Aei-405

DEPARTMENT OF TECHNICAL EDUCATION ANDHRA PRADESH Name

: M. Vani

Designation

: Lecturer

Branch

: AEI

Institution

: Dr. B. R. Ambedkar GMRP,KNR

Year/sem

: IV-SEM

Subject

: Process Instrumentation-II

Subject code

: AEI-405

Topic

: Miscellaneous measurement

Sub topic

: Audio sensors

Duration

: 100 minutes

Teaching aids

: PPT, Visuals AEI405.88 To 89

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Recap In the last class we have studied about :  Leak detector  Water leak detectors

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Objectives Upon completion of this topic you would be able to know about :  Audio sensor (or) detector.  Types of audio sensor.

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Introduction  Sound is defined as an oscillation in an elastic medium, occurring within the frequency range to which the human ear is sensitive.

 The audio frequency range is 20 to 20,000cycles /sec (Hz).

 The elastic medium is air. AEI405.88 To 89

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Introduction…  Sound wave occur  as pressure wave or  as particle -velocity or  particle-displacement.

 Microphone is the device which converts pressure wave into electrical. AEI405.88 To 89

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Classification  Microphones are classified according to the type of response, whether the instrument is activated by velocity, displacement, pressure of the sound waves.  Ribbon microphone responds to velocity.  Pressure –gradient microphone are sensitive to difference in pressure between two points. AEI405.88 To 89

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Classification…  Ultrasonic microphones, respond only to frequency above the hearing range i.e. about 25,000 to45,000 Hz.

 Other microphones are carbon, condenser, capacitor, crystal.

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Classification…  Audio sensor is a device which gives information about the sound.  Sound may be of three types 1) low 2) medium 3) high  The low, medium sound is good to hear but a high sound is not audible to the human ear. AEI405.88 To 89

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Classification…  Audio sensor is a device which converts the mechanical energy in electrical energy  The sound is measured in decibels (db).  The sound is nothing but vibrations caused in air.

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Classification…

 If we consider about our surroundings, apart from the air and water pollution we are also facing the problem of sound pollution, which is to be reduced.  Measures are to be taken to reduce the sound pollution.  Thus different audio sensors are developed.

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Explanation  This type of microphone is mostly used for precision measurements because of good frequency and large dynamic pressure range  This microphone consists of thin metallic diaphragm in close proximity to a rigid back plate  The diaphragm and the back plate form the plates of the capacitor AEI405.88 To 89

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Condenser type microphone

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Explanation  The movement of the diaphragm caused by the impinging of sound pressure results in a voltage given by E ≈ Qd  Where

E = output Q = Charge provided by the polarization voltage d = Separation of the plates AEI405.88 To 89

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Explanation  The microphone is provided with an air-leak for equalization of the pressure on both sides of the diaphragm to prevent the diaphragm from bursting  The black plate also consists of damping holes  The motion of air diaphragm causes air flow through the holes which results in energy dissipation due to fluid friction AEI405.88 To 89

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Explanation  This damping effect is utilized in the control of resonant peak of the diaphragm response

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Electrodynamic microphone • It is based on the principle of generation of emf when a moving coil is placed in magnetic field • The Fig. shows the typical construction of it • The sensing diaphragm is attached to a coil or ribbon placed within the poles of a permanent magnet • The movement of the magnet due to acoustic pressure generates the analogous induced voltage in the coil

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Electrodynamic microphone

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Audio sensor 1

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Audio sensor 2

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Audio sensor 3

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Summary In this class we have learnt :  Audio sensor  Types of audio sensors

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Quiz 1.

Sound energy is measured in a) Decibels b) Kilograms c) Liters d) none

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Frequently asked questions 1.

What is meant by audio sensor. Explain ?

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Thank you

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