Setting up a TSI so that it is level and vertically over the ground point at the same time is one of the most frustrating exercises for the beginning surveyor. Initial patience and continued practice makes the process easier.
Every surveyor has his or her own "right" method to set up a TSI. Some methods are more efficient than others. Any method with which the surveyor is comfortable and accomplishes an accurate set up is a "right" one. The method described here assures a good setup through procedure rather than by depending on luck. It is a two stage process:
- Centering and rough leveling, and,
- Accurate leveling.
Each process uses a logical progression through discrete steps. At a few places, the surveyor is instructed to
perform a particular action when an error is encountered (such as a bubble run). These help compensate instrumental errors already discussed in the section on axes relationships.
Before starting, the tribrach leveling screws should be set to mid-run, Figure C-1. This should allow sufficient screw in either direction when leveling.
In most cases, more than one leveling screw must be turned or leg length changed. The novice surveyor should concentrate on a single action at a time otherwise he/she may wind up "chasing the bubble." As experience is gained, the surveyor will be able to perform multiple actions simultaneously to achieve the desired condition.
The tripod must provide a stable platform for the instrument. Hardware should be snug allowing for smooth leg movement and adjustment. Legs must be firmly pushed into the ground - extreme care must be taken if one or more legs has to be placed on concrete. Setting up on asphalt should be avoided. Not only does it create serious heat waves on a sunny day, it is also soft enough that over time a tripod will sink into it disturbing the instrument set up.
Temperature can be an important consideration.
If there is a substantial temperature difference between equipment storage and use, the equipment should be allowed time to acclimate. If not then set up and use errors might occur. For example if a metal tripod, which was in 70° storage, is immediately used in 40° conditions its metal will begin to shrink. The leg locks may initially hold, but over time slip as the metal cools causing the TSI to shift.
TSI cases are often lined with expanded foam. While excellent shock protection, foam can also act as an insulator. The case should at least be opened, even better the TSI removed, in order to allow quicker instrument temperature stabilization. A common temperature change problem occurs if slow motions were locked when the TSI was last put away. The locks should always be released when packing away the TSI.
Take into account temperature differences and allow for equipment acclimation to prevent errors later on.
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