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Manual Control
Because measurement
problems can limit the applicability of automatic feedback control
schemes, a common approach to effecting control on the process is to control
it manually.
Here, an
operator takes in all the information that he has at hand, and tries to
anticipate the possible outcomes that can occur as a result of current
operating conditions and observed process states.  If
deemed necessary, he then makes the appropriate adjustmensts, based
on his experience, perhaps aided by operating procedures. Further adjustments
are made when instrument readings or results of laboratory analyses become
available.
Such
a strategy is usually adopted when the return of information for control
purposes is slow and irregular. Its success depends on the operator's
training and experience. The physical and mental state of the operator
can have significant impact on his efficiency, and he may also have a
number of other duties to perform. These factors can be highly variable
and therefore production can be correspondingly inconsistent.
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