Specifications

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Continuous Processes Continuous processes are less understood by most people;
however, they have some similarities to batch processes.
Ingredients must be combined in precise ways at precise points
in the process. Precise control of process conditions must be
maintained to ensure product quality and safety of operations.
Some industries, such as chemical and petrochemical industries,
use continuous processes extensively. Many other industries,
however, use continuous processes as some part of their
operations for purifying air and water, treating waste products,
etc.
Both batch and continuous processes use many of the
products discussed thus far. However, there are some unique
characteristics of batch and continuous processes that either
require the use of additional types of equipment or require some
of the equipment previously discussed to be applied differently.
Closed-Loop Control One characteristic of batch and continuous processes is
their extensive use of analog data. Analog values can vary
continuously within a specified range. The analog data may be
representative of temperature, pressure, rate of flow, weight,
thickness, viscosity, humidity, or any other characteristic of
importance to the process. Both batch and continuous processes
require continuous monitoring at numerous points throughout
the process. In addition, a corrective action is often required
to insure that the process stays within specifications. This type
of control that involves measuring a value, comparing the
measured value to a desired value or set point, and correcting
for the error is called closed-loop control.
Set Point
(Desired Value)
Control Device Process
Feedback
(Actual Value)
+
-
Transmitter Sensor
Controller