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IndustrialControl System
dr in. Anna Czemplik
(na prawach rkopisu)
Instrumentation of a technological process
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Industrial Control System (ICS) usually performs the following tasks:
1) an instrumentation of a technological process2) a data acquisition and a process control
3) a data transfer
4) human-machine interface (HMI)
These tasks correspond to the following subsystems of ICS:
I. measuring devices and actuators
II. field devices
III. a communication infrastructure
IV. supervisory computers (a complex system)
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The main topics:
I. Measurement devices
II. Actuating elements
III. Field devices - controllers
IV. Communication networks
V. SCADA & DCS
What is it? Definition
How does it work? Principle of operation
Main features
}
Instrumentation of a technological process
15 hours
} 15 hours
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I. Measurement devices
Ia. Sensors Ia-1. Thermometers: a) Expansion thermometer; b) Pressure spring thermometer; c) Resistance thermometer; d) Thermoelectric thermometer;
e) Optical thermometer. Selection of thermometer and measuring circuit
Ia-2. Displacement and force sensors: a) Resistance displacement sensor; b) Piezoelectric displacement sensor; c) Piezomagneticdisplacement sensor; d) Inductive displacement sensor; e) Capacitive displacement sensor; f) Hall effect displacement sensor
Ia-3. Manometer: a) Hydrostatic manometer; b) Hydraulic manometer; c) Elastic manometer; d) Electronic manometer (strain gauge, inductive,
capacitive); e) Manometer with a force sensor. Selection of manometer
Ia-4. Level indicator: a) Water-level indicator; b) Float level gauge: c) Hydrostatic level gauge; d) Displacer level gauge; e) Ultrasonic level
gauge; f) Radar level gauge; h) Another l.g. (capacitive, eletrical, thermometer). Selection of level gauge
Ia-5 Flowmeter: a) Differential pressure flowmeter; b) Rotameter; c) Velocity-type flowmeter; d) Positive displacement flowmeter; e) Inductive
flowmeter; f) Ultrasonic flowmeter; g) Calorimetric flowmeter; h) Vortex flowmeter; i) Coriolis flowmeter; j) Open channel flowmeter. Selection of
flow meter Ia-6. Speed: a) Tachometer; b) Digital speed sensor
Ia-7. Relays: a) Non electrical relays; b) Electrical relays and switches
Ia-8. Physico-chemical properties: a) pH meter, ...
Ia. Sensor selection
Ib. Converters Ib-1. Measuring converters types and selection
Ib-3. Separating converters
Ib-4. Analog-to-digital converters
Ib-5. Digital-to-analog converters
Measuring devices; Instrumentation and control tag
II. Actuating elements
IIa. Final control element IIa-1. Valves
IIa-2. Pumps
IIb. Actuators IIb-1. Pneumatic actuator
IIb-3. Electric actuator - Electric motors: a) Brushed DC electric motor; b) Synchronous motor; c) Inductive motor
Electro-mechanical drive system
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control devices
plant
measurement
devices sensorsensin element
measuringconverter
actuating
equipmentfinal controlelement
actuator(actuating driver)
controller
A/D
converter
D/A
converter
communication system
supervisor system
Block diagram of a control system
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.
I. Measurement devicesa) Sensors
1 - temperature,2 - displacement,
3 - pressure,
4 - level,
5 - flow,
6 - rotational speed,7 - relays,
8 - electrochemical
b) Converters
1 - measuring,
2 - signaling,
3 - separating,
4 - A/D,
5 - D/A
c) Control engineering design
plant
sensorsensin element
measuringconverter
final controlelement
actuator(actuating driver)
controller
A/Dconverter
D/Aconverter
communication system
supervisor system
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.
Sensor (transducer, measuring converter) - a device that converts a physical (chemical,
biological, ...) quantity into another signal (usually an electric signal). There are many
types of sensors base on different principles.
Measurement of a basic physical quantity:
1) temperature
2) displacement and force (also stress, strain)
3) pressure (also pressure difference)
4) level (also volume)
5) flow
6) rotational speed
More: http://www.omega.com/literature/transactions/
http://www.sensorland.com/
}force-related measurement
}amount-related measurement
and another:7) relays (two-stage transducer)
8) electrochemical transducer
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1.
liquid-in-glass mechanical
bi-metallic elongation-type
Principle: Thermal expansion of liquids or solid bodies
e.g. mercury-in-gas thermometeror alcohol thermometer
The difference in thermal expansion in the two metals
leads to a difference of lenght or to a twist of element
in proportion to the temperature
With increasing temperature,
the volume of liquid expands
and the meniscus moves up the capillary.
