This presentation is all about the micrometer screw gauge. First the presentation explains about the basics (parts, special definitions and errors) of a micrometer and finally , using example readings, explains as to how a measurement can be taken.

1. MICROMETER SCREW GAUGE
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By Aditya Abeysinghe

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3. Micrometer screw gauge has a fine threaded movement so
that small distances can be measured, with a vernier scale
which allows measurement down to thousandths of an inch.
INTRODUCTION

4. PARTS OF A MICROMETER
Anvil
Spindle
Frame
Lock
nut
Thimble(with
rotating vernier
scale) Ratchet
Sleeve
(with
main
scale)
Main scale Micrometer scaleBase line

5. Pitch- Pitch of the screw is the distance moved by the
spindle per revolution
Pitch may vary for different micrometers
Least count = Pitch / No.of divisions on the circular scale
E.g.: The least count for a micrometer of 100 equal divisions
and of pitch 0.5 mm is,
Least count = 0.5mm/100 =0.005mm
SPECIAL DEFINITIONS ON MICROMETER
MEASUREMENTS

6. Although the least count may vary between different
micrometers, the length formula for any micrometer is as
follows:
Total observed reading = main scale reading +
[(circular scale division coinciding the
base line of main scale) x least count]
LENGTH FORMULA FOR
MICROMETER

7. There can be two types of zero errors in a micrometer reading:
1. Positive zero error
Happens when the zero of the circular/auxillary scale places below the
zero of the meter scale reading
2. Negative zero error
Happens when the zero of the circular/auxillary scale places above the
zero of the meter scale reading
ERRORS IN A MICROMETER READING

8. No zero error is the precise arrangement of the meter scale
and the cicular scale so that the zeros of both scales fit each
other as follows:
To take precise measurements, we have to ensure that the
micrometer we are using is of no zero error.
NO ZERO ERROR

9. 1. First find whether there’s an error on the micrometer
2. Then find its least count using the pitch
3. Move away the rachet and place the object. Then
move the rachet in the opposite direction
4. For accurate reading, the thimble should be moved
until three clicks are heard from the ratchet.
5. Find the main scale reading. If the main scale shows
an additional 0.5mm, we have to add that as well.
TAKING MEASUREMENTS

10. 6. Then find the value of the circular/auxillary scale that
coincides with the main scale.
7. Finally multiply the reading from the circular/auxillary
scale by the least count and add this product to the main
scale reading to get the final reading.
Example:
0.5 mark not
visible
Therefore, the reading
would be = 0.7 +
(38×0.01) =
0.738 cm
0.5 mark
visible
Therefore, the reading would
be = 0.7 +0.05+ (22×0.01) =
0.772 cm