Theodolite and its working mechanism

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Theodolite And Its Working Mechanism

Binabh Devkota

[email protected]

Course: Control Surveying (GEOM 202)Teacher: Er. Shangharsha Thapa

Introduction

• Theodolite

-Optical instrument

-Angle measurement (horizontal and vertical)

-One of the most used instruments

• Theodolite Survey

-Survey using theodolite

-Traversing, triangulation, trilateration

-Contouring and detail mapping

-Setting out on ground

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History Of Theodolite

• First made in 1831 by Philadelphian William J. Young

• Adaptation of the theodolite invented in 1720 by John Sisson of England

-telescope (invented circa 1608)

-Vernier

-device for subdividing measurements by 10ths (1631)

-spirit level (1704)

• Improved versions of Young's transit were still in use for land surveying in the 1950s

• Are still broadly used

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Parts of Theodolite(Vernier)

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SN

Parts SN

Parts

1 Vertical Circle 10 Horizontal Clamp

2 Gun Sight 11 Foot Screw

3 Eye piece (telescope)

12 Objective

4 Eye piece (Reading)

13 Micrometer Screw

5 IlluminatingMirror

14 Vertical Clamp

6 Plate bubble 15 Vertical slow motion

7 Reading Slow Motion

16 Optical plummet

8 Reading Clamp 17 Horizontal circle

9 Horizontal Slow Motion

18 Circular bubble

Additional Parts (Digital Theodolite)

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1. On Board Battery2. Keypad3. LCD Screen

-measured value displayed on screen(no need of reading eyepiece)-may have storage capacity

Terms Used In Theodolite Survey

• Vertical axis: axis about which instrument can be rotated in horizontal plane

• Horizontal(trunnion) axis: axis about which instrument can be rotated in vertical plane

• Line of sight or line of collimation: line through intersection of cross hairs, optical center of object glass and continued

• Swinging: rotating 180⁰ in horizontal plane about vertical axis

• Transiting: rotating 180⁰ in vertical plane about horizontal axis

• Face left observation: observation done when vertical circle is left to observer

• Face right observation: observation done when vertical circle is right to observer

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Adjustments Of Theodolite• Temporary adjustments

-Centering: process in which the vertical axis of the instrument is coincided with the plumb line

-Levelling: making the vertical axis of instrument truly vertical

-Focusing: adjustment of telescope to obtain clear visibility of image through eyepiece and objective lens

• Permanent adjustments

-Horizontal axis adjustment: it must be perpendicular to the vertical axis

-Vertical circle index adjustment: it must read zero when the line of collimation is horizontal

-Adjustment of altitude level axis: it must be parallel to the line of collimation

-Collimation adjustment: line of collimation/line of sight should coincide with axis of the telescope

-Adjustment of horizontal plate level axis: it must be perpendicular to the vertical axis

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Reading The Angles

• Reading horizontal angle

-the horizontal angle reading is set zero

-the signal(ranging rod) is bisected

(opening horizontal clamp)

-horizontal clamp closed, reading clamp open

and bisected to another signal

-angle noted looking at reading eyepiece, exactly adjusted using micrometer screw

• Reading vertical/zenithal angle

-Vertical/zenithal angle can be read simply by intersecting

the point and adjusting the micrometer screw

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Sources of errors in Theodolite Survey

• Instrument Errors

-Non-adjustment of plate bubble

-Line of collimation not being perpendicular to horizontal axis .

-Horizontal axis not being perpendicular to vertical axis.

-Eccentricity of Inner and Outer axes

-Graduation not being Uniform.

• Personal Errors

• Natural Errors

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Inside the theodolite

• Horizontal circle(In horizontal plane)

-graduated from 0⁰ to 360⁰

-can be adjusted

-viewed by reflection to reading eyepiece

• Vertical circle(In vertical plane)

-graduated from 0⁰ to 360⁰

-can’t be adjusted

-viewed by reflection to reading eyepiece

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References

• Geodetic Survey, L. (n.d.). Retrieved January 19, 2017, from History of Surveying - Chicago Area Land Surveying: http://gslandsurveying.com/history-of-surveying

• surveyhistory.org. (n.d.). The Surveyor's Basic Tools. Retrieved January 20, 2017, from Survey History: http://www.surveyhistory.org/the_surveyor's_basic_tools.htm

• Punimia, D. B., Jain, K. A., & Jain, K. A. (2005). SURVEYING VOL. I. Jodhpur: Laxmi Publications (P) LTD.

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