Wednesday, November 30, 2022

Introduction to the Optical Level

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One of the most widely applied tools in the construction area is the optical level. Its use is essential to perform traditional leveling tasks, such as the determination and transfer of heights or the measurement of angles, both in open field and in buildings of all kinds.

Engineers and surveyors employ optical levels to prepare land, construct terraces and retaining walls, excavate and establish foundations, foundation dies, containment ponds and septic tanks. They are used by concrete contractors for pour control, as well as alignment and plumbing of concrete surfaces. Deck and patio builders use them to level floors, establish diagonals and foundations. On the other hand, optical levels They also find wide application in the agricultural sector to lay drains and carry out sustainable practices in the field, such as plowing, planting, cultivating and harvesting in the contour or the right angle of a natural slope.

Currently there are various types of optical levels. However, the automatic or self-leveling They have been established because they are easier to configure and use, since they remain level providing accurate readings, regardless of the vibrations of the ground, changes in temperature or the stable conditions in which they are handled.

This technical article will therefore refer to the automatic optical levels.

Parts of an Optical Level

Like other professional level classes used primarily in construction, a automatic optical level also owns leveling screws, a circular bubble level and a objective. However, the characteristic that distinguishes it from others is a compensator, that is, an optical pendulum that corrects, or compensates, for variations in a focused level line.

They also make up the structure of a optical level many other parts that perform important functions. In the figure below we see an example of all these fundamental parts.

Parts of an Optical Level

  • Objective: It contains the lenses that magnify the objects in focus.
  • Focus button: allows you to view objects clearly and clearly.
  • Ocular: located at the other end of the lens, it can be rotated to focus the lattice cross.
  • Circular level: ensures that the instrument is at a true level point.
  • Leveling screws: allow adjustments to be made to ensure leveling of the instrument.
  • Horizontal circle: Marked in degrees, it is used for setting and reading horizontal angles.
  • Horizontal adjustment screw: It can be adjusted to move the instrument to the left or right on the motherboard.
  • Motherboard: piece by which the optical level is attached to a tripod.
  • Compensator: It is a system of prisms suspended on fine wires that work according to the pendulum principle under the action of gravity or magnetism, depending on the model. The lengths of the wires and the positions of the suspension points are defined in such a way that the rays of light that the prism system sends to the wires of the reticular cross are horizontal rays. Therefore, as long as the prism system can rotate freely, the collimation line will remain horizontal, even when the telescope is not exactly horizontal.

How to use an Optical Level?

The correct use of a automatic optical level It requires following a few simple and quick steps that we can summarize in the following guide.

1) Setting the Level

The optical levels are always used on a tripodTherefore, when we go to fine-tune our instrument, it is important to make sure that we have the appropriate tripod, that is, that the tripod thread matches the tripod fixing element that the device has. Many manufacturers supply the tripod with the kit of the optical level; others sell it separately. Also included in the kit (or otherwise, we must purchase it separately) is a stadal or stadia look to focus the optical level after its leveling.

Fine-tuning the Optical Level

Fine-tuning the Optical Level

Therefore, once we have these elements properly selected we can begin the assembly process.

2) Mounting the optical level

When we remove the instrument from its case, it is important to place it directly on the tripod head. If we deposit it in another place, we could cause damage to it.

After mounting on the tripod, the next step is to screw the level to the tripod base. At this time, we can safely remove the protective cap from the lens and place it in the briefcase. Afterwards, the briefcase must be closed and placed in a sheltered place, so that it does not obstruct the passage of other workers or the movement of other tools or machines.

After these steps, the assembly process is finished, but before proceeding further we must verify that:

  • The tripod is perfectly stable and firm. This is important to ensure that the instrument will not tilt while the leveling process is in progress.
  • The connection between optical level and the tripod is secure.
  • The leveling screws are not too tight against the base plate.

3) Leveling the optical level

To make accurate and precise measurements we must ensure that the instrument is level within a 360 degree radius. The procedure to follow in this case is similar for all optical levels, although there may be slight differences depending on the manufacturer.

