Note for Surveying-1 - s-1 by Noor Mohd

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The theodolite 1.1 Introduction: - Theodolite is an instrument used to measure horizontal and vertical angles. It consists of a telescope by means of which distant objects can be sighted. The telescope has to distinct motions one in the horizontal plane and the other in the vertical plane, the former being measured on a graduated horizontal circle by means of a set of verniers, and the latter on a graduated vertical circle by two verniers. It can also be used for various other purposes such as lying of horizontal angles, locating points on a line, prolonging survey lines, establishing grades, determining differences in elevation etc. Theodolites are mainly used for surveying applications, and have been adapted for specialized purposes in fields like metrology and rocket launch technology. When the telescope is pointed at a target object, the angle of each of these axes can be measured with great precision, typically to seconds of arc. 1.2 Classification: - Theodolite may be classified into two types are as follows: • Transit theodolite • Non-transit theodolite Theodolite is also classed as• Vernier theodolite • Micrometer theodolite 1

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1.2.1 Transit theodolite: - A theodolite is said to be a transit then its telescope can be revolved through 180° in a vertical plane about its horizontal axis. The transit type is largely used, while the other two types have now become obsolete. Fig.- tansist theodolite 2

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1.2.2 Non-transit theodolite: - A theodolite is said to be a nontransit when its telescope cannot be revolved through 180° in a vertical plane about its horizontal axis. Fig.-non transit theodolite 3

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1.3 The essentials parts of the theodolite: 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. Telescope Vertical Scale (or Vertical Circle) The index frame Vertical Clamp and Tangent Screw Upper Plate The Lower Plate Horizontal Scale (or Horizontal Circle) The Upper Horizontal Clamp and Tangent Screw. The Lower Horizontal Clamp and Tangent Screw. The Plumb Bob Leveling screw Tripod All of these parts are explained in following:- 1. Telescope: - 2. The vertical circle: - 3. The index frame: - the index frame is a t-shaped frame consisting the telescope is an integral part of the theodolite and is mounted on a spindle known as horizontal axis or trunnion axis. The vertical circle is a circular graduated arc attached to the trunnion axis of the telescope. of a vertical leg known as clipping arm and a horizontal bar is known as vernier arm or index arm. 4. The upper plate:- The upper plate is the base on which the standards and vertical circle are placed. 4