WINSEM2020-21 EEE4033 ETH VL2020210501456 Reference Material I 03-Feb-2021 MODULE-I Lecture 1
WINSEM2020-21 EEE4033 ETH VL2020210501456 Reference Material I 03-Feb-2021 MODULE-I Lecture 1
WINSEM2020-21 EEE4033 ETH VL2020210501456 Reference Material I 03-Feb-2021 MODULE-I Lecture 1
INDUSTRIAL INSTRUMENTATION
EEE 4033
LECTURE 1:
PRESSURE MEASUREMENT
Course Instructor:-
Dr. K.V.Lakshmi Narayana,
Sr. Associate Professor
SELECT, VIT, Vellore.
Course Outcomes
On successful completion of this course, the student will be able to
2/5/2021 5
Cement industry Fertilizer industries
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Scope of
instrumentation
Controlling
Measuring • Machine/Factory
automation
• Monitoring • Plant/Process
• Calibration automation
• Data acquisition
Functional Block Diagram of Computer
Control System
Outline of Lecture-1
• Syllabus ( Module-1 to 8)
• Fundamentals of Measurement Systems
• Pressure Measurement--- Significance, Types, Units and so on
• Elastic type pressure gauges
• Electric Methods: Elastic elements with LVDT,
Strain gauge, capacitive techniques…
• Piezoresistive pressure sensor
• Resonator Pressure sensor
Dr.K.V.L.Narayana
Industrial Instrumentation: Module-1
• Pressure Measurement:
Elastic type pressure gauges – Bourdon tubes,
bellows, diaphragms;
Electrical methods – elastic elements with
LVDT and strain gauges –capacitive type
pressure gauge – piezoresistive pressure sensor
–resonator pressure sensor ;
Measurement of vacuum – McLeod gauge –
pirani gauge - thermal conductivity gauges –
Ionization gauge, cold cathode and hot cathode
types. Dr.K.V.L.Narayana
Industrial Instrumentation: Module-2
• Flow Measurements:
• Pressure gradient techniques, Positive
displacement flow meters, turbine flow meter;
Rotameter: Design– Coriolis mass flow meters –
thermal mass flow meter – volume flow meter;
• Electrical type flow meter: Electromagnetic flow
meter, different types of ultrasonic flow meters –
laser doppler anemometer systems; vortex
shedding flow meter – target flow meter – solid
flow rate measurement.
Dr.K.V.L.Narayana
Industrial Instrumentation: Module-3
• Temperature, Measurements:
RTDs and Thermistor characteristics;
Thermocouples-Laws, Principles, cold junction
compensation;
Radiation methods of temperature measurement
total and selective radiation pyrometers –optical
pyrometer;
Thermal conductivity measurements-liquids and
gases.
Dr.K.V.L.Narayana
Industrial Instrumentation: Module-4
• Level Measurements:
• Gauge glass technique coupled with photo
electric readout system; float type level indication
– different schemes – level switches level
measurement using displacer and torque tube –
bubbler system;
• differential pressure method;
• electrical types of level gauges using resistance,
capacitance.
• nuclear radiation and ultrasonic sensors.
Dr.K.V.L.Narayana
Industrial Instrumentation: Module-5
Dr.K.V.L.Narayana
Industrial Instrumentation: Module-6
• Speed measurement:
Revolution counter – Capacitive tacho-drag cup
type tacho – D.C and A.C tacho generators –
Stroboscope.
Dr.K.V.L.Narayana
Industrial Instrumentation: Module-7
• Vibration Measurement:
• Nature of vibrations – Seismic transducer – Types of
accelerometers – Potentiometric type – LVDT
Accelerometer – Piezo electric type.
Dr.K.V.L.Narayana
Dr.K.V.L.Narayana
Introduction to Measurement Systems
Definitions
• Measurement
– It is basically an act or result of comparison between
the quantity (whose quantity is unknown) and a
predefined standard.
(or)
– The process of converting physical parameters to
meaningful numbers.
• Instrumentation
– The technology of using instruments to measure and
control the physical and chemical properties of the
materials.
Dr.K.V.L.Narayana
Introduction to Measurement Systems
• There are two basic requirements in order to have meaningful
results of the measurand.
Dr.K.V.L.Narayana
Significance of Measurement Cont..
• The measurement is essential in all the disciplines
for the following major functions
1. Design of equipment and processes.
2. Proper operation and maintenance of equipment and processes.
• Significance of Instrumentation
1. To acquire data or information (hence data acquisition) about
parameters, in terms of:
– putting the numerical values to the physical quantities
– making measurements otherwise inaccessible.