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1.
thermometricbulb
capillary
manometer(spring-type pressure gauge)
(gas thermometer)
Principle: The relation between temperature and pressure in a constant volume
The bulb is immersed in a heated substance.
The liquid (gas) expands causing the pressure spring to unwind.
Types:
liquid filled (mercury, ethyl alcohol, ...) gas filled (nitrogen, argon, helium)
vapor pressure (volatile liquid)
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1.
bifilar winding of metallic t.
PTC
Temperature dependence of resistance
NTC
platinum
R
T
metallic
thermistor (semiconductor)
NTC, PTC, CTC
ceramic
PTC
Pt 100, Ni 100 (i.e. 0C = 100 )
Principle: Temperature dependence of resistance
platinum
nickel
copper
Metal resistance increases under the influence of temperature
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1.
E=f(T1-T2)
T1 T2metal A
metal B
measuring junction
(hot junction)
connecting
head
1) Fe-konstantan2) NiCr Ni3) PtRh - Pt
500 1000 1500
2
1
E[mV]
C
3
(thermocouple, thermoelement)
Principle: Thermoelectric effect - if junctions of two different metal have a different
temperatures than a voltage is generated.
The construction of joint and shield
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1.
global radiation monochromatic
two-colour
(pyrometer)
Principle: Measurement of thermal radiation emitted by any matter with a temperature
greater than 0K
Measuring area
Non-contacting measurement
based on an optical system and a detector
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1.
0 C
expansion-200
500pressure spring -50 700
resistance -270 900
thermoelectric -100 1600optical 400
2700
1) Temperature range:
2) Contact or non-contact
(The main selection criteria)
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1.
Uz R0 Rw Rt
R1 R2
R3connecting wiring
Uz R0 Rw Rt
R1 R2
R3 connecting wiring
2-wire circuit
3-wire circuit
The connecting wiring
occur in
two legs of the bridge
The connecting wiring
are added to
the measured resistance
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R1 R2
Rt
Uz
R3
t0ehotjunction
mV
cold junction
e1
e2 e4
e3
mVt0
A
B A
C
Chot
junction
thermostat
cold junctions
1.
.
Circuit with the cold junction compensation
e=e1-e2 (e2=const), e3 = - e4
Simple circuit
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2.
Measurements of displacement (position) and force are similar on account of that the
displacement is a result of some force.
The force-related measurements contain a wide gamut of sensors for measuring:
stress (calculated by dividing the force applied by the unit area)
strain (defined as the deformation per unit length)
weight (the force on the object due to gravity)
acceleration (accompanied by a force)
torque (moment of force)
pressure (by definition the force per unit area)
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2.
l
R=rl
R=r
l
potentiometer
Principle: The resistance depends on the geometry of the resistor (and the resistivity of
the material)
linear
rotary
The linear or angular motion of a wiper
is converted into a changing resistance of potentiometer
strain gauge
The gauge is attached to the object by a suitableadhesive. As the object is deformed, the foil is deformed,
causing its electrical resistance to change.
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2.
Principle: Piezoelectric effect - some materials (e.g. quartz) generate a voltage under
influence of a mechanical stress.
In most cases, the same element can be used as:
piezo sensor that converts mechanical energy into electrical energy (it is referred to as "generators)
piezo actuators that converts electrical energy to mechanical energy (it is referred to as "motors)
[http://www.americanpiezo.com/knowledge-center/piezo-theory/piezoelectricity.html]
polarizationdisk compressed:
generated voltage
has the same polarity
as poling voltage
disk stretched:
generated voltage
has polarity opposite
that of poling voltage
applied voltage
has the same polarity
as poling voltage:
disk lengthens
applied voltage
has polarity opposite
that of poling voltage:
disk shortens
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2.
mAF
coil sensor
Principle: Mechanical strain has an influence on a magnetization of ferromagnetic
materials
transformer-type sensor
F
L
Measurement of inductance
Measurement of current in the secondary circuit
consisting of two push-pull winding(a differential measurement)
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2.
coil sensor
s
Ls0W2/
s
differential coil sensor
x
1
2
differential transformer-type sensor transformer-type sensor
x2
3U2
Principle: Displacement of a part of core involves changes in inductance
1) Measurement of inductance
2) Measurement of eddy current(eddy current linear encoder)
The primary winding are energised with a
constant amplitude A.C. supply. Thisproduces an alternating magnetic field in the
core and induces a signal into the secondary
winding (2,3) depending on the position of
the core.
