(v) The error due to dishevelment of the bubble can be minimised by taking precautions in levelling. If not, the discrepancy is equally distributed among all the measured angles. [gravityform id="1" title="false" description="false" ajax="true"]. (v) Loosen the upper clamp and turn the telescope clockwise until the line of sight is set nearly on the right hand object (B).
Account Disable 12. Report a Violation 11. (b) Error due to the unequal graduations. The mean of the two vernier readings gives the second value of the angle ABC which should be approximately or exactly equal to the previous value. This method is used for very accurate work. Bisect it accurately by using the lower clamp and its tangent screw.
(iii) Direct the telescope to some well-defined object (P) or say, the station point A, which is known as the ‘Reference object’. All Rights Reserved BNP Media. In this method; the same angle is added several times mechanically and the correct value of the angle is obtained by dividing the accumulated reading by the number of repetitions. The mean of the two vernier readings (after deducting 180° from the reading at vernier B) will give the value of the angle AOB. Disclaimer 8. By visiting this website, certain cookies have already been set, which you may delete and block. This is done to detect the error caused by turning the wrong tangent screw. The method provides an easy way for a beginner to test instrument readings and pointings. Three repetitions with face left and three repetitions with face right are quite sufficient except in cases of very precise work.
These cookies will be stored in your browser only with your consent. Bring the point A into exact coincidence with the point of intersection of the cross-hairs at diagram by using the vertical circle clamp and tangent screws. (The face of the instrument should be left.). (vii) Loosen the upper clamp, turn the telescope clock-wise and again sight towards B. Bisect B accurately by using the upper tangent screw. Alternatively bring the vertical cross-hair exactly on the lowest visible portion of the arrow or the ranging rod representing the point A in order to minimise the error due to non- verticality of the object. The reading of the vernier A which was initially set at zero gives the value of the angle AOB directly and that of the other venier B by deducting 180°. Bisect A accurately using the lower tangent screw. Copyright 10.
The observations are recorded in the tabular form as given in Table 9.1. This website requires certain cookies to work and uses other cookies to
(v) Read both verniers- The object of reading the verniers is to obtain the approximate value of the angle. In this operation, the lower clamp and its tangent screws should not be touched. The vernier A is initially set to zero for convenience only. this website, certain cookies have already been set, which you may delete and Turn the instrument and direct the telescope approximately to the left hand object (A) by sighting over the top of the telescope. To measure the horizontal angle AOB by repetition: (i) Set up the theodolite at station -point O and level it accurately.
Problems in Ranging and Chaining of a Line | Chain Surveying | Surveying, Unconventional Machining Processes: AJM, EBM, LBM & PAM | Manufacturing, Material Properties: Alloying, Heat Treatment, Mechanical Working and Recrystallization, Design of Gating System | Casting | Manufacturing Science, Forming Process: Forming Operations of Materials | Manufacturing Science, Generative Manufacturing Process and its Types | Manufacturing Science. (v) Similarly bisect C and D successively, read both verniers at each bisection, find the values of the angles BOC and COD. (viii) Repeat the process until the angle is repeated the required number of times (usually 3). (xii) Close the horizon and apply the necessary correction to all the angles as before. It may be set at any other reading, and the difference between the initial and the final readings of the vernier A will give the value of the angle AOB. Check the reading at vernier A which should still be 0 or 360° and note the reading at vernier B. In this way, angles can be measured to a finer degree of accuracy than that obtainable with the least count of the vernier. Closing the horizon is good for spur points, to show that a mistake wasn't made.
If large, the readings should be discarded and a new set of readings be taken.
(iv) Loosen the upper clamp and turn the telescope clockwise until the point B is exactly sighted by using the upper tangent screw. (vii) Change the face of the instrument and repeat the whole process.
Repetition Method. Tighten the upper clamp and turn its tangent screw to bring the two zeros into exact coincidence. It is generally preferred when several angles are to be measured at a particular station. Reiteration is another precise and comparatively less tedious method of measuring the horizontal angles. Read the vernier B and record both vernier readings. Then to measure these angles by reiteration method: (i) Set up the instrument over station point O and level it accurately. Divide the sum by the number of repetitions and the result thus obtained gives the correct value of the angle AOB. Plagiarism Prevention 5. (vi) Loosen the lower clamp and turn the telescope clock-wise until the object (A) is sighted again. If not, note down the error. Prohibited Content 3.
(vi) Finally, close the horizon by sighting towards the reference object (P) or the station-point A. The mean of the two vernier readings (after deducting 180° from the reading on vernier B gives the value of the required angle AOB.). data. Check the vernier readings which must be the same as before. : To measure horizontal angle AOB: (i) Set up the theodolite at station … Suppose it is required to measure the angles AOB, BOC and COD.
Ordinary Method (Fig.