– producing data agreeable to analysis (mostly in electrical form)
Dr.K.V.L.Narayana
4. Data Processing Element:
Data processing element is an important element used in many measurement
systems. It processes the data signal received from the variable manipulation
element and produces suitable output.
Data processing element may also be used to compare the measured value
with a standard value to produce required output.
5. Data Transmission System:
Data Transmission System is simply used for transmitting data from one
element to another. It acts as a communication link between different
elements of the measurement system. Some of the data transmission elements
used are cables, wireless antennae, transducers, telemetry systems etc.
6. Data Presentation Element:
It is used to present the measured physical quantity in a human readable form
to the observer. It receives processed signal from data processing element and
presents the data in a human readable form. LED displays are most
commonly used as data presentation elements in many measurement systems.
Dr.K.V.L.Narayana
Dr.K.V.L.Narayana
1. Analog Displays: Pointer–scale indicators
Pointer–scale indicators
• Simplified diagram for a moving coil indicator connected to a
Thevenin signal source ETh, RTh is shown in figure.
• The coil is situated in a radial magnetic field of flux density B, so
that a current i through the coil produces a deflecting torque. This
deflecting torque is opposed by the restoring torque of control
springs attached to the movable coil.
• When the torques are balanced the moving coil will stopped.
According to the fundamental law of electromagnetic force, the
coil will rotate in the magnetic field when it carries an electric
current by electromagnetic (EM) torque effect.
• A pointer which is attached to the movable coil will deflect
according to the amount of current to be measured which applied
to the coil. Its angular deflection represents the amount of
electrical current to be measured. If the permanent magnet field is
uniform and the spring is linear, then the pointer deflection is also
linear.
2. Digital Displays: Data Presentation Elements
• There are four types of digital display technology in wide
current use: light emitting diodes (LED), cathode ray tubes
(CRT), liquid crystal displays (LCD) and electroluminescent
displays (EL).
• LEDs have high power consumption, which makes them only
suitable for small-scale character displays; they are not used
in graphic displays.
• CRTs are used for character and graphics displays,
monochrome and colour, but have the disadvantage of high
operating voltages and are high-volume bulky devices.
• LCDs are used for both character and graphics displays. LCD
character displays, usually monochrome, have much lower
power consumption than equivalent LED displays.
Dr.K.V.L.Narayana
Data Presentation Elements
• Electroluminescent displays are also flat screen and are used for
both character and graphics monochrome displays. They have higher
operating voltages and power consumption than equivalent LCD
devices but greater contrast ratio and viewing angle.
• Chart recorders give a record, on paper, of the time variation of a
measured variable; these can be analogue or digital and the record
can be either a continuous line or a series of dots. They can record
up to six variables but have limited speed of response; they also
require regular replacement of paper and pens.
• Paperless recorders use LCD displays and digital archive memory;
these typically can record four measured variables and have less
maintenance requirements than chart recorders. They also have a
fast speed of response.
• Laser printers can print large amounts of data, in character or
graphics form, on paper. A laser printer is used where large tables of
numerical data need to be printed out for checking and calculation.
Dr.K.V.L.Narayana
Various components of elements
Dr.K.V.L.Narayana
Example 1: Bourdon Pressure Gauge
Dr.K.V.L.Narayana
Example: Bourdon Pressure Gauge
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Example 2: Pressure Transmitter with voltage output
Dr.K.V.L.Narayana
Pressure Measurement
Dr.K.V.L.Narayana
The Importance of Pressure Measurement
• Across various industries, measuring the pressure of a substance is an
important part of the manufacturing process. Obtaining accurate and
meaningful data is important in determining the quality and consistency
of the product. For these reasons, accurate sensors are absolutely
critical in obtaining this information. Each sensor takes the physical
pressure of the element and transfers it into electrical energy of some
kind that can be measured.
• Accurately measuring liquid, gas, and steam pressure is a basic
requirement for many industrial processes to operate safely, efficiently,
and with optimum quality control.
• In addition to directly measuring pressure values, pressure
measurements can be used to determine or infer flow rates, fluid levels,
product density, and other parameters. As a result, many plants rely on
pressure-measurement devices to get required field measurements.
Dr.K.V.L.Narayana
Pressure Measurement
• Gramercy Works Alumina Plant
Explosion July 5, 1999 St. James
• Why is it important? Parrish Louisiana
• Reason: Turned off pressure
devices
What is pressure?
Pressure is the force per unit area that a liquid or gas
exerts on its surroundings, such as the force or pressure
of the atmosphere on the surface of the Earth, and the
force that liquids exert on the bottom and walls of a
container.