The target is part of magnetic circuit
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2.
parallel-plate c.
x
x
differential parallel-plate c.
rotary c.
x
cylindrical c.
Principle: Displacement of a capacitor plate involves changes in capacity
x
Target
Sensor The target is one plate of the capacitor
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2.
x
N
SI+
-
UH
UH=kIB
Principle: Hall effect an electric current in the conductor placed in a magnetic field
causes a voltage difference (the Hall voltage)
The Hall voltage is developed between the two
edges of a current-carrying conductor whose faces
are perpendicular to an applied current flow.
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h
p1 p2
p1-p2=gh(1-2)
21
U-tube
p
float sensor
3.
(Hydrostatic pressure gauge)
Principle: Hydrostatic equilibrium between the pressure and the hydrostatic force per
unit area at the base of a column of fluid
(U-pipe)
Pipes and tubes are not the same
Pipe: The purpose with a pipe is the transport of a fluid like water, oil or similar, and the most import property is the capacity orthe inside
diameter.Tube: The nominal dimensions of tubes are based on the outside diameter. The inside diameter of a tube will depend on the thickness of the
tube. The thickness is often specified as a gauge.
The pressure is indicated by the difference in levels in
the two arms of the tube
The pressure causes a change of liquid
level and the float transfers it to an
indicator
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p
p1 p2
bell pressure gauge
p2p1
p2
p1
p1-p2=gh
p2
ring differential manometer
y
p
cy+mg=pA
piston pressure gauge
p
3.
(bell-type manometer)
(Hydraulic pressure gauge)Principle: Hydraulic equilibrium of the pressure and another force
(ring balance)The force of pressureis in balance with the spring
The balance the
force of pressure
and bouyant force
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Bourdon tube
p
diaphragm pressure gauge
p p
bellows pressure gauge
3.
(tube pressure gauge,spiral pressure gauge)
Sensor uses the deflectionof a flexible membrane
that separates regions of
different pressure
(Spring-type pressure gauge)Principle: Equilibrium of the pressure and a spring force
The curved tube is open to external
pressure input on one end and is
coupled mechanically to an indicatingneedle on the other end. The external
pressure is guided into the tube and
causes it to flex.
The bellows is stretched on
pressure influence
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capacitive
p
differential capacitive
p1p2
3.
Differential manometer withan elastic membrane is a
double capacitor
Principle: Conversion the pressure to a displacement or a mechanical stress and next an
electric measurement of this displacement.
inductive strain gauge
(measurement of inductance)
(measurement of resistance)
(measurement of capacity)
Displacement sensors and manometers
differ in a process connection
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3.
with piezoresistive
strain gauge
with piezoelectric sensor
with strain gauge
with strain gauge
Principle: Conversion the pressure to a force or a strain and next an electric
measurement this parameter.
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3.
1) Type of measured pressure
absolute pressure is zero-referenced against a perfect vacuum, so it is equal to
gauge pressure plus atmospheric pressure. gauge pressure is zero-referenced against ambient air pressure, so it is equal to
absolute pressure minus atmospheric pressure.
differential pressure is the difference in pressure between two points.
2) Compromise between an accuracy and susceptibility to overload3) Inertia measurement of slow/fast pressure changes
4) Process connection1 2A
h2-h1
h1h2
1 2
h2 h1
h2-h1
A
h2-h1 the pressure arisen from a liquid flowAssumption: no pipe resistance
p1=p2 p1>p2
(The main selection criteria)
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4.
glass level gauge
magnetic level indicator
Principle: Communicating vessels
It is perfect for high temperature and pressure
applications in case sight glasses and indicating
glass parts cannot be used for safety reasons
(tubular level gauge)
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4.
resistance
inductive
Principle: Liquid level float is buoyant in liquid and indicates the level
Float moves
on a linear resistor
Float causes a displacement
of a coil core
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4.
PP=p1-patm
patm
P=gh
h1
bell-type
P
capacitive
(Manometric level gauge)
Principle: The static pressure in the bottom is proportional to the liquid column in the tank
The pressure at a given depth in a static liquid
depends upon the density of the liquid and the
distance below the surface of the liquid
plus any pressure acting on the surface of the
liquid
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4.
