Unit 5

THEODOLITES

Prepared By : HITESH PATIL

THEODOLITES►General Background:

►Theodolites or Transits are surveying instruments designed to precisely measure horizontal and vertical angles.


THEODOLITES►Transit theodolite or Transit

In this the line of sight can be reverse by revolving the telescope through 1800 in vertical plane, it is widely used.

►Non Transit theodolite

It is also known as plain theodolite.

This cannot transited


THEODOLITESVertical Axis

Line of collimation

Bubble axis or altitude level axis

A- frame

Hz circle

Plate bubble axis

Plate bubble

Tribrach Foots screws

Trivet Prepared By : HITESH PATIL

THEODOLITES


Essential parts of theodolite1) Telescope: mounted on a spindal known as

Horizontal Axis or trunion axis, internal focusing screw is widely used

2) Vertical Circle: circular graduated arc attached to the trunion axis of telescope . Controlled by vertical circle clamp and its corresponding slow motion screws

3) Index frame: Two Verniers are fitted to this frame. To read the vertical circle. Clip screws is used to slight adjustment. Altitude bubble is place on top of index frame


Essential parts of theodolite4) A-frame: support the index fame

5) Levelling head: It consist of two parallel plates known as Tribrach and trivet plates.

6) Lower plate or scale plate: Size of theodolite is represented by scale of plate ie 10 cm theodolite etc.

7) Upper plate or Vernier plate:

8) Plates levels

9) Tripod

10)Plumb bob

11)Compass Prepared By : HITESH PATIL

Definitions and terms1) Centering: process of setting up theodolite exactily

over station mark by using plumb bob

2) Vertical Axis: Axis about which instruments rotate in horizontal plane . Also known as Azimuth Axis.

3) Horizontal Axis: Axis about which telescope & vertical circle rotate in vertical plane and also known as trunion Axis

4) Line of sight or line of collimation: The line passing through intersection of Hz &Vertical cross hairs and optical center of object glass

(Very IMP)


Definitions and terms5) Transiting : The process of turning the telescope in

vertical plane through 1800 about hz axis. Also known as plunging or reversing .

6) Axis of level tube or Bubble line: A straight line tangential to longitudinal curve of the level tube at its center. It is Horizontal when bubble is at center.

7) Swinging : process of turning the telescope in horizontal plane(left swing & right swing)

8) Face left: the observation of the angle (HZ or VT) if the face of the VT circle is to the LEFT of observer. It is also known as Plus Sight

(Very IMP)


Definitions and terms9) Face Right: the observation of the angle (HZ or

VT) if the face of the VT circle is to the RIGHT of observer.

10) Telescope normal or Direct: When the face of VT circle is to the left & ‘Bubble of telescope is UP’ .

11) Telescope Inverted or reversed: When the face of VT circle is to the right & ‘Bubble of telescope is DOWN’

12) Changing Face: Operation of bringing the face of telescope from left to right & Vice versa

13) Double Sighting: Measure angle twice ie from telescope normal & Inverted Condition

(Very IMP)


Fundamental Lines or axes

1) Vertical Axis: (Azimuth Axis)

2) Horizontal Axis: (Trunion Axis).

3) Line of collimation: (Line of sight)

4) Altitude Level axis: (A.L.A)

5) Plate Level Axis: (P.L.A)

when the theodolite is in proper adjustment the following conditions between fundamental lines are satisfied

(Very IMP)


Fundamental Lines or axes

1) The Axis of plate level is Perpendicular to the Vertical Axis

2) The Horizontal Axis is perpendicular to the Vertical Axis

3) The Line of collimation Axis is at right angles to the Horizontal Axis

4) The Altitude Level axis is parallel to the L.O.C when it is horizontal & vertical Circle read Zero

(Very IMP)


Functions of clamps & tangent screw 1) Clamp Screws: when the upper clamp screw is

tighten but lower clamp screw is loose, the instruments is rotates on outer axis without any relative motion between the two plates. The Vernier readings do not Change.

a. when the lower clamp screw is tighten, but upper clamp screw is loose the instruments rotates on inner axis with a relative motion between the two plates. The Vernier reading is change.

b. Both clamp screws are tightened then instrument cannot rotate at all.


Functions of clamps & tangent screw

2) Tangents Screws:

for small movement of plates, corresponding tangents screws are used when corresponding clamp screws are tightened.


