Transducer

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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

• Based on principle of transduction
• Active passive
• Analog digital
• 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 xtal 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 - youngs modulus of elasticity
• Rx radius of diaphragm
• P 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

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Pot type accelrometer
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LVDT accelorometer
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