RANGING INSTRUMENT

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Survey Instruments and concepts

  Ranging Instruments

 1.   Signals and Ranging Rod.

1.a.   Pegs:

Generally, pegs are made up of wood. The Size of pegs depends on the type of survey work They are used for, and the type of soil they have to drive in. The peg should be driven vertically into the soil & the top portion should be visible clearly. pegs are the exact point from which the measurements are to be taken or over which an instrument is to be set. A nail or brass stud is driven into the flat top of the peg for permanent mark. Markers may be also used for very Temporary marks.

Generally, pegs are;

 1) Made of Timber or steel 

2) used to mark the position of stations. 

3) pegs are in length of 15 cm to 60cm (depends up on nature of ground)

 

 

 

 

 

 

 

 

 

1.b.   Ranging Rod :

It is surveying Instrument which is used to mark the position of a station and to set out straight lines on the field. It's Also used for ranging straight lines. At first It was made up of strong and straight bamboo or tree branches. Metals point are attached at bottom and a flag of 25cm square shape at the top (also called a ranging pole) (3m to 6m). Now a day it was made up of wood, metal or fiberglass. The rods are usually about 30 to 40 mm in diameter and 2 to 3 m long and painted with Red & white color alternative with 20cm apart. A Ranging rod which has no flag at the top and used for measuring Small offset from the survey line is known as offset rod.

 There are two types of ranging rods, such as screw type & socket type.

 Features of Ranging Rod:

1.   International standard, manufactured under strict quality. 

2.   The Ranging rods are of high accuracy & durability

3.   Strong steel alloy pipe is used.

4.   Painted with long lasting waterproof paint 

5.   Brightly colored for high on-site visibility

 

 

 

1.c.   Plumb bob:

A plumb bob or plummet is a piece of metal usually with a pointed tip on the button and suspended with the help of string and used to check the object is vertical or not. It is also used in different other instruments to fix the instrument just over the station, called centering. It comes in use from the time of ancient Egypt.


 1.2   Line Ranger:

It is an optical instrument which is used for locating a point on a line and hence it is useful for ranging. It is light and easy to use. It consists of two (2) plane mirrors or 2 right-angled isosceles prisms placed one over the other. The diagonals of the prism are silvered so as to reflect the rays. Lower prism is fixed while the upper prism is moveable. It is provided with handle at bottom which make easy to user for using instrument. Its advantage is, it needs only one person to range a line and locale a point. Two Ranging rods are fixed at inter-visible points. Then Surveyors moves to and fro at right angle of line with the line ranger. The point where 2 images coincide in line ranger, that is the point. At this point a plumb Bob is dropped from the handle of line ranger and point is marked on ground.

 

1.3.   Cross staff

1.3.a.   Cross Staff:

It is a simple instrument used for setting out a right angle(offset). 

There are three types of cross staff.

 A.     Open cross staff:   

The simplest form of cross staff is the open cross staff. It consists of two parts (1) Head & (2) Leg. The head consists of four arms with vertical slits. The two pairs of arms are at right angles to each other. The vertical Slits are meant for Sighting the object and the ranging rods. It used to set perpendicular only(right angle).


B.     French cross staff:

It consists of octagonal brass box with slits cut in each face so that the opposite pairs form a sight line. It was mounted over a short ranging rod. It is used to set 90 degree , 45 degree and 134 degree.


C.     Adjustable cross staff:

 It consists of a brass cylinder tube divided at the middle. The lower portions remain fixed and upper portions can be rotated relative to the lower one by circular rack. Sighting slights are provided in both parts. The lower part graduated into 'degrees and their subdivisions while the upper one carries a Vernier. It can be used to set any angle.


 

 

 


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