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EI2251 / INDUSTRIAL INSTRUMENTATION – I

3/27/2014 1 EI2251/INDUSTRIAL INSTRUMENTATION – I

C.MAGESH KUMAR/AIHT

YEAR / Semester: II A / IV COURSE CO-ORDINATOR: C.MAGESH KUMAR https://sites.google.com/site/mrcmageshkumar

COURSE AIM

To equip the students with relevant knowledge to suit the industrial requirements.

COURSE OBJECTIVES • To provide sound knowledge about various techniques used

for the measurement of industrial parameters. • Discussion of load cells, torque meter and various velocity

pick-ups. • Exposure to various accelerometer pick-ups, vibrometers,

density and viscosity pick-ups. • To have an adequate knowledge about pressure

transducers. • To have an idea about the temperature standards,

calibration and signal conditioning used in RTD’s. • To have a sound knowledge about thermocouples and

pyrometry techniques.


C.MAGESH KUMAR/AIHT

COURSE OUTCOMES (CO) 1. The students will acquire familiarity about various industrial instrumentation types, their parameters and different types of measurement techniques. 2. The students will understand the principles of industrial parameter standards and its calibration methodology. 3. The student will acquire extensive knowledge about pressure and temperature measurement, thermocouples and pyrometry techniques. PROGRAM OUTCOMES (PO) •(B) The students will be familiar with different sensors and transducers, electrical and electronic circuits. •(H) The students will possess the knowledge about the functions and instrumentation available in a modern power generation plant which enable them to match the industrial scenario and would be able to prove as the best of engineers in this modern world of technologies handling sophisticated instruments.


C.MAGESH KUMAR/AIHT

UNIT I MEASUREMENT OF FORCE, TORQUE

AND VELOCITY

3/27/2014 EI2251/INDUSTRIAL INSTRUMENTATION – I

C.MAGESH KUMAR/AIHT 4

UNIT I MEASUREMENT OF FORCE, TORQUE AND VELOCITY

• Force measurement – Electric balance – Types of load cells

• Hydraulic, • pneumatic, • strain gauge • Magneto elastic & • Piezo electric load cell

• Different methods of torque measurements: – strain gauge – Relative angular twist

• Speed measurement:- – Capacitive tacho & Dragcup type – D.C and A.C tacho generators

• Stroboscope


C.MAGESH KUMAR/AIHT

Force measurement

–Electric balance –Types of load cells

•Hydraulic, •pneumatic, • strain gauge •Magneto elastic & •Piezo electric load cell



Force • Force is any influence that causes an object to

undergo a certain change, either concerning its movement, direction, or geometrical construction.

• Newton's second law states that “the net force acting upon an object is equal to the rate at which its momentum changes with time.”

• If a force of magnitude, F, is applied to a body of mass, M, the body will accelerate at a rate, A, according to the equation: F = MA.

• Unit of force is the Newton



Measurement methods

• Comparison type

–Direct method

– Indirect method

• Deflection type



• Balance

– Electric / electronic

– Elastic

–Analytical balance.

• Scale:

»Pendulum equal arm balance

»lever,

»Spring spring balance

»hydrostatic plunger



• The electronic load cell uses the physical principle that a “force applied to an elastic element produces a measurable deflection.”

• Electronic load cells have significant advantages in terms of – cost,

– wide measurement range,

– tolerance of dusty and corrosive environments,

– remote measurement capability,

– tolerance of shock loading and

– ease of installation.



Electric balance / electronic balance (Electronic load cell)

Electronic balance

• The electronic balance is a device that contains several compression-type load cells

• Commonly, either three or four load cells are used in the balance, with the output mass measurement being formed from the sum of the outputs of each cell.



EQUAL ARM BALANCE



PRINCIPLE: “MOMENT COMPARISON” “The beam of equal arm balance is in equilibrium position when clockwise rotating moment is equal to anti clockwise rotating moment”

WEIGHT BEAM



ELASTIC FORCE METER (PROVING RING) – use micrometer



ELASTIC FORCE METER (PROVING RING)



ELASTIC FORCE METER (PROVING RING) – use micrometer



• Principle – “Displacement caused by force resulting in a proportional voltage”

• Principle of LVDT (Linear Variable Differential Transformer)

LOAD CELL: FORCE METER Device that convert force into pressure. Pressure is measured which is proportional to force. P α F P = x.F

• TYPES

– Hydraulic Load Cell

– Pneumatic Load Cell

– Magneto – Elastic Load Cell

– Piezo Electric Load Cell

– Strain Gauge Load Cell



LOAD CELL

HYDRAULIC LOAD CELL

• PRINCIPLE: “FORCE COUNTER BALANCE”

“Force is applied on liquid medium contained in closed space, the pressure of liquid will increase”

•Deflection = 0.05 mm at full load.

