Optical theodolite and electronic theodolite are the different types of theodolites, a measuring instrument primarily focusing on determining azimuth angle. It can measure the horizontal and vertical angles and distance. 

What are the classifications of optical theodolites?

There are three main classifications as per the technological development process:

1. Vernier Theodolite.

2. Optical Theodolite

3. Electronic Theodolite. 

The last two types are widely used. The optical theodolite is based on the principle of magnification, reflection, and refraction of the integrated optics to read the dial. In contrast, the electronic theodolite is based on the principle of physical optics, electronics, and photoelectric conversion to display the dial reading. 

Vernier theodolite

The three dials: leveling, straightness, and vernier are made of metal. The vernier scale reads the readings of less than an entire division on the dial. The horizontal and vernier dials consist of braking and fretting screws, which helps with rotation and observation of horizontal angle with the help of the re-measurement method. Therefore, the vernier theodolite comes under the re-measurement theodolite category. 

Optical Theodolite

The leveling and straightness dials are made of optical glass, unlike vernier theodolite. A relatively complex optical system is present in the reading device. The reading system presents the reticle images of dials and diameters in the same reading microscope. The microscopic tape, a part of the micro-measurement methods used by angle measuring equipment, measures optical micrometer, single glass flat plate optical micrometer, and conforming reading optical micrometer. Next to the eyepiece of the telescope, a reading microscope is present. Improvement has been observed in the optical system and mechanical structure of optical theodolite. 

Electronic theodolite

The encoder, grating, electric grid dial, or chronograph angle measuring dial are used in angle measuring equipment to achieve electronic digital automatic angle measurement.

What are the measurement factors that affect the measurement accuracy of electronic theodolites?

The factors which affect the measurement accuracy are: 

1. Imaging error: Discrimination rate and aberration of the telescope determine the image quality. The error of the foresight axis changes as the telescope is focused. 

2. Shafting error: Accuracy depends on the manufacturing accuracy of the shaft, the gap between the shaft, the verticality of the vertical and horizontal axis, and the verticality of the sight axis and the horizontal axis (Note: The vertical axis is not vertical). 

3. Eccentricity difference: It includes the eccentricity difference of the sighting part, horizontal dial, and vertical degree. 

4. The compensation accuracy of the automatic compensator of the vertical plate index also influences the measurement accuracy. 

5. The division error of the micrometer grating and the precision of the code disc or grating disc are essential. 

6. The stability of the instrument base and reliability of the electrical components. 

7. Orthogonality of the phase. 

What is the difference between laser theodolite and Level?

The primary difference between laser theodolite and level instruments is the vertical alignment, horizontal and vertical angle, line-of-sight, zenith, and orientation. In short, laser theodolite can be used as a vertical collimator, whereas the level instrument only allows horizontal plane detection. 

Apart from having all the functions of a basic theodolite, they are convenient to use because of their ability to emit powerful laser beams. Long-term measurement can be difficult; likewise, multiple people measuring simultaneously becomes a cause for the error. Laser theodolites adapt and perform excellently at night when the laser spot is brighter, and a flashlight can be used to measure at night. 

Measurements in summer can be challenging as the intense sunlight can cause ship and steel structure deformation, which gives inaccurate results. Furthermore, the laser theodolite’s power supply is simple to operate. It can be used with a 220 V single-phase AC power source or a charged battery for power supply measurement.

What is the difference between a total station and an optical theodolite?

The difference between an optical theodolite and a total station is based on the dial reading and display system. The horizontal and vertical dials and their readings devices employ similar grating dials and reading sensors to determine the angle. 

An (electronic) total station is a device that specializes in measuring instruments integrating light, machine, and electricity. It is used for surveying and mapping, where the system combines the horizontal and vertical angle, distance, height, etc. The reason for its name lies in its function; it offers complete measurement work on the station once the instrument starts to operate. It’s commonly employed in precision engineering measurement and deformation monitoring applications, such as large-scale above-ground building and underground tunnel construction.

What are the focusing methods of telescopes in theodolites?