(Buoyancy transmitter)
F
Principle: Archimedes' Principle - a body which is completely or partially submerged in
a fluid experiences an upward force (the buoyant force)
Sensor
in a side-and-bottom chamber
Sensor
without
chamber
Weighing of
the displacer element
Intelligent level transmitters based on
Archimedes buoyancy principle are
designed to measure liquid level,
interface and density.
Buoyant force moves a coil core
and changes its inductance
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4.
Example applications
Principle: Reflection of high frequency acoustic waves
The sensors emit waves (20 kHz to 200 kHz) that are reflectedback to and detected by the emitting transducer. The elapsed time
period between transmission and reception of the signal - at the
speed of sound - is measured and calculated as a distance and
computed into level or volume.
In order to improve the accuracy of
measurement it is important to take into
account a moisture, temperature, and
pressure changing speed of sound.
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4.
Principle: Reflection of microwaves
(Microwave sensor)
Speed of microwave is independent of moist,
vaporous, dusty, and temperature environments
The sensors emit waves (1 GHz to 30 GHz ) and measure the time
period between transmission and reception of the signal.
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4.
..
..
Principle: Property of sounder depends on its draught in liquid
Draught cools the measuring element, e.g. the resistance thermometer
Sounder is a superconductor and his resistance
depends on draught in a low temperature liquid
Sounder is a long capacitor and his capacity depends on draught
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4.
1) Type of medium (phase): liquid, solid or slurry
(the main selection criteria)
3) Conditions of measurement, e.g. temperature, pressure (or vacuum)
2) Properties of medium, e.g. dielectric constant, density
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5.
flow nozzle Venturi tube
orifice plate
p
(Orifice flowmeter)
Principle: Bernoullis principle an obstruction inserted in the flow causes a pressure
drop proportional to the square flow speed.
(Venturi meter)
Nozzle and tube offer advantages over orifice plates in that they require lessupstream piping and incur lower permanent pressure loss.
Pressure sensor measures the differential pressure before and within the constriction
5
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5.
plastic
glass
metal
Principle: Balance between the flowing force and the weight of the float
The rotameter consists of a vertically oriented glass (or plastic) tube with a larger
end at the top.The substance flows through the meter vertically from bottom to top and lifts the
float proportionally to the flow quantity.
5
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5.
screw f.
blade f.
turbine f.
impeller
counter
12 impeller
counter
Principle: The fluid flow actuates the movement of blades, screw or turbine-type impeller
proportionally to flow rate.
(Rotating meter)
The flow is calculated by
measuring and integrating
the flow speed over the
flow area
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5.
piston
four-wayvalve
Principle: Counting repeatedly the filling and discharging of known fixed volumes
A typical positive displacement flowmeter comprises a chamber that obstructs the
flow. Inside the chamber, a rotating/reciprocating mechanical unit is placed to
create fixed-volume discrete parcels from the passing fluid.
Piston is operated to fill a cylinder with the fluid
and then discharge the fluid. Each strokerepresents a finite measurement of the fluid
See also: http://www.efunda.com/designstandards/sensors/flowmeters/flowmeter_pd.cfm
5
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5.
electromagnet
electrode
(electromagnetive)
Principle: Faraday's law of electromagnetic induction - when a conductor moves through
a magnetic field then a voltage will be induced
The liquid serves as the conductor and the
magnetic field is created by energized coils
outside the flow tube. The inducted voltage isdetected with the aid of an electrode.
It can only be used for electrical conductive fluids as water.
5
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scheme
Z V
5.
Principle: Doppler effect - The frequency of the reflected signal is modified by the
velocity and direction of the fluid flow
(Ultrasonic Doppler flowmeter)
By measuring the frequency shift between the
ultrasonic frequency source, the receiver, and thefluid carrier, the relative motion are measured.
Doppler meters may be used where other meters don't work.
It can be installed outside the pipes (do not obstruct the flow )
It is sensitive to changes in density and temperature the fluid.
5
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5.
Principle: Intensity of cooling depend on the flow rate of the fluid
Two temperature sensors are in close contact with the fluid but thermal insulated from each
other. The flowing fluid cools both sensors but one of the two sensors is constantly heated.
The temperature difference between the two sensors is proportional to the flow rate.
5
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5.
Principle: Karman effect - an obstruction in a fluid flow creates vortices in a downstream
flow
Animation http://en.wikipedia.org/wiki/File:Vortex-street-animation.gif
Karman vortex street
Vortices cause a local disturbance of pressure
detected by the sensor. Frequency of vortices is
proportional to the flow rate
5
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Animation: http://www.emersonprocess.com/micromotion/tutor/42_densityoperatingprincipal.htm
5.
