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.

1. Lar Rochain Arlante
Jemar Palermo
INSTRUMENTATIONINSTRUMENTATION

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?)