•Load range = 20 to 500 tons

20 tons with good resolution & accuracy.

•Measurement range = (0 - 30000) to (0 - 5 million) Newton



HYDRAULIC LOAD CELL



Pneumatic Load Cell

• PRINCIPLE: “FORCE BALANCE” “IF Force is applied to one side of a diaphragm (top side) and air pressure is applied on other side (bottom) contained in closed space, there needs a particular pressure value to balance the force exactly. Measured Pressure is proportional to applied force”

•Corrugated diaphragm

•Example of closed loop control system

•Measurement range = (0 - 35) to (0 - 12250) Newton

3/27/2014

EI2251/INDUSTRIAL INSTRUMENTATION – I C.MAGESH KUMAR/AIHT

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Pneumatic Load Cell



Magneto – Elastic Load Cell



• Principle : “Magneto elastic principle” – Villari effect.

• When a ferromagnetic material undergoes a mechanical stress, it changes the magnetic permeability of the material.

• Depends on permeability property of magnet

• “the measure of the ability of a material to support formation of magnetic

field within itself”

• Also called as “Pressductor”

Magneto – Elastic Load Cell



Magneto – Elastic

Load Cell



Piezo electric load cell

• Principle: “If dimension of Piezo electric material changes an electric potential appears across certain surfaces of crystal material. This potential is produced by the displacement of charges”.

• When force is applied displacement of charges occurs.



Piezo electric load cell



Strain gauge load cell

• Principle: “translates change in force into change in voltage”

• An electro-mechanical transducer.

• “when a steel cylinder id subjected to force, it tends to change in dimension inturn it changes the resistance”

• Accuracy : ±0.1 % in full scale



Strain gauge load cell



TORQUE • “The force that tends to cause rotation”

• Unit: Radian /sec

• Defn.: – “Force which tens to change the linear motion or

rotation of a body”.

– Turning or twisting moment of a force about the axis.

–T = FD » Where

• T – torque,

• F- force,

• D – perpendicular distance from axis of rotation of the line of action of force.



TORQUE MEASUREMENT

• Different methods of torque measurements:

– strain gauge (In-Line Rotating torque sensor)

– Relative angular twist. (Proximity torque sensor)

• Magnetic pick up type

• Optical stroboscopic type

– In-Line stationary torque sensor



Torque measurement – STRAIN GAUGE



• When a gauge is stretched its resistance will change.

• Due to unbalance in bridge (change in resistance) an A.C voltage is developed in output side.

• Input Supply – A.C (oscillator)

• Output – via transformer

Torque measurement – STRAIN GAUGE



• Relation between strain & applied torque Ɛ = ±8TD0 / [πC (D0 4 – Di

4)] » Where

• T= applied torque

• D0 = outer diameter

• Di = inner diameter

• C = shear modulus (Rigidity)



In-Line stationary torque sensor



Relative angular twist method- Magnetic pick-up type



When shaft rotates due to applied torque, the tooth of wheel passes the magnetic pick-up sensor due to which alternating voltage is produced, whose difference is proportional to applied torque

Optical stroboscopic type

• Principle:

– When a shaft is connected between a driving engine and driven load, a twist occurs on shaft between the ends.

– The angle of twist is measured and calibrated in terms of torque.



Optical stroboscopic type



Assignment 1

• Performance characteristics of instruments. (Page no. 4 - 10)

• Units & standard of measurement

(Page no. 13-21)

Reference:

“Industrial instrumentation & control” – McGraw-Hill, S.K.Singh

Date of submission: 23.01.2014 3/27/2014


42

SPEED MEASUREMENT

• MOTION MEASUREMENT – displacement, velocity (speed) and acceleration measurement.

• Speed is defined as rate of change of position of an object with respect to time.

• Speed = velocity

• V = dx/dt Velocity is the rate of change of displacement,

• Units of speed – Meters per second ( ms−1 or m/s), Kilometers per hour (km/h); Miles per hour

(mph);

– Knots (nautical miles per hour, kn or kt);

– Feet per second (fps or ft/s);

– Mach number, speed divided by the speed of sound;

– Revolution per minute (rpm)



TYPES OF VELOCITY 1. Linear velocity (along the axis of movement)

– Velocity of a body moving in linear fashion (m/s).

– Application:

• Velocity measurement of vehicle in highways

• Missile targeting

• Tracking movement of aircraft.

2. Angular velocity (along the axis) ― Velocity of a body moving in rotational fashion

― Measured in Revolution per minute (rpm) or radian / sec.



Linear velocity (along the axis of movement)

• Velocity of a body moving in linear fashion (m/s).

• The conventional type for linear velocity measurement is by using electromagnetic transducer.

• A permanent magnet core moves as a result of velocity in core and depending on magnitude of velocity of core a voltage is induced in coil which is given by

V α dɸ/dt V= -Ndɸ/dt

where V – velocity of core & dɸ/dt – rate of change of flux.

