2. Process
A process denotes an operation or series of operations
on fluid or solid materials during which the materials are
placed in a more useful state
3. Objectives of process
The objective of a process is to convert certain raw
materials (input feedstock) into desired products (output)
using available sources of energy in the most
economical way.
Unit process may involve either a change of chemical
state or a change in physical state.
Many external and internal conditions affect the
performance of a process.
These conditions may be expressed in terms of process
variables such as temperature, pressure, flow, liquid
level, dimension, weight, volume etc.
4. Requirements of Process
A process must satisfy several requirements imposed by
its designers and the general technical, economic and
social conditions in the presence of ever changing
external influences (disturbances)
5. The Requirements
Safety of men and machine
Environmental regulations
Production specifications
Operational constructions and economics
6. Control
The term control means methods to force parameters in
the environment to have specific values
15. Process variables
Controlled variable: it is the variable that needs to be maintained or controlled at some desired
value or range. Sometimes also referred to as process variable.
Set Point: it is the desired value of the controlled variable. Thus the job of a control system is to
maintain the controlled variable at its set point.
Manipulated variable: is the variable used to maintain the controlled variable at its set point.
Disturbance: any variable that causes the controlled variable to deviate from its set point. Also
referred to as upset.
18. Types of feedback system
Negative feedback system
When the measured variable is subtracted from the set point it is called as negative feedback
system
Positive feedback system
When the measured variable is added from the set point it is called as positive feedback
system
21. Reasons for positive feedback to stop
When the output reaches the saturation
Till the system breakdowns
22. Advantages of feedback system
Automatically reduce errors
Improve stability
Increase robustness against external disturbances
Reliable and repeatable