-
7/27/2019 Process Control Fundamental
1/30
-
7/27/2019 Process Control Fundamental
2/30
Process as used in the terms process control and process
industry,refers to the methods of changing or refining raw
materials tocreate end products. The raw materials, which either
pass throughor remain in a liquid, gaseous, or slurry (a mix of
solids and liquids)state during the process, are transferred,
measured, mixed,heated or cooled, filtered, stored, or handled in
some other way toproduce the end product.
The following industries are examples of process industries:
Chemical
Oil and gas refining Food and beverage Pharmaceutical Water
treatment Power
-
7/27/2019 Process Control Fundamental
3/30
Process control refers to the methods that are used tocontrol
process variables when manufacturing aproduct. For example, factors
such as the proportionof one ingredient to another, the temperature
of thematerials, how well the ingredients are mixed, and
thepressure under which the materials are held cansignificantly
impact the quality of an end product.
Manufacturers control the production process forseveral reasons,
including: Reduce variability Increase efficiency/throughput Ensure
health, safety, and the environment
-
7/27/2019 Process Control Fundamental
4/30
A process variable is a condition of the process fluid (a liquid
or gas) thatcan change the manufacturing process in some way. In
the example ofsitting by the fire, the process variable was
temperature.
Common process variables include: Pressure
Flow
Level
Temperature
Density
Ph (acidity or alkalinity)
Oxygen content
Carbon monoxide content
Liquid interface (the relative amounts of different liquids that
are combined in a vessel [e.g., in a mixof oil and water, how much
oil is in the tank and how much water is in the tank])
Mass
Conductivity
-
7/27/2019 Process Control Fundamental
5/30
-
7/27/2019 Process Control Fundamental
6/30
-
7/27/2019 Process Control Fundamental
7/30
-
7/27/2019 Process Control Fundamental
8/30
-
7/27/2019 Process Control Fundamental
9/30
-
7/27/2019 Process Control Fundamental
10/30
-
7/27/2019 Process Control Fundamental
11/30
-
7/27/2019 Process Control Fundamental
12/30
-
7/27/2019 Process Control Fundamental
13/30
-
7/27/2019 Process Control Fundamental
14/30
-
7/27/2019 Process Control Fundamental
15/30
-
7/27/2019 Process Control Fundamental
16/30
-
7/27/2019 Process Control Fundamental
17/30
Pneumatic Control (1950)
Analog Controllers (1960)
PLC Control (1970)
DCS - Distributed Control Systems (1975 )
Smart Field Instruments (1985 )
Fieldbus Control Systems (1996 )
-
7/27/2019 Process Control Fundamental
18/30
Simple control scheme Local control in the field
Difficult for sophisticated control scheme Difficult for central
monitoring of process
-
7/27/2019 Process Control Fundamental
19/30
Standalone controller/transducers/control valves Analog
controllers are located in a central control room Distributed
control & monitoring
High cost of cabling Large central monitoring panel for large
number of
controllers Difficult to implement control algorithms other than
PID Difficult for coordination of control loops
-
7/27/2019 Process Control Fundamental
20/30
Programmable Logical Control Mainly for discrete control
(ON/OFF)
Simple continuous control Faster response - system shut &
emergency
shut down
-
7/27/2019 Process Control Fundamental
21/30
Digital components are less susceptible to aging
&environmental variations
Digital components are more reliable & less sensitiveto:
parameter variations noise Disturbance
Digital processors are more compact & lightweight
Single chip microprocessor are versatile, flexible andpowerful
for different control applications The cost of microprocessors is
continuously going
down
-
7/27/2019 Process Control Fundamental
22/30
DDC - Direct Digital Control DCS - Distributed Control
Systems
-
7/27/2019 Process Control Fundamental
23/30
Central Computer 64 - 128 loops per computer PID algorithm
Centralized : control,monitoring, danger Long cables - high cost
A simple replacement of
analog controllers
-
7/27/2019 Process Control Fundamental
24/30
Distributed computers/controllers 8 loops per controller
Function blocks in controllers : PID, ratio,
select control Continuous control + discrete control Local
controllers : savings in cabling,
distributed control, distributed danger Centralized monitoring :
digital
communication Advanced control, customized control &
plant management
-
7/27/2019 Process Control Fundamental
25/30
Analog field instrument carries one piece ofinformation (4-20
mA)
Signal calibration is done by field instruments Digital pulse
signal to replace 4-20 mA Diagnostic signal is transmitted by a
digital
signal together with 4-20 mA HART Protocol Always one-to-one
communication
-
7/27/2019 Process Control Fundamental
26/30
The logical step improvingon the familiar DCS even more
distributed control
function
even more digital fielddevices
Digital : replaces 4-20 mAsignal
Replaces the DCS
architecture
-
7/27/2019 Process Control Fundamental
27/30
-
7/27/2019 Process Control Fundamental
28/30
-
7/27/2019 Process Control Fundamental
29/30
-
7/27/2019 Process Control Fundamental
30/30
