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Instrumentation
Instrumentation plays a key role in process automation by measuring and controlling various process variables. Common instrumentation includes transmitters to measure pressure, temperature, level and flow as process variables. Controllers like PID controllers compare the process variable to a set point and operate final control elements, usually valves, to maintain process equilibrium by minimizing differences between the process variable and set point. This closed loop control model is used widely in industrial automation to control temperature, pressure, level and other process conditions.
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Instrumentation
- 1. Lar Rochain Arlante JemarPalermo INSTRUMENTATIONINSTRUMENTATION
- 2. WHAT IS IT?WHATIS IT? Definitions of Instrumentation from the Web: • The use of rods, screws, plates, hooks, wires, bolts, etc. to correct and stabilize abnormalities of the spine. • The art of composing, orchestrating, or arranging for an instrumental ensemble. • An electrical or pneumatic device placed in the field to provide measurement and/or control capabilities for the system.
- 3. RESOURCESRESOURCES Text Book: Industrial ControlElectronics 3rd edition by Terry Bartelt, Published by Thompson (Delmar Learning) ISBN 1 4018 6292 6 ISA (Instrumentation, Systems, and Automation Society) The International Society for Automation - Setting the Standard for Automation www.isatoronto.org
- 4. AUTOMATION TECHNOLOGYAUTOMATION TECHNOLOGY Instrumentationplays an important role in almost every aspect of Automation Technology. • Industrial Automation • Manufacturing Automation • Process Automation • Building Automation Everyone needs to measure and/or control something – and that’s what instrumentation is all about.
- 5. MEASUREMENTMEASUREMENT Things that aremeasured include: • Pressure, temperature, level, flow, humidity, speed, motion, position, weight, density, conductivity, pH, light, quality, quantity, and more. Devices that process or do the measuring are called: • Sensors, transducers, transmitters, indicators, displays, recorders, data loggers, and data acquisition systems.
- 6. CONTROLLERSCONTROLLERS These are thedevices that do the controlling: • Programmable Logic Controllers (PLCs) • Programmable Automation Controllers (PAC) • Distributed Control Systems (DCS) • Proportional, Integral, Derivative (PID) Controllers • Supervisory Control and Data Acquisition (SCADA) • Building Automation Controllers (BAC) • Energy Management Systems (EMS)
- 7. CONTROL ELEMENTSCONTROL ELEMENTS Theseare the devices the controller operates: • Pneumatic valves, solenoid valves, rotary valves, motors, switches, relays, variable frequency drives.
- 8. OVERVIEW OF PROCESSAUTOMATIONOVERVIEW OF PROCESS AUTOMATION The process is “that portion of an automation operation which use energy measurable by some quality such as pressure, temperature, level, flow, (and many others) to produce changes in quality or quantity of some material or energy.” PROCESS Some Quality or Quantity of the Material or Energy Input Energy or Material Desired Result
- 9. EXAMPLE OF ATEMPERATURE PROCESSEXAMPLE OF A TEMPERATURE PROCESS Heating Element Water Bath Temperature The objective of this process is to maintain a constant water bath temperature.
- 10. TEMPERATURE PROCESS TERMINOLOGYTEMPERATUREPROCESS TERMINOLOGY Heating Element Water Bath Temperature This is a Temperature Process The measuring means is the thermometer. (Temperature Indicator- TI) The process temperature is maintained at a desired point (Set Point – SP) Steam (Control Agent) is used to vary the temperature by opening and closing the control valve (Final Control Element)
- 11. LEVEL PROCESSLEVEL PROCESS OilStock Level Indicator Oil Feed to next process The control objective is to maintain a constant liquid level of oil inside the tank (e.g. 100 gallons +/- 20 gallons). The hand valve is opened and closed as required to maintain the desired tank level.
- 12. TERMINOLOGY USED TODESCRIBE THE PROCESSTERMINOLOGY USED TO DESCRIBE THE PROCESS • PROCESS: Level • CONTROLLED VARIABLE: Head pressure at bottom of tank • CONTROL POINT: The level of oil in the tank (Set Point = 100 gallons) • MEASURING MEANS: Level Indicator (Head Pressure) • CONTROL AGENT: Volume of oil stock • MANIPULATED VARIABLE: Flow rate of oil (gpm) Oil Stock Level Indicator Oil Feed to next process
- 13. BASIC MODEL OFA PROCESSBASIC MODEL OF A PROCESS The process is maintained at the desired point (SP) by changing the FCE based on the value of the PV Manipulated Variable Desired Result Control Agent PROCESS (Temperature, pressure, level, flow) FINAL CONTROL ELELMENT (valve) Measuring Means (transmitter) Process Variable (PV) Controlled Variable Actuating Input pH, conductivity, humidity, density, consistency, etc. Process equilibrium (balance) is when the input energy maintains the output at a constant “desired” point.
