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Process Variables
Process Control Systems 3B
Durban University of Technology
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PROCESS
VARIABLES
Process Variables
####### Input variables
####### Output variables
####### Controlled variable
####### Manipulated variable
INPUT Disturbances measurable immeasurable OUTPUT Controlled variable INPUT measurable Manipulated variables PROCESS
Classification of the variables
Input variables
1. Manipulated variable
Variable which can be easily adjusted by a control
mechanism or operator
2. Disturbance, load effect (bozan etken, yük etkisi,
düzensizlik)
Input variables which are effective on controlled
variable but which cannot be easily manipulated
Output Varibles
1. Measurable variable or controlled variable
Its value can be easily determined by measurement
methods
e. The temperature of the product in a pasteurizer
2. Immeasurable output variables
It cannot be measured directly
Example : Temperature control for a heat
exchanger
####### Condensate
####### Feed
####### Product
Fo, To Fi, Ti Fout, Tout F 1 , T 1 Controlled variable- Output temperature of product stream Measuring instrument- Thermocouple on product stream Manupilated variable- Flow rate of steam Final control element-Control valve on steam stream Disturbance(Noise)- Variation of feed temperature
Example : Mixing Process
####### Notation:
- w 1
####### , w
2
####### and w; mass flow rate
- x 1
####### , x
2
####### ve x; mass fraction of component A
8
10
Example: IQF system
Controlled variable- Temperature in IQF Measuring instrument- Thermocouple in IQF Manipulated variable- Rate of air entering the system Final control element- Valve on air inlet stream Disturbance(Noise)- Input temperature of peas
What are the input and
output variables
of fermentation process?
11
HOMEWORK: Fermentor (pH control)
According to pH control, decide the following unknowns? Controlled variable-? Measuring instrument-? Manipulated variable-? Final control element-? Disturbance (Noise)-?
Process Variables
Course: Process Control Systems 3B
University: Durban University of Technology
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