Testing theodolite should be carried out regularly. This is relevant for all accuracy classes. Theodolites intended for work in the field of state responsibility are required to have a certificate of passing primary and subsequent verification of metrological services with a period specified by the manufacturer. In an abnormal situation, if the device has been exposed to unexpected mechanical or climatic effects, an extraordinary calibration and adjustment of the theodolite is carried out, since the measurement results will have a large error. According to the results of verification, a conclusion is issued on the suitability or unsuitability for further operation of the theodolite, indicating the period of the next verification. In the absence of this document, the device should be considered faulty and not allowed to work. Special metrological services equipped with appropriate equipment and documentation, such as, have the right to repair, calibrate and adjust theodolites.
A theodolite is a device for measuring horizontal and vertical angles in geodesic, topographic and surveying surveys.
- schemes and methods for the verification and adjustment of theodolite;
- initial standards of measuring units;
- measuring equipment of the appropriate accuracy class;
- standards of conformity of the results of theodolite's calibration and adjustment;
- Qualified personnel, possessing verification techniques.
Theodolites can have the following accuracy classes:
- Technical devices with an average margin of error of +/- 20 "to +/- 60".
- Devices are accurate with the margin of error from +/- 2 "to +/- 15" when determining the angle of one meter.
- High-precision devices with a margin of error from +/- 0.5 "to +/- 1" when determining the total angle.
Setting theodolite for work
To perform the calibration, the theodolite must be set to the working position and the instrument must be configured.
The device is a typical theodolite.
First you need to center the instrument. The vertical axis of the theodolite must be exactly aligned with the point of reference on the surface. For this, a plumb line is attached to a special hook at the bottom of the stand. The stand with the device on the tripod moves to an approximate coincidence of the reference point with a plumb, while you need to monitor the horizontal position of the stand. With approximate alignment, you need to check the stability of the tripod and go to fine tuning. To do this, loosen the screw on the frame and, moving the theodolite along the stand, achieve a matching accuracy of 2 to 5 mm. Then secure the screw.
Set horizon. The vertical axis of the device must be leveled to a plumb line. To do this, place the level on a horizontal circle approximately midway between any two screws for lifting. Then, adjusting the inclination of the screws, set the level to zero. Turn the alidade at right angles to the original position and again set the third screw to zero level. Monitor the installation. When turning the alidade to any arbitrary position, the level should not change more than one division. If the deviation is greater, the leveling procedure should be repeated.
Adjustment of optics for individual vision. The optical tube should be aimed at something light and adjusting the eyepiece to get a clear view of the reticle. Image sharpness can be adjusted using cremal screws. When working with objects at different distances, the sharpness must be corrected depending on the distance.
At this, the setting of the theodolite can be considered complete and proceed to the calibration.Back to table of contents
Theodolite Calibration Operations
To reliably and correctly establish a theodolite, use a special geodetic tripod.
The device manufacturer must specify the accuracy parameters of the device. For theodolites, they can be divided into two groups: geometric and optical-mechanical. Accuracy and adjustment of optical parameters can be checked and performed only in factory conditions. Geometric parameters can be checked in the metrological service.
Verification of leveling accuracy. Begin calibration with setting the level to the zero position when in between two set screws. Then rotate 180 ° and check. When changing the position of the bubble is not more than one division theodolite meets the requirements of accuracy. If the change is more than one division, adjustments should be made. 50% of the offset should be selected by adjusting the level, 50% - by lifting screws. Adjustment is necessary to perform several times to fully comply with the manufacturer.
Verification of the accuracy of the installation of the line of sight. At this stage, it is necessary to check the perpendicularity of the axes of rotation of the telescope and the sighting axis. It is necessary to choose a noticeable point in the distance and make two measurements. One measurement is performed when aiming the viewfinder to a point on the left side, the second - from the right. The tube should be turned through a full circle. Then you should change the position of the dial to 180 ° and repeat the same measurements in the same sequence. According to the obtained results, you can perform the calculation of the collimation error by the formula:
Types of verification of theodolite: a - installation by two screws; b - installation on the third screw; in - checking the correctness of the installation level.