- 14. BASIC MODEL OFA PROCESSBASIC MODEL OF A PROCESS The measuring means provides the standardized signal that represents the condition of the process, i.e. is the process at the desired point? Manipulated Variable Desired Result Control Agent PROCESS (Temperature, pressure, level, flow) FINAL CONTROL ELELMENT (valve) Measuring Means (transmitter) Process Variable (PV) Controlled Variable Actuating Input pH, conductivity, humidity, density, consistency, etc. Manipulated Variable Control Agent PROCESS (Temperature, pressure, level, flow) FINAL CONTROL ELELMENT (valve) Measuring Means (transmitter)Actuating Input pH, conductivity, humidity, density, consistency, etc.
- 15. MEASURING MEANS Pressure Level Flow Temperature pH Humidity Density Speed Thermocouples RTDs /Thermistors Filled Systems Bi-metallic Strain gauge Piezo-electric Capacitance Bourdon Tube Head meters (orifice, venturi) Coriolis, velocity, Mass, Mechanical Floats Guided Wave Weight (load cell) Ultrasonic Differential Pressure Transmitters Pressure Transmitter Level Transmitter Differential Pressure Cell Flow Transmitter Temperature Transmitter Pneumatic 3-15 PSI Electrical Current 4 – 20 mA 0 – 20 mA 10 – 50 mA Voltage 0 – 5 V 1 – 5 V 0 – 10 V Digital ON/OFF Field Bus ModBus ProfiBus HART
- 16. OPEN LOOP CONTROLOPENLOOP CONTROL Open loop (or manual control) is used when very little change occurs in the Process Variable (PV) Manipulated Variable Desired Result Control Agent PROCESS (Temperature, pressure, level, flow) FINAL CONTROL ELELMENT (valve) Measuring Means (transmitter) Process Variable (PV) Controlled Variable Actuating Input pH, conductivity, humidity, density, consistency, etc. Corrective action is provided by manual feedback
- 17. CLOSED LOOP CONTROLCLOSEDLOOP CONTROL Closed loop or feedback control provides a corrective action based on the deviation between the PV and the SP Automatic Controller Output (3-15 psi, 4-20mA etc) CONTROLLING MEANS Manipulated Variable Desired Result Control Agent PROCESS (Temperature, pressure, level, flow) FINAL CONTROL ELELMENT (valve) Measuring Means (transmitter) Controller Input (PV) (3-15psi, 4-20mA etc) Controlled Variable pH, conductivity, humidity, density, consistency, etc. Manual SP
- 18. CONTROLLING MEANSCONTROLLING MEANS Controllersprovide the required control action to position the FCE at a point necessary to maintain the PV at the desired SP. •PID (single loop feedback controller) •DCS (distributed controllers) •PLC (programmable logic controllers)
- 19. SINGLE LOOP FEEDBACKCONTROLSINGLE LOOP FEEDBACK CONTROL 1. Measuring Means 2. Controlling Means 3. Final Control Element 4. Temperature Process Temperature Controller and Recorder Sensing Bulb Temperature Transmitter Pneumatic Control Valve Heat Exchanger Steam 2 3 4 1 The TT provides the signal (PV) that represents the condition of the process being controlled. The TIC compares the PV to the SP and opens and closes the FCE to maintain the process at equilibrium.
- 20. SUMMARYSUMMARY • Process automationmakes use of instrumentation to maintain the process at some desired condition. • Common instrumentation used in a process loop are the measuring means (usually transmitters), the controlling means (usually a PID controller), and the Final Control Element (usually some type of valve) • The measuring means provides the feedback signal (PV) used in the process loop. The controlling means operates the FCE based on the difference between the PV and the SP. • Process equilibrium is maintained when the difference between the PV and SP is zero or constant (offset?)