Some Typical Theodolite Diaphragms

This is roughly what the diaphragm in our theodolites looks like

This is FACE LEFT This is FACE RIGHT


Reading the venire theodolite:Least Count of venire is to determine.The 1 degree is divided into 3 parts so least count(one part) of main scale is = 60’/3=20’ The venire scale has 20 big & 60 small divisions.L.C =smallest div on main scale / No. of divisions on venire scale =(20 x 60)”/ 60 = 20” L.C for one big division = (20” x 3 )=60”=1’

10020’12’20”+

Final Angle

10032’20”

Reading a Wild T2After sighting pointFirst have to useAn adjustment screwTo bring things intoalignment

`Note that the center line is pointingBetween 265 and 266.

We know the angle is >265º

The Next StepNote that 265 is toThe left of theCenter line

That means theNext reading willBe to the right sinceThe center line isTelling us we haveMore than 265º

We note the center line matches with the second of 3 lines or 40 minutes

Thus we now know our angle is 265º 40’

Note that 265 to 266 is divided into3 or 20 minutes per division

Now for the Exciting Lower Scale

` Scale reads 7All over

We thus know weHave 7 moreminutes

Now we have265º 47’

Read the upper part of the scale – 23.6Upper part of the lower scale gives us our seconds

The Angle is 265º 47’ 23.6”

Newer T2 are a little less Polish

We read 94º 10’

We read 2’ 44.3 “

We Add

94º 12’ 44.3”

Note there is still a coincidence window forLines to line up with the micrometer

THEODOLITES

► They are used to establish straight and curved lines.

► To establish or measure distance (Stadia)

► To establish Elevation when used as a level. (When we set the vertical angle to 90°).


THEODOLITES

They have:►3 screw level base►Glass horizontal and vertical circles,

read directly or through micrometer.►Right angle prism (optical plummet)►High precision


ELECTRONIC THEODOLITE

Electronic read out 1” eliminate mistakes and reading the angles.

Precision varies from 0.5” – 20” Zero is set by a button. Repeated angle averaging. Replacing optical theodolites (It is less

expensive to purchase and maintain).



THEODOLITES

Top image shows the Electronic Theodolite. Bottom shows the Scale readings.


THEODOLITES

► ELECTRONIC THEODOLITE DETAILS


THEODOLITES

► OPERATION KEYS AND DISPLAYS

THEODOLITES

Repeating optical theodolite:►Has 3 leveling screws►Optical plummet, light weight, glass

circle, micrometer (to read the angles).►Most theodolites are equipped with

compensating device (automatic horizontal).

►90° or 270° vertical angle of horizon.


THEODOLITES

►Micrometer used to read vertical and horizontal angles.

►2 independent motion (upper and lower). If you move the upper motion, then the angle does not change. But if you move the lower motion, the angle will change.


THEODOLITES


Angle Measurement with an Optical Theodolite


DIRECT OPTICAL THEODOLITE


Temporary Adjustments of Theodolite1) Setting over station:

2) Approximate levelling by tripod stand:

3) Centering:

4) Levelling:


(a) Plate bubble place parallel to 2 & 3 foot screws & rotate both screws inward or outward until bubble comes to center

(b)Plate bubble turned by 900 & rotate screw 1 until bubble comes to center

2 3

MoveInward or OutwardAt a time

11 Move

Inward or OutwardAt a time

2 3

(c) The process should be repeated until the bubble can be centered in both positions

(d)Rotate instrument through 3600about VT axis & this position also bubble should remain in center

Temporary Adjustments of Theodolite5) Elimination of parallax:

Parallax is the condition arising when the image form by the objective is not in a plane of cross hairs.

It can be eliminated by following two steps:

6) Focusing eyepiece:

For distinct vision of crosshairs.

2) Focusing Objective:

To bring the image of object in plane of cross hairsPrepared By : HITESH PATIL

Permanent Adjustments of Theodolite1) Adjustment of plate level:

To make axis of plate bubble Perpendicular to the vertical axis when bubble is at centre.

2) Adjustment of Line of sight:

The line of sight should be coincide with optical axis of the telescope.


Permanent Adjustments of Theodolite3) Adjustment of horizontal Axis:

Horizontal axis should be perpendicular to vertical axis .Spire test is done.

4) Adjustment of Altitude level & vertical Index frame:

Clip & tangent screws are made use of this adjustment.


Uses of Theodolite


1) Direct Measurement of Angle:

Let ∟AOB

θ

A B

1. Set instrument at “O”2. Lower clamp fix & upper is loose & by turning

the telescope clockwise set 00 at venire A & at B set 1800 . Tightened screw by using tangent screws set venire A & B exactly 00 & 1800 resp.

