Checks and adjustments of the nivelir

1. Verification of the installation of a circular level. The axis of the circular level must be parallel to the axis of rotation of the level. The axis of the circular level is normal to the tangent plane to the inner surface of the ampoule at the zero point.

To check the fulfillment of the specified condition, a bubble of a circular level is brought to the middle with the help of lifting screws, after which the level is turned by 180 °. The bubble at the same time should not deviate by more than one division. If the actual deviation is greater than the specified tolerance, then the bubble is returned to the half of the arc of deflection by means of the leveling elevator screws, and to the second half of the deflection arc by using round-level correction screws. After correcting the position of the round level, its calibration is repeated.

2. Checking the installation of the grid of threads. The horizontal thread of the grid should be perpendicular to the axis of rotation of the level.

The axis of rotation of the device is brought into the steep position, for which with the help of lifting screws a bubble of a circular level is brought to zero point. At 10-20 m from the level set rail and guide it to the pipe. The middle thread of the reticulation mesh will then fall on some division of the staff, called the counting by rail. Rotate the guide screw of the telescope and at the same time monitor the reading on the rail. When turning the pipe on the horizon, the rail reading should not change. If the counting changes, then remove the protective cap of the mesh of the threads, unfasten the fixing screws of the mesh of the threads and, turning it in their plane, achieve such a position that the count does not change, after which the fixing screws of the mesh of the threads are fixed, the protective cap is installed and the calibration is repeated.

3. Verification of the installation of a cylindrical level. The axis of the cylindrical level should be parallel to the sight axis of the pipe. This condition is also called the main condition of the level. The check of its implementation is carried out as follows (Fig. 7.5).

At the point "A" is set the level, and above the point "B" put the rake. After bringing the device into position on a circular level, measure its height i1 above point “A” with an accuracy of one millimeter.

Send the pipe to the rail, and after the elevator screw aligns the ends of the level bubble, a “b” count is taken on the black side of the rail.

Taking into account the error x, arising due to the non-parallelism of the axes, the excess will be equal to

Let's change the level and rail in some places and perform the second leveling of the segment AB. Excess h in this case is calculated by the formula

Equating these exceedances, we get that

i1 - b + x = a - x - i2, from where 2x = -i1 + b + a - i2 and, finally,