Vernier Caliper
A vernier caliper is a measuring device used to
precisely measure linear dimensions.
It is a very useful tool to use when measuring
the diameter of a round objects like cylinders because the measuring jaws
can be secured on either side of the circumference.
Vernier calipers have both a fixed main scale and a
moving vernier scale.
The main scale is graduated in either millimetres or
tenths of an inch.
The vernier scale allows much more precise readings to
be taken (usually to the nearest 0.02mm or 0.001 inch) in comparison to a
standard ruler (which only measures to th nearest 1mm or 0.25 inch).
Uses of a vernier calipers:
Vernier callipers are used to measure,
(i)The length of a rod
or any object
(ii)The diameter of a
sphere
(iii)The internal and
external diameter of a hollow cylinder
(iv)The depth of a
small beaker.
Description of vernier callipers:
The main parts of Vernier Callipers are;
1.
Main Scale - The main scale is similar to that on a ruler,
graduated in mm and cm on one side ; inches on the other side.
2.
Vernier Scale – The vernier scale is a sliding scale
.It slides parallel to the main scale and enables readings to be made to a fraction
of a division on the main scale.
3.
Screw -The vernier scale can be fixed at any position on
the main scale with the help of a screw.
4.
Jaws
–It has two jaws. The lower jaws are called outside jaws and they are used to
measure the length of a rod, diameter of a sphere or the external diameter of a
cylinder. The upper jaws are called the inside jaws which are used to measure
the internal diameter of a hollow cylinder or pipe .
5.
Strip - The thin strip is used to measure the depth of
the objects like beakers.
Least
Count of Vernier Caliper:
Least count (L.C.) = 1 M.S.D - 1 V.S.D
In this Vernier caliper one main scale division
(49mm) are divided in to 50 equal part in the Vernier scale.
1
main scale division (1MSD) = 1 mm
1Vernier scale division
(1VSD) = 49\50 mm
Least count = 1mm – 49\50 mm
= (1- 0.98) mm
Least
Count = 0.02mm
How
to use a Vernier caliper:
1) The jaws are first
gently closed on the object to be measured.
2) Note the main scale
reading (M.S.R)
3) Note the division on
vernier scale which coincides with any division of the main scale. Multiply
this number of vernier division with the least count. This is the vernier scale
reading(V.S.R)
Hence V.S.R = Vernier scale Divison
x Least count(L.C.)
4) Add the main scale
reading to the vernier scale reading. This gives the observed length.
Hence, Observed Reading = Main scale reading +
Vernier scale reading
Observed Reading = Main scale
reading +( Vernier scale Divison*Least Count)
Vernier height gauge
A height
gauge is a measuring device used either for determining the height of
objects, or for marking of items to be worked on.
These
measuring tools are used in metalworking or metrology to
either set or measure vertical distances; the pointer is sharpened to allow it
to act as a scriber and assist in marking out work pieces.
Height
gauges may also be used to measure the height of an object by using the
underside of the scriber as the datum. The datum may be permanently fixed or
the height gauge may have provision to adjust the scale, this is done by
sliding the scale vertically along the body of the height gauge by turning a
fine feed screw at the top of the gauge; then with the scriber set to the same
level as the base, the scale can be matched to it. This adjustment allows
different scribers or probes to be used, as well as adjusting for any errors in
a damaged or resharpened probe.
In a vernier height gauge, as illustrated in Fig. ,
the graduated scale or bar is held in a vertical position by a finely ground
and lapped base. A precision ground surface plate is mandatory while using a
height gauge. The feature of the job to be measured is held between the base
and the measuring jaw. The measuring jaw is mounted on a slider that moves up
and down, but can be held in place by tightening of a nut. A fine adjustment
clamp is provided to ensure very fine movement of the slide in order to make a
delicate contact with the job.
Fig. Vernier
Height Gauge
Unlike in depth gauge, the main scale in a height
gauge is stationary while the slider moves up and down. The vernier scale
mounted on the slider gives readings up to an accuracy of 0.01 mm.
Vernier height gauges are available in sizes ranging
from 150 to 500 mm for precision tool room applications. Some models have quick
adjustment screw release on the movable jaw, making it possible to directly
move to any point within the approximate range, which can then be properly set
using the fine adjustment mechanism.
Vernier height gauges find applications in tool rooms
and inspection departments. Modern variants of height gauges such as optical
and electronic height gauges are also becoming increasingly popular.
Vernier Depth Gauge
A vernier depth gauge is a more versatile instrument,
which can measure up to 0.01 mm or even finer accuracy. Figure 1 illustrates
the constructional features of a Vernier depth gauge. The lower surface of the
base has to butt firmly against the upper surface of the hole or recess whose
depth is to be measured.
The vernier scale is stationary and screwed onto the
slide, whereas the main scale can slide up and down. The nut on the slide has
to be loosened to move the main scale.
The main scale is lowered into the hole or recess,
which is being measured. One should avoid exerting force while pushing the
scale against the surface of the job being measured, because this will not only
result in the deformation of the scale resulting in erroneous measurements, but
also accelerate the wear and tear of the instrument.
This problem is eliminated thanks to the fine
adjustment clamp provided with the instrument. A fine adjustment wheel will
rotate the fine adjustment screw, which in turn will cause finer movement of
the slide. This ensures firm but delicate contact with the surface of the job.
Vernier depth gauges can have an accuracy of up to 0.01 mm. Periodic cleaning
and lubrication are mandatory, as the main scale and fine adjustment mechanism
are always in motion in the process of taking measurements.