Types Of Compass| Civil Easy Learning

Types of Compass

PRISMATIC COMPASS 

SURVEYOR’s COMPASS

INSTRUMENTS  USED  FOR  COMPASS SURVEYING

The various instruments used in the compass survey are : 

Prismatic compass

Tape

Ranging rods

Tripod

Arrows

Plumb Bob

PRISMATIC COMPASS

Prismatic Compass comprises of a magnetic needle attached to the circular ring made up of aluminum.

The needle is on the pivot and will orient itself in the magnetic meridian

The line of sight is defined by the objective vane and the eye slit, both attached to the compass box.

A triangular prism is fitted below the eye slit.

The readings increase in clockwise direction.

The object vane frame can be folded on the glass lid which covers the top at box.

lever which lifts the needle of the pivot and holds it against the glass lid.

When bright objects are sighted dark glass may be interposed in to the line of sight.

Adjustments of Prismatic  Compass:

The following are the adjustments usually necessary in the prismatic compass:

Centering

Leveling

Focusing the prism.

CENTERING:

The center of the compass is placed vertically over the station point by dropping a small piece of stone below the center of the compass, it falls on the top of the peg marking that station.

LEVELING:

By means of ball and socket arrangement the Compass is then leveled the graduated ring swings quite freely. It may be tested by rolling a round pencil on the compass box.

FOCUSING THE PRISM :

The prism attachment is slid up or down focusing till the readings are seen to be sharp and clear.

THE SURVEYOR’S COMPASS

WORKING OF SURVEYOR’S COMPASS

Centering

Levelling

Observing the bearing line

In this type of compass , reading is taken from the top of glass and under the tip of north end of the magnetic needle directly. No prism is provided here .
 Construction and bearing system of the surveyor’s compass differs from prismatic compass .

Uses of a compass survey (or traverse):

Map very small areas

Map in a lot of detail

Learn basic principles of scale mapping