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.
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Chapisha Maoni