Automatic Control System

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Automatic Control System

• VIII.
• Devices

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Terms of transmitter

• The most frequently measured variable are the
  next level, temperature, pressure, flow and
  angular velocity.
• Accuracy Define in percent such as the
  difference of the indicate and real value is
  divided by the maximum scale value and multiply
  100.
• Linearity Define in percent such as the maximum
  deviation of the real value from the best
  straight line is divided by the maximum scale
  value and multiply 100.
• Resolution This is the smallest change in
  transmitters input that can be detected. Usually
  expressed as a of full scale.
• Repeatability The ability of the transmitter to
  give the same measured signal whenever the
  measured variable is in a particular state. Its
  sometimes more important than the absolute
  accuracy.
• Sensitivity This is the change of the measured
  signal divide by the the change of measured
  variable.

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Actuator

• The most frequently used actuators the next
• motors, pump, ventilator
• valve, slide-valve
• circuit-breaker (closed contact, breaker contact)
• pneumatic cylinder (shaft, operating pressure)

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Structure of control system
Control software
actuator
Process the name of mathematical model is
the plant
actuating unit
actuating drive
controller
transmitter
sensors
transducer
Standard signals
operator desk
Standard industrialI/O interface
Material flow
Simulation software
Visualization software SCADA (Supervisory control
and data acquisition)
Variables
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Classifying of sensors

• On/Off sensorsImportant feature is the
  repeatability and not important is the linearity.
  Output is a pure contact or standard 0-24 Vdc
  digital signal. Position sensors Limit switches
  of state variable Series of rectangular impulse
  with 11 impulse ratio
• Analog sensorsImportant features are the
  repeatability and the linearity too. Typical
  output is the standard 4-20 mA signal. The so
  called main five variables temperature, level,
  pressure, flow, and angular speed or position.

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Classifying of position sensors

• Mechanical switches Output is a pure contact.
• Proximity switches Output is standard 0-24 Vdc
  digital signal. Special output is a pure contact
  or analog signal.
• Optoelectronic switches Output is standard 0-24
  Vdc digital signal. Special output is a pure
  contact.
• The application is to detect an object is in the
  required position or not.

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Mechanical switches

• On the switch desk or box
• Pushbuttons
• Switches
• Switching wheel
• From the process
• Mechanical limit switches

telescope rod
switch rod
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Mechanical limit switches

• Snap-action or slow-action contact for accurate
  switching with safe operation via direct drive
  positive contact opening even with metal
  deposition between mating contacts.
• Two sets of contact one (NC) for safety circuit
  and the other (NO) for control circuit.
• Degree of protection IP67 Actuators are
  interchangeable and can be mounted in any of four
  directions.
• 3-conduit switches are available.

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Form of proximity switches
screwed

• Cylindricalmetal or plastic housing
• Rectangularmetal or plastic housing
• Only inductive
• Slot typeplastic housing
• Ring typeplastic housing

Screwed flange
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Proximity switches
active face

• Inductive sensor
• The basis of the inductive sensor principle is a
  high frequency oscillator, which can be
  influenced from the outside by metal objects. The
  oscillator coil incorporated in a ferrite core,
  generates an alternating electro-magnetic field,
  which is passing the active face.
• Correction factor
• All details regarding switching distance of
  inductive sensors are based on the use of targets
  of St 37 with defined dimensions (source EN
  50010). Other materials or other dimension lead
  to changes of the switching distance.

oscillator coil
high frequency magnetic field
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Proximity switches

• Capacitive sensor
• The active face of a capacitive sensor is formed
  by two concentrically positioned metallic
  electrodes. The electrodes (A, B) are placed in
  the feedback loop of high frequency oscillator
  which is inactive with No target present.
• As the target enters the electrical field the
  coupling capacitance increases between A and B
  and the circuit begins to oscillate.
• Capacitive sensor are activated by both
  non-conductive and conductive targets. The
  largest switching distances are achieved by metal
  targets.

