I fabricated a fixture to perform crane rail surveys but it doesn't seem to be as accurate as I had hoped. My process is to place the aluminum bar on the rail and rotate it until the dowel pins make contact with each side of the rail. Then use the bubble level on the prism to level it out before taking a shot with a 3 deg total station. The client is claiming that the numbers are off. I can't see what source of error I am missing unless the technician holding the fixture is just doing a sloppy job. On the most recent project, the rail was about 20 ft up, 40 ft span and 150 ft runway length. The station was set up about 2/3 the runway length. After the survey, the client straightened the runway with a piano wire and calibrated tape measure. I surveyed it again and it still didn't meet specifications. I'm starting to wonder if my process is flawed.
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Crane Rail Fixture
- Thread starter SJBombero
- Start date
I'm not into surveying, but there are so many possible sources for error that I would think that it would be difficult to get a repeatable reading. Can you not secure a small bent plate (steel or aluminum), that wraps around the rail, to the bottom of a total station 'rod'?
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-Dik
SJBombero said:
1. Bubble levels to prisms are one source of error. Depending on the brand, some are accurate to only 40".
2. Did you mean your total station has a 3" angle measurement accuracy, not 3 deg?
What was the difference between your measurement/s and your clients?
I would never trust aluminum for any sort of angular reference surface; we had a 20-inch long, 1-inch thick bar that deflected 20" with thumb pressure.
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Do the specs encompass loaded, or only unloaded, conditions?
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