Introduction on instruments used for chaining

Instruments Used in Chaining
• The following instruments are used while
chaining.
• Chains
• Tapes
• Arrows
• Ranging rods and offset rods
• Laths & Whites
• Pegs
• Plumb bob
• Line Ranger

Chains
• Various types of chains used in surveying are
• Metric Chain
• Gunter’s Chain or Surveyor’s Chain
• Engineer’s Chain
• Revenue Chain
• Steel Band or band chain

Metric Chain
• Normally this chain consists of galvanized
mild steel wire of 4 mm diameter known
as link. The ends of the links are bent into
loop and connected together by means of
three oval rings which provide the
flexibility to the chain and make it less
liable to kinking. Both ends of the chain
have brass handle with swivel joint so that
the chain can be turned round without

Metric Chain
• In a metric chain at every one meter interval of
chain, a small brass ring is provided. Brass tallies
are also provided at every 5.0 m length of chain.
Each tally has different shape which indicates 5 ,
10, 15m from any one side of the chain, metric
chains are available in 20 m and 30 m length.
• A 20 m chain has 100 links each of 20 cm and 30
m chain has 150 links. Length of chain is
embossed on the brass handles of the chain.

Günter's chain
• A 66 feet long chain consists of 100 links each
of 0.66 ft it is known as Gunter’s Chain
• Here, 10 sq chain are equal to 1 acre,
• 10 chains= 1 furlong and 8 furlongs = 1 mile
• This chain is suitable for taking length in miles
and areas in acres.

Engineer’s Chain
• A 100 ft chain of 100 links each of 1 foot is
known as Engineer’s chain. Brass tags are
fastened at every 10 links. This chain is used to
measure length in feet and area in square
yards.

Revenue Chain
• Revenue chain is 33 ft long chain consisting of
16 links. This chain is used for distance
measurements in feet & inches for small areas.

Steel Band or Band Chain
• Steel bands are preferred than chains because
they are more accurate, but the disadvantages
is that they get broken easily and are difficult
to repair in the field. They are 20 and 30 m
long, 12 to 16 mm wide and 0.3 to 0.6 mm
thick. They are numbered at every metre and
divided by brass studs at every 20 cm

Testing and Adjustment of Chain
• During continuous use, the length of a chain
gets altered. Its length is shortened chiefly due
to the bending of links. Its length is elongated
either due to stretching of the links and joints
and opening out of the small rings. For
accurate work it is necessary to test the chain
time to time. The chain can be thus tested by a
steel tape or by a standard chain. Sometimes, it
is convenient to have a permanent test gauge
established where the chain is tested.

• When the length of a chain is measured at a
pull of 8 kg at 20 0C the length of the chain
should measure 20 m ± 5 mm and 30 m ± 8
mm for 20 m and 30 m long chain shall be
accurate to within 2 mm. Following measures
are taken to adjust the length of a chain.

If chain is found to be too long
• It can be adjusted by;
• Closing up the joints of the rings if found to be
opened out
• Reshaping damaged rings
• Removing one or more small rings
• Adjusting the links at the end.

• If the chain is found to be too short
• Straightening the bent links
• Opening the joints of the rings
• Replacing one or more small circular rings by
bigger ones.
• Inserting new rings where necessary.
• Adjusting the links at the end.

Measuring Tapes
• Tapes are used for more accurate
measurement. The tapes are classified based
on the materials of which they are made of
such as:
• Cloth or linen tape
• Fibre Tape
• Metallic Tape
• Steel tape
• Invar Tape

Measuring Tapes
Cloth or linen Tape
• Linen tapes are closely woven linen and
varnished to resist moisture. They are
generally 10 m, 20 m, 25 m and 30 m long in
length and 12 to 15 mm wide. They are
generally used for offset measurements. These
tapes are light and flexible.

Measuring Tapes
• Fibre Glass Tape
• These tapes are similar to linen and plastic
coated tapes but these are made of glass fibre.
The tapes are quite flexible, strong and non-
conductive. These can be used in the vicinity
of electrical equipment. These tapes do not
stretch or shrink due to changes in temperature
or moisture. These tapes are available in length
of 20 m, 30 m and 50 m length.