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Terms of proximity switches

• Sensing distanceIt signifies the distance
  between the target and active face. (nominal,
  effective, and usable sensing distance)
• Switching frequencyIt is the maximum number of
  changes per second (Hz) between the activated and
  non-activated state.
• Switching hysteresisIt is the differential
  between the switch-on, -off points of the sensor,
  with axial motion of target.
• Repeat accuracyIt is defined as the tolerance of
  sensing distance between two consecutive
  measurement.
• OutputNormally open, or closed, or
  complementary.(normal no target present)

Sensor off
Sensor on
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Inductive proximity sensor

• Grooved TL-G3D is ideal for high-speed pulse
• generator and high-speed revolution control.
• TL-Q2 and TL-Q5 save mounting space and are
• convenient for incorporation into miniature
  controllers,
• office equipment, etc.

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Long distance proximity sensor

• Proximity Sensor with a Sensing Distance of 100
  mm Detects Ferrous and Non-ferrous Objects

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Opt electric switches

• Using monochromatic light source at ultra red
  range or laser.
• SeparateIndependent light source and
  receiverTwo wiring pointsLarge sensing distance
  
• ReflectiveCombined light source and receiverOne
  wiring point and reflector.Half sensing distance
  
• Auto-reflectiveSimilar to reflective typeThe
  sensing distance depends on the targets surface.

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Terms of opt electric switches

• Sensing distanceIt signifies the distance
  between the light source and receiver or
  reflector.
• Switching hysteresisIt is the differential
  between the switch-on, -off points of the sensor,
  with alternate horizontal motion of object.
• Sensing wayIt is the differential between the
  switch-on, -off points of the sensor, with direct
  horizontal motion of object.
• OutputNormally open (light logic), or closed
  (dark logic), or complementary.(normal no
  target present)

Sensor off
Sensor on
Sensing way
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Small sensing head photoelectric sensor

• Compact sensing head available in a wide
  variation of designs features installation in a
  narrow space.
• Mutual interference preventive function allows
  side-by-side mounting of two sensors.
• Light indicator provided in the sensing head.

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Grooved head photoelectric sensor

• A 1-cm groove type detects marks on transparent
  film.
• A 3-cm groove type detects edges, labels, and
  marks.
• LIGHT and STABILITY indicators make sensitivity
  adjustment easy.

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Classifying of limit switches of state variable

• Level switches Output is standard 0-24 Vdc
  digital signal. Special output is a pure contact
  or analog signal.
• Pressure switches Output is standard 0-24 Vdc
  digital signal. Special output is a pure contact
  or analog signal.
• Temperature switches Output is standard 0-24
  Vdc digital signal. Special output is a pure
  contact.

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Level switches with contact operation

• CapacitiveLevel dependent capacitance are
  detected via the electrode.Various electrode
  types are available for conductive or
  non-conductive liquids, solids products.This
  procedure is suitable for continuous measurement
  too.
• VibrationThe piezo-electrically generated
  vibration of a sensor modified by the contact
  with the product. The sensors form tuning fork
  for liquid, and single-rod for solids. The
  electronics detects this change which is then
  converted a switched signal.
• ConductiveThe circuit is closed when the
  electrode contacts the conductive liquid. Due to
  the use of alternating voltage, galvanic action
  between the electrode and vessel is prevented.

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Level switches with non-contact operation

• MicrowaveMicrowaves are electro-magnetic waves
  in the GHz-range.If the product is between
  transmitter and receiver of a microwave barrier,
  the signal is damped and it is detected.Microwave
  penetrate plastics, glass or ceramics with
  virtually no loss. This enables the measurement
  through a window in the vessel.
• RadiometricWith this gamma barrier the
  absorption of gamma rays by the products is
  measured and evaluated with a Gieger-Müller
  counter-tube. The radio-active product of the
  source is located in a source container. The
  measurement is possible through closed vessel
  with aggressive products and/or high pressure and
  temps.