Principle: Coriolis effect -
It is a direct measurement mass (not sensitive to changes in pressure, temperature, viscosity and density )
The fluid runs through a U-shaped
tube that is caused to vibrate in an
angular harmonic oscillation. Due
to the Coriolis forces, an
additional vibration arise thatdeform the tube
5
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5.
Principle: An obstruction inserted in the flow causes a backwater
A common method of measuring flow through an open channel is to
measure the height of the liquid as it passes over an obstruction as aweir or flume in the channel.
Venturi flume V-notch weir
Common used obstruction types:
the sharp-crested weir,
the V-notch weir,
the Cipolletti weir, the rectangular-notch weir,
the Parshall flume
Venturi flume.
c
sharp-crested weir
5.
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1) If the flowrate information should be continuous or totalized?
5.
(The main selection criteria)
2) Type of medium: steam, gas, liquid
3) Properties of medium: viscosity (Reynolds number), density
4) Conditions of measurement, e.g. pressure, temperature
5) Unit
m3/s (volumetric flow rate, volume flow rate, rate of fluid flow, volume velocity) kg/s (mass flow rate)
6.
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Uzasil eg
dc generator
U1
eg1
ac generator
6.
Principle: A small ac/dc generator that develops an output voltage proportional to its rpm
(Rate generator)
The dc rate generator often has
permanent magnetic field excitation.
The rotor of the tachometer is mechanically connected, directly or indirectly, to the load .
The ac rate generator field is excited
by a constant ac supply
The phase or polarity of output voltage (eg) depends on the rotor's direction of rotation
6.
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6.
fn
fn
fzUz
N S
S N
Principle: A pulse generator plus a pulse counter
(rotational speedsensor)
(reed swich)
.
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- vibrating fork liquid level switch (submergence, filling)
Principle: Overflow of a definite input value causes an abrupt change of output value
(usually closure of contacts used e.g. to direct control)
(Two-stage transducers)
Measurement sensors used to a detection of only two-stage.
liquid level switch, e.g.
pressure rise relay, e.g.
temperature rise relay, e.g.
- float switch (exceeding the level)
- bimetallic switch (overflow of temperature)
U-tube (mercury join contacts after the overflow of pressure)
acoustic
light-, ...- photodiode, photoresistor (proximity detector )
- microphone (detection of sound intensity, frequency)
.
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Principle: Relay - overflow of a definite input value causes a closure of contacts
reed switch
electrical activated device
close relation
N Sturn
N Stern
N S
tern
limit switch
Switch is operated by the motion of a machine part or presence of an object
.
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a) pH pH meter
b) redox potential (oxidation/reduction potential, ORP) ORP meter
c) humidity hygrometer
d) oxygen (proportion of O2 in the gas or liquid ) oxygen meter, lambda sensor
e) conductivity conductometerf) suspension densitometer, suspension turbidity meter
g) water hardness
h) concentration refractometer
....
The main type of measurement:
.
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- concentration of hydrogen ions (H+)
- in practice from 10mol/l to 10-15 mol/l
pH
10-7 mol/l10010-14
14
7
0
H2O acidic solutionbasic solution
A typical pH probe consists of a
combination electrode, which combines
both the glass and reference electrodesinto one body. The probe produces a
small voltage (about 0.06 volt per pH
unit) that is measured and displayed as
pH units by the meter
Principle: The measurement bases on an electrode made of a doped glass membrane
that is sensitive to a specific ion
The ph meter requires a cleaning and a frequent calibration
because the glass electrode does not givea reproducible e.m.f. over longer periods of time
.
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Requirements:
measurement value (temperature, pressure, ..)
range
accuracy class mounting of the instrument (process connection, location)
frequency response
environmental condition (e.g. Ex, dustiness, moisture)
operational reliability (e.g. periodical calibration)
dimensions, weight complexity of additional equipment
qualification of service staff (method of calibration or programming)
price of sensor and an additional apparatus
resolution of the measured signal
The main directions
Procedure of the sensor selection:
1) statement of the main requirements for sensor
2) review of available sensors from the point of view of fulfilment of requirements
.
