bem4843 ch1 industrial control
TRANSCRIPT
-
8/8/2019 BEM4843 Ch1 Industrial Control
1/27
Engr. Hairulazwan [email protected]
mailto:[email protected]:[email protected]:[email protected] -
8/8/2019 BEM4843 Ch1 Industrial Control
2/27
Chapter 1 Introduction to
industrial control
system
Chapter 2 Interfacing
devices
Chapter 3 Thyristor
-
8/8/2019 BEM4843 Ch1 Industrial Control
3/27
Industrial Control Classification
Elements of Open-Loop and Closed-Loop Systems
Feedback Control
Practical Feedback Application
Dynamic Response of a Closed-Loop System
Feed-Forward Control
-
8/8/2019 BEM4843 Ch1 Industrial Control
4/27
Motioncontro
l an automatic control system thatcontrols the physical motion orposition of an object.
also referred to as servos, or
servomechanisms.
Eg: industrial robot arm which
performs welding operations and
assembly procedures.
Other eg: CNC machine toolequipment, printing presses, office
copiers, packaging equipment, and
electronics parts insertion machines
that place components onto a PCB. Proce
sscontro
l one or more variables are regulatedduring the manufacturing of aproduct.
Variables such as temperature,
pressure, flow rate, liquid and solid
level, pH, or humidity.
2 categories i.e batch and
continuous.
-
8/8/2019 BEM4843 Ch1 Industrial Control
5/27
a sequence of timedoperations executed on theproduct beingmanufactured
Figure 1-1 shows anindustrial machine thatproduces various types ofcookies.
-
8/8/2019 BEM4843 Ch1 Industrial Control
6/27
one or more operations arebeing performed as theproduct is being passedthrough a process.
Raw materials arecontinuously entering andleaving each process step.
Figure 1-2: Producingpaper.
-
8/8/2019 BEM4843 Ch1 Industrial Control
7/27
The purpose of any industrial system is tomaintain one or more variables in aproduction process at a desired value.
Industrial control systems are also classifiedby how they control variables, either manuallyin an open-loop system or automatically in aclosed-loop system.
-
8/8/2019 BEM4843 Ch1 Industrial Control
8/27
The simplest way to controla system.
Figure 1-3 shows a systemcomposed of a storagetank.
Manually controlled thevalve and an outlet pipe.
Ideally, the flow controlvalve setting and the size ofthe outlet pipe are exactlythe same and hence thewater level in the tankremains the same.
Process reaches a steady-state condition (balanced.)
Problem occur when anychange or disturbance will
upset the balance. Eg. substantial rainfall may
cause overflow.
Require operatorperiodically inspects the
tank.
-
8/8/2019 BEM4843 Ch1 Industrial Control
9/27
Antenna will rotateclockwise andanticlockwise depending onthe output signal, negativeor positive.
Antenna will stationary ifthe input signal is 0v.
When the antenna isapproaching the desiredangle or position, the inputsignal must approach 0v.
It can be conclude that thecontrol action isindependent of the output.
-
8/8/2019 BEM4843 Ch1 Industrial Control
10/27
Some manufacturingapplications requirecontinuous monitoring andself-correcting action of theoperation for long periods
of time withoutinterruption.
The automatic closed-loopconfiguration performs theself-correcting function.
This automatic systememploys a feedback loop tokeep track of how well theoutput actuator is doing the
job it was commanded to
do.
Replacing the manual valvewith an adjustable valve
connected to a float. The valve, the float, and the
linkage mechanism providethe feedback loop.
-
8/8/2019 BEM4843 Ch1 Industrial Control
11/27
From diagram, if0= ithen V0 =Vi so the errorsignal, Ve = Vi V0 = 0V
If the V0 not equal Vi ,Vegreater or less than 0V, theantenna will rotateclockwise, anticlockwise(depends on Ve polarity).
The antenna will continuerotating until V0 = Vi .
In this example, the systemautomatically corrects theoutput when the system isdisturbed. This system isknown as automatic
control system.
-
8/8/2019 BEM4843 Ch1 Industrial Control
12/27
Elements of Open-
and Closed-Loop
Systems
Controlled
variableMeasured
variable
Measurement
device
Feedback
signal
Set
point
Error
detectorError
signal
Controller
Actuator
Manipulated
variable
Manufacturing
process
Disturbance
-
8/8/2019 BEM4843 Ch1 Industrial Control
13/27
Closed-loop block diagram that showselements, input/output signals, and
signal direction
-
8/8/2019 BEM4843 Ch1 Industrial Control
14/27
the actual variable being monitored and maintained at a desired value.Eg. (process control): temperature, pressure, and flow rate.
Eg. (motion control): position or velocity.
Eg. (water reservoir): the water level is the controlled variable.
Controlled
Variable.
The condition of the controlled variable at a specific point in time.Various methods are used for measurements.Eg. (water level): measure the pressure at the bottom of a tank. Thepressure that represents the controlled variable is taken at the instant of
measurement.