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Capacitance Level Sensors

• Capacitive Level Transmitters VEGA EK Series
• Cost effective compact capacitive level
  transmitters use latest technology for
  performance and accuracy. Ranges and lengths up
  to 4m for conductive and non conductive products.
• Level Switch VEGACAP
• Level switches for liquids and Solids with
  Relay, Transitor or Non Conact switch outputs.
  Rod or cable electrodes to suit material or
  application

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Microwave Level Sensors

• Liquids Guided Microwave FLEX 61
• Measures using a microwave pulse transmitted down
  a rod or cable which is reflected back from the
  product surface. can be used on liquids or
  powders. Easy to install and set up.
• High Temp/Pressure Guided Microwave FLEX 66
• The new Guided Microwave (TDR) sensor VEGAFLEX 66
  is especially designed for hot processes and/or
  high pressure applications. It combines the
  proven technology from the VEGAFLEX 61 and
  VEGAFLEX 65 with new inovations to provide you
  with a sensor for challenging conditions.

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Nucleonic Non-contact Level Sensors

• Scintillation Detector
• Scintillation detectors employ an artificial
  crystal material that produces visible light when
  exposed to gamma radiation.
• FiberFlex Scintillation Detector
• The FiberFlex is a new and unique detector that
  uses scintillation material in the form of a
  fibre optic bundle to provide a highly flexible
  detector.

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Detectors for continuous level measurement

• Pulse-echo, Pulse-radar, LaserThe product
  surface reflects the sound waves, radar pulses
  (extremely short microwave), laser (infrared
  light) to the combined transmitter / receiver
  system. The level is calculated from the measured
  pulse running period. These are typically
  non-contact operations.
• HydrostaticThe hydrostatic measurement principle
  enables precise level measurement by pressure..
• Electro-mechanicThis principle has been proven
  over decades, a cable with sensing weight is
  lowered into a vessel via a electric motor. When
  sensing weight contacts the product, the cable is
  rewound. The cable length is a measure of the
  level.

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Ultrasonic Level Sensors

• Ultrasonic Level Transmitter VEGASON 61
• Low-cost, compact ultrasonic sensor for
  continuous level measurement.Suitable for
  measurement of liquids and solids in virtually
  all industries, particularly in the water and
  waste water economy or storage of non volatile
  products.
• Ultrasonic Level Transmitter VEGASON 64
• Ultrasonic sensor for continuous level
  measurementEspecially suitable for the
  measurement of solids with optional aiming swivel
  holder for optimum adaption to the vessel
  geometry and material profile.

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Hydrostatic Level Sensors

• Flush Ceramic Pressure Transmitter
• Hydrostatic Pressure transmitter, flush
  CERTEC ceramic cell for level and pressure
  measurement in food processing, dairy, brewing,
  pharmaceutical, paper and water industries.
• Suspended Flush Ceramic Pressure Transmitter
• Top mounted suspension pressure transmitter with
  totally flush CERTEC Ceramic-capacitive cell at
  end designed specifically for mounting in from
  the top on level and gauge measurement in tanks,
  deep wells, rivers, reservoirs.

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Applications

• Liquid bitumen in storage tanks
• The brew house the centre stage of the brewery

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Applications

• Chocolate food for the soul
• Waste paper and pulpers

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Applications

• Water treatment plant for High Purity Water (WFI)

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Positioning

• Submersible, hydrostatic liquid level
  sensor/transmitter for use in reservoirs, pumping
  stations, stumps, bore holes and tanks.

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Pressure sensors

• Incorporates double diaphragms consisting of
  SUS316L stainless steel and silicone diaphragms
  that are applicable to a variety of gases and
  liquids.
• Pressure sensing range of 0 to 490 kPa (0 to 5
  kgf/cm2) or 0 to 980 kPa (0 to 10 kgf/cm2) is
  available. Two models are available according to
  the application.
• Linear output of 4 to 20 mA.

