compass surveying lesson 2

TYPES OF COMPASS

   There are two types of Compass

   1. Prismatic Compass(0 to 360 Degrees)

   2. Surveyor’s Compass(0 to 90 Degrees)

PARTS OF PRISMATIC COMPASS

      COMPASS BOX:

1.             Circular 8 to 10 cm (80mm to 100mm) metallic

2.             At the center of box pivot is provided.

3.             Magnetic Needle and Graduated Ring:

4.             On pivot the magnetic needle rests

5.             Aluminium graduated ring is attached to needle

6.             Graduated ring has 0 degree to 360 degrees clockwise

7.             i.e. 0⁰ at south ,90⁰ at west ,180⁰at north ,270⁰ at east

8.             Least count is 30minutes

SIGHT VANE AND OBJECT VANE OF COMPASS:

1.             Sight vane and Object vane are fixed diametrically opposite to the each other.

2.             Object vane consists of vertical hair attached to the frame

3.             Sight vane ( or eye slit )consists of vertical slit cut into upper assembly of the prism unit

4.             Prism unit is hinged to the box

DARK GLASSES

1.             Red glasses       Sighting luminous objects.

2.             Blue glasses      Reduces strain to observer.

ADJUSTABLE MIRROR

1.             Provided with sight vane horizontally vertically and Inclined manner.

BRAKE PIN

1.       At the base of sight vane.  If pressed, oscillation is stopped

LIFTING PIN

1.       Below the sight vane

2.       Lifts magnetic needle

ADJUSTMENTS OF PRISMATIC COMPASS

1.       Fixing the compass with tripod stand.

2.       Centering.

3.       Leveling.

4.       Adjustment of prism.

5.       Observation of bearing.

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