A comparator is a precision instrument used to compare the dimensions of a component to a standard. It indicates the differences in size but does not directly measure dimensions. Comparators can be mechanical, optical, pneumatic, electrical or electronic. Mechanical comparators use linkages and levers to magnify movements, while optical comparators use both mechanical and optical systems. Pneumatic comparators measure air pressure or flow differences. Electrical/electronic comparators convert displacements to electrical signals. Each type has advantages like accuracy, but may also require external power sources or have limited ranges.

1. COMPARATOR
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2. Introduction
 A device used for comparing a measurable property or
thing with a reference or standard.
 It is a precision instrument employed to compare the
dimension of a given component with a working
standard.
 It does not measure the actual dimension but indicates
how much it differs from the basic dimension.
 The general principle of comparator is to indicate the
differences in size between the standard and the work.

3. Need For A Comparator
 In mass production, where components are to be
checked at a very fast rate.
 As laboratory standards from which working or
inspection gauges are set and correlated.
 For inspecting newly purchased gauges.
 Attached with some machines, comparators can be
used as working gauges to prevent work spoilage
and to maintain required tolerances at all stages of
manufacturing.
 In selective assembly of parts, where parts are
graded in three or more groups depending upon their

4. Desirable features of
Comparators
 Robust design and construction
 Linear characteristics of scale
 High magnification
 Quick in Results
 Versatility
 Minimum Wear of contact Point
 Free from Oscillations
 Free from backlash
 Quick insertion of work piece
 Adjustable table
 Compensation from temperature effects
 Means to prevent damage

5. Principle of Comparators
All comparators consist of three basic features:
1)A sensing device
Which faithfully senses the input signal
2) A Magnifying or amplifying system
To increase the signal to suitable magnitude.
Mechanical, Optical, Pneumatic, hydraulic and electronic
methods are used for this purpose.
3) A display system (usually a scale and pointer)
Which utilizes the amplified signal to provide a
suitable readout.

6. Classification of Comparators
Mechanical comparators
Optical comparators
Electrical and Electronic comparators
Pneumatic comparators
Fluid displacement comparators
Projection comparators
Multi-check comparators
Automatic gauging machines
CMM

7. Mechanical Comparator
 The mechanical comparator is also called as
“microcator”.
 In mechanical comparators, magnification is achieved
by various mechanical devices and mechanical
linkages.
 Mechanical comparator is a measuring instrument.
 The mechanism of this instrument is in the form of
tape spring twisted, and that is positioned in the
middle part.
 The middle part of the mechanical comparator rotates
through a fixed angle upon tension.

8. Working principle of a Mechanical
Comparator
 A mechanical comparator employees mechanical
means for magnifying the small movement of the
stylus.
 the magnification of the small stylus movement is
obtained by means of levers, gear trains, rack and
pinion or a combination.
 The usual magnification obtained by these
comparators ranges from about 250 to 1000.

9. Types of Mechanical
Comparators
 Dial Indicator
 Johansson Mikrokator
 Sigma Mechanical Comparator
 Dial Thickness Gauge
 Reeds Type Comparator
 External & internal Groove Comparator
 Plate Gauge Type comparator

10. Dial Indicator
 Instrument which sense the measuring distance variations.
 It has a rack & pinion Mechanism Which Convert the axial
displacement of a measuring spindle into rotational
movement.
 The movement is then amplified & displayed on a pointer
graduated scale or digital display.
 It has following Types:
 Mechanical Dial Indicator
 Mechanical Dial indicator with Limit Contacts
 Micrometer Dial Comparator
 Lever Type dial Indicator

12. Johansson Mikrokator

14. Reeds Type Comparator

15. Advantages of Mechanical Comparator
 Cheaper than all the other type of comparators
 Does not require any external source of power or air
supply
 These comparators use a linear scale that can be easily
understood.
 Usually these comparators are robust and compact but
are very easy to handle
 These are small in size and can are portable from one

16. Limitations of Mechanical
Comparator
 Contains more number of moving parts so there develops
friction which in turn reduces the accuracy
 Slackness in the moving parts reduces accuracy very
drastically
 These have more inertia so the instrument is prone to
vibrational effects
 Limited range of the instrument is another drawback as the
pointer moves over a fixed scale

17. Optical Comparators
 In this comparator a small dislocation of the measuring
plunger is first amplified by a mechanical system
comprising of pivoted levers.
 The mechanical movement which is amplified by an
optical system connecting the outcrop an image.
 The general arrangement of mechanical system causes
a reflector to angle near the image
 An axis of an index estimated on a scale on the inner
glass screen.

