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Pilot Balloon Observation Theodolite Setup
The following section relates to David White/Warren-Knight instruments which are the most commonly found instruments in the United States. Procedures differ only slightly for instruments from different manufacturers. Check the operations manual for the instrument model you are using for information specific to your instrument. Please note that this section assumes that your instrument is properly collimated and aligned. If it is not you can either obtain a service/repair manual for your instrument and do the work yourself or bring the instrument to a qualified optical shop or surveying equipment maintenance facility.
Inspect the theodolite for loose parts and screws. Remove dust from the objective lens and eyepiece with a lens brush and lens tissue using procedures consistent with delicate optics. Keep the lens covered whit the theodolite is not in use. Use a sun shade to protect the lens from the direct rays of the sun.
The graduated circles and venires are coated with a lacquer to retard oxidation. Avoid touching these parts. A thin film of oil applied with a lintless cloth will aid in keeping the surfaces clean.
Store the theodolite in its case or other dry dust free location when not in use.
If the theodolite is to be taken from a cool environment to a warm one (especially in humid conditions) allow the theodolite to warm up inside its case where it will not be subject to condensation.
Mounting the theodolite
Remove the theodolite from its case and loosen the lower clamp so that the leveling plate and leveling head can be rotated independently of the centers.
While holding the theodolite have an assistant rotate the leveling plate and leveling head affixing it to the tripod.
Leveling the theodolite
The bubble moves in the same direction as that of the right index finger. Leaving the position of the theodolite unchanged, adjust the two leveling screws A and C until the other bubble is centered (reads level). You may have to repeat the step with screws B, and C for the other level (over A) if it has drifted slightly.
Rotate the instrument 180 degrees about its vertical axis, and observe whether both bubbles remain in the center of their respective levels. If not, readjust the leveling screws. and repeat. When the theodolite is finally leveled, the four leveling screws must be resting securely, with an even amount of pressure (but not too much - lightly finger tightened). If any one of the screw is tightened too much, the base plate will be distorted and the theodolite will be impossible to level.
If the above procedure does not allow the bubbles to remain centered when the theodolite is rotated, the plate bubble levels must be adjusted.
Plate Bubble Level Adjustment:
Rotate the instrument 180 degrees and observe the position of the level. Use an adjusting pin to reset the bubble level adjusting screw so that the bubble returns exactly 1/2 the distance to the centered position. Re-level the theodolite with the leveling screws. Rotate the theodolite 180 degrees again, the bubble should maintain its position in the center.
Repeat the Plate Bubble Level Adjustment procedure for the other bubble level. After doing both levels you should be able to level the theodolite using the procedure in the preceding section.
If the theodolite is in use for a long period of time it may require re-leveling periodically due to temperature effects on the tripod and theodolite base.
Orienting the Theodolite
Now the azimuth scale is correctly oriented to true north.
If your theodolite does not have an integrated compass you must use a bearing compass or a compass where you can take a sighting on a distant point and read its direction. Take this sighting from the location of your theodolite and note its bearing. If your declination is East add the degrees of declination to the bearing you read off your compass. Set this value on the azimuth scale of your theodolite and engage the tangent screw. If your local declination is West than subtract this value from the bearing. For example if I see a tower on the horizon at 87 degrees, I add 14.2 (my local declination) and set my azimuth to 101.2 degrees and engage the tangent screw. After engaging the tangent screw loosen the wing screw on the theodolite base and rotate the base so that you can site the object of known bearing in the cross hairs of the theodolite. Use the elevation tangent screw to get the object vertically aligned and rotate the base of the theodolite for horizontal alignment. When you are very close to centered horizontally tighten the wing screw. Use the slow motion control on the base to finish the centering. Once this step is complete the theodolites azimuth circle is oriented to true north.
The theodolite is now level, oriented and ready for use!