Auto Levelling Survey | Advantages And Disadvantages | Typical Parts Of An Auto Level | Principle

AUTO LEVELLING

An automatic level, also known as dumpy level or builder’s auto level, is a laser marking, optical measuring device used to establish a horizontal plane. The instrument can be used for small scale such as residential building construction to a big civil engineering project. Due to its wide range of use, this instrument has become very popular among professionals.

The term automatic level can also refer to digital and laser levels that use different technologies to ensure accurate levelling operation, which is very important in a construction project. There are various types of auto levels available in the market, each one designed for a specific job type.   They are as follows:

 

1. Dumpy Level

Dumpy levels, sometimes called tilting levels, are older pieces of surveying technology that are still in use, although they are being steadily replaced, as modern devices probe its reliability. This level is used in general survey work such as setting property lines, laying out highways, power lines, etc.

 

2. Builder’s Auto Level

When the level is set on the tripod, levelled approximately, a swinging prism inside the level adjusts to compensate for imperfections in the tripod levelling. This level can be set up quickly and is easy to operate for most professionals. This instrument is suitable for making horizontal markers for memory work, like the laying of bricks and blocks. It is useful in setting foundations and flooring in residential buildings.

 

3. Laser Level

This level is also mounted on a tripod at work sites. After levelling the tripod along with the laser level mounted on it, the laser marker is spun to a horizontal angle illuminating a horizontal plane. The beam is picked up by a sensor, attached to a graduated staff, making an audible beep sound indicating that a level horizontal plane has been achieved. This is useful for setting out masonry work and laying of foundation work of a building.

 

4. Digital Level

This is the form of auto-level that uses an electronic eye to read digital bar-code data on the graduated staff. The beauty of this instrument is its ability to record the data being measured along with correlating information on curvature and refraction values, which gives a better quality job. This is useful in road projects.

 

5. Laser-Line Level

This is the most common level used by the general public. They are compact and easy to use. A horizontal or vertical laser line is displayed across the surface, the level set on, providing a level line to fix up interior details of a house. This has been used in electrical, plumbing works in domestic and commercial buildings.

 

 

A. Typical Parts of an Auto Level

The auto level has the following components in three different views:

1. Right-side View

The levelling head is a very important component in this view. It has three parts:

(a) A circular plate, or tribrach, which carries a spirit level and  the  instrument

(b) Three levelling screws or foot screws

(c) A footplate or trivet attached to the tripod head

The horizontal circle, just above the tribrach, allows the instrument to rotate for measuring horizontal angles.

 

2. Top View

This view shows the following parts:

(a) Spherical level, practically a spirit level where the bubble must be within the circle to give a horizontal line of sight.

(b) The instrument can be rotated by hand using ‘gun sight’ at the telescope.

(c) The object focusing screw to focus the staff or other object image properly.

(d) Tangent screws on each side help in finer adjustment for focussing the image of the object.

 

3. Left-Side View

A mirror fitted over the spherical level is the only new component in this view.

 

B. Principle of Autolevel Operation 

The auto level has a compensator mechanism that uses a combination of fixed prisms or mirrors and a moving prism, suspended on a pendulum to give a horizontal reference. By setting up the compensator correctly, it will ensure that the ray of light through the centre of the reticule is exactly horizontal.

A damping mechanism is also introduced within the pendulum system to prevent unwanted swinging during movement of the auto level.

The reticule is a glass plate with fine cross-hair embedded to provide height reference. The eyepiece should be adjusted to give a clear focus of the image. The internal focusing lens is controlled by the focussing screw, situated at the side of the telescope, to bring the object image clear.

 

 

 

Fig. Components of Auto Level

 

C. Advantages and Disadvantages of Auto Levels

The levelling operation can be possible more accurately by using an auto-level. This level can be used in small-scale residential building projects to large civil engineering projects. The wide range of use of this instrument is advantageous for professionals. The telescope of this instrument needs only be approximately levelled over the tripod stand and then the compensating device, usually based on the pendulum system inside the telescope, corrected for the residential establishments. So, the levelling operation is made very simple over the other kinds of levelling instruments. The horizontal line of sight is very much ensured by incorporating an additional fixed and pendulum-type prism with the traditional focusing lens. This gives better quality of reading in levelling operations.

In spite of its user-friendliness for correct measurement opportunities, it suffers from an instability problem. Due to its novel features inside, it is much more complex in construction. The cost of construction is also high compared to other types of levelling instruments available in the market.

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