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Lar Rochain Arlante
Jemar Palermo
INSTRUMENTATIONINSTRUMENTATION
WHAT IS IT?WHAT IS 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.
RESOURCESRESOURCESText Book:
Industrial Control Electronics 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
AUTOMATION TECHNOLOGYAUTOMATION TECHNOLOGYInstrumentation plays 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.
MEASUREMENTMEASUREMENT
Things that are measured 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.
CONTROLLERSCONTROLLERSThese are the devices 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)
CONTROL ELEMENTSCONTROL ELEMENTS
These are the devices the controller operates:
• Pneumatic valves, solenoid valves, rotary valves, motors, switches, relays, variable frequency drives.
OVERVIEW OF PROCESS AUTOMATIONOVERVIEW 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.”
PROCESSSome Quality or
Quantityof the
Material or Energy
Input Energy
or Material
DesiredResult
EXAMPLE OF A TEMPERATURE PROCESSEXAMPLE OF A TEMPERATURE PROCESS
Heating Element
Water BathTemperature
The objective of this process is to maintain a constant water bath temperature.
TEMPERATURE PROCESS TERMINOLOGYTEMPERATURE PROCESS TERMINOLOGY
Heating Element
Water BathTemperature
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)
LEVEL PROCESSLEVEL PROCESS
Oil Stock
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.
TERMINOLOGY USED TO DESCRIBE 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
BASIC MODEL OF A PROCESSBASIC MODEL OF A PROCESSThe process is maintained at the desired point (SP) by
changing the FCE based on the value of the PV
Manipulated Variable
DesiredResult
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.
BASIC MODEL OF A 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
DesiredResult
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.
MEASURING MEANSPressure
Level
Flow
Temperature
pH
Humidity
Density
SpeedThermocouplesRTDs / ThermistorsFilled SystemsBi-metallic
Strain gaugePiezo-electricCapacitanceBourdon Tube
Head meters (orifice, venturi)Coriolis, velocity, Mass,
Mechanical FloatsGuided WaveWeight (load cell)UltrasonicDifferential Pressure
Transmitters
Pressure Transmitter
Level Transmitter
Differential Pressure Cell
Flow Transmitter
Temperature Transmitter
Pneumatic3-15 PSI
Electrical
Current4 – 20 mA0 – 20 mA10 – 50 mA
Voltage
0 – 5 V
1 – 5 V0 – 10 V
DigitalON/OFFField BusModBusProfiBusHART
OPEN LOOP CONTROLOPEN LOOP CONTROL
Open loop (or manual control) is used when very little change occurs in the Process Variable (PV)
Manipulated Variable
DesiredResult
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
CLOSED LOOP CONTROLCLOSED LOOP CONTROLClosed 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)
CONTROLLINGMEANS
Manipulated Variable
DesiredResult
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
CONTROLLING MEANSCONTROLLING MEANSControllers provide 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)
SINGLE LOOP FEEDBACK CONTROLSINGLE LOOP FEEDBACK CONTROL
1. Measuring Means
2. Controlling Means
3. Final Control Element
4. Temperature Process
Temperature Controller and Recorder
SensingBulb
Temperature Transmitter
Pneumatic Control Valve
Heat Exchanger
Steam
2
34
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.
SUMMARYSUMMARY
• Process automation makes 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?)
