This presentation by Hooria Shahzad is about measuring instruments in which we study metre rule, measuring tape, vernier callipers and screw gauge ; construction of vernier callipers and screw gauge.
1. MEASURING INSTRUMENTS
• Measuring instruments are used to measure physical
quantities.
• Scientists, engineers and other humans use a vast range
of instruments to perform their measurements.
• Measuring instruments:
METRE RULE
MEASURING TAPE
VERNIER CALLIPERS
SCREW GUAGE
2. METRE RULE:
• A metre rule is used to measure length of an object or
distance between two points.
• It is one metre long which is equal to 100 centimetres and
each centimetre is divided into 10 small divisions called
millimetre (mm).
• Metre rule is made up of different materials and in a wide
range of size.
3. MEASURING TAPE:
• Measuring tapes are used to measure length in metres
and centimetres.
• It is a common measuring tool.
• It is used by blacksmith and carpenters.
• It consists of a ribbon of cloth, plastic, fiber or glass .
• Its design allows for a measure of great length.
4. VERNIER CALLIPERS:
• A vernier calliper is an instrument used to measure the
internal or external diameters of an object.
5. VERNIER CALLIPERS:
• Vernier callipers consists of two jaws.
• One is a fixed jaw with main scale. It has centimetre and
millimetre marks on it.
6. VERNIER CALLIPERS:
• The other jaw is a moveable jaw having vernier scale on
it. A vernier scale has 10 divisions on it and each division
is 0.9 mm.
7. LEAST COUNT OF VERNIER SCALE:
• The difference between one small division on main scale
and one vernier scale division is 0.1 mm.
• It is called least count of the vernier callipers.
• To find the least count of vernier callipers, we use this
method:
Least count of Vernier Callipers = smallest reading on main scale /
no. of divisions on vernier scale
= 1mm / 10 divisions = 0.1 mm
Hence, Least Count = 0.1 mm = 0.01 cm
8. ZERO ERROR AND ZERO
CORRECTION
• What is zero error?
If there is any error in the measuring instrument then it is
called zero error of the instrument.
• What is zero correction?
If zero line of vernier scale is not coinciding with main scale
the zero error will exist. Knowing the zero error necessary
correction can be made to find the correct measurement.
Such a correction is called zero error.
9. ZERO ERROR:
• There is no zero error as zero line of vernier scale is
coinciding with the zero of main scale.
10. POSITIVE ZERO ERROR:
• Zero error is (0+0.03) cm as 3rd line of vernier scale is
coinciding with main scale.
• Zero error is positive if the zero line of vernier scale is on
the main scale.
11. NEGATIVE ZERO ERROR:
• Zero error is (-0.1+0.05) cm as 5th line of vernier scale is
coinciding with main scale.
• Zero error is negative if the zero line of vernier scale is
outside the main scale.
12. SCREW GAUGE:
• A Screw gauge is an instrument used to measure small
lengths such as diameter of a wire, thickness of a sheet,
etc.
• It is also called as micrometer screw gauge.
13. CONSTRUCTION:
• SCREW:
A simple screw gauge consists of a U-shaped metallic
structure attached to a hollow cylinder on one end.
• Hollow cylinder:
A hollow cylinder has millimetre scale over it along a line
called index line parallel to its axix.
• Spindle:
A spindle is a very accurately machined screw and the
object is measured between the spindle and the anvil.
14. CONSTRUCTION:
• Thimble:
The thimble is the end of the cylindrical tube and is turned
to move and adjust the spindle. The thimble carries the
vernier or secondary scale.
Ratchet; Ratchet it itself a small device which is used to provide a
limited applied force, it is installed at the right end of screw gauge,
ratchet acts as a safety device for instruments and also adds more
precision in measurement.
• Locking device:
Some screw gauge also consists of locking device which is
usually used to hold the scale at a particular position for
prevent any kind of error while taking readings.
