By
K.NAGAVEERENDER,AE/CETD
What is Instrumentation?
 It is the collective term for Measuring Instruments.
 It is the study of Measuring Instruments which are
used for indicating certain parameters .
 It is the “ART and SCIENCE’’ of measurement of
Process variables in industry and its Control.
Why Instrumentation is needed?
 Economic Operation of plant.
 Efficient Operation of plant.
 Safe operation of plant.
 Pollution Control.
Why C& I ?
Without automatic controllers, all regulation
tasks will have to be done manually. For
example: To keep constant the temperature
of water discharged from an industrial gasfired heater, an operator has to watch a
temperature gauge and adjust a gas control
valve accordingly (Figure 1). If the water
temperature becomes too high, the operator
has to close the gas control valve a bit - just
enough to bring the temperature back to
the desired value.
If the water becomes too cold, he has to
open the valve
To relieve our operator from the tedious task of
manual control, we automate the controls - i.e. we
install a PID controller (Figure 2). The controller
has a Set Point (SP) that the operator can adjust to
the desired temperature. We also have to automate
the control valve by installing an actuator (and
perhaps a positioner) so that the Controller's
Output (CO) can change the valve's position. And
finally, we'll provide the controller with an
indication of the temperature or Process Variable
(PV) by installing a temperature transmitter. The
PV and CO are mostly transmitted via 4 - 20mA
signals . So, when everything is up and running, our
PID controller compares the process variable to its
set point and then calculates the difference
between the two signals, also called the Error (E).
Then, based on the error, a few adjustable settings
and its internal structure (described next), the
controller calculates an output that positions the
control valve.
Decides
Controller/
Receiving element
Senses
Influences
Measuring
Device/element
Final control
device/element
Reacts
The Process
Process:
Furnace
Separator
Boiler
Measuring element:
Sensor
Transmitter
Transducer
Receiving element:
Indicators
Recorders
Controller
Alarm units
Final Control element:
Control Valves
Dampers
Drives
MEASUREMENT DONE IN POWER
PLANT
Process measurements :
Pressure, Temperature,
Flow and Level.
Analytical measurements
(SWAS) : pH,
Conductivity, Silica,
Hydrazine and Dissolved
Oxygen.
• Condition monitoring
measurements for
rotating equipment :
Vibration, speed, bearing
temperatures,
eccentricity, axial shift,
displacement.
• Emission monitoring
(CEMS): CO, SOx, NOx
• Environmental
measurements : Wind
velocity, Ambient
temperature, Humidity,
Rainfall etc.
MEASUREMENT PARAMETER
• Indication of the parameter can be either LOCAL or
REMOTE
• LOCAL means indication of
the parameter at the field by
a dial type gauge, liquid level
gauge or flow glass.
• REMOTE means that the
primary signal is converted
to an electrical analog signal
and transmitted to the
control room for indication /
control.
CONTROL SYSTEM
• A control system is a device or
set of devices to manage,
command, direct or regulate the
behavior of other devices or
systems.
• There are two common classes of
control systems, with many
variations and combinations:
logic or sequential control and
feedback or linear controls.
There is also fuzzy logic, which
attempts to combine some of the
design simplicity of logic with the
utility of linear control.
Why DCS?
•
•
•
•
•
•
•
•
•
•
•
High Reliability
Improved Response Time
Improved Interface to plant
Improved accessibility of plant
data to engineering and
management personnel.
Historical Storage and Retrieval
System
Safe operation of Plant
Lowest Cost of Generation
Longest Equipment Life
Minimum Environmental Effect
Maximum Efficiency
Energy Conversation
DCS IN POWER PLANT
• The control system is
responsible for
controlling action of all
the measurement.
• In power plant this DCS
(Distributed Control
System ) plays the role
of this control system.
• All interlocking,
monitoring and
annunciation operations
are performed in DCS.
Large Video Screen (Optional)
Remote maxVUE
(Optional)
NETWORK PRINT
:
Operator
Station # 1
Operator
Station # 2
Peformance
Operator
Station # n Calcs. Station
ENGG.
STATION
maxSTORIAN
STATION
…
…
CD R/W
UNIT CONTROL DESK
(minimum/trip related)
ETHERNET SWITCH
PB STN (TRIP).
maxLINKS
maxNET
RPUs (I/O + DPU + Network Components)
ETHERNET SWITCH
RPU
DPU
I/O Modules
RPU
RPU
DPU
DPU
I/O Modules
I/O Modules
…
FG # Turbine
…
RPU
RPU
DPU
DPU
I/O Modules
I/O Modules
FG # Boiler
LOCAL JB
DPU
I/O Modules
I/O Modules
FG # STN. C&I +ELECT.
LOCAL JB
+
CONTACT
INPUTS
DPU
…
CJC BOX
LOCAL JB
RR
RPU
RPU
RPU
…
DPU
I/O Modules
SWITCH YARD SCAD
LOCAL JB
~
E
-
ANALOG
(4-20mA)
T/Cs
RTDs
P
POWER
AMP.
MOTORISED
VALVES/
DAMPERS
MOTORS
PUMPS/
BREAKERS
DCS HARDWARE
Controller card
Input Cards (4-20 m A)
Thermocouple, RTD, SOE
Output Cards(4-20 m A,
Digital)
 Power Supply Module
 Communication Card Cables
• Controller with I/O card
•
•