Editor's Notes
- #4 ISA – Instrumentation, Systems, and Automation Societywww.isa.org ISA – Toronto Sectionwww.isatoronto.org HART Communication Foundationwww.hartcomm.org American Society for Testing and Materials www.astm.org Canadian Environment Industry Associationwww.ceia-acie.ca Measurement, Control & Automation Associationwww.measure.org Canadian Process Control Associationwww.cpca-assoc.com Fieldbus Foundationwww.fieldbus.org Ontario Pollution Control Equipment Associationwww.opcea.com Canadian Centre for Occupational Health and Safety www.ccohs.ca Canadian Fluid Power Association (CFPA) www.cfpa.ca Industrial Accident Prevention Association (IAPA) www.iapa.ca Industry Canada www.ic.gc.ca Institute of Electrical and Electronic Engineerswww.ieee.org American Society of Mechanical Engineerswww.asme.org Water Environment Association of Ontario (WEAO)www.weao.org Water Environment Federation (WEF)www.wef.org Ontario Water Works Association (OWWA) www.owwa.com Consulting Engineers of Ontariowww.ceo.on.ca American Institute of Chemical Engineers (AIChE)www.aiche.org Air & Waste Management Association www.awma.org Canadian Society of Civil Engineerswww.csce.ca Canadian Consulting Engineers of Ontariowww.ceo.on.ca Canadian Water and Wastewater Associationwww.cwwa.ca Municipal Electric Association (Ontario)www.mea.on.ca Ontario Society of Professional Engineerswww.ospe.on.ca
- #5 Automation Technology is a term that can be used to describe an industry that makes use of Instrumentation to meet the objectives of its existence i.e. produce a high quality product (or service) in an efficient and profitable manner while maintaining a safe and healthy environment. (Most of the time) Make more as cheap as you can Make it better than the other guy Make sure we don’t void our liability insurance The field of Automation Technology is wide and diverse and comes in many different flavours, but the main ingredient remains the same – Instrumentation.
- #10 The control objective is to maintain the temperature of a water bath at a constant temperature (e.g. 85 ‘F +/- 1 degree). A steam heating element will be used to supply the required heat energy to maintain the bath at the desired temperature. By opening and closing the control valve the amount of steam flowing through the heating element will determine the temperature of the water bath. (i.e. opening the valve increases the bath temperature)
- #11 Terminology used to describe the process: PROCESS: Temperature CONTROLLED VARIABLE: Temperature of the water in degrees F. CONTROL POINT: The desired temperature of the process 85’ F (Set Point) MEASURING MEANS: Stem thermometer indicates the desired result process CONTROL AGENT: Steam is applied to maintain the process temperature at SP MANIPULATED VARIABLE: Flow rate of steam. (lbs/hr)
- #14 The basic model of a “process” can be applied to most measurement and control applications used in Automation Technology. The major components are the Final Control Element, the actual Process that is being controlled and the Measuring Means. The loop is completed when the Controlling Means (not shown here) is added, this can be done manually (open loop control) or via some controlling device (closed loop control or automatic control or process control). The Final Control Element is defined as “the device that directly controls the manipulated variable of a control loop”, the most common type being the control valve (pneumatic, electric, solenoid). However there are many other devices that fit the definition of a FCE and may include things such as relays or switches, and variable speed drives, mixers, motors or pumps.
- #15 The Measuring Means is that portion of the control loop that measures the controlled variable and provides the necessary information required to determine if the process is at its desired condition. The measuring means can consist of one standalone field device or it can be made up of several individual components depending on what type of controlled variable is being measured. The output is then conditioned and standardized to either a pneumatic or electrical (analog/digital) signal that represents the condition of the process. The output is also referred to as the Process Variable (PV) and the device is often called a transmitter, (e.g. temperature transmitter, pressure transmitter)
- #20 1) Measuring Means: The Controlled Variable (temperature) is measured using a pneumatic Filled Thermal System Temperature Transmitter that converts the temperature into a pneumatic signal and sent to the controller. 2) Controlling Means: The Pneumatic Controller will compare the signal sent by the temperature transmitter and compare it to the desired temperature as determined by its setpoint adjustment. The controller will then provide a pneumatic output that will be a function the difference between the setpoint and the actual value of the process temperature. 3) Final Control Element: The Pneumatic Control Valve will open and close in proportion to the signal received from the controller thereby changing how much of the Control Agent (steam) is required to maintain the water at the desired temperature. 4) Temperature Process Feedback Loop: The loop is complete. Any deviation between the desired temperature (setpoint) and the actual process temperature (controlled variable) will result in an error signal and the self-correcting action of the loop will continue until the error signal is zero or the process has reached equilibrium. However the stability of the loop can only be achieved when the various loop parameters such as the control mode and tuning parameters are properly set.