 The imaging principle of the telescope portrays the idea that the target’s position is different from the objection lense and the imaging position is also different. Telescopes are used to see objects at a great distance. Therefore, the process of distant imaging objects with very different distances on the crosshair surface is called the focusing of the telescope. According to the focusing methods, there are two types of telescopes:

· External Focusing

· Internal Focusing.

External focusing telescope

The external focusing telescope works by changing the image distance to adapt to the requirements of different object distances. Primarily, there are two types:

· The objective lens stays put, and the crosshair reticle is moved to adjust the focus. 

· The crosshair reticle says put, and the objective lens is moved to focus. 

The outer focusing telescope is most frequent on old-fashioned vernier theodolites, while all modern geodetic equipment uses the inner focusing telescope.

Internal focusing telescope

The position of the objective lens and reticle remains constant with an addition of a concave lens between them. The lens is moved along the optical axis such that the targets of different distances can be imaged on the reticle board. A tele objective lens is a combination objective that includes both an objective lens and a focusing lens.

How to use the theodolite?

Procedure (Optical Alignment Method)

1. Set up the instrument:

Carefully position the theodolite on the frame head such that the frame head is horizontal. Tighten the connecting screw. 

2. Centering:

Make sure the instrument is in the centre and aligned with the measuring point on the same plumb line. The tripod and foot screw can be re-adjusted to ensure accurate alignment with the centre of the measuring station. 

3. Leveling:

Make sure the vertical axis of the instrument plumb and horizontal dial are levelled to one another. The definition of horizontal angle states: “It is the projection of an angle between the two direction lines on the horizontal plane. Therefore, the horizontal dial must be leveled. 

Rough leveling: Extend the legs of the tripod to centre the circular Level.

Check and Accurate Alignment: Observe the alignment mark. It there’s deviation, loosen the connecting screw on the tripod. Translate the base such that the alignment mark is appropriately aligned with the centre of the measuring point. Tighten the connecting screw. 

Fine leveling: Rotate the foot screw to centre the tube level bubble.

4. Aiming and reading:

Eyepiece alignment: Eyepiece focusing is essential to make crosshair clear. 

Aiming and objective lens alignment: Aim roughly at the target. Focus the objective lens on making the target visible. Take special care to avoid parallax. 

Reading: Adjust the illumination reflector to make the reading window moderately bright. The scrub line can be made clear by rotating the eyepiece of the reading microscope. 

FAQ:

What are the main components of the theodolite?

The primary components of a theodolite are:

· Telescope braking screw 

· Telescope

· Telescope fretting screw

· Horizontal braking

· Horizontal fretting screw

· Foot screw

· Optical sight

· Objective lens focusing

· Eyepiece focusing 

· Dial reading Microscope focusing 

· Vertical disk indicator tube level micro-moving screw 

· Optical plummet 

· Base circular level 

· Instrument base 

· Vertical scale

· Vertical scale illuminating mirror 

· Sighting part Pipe level 

· Level dial position change handwheel

The telescope is connected with the vertical plate and installed on the bracket of the instrument. This particular part is referred to as the sighting part and comes under the upper parts of the instrument category. The telescope and vertical plate can be rotated around the horizontal axis in the vertical plane. It’s important to ensure that the collimation axis lies orthogonal to the horizontal axis. The sighting part’s number axis is put into the instrument base’s shaft sleeve. The sighting part can be rotated horizontally.

What is the difference between a laser theodolite and an optical theodolite?

The electronic theodolite work by eradicating the complex reading approach of the optical theodolite and the parallax of the human eye. The current urban development focuses on sky-high buildings. Therefore, the laser collimator is adapted to the ever-changing infrastructure and can be used in high-rise areas. It’s mainly used for reference points. The ordinary electronic theodolite and laser collimator have been merged to form the laser theodolite. It’s fair to call electronic laser theodolite an upgraded version of the regular electronic theodolite with higher accuracy. 

Can the theodolite measure the level difference?

The theodolite can only measure the elevation and side angle. Distance measurement is side angle measurement.