Prepared by:-Nikul pithva(m-36)Rabari tagesh(m-35)

Instrument of levellingECE(210004)

Guided by:-Nutan Patel

Mechanical department

The art of determining the relative heights (elevations) of different points on or below the surface of the earth is known as levelling.

Aims of levelling:-The aim of levelling is to determine the relative heights of different points on or below the surface of the undulation of the earth and to determine the undulation of the ground.

INTRODUCATION

The instruments commanly used in levelling are:-

1) A level2) A levelling staff

1) Dumpy level:-

description of dumpy level:-

1) Tripod stand :- The tripod stand consists of three legs which

may be solid or telescopic. The legs are made of wood or aluminium. The lower ends of the legs are fitted with iron

shoes.

2) Levelling Head:- The levelling head consists of two parallel

plates (trivet and tribrach) having three grooves to support the foot screws.

3) Foot screws:- Three foot screws are provided

between the trivet and tribrach. These are used for levelling. By turning the foot screws the tribrach

can be raised or lowered to bring the bubble to the centre of its run.

4) Telescope:- The telescope consists of two metal

tubes. One moving within inside of other. It also consists of an object glass and

eye-piece on opposite ends. A diaphragm is fixed with the

telescope just in front of the eyes.

5) Bubble tubes:- the bubble tubes are fixed on top of

the telescope. Two bubble tubes, one called the

longitudinal bubble tube and other the cross-bubble tube, are placed at right angles to each others.

These tubes contain spirit bubble.

6) compass:- In some instrument compass is

provided just below the telescope for measuring the magnetic bearing of a line when required.

7) Axis of the telescope:- This axis is an imaginary line

passing through the optical centre of the object glass and the optical centre of the eye piece.

8) Line of collimation:- It is an imaginary line passing

through the intersection of the cross-hairs at the diaphragm and the optical centre of the object glass and its continuation.

It is also known as the line of sight.

2) Levelliing staff:-The levelling staff is used for measuring the vertical distances between the points on the ground and the line of collimation.

Types of levelling staves:

1. Self reading: a) Solid staff b) Telescopic staff c) Folding staff

a) Solid staff:-

the metric solid staff is generally 3 m long, 75 mm wide and 25 mm thick, with a metal shoe at the bottom, and graduated on one face.The smallest division is of 5 mm in metric system.They are generally made of good-quality wood of pine,devdar,etc. Fig. Solid

staff

b) Telescopic staff:-A telescopic staff consists of two hollow pieces and one solid top piece, each telescoping into the bottom one.When the staff is folded up, it is only a little longer than the lowest piece.When the upper sections are pulled out for use, they are engaged and held by brass spring-catches.It is thus longer than a solid staff up to 4 m to 6 m.

Fig. telescopic staff

c) Folding staff:- A folding staff is generally 4 m long and is divided into two equal parts of 2 m each.

It is hinged in the middle so that top half can be folded over to lie against the lower half.

Fig. Folding staff

2) Target staff:-

A target staff has a sliding target equipped with vernier which can be clamped at any point along the staff.

For taking the reading ,the level man directs the staff man to raise or lower the target till it is bisected by the line of sight.

Thank you