Aei405

DEPARTMENT OF TECHNICAL EDUCATION ANDHRA PRADESH Name

: A.Vinay Kumar

Designation

: H.O.D

Institute

: Q.Q.GPT

Branch

: AEIE

Subject Semester

: Process Instrumentation – II : IV

Code No

: AEI-405

Major Topic

: Pressure

Duration

: 50 Mins.

Sub Topic

: Force-Balance transducer

Teaching Aids

: PPT, Animations, diagrams AEI405.14TO15

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Objectives Upon completion of this topic you will be able to know about Force-Balance pressure transducer • Introduction • Description • Principle • Operation

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Recap In last class we have learnt about the • Thin film pressure Transducer

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Force-Balance transducer

KA

KD

i

LVDT

A

Lf

LD

B

LM

Beam S

N

Bellows assembly

Servo R amplifier

Out put

S Force coil

Kf

Magnet P AEI405.14TO15

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Introduction • Performance of Pressure transducers is based on the measurement of deflection of elastic element • The material characteristics of hysteresis and creep can degrade the accuracy • For higher sensitivity these elements must have low stiffness and /or large area

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Introduction… • It makes the transducer bulky which is affected by vibration • Feedback principle employing balance of forces have been applied to overcome the problem • They employ electro dynamic devices or electric static force generators to balance the forces produced by the elastic elements which is subjected to the pressure

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Description It consists of • Bellows

• Fulcrum AEI405.14TO15

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• Beam

• Displacement transducer

• Amplifier

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• Electro magnetic coil

• Resistor

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Operation

• It uses the electro dynamic force balance principle • Pressure difference between inside and out side of the bellows gives rise to a force at the point ‘A’ • The resultant displacement of the balancing beam is detected by a displacement transducer like LVDT •

It is located at point ‘B’

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Operation…

• The electrical output of transducer is amplified • It causes a current ‘I’ to flow through the balancing coil • Which is attached to the beam

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Operation… At balancing position • The electro dynamic force exerted by the coil opposes the force exerted by the bellows • The current required to get such a balance is taken as a measure of the unknown pressure ‘P’ acting on the bellows

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Advantages • High loop gain • Small deflections can be measured • Good linearity • High accuracy • Good sensitivity

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Disadvantages • It is heavy because of magnet and coil assembly • Low frequency response limited to 100 Hz

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Uses

•

It can be used as secondary standard

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Summary In this class we have learnt about Force-balance pressure transducer • Operation • Advantages • Limitations

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Quiz 1. Force- balance pressure transducer can be used as a) Primary standard b) Secondary standard c) International standard d) None

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Frequently Asked Questions

1) Explain the principle of operation of Force balance transducer?

3) Draw the block diagram of Force balance transducer?

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