Posted By Alexander Thorp on 5/28/2008 at 1:12 PM
 
Hi guys:
 
I've been struggling with the leveling procedure on a Topcon GTS 225 total station that we use for rough work. Like most total stations today, it has three leveling screws.
 
I believe I understand the correct procedure to level the instrument:
 
1. Place plate level over screw A and B, center bubble.
2. Rotate 90 degrees, placing plate level in line with leg C. Center bubble again.
3. Go back to first position, checking that bubble is still centered.
4. Rotate instrument 180 degrees. If bubble moves off center, move it back 1/2 way, using the leveling screws to adjust for remainder.
5. Position instrument over screw C again, checking bubble is level, and rotate 180 deg. and move again 1/2 way back.
6. Adjust the plate level as required to minimize effort leveling the instrument.
 
When I'm inside, on a concrete floor, performing the above stated procedure, I get good results. However, when I go out to the field, I can't seem to repeat it to the same degree of precision.
 
Of course, if the ground were soft or otherwise unstable (thawing ice), this would affect the ability to level. But, even on relatively stable ground, I'm experiencing bubble drift that seems more than should be.
 
I'm suspecting that sunlight has a strong power to cause the instrument to go out of level. My gut feeling is that sunlight does not affect the properties of the liquid within the glass vial, but rather that sunlight on one of the two tripod legs will cause expansion of this leg and thus cause it to be raised on this leg. Could someone elaborate on to what extent this is true?
 
Other factors to consider? We had the total station calibrated last June at the Topcon repair facility and they replaced the plate level bubble, saying that it was defective. What would cause a plate level to be defective? How would I know if my plate level were defective? Also, just curious, do some of you just rely upon the automatic tilt correction features of most new total stations, and avoid getting too fussy about the plate level bubble?

Modified By Alexander Thorp on 5/28/2008 at 1:14 PM