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Definition and classification
Classification of converters according to function:
1) measuring
conversion of a sensor signal into a standard signal
typical electric standard signals: 0-5mA, 0-10mA, 0-20mA, 4-20mA, 0-10V2) signaling
matching circut - exchange of one standard to another
current-current, voltage-voltage, current-voltage, voltage-current, current-
pressure (intersystem converter);
3) separating assurance of the galvanic isolation between functional sections of system
the same standard of input and output and the gain equal 1
4) analog-to-digital converter (ADC, A/D, A to D)
conversion a continuous quantity to a discrete time representation in digital form
typically the digital output is a twos complement binary number
5) digital-to-analog converter (DAC, D/A, D to A)
conversion of a digital (usually binary) code to an analog signal (current, voltage
or electric charge)
1.
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a sensor signal to the standard signal
According to input value:
converter of force, voltage, resistance, pressureAccording to principle of operation:
parametric, generating
According to construction (electric circuit)
open circuit (without a feedback)
close circuit (with a feedback)
According to modulation of output signal:
a) modulation of direct current levelb) frequency modulation
c) discrete output with modulation pulse-width (PWM)
1.
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with modulation of direct current level
measuring converter of a resistance measuring converter of a small voltage
Rs
Rb
Rf
Us
Rr
Iout
Us
Rb
Rf
Us
Rr
Examples:
Rs resistance of sensor; Us voltage of sensor
Rb balancing resistance of the circuit; Rf feedback resistance; Rr receiver
1.
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with frequency modulation
generating
tachometer generator
oscillatory with a free vibration
MC OS Cout
AC
in out
AF
l
string-type converter
(the force F into the frequency f)
ml
Ff
2
1=
Types:
position-type} modulating digital speed measurement
oscillatory with a forced vibration
MC matching,AC activation
OS - oscillatory system
Cout output converter
1.
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with pulse-width modulation
LG C
Uout
UA
ULG
UX
UC
UA
UX
T
UULG
Uoutti
Example:
LG linear generator (g. of linear signal)
UA activation; C- comparator
Ux input voltage
Uout output voltage
1.
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The main directions
Requirements:
a suitable static characteristic (linear or non-linear)
stability of characteristic
a small conversion error (e.g.
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measuringconvertersensor
RA RBUR CB
Disturbing signals:
serial voltages
parallel voltages
galvanic separation
result of a inductive coupling between two wiresprimarily frequency of 50Hz and 100Hz
result of a ground loop
frequency of 50Hz5kHz,
high voltages, constant component
Suppression with the help of low-pass filter
passing the measured signal (frequency
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xin=
= xout
GZ
M DTO
Iin
Iout
Application of galvanic separation
UP U I I I
UP UI
II
sys
I1
I21
2
100
200
200
200
200
3
4
5
6
Realization of galvanic separation
galvanic separation
transformer-type optoelectronic
4.
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A/D
Conversion process
Parameters of A/D converter: range of input signal
resolution (bits) - quantization error (%)10 bits = 210 = 1024 qantums= 0,1%
12 bits = 212 = 4096 qantums = 0,025%
sampling rate (sampling frequency)
conversion time (for one sample)
If a single converter services n inputs, than sampling rate = 1 / (n*conversion time)
Ux
t
Sampling
Analog signal
(continues in bothtime and amplitude)
Sampled-date signal
(discrete in time andcontinues in amplitude)
Quantization
Discrete timediscrete amplitude
si nal
Digital signal
Encodingu(t) u[k]
Minimum of sampling rate (Shannon-Kotielnikov sampling theorem*)
- theoretically: fs >= 2fw-practically: fs >= 2fb, (fb=10fw)
*Shannon-Kotelnikov, WhittakerNyquistKotelnikovShannon
fs sampling rate,
fx the highest frequency of the original signal
fb used pass band (gain>=0.7)
4.
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Integrating ADC (dual slope ADC)
Ux
Uw U1
US
K
GW
LU2 U3
T1 T2
U1
U2
U3Nx= Nmax
Nmax Nx
Ux
Uw
t
t
t
T1 T2
Ux Uw
Types
4.
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ramp-compare ADC
Types
UX
U
Uout
tit
a direct-conversion ADC (flash ADC)
a successive-approximation ADC
a delta-encoded ADC or counter-ramp
a pipeline ADC (a subranging quantizer)
a sigma-delta ADC (a delta-sigma ADC)
a time-interleaved ADC
an ADC with intermediate FM stage
...
cfx
Forming Gate Counter
Controler
Pulse generator
Cancel
Nx
frequency-type ADC
frequencyinput
counting fxfor a determinate
time period
5.
