I'm ready to put this one to rest.
> In other words, the EDM is returning a range with a cyclic error of 0.0mm at 24.0m and would be expected to do the same every 2.5m step away from 24.0m, i.e. at 26.5m, 29.0m, and so on.
Zero sounds well below any threshold my grasshopper abilities are going to be able to measure. Let's move on from cyclic errors.
In Part II, Scott Zelenak said:
>We checked three instruments on a CBL last year;
>A Leica TCRA1101+ (manufacturer spec 2mm, +/- 2ppm) tested at 0.0006m, +/-0.0003m and 1.2ppm, +/- 0.6ppm.
>A Leica 1201 (manufacturer spec 1mm, +/-1.5ppm) tested at 0.0004m, +/-0.0003m and 0.1ppm, +/-0.5ppm.
>A Leica 1201 (manufacturer spec 1mm, +/-1.5ppm) tested at -0.0004m, +/-0.0003m and 0.8ppm, +/-0.5ppm.
>The CBL test utilized a Leica NL (1:200,000) to center and GPH1P prisms on GZR3 carriers, GDF321 tribrachs and GST-20 tripods.
>We were quite happy with the results.
>And we like the Swiss.
If cyclic errors are not a substantial contributing factor to my instrument manufacturer's statement of +/-2mm and 2 ppm, then what's next in line, so far as the instrument's ability to measure distances is concerned?...in the order of increasing contribution, where are the distance errors coming from? Are they including Temperature and Pressure variations in their stated accuracy numbers? Are most modern EDM's, if carefully handled, likely to produce results as Scott states above?
I'm ready to put this one to rest.
> > In other words, the EDM is returning a range with a cyclic error of 0.0mm at 24.0m and would be expected to do the same every 2.5m step away from 24.0m, i.e. at 26.5m, 29.0m, and so on.
>
> Zero sounds well below any threshold my grasshopper abilities are going to be able to measure. Let's move on from cyclic errors.
I think you misunderstand. The error is zero at some point as the wave switches from one sign to the other. You could have an instrument with the worst cyclic error ever measured and it will still be zero at regular points along the range.
>
> In Part II, Scott Zelenak said:
>
> >We checked three instruments on a CBL last year;
> >A Leica TCRA1101+ (manufacturer spec 2mm, +/- 2ppm) tested at 0.0006m, +/-0.0003m and 1.2ppm, +/- 0.6ppm.
> >A Leica 1201 (manufacturer spec 1mm, +/-1.5ppm) tested at 0.0004m, +/-0.0003m and 0.1ppm, +/-0.5ppm.
> >A Leica 1201 (manufacturer spec 1mm, +/-1.5ppm) tested at -0.0004m, +/-0.0003m and 0.8ppm, +/-0.5ppm.
> >The CBL test utilized a Leica NL (1:200,000) to center and GPH1P prisms on GZR3 carriers, GDF321 tribrachs and GST-20 tripods.
> >We were quite happy with the results.
> >And we like the Swiss.
>
> If cyclic errors are not a substantial contributing factor to my instrument manufacturer's statement of +/-2mm and 2 ppm...
We don't know this. Cyclic error may well be the major component at regular ranges. Don't take those leica results as indicative of your gear. I've used both of those instruments and conducted my own cyclic error test using a precise corner cube reflector and two mutually collimated total stations for the 1102+ and can report the the cyclic error was barely noticeable. Despite what you may read or gather, Leica make what seems to be a VERY fine product indeed.
>Are most modern EDM's, if carefully handled, likely to produce results as Scott states above?
I couldn't speak for other instruments but don't bank on it. As I said, leica make as fine an instrument as you'd want.