18. Principle Of Optical Comparator

19. Types of Optical Comparator
 Profile (optical) Projector
 Mechanical Optical Comparator
 Zesis Optical Comparator
 Electrical Optical Comparator

20. Mechanical Optical Comparator

21. Zesis Ultra Comparator
 It gives very high magnification, as it works on
double magnification principle.

23. Advantages of Optical
Comparators
 It has small number of moving parts and hence a
higher accuracy.
 In the optical comparators, the scale can be
made to move past a datum line and thus have
high range and no parallax errors.
 It has very high magnification.
 Optical lever is weightless

24. Limitations of Optical
Comparators
 As the instrument has high magnification, heat from the
lamp, transformer etc. may cause the setting to drift.
 An electrical supply is necessary.
 The apparatus is usually large and expensive.
 When the scale is projected on a screen, then it is essential
to use the instrument to a dark room in order to take the
readings easily.
 The instruments in which the scale is viewed through the
eyepiece of a microscope are not convenient for continuous

25. Pneumatic Comparator
 In pneumatic comparators, either air flow or air
pressure is measured to give measurement
deviations from a standard.

26. Basic Principle of Pneumatic

27. Types of Pneumatic
Comparator
 Differential Back-Pressure-Type Comparator
 Solex Comparator
 Velocity Differential-Type Air gauge with Barr
Graph & Digital Display

30. Advantages of Pneumatic
Comparator
 The gauging member does not come into contact with the
part to be measured and hence practically no wear takes
place on the gauging member.
 It has usually very small number of moving parts and in
some cases none. Thus the accuracy is more due to less
friction and less inertia.
 Measuring pressure is very small and the jet of air helps in
cleaning the dust, if any, from the part to be measured.
 It is possible to have very high magnification.
 The indicating instrument can be remote from the measuring
unit.
 It is very suitable device for measuring diameter of holes
where the diameter is small compared with the length.

31. Limitations of Pneumatic
Comparators
 It requires elaborate auxiliary equipment such as accurate
pressure regulator.
 The scale is generally not uniform.
 When indicating device is the glass tube, then high
magnification is necessary in order to avoid the meniscus
errors.
 The apparatus is not easily portable and is rather
elaborate for many industrial applications.

32. Electric & Electronic
Comparators
 It is essentially consist of a transducer for
converting a displacement into a corresponding
change in current or Potential difference.
 The change in displacement is calibrated in three
ways:
 Using Inductive Principle
 Using Capacitive Principle
 Using Resistive principle

33.  It requires elaborate auxiliary equipment such as accurate
pressure regulator.
 The scale is generally not uniform.
 When indicating device is the glass tube, then high
magnification is necessary in order to avoid the meniscus
errors.
 The apparatus is not easily portable and is rather elaborate
for many industrial applications.
 Different gauging heads are required for different
dimensions.
 It breaks against the W and spring and W1.
 If the armature is located between the coils W & W1, then
Working Principle Electrical
Comparators

34.  When the work piece is located under the stylus for the
measurement purpose due to the difference in datum.
 The armature, component size would either be raised up or
down.
 It defeats the Wheatstone bridge balance that results the
unbalanced current flow.
 This current is directly adjusted into difference in size of the
component which is expanded by an amplifier specified by
the galvanometer.
 This current is directly adjusted into difference in size of the
component which is expanded by an amplifier specified by
the galvanometer.
 The main advantages of these comparators are no moving
parts, sensitivity and accuracy over long periods.
Working Principle Electrical
Comparators

35. Linear Variable Differential
Transducer
 This instrument works on inductive principle.

36. Advantages & Limitations of
Electrical Comparators
 Advantages:
 It has got small number of moving parts.
 It is possible to have high & more number of
magnification by an instrument.
 The mechanism carrying the core is very light & is not
sensitive to vibrations.
 Limitations:
 Heating of the coil in measuring unit may cause zero
drift and hence alter the calibration.
 This is generally more expensive than others
comparators.
 External Power source is required.