Tacho-generator located in the feedback path functions to provide information
about the status of the output (speed converted to signal) as feedback information.
This question was on amplifiers.
Candidates performed poorly in part (a).
Candidates were able to identify the functions of error detector and power amplifier but majority failed in the case of tachogenrator.