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Types of Plants and Control 1.3Syst

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Title: Industrial Automation Subject: Types of Plants and Control Author: Hubert Kirrmann Keywords: Continuous and batch processes Description: Behavior of plants and ... – PowerPoint PPT presentation

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Title: Types of Plants and Control 1.3Syst


1
Types of Plants and Control 1.3 Systèmes
contrôlés et contrôle Strecken und Steuerungen
Industrial Automation Automation
Industrielle Industrielle Automation
Prof. Dr. H. Kirrmann
ABB Research Center, Baden, Switzerland
2008 February, HK
2
1.3 Contents
1 Introduction 1.1 Automation and its
importance 1.2 Applications of automation
1.3 Plants and controls 1.3.1 Open loop and
closed loop control 1.3.2 Continuous
processes 1.3.3 Discrete processes 1.3.3 Mixed
processes 1.4 Automation hierarchy 1.5 Control
system architecture
3
Plant types
In spite of wide diversity of applications, the
principles of automation are similar. There are
a few basic types of plants and the same control
system hardware and basic software is shared by
most applications. Distinction is often question
of a point of view, profession-specific
vocabulary and marketing.
4
Control Tasks
measure - command - control
mesure - commande - régulation - conduite
messen - steuern - regeln - leiten
Conduite l'ensemble des mesures qui permettent
d'influencer l'état d'un processus dans un but
fixé.
Leiten - die Gesamtheit aller Massnahmen, die
einen im Sinne festgelegter Ziele erwünschten
Ablauf eines Prozesse bewirken (DIN 19222)
5
Open loop and closed loop
temperature
3
2
4
1
5
open loop temperature is imprecise, depends on
ambient temperature and cooking quantity but
time of heating can be modulated.
180
140
200
closed loop temperature closely controlled,
requires measurement of the output variable
(temperature)

higher/lower
120
220
-
temperature sensor
6
Open loop and closed loop
closed-loop control / regulation
open-loop control / command
(régulation, Regelung)
(commande / pilotage, steuern, )
keywords feedback, analog variables, continuous
processes, "process control"
keywords sequential / combinatorial, binary
variables, discrete processes, "batch control",
"manufacturing"


set-point (solicited) valeur de
consigne Sollwert,
control variable (analog)
binary
output
controller
output

plant
sequencer
plant
-
error (deviation)
plant state
clock
plant state
display
display
measurement
measurement

on/off
process value (valeur mesurée, Istwert)
7
Function of computers in control systems
open-loop functions
closed-loop functions
Data acquisition and pre-processing
Protection and interlocking
Data transfer between plant and operator
Regulation
Display the plant state
Process-driven sequential control
Logging and history recording
Simulation and training
Process optimization algorithms
the control system acts directly and autonomously
on the plant
Interlocking prevent dangerous actions, such as
all lights on green at a crossing
8
Discrete and continuous plants
discrete control
continuous control
9
Continuous plants
Examples Drives, Ovens, Chemical Reactors
y
x
F(p)
Continuous plants (processes) have states that
can be described by a continuous (analog)
variable (temperature, voltage, speed,...)
Between plant input and plant output, there
exists a fixed relation which can be described by
a continuous model (transfer function).
Continuous plants are mostly reversible and
monotone This is the condition necessary to
control them, i.e. impose the value of their
output.
The transfer function may be described by a
differential equation, simplified to a Laplace
or a z-transform when the system is linear.
The principal control task in relation with a
continuous process is its regulation (maintain
the state on a determined level or trajectory)
10
Discrete plants
b
c d
init
2
3
4
a
e
c d
e
1
6
5
7
A discrete plant is modeled by well-defined,
exhaustive and non-overlapping states, and by
abrupt transitions from one state to the next
caused by events.
Discrete plants are mainly reversible, but not
monotone the removal of the stimulus which
caused a state transition will not
necessarily bring the plant back to the previous
state.
Example a lift will not go back to the previous
floor when releasing the button that called it.
Going back to a previous state may require
transit through several other states.
Discrete plants are described by Finite State
Machines, Petri Net, State transition tables
Grafcet, SDL or Sequential Function Chart
diagrams.
The main task of a control system in relation
with discrete plants is their command.
11
Continuous and batch processes
Continuous process (processus continus,
kontinuierliche Prozesse) continuous flow of
material or energy e.g. motor control, cement,
glass, paper production, rolling mill for wires,
plate or profiles, newspaper printing 23 m/s,
steel wire 90 m/s Main task regulation Batch
process (processus de charge (par lots),
Stückgutprozesse) discrete processes with
handling of individual elements e.g. Numerical
Controlled machine, packing machines, Bottle-fill
ing, manufacturing, pharmaceutical and chemical
processes. Main task command


12
Mixed plants
In reality, all plants consist of discrete and of
continuous processes.
Example 1 Motor Control of a cable-car with
speed control and stop at stations
Example 2 A bottle-filling line is in principle
a continuous process, but each step consists of
a sequence of operations
All parts must de described individually.
Processes can be described as continuous within a
discrete state or as non-linear, continuous
process.
Example Time-triggered set-point of an oven
temperature.
Mixed Plants are the normal case - a question of
point of view.
All processes have some continuous and some
discrete behavior
13
Accent depends on industrial process
Automotive Manufacturing Electronics Machinery Tex
tiles Pharmaceuticals Fine Chemical Food
Beverage Metals Mining Water Waste Pulp
Paper Vehicles Petrochemicals Oil
Gas Electrical Power
discrete
continuous
source ARC
14
The main categories in industry
industry distinguishes the following categories
of applications
"process control" continuous processes,
associated with fluxes, e.g. sewage water
treatment, petrochemical process, cement
"batch control" semi-continuous processes,
associated with individual products, e.g. fine
chemicals, pharmaceutical, brewery
"manufacturing" also called factory
automation discrete processes, associated with
transformation of parts, e.g. automobile
industry, bottle-filling, packaging
15
Assessment which answer is correct ?
open loop control is used when the plant can
produce indefinitely when the plant is operated
in on/off mode when the operator can supervise
the plant closed loop control is needed
because the plant is insufficiently known the
plant is subject to perturbations the plant
cannot be described by differential
equations the main task of a controller in a
continuous process is to keep the output always
at the same value to bring the output to a
specific value in function of time to keep the
output within a certain range the main task of a
controller in a discrete process is to maintain
the speed of production constant to measure the
state and present it to the operator to sequence
the work which of the following is a consistent
plant categorization open loop continuous
closed loop discrete - continuous-
hybrid process control - manufacturing- batch
16
(No Transcript)
17
Fill in the grid
continuous (process)
batch
manufacturing
hydraulic power plant car factory paper
mill container harbor luggage transport electrical
substation printing machine locomotive water
treatment building automation petrochemical
plant pharmaceutical
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