Temporary Adjustment of Theodolite
Learn how to perform a temporary adjustment of theodolite with this detailed guide. Discover the correct procedure for setting up and leveling the instrument, including centering, focusing the eyepiece and object glass, and adjusting the vernier. Whether you’re a beginner or an experienced surveyor, this guide covers essential steps for ensuring precise measurements and reliable performance. Follow the expert tips to calibrate theodolites, including methods for leveling, centering, and focusing, ensuring optimal accuracy in your surveying tasks.
what are the temporary adjustment of theodolite.?
Such adjustment involves the following steps.
1. Setting the Theodolite over the Station
The tripod stand is positioned over the desired station. The theodolite is then removed from its box and secured to the top of the stand using a wing nut or the specific fixing mechanism provided with the instrument. The Temporary Adjustment of Theodolite is essential for ensuring accurate measurements in surveying and construction projects.
2. Approximate Levelling by Tripod Stand
The legs of the tripod stand are spread wide and securely fixed on the ground. Approximate leveling is then carried out using the stand. This is achieved by firmly anchoring two legs and adjusting the third leg by moving it in or out, or rotating it clockwise or anticlockwise, until the bubble is approximately centered within its range.
Proper Temporary Adjustment of Theodolite involves setting the instrument over the station, leveling it, and focusing to achieve precise results.
3. Centering
Centering is the process of positioning the instrument precisely over a station. After approximate leveling using the tripod stand, the plumb bob suspended from the hook beneath the vertical axis should roughly align over the station peg. Accurate centering is then achieved using the shifting head (movable capstan nut) to ensure the plumb bob is directly over the nail of the station peg.
4. Levelling
Master the Temporary Adjustment of Theodolite process, which includes centering, leveling, and focusing, for improved surveying accuracy.
Before beginning the leveling process, all the foot screws are adjusted to the middle of their range. The following procedure is then carried out:
- The plate bubble is aligned parallel to a pair of foot screws (e.g., the first and second screws). By simultaneously turning these screws equally either inwards or outwards, the bubble is centered.
- The plate bubble is rotated 90° so that it becomes perpendicular to the line connecting the first and second foot screws. The third foot screw is then turned, either clockwise or anticlockwise, to center the bubble.
- In some instruments, there are two plate bubbles positioned perpendicular to each other. In such cases, one bubble is aligned parallel to a pair of foot screws, while the other bubble is automatically perpendicular to the first. This eliminates the need to rotate the instrument. The first bubble is centered by adjusting the first and second foot screws, and the second bubble is centered by adjusting the third foot screw.
- The process is repeated multiple times to ensure that the bubble stays in the center of the plate bubble in both perpendicular directions.
- The instrument is rotated through 360° about its vertical axis. If the bubble consistently stays in the central position, the bubble adjustment is accurate, and the vertical axis is properly aligned as truly vertical.
5. Focusing the Eyepiece
The eyepiece is focused to make the cross-hairs clearly visible. This is done by pointing the telescope towards the sky or holding a piece of white paper in front of the objective lens. The eyepiece is then adjusted by rotating it clockwise or anticlockwise until the cross-hairs appear sharp and distinct.
6. Focusing the Object Glass
This step ensures a sharp image of the object or target is formed in the plane of the cross-hairs, eliminating parallax. The telescope is aimed at the object or target, and the focusing screw is rotated clockwise or anticlockwise until the image becomes clear and sharp, with no relative movement between the image and the cross-hairs. The absence of relative movement is confirmed by shifting the eye up and down.
Learn the steps for Temporary Adjustment of Theodolite to ensure optimal performance and precision during field measurements.
7. Setting the Vernier
Vernier A is set to 0°, and Vernier B is set to 180°. To achieve this, the lower clamp is tightened. The upper clamp is loosened, and the upper plate is rotated until the arrow on Vernier A roughly aligns with the zero mark (360°) and the arrow on Vernier B aligns with the 180° mark. Once this is done, the upper clamp is tightened, and the upper tangent screw is used to precisely align the arrows for exact coincidence.
This completes the temporary adjustment required for taking readings with the theodolite.
Note: Instruments with four foot screws are absolete nowadays. However, the procedure of levelling involves making the bubble parallel to the line joining the foot screws AB and CD successively, and by turning these foot screws equally inwards or outwards the bubble is brought to the center of its run.
The Temporary Adjustment of Theodolite requires careful attention to leveling, focusing, and setting the vernier for reliable readings.
The process is repeated multiple times, and the permanent adjustment of the instrument is verified by rotating the bubble through 180°. This ensures that the adjustments remain accurate and consistent.
In conclusion, the Temporary Adjustment of Theodolite is a crucial procedure for achieving accurate and reliable survey measurements. By carefully setting the instrument, leveling it, centering it over the station, and ensuring proper focusing and vernier alignment, surveyors can ensure precise readings. Mastering this adjustment process is essential for maintaining the accuracy and efficiency of surveying tasks, ultimately contributing to the success of civil engineering and construction projects.