3. Upper clamp tight & loose lower clamp telescope direct to left of A, bisect ranging rod at A exactly & tight lower clamp

4. Loose upper clamp & telescope turn clockwise & bisect ranging rod at B exactly

5. The reading on verniers A & B are noted.6. At vernire A angle = θ & at Vernier B angle = Initial reading – Final

reading7. The face of instrument is change i.e face right and

measure same angle8. The mean of these observations is ∟AOB

Uses of Theodolite


2) Repetition MethodIn this method the angle is added a number of

times . The total is divided by no. of readings to get the angle

1. The theodolite is set up at st O by doing all temporary adjustments & set 00 at A & 1800 at B

2. Upper clamp is fix & loose lower clamp in this position bisect rod at pt A & tight lower clamp check 00 at vernier A

3. Loose upper clamp move telescope clockwise & bisect exactly rod at B then tight upper clamp take reading at vernier A is 300.

θ

A B

Uses of Theodolite


4. Loose lower clamp and telescope turn anticlockwise & exactly bisect ranging rod at A. here the Initial reading is 300 for second observation

5. Lower clamp is tight, loose upper clamp & turn telescope clockwise & exactly bisect rod at B. reading on vernier A be 600

6. The initial reading for 3rd observation set is 600. ∟AOB is again measured . The reading at vernier A is 900.

7. ∟AOB =accumulated angle/ no. of readings

= 900/3=300

8. Change the face & repeat above steps

9. The mean of these reading is actual ∟AOB

00

A B

300

1

300 600

600 900

2

3


Table For Repetition Method

Uses of Theodolite


3) Reiteration MethodIn this method is suitable when several angles were to measure from one station. In this method all angles are measure and finally horizon is closed(i.e angle between first & last station is measure). So final reading and initial reading is same .suppose ∟AOB &∟BOC were measure from station O. the procedure is as follows(First Set of reading)

A

C

BO

1. The theodolite is set up at st O by doing all temporary adjustments & set 00 at A & 1800 at B

2. Upper clamp is fix & loose lower clamp in this position bisect rod at pt A & tight lower clamp check 00 at vernier A

3. Loose upper clamp move telescope clockwise & bisect exactly rod at B & take reading on both verniers. ∟AOB is recorded.

Uses of Theodolite


4. Similarly object C is bisect & reading on both verniers are take. ∟BOC is recorded

5. Horizon is closed i.e ∟COA is measured & position of vernier is noted & then final reading is same as the initial reading if not the discrepancy is distributed equally among all angles(Second Set of reading)

1. This time change face & measure angles Anticlockwise

2. Upper fix & loose lower clamp , bisect pt A

3. Tight lower clamp, telescope turned anticlockwise bisect pt C by loosing upper clamp measure ∟COA

4. Bisect pt B turning telescope anticlockwise & record ∟BOC 5. Finally closed horizon by bisecting pt A reading should be

00.note ∟AOB . Take mean of all angles give actual values of angles.

A

C

BO


Table For Reiteration Method

Uses of Theodolite


4) Measurement of vertical AngleThe vertical is the one between horizontal L.O.C & inclined Line of sight.

When it is above Hz line is called as angle of Elevation & it is below Hz line is called as angle of Depression.

Let ∟AOC (elevation)& ∟BOC(depression) are measured .

A

C

B

O

O

Uses of Theodolite


1. The theodolite is set up at stn O by doing all temporary adjustments & set 00 at C & 1800 at D of vertical circle vernires resp. & clamp telescope.

2. Make Plate bubble & altitude level bubble is at center so that L.O.C is exactly horizontal.

3. To measure angle of elevation raise telescope slowly & bisect pt A read the both verniers . This is angle of elevation.

4. The face of instrument is changed and the point A is again bisect .

the reading of both vernier is noted.

5. The mean of these reading is Angle of Elevation.

6. Similar process is for the angle of depression , in that case bisect object B by depressing telescope slowly.

Uses of Theodolite


4) Measurement of Deflected AngleThe defected angle is the angle which a line is from its original direction

Consider AB is survey line suppose it is deflected in direction of BC. The line is extended to point P. then ∟PBC(Φ) is known as known as Deflected Angle.

A

B

P

C

Φ

Uses of Theodolite


1. The theodolite is set up at stn B by doing all temporary adjustments , set 00 at A & 1800 at B verniers of Hz circle. Tight upper screw & loose lower & by turning telescope bisect ranging rod at A perfectly then clamp screw.

2. Telescope is transited & a ranging rod at P is fixed along prolongation of AB

3. Now upper loose upper screw & turn telescope clockwise bisect ranging road at C perfectly, then reading on both verniers taken & tight upper clamp. Reading on vernier is Deflected angle.

4. Now loose lower clamp & turn telescope clockwise bisect rod at A(in this position readings will not change).

5. Transit telescope loose upper clamp by turning telescope clockwise bisect rod at C again.

6. Thus deflected angle is doubled & average of these two angles give deflected angle.

Unit 5

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Transcript of Unit 5