OPERATOR WORK STATION
Alarm Monitoring
Mimic Or Graphic Display
Trend Display
Operator Guidance Display
System and Diagnostic
Display
Control
Bar Chart
Sequence Display
Fault Analysis Display

Pressure
Pressure is the force exerted per unit area
Pressure is the action of one force against another force. Pressure is force applied
to, or distributed over, a surface. The pressure P of a force F
distributed
over an area A is defined as P = F/A
GAUGE
COMPOUND
ABSOLUTE
BAROMETRIC RANGE
ATMOSPHERIC PRESSURE
NOM. 14.7 PSIA
PRESSURE
TOTAL VACUUM - 0 PSIA
PRESSURE GAUGES:
 A Pressure Gauge is used for measuring the pressure
of a gas or liquid.
 A Vacuum Gauge is used to measure the pressure in a
vacuum.
 A Compound Gauge is used for measuring both
Vacuum and Pressure.
 Pressure Gauges are used for Indication only.
Measuring Principle
 Bourdon tube measuring element is made of a thin-walled C-shape
tube or spirally wound helical or coiled tube. When pressure is
applied to the measuring system through the pressure port (socket),
the pressure causes the Bourdon tube to straighten itself, thus
causing the tip to move. The motion of the tip is transmitted via the
link to the movement which converts the linear motion of the bourdon
tube to a rotational motion that in turn causes the pointer to indicate
the measured pressure.
Helical Bourdon
“C” Type Bourdon
Coiled Bourdon
Diaphragms
Bellows:
 Snubber
Used for dampening and filtering and reducing the damaging
effects of pulsation on a gauge. The snubber has a metal
Disc available in standard grades of porosity.
 Siphon Tubes
Used to dissipate heat by trapping condensed liquid to
keep high temperature steam or condensing vapor from
damaging the pressure gauge.
PIG TAIL
COIL PIPE
Electrical Pressure Sensors
 1. Potentiometer Sensor
 2. Inductive
 3. Capacitive
 4. Piezoelectric
 5. Strain Gauge
Usually generate output signals in the mV range (spans
of 100 mV to 250mV). In transmitters, these are
amplified to the voltage level (1to 5 V) and converted to
current loops, usually 4-20 mA dc
Pressure Switch
A pressure switch turns an electric circuit on or off at a
preset pressure.This pressure is referred to as the
setpoint of the switch. A bourdon tube,a diaphragm,
or a bellows can actuate the switch
Deadband is the difference between the value at which
a control action occurs and the value at which at which
the control action is cancelled.
Pressure Switches
Applications
 Alarm (Status)
 Shutdown (Hi/Lo Limits)
 Control (ON/OFF)
A “switch” is an instrument that automatically senses
some process variable
(such as pressure) and provides an on/off signal relative
to some reference point.
Pressure Transmitter
A Pressure Transmitter is used where
indication and/or record of pressure is
required at a location not adjacent to the
primary element.
A Pressure Transmitter is used for both
indication and control of a process.
A Pressure Transmitter is used where overall
high performance is mandatory.
Both Electronic and Pneumatic Transmitters
are used.
These can be either Gauge, Absolute or
Differential Pressure Transmitters.
Pressure Transmitter
Pressure Regulator
Temperature:
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°C – degrees Celsius (or Centigrade)
°F – degrees Fahrenheit
K – Kelvin
R – Rankine
Relationship between different units
 °C = (°F - 32)/1.8
 °F = 1.8 x °C + 32
 K = °C + 273.15
 R = °F + 459.67
Conversion tables or software can be utilized to facilitate
with converting between these units.
Types of Temperature Instruments:
 Thermocouple (T/C)
 Resistance Temperature Detector (RTD)
 Thermowell
 Thermistor
 Bi-metallic Thermometers
 Filled Thermal Systems
RTD’s:
RTDs (Resistance Temperature Detectors) operate under the principle that the
electrical resistance of certain metals increases and decreases in a repeatable and
predictable manner with a temperature change.
Wire Wound Element
Precise lengths of wire are wrapped around a
ceramic mandrel, then inserted inside a ceramic
shell which acts to support and protect the wire
windings.
Inner Coil Element
Wires are coiled then slid into the holes
of a ceramic insulator. Some
manufacturers backfill the bores with
ceramic powder after the coils are
inserted. This keeps the coils from
shorting against each other.
Thin Film Element
Metallic ink is deposited onto a ceramic substrate.
Lasers then etch the ink to provide a resistance
path. The entire assembly is encapsulated in
ceramic to support and protect.
Thermocouple measuring circuit
Equivalent to
80ºC reading
Iron (Fe)
100ºC
Hot Junction:
Copper (Cu)
Constantan (CuNi)
10
0
20ºC
mV
Copper (Cu)
In Process
Cold Junction:
Needs to be held constant to give a
fixed reference. ( early methods
held cold junction at 0ºC using ice
or refrigeration unit).
• Thermistors are temperature sensing devices that
are similar to RTD’s in that their resistance changes
as temperature changes.
• The major difference is that for most thermistors the
resistance decreases as temperature increases.
• Thermistors are an inexpensive alternative to RTD’s
when temperature ranges are below 150°C.
Thermistors can be used from temperatures of –80°C
to 300°C.
A Bimetallic Thermometer consists of an
indicating or recording device, a sensing
element and a means for connecting the two.
Thermowell
Flow
 Flow is measured as a quantity (either volume or
mass) per unit time
 Volumetric units
 Liquid

