Intro of Vernier Caliper

1. Vernier Caliper

2. Introduction to
Vernier Caliper
Introduction to Vernier Caliper. The main use
of Vernier calipers is to measure the internal
and external dimensions or distances
accurately. Vernier calipers are preferred over
other flat devices, such as rulers, as they have
an extremely small reading error of 0.05mm,
which is around 0.0019 inches.

3. Main Scale
Vernier (auxiliary) Scale
Why??

4. Parts of Vernier Caliper

6. General Concept of Least Count

7. You will notice that one of the vernier scale
divisions coincides with one of the main scale
divisions.

8. Principle of Vernier
N divisions on the vernier
scale is equal to
(N-1) divisions on the
main scale.

9. Least Count indicates the degree of Precision of
measurement that can be achieved by the measuring
instrument.
Suppose, Two different vernier callipers have different number of equal
divisions on their vernier scales
i) 10 equal divisions ii) 50 equal divisions.
Which can measure more precisely ?
The least count of the I vernier callipers = 1/10 =0.1mm
The least count of the II vernier callipers = 1/50 =0.02mm.
That is, the II vernier callipers with 0.02mm of L.C can measure up to
0.02mm accurately.
Hence, the precision of II vernier callipers in more than I vernier callipers.

10. Question: What happens if instead if N-1 divisions, the N divisions of my
vernier callipers divides N-2 or N-3 divisions on the main scale? Is it
possible? what changes should we make to find the least count? which
calliper would be more precise?
Ans: if (n-2) M.S.D = n V.S.D
Then 1 V.S.D = {(n-2)/n} M.S.D
L.C = 1 M.S.D – 1 V.S.D = 1mm – {(n-2)/n} mm = 2/n if n =10
L.C = 2/10 = 0.2 mm
i.e. when (n-1) divisions are changed to (n-2)divisions least count is
increased from 0.1mm to 0.2mm
i.e. the precision of the vernier callipers is decreased.
so, if (n-3) M.S.D s are divided in to n equal divisions on vernier scale
the L.C further increases and the precision further decreases.

11. Principle of Vernier
The reading on the main scale just before (LEFT) the zero of the vernier is noted.
This is called Main scale reading (M.S.R).The number of division (n) on the vernier
which coincides perfectly with any one of the main scale divisions is noted. This is
called vernier coincidence (V.C).The vernier coincidence (V.C=n) is multiplied by
least count to get the fraction of a main scale division. This is added to the main
scale reading (M.S.R)
Reading of the instrument = MSR + (n x L.C.)

12. Reading of the instrument = MSR + (n x L.C.)

13. Main Scale reading = 1.2 cm;
vernier scale reading = 3×0.01 cm = 0.03 cm
So,
Reading = 1.2 + 0.03 = 1.23 cm
How to take reading of a Vernier scale
1 cm

14. Another Example

15. Another Example
2.4cm

16. Another Example

20. Click on the picture for Video on Vernier Scale

21. http://members.shaw.ca/ron.blond/Vern.APPLET
Java Applet for Vernier Scale
Tutor Vista animation

22. No zero error. Positive zero error
Zero Error
When jaws of the vernier callipers are in contact, and if the
zero division of main scale does not coincide with the zero
mark on vernier scale, such vernier calipers will have zero
error.
Types of Zero Error in vernier callipers
i) Negative Zero error ii) Positive Zero error

24. Positive zero error: When the jaws of the vernier callipers are closed,
and if the zero mark on the auxiliary (vernier) scale lies to the right of the
main scale zero-mark, then error is called Positive Zero error. So, the zero
correction should be subtracted from the reading which is measured.
Zero error = +0.01 cm
Zero error = +0.04 cm

25. when the jaws are closed and if the reading is 0.10mm, the zero error is
referred to as +0.10mm.
'actual reading = main scale + vernier scale - (zero error)'
thus the actual reading is 19.00 + 0.54 - (0.10) = 19.44 mm

26. Negative zero error: When the jaws of the vernier callipers are in contact, and if the
first mark on the auxiliary (vernier) scale lies to the left of zero of main scale such an
error is called Negative Zero error. So, the zero correction should be added to the
reading which is measured.
Zero error = - 0.02 cm
Zero error = - 0.08 cm

27. when the jaws are closed and if the reading is -0.08mm, the zero error is
referred to as -0.08mm
'actual reading = main scale + vernier scale - (zero error)'
thus the actual reading is 19.00 + 0.36 - (-0.08) = 19.44 mm