Measured
Variable.
The eye of the system.It senses the measured variable and produces an output signal thatrepresents the status of the controlled variable.
Eg. (process control): use thermistor to measure temperature or a
humidity detector to measure moisture.
Eg. (motion control): use optical device to measure position or a
tachometer to measure rotational speed.
Eg. (water reservoir): use float.
Other terms used are detector, transducer, and sensor.
Measurement
Device.
-
8/8/2019 BEM4843 Ch1 Industrial Control
15/27
The output of the measurement device.Feedback Signal.
The prescribed input value or desired condition of the controlled variable.
May be manually set by operator, automatically set by an electronic
device/programming.Eg. (water reservoir): position at which the float is placed along rod A.
Other terms used are command, or reference.
Set Point.
Compares the set point to the feedback signal.
Produces an output signal that is proportional to the difference between
them.
Eg. (water reservoir): the entire linkage mechanism.
Other terms used are comparator or comparer and summing junction.
Error Detector.
The output of the error detector.
If signal are not equal, an error signal proportional to their difference
develops.
When equal, the error signal goes to zero.
Eg. (reservoir): the angular position of member B of the linkage
mechanism.
Other terms used are difference signal and deviation.
Error Signal.
-
8/8/2019 BEM4843 Ch1 Industrial Control
16/27
-
8/8/2019 BEM4843 Ch1 Industrial Control
17/27
Operation performed by the actuator to
control a physical variable.
Manufacturing
Process.
A factor that upsets the manufacturing
process being performed, causing a change in
the controlled variable.
Eg. (reservoir): the rainfall and evaporation
that alter the water level.
Disturbance.
-
8/8/2019 BEM4843 Ch1 Industrial Control
18/27
The basic concept of feedback control is that an error
must exist before some corrective action can be made.
An error can develop in one of three ways:
The set point is changed.
A disturbance appears.
The load demand varies.
-
8/8/2019 BEM4843 Ch1 Industrial Control
19/27
Feedback system is a system that maintains a relationship between the output
and some reference input by comparing them and using the difference as a
means of control.
Feedback is used to reduce the error between reference and the system output .
Feedback effect on performance characteristic:
Stability
Overall gain
Sensitivity
External disturbances
-
8/8/2019 BEM4843 Ch1 Industrial Control
20/27
Open-Loop Closed-Loop
The output is
not measured.
Control system
is independent
of the output.
System cannot
compensate for
disturbance.
Eg.: toaster,
washingmachine, fan
System hasfeedback and
output is
measured.
System output has
an effect on the
control action.
System can
compensate for
disturbance.
Eg.:air
conditioner, robot
(arm)
-
8/8/2019 BEM4843 Ch1 Industrial Control
21/27
Open-Loop Closed-Loop
Advantages
Low cost
More reliable
Easier to build/maintain.
Stability is not major problem
Disadvantages
Not accurate (depends on equipments
calibration)
Slow system response (small bandwidth)
Limitations on application.No error correction by a controller.
Advantages
High accuracy
Fast system response
More complex
Disadvantages
Cost expensive
Less reliable
Difficult to maintain
Stability problem, which may tend to
overcorrect errors that can cause
oscillations of constant.
-
8/8/2019 BEM4843 Ch1 Industrial Control
22/27
Step 1Transform
requirements
into a physical
system
Step 2Draw a
functional
block diagram
and schematic
Step 3Develop a
mathematical
model (block
diagram)
Step 4Reduce the
block diagram
Step 5Analyze and
design
22
-
8/8/2019 BEM4843 Ch1 Industrial Control
23/27
Determine physical system and specification fromrequirements
First of all, the design requirements of the system which
are desired transient response and steady state error
are determined.
Step 1Functional block diagram and schematicBased on the systems requirements, a functional block
diagram is drawn. Based on the block diagram, aschematic of the system is obtained. This schematic can
be in a form of electrical model, mechanical model or
both.
Step 223
-
8/8/2019 BEM4843 Ch1 Industrial Control
24/27
Mathematical representation A mathematical model of the system is obtained
from schematic using physical laws such as
Kirchoff's Voltage Law, Kirchoff's Current Law
and Newton's Law
Step 3 Reduction of block diagram Initial block diagram might be too complicated.
Therefore, it is reduced to simple block in orderto get Simple equations that represent the
systemStep 424
-
8/8/2019 BEM4843 Ch1 Industrial Control
25/27
Analyze and design Once the simple representation of the system
is obtained, it is easier to analyze the system.The system is analyzed to see whether the
transient response specification, steady state
error and stability requirements are met. If
the requirements are not met, then the
controller is designed to meet the
specification.
Step525
-
8/8/2019 BEM4843 Ch1 Industrial Control
26/27
Find the home appliance which appliedclosed-loop system. Identify the following: System operation
Element of system (such as set point, controller,
actuator, manipulated variable, process,disturbance etc.)
Block diagram
-
8/8/2019 BEM4843 Ch1 Industrial Control
27/27
27