Instrument

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Instrument

• ??
• May 16, 2005

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Introduce

• At one time, operators controlled processes
  manually, it required the technician to open and
  close valves in piping lineups manually, which
  has not adopt to industrial produce
• Now an instrument or computer can control the
  opening, closing, and positioning of valves
  start and stop equipment, measure process
  variables, and respond automatically
• In a control center a single process technician
  to monitor and control large, complex process
  networks

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Introduce
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Temperature Measurement

• Temperature is a important parameter in the
  process industry, common thermometer cannot apply
• Local temperature indicators usually contain a
  bimetallic strip that differentially expands with
  increasing temperature, causing a deflection that
  is correlated with temperature
• The most common temperature-measuring devices
  used in the chemical-processing industry are
  thermoelectric resistive temperature
  detectors(RTDs) and thermocouples

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Temperature Measurement

• RTD composed of a small platinum(?) or nickel(?)
  wire encased in a rugged metal tube, the
  electrical resistance in the wire changes with
  temperature, electronic circuit is formed and
  directed to a indicator
• Thermocouples are composed of two different types
  of metal, J-type and K-type thermocouples are the
  most common

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Temperature Measurement
Temperature element
transmitter
controller
transducer
valve
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Pressure Measurement

• Pressure is an important variable
• Pressure is measured in psi(pounds pre square
  inch), pa(N/m2)
• There are three commonly used pressure scales
  gauge, absolute, and vacuum
• There are three basic types of manometer U-tube,
  well manometer(?????), micromanometer(???)
• Primary pressure elements designed to sense
  changes in pressure and convert it to mechanical
  motion, such as bellows pressure and bourndon tube

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Pressure Measurement
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Pressure Measurement

• A pressure transmitter uses a pressure element to
  sense pressure and sends a signal to a controller
  or recorder
• Pressure control loop includes a pressure
  transmitter, controller, transducer, and control

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Fluid Flow Measurement

• Continuous chemical reactions require precise
  measurements to ensure that all of the reactant
  are combined in the proper proportions to form
  the final products
• Flow transmitters use differential pressure to
  measure flow rate, such as orifice plates,
  venturi tubes, or flow nozzles

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Fluid Flow Measurement

• There are two types of positive displacement
  meters nutating disc and oval gear
• A rotameter is composed of a tapered tube, scale,
  ball or float, and inlet and outlet

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Fluid Flow Measurement

• Weir flow-measuring devices, when a weir is
  placed into a process stream,it creates a
  restriction that forces the level to build
• Flume is a narrow, sloping pass that funnels
  flow, which are used for higher flows
• Flow control loop is like pressure or temperature
  control loop

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Level Measurement

• Level measurement is also important
• Such as vessel tap, the lowermost tap represents
  zero level, and the uppermost tap is 100
• Lever-measurement devices can be classified as
  direct or indirect
• Direct type is as follows
• Indirect type is a pressure-sensitive instrument
  that measures hydrostatic pressure in open
  vessels and converts it to a level indication
• A bubbler system is a level-measurement device
  that forces air through a tube to measure the
  liquids resistance

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Level Measurement
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Basic Elements of a Control Loop

• Instruments include a transmitter coupled with a
  sensing device or primary element,a controller, a
  transducer, and a control valve
• The basic elements of a control loop are
• Measurement device----primary elements and sensors

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Basic Elements of a Control Loop

• Transmitter----a device designed to convert a
  measurement into a signal, this signal will be
  transmitted to another instrument
• Controller----a device designed to compare a
  signal with a set point and transmit a signal to
  final control element
• Transducer----a device designed to convert an sir
  signal to an electric signal to a pneumatic
  signal, sometimes referred to as an I to P or as
  a converter
• Final control element----the part of a control
  loop (control valve, damper, governor for speed
  control) that actually makes the change to the
  process the final control element is governed by
  a controller

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Basic Elements of a Control Loop

• Controllers are mounted between 400(closed loop)
  and 1000(open loop) feet from the transmitter
• The signal is proportional
• Standard output signals are 420mA, or 15V
• Pneumatic transmitters require a 2030 psig air
  supply in order to run the standard 315 psig
  output
• Smart transmitters have an internal diagnostic
  system that warns the operator if a problem is
  about to occur,advantageous features are speed,
  reliability, internal diagnostics, strong digital
  signal, remote calibration

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Basic Elements of a Control Loop

• Controllers and controller modes
• Controller is to receive a signal from a
  transmitter, compare this signal with a set
  point, and adjust the process to stay within the
  range of the set point
• There are three basic designs pneumatic,
  electronic, and computer
• Compare with pneumatic, electronic mode are the
  reduction of lag time, low installation expense,
  ease of installation, of course computer mode
  more advance
• Controllers can be operated in manual, automatic,
  remote control

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Basic Elements of a Control Loop

• The proportional band describes the scaling
  factor used to take a controller from 0100
• Controller modes are designated as
  proportional(P), proportional plus integral(PI),
  proportional derivative(PD), proportional-integral
  -derivative(PID)
• Proportional control is used to provide
  gain(??,????),PI works best where large changes
  occur slowly, PD works best when frequent small
  changes are required, PID is applied where
  massive rapid load changes occur, it reduces
  swinging

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Final Control Elements

• Final control elements typically are automatic
  valves,but motors or other electric devices can
  be used.
• Automates valves open or close to regulate the
  process
• An actuator is the device that automates a valve,
  it come in three basic designs pneumatic,
  electric, and hydraulic
• Pneumatic actuators convert air pressure to
  mechanical , which is the most common
• Electrically operated actuators convert
  electricity to mechanical
• Hydraulically operated actuators convert liquid
  pressure to mechanical

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Final Control Elements

• The most common type of automatic valve is a
  globe valve because of its versatile, on/off or
  throttling feature
• An interlock is a device designed to prevent
  damage to equipment and personnel by stopping or
  preventing the start of certain equipment
• There are two types of interlocks software and
  hardwire, hardwire interlocks cannot be bypassed,
  they must be satisfied before the process they
  are part of can take place

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Virtual Instrument
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Virtual Instrument
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Virtual Instrument

• The hardware is consisted of sensor, computer and
  Data Acquisition Card etc. The software is write
  by LabVIEW

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Virtual Instrument
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Virtual Instrument
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Virtual Instrument
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Industrial Control System
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Industrial Control System
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summary