I would suggest the 5 seconds or whatever spec is not imperfection in the glass scale nor an artificially introduced error, but rather the residual centering mismatch between the glass circle and the mechanical rotation. If you take 5 seconds on a 50 mm radius, that gives an allowable offset on the order of micons.
The manufacturer must spend time either tweaking adjustments or finding calibration values for the electronics to compensate. More care and time is needed for a tighter spec instrument.
Bill93, post: 374898, member: 87 wrote: I would suggest the 5 seconds or whatever spec is not imperfection in the glass scale nor an artificially introduced error, but rather the residual centering mismatch between the glass circle and the mechanical rotation. If you take 5 seconds on a 50 mm radius, that gives an allowable offset on the order of micons.
The thing to keep in mind is that software corrections have largely replaced fine mechanical adjustments in the designs of most modern total stations. Conrad's testing of the Leica instruments fairly convincingly demonstrated that the software corrections are what make the instrument, not the hardware. GPS manufacturers have used the same strategy for years, selling hardware with all the bells and whistles that require only a licensing fee to turn them on.
Bill93, post: 374898, member: 87 wrote: I would suggest the 5 seconds or whatever spec is not imperfection in the glass scale nor an artificially introduced error, but rather the residual centering mismatch between the glass circle and the mechanical rotation.
Hi Bill,
I have revised my conclusion about the method of introducing 'error' into the displayed directions on leica total stations. after learning more about the construction and calibration of leica instruments i find it likely that the circles are printed 'perfect' and that it is totally software. so i'm off the idea that the error is printed on the circle, just to clarify.
Certainly what you describe is circle eccentricity. It is a well known effect and is eliminated by reading in two faces, or taking the mean of diametric circle readings. the leica instruments I tested have diametric circle readers, which eliminates errors due to circle eccentricity.
At the end of my final tests there were no residuals out of place in any of the final error fits of the angles i took - for any instrument. The error was/is perfectly regular and it was an even harmonic of a sine wave, which makes sense as it is the only harmonic that could exist after an evenly divided sampling of the circle, which diametric readings are. I would definitely be interested in an explanation of how this 'error' could have a mechanical source though.
The manufacturer must spend time either tweaking adjustments or finding calibration values for the electronics to compensate. More care and time is needed for a tighter spec instrument.
From what i hear, leica does submit each instrument to a good battery of tests, under varying climatic conditions, in order to find these calibration coefficients. what would make us think that the standard testing regime isn't good/extensive enough to produce coefficients that allow leica to model the mechanical imperfections out of existence?