Levelling – Temporary and Permanent Adjustments & Procedure of Setting Up

Levelling – Temporary and Permanent Adjustments & Procedure of Setting Up

Levelling instruments must be properly adjusted before taking observations to ensure accuracy in measurements. Adjustments are classified into temporary adjustments and permanent adjustments. In ITI Draughtsman Civil, students must understand these adjustments and the correct procedure of setting up the instrument in the field.

1. Temporary Adjustments

Temporary adjustments are those adjustments that are made at every new setup of the levelling instrument. These are necessary to make the instrument ready for use.

Steps in Temporary Adjustments

(a) Setting Up

• Fix the levelling instrument on the tripod stand.
• Spread the tripod legs and place them firmly on the ground.

(b) Levelling

• Use levelling screws to center the bubble in the spirit level.
• Ensure the instrument is perfectly horizontal.

(c) Focusing

• Adjust the eyepiece to make crosshairs clear.
• Focus the objective lens on the levelling staff.

These adjustments are repeated each time the instrument is moved to a new position.

2. Permanent Adjustments

Permanent adjustments are those that are made occasionally to maintain the accuracy of the instrument. These adjustments are usually done in workshops or by skilled personnel.

Main Permanent Adjustments

• Adjustment of Bubble Tube: Ensures that the bubble remains centered when the line of sight is horizontal.
• Collimation Adjustment: Ensures that the line of sight is perfectly horizontal when the bubble is centered.
• Axis Adjustment: Ensures correct alignment of instrument parts.

Permanent adjustments are important to maintain the instrument’s accuracy over time.

3. Procedure of Setting Up Levelling Instrument

Proper setup of the levelling instrument is essential for accurate readings. The following procedure is followed:

1. Fixing the Instrument: Mount the instrument on the tripod stand.
2. Rough Levelling: Adjust tripod legs to bring the instrument approximately level.
3. Fine Levelling: Use levelling screws to center the bubble accurately.
4. Focusing Eyepiece: Adjust eyepiece until crosshairs are clear.
5. Focusing Object: Focus on the levelling staff for a clear image.
6. Check Alignment: Ensure the instrument is stable and properly leveled.

4. Importance of Adjustments

• Ensures accurate measurement of levels.
• Reduces errors in observations.
• Improves reliability of survey data.
• Maintains proper functioning of the instrument.

5. Precautions

• Always check leveling before taking readings.
• Handle the instrument carefully.
• Do not disturb the setup during observations.
• Regularly check for instrument errors.

Role of Draughtsman Civil

A Draughtsman Civil uses levelling data to prepare accurate plans and sections. Proper adjustments and setup of instruments ensure correct data collection and reliable drawings.

Conclusion

Temporary and permanent adjustments are essential for the correct functioning of levelling instruments. Proper setup procedures ensure accurate and efficient survey work.

For ITI Draughtsman Civil students, understanding these adjustments and procedures is important for professional surveying and construction practices.