2. Objectives for this session
Learning the fundamentals of industrial
instrumentation
• Terminology, Symbols and Standards
• Measuring Means
• Pressure, Temperature, Level, Flow
• Controlling Means
• Simple Closed Loop Control
• PID Loop tuning
3. What is it?
Definitions of Instrumentation :
• An electrical or pneumatic device
placed in the field to provide
measurement and/or control
capabilities for the system.
• ISA Definition: A collection of
instruments or their application for the
purpose of observation, measurement
and control.
4. Scope of Instrumentation
1. Information Technology
2. Electronics and Communication Engineering
3. Computer Engineering
4. Aerospace / Avionics
5. Marine Sciences / Marine Biology
6. Metrology
7. Automation (Mechanical and process)
8. Analytical
9. Bio – medical
10. Cryogenics
11. Nuclear Instrumentation
12. Power Instrumentation
5. Definition of terms:
• Instrument are used to monitor a process
and to make adjustment to the process to get
the desired output.
• Process Control is a techniques of balancing
supply and demand over a period of time at
a pre – determined level of operation called
Set Point (SP)
• Process is a physical or chemical change of
matter or conversion of energy.
• Controlled variable is the process
parameters we wish to control at some
desired level (Temperature, Pressure, Flow
and Level)
6. Definition of terms:
• Measured Variable (PV)used to represent the
actual condition of controlled variables.
• Set-point represent the desired value of the
controlled variable.
• Manipulated variable is a variable adjusted to
cause a change in the controlled variable
bringing it back to the set-point.
• Error signal difference between set point and
measured variable (e=PV-SP)
7. Automation 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.
8. Signal Transmission
• Transmitter is a device that changes the value of
measured variable to a standard signal that can be
easily sent to other instrument or devices. Is used to
extend the distance between sensing element and the
display.
• Signal Conditioning is a processing of transducer
signal from the point of measurement to the set point
of display.
• Converter / Transducer is the system component that
convert a signal into another kind of signal.
9. Signal Transmission
Type of Signal
1. Electrical Signal – The value of current or voltage
represent the value of the measured variable. (4-20 mA /
1-5 Vdc)
2. Pneumatic Signal – The value of the air or gas pressure
represent the value of the measured variable. (3-15 psig)
3. Hydraulic Signal – The value of the fluid pressure
represent the value of the measured variable.
10. Measurement
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.
11. Controllers
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)
12.
13. Control Elements
These are the devices the controller operates:
• Pneumatic valves, solenoid valves, rotary valves,
motors, switches, relays, variable frequency drives.
14. Overview 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
15. Basic 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.
16. Basic 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.
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)
17. 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
18. Open 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
19. Closed 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
20. Controlling 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)
21. Single 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.
23. Accuracy
Data points with
low accuracy
high accuracy
value
true
value
measured
value
true
accuracy
Accuracy: closeness with which an
instrument reading approaches the
true or accepted value of the variable
(quantity) being measured. It is
considered to be an indicator of the
total error in the measurement without
looking into the sources of errors.
Accuracy is often expressed in percentage
24. Precision Data points with
low precision
high precision
1. A measure of the reproducibility
of the measurements; i.e., given a
fixed value of a variable,
precision is a measure of the
degree to which successive
measurements differ from one
another.
2. Number of distinguishable
alternatives. 2.434 V is more
precise than 2.43 V.
25. Resolution
• The smallest change in measured value to which the
instrument will respond.
Statistical control: random variations
in measured quantities are tolerable,
Coulter counter example
26. Tolerance
• Maximum deviation allowed from the conventional
true value.
• It is not possible to built a perfect system or make an
exact measurement. All devices deviate from their
ideal (design) characteristics and all measurements
include uncertainties (doubts).
• Hence, all devices include tolerances in their
specifications. If the instrument is used for high-
precision applications, the design tolerances must
be small.
• However, if a low degree of accuracy is acceptable,
it is not economical to use expensive sensors and
precise sensing components
28. Static sensitivity constant over a limited
range
2
2
)
(
)
)(
(
d
d
d
d
x
x
n
y
x
y
x
n
m
2
2
2
)
(
)
)(
(
)
)(
(
d
d
d
d
d
x
x
n
x
y
x
x
y
b
30. Linearity
Dr. Bahauddin Karagozuglu 30
Output
Input
Output
Input
A linear system fits the equation y
= mx + b.
A nonlinear system does not fit a
straight line
31. Calibration for linearity
Dr. Bahauddin Karagozuglu 31
Output
Input
Output
Input
The one-point calibration may miss
nonlinearity
The two-point calibration may also miss
nonlinearity
Measuring instruments should be calibrated against a
standard that has an accuracy 3 to 10 times better
than the desired calibration accuracy
34. Input ranges
Time
Amplitude
5 mV
-5 mV
Dynamic
Range
Time
Amplitude
1 V
-1 V
An input signal which
exceeds the dynamic
range
The resulting amplified signal is
saturated at 1 V
35. Input impedance
System
Xd1 : effort
variable
Xd2 : flow
variable
iable
flow
iable
effort
X
X
Z
d
d
x
var
var
2
1
2
2
2
1
2
1 d
x
x
d
d
d X
Z
Z
X
X
X
P
Output
36. Summary
• 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?)