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Thermocouple Temperature Sensors

• Thermocouples are among the easiest sensors of
  temperature to use and obtain and are widely used
  in science and industry. They are based on the
  Seebeck effect that occurs in electrical
  conductors that experience a temperature gradient
  along their length. Have a read through, click on
  the key topics below to get more detail about the
  thermocouple, how it works, color codes,
  recommended use limits and thermocouple
  standards.

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Thermistor Temperature Sensors

• Thermistors abound inside many devices as well as
  in specialty temperature sensing probes. Some of
  those new-fangled medical thermometers that get
  stuck in one's mouth by a nurse with an
  electronic display in her other hand are based on
  thermistors. They typically work over a
  relatively small temperature range and can be
  very accurate and precise within that range.

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Resistance Temperature Detectors (RTDs)

• RTDs are wire wound and thin film devices that
  work on the physical principle of the temperature
  coefficient of electrical resistance of metals.
  They are nearly linear over a wide range of
  temperatures and can be made small enough to have
  response times of a fraction of a second. They
  require an electrical current to produce a
  voltage drop across the sensor that can be then
  measured by a calibrated read-out device.

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Angular speed or position

• Series of rectangular impulse with 11 impulse
  ratio.
• The frequency of the pulse depends on the number
  of the detected point around of the circle and
  the rotation speed.
• Counting the position needs an independent sensor
  to check a basic point.
• To check the direction of motion needs two
  sensors and two series of the detected points.

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Incremental sensors
E.g. Hengstler RI-57
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Absolute sensors
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The sensing distance is defined as the distance
between the front of the sensor and the tips of
the teeth.

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The rotational speed sensor include an advanced
bipolar signal conditioning circuit.The following
figure shows its block diagram

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Rotary encoder

• Various models available in series with supply
  voltages and output forms adaptable to various
  input devices.
• Models with zero index function ideal for
  positioning applications.
• High response frequency and noise immunity make
  encoders ideal for factory automation
  applications.
• Ensures higher-than-ever measurement precision.

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On/Off actuators

• Pneumatic piston with electropneumatic
  converterlinear moving, robust feature5/2, 5/3,
  4/2, 4/3, 3/2 means airway/static state
• Industrial relayswitch AC/DC current, galvanic
  isolation, multiply signals
• Contactorswitch powerful AC/DC current, galvanic
  isolation, multiply signals
• Valveall types, if these operate on/off.
  (opened/closed)
• Motorventilators, pumps, and so on, if these
  operate on/off. (start/stop)

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Pneumatic piston
Piston rod
Air cable
Piston-chamber
Pulse valve 5/2
Its a bistable arrangement
Magnet valve with electro-pneumatic converter
Air supply
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Terms of pneumatic piston

• Operating pressureIt is the actual value of the
  air supply pressure. The typically nominal value
  is 3-6 Bar. The operating pressure multiplied by
  the inside diameter of the cylinder gives the
  operating force.
• Repeatability frequency It is the maximum value
  of the alternate horizontal motion of piston rod
  between ends.
• Piston rods displacementIt is the maximum
  horizontal motion of piston rod.
• Piston rods diameter and buckling forceThe
  piston rod diameter depends on the needed force.
  The maximum value of the force is less than the
  buckling force.
• Consumption of airIt depends on the motions
  frequency and content of the cylinder.

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Cylinder for food industry
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Bistable and monostable valves
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Industrial relay and magnet-contactor

• The main feature is a coil which encircles a high
  permeability metal rod. Energising the coil the
  rod moves opposite of a spring force and
  operates a mechanical system which opens or
  closes contacts. The energising power is more
  less than the switching power. The energising
  power may be AC or DC too. Cutting high current
  an arc becomes between the contacts. The
  contactor has a system which eliminates this arc
  current.
• Industrial relayswitch AC/DC current, galvanic
  isolation, multiply signals
• Contactorswitch powerful AC/DC current, galvanic
  isolation, multiply signals