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DAC
1 1 1
0 0 0X0 X1 Xi
21R 22R 2iR
U Uout
In: number X= X020 + X12
1 + ... + Xn2n
21R
22R
U
Uout
2 R
weigh-resistive
Out: signal Uoutif Xi=1 then switch=1
1 1 1
0 0 0
2R 2R 2R
U
X0 X1 Xi
Uout
2R2R
2R
2RU
Uout
2R
voltage ladder
...
.
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()
+ i
controller
sensor. measuring c. separating c. A/D
AD
()
+ + +
controller
sensor communication port
PAD
.
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TRCA154
H
process parameter
TRCA154
function: R - recordingI - indicationC - control
A - alarm
alarm
specification
TRCA154
D density
F flow rate
G distance, length, positionL level
P pressure
Q material properties
T temperature
W velocity, mass
programmable
deviceconfigurable
device
For further details, see DIN 19227
Graphical symbols and identifying letters in control engineering design
More: http://www.samson.deServicesTechnical Information
.
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Standards
US Standards:
ANSI Y32.2.3 Graphical Symbols for Pipe Fittings, Valves and Piping
ANSI Y32.2.11 Graphical Symbols for Process Flow Diagrams
ISA 5.5 Graphical Symbols for Process Displays
British Standards:
BS: 1646 1-4 Symbolic Representation for Process Measurement, Control
Function and InstrumentationGerman Standards:
DIN 19227 P1-P3 Graphical Symbols and Identifying Letters for Process
Measurement and Control Functions
Polish Standards:
PN-M-42007 (archive)
More: http://enormy.plhttp://www.samson.deServicesTechnical Information
.
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II. Actuating equipmenta) Final control element
1 valve
2 - pumpb) Actuator
1 - electrical motors
2 - pneumatic actuator
3 - hydraulic actuator
c
plant
sensor(sensing element)
measuringconverter
final controlelement
actuator(actuating driver)
controller
A/D
converter
D/A
converter
communication system
supervisor system
controlled system
controlingsystem
Examples:
Actuating equipment (final control equipment): Control valve:
- final control element - valve (closure element, body of valve)- actuator - actuating driver
- positioner (measuring element)
Body of valve manipulates the mass and energy flow.
The opening or closing of control valve is usually done by electrical, hydraulic or pneumatic actuator.
Positioner is used to control the opening or closing of the actuator based on electric, or pneumatic signals.
.
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Final control element a part of the controlled system that manipulates the mass and
energy flow.
Classification valves according to function:
control valve
throttling (choke) valve
gate (sluice) valve safety-valve
reflux valve
Classification valves according to construction:
ball (globe) rotary (butterfly)
knife
neadle
flap
Basic type of final control element:
1) valves 2) pumps
Classification pumps according to principle of operation:
positive displacement pump
impulse pump
velocity pump
gravity pump
1.
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butterfly valve
(globe valve)
Inside a spherical discFeatures: simplicity, sealing
V-port ball valve ball valve(V-notch valve; a segmented ball valve )
Inside a spherical disc with a notchFeatures: simplicity, sealing, precise control
knife gate valve(quarter-turn valve)
Inside a metal disc mounted on a rodand positioned in the center of the pipe
Features: low cost, light
More: http://www.valtorc.comValves
Valve a device that manipulates the mass flow on basis of a throttling.
2.
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Pomp a device used to move fluids (liquids, gases, slurries) by mechanical actions
(often a reciprocating or rotary mechanism).
positive displacement pump
The pump moves a fluid by trapping a fixed
amount of it and then forcing (displacing) that
trapped volume into the discharge pipe
impulse pump
The pump use pressure created by gas (usually air) and pushing part of the liquid upwards
velocity pump
The pump increases the flow velocity thereby
kinetic energy and this energy is converted to
pressure
(rotodynamic pump, dynamic pump)
The velocity pump can be safely operated
under closed valve conditions
The positive displacement pump physically displaces the fluid
resulting in a continual build up in pressure and finally
mechanical failure of either pipeline or pump
Operation under closed valve conditions
screw
lobe
centrifugal
.
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Actuator - a type of motor for moving or controlling a mechanism (final control element).
It is operated by a source of energy (an electric current, hydraulic fluid pressure,
pneumatic pressure) and converts this energy into some kind of motion.
Basic type of actuator:
1) pneumatic actuator
2) hydraulic actuator3) motor-driven actuator (electrical servomotors)
Actuator processes and amplifies the output signal of controller
(effectors, servomotor)
Actuators are also known as:
effectors (in robotics)
servomotor linear actuator, rotary actuator
1.