Measuring Tapes
• Metallic Tape
• A linen tape reinforced with brass or copper wires
to prevent stretching or twisting of fibres is called
a metallic tape. As the wires are interwoven and
tape is varnished these wires are visible to naked
eyes. This is supplied in a lather case with a
winding device. Each metre length is divided into
ten parts (decimetres) and each part is further sub-
divided into ten parts. It is commonly used for
taking offset in chain surveying.

Measuring Tapes
• Steel Tape
• The steel tape is made of steel ribbon of width
varying from 6 to 16 mm. The commonly
available length are 10 m, 15 m, 20 m, 30 m
and 50 m. It is graduated in metres,
decimetres, and centimetres. Steel tapes are
used for accurate measurement of distances.

Measuring Tapes
• Invar Tape
• Invar tape are made of alloy of nickel 36 %
and steel 64 % having very low co-efficient of
thermal expansion. These are 6 mm wide and
generally available in length of 30 m, 50m,
100m. It is not affected by change of
temperature therefore, it is used when high
degree of precesion is required.

Arrows
• Arrows are made of tempered steel wire of
diameter 4 mm. one end of the arrow is bent
into ring of diameter 50 mm and the other end
is pointed. Its overall length is 400 mm.
Arrows are used for counting the number of
chains while measuring a chain line. An arrow
is inserted into the ground after every chain
length measured on the ground.

Ranging Rods and Offset Rods
• Ranging rods are used for ranging some intermediate
points on the survey line. Ranging rods are generally 2
to 3 m in length and are painted with alternate bands of
black or white or red and white colour with length of
each equalizing 20 cm. The location of any survey
station can be known from long distances only by
means of ranging rods. If the distance is too long, a rod
of length 4.0 to 6.0 m is used and is called ranging pole.
• The offset rod is similar to ranging rod with the
exception that instead of the flag, a hook is provided at
the top for pushing and pulling the chain or the tape. It
is also used for measuring small offsets

Laths & Whites
Laths
• Laths are 0.5 to 1.0 m long sticks of soft wood. They
are sharpened at one end and are painted with white or
light colours. They are used as intermediate points
while ranging or while crossing depressions.
Whites
• Whites are the pieces of sharpened thick sticks cut from
the nearest place in the field. One end of the stick is
sharpened and the other end is split. White papers are
inserted in the split to improve the visibility. Whites are
also used for the same purpose as laths

Pegs
• Pegs are made of timber or steel and they are
used to mark the position of the station or
terminal points of a survey line. Wooden pegs
are 15 cm long and are driven into the ground
with the help of a hammer.

Plumb Bob
• Plumb-bob is used to transfer points on the
ground. It is also used for fixing the
instruments exactly over the station point
marked on the ground by checking the centre
of the instrument whether coincides with the
centre of the peg or station not, by suspending
the plumb-bob exactly at the centre of the
instrument under it. Plumb bob is thus used as
centring aid in theodolites and plane table.

Line Ranger
• It is an optical instrument used for
locating a point on a line and hence
useful for ranging. It consists of two
isosceles prisms placed one over the other
and fixed in an instrument with handle.
The diagonals of the prisms are silvered
so as to reflect the rays.

Line Ranger
• Its advantage is it needs only one person to
range. The instrument should be occasionally
tested by marking three points in a line and
standing on middle point observing the
coincidence of the ranging rods. If the images
of the two ranging rods do not appear in the
same line, one of the prism is adjusted by
operating the screw provided for it.

Line Ranger
• To locate point C on line AB (ref. Fig.) the surveyor
holds the instrument in hand and stands near the
approximate position of C. If he is not exactly on line
AB, the ranging rods at A and B appear separated as
shown in Fig. (b). The surveyor moves to and fro at
right angles to the line AB till the images of ranging
rods at A and B appear in a single line as shown in
Fig. (c). It happens only when the optical square is
exactly on line AB. Thus the desired point C is
located on the line AB.

Introduction on instruments used for chaining

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Introduction on instruments used for chaining