Instruments used in Surveying
Instruments
Used for Measuring Distance:
1. Chain
a. Metric chain
b. Steel band chain
c. Günter’s Chain
d. Revenue Chain
e. Engineers chain
2. Arrows (chain
pins)
3. Tapes
a. Cloth or linen Tape
b. Metric Woven
Metallic Tape
c. Metric steel Tape
d. Invar tape.
e. Synthetic Tape.
f. Wooden pegs.
5. Ranging Road.
6. Ranging Poles.
7. Offset Rod.
8. Laths
9. Whites
10. Plumb Bob
1. Chain
The chain is
composed of 100 or 150 pieces of galvanized mild steel wire 4mm in diameter
called links. The end pf each link are bent into a loop and connected together
by means of three oval rings. The ends of the chain are provided with brass
handles for dragging the chain on the ground. The length of link is the
distance between the centers of the two consecutive middle rings. The end links
includes the handles. Metallic tags or indicators are fixed at various
distinctive of the chain to facilitate quick reading.
a.
Metric surveying chains:
The chains are made
in lengths of 20 and 30 meters. To enable the reading of factious of a chain,
tallies (tags) are fixed at every five meter length and small brass rings are
provided at every meter length. To facilitate holding of the arrows in position
with the handle, a groove is cut on the out side surface of the handle. The
handle joints are flexible. the tallies used for marking the distances in a
metric chain are marked with letters ‘Me’ and ‘m’.
b. Steel Band Chain:
It consists of a
ribbon of steel with bras handle at each end. It is 20 or 30long and 16 mm
wide. It is wound on an open steel cross or on the metal reel in a closed case.
The graduations are etched as meters decimeters, centimeters on one side and 0.2
m links on the other. Brass tallies are fixed at every 5 m length of the band.
c. Günter’s Chain:
It is 66 fit long
and is divided into 100 links. Each link is 0.66 ft long. It is very convenient
for measuring distance in miles and furlongs. Also for measuring area and when
the units of area is an acre
d. Revenue Chain:
It is commonly used
for measuring fields in cadastral survey. It is 33 ft long and divided into 16
links. Each link is 2.0625 ft long.
e. Engineer’s chain:
It is 100 ft long
and it is divided into 100 links. Each link is 1 ft in a length. Used in all
Engineering surveys.
2. Arrows (chain
pins):
They are also called
as marking or chaining pins and are used to mark the end of chain during the
process of chaining. They are made up of good quality hardened and tempered
steel wire of 4mm in diameter. The arrows are made 400 mm in length. They are
pointed at one end of inserting in to the ground. The other end is in to a
ring.
3. Tapes:
a. Cloth or Linen
Tape:
Used for taking
subsidiary measurements, such as offset. It is very light and handy. It is
easily affected by damp. If wet it shrinks. It stretches easily and likely to
twist.
b. Metric Woven
Metallic Tape:
They are available
in 2, 10, 30, and 50 meters. The tape is made of yarn and metal wire. A metal
ring is attached to the outer end of tapes. The length of the tape includes the
metal ring. At every centimeter a black line 8 to 10 mm in height is drown.
Every 5 centimeters is marked with an arrow in black. Every decimeter and meter
is marked with a back line extending over the full width of the tape/ the
graduation marks at every decimeter and meter are numbered with black and red
figures, respectively.
c. Metric Steel
Tape:
Tape is available in
1, 2, 10, 30, and 50 meters. The tape is of steel or stainless steel. The outer
end is provided with a ring. The length of the tape includes the metal ring.
The tape is marked with a line at every five millimeters, centimeters,
decimeters, and meter. Every decimeter and meter shall be marked with Hindu
Arabic numerals in bold. When the button release devised is pressed, the tape
automatically rewind in to the case.
d. Invar Tape:
For highest
precision work the invar tape in used. It is made of an alloy of steel and
nickel (36%).
It is 6 mm wide and
may be obtained in length of 30m and 100m. It is not calibrated through its
length but has terminal lines. Each terminal division has ten 1 mm division. It
is very expensive.
e. Synthetic Tape:
The tapes are
manufactured of glass glass fiber having PVC coating. They are graduated every
10 mm and figured every 100 mm. Meter, figures are shown in red. They are
convenient for measuring shorts lengths.
Instruments for
marking stations:
1. Wooden Pegs:
These are used to
mark the positions. They are made of hard timber and tapered at one end. They
are usually, 2.5 cm square and 15 cm long. But in soft ground 40 to 60 cm long
and 4 to 5 cm square is suitable. They should be driven in the ground with about
4 cm lengths, projecting above the ground.
2. Ranging rods:
Used for making the
positions of stations and for ranging. They are made of seasoned timber of
teak, blue pine, sisov or deodar. They are circular or octagonal in cross
section of 3 cm diameter. Lower shoe is 15 cm long. They are made in two sizes
as 2 meters and 3 meters and are divided in to equal parts each 0.2 m long.
They are painted alternatively black and white or red and white. Now a day
instead of timber, mild steel hallo pipes are used.
3. Ranging Poles:
Similar to the
ranging rods but are heavier, they vary in length from 4 m to 6 m or more. Used
in the case of very long lines.
4. Offset Rod:
Similar to the
ranging rod, they are usually 3 m long and is divided into parts each 0.2 m
length. Top is an provided with an open ring for puling or pushing the chain
through a hedge. It has two short narrow vertical slots. It is used for
aligning short offsets.
5. Laths:
Useful for ranging
long lines, also used over uneven ground where the ranging rod is not visible
due to obstructions, they are light, cheap, being white; they are easily
visible at a great distance. Unusually 1.0m long
6. Whites:
When the ranging rod
is not available or insufficient, whites are used. These are thin strip of
bamboo and 40 cm to 1 m in length. One end is sharp and the other end is split
for inserting pieces of white papers. They are also useful for temporary
marking of counter points.
7. Plumb Bob:
The plumb bob is
required when measuring the distance along slopes in order to transfer points
to the ground. It is also used for testing the verticality of ranging poles.