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Principle: Pneumatic actuator converts energy of compressed air into a mechanical motion
diaphragm actuator
Actuator that has a chamber divided in half by a
diaphragm that separates areas with different
pressure levels.
bellow actuator
More: http://heating.danfoss.com
Self-acting thermostatic actuator
(e.g. used for temperature control)
pneumatic cylinder
3.
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Definitions:
actuator - a device converting a low-power signal into a large-force displacement
(linear or rotary )
motor a device converting a heat, electrical energy, mechanical energy into energy
to drive machines (usually electrical energy into energy of rotational motion)
Actuator
a large force
a small velocity
Motor
a small torque
a high velocity
Electric actuator (servomotor):
a) an electric motor + a gear
b) an electric motor giving a suitable displacement (e.g. stepper motor)
3.
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General principle: Lorentz force - any current-carrying conductor placed within an
external magnetic field experiences a torque or force
rotorstator
[http://www.allaboutcircuits.com/vol_2/chpt_13/1.html]
Classification:
3.
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series m.
MMM
shunt m. separately excited m.
+ - +
-
+ -
Principle: Statorwith a stationary magnets and the rotorpowered from a DC power by
brushes and commutator.
permanent magnets electromagnets
The type of connection determines the characteristics of the motor
Advantages: low initial cost, high reliability, simple control of motor speed
Disadvantanges: sparking and wear of the electric contact commutator-brushes
MN S
brushes
+ -
Magnetic fields of the stator and the rotor interact and a generated torque causes a turn of the rotor.
The commutator consisted of a split ring reverses the current each half turn of the rotor.
Control:- the sense of rotation depends on the polarity of the excitation winding control by change of the polarity
- the rotational speed is proportional to the EMF in its coil - control by variable supply voltage, resistors or
electronic controls (e.g. PWM)
- the torque is proportional to the current
3.
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Principle: Rotorwith a stationary magnets and the statorpowered from the AC power
and generating a rotating magnetic field.
single phase s.m. stepper m.
Advantages: speed independent of the load,
accurate control in speed and position for stepper motor
Disadvantanges: above a certain size, synchronous motors are not self-starting motors
Electromagnets on the stator create the magnetic field which rotates in time with the oscillations of the
line current and the rotor turns in step with this field, at the same rate (the motor speed is synchronized
with the frequency the AC supply current )
Control:- sense of rotation depends on the direction of rotating magnetic field control by change of the phase order
- motor speed is synchronized with the supply frequency control by a variable-frequency driver
MN
S
three-phase s.m.
M
3.
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Principle: Rotorcontained no powered circuit and the statorpowered from the AC power
and generating a rotating magnetic field.
wound-rotor induction motor squirrel-cage rotor induction motor
Advantages: ruggedness, simplicity, 90% of industrial motors are induction m. (mainly the squirrel-cage rotor)
Disadvantanges: hard starting (it is accompanied by inrush currents up to 7 times higher than running current)
Electromagnets on the stator create the rotating magnetic field which induces an electric current in the
windings of rotor. Interaction between magnetic fields of stator and rotor produces a torque. The rotor
rotates at a slower speed than the stator field
Control:
-sense of rotation depends on the direction of rotating magnetic field control by change of the phase order
- motor speed is proportional to supply frequency control by a variable-frequency driver.
U W
V
MM
U W
V
(asynchronous motor)
Windings of rotor brought out via slip rings and
brushes which allows to connect a resistance during
start-up and to short-circuit windings during work.
Windings of rotor in the form of cage (poured
or welded)
Starting with:
star-delta switch
motor soft starter
3.
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A variable-frequency drive (VFD)
(adjustable-frequency drive, variable-speed drive, AC drive, micro drive, inverter drive)
- a type of adjustable-speed driver used to control AC motor speed and torque by
varying motor input frequency and voltage
electronic - frequency converter (frequency changer)
electromechanical = motor + generator
A motor soft starter
- a device used with AC electric motors to temporarily reduce the load and torque in thepowertrain of the motor during startup. This reduces the mechanical stress on the motor
and shaft, as well as the electrodynamic stresses on the attached power cables and
electrical distribution network, extending the lifespan of the system
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The main topics:
I. Measurement devices
II. Actuating elements------------------------------------------
I. Field devices - controllers
II. Communication networks
III. SCADA & DCS
}Instrumentation of a technological process
15 hours
} 15 hours
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