This includes a very breif presentation about Comparators and its differnt types

1. COMPARATOR
S

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.