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Linear velocity (along the axis of movement)



Angular velocity & measuring types • Generally speed is calculated using tachometers

which calculates the angular speed in revolution per minute (rpm) of the object.

• Types of Tachometer: – Mechanical tachometer: Associated only with

mechanical units to measure speed.

– Electric tachometer: Associated with transducer for converting rotational speed to electrical quantity. The electric signal is proportional to speed.



Tachometer Mechanical tachometer

1. Revolution counter with time counter

2. Centrifugal force tachometer

3. Resonance tachometer



Electric tachometer 1. Capacitive Tachometer 2. Eddy current/drag cup

type/magnetic drag tachometer

3. Electric generator tachometer a. DC TACHO generator b. AC TACHO generator

4. Contactless tachometer 5. Frequency type tachometer 6. Ignition type tachometer 7. Stroboscopic tachometer

Capacitive Tachometer

• Principle: – Capacitor – charges & discharges.

– charging a capacitor and discharging through a meter continuously.

• If charging and discharging is controlled by speed of the device which is to be measured, then the average discharge current would be proportional to the speed.

• Average discharge current (I) is given by I = RCω

where R – resistance, C – capacitance, ω - speed of rotation (rpm)

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• to measure the rotational speed.




• to measure the direction of rotation along with rotational speed

• when the direction of rotation reverses, the direction of current also gets changed since the polarity of capacitor changes.



Eddy current/drag cup type/magnetic drag tachometer

• PRINCIPLE:

• “An emf is induced due to change in magnetic flux”

• An analog signal is produced in form of continuous drag due to eddy current induced in the cup which is proportional to speed.



Eddy current/drag cup type/magnetic drag tachometer



Electric generator tachometer • The transducer that converts rotation speed directly

into electrical signal is an induction pick-up type.

• Such types of tachometers are used for speed control of rotating equipment.

• Electric generator tachometer are 2 types as follows

– D.C tacho generators

– A.C tacho generators

Pre-requisite: Knowledge about working of AC and DC motor.



D.C TACHO GENERATORS

• PRINCIPLE:

“An emf is induced due to change in permanent magnetic flux. The induced emf is proportional to flux and rotational speed”

• Rotating armature cuts the permanent magnetic flux, so an emf is produced which is proportional to flux and rotational speed.

• Since the magnetic flux is constant, the generated voltage is proportional to speed.

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D.C tacho generators

• The output voltage of a DC generator (e0) is given by

e0 = (np nc ω ɸp * 10-8) / (60 npp))

where np – number of poles.

nc – number of conductors in armature

ω – rotational speed to be measured (rpm)

ɸp - flux per pole

npp – parallel paths between positive & negative brushes

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D.C tacho generators



Rotating armature cuts the permanent magnetic flux, so an emf is produced which is proportional to flux and rotational speed.

A.C TACHO GENERATOR

• PRINCIPLE:

“An emf is induced due to change in permanent magnetic flux. The induced emf is proportional to flux and rotational speed”

• To overcome the brush & commutator problem A.C tacho generators are used.



A.C TACHO GENERATOR • Due to rotation of shaft, the magnet also rotates

which induces an emf in stator coil. • Since the AC voltage is in form of pulse (the

polarity of pulse changes when north pole passes the coil and the polarity of pulse changes in opposite direction when south pole passes the coil.)

• When speed of shaft changes it changes the amplitude and rise time of output voltage which should be conditioned using a rectifier circuit for direct measurement of speed.

• For negligible load current, output voltage e0 = kω. 3/27/2014


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A.C TACHO GENERATOR



STROBOSCOPE • Stroboscopes are simple, portable manually operated

device used to measure the speed of rotation or frequency of vibration of a mechanical system.

• An electronic stroboscope uses a (variable frequency flashing light) multivibrator type circuit to produce flashes of light at known and adjustable rates.

• The variable frequency flashing light source is called strobotron.

• The frequency is set by operator. The speed is measured by adjusting the frequency so that the moving objects are visible only at specific intervals of time.



• Working: (to measure rotational speed (shaft speed))

– A distinctive mark is made on the shaft whose rotational speed is to be measured.

– A stroboscope is made to flash directly on the mark. The flashing is adjusted until the mark appears stationary even though the shaft rotates.

– At this condition, the speed of shaft (n in rpm) is equal to frequency (f in Hertz) of light flashed on shaft. i.e., n = f

• In general, if no. of marking in shaft is ‘m’, then n = f/m.

• If no. of marking is 1, then n = f

• If no. of marking is 2, then n = f/2

• If no. of marking is 3, then n = f/3



simple stroboscope circuit



ei2251 / industrial instrumentation - … · ei2251 / industrial instrumentation – i 3/27/2014 1...

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