JNTU B.Tech II PRINCIPLES OF CIVIL AND STRUCTURAL ENGINEERING Previous Question Paper (September 2021 - R13)

The repetition method of measuring horizontal angles eliminates errors due to: 1) Imperfect adjustment of the instrument, such as the horizontal axis not being perpendicular to the vertical axis; 2) Inaccurate graduation of the horizontal circle; 3) Errors in bisection of the signal; and 4) Errors in reading the vernier scale. By repeating the measurement multiple times and averaging, these systematic and observational errors are significantly reduced.

To set out a horizontal angle by the repetition method: 1) Set up the theodolite at the station point and level it. 2) Bisect the first point (A) and set the horizontal vernier to zero. 3) Loosen the upper clamp, turn the telescope to the second point (B), and clamp the upper screw. 4) Read the vernier; this is the first measurement. 5) Without resetting the vernier to zero, loosen the lower clamp, turn the telescope back to point A, and clamp the lower screw. 6) Loosen the upper clamp, turn the telescope to point B, and clamp the upper screw. 7) Repeat this process for the desired number of repetitions (usually three or six). 8) The final reading divided by the number of repetitions gives the mean horizontal angle.

A total station integrates an electronic theodolite and an electronic distance meter (EDM) into a single unit, allowing for the simultaneous measurement of both angular and linear coordinates. The electronic theodolite component measures horizontal and vertical angles using digital encoders, which replace traditional optical verniers, providing higher precision and eliminating reading errors. The EDM component uses infrared or laser beams to measure the distance to a prism or reflective target based on the phase shift or time-of-flight of the light wave.

By combining these, the total station performs real-time trigonometric calculations to determine the 3D coordinates (X, Y, Z) of a point relative to the instrument station. It includes an onboard microprocessor that stores data, manages instrument settings, and performs onboard computations like coordinate geometry (COGO) and area calculations. This integration eliminates the need for separate instruments, reduces manual recording errors, and significantly increases the speed and accuracy of surveying tasks.