Instrument used for chain surveying
The various instrument used for the determination of the length of the line by chaining are as follows
- Metric surveying chain
- Tapes
- Arrows
- Pegs
- Ranging rods
- Offset rods
- Plasterers’ laths and whites
- Plumb bob.
Metric surveying chains
There are two varieties of metric chains. One is the 20m length and other is 30m length chain is divided into 100 or 150 links of 20 cm length. The links are 4 mm in diameter and are galvanized mild steel wire and are connected to each other by means of three rings two are the oval and central one being circular of the same wire. Brass handles are provided to the links at either end, which are connected to the links through swivel joints so that the chain can be turned around without twisting. The length of the first link includes the length of the handle. To enable the easy reading, the tallies are fired at every five-meter length and small brass rings are provided at every meter length. The brass tags of a particular shape are fined at the specific middle oval rings to read the round-numbered distance.
Tapes
Tapes are grouped into four categories depending upon the material used for its construction
- Cloth or Linnen tape
- Woven metallic tape
- Metric steel tape
- Inver tape
- Synthetic tape
- Cloth or linen tape
It is made of a varnished strip of woven linen 12 to 15 mm wide. It is available in lengths of 10m, and 30m and 30m it is little used in surveying, but can be used for making subsidiary measurements such as offsets of a building.
Woven metallic tape
It is made of cloth strip woven with fine brass wires. It is also 16mm wide and available in length of 10, 15, 30 and 60m. The brass wires durable prevent the tape from twisting and stretching. It is more durable than cloth tape. Hence, it is used for general purposes.
Metric steel tap
It is made of steel or strain – less steel, may be provided with a vinyl coating. It is also 6mm to 10mm wide and available in length of 10, 15, 30 and 60m. it is used to measure the distance accurately.
Inver tape
It is made of an alloy of steel and nickel. It is also 6mm wide and available in length 15, 30, and 100m. It has a great accuracy. Hence, it is used for work of the highest precision such as measurement of the baseline in triangulation survey and in city work.
Synthetic tape
It is made of glass – fiber having P.V.C coating. It maintains its length. It is strong and durable. So it is used for measuring length with a good degree of precision. It is available in 5m, 10m,20m and 30m length.
Arrows
Arrows or chain pin is a rod of iron or steel, of diameter 4mm. it is 300 to 400mm in length. The arrow has a loop of diameter 50mm at one end whereas the other end is pointed for a length of 15mm. they are used for recording the chain length measured.
Pages
It is made of hardwood and is 2.5cm square in cross-section and 150mm long. It is tapered
At another end to facilitate easy driving. It is used to mark the position of the survey station or the endpoints of surve line. The pegs are driven into the ground using a mallet or wooden hammer such that its length of about 40 mm project above the surface of the ground.
Ranging rods
These are made of timber and steel. They are circular, octagonal in shape and of diameter 2 to 3cm. they are provided with a tapering edge and shade with cross shoe 150mm long at the bottom end facilitate easy driving. There is order to make them visible from a distance, they are pointed alternately black and white or red and white. Ranging is necessary before starting the measurement of a line whose length is more than the chain length so that the measurement is done in a straight line.
Offset rods
An offset rod is a similar ranging rod and has a length of 3. They are round wooden rod shoed with a pointed iron shoe at the one end and provided with a notch or a hook at the other. The hook facilities pulling and chain through hedges and other obstructions.
Plaster’s lath
The laths used by plasters for plastering the walls may be used for ranging in a level or open ground with an obstruction such as hedges, walls, or when crossing a depression. They are very light in weight and can be carried from place to place easily. The lower end can be easily sharpened to a point and cut to any desired length when required.
Plumb Bob
The pump is a ball made of brass or bronze of the shape of a pear. It has a fine steel point. There is a hook at the top for attaching a string of nylon. Its length is about 50mm. the plumb bob is used for measuring distance on the sloping ground. used in centering of various instruments such as a magnetic compass, plane table, dumpy level or theodolite etc.
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