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Shaft Power Measurement (Dynamometers)

Presented by

S.Nandhini(09MN06)

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Dynamometer

A dynamometer or "dyno " for short, is a device formeasuring force, moment of force (torque), or power.

http://en.wikipedia.org/wiki/File:Dynamometer01CJC.svg

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For example, the power produced by an

engine, motor or other rotating primemover can be calculated bysimultaneously measuring torque androtational speed (rpm).

P . !"here, P#$ Power in watts

#$torque in %m !#$ angular velocity in radians per

second

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Dynamometer

&he dynamometer applies a resistanceto the rotation of the engine.'f the dynamometer is connected to theengine s output shaft it is referred to asan Engine Dynamometer ."hen the dynamometer is connected tothe vehicles drive wheels it is called aChassis Dynamometer .

&he force exerted on the dynamometerhousing is resisted by a strain measuringdevice (for example a strain gage).

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Type of dynamometer

&ype of dynamometer depends onthe nature of machine to be tested.

Power generator# dynamometer mustabsorb its power

Power absorber# dynamometer mustdrive it

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Absorption Dynamometers

easures and absorbs the poweroutput of the engine to which they arecoupled. &he power absorbed is usuallydissipated as heat by some means.*xamples of such dynamometers are

Prony bra+e dynamometer

ope bra+e dynamometer-ydraulic dynamometer*ddy current dynamometer

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Prony brake dynamometer

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Prony brake dynamometer

• 't wor+s on the principle of convertingpower into heat by dry friction.

•

&his method of measuringhorsepower is to attempt to stop theengine by means of a bra+e on the

ywheel and measure the weight

which an arm attached to the bra+ewill support, as it tries to rotate withthe ywheel.

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Prony brake dynamometer

Advantages/0imple mechanical bra+e

Friction torque is manually ad1ustedby varying the normal force with ahand wheel

&orque is available at 2ero speed3isadvantage/

4er+y operation because of thenature of dry friction

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Rope brake dynamometer

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't consists of a number of turns of rope woundaround the rotating drum attached to the outputshaft. 5ne side of rope is connected to a springbalance and the other to a loading device. &he

power is absorbed in friction between the ropeand the drum. &he drum there for requirecooling.

ope bra+e is cheap and easily constructed .

't is not very accurate because of changes in thefriction coe6cient of the rope with temperature.

Rope brake dynamometer

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Hydraulic dynamometer

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't wor+s on the principle of dissipating the powerin uid friction rather than in dry friction.

't consists of an inner rotating member orimpeller coupled to the out put shaft of engine.

&his impeller rotates in a casing 7lled with uid.

&he heat developed due to dissipation of power

is carried away by a continuous supply ofwor+ing uid, usually water. &he output can becontrolled by regulating the sluice gates whichcan be moved in and out to partial or whollyobstructive ow of water between impeller and

the casing.

Hydraulic dynamometer

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Eddy current dynamometer

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't consists of a stator on which are 7tted a number ofthe electromagnets and a rotor disc made of copper orsteel and coupled to the output shaft of the engine.

"hen the rotor rotates eddy currents are produced inthe stator due to magnetic ux set up by the passageof 7eld current in the electromagnets.

&hese eddy currents oppose the rotor motion, thusloading the engine. &hese eddy currents are dissipatedin producing heat so that this type of dynamometeralso requires some cooling arrangement .

Eddy current dynamometer

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Advantages

-igh horsepower per unit weight ofdynamometer.

&hey o8er the highest ratio ofconstant horsepower speed range.

3evelopment of eddy current issmooth hence the torque is alsosmooth and continuous under allconditions.

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Disadvantage

9annot produce any torque at2ero speeds

5nly small torque at low speeds

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References

http/::www.britannica.com:*;chec+ed:topic:?

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