Permanent Adjustment of Automatic Level |
In case of automatic level, prior to leveling, the circular bubble and the activity of the compensator are required to be checked. In this case, after setting the instrument, the circular bubble is brought to the centre of the engraved circle. Then, the instrument is rotated through 180° or to a direction in which the displacement of the bubble is maximum. If the displacement is less than half the diameter of the bubble, the instrument is in adjustment. Otherwise, an adjustment is necessary. Adjustment is performed in two steps by reducing the horizontal and vertical components of the displacement and bringing the bubble to the centre of the engraved circle. First remove the half of horizontal component of displacement using the appropriate level screws.and then remove the remaining half by manipulating the adjusting screws. Next, one-half the vertical component of displacement (Figure 12.6) is then removed by the level screws and the remainder is compensated using the adjusting screws to bring the bubble to the center of the engraved circle. Turn 180° and check the bubble. Repeat the entire procedure until the bubble remains centered in all positions. To check the compensator, sight a target about 30 m away. Center the bull's-eye bubble. Next, tap one tripod leg with a hand. The image of the target will appear to swing in the field of view but the target will return to its original position. Next, turn a level screw, causing the line of sight to slope slightly. Once again the target will appear to swing but will return to the original Position. This indicates that the instrument is in adjustment. Otherwise, an adjustment is necessary. For automatic level also, the third fundamental relation is tested by two peg test but for permanent adjustment manual of the instrument is required to be referred.
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