С = ((Л1-П1 ± 180) + (Л2-П2 ± 180)) / 4
where L1, L2, P1, P2 - measurement results;
C - collimation error.
The result obtained should not exceed the accuracy limit specified by the manufacturer and multiplied by 2. Otherwise, it is necessary to perform the adjustment. To perform the adjustment, it is necessary to determine the correct value using any of the formulas:
M = P2 + SiliM = P2-C, where
M is the adjustment value;
P2 - measurement result;
C - calculated error.
With the help of an installation screw, fix the position of the alidade equal to the calculated value. The image of the viewer should be shifted from the point used. Using the side adjustment screws, it is necessary to reconstruct the alignment of the reticle and the measured point. The operation should be performed several times to fully comply with the specified accuracy parameters.
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Verification of the perpendicularity of the axes of rotation of the theodolite and telescope
This parameter should be checked in this way. On the wall you need to choose a point A. located somewhere at a height. Place the theodolite on it and project it down to the height of the instrument. Mark and mark the position on the wall as A1. Then you need to turn the pipe through the zenith and repeat the projection. If the second projection coincides with the first, then the instrument check is passed. Otherwise, it is necessary to adjust the height of the stand with the correction screw.
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If there is no possibility of adjustment on the tested model, the device should be sent to the manufacturer or to a specialized workshop.
Verification of the accuracy of installation of the sight lines
The optimal direction of the tube to a point is considered to be the position of the point in the center of the visual field. To do this, a glass plate with applied lines in the form of a cross is inserted into the pipe. The image on the models of different manufacturers is executed in its own way. The common is the presence of vertical and horizontal stripes, as well as the adjusting screws, a pair for adjusting vertically, a pair - horizontally. Verification can be performed on any of the bands. Arbitrarily choose a point, aim the reticle at it so that the edge of one of the lines coincides with the point. Then slowly rotate the pipe vertically or horizontally, controlling the coincidence of a point and a line. If the point goes off the line, you should adjust the reticle. To do this, remove the protective cover, providing access to the adjusting screws. Rotating the screws, you should achieve full alignment around the angle of rotation of the pipe. This operation can also be performed using a plumb bob. Plumb line should be placed no closer than 10 meters from the theodolite. To get rid of vibrations of a plumb, you can put the load in a container with water, after waiting for some time, until it calms down and stops swaying.Back to table of contents
Combining the verification of two parameters
Verification of theodolite supports and collimation error consists of the same operations and can be performed together. At the same time, you can save time on work and get a more accurate result.
The verification procedure is as follows:
- The device should be installed in the working position according to the manual.
- Mark two objects for measurements: the first A is on the horizon line, the second B is at an angle V of about 30 ° relative to the level.
- Next, send a viewfinder from the left side in order to each of the objects and record the measurement results.
- Then you need to rotate the telescope and measure these objects, summing up the viewfinder on the right side. The results also fix.
- Then, similarly to the method of separate calibration, it is necessary to turn the dial to 180 ° and repeat the whole complex of measurements.
Collimation error is determined by the following formula:
С = ((Л1-П1 ± 180) + (Л2-П2 ± 180)) / 4
from the additional measurement results determine the auxiliary value
С11 = ((Л11-П11 ± 180) + (Л21-П21 ± 180)) / 4, where:
C and C11 - the main and auxiliary error values
L1 and L21 - results of measurements of objects A and B during the first operation on the left side
P1 and P21 - results of measurements of objects A and B during the first operation on the right side
L11 and L2, P11 and P2 - respectively, the results of measurements of the second operation
The error of the slope of the axis of rotation of the pipe I should be determined by the following formulas:
C1 = SsecV + itgV
I = c1ctgV-ccosecV
where V is the angle of inclination of object B relative to the level.
Further actions should be carried out according to the points of separate verification.