Introduction to different surveying instruments.

Object: Introduction to different surveying instruments.

Following are the three types of measurements taken generally in a survey:

Distance
Angular Measurement
Elevation/Depression/Height/Depth

Instruments for measuring distance:

Chains

Chain consists of many small parts used for handling or reading the measurements. They have designated lengths. There are 4 types of chains:

Gunter’s Chain (66 ft standard length divided in 100 links)
Engineering Chain (100 ft length divided in 100 links)
Metric Chain (5, 10, 20 and 30 m lengths. Most commonly used is 20m divided into 100 links)
Revenue Chain (33 ft standard length divided in 16 lengths)

Tapes

A tape is a flexible ruler and used to measure distance. There are different types of tapes:

Cloth or Linear Tape
Invar Tape (36% nickel & 64% steel)
Steel Tape
Fiber glass Tape

Passometer

Passometer is an instrument that is used to count the number of a person’s steps.

Pedometer

Pedometer is an instrument that not only counts the number of a person’s steps, but also the distance traveled by walking directly with the help of average human steps already fed.

Odometer

Odometer is an instrument used for measuring the distance travelled by a vehicle. It does this with the help of wheels.

Perambulator

It is a handy device in which a single wheel is attached to a handle and the device can be pushed or pulled along by a person walking, while simultaneously measuring the distance moved. A dial is also present.

Instruments for Angular Measurements:

Surveyor’s Compass

This type of compass has a graduated scale and a freely suspended needle. It points magnetic north and gives quadrantal bearing.

Prismatic Compass

This type of compass has a graduated scale and an attached needle. It gives whole-circle bearing.

Clinometer

Clinometer is a device used to measure angle of elevation and the angle of depression. A surveyor’s compass is attached to it.

Indian Clinometer

Indian clinometer is used for determining difference in elevation between two points and is often used in plane-table surveying.

Abney Level

It is a handy instrument that measures angle of elevation as well as angle of depression. A protractor scale and an internal mirror are attached to it to measure angles accurately.

Optical Square

This instrument measures the angles when two points on a mirror are at 90 degrees from original points.

Plumb bob

It is used to locate points in optical square and for instrument standing.

Sextant box

Sextant box can measure angles up to 120 degrees due to double reflection property. An arc of 1/6th of circle (60 degrees) has been designed. The vernier is moved until the image is clearly seen on the telescope. Sextant box is used to measure the areas of objects and also to observe horizon.

Auto Level

This instrument measures horizontal angles. It is used for leveling and cross-sections. The various parts of an Auto Level are:

Tribatch(base)
Bull’s Eye
Telescope
Object Lens
Leveling Screw
Cross-air Focusing Screw
Horizontal Tangential Screw

Theodolite

This instrument measures horizontal as well as vertical angles. It is transit i.e. it can rotate to 360 degrees.

Total Station

This instrument has same function as that of theodolite except that it is advanced because EDM (Electromagnetic Distometer) is attached.

Instruments used to measure Elevation/Depression/Height/Depth:

Staff/Level Staff/Staff Rod

A level staff is a graduated rod used to measure the level of the object vertically with respect to other object. It has two scales i.e. imperial scale having units m, cm, mm and metric scale having units ft, inch, furlong.

Ranging Rod

A ranging rod is a surveying instrument used for marking the position of stations and for sightings of those stations as well as for ranging straight lines. There may be direct as well as indirect measurements possible.

Tacheometer

A transit theodolite fitted with special stadia diaphragm is known as tacheometer. Its telescope contains two horizontal hairs called stadia hairs in addition to the regular crosshairs. The stadia hairs are equidistant from the central cross-hairs. Tacheometry is a system of rapid surveying, by which the positions, both horizontal and vertical, of points on the earth’s surface relatively to one another are determined without using a chain or tape.