To level we use the leveling screws that contains the instrument, marked in the figure below as A, B and C.

Optical Level Leveling

Optical Level Leveling

First we use screws A and B, turning them in the direction indicated by the arrows until the bubble of the circular level that we see in the upper part of the figure is in an intermediate position between both screws (Step 1).

Next, we turn screw C until the bubble is in the center of the circular level (Step 2). Then we rotate the level 180 degrees and check that the bubble remains centered; otherwise we repeat steps 1 and 2. It is important that the bubble always remains centered, otherwise the measurements will be incorrect.

4) Optical level focus

After making sure the instrument is level, the next step is to bring it into focus.

To do this, we point the objective towards an object. At first, this object will appear blurry, but by turning the eyepiece, either to the left or right, we will make the object look sharp. This indicates that the approach is correct.

5) Setting a reference line

Once we focus the eyepiece, we point the objective towards the stadal, located a few meters away in a perfectly vertical way (if necessary, it will be held by another person) and we use the focus button so that the staff markings appear sharp.

Finally, with the side fine adjustment we exactly match the lattice cross with the staff center, as we see in the following figure.

Optical Level - Set Reference Line

Optical Level – Set Reference Line

If the objective focus is correct, the cross hairs and the staff image should not shift from each other when moving the eye behind the eyepiece.

6) Take measurements

After performing steps 1 to 5, we can now make the measurements of the objects of interest. To do this, we simply aim the instrument leveled and focused against the staff, so that the crosshairs coincide with the center of the staff. Depending on the capacity of the optical level, we can measure heights, distances and angles, and for this, just follow the manufacturer’s instructions.

Helpful Tips for Using Optical Levels

Making good use of our instrument will not only allow us to obtain reliable measurements, but will also extend its useful life. Here are some tips to follow.

  • The optical levels should always be transported in their briefcase to avoid damage to the compensator, especially models that do not come supplied with compensator lock button.
  • If the distance is short, the optical level It can be transported mounted on the tripod, but as long as it is kept in an upright position.
  • When the objective lens is not in use, it must be covered with the corresponding cap to prevent damage to the instrument.
  • Accurate and accurate measurements are only achieved when:
    • The two leveling screws are turned at the same time and speed during the leveling step.
    • The instrument is level within a 360 degree radius.
    • The leveling screws are not too tight. Otherwise, the motherboard may also deform, causing permanent damage.
  • We should never focus the lens directly towards the sun.
  • When we look through the objective we must keep both eyes open. This prevents tired eyes and prevents us from squinting.
  • The in-focus image is sharpest when it falls within the crosshairs; this is the most precise place on the lens (see figure above).
  • The jump of an image is called parallax. That is why every time the optical level moves, we must turn the focus button until the parallax is completely eliminated.

Some examples of optical level measurement

Before you begin, position the leveling staff perfectly vertical. Aim the measuring device leveled and focused against
the leveling rod so that the cross hair coincides with the center of the leveling rod.

Distance Measurement with Optical Level

Distance Measurement with Optical Level:

Position and center the optical level on the point of origin for distance measurement. Take the height reading on the leveling staff using the upper and lower lines of the cross hairs. Multiply the difference between the two heights by 100 to obtain the distance of the measuring device from the leveling rod.

In the figure, the measured distance is: (1.347 m – 1.042 m) x 100 = 30.5 m.

Height Reading with Optical Level

Height Reading with Optical Level

Take the height reading on the leveling staff using the center line of the cross hairs.
In the figure, the measured height is: 1,195 m.

Angle Measurement with Optical Level

Angle Measurement with Optical Level

Position and center the optical level with the origin point for angle measurement. Aim the optical level against point A. Rotate the horizontal circle 10 until the zero point coincides with the reading index 9. Then orient the optical level
against point B. Take the angle reading at reading index 9.

In the example the angle is 45º / 45 gon.

Optical levels are robust instruments, of moderate size and complex technology, so the acquisition of one of these devices implies a long-term investment. In this technical article we will detail the main parameters to take into account when we have to make the purchase of an automatic optical level.

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