gpm, bbl/day, m3/hr, liters/min, etc.
 Gas or Vapor

ft3/hr, m3/hr, etc.
 Mass units (either liquid, gas or vapor)

lb/hr, kg/hr, etc.
 Flow can be measured in accumulated (totalized)
total amounts for a time period
 gallons, liters, meters passed in a day, etc.
Flow Measurement
COMMONLY USED FLOW DEVICES
Differential Pressure (Head) Type
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Orifice Plate - Concentric, Eccentric, Segmental, Quadrant Edge, Integral, Conditioning
Venturi Tube
Flow Nozzles
Elbow
Pitot Tube, Averaging Pitot Tube (Annubar)
Variable Area (Rotameter)
Wedge Meter
V-Cone
Mass Type – measures the mass flow rate directly.
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Coriolis
Thermal
Velocity Type
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Magnetic
Ultrasonic - Transit Time, Doppler
Turbine
Vortex
Open Channel Type
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Weir
Parshall Flume
Other Types
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Positive Displacement
Target
 Flow meters can further classified into four types:
 • Volumetric flow meters that measure volume
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directly
Positive displacement meters
• Velocity
Magnetic, turbine and ultrasonic
• Inferential flow meters
Differential pressure, target, and variable area flow meters
• Mass flow meters that measure mass directly
Coriolis
Level Instrumentation
Concepts – Measurement Types
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Level Gauges
Radar
Differential Pressure
Float / Displacer
Ultrasonic
Capacitance
Nuclear
Other
Level Measurement
Measures Hydrostatic Head of
Liquid in a Vessel
Liquid Height Multiplied by a
Density
Hydrastep
The purpose of a float level switch
is to open or close a circuit as the
level of a liquid rises or falls.
Oxygen Analyser:
 Principle of Measurement
Zirconia oxygen analyzers determine oxygen concentration using the
conductivity of a zirconia ceramic cell. Zirconia ceramic cells only allow oxygen
ions to pass through at high temperatures. With reference gas on one side and
sample gas on the other, oxygen ions move from the side with the highest
concentration of oxygen to that with the lowest concentration. The movement
of ions generates an EMF (Electro Motive Force) which can be measured to
determine the oxygen content.
Turbo supervisory Parameters:
 Eccentricity
 Vibrations
 Differential Expansion
 Overall Thermal Expansion
 Axial shift
 Turbine speed
SPEED MEASUREMENT
 Tachometer is used for measuring rotational speed
Classification of tachometers:
• Mechanical Tachometers
Revolution counter • Hand speed indicator • Tachoscope •
Centrifugal tachometer • Resonance (vibrating read)
tachometer •
Electrical Tachometers • Eddy current or drag cup
tachometer • Tachogenerator (DC and AC) •
Contactless electrical Tachometers • Magnetic pickup
tachometer • Photo-electric tachometer • Stroboscopebe
Coal
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Usually, in a thermal power plant it is required or most compulsory requirement to measure the flow of coal which is to
be sent into the boiler (Sometimes through pulveriser mill in PC Fired Boiler).
For this we used to weight the coal that is fed in the conveyor belt continuously. to weight the coal we are using belt
weighter - Beltweigher
Usually the weight of the coal has been measured in Raw Coal Feeder (RC Feeder). The Raw Coal feeders are classified
according to the method by which the rate of coal flow is determined
Volumetric Coal Feeder
the rate of coal flow through the feeder is derived as by
R=QxBxN
R - rate of coal flow in Kg/s
Q - vol. of coal delivered by the feeder per rotation in m3/rotation
B - bulk density of coal in m3/kg
N - speed of feeder rotation per second
Q & B - making these two contant
N - adjusting the speed or varying the speed we can able to maintain the required coal flow in it.
2. Gravimetric Feeder
the rate of coal flow is obtained by
R=MxN
R - rate of coal flow in kg/s
M - mass of coal on unit length of feeder belt in kg/m
N - speed of feeder belt in m/s
Electric Actuator
Pneumatic Actuator
Actuator Accessories
Thank You