Adjustments of Different Leveling Instruments

Adjustment of the Dumpy Level:

On the supports of the dumpy level, the telescope leveled and rigidly fixed. There are only two adjustments.

1: First Adjustment:

In the first adjustment, we make the bubble tube axis perpendicular to the vertical axis.

Necessity:

The adjustment is made for convenience only. Note: suppose the angle between the axis of the bubble and the vertical axis is 90 degrees a when the bubble is brought to its mid-position (first position). The vertical axis makes an angle with the true vertical.

When the bubble is reversed (second position), the axis of the bubble makes an angle of 2 a with horizontal. Thus the apparent error on reversal indicated by the deviation of the bubble is twice the actual error. Hence the actual error is a. i.e. half the deviation (n divisions) of the bubble.

2: Second Adjustment:

In the dumpy level, the bubble in the tube will make the line of collimation parallel to the axis.

Necessity:

This condition is highly important and is the basis of its leveling. If this condition is fulfilled the line of collimation becomes horizontal when the bubble is brought in the center its tube.

Adjustment of Cooke's Reversible Level:

In the Cooke's reversible level, the telescope can be revolved around its longitudinal axis within the socket. It can also be withdrawn from its socket and replaced end for end. For this level, there are three adjustments,

First Adjustment:

To place the line of collimation in the axis of the telescope.

Second Adjustment:

At the vertical axis of the right angle, to place the line of collimation.

Third Adjustment:

To make the bubble perpendicular to the axis of the vertical axis.

Adjustment of Cushing's Levels:

In Cushing's level, the telescope can neither be rotated about its longitudinal axis in its socket nor can it be withdrawn from its socket and reversed end for end. But the eyepiece and diaphragm can be rotated through 180 degrees in their fittings, and the eyepiece and object glass can be interchanged, which amounts to reversing the telescope end for end. The fundamental lines of this level and the relations between them the same as those for Cooke's level. The methods and means of adjustment are exactly identical to those employed in the case of is Cooke's level.

First Adjustment:

To set the line of collimation in the axis of the telescope.

Second Adjustment:

To set the line of collimation at the right angle to the vertical axis.

Third Adjustment:

To set the axis of the bubble perpendicular to the vertical axis.

Adjustment of the Y Level:

In the Y-level the telescope can be revolved about its longitudinal axis in the Y's. It can also be lifted from the Y's by loosening and raising the wye clips and replaced end for end. The bearing surface of the collars is made parallel to the axis of the telescope. The construction demands that the collars are equal cylinders co-axial with the axis of the telescope. There are three permanent adjustments.

First Adjustment:

With the axis of the telescope, make the line of collimation coincide.

Second Adjustment: 

In the second adjustment, the axis of the bubble parallel to the line of collimation.

Third Adjustment: 

To make the bubble tube perpendicular axis to the vertical axis.

Adjustment of the Tilting Level:

In the tilting level, the telescope with its attached bubble tube can be tilted independently of the vertical axis. With this type of the level, there is only one condition of adjustment, viz, this axis of the bubble tube should be parallel to the line of collimation so that the line of collimation is, horizontal when the bubble is center. There are two types of tilting levels, viz.

(1) Reversible, and (2) Non-reversible.

In the reversible type, the telescope can be rotated about its longitudinal axis through 1809 and carries the bubble tube with it.

Adjustment:

To place the axis of the bubble tube parallel to the line of collimation.

Reversible Type:

Test:

1: Set up the level with the level tube on the left face of the instrument, and level it approximately by means of the foot screws. Hold the staff on a firm point or peg at a distance of about 100 m.

2: Bring the main bubble exactly to the center of its run by means of the tilting (or micrometer) screw, and read the staff. Let the reading be a1.

3: Turn the telescope about its longitudinal axis through 180 degrees bringing the main bubble to the right face of the instrument.

4: With the bubble exactly centered, again read the staff. Let the reading be a2.

Non-Reversible Type:

Test:

The level is tested by the two-peg method as already explained with reference to the second adjustment, of the dumpy level.

Adjustment of the Zeiss Level:

The Zeiss level is the type of the reversible tilting modern level. The telescope is of the internal focusing type and can be rotated along with the attached level tube through 180° in its bearings about its longitudinal axis.

The distinguishing feature of the telescope is that it is fitted with an additional achromatic Plano-convex lens exactly similar to the normal object-glass, and is placed in front of the eyepiece. This objective (subnormal objective) is used in testing the permanent adjustment of the instrument. In order to reverse the telescope end for end, the eyepiece is removed and slipped into the objective cap placed over the normal objective.

The fundamental lines of the level are

1. The axis of the bubble tube (the bubble axis), and

2. The line of collimation

Adjustment: To make the bubble tube axis parallel to the line of collimation. Means of adjustment is the prism box screw or the level tube screws.

Adjustment of the Ni2 Automatic Level:

First adjustment:

To set the axis of the circular bubble perpendicular to the vertical axis. Tests and adjustments are similar to those of a dumpy level.

Second adjustment:

To set the line of collimation truly horizontal. Use the two peg method for testing and adjust the cross line by the capstan screw to give the required reading on the leveling staff.