Comparators used in Measurement Metrology And Control.

1. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
COMPARATORS
By
Vaibhav Aggarwal
Mechanical Engineering
R113213066 @UPES

2. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066

3. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
The general principle of comparator is to indicate the
differences in size between the standard and the work
being measured by means of some pointer on a scale
with sufficient magnification
It thus does not measure the actual dimension but
indicates how much it differs from the basic
dimension

4. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
Characteristics of Good Comparators:
• 1. compact.
• 2. easy to handle.
• 3. quick response or quick result.
• 4. reliable, while in use.
• 5. no effects of environment
• 6. less weight .
• 7. Cost
• 8. availability
• 9. sensitivity
• 10. It should be linear in scale so that it is easy to read
and get uniform response

5. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
Need for a comparator
• In mass production, where components are to
be checked at a very fast rate.
• close tolerances with high degree of precision
and speed.
Ex: Piston

6. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
TYPES OF COMARATOR
(1) Mechanical comparators
(2) Optical comparators
(3) Electrical and Electronic comparators
(4) Pneumatic comparators
(5) Fluid displacement comparators
(6) Projection comparators
(7) Multi-check comparators
(8) Automatic gauging machines

7. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
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

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Types of Mechanical Comparators
1. Dial indicator (Dial Gauge)
2. Reed Type
3. Johansson Mikrokator
4. Sigma Comparator

9. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
Dial indicator/ Dial Gauge

10. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
This type is generally used for inspection of small
precision machined parts
The dial gauge with various attachments are commonly
used
This comparator is ideal for the checking of components
with a tolerance of + 0.005 mm

11. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
Johansson Mikrokator

12. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
Working of the comparator
A very thin metal strip at the centre carries a light
pointer made up of glass .
One end of the strip is connected to the adjustable
cantilever strip and the other end is to the spring
elbow, in turn connected to the plunger.
The slight movements of the plunger will make the
bell crank lever to rotate.
This rotation will create tension in the strip and causes
the strip to rotate thereby the strip start to untwist
resulting in the movement of the point

13. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
Reed Type Comparator

14. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
The amount of target swing is proportional to the
distance the floating block has moved but of course
very much magnified.
The scale may be calibrated by means of gauge block
(slip gauges) to indicate any deviation from an initial
setting.
Sensitivities of the order of 0.25 micron per scale
division.
The mechanical amplification is usually less than 100,
but it is multiplied by the optical lens system. It is
available in amplifications ranging from x 500 to x
1000.

15. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
Sigma Comparator

16. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
• Y-arm which is attached to the moving block
transmits the rotary motion to the driving drum of
radius r. This deflects the pointer and then the
reading is noted.
• Ifl = Distance from hinge pivot to the knife edge..
• L = Length of y-arm.
• R = Driving drum radius.
• D = Length of the pointer.
• Then the total magnification=

17. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
Mechanical - Optical Comparator
• In mechanical optical comparator, small
variation in the plunger movement is
magnified: first by mechanical system and
then by optical system.

18. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066

19. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
Pneumatic comparator

20. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
• It works on the principle of pressure
difference generated by the air flow. Air is
• supplied at constant pressure through the
orifice and the air escapes in the form of jets
• through a restricted space which exerts a back
pressure. The variation in the back pressure is
• then used to find the dimensions of a
component.

21. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
Electrical Comparators
• no moving parts.
• high degree of reliability
• Generally there are two important applications
of electrical comparators:
1. Used as measuring heads
2. Used for electrical gauging heads

22. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066

23. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
Principle

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LINEAR VARIABLE DIFFERENTIAL
TRANSFORMER(LVDT)

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Advantages:
• 1. Measuring units can be remote from indicating units.
• 2. Variable sensitivity which can be adjusted as per requirement.
• 3. No moving parts, hence it can retain accuracy over long periods.
• 4. Higher magnification is possible as compared to mechanical
comparator.
• 5. Compact sizes of probes arc available.
Disadvantages:
• 1. The accuracy of working of these comparators is likely to be affect
due to temperature
• and humidity.
• 2. It is not a self contained unit; it needs stabilized power supply for
its operation.
• 3. Heating of coils can cause zero drifts and it may alter calibration.
• 4. It is more expensive than mechanical comparator

26. Vaibhav Aggarwal, Mechanical Engineering @UPES | R113213066
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