Object:Introduction to the temporary adjustment of an Auto level.
Apparatus:
Auto level and Tripod
Theory:
The adjustments which are required to be made at every instrument station before making an observation are known as temporary adjustments.
Auto level is an optical instrument used in surveying and building to transfer, measure, or set horizontal levels and is used in conjunction with a levelling staff to establish the relative heights levels of objects or marks.
Following are temporary adjustments of Autolevel:
- Setting
- Levelling
- Focusing (Elimination of parallax)
Procedure:
Setting:
During Setting, the tripod stand is set up at a convenient height having its head horizontal (through eye estimation). The instrument is then fixed on the head by rotating the lower part of the instrument with the right hand and holding firmly the upper part with the left hand. Before fixing, the levelling screws are required to be brought in between the tribrach and trivet. The bull’s eye bubble (circular bubble) is then brought to the centre by adjusting the tripod legs.
Levelling:
Levelling of the instrument is done to make the vertical axis of the instrument truly vertical. It is achieved by carrying out the following steps:
Step1:The level tube is brought parallel to any two of the foot screws, by rotating the upper part of the instrument.
Step 2: The bubble is brought to the centre of the level tube by rotating both the foot screws either inward or outward. (The bubble moves in the same direction as the left thumb.)
Step3:The level tube is then brought over the third foot screw again by rotating the upper part of the instrument.
Step 4: The bubble is then again brought to the centre of the level tube by rotating the third foot screw either inward or outward.
Step5:Repeat Step 1 by rotating the upper part of the instrument in the same quadrant of the circle and then Step 2.
Step 6: Repeat Step 3 by rotating the upper part of the instrument in the same quadrant of the circle and then Step 4.
Step7:Repeat Steps 5 and 6, till the bubble remains central in both the positions.
Step 8: By rotating the upper part of the instrument through 180°, the level tube is brought parallel to the first two foot screws in reverse order. The bubble will remain in the centre if the instrument is in permanent adjustment.
Focusing:
To obtain an accurate clear sighting, the crosshairs should be in focus.
Focusingof eyepiecelens:
To focus on the eyepiece, point the telescope to the sky or hold a piece of white paper in front of the telescope. Move the eye-piece in and out until a distinct sharp black image of the cross-hairs is seen. This confirms proper focusing.
Focusingofobjectivelens:
It is done for each independent observation to bring the image of the object in the plane of crosshairs. To focus the objective, the telescope is first pointed towards the object. Then, the focusing screw is turned until the image of the object appears clear and sharp and there is no relative movement between the image and the cross-hairs. This is required to be done before taking any observation.
