2. 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.
3. RESOURCESRESOURCES
Text 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
4. AUTOMATION TECHNOLOGYAUTOMATION TECHNOLOGY
Instrumentation 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.
5. 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.
6. CONTROLLERSCONTROLLERS
These 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)
7. CONTROL ELEMENTSCONTROL ELEMENTS
These are the devices the controller operates:
• Pneumatic valves, solenoid valves, rotary
valves, motors, switches, relays, variable
frequency drives.
8. 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.”
PROCESS
Some Quality or
Quantity
of the
Material or Energy
Input
Energy
or
Material
Desired
Result
9. EXAMPLE OF A TEMPERATURE 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 TERMINOLOGYTEMPERATURE PROCESS 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
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.
12. 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
13. BASIC MODEL OF A 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 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
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 CONTROLOPEN LOOP 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 CONTROLCLOSED LOOP 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
Controllers 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)
19. SINGLE LOOP FEEDBACK CONTROLSINGLE 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 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?)
Hinweis der Redaktion
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
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.
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)
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)
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.
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)
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.