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Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
Back to Practice Questions
CivilAdvanced Survey
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The bubble of altitude level tube centered by_______.

A

Foot screw

B

Clamp screw

C

Clip screw

D

Slow-motion screw

Correct Answer

⚙️ TE • Technical Concept & PrincipleCivilAdvanced Survey
Option C

Clip screw

Quick Summary:

In a theodolite, the bubble of the altitude level tube (which ensures the telescope's axis is horizontal) is centered using the clip screw. This fine adjustment is necessary because the main foot screws are used for preliminary leveling, while the clip screw provides precise vertical control for the altitude bubble.

⚙️TETechnical SolutionConcept & Principle
💡 Explanation

In a theodolite, the bubble of the altitude level tube (which ensures the telescope's axis is horizontal) is centered using the clip screw. This fine adjustment is necessary because the main foot screws are used for preliminary leveling, while the clip screw provides precise vertical control for the altitude bubble.

🔢 Key Formulas

Δθ=sR\Delta\theta = \frac{s}{R}Δθ=Rs​ — where sss is the shift of the bubble and RRR is the radius of curvature of the level tube.

⚙️ Working Principle

The clip screw acts as a fine motion tangential screw for the telescope's vertical movement. By manipulating the clip screw, the user applies a minute torque against a spring-loaded system, effectively tilting the telescope slightly to bring the altitude bubble to the center of its run.

📌 Key Points
  • ▸

    The altitude level is attached to the index arm of the vertical circle.

  • ▸

    The clip screw is specifically designed for precise adjustments rather than coarse leveling.

  • ▸

    Improper use of the clip screw can lead to indexing errors in vertical angle measurements.

✅ Advantages
  • ▸

    Allows for sub-arcsecond precision in vertical alignment.

  • ▸

    Provides independent control from the primary foot screw leveling system.

❌ Disadvantages / Limitations
  • ▸

    Requires careful operation to avoid mechanical wear on the fine threads.

  • ▸

    Sensitive to temperature fluctuations affecting bubble sensitivity.

🛠️ Applications / Uses
  • ▸

    Precise trigonometric leveling.

  • ▸

    Vertical angle determination in topographic surveying.

📄 Additional Information
  • ▸

    Foot screws are used for leveling the base (plate) of the instrument.

  • ▸

    Clamp screws are used for locking rotation in the horizontal or vertical axis.

  • ▸

    Slow-motion (tangential) screws are used for final alignment in azimuth or altitude after clamping.

📊 Diagram / Illustration
Altitude Leveling Mechanism
Fine Vertical Tilt (Δθ\Delta\thetaΔθ)
Controlled by Clip ScrewBubble Centering
✅

C is correct — The clip screw is the specialized component used to center the altitude level bubble on a theodolite.

Core Concepts Used
Click any tag to open in AI Tutor
Theodolite Leveling Altitude Bubble Adjustment Instrument Metrology
💡 EXAM TIP

Always remember that the foot screws perform 'primary leveling' while the clip screw performs 'final leveling' for the altitude index.

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