Transducer
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![Page 1: Transducer](https://reader036.fdocuments.us/reader036/viewer/2022081603/56812d0e550346895d91e46f/html5/thumbnails/1.jpg)
Transducer
Device when activated from one form energy converted to another quantity
or
Device which converts one physical quantity or condition to another
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Physical quantity – heat , intensity of light, flow rate, liquid level, humidity etc
Sensor : sense physical quantity
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Classification of transducers
1. Based on principle of transduction
2. Active & passive
3. Analog & digital
4. Inverse transducer
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Based on principle used
• Thermo electric
• Magneto resistive
• Electro kinetic
• Optical
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Passive transducer
Device which derive power reqd. for transduction from auxiliary power source
- externally powered
Eg : resistive, inductive, capacitive
Without power they will not work
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Active transducer
• No extra power reqd. to produce I/p
• Self generating
• Draw power from input applied
• Eg. Piezo electric x’tal used for accelartion measurement
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Analog transducer
• convert I/p quantity into an analog o/p
• Analog o/p- a continuous fn. Of time
• Eg. Strain gauge, L VDT, thermocouple
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Digital transducer
• Converts I/p into an electrical o/p in the form of pulses
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Inverse transducer
• Which converts electrical signal to physical
• quantity
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Transducer for pressure measurement
• What is pressure?
force/ unit area
Unit – (N/sq.m) Pa
Pressure measured can be absolute , gauge or differential depending on type of reference
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Types of pressure transducers
• Gravitational
eg : manometer
• Elastic – force converted to strain
eg. Diaphragm, capsule, bellows, bourdon tubes
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Diaphragm
Common pressure sensing elastic element
Thin circular plate stretched & fastened at its periphery
Made of elastic alloys of bronze,phosphor bronze, stainless steel or alloys like Monel, Nickel span -C
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Structure – flat or corrugated
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Top view of flat type
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Top view of corrugated type
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• Flat type – high natural frequency
• Corrugated – for large deflections
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Capsule
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Capsule
• Two corrugated metal diaphragms sealed together at periphery
• Forms a shell like structure
• One diaphragm has a port at centre to admit pressure to be measured
• Other diaphragm linked to a moveable mechanical part.
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Capsule
• Displacement proportional to difference b/w outer & inner pressure.
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Bourdon tubes
• curved or twisted metallic tubes with elliptical cross section
• Sealed at one end
• Tends to straighten when pressure applied.
• Angular sensitivity proportional to pressure applied
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Spirial bourdon tubes
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Bourdon tubes –C type
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Helical type
• Tube in the form of helix
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Bourdon tube
• More sensitive to shock & vibrations
• Good repeatability
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Bellows
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Bellows
• Thin walled cylindrical sheets with deep convolutions sealed at one end
• Sealed end moves axially when pressure is applied
• No. of convolution s – vary from- 2 to 50 – depends on range, operating temp
• Used for low pressure measurement
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Bellows
displacement y = 2.n. A q P Rx 2 /( Et 2 .) where n – no. of convolutions
A q- effective area
Et - young’s modulus of elasticity
Rx – radius of diaphragmP – pressure ie, Y P
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Resistive type
Eg. Strain gauge
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Capacitive
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Inductive type
• Eg. LVDT
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Measurement of velocity
Velocity – linear or angular
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Linear velocity
• Electromagnetic transducers• O/p voltage E = /t
• = N I/ R2 . dR/dt
where N I/ R2 is a constant
R- reluctance
so E proportional to reluctance
R proportional to air gap & air gap proportional to velocity
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• Types
• Moving coil
• Moving magnetic
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Angular velocity
• Tachometer - types
Mechanical
Electrical
MHD sensor – magneto hydrodynamic sensor
highly sensitive
High precision
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Transducer for vibration
• Vibrations give early warning of impending conditions which may develop &vlead to complete failure & destruction of equipment
• Used in power plants, turbines
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• Most vibrations are sinusodial in nature
• Got amp & freq.
• Amp gives displacement
• By measuring displacement, velocity or acceleration - vibrations measured
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Vibration transducer
Accelometer – measures shock or vibration
Pot type or LVDT type
![Page 40: Transducer](https://reader036.fdocuments.us/reader036/viewer/2022081603/56812d0e550346895d91e46f/html5/thumbnails/40.jpg)
Pot type accelrometer
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LVDT accelorometer
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THANK UTHANK U
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