Measurements and Instumentation

8/9/2019 Measurements and Instumentation

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1 Temperature

MeasurementTemperature is a fundamental quantity.Zeroth law of thermodynamics denestemperature

Temperature could be dened asThe degree of hotness or coldness of a body o

an environment measured on a denite scale

Condition of body by virtue of which heat is

transferred to or from other bodiesDierent scales of measuring commonly Celsiu


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2 Importance

Conventional Cocpit !lass Cocpit


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3 Importance

Commonly measured entities


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4 MeasurementMethods

Temperature cannot be measured directly

"ust be measured by observing the eect thattemperature variation causes on the measuring

device

"ainly # main methods

$on%electrical methods

&lectrical methods 'adiation methods


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5 Non ElectricalMethods

Temperature measurement based on

Change in the physical state

Change in chemical properties

Change in physical properties(f these one of mostly used instrument is thebimetallic thermometer

The principle of measurement is the physical

change i.e. elongation or contraction of bimetallistrip when calibrated.


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6 BimetallicThermometer

Two dissimilar metals of dierentcoe)cients of e*pansion bondedtogether

(ne end of the coil is *ed

(ther end has a pointer attachedto it

+hen heated the coil unwindsand when cooled the coil rewinds

Thus the pointer moves and is anindication of temperature when


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7 Applications

Direct reading bimetallictherm. (ften used in lightaircraft for outside airtemperature measurement.

Combined sensing andcontrol systems

2elf generating3 low cost3 nomaintenance e*penses3

e*tended operation period,nability to measure rapid Use in a liht aircr


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" Bourdon Tu#e

direct reading non%electrictemperature gauge


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$ %rinciple

Consistent e*pansion ofthe vapour produced by avolatile liquid in an enclosedarea.

This vapour pressurechanges directly withtemperature.

4y lling a sensing bulb

with such a volatile liquidand connecting it to abourdon tube


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1& Mechanical Mo'ementIndicators

Tachometers

"echanical tachometers

&lectric tachometers

2ynchrometers

They feedbac the conditionof the aircraft in 6ight


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11 Tachometers

The tachometer3 or tach3 is an instrument thatindicates the

speed of the cranshaft of a reciprocating engine.

,t can be a direct% or remote%indicating instrumen

(n reciprocating engines3 the tach is used tomonitor engine power and to ensure the engine isoperated within certied limits.

!as turbine engines7 used to monitor the speed8s

the compressor section8s9 of the engine.

,n addition to the engine tachometer3 helicopters


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12 Mechanical Tachometers


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Found on small3 single%engine light aircraft in wha short distance e*ists between the engine and theinstrument panel.Consist of an indicator connected to the engine b

6e*ible drive shaft. +hen the engine turns3 so doethe shaft.The indicator contains 6yweight assembly coupleto a gear mechanism that drives a pointer.Centrifugal force acts on the 6yweights and movthem to an angular position % varies with the rpm othe engine.


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Found on small3 single%engine light aircraft in wha short distance e*ists between the engine and theinstrument panel.Consist of an indicator connected to the engine b

6e*ible drive shaft. +hen the engine turns3 so doethe shaft.The indicator contains 6yweight assembly coupleto a gear mechanism that drives a pointer.Centrifugal force acts on the 6yweights and movthem to an angular position % varies with the rpm othe engine.


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Drive shaft turns3 it rotates apermanent magnet in a close%tolerance cup.: shaft attached to the

indicating point is attached tothe e*terior centre of the cup.:s the magnet is rotated bythe engine 6e* drive cable3 itsmagnetic eld cuts throughthe conductor surrounding it3creating eddy currents in the


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16 Electrical Tachometers

!reater accuracy with lower maintenance is achievthroughthe use of electric tachometers.


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17 Electrical Tachometers

:C generator mounted to a reciprocating engine;gear case or the accessory drive section of aturbine engine.

:s the engine turns3 so does the generator.

The frequency output of the generator is directlyproportional to the speed of the engine.

,t is connected via wires to a synchronous motorin the indicator that mirrors this output.

: drag cup3 or drag dis lin3 is used to drive theindicator as in a mechanical tachometer.


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1" ()nchroscope

The synchroscope is aninstrument that indicateswhether two or more rotatingdevices3 such as engines3 are

synchroni


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Measurements and Instumentation

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