• Many industrial processes operate at pressures that are
referenced to atmospheric pressure, and are known as
gauge pressures. Other processes operate at pressures
referenced to a vacuum, or can be referred to as
negative gauge pressure. Atmospheric pressure is not a
fixed value, but depends on factors such as humidity,
height above sea level, temperature, and so forth.
Dr.K.V.L.Narayana
Overview
Pressure (P ) expresses the magnitude of normal force (F-N) per unit area (A-
m2) applied on a surface
F F
P or P
A A
Pressure units are a measure of force acting over unit area. It is
most commonly expressed in pounds per square inch (psi) or
sometimes pounds per square foot (psf) in English units; or Pascals
(Pa) in metric units, which is the force in Newtons per square meter
(N/m2).
Units: Pa(= N/m2), psi(=lbf/in2), bar (=105 Pa=100 kPa), mbar (=100 Pa=1 hPa),
atm (=101.3 kPa), mmHg (or Torr), inHg, etc.
Note: For every Unit: hUnit=hectoUnit=100 Unit
Dr.K.V.L.Narayana
Gauge pressure is the pressure measured with respect to
atmospheric pressure, and is normally expressed in psig
or kPa(g).
Vacuum is a pressure between total vacuum and normal
atmospheric pressure. Pressures less than atmospheric
pressure are often referred to as “negative gauge,” and
indicated by an amount below atmospheric pressure. As
an example, −5 psig corresponds to 9.7 psia.
Differential pressure is the pressure measured with
respect to another pressure, and is expressed as the
difference between the two values. This represents two
points in a pressure or flow system, and is referred to as
the “delta p,” or Δp. Dr.K.V.L.Narayana
Figure 7.1 shows graphically the relation between
atmospheric, gauge, and absolute pressures
Dr.K.V.L.Narayana
Relationship between absolute and gauge pressures
Pabs=Pgauge+Patm
Forms of pressure
Dr.K.V.L.Narayana
Pressure Measuring Instruments
• Several instruments are available for pressure
measurement, these instruments can be divided
into pressure measuring devices and vacuum
measuring devices.
• Gauges are a major group of sensors that
measure pressure with respect to atmospheric
pressure. Gauge sensors are usually devices that
change their shape when pressure is applied.
These devices include diaphragms, capsules,
bellows, and Bourdon tubes.
Dr.K.V.L.Narayana
Types of Measurement
• Mechanical Pressure transducers
– U-tube manometer, Bourdon tube, Diaphragm
and Bellows
• Electrical Pressure transducers
– Elastic elements + Strain Gauge, Capacitive sensor,
Potentiometric, Resonant Wire, Piezoelectric,
Magnetic, Optical
Mechanical Pressure Transducers
• Mechanical pressure measurement devices are
large and cumbersome.
• Not suited for automated control loops typical in
industry.
• Mechanical devices:
– U-tube Manometer
– Bourdon tube
– Diaphragm and Bellows element
Elastic type Pressure gauges: 1) Diaphragms
• Diaphragm consists of a thin layer or film of a
material supported on a rigid frame, as shown in
Figure (a).
• Pressure can be applied to one side of the film for
gauge sensing, with the other inlet port being left
open to the atmosphere.
• Pressures can be applied to both sides of the film for
differential sensing, and absolute pressure sensing can
be achieved by having a partial vacuum on one side of
the diaphragm.
• A wide range of materials can be used for the sensing
film: rubber or plastic for low pressures, silicon for
medium pressures, and stainless steel for high
pressures.
Dr.K.V.L.Narayana
Elastic type Pressure gauges: 1) Diaphragms
a) Capacitive type Pressure Sensor using Diaphragm
Dr.K.V.L.Narayana
b) Microminiature silicon pressure sensor:
Applications
Dr.K.V.L.Narayana
Diaphragms: Mathematical description
The mathematical relation between pressure and central deflection for a flat
circular diaphragm is given by
3 p 4
dm 3
D (1 2
)
256 Yt
Materials of the
Bourdon tube are
Phosphor bronze,
Beryllium bronze or
Beryllium Copper.
Elastic type Pressure gauges: 2) Bourdon Gauges
Types of Bourdon Tubes
Dr.K.V.L.Narayana
Elastic type Pressure gauges: 3) Bellows
Range of Elastic-Element Pressure Gauges
Bourdon tubes,
diaphragms,
capsules, and
bellows .
Dr.K.V.L.Narayana
Conversion factors for units of pressure