mechanical comparators

7/17/2019 Mechanical Comparators

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Name:- Achuat S Deo

Topic:-Mechanical Comparators



COMPARATORS

•

It is an indirect type of instrument andused for linear measurement.

• They are employed to nd out, by howmuch the dimensions of the givencomponent dier from that of a knowndatum.

•It gives only the dierence betweenactual and standard dimension of thework piece.



MECHANICAL COMPARATORS

•It is self controlled and no power or anyother form of energy is required.•It employs mechanical means formagnifying the small movement of the

measuring stylus.• The movement is due to the dierencebetween the standard and the actualdimension being checked.•

The various types of mechanicalcom arators are dial indicator rack and



! DIAL INDICATOR



Principle:-

It operates on the principle, that a very slight upward

pressure on the spindle at the contact point ismultiplied through a system of gears and levers. It isindicated on the face of the dial by a dial nger.

Construction:-

. !ial indicators basically consists of a body with around graduated dial and a contact point connectedwith a spiral or gear train so that hand on the dialface indicates the amount of movement of thecontact point.

". They are designed for use on a wide range ofstandard measuring devices such as dial bo# gauges,portal dial, hand gauges, dial depth gauges,diameter gauges and dial indicator snap gauge.



Applications:

. $omparing two heights or distances between narrowlimits.

". To determine the errors in geometrical form such asovality, roundness and taper.

%. &or taking accurate measurement of deformation such asintension and compression.

'. To determine positional errors of surfaces such asparallelism, squareness and alignment.

(. To check the alignment of lathe centres by using suitable

accurate bar between the centres.

). To check trueness of milling machine arbours and tocheck the parallelism of shaper arm with table surface orvice.



". "OHANSSON MICRO#ATOR



Principle:-It works on the principle of a *utton spring, spinning on aloop of string like in the case of children+s toys.

Construction:-. The method of mechanical magnication is shown in &igure.

It employs a twisted metal strip.

". very light pointer made of glass tube is attached to the

centre of the twisted metal strip.

%. The measuring plunger is on the slit washer and transmitsits motion through the bell crank lever to the twisted metalstrip. The other end of the twisted metal strip is fastened tothe cantilever strip.

'. The overhanging length of the cantilever strip can bevaried to ad-ust the magnication of the instrument.

(. The longer the length of the cantilever, the more it willdeect under the pull of the twisted metal strip and lessrotation of the pointer is obtained.



AD$ANTA%ES DISAD$ANTA%ES

!o not require any e#ternalsource of energy.

/imited 0ange

$heaper, portable andcompact design and robustconstruction.

1ointer scale system used cancause paralla# error.

2imple linear scales are easyto read.

/ess accuracy

0emains unaected by

variations due to e#ternalsource of energy , electricityetc.

3ay become sensitive to

vibrations due to high inertia.



%. MECHANICAL OPTICALCOMPARATOR



Principle:-

In mechanical optical comparator, small variation in

the plunger movement is magnied4 rst bymechanical system and then by optical system.

Construction:-. The movement of the plunger is magnied by the

mechanical system using a pivoted lever. &rom the&igure the mechanical magnication 5 #" 6 #.

". 7igh optical magnication is possible with a smallmovement of the mirror. The important factor isthat the mirror used is of front reection type only.

%. The back reection type mirror will give tworeected images as shown in &igure, hence thee#act reected image cannot be identied.



T789 :;<

mechanical comparators

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