The ordinary surveyor will break out a level and chain and "run up" a stair from the ground floor to the roof. Having done that he will report his determination of the difference between the "fixed" ground floor benchmark and the roof benchmark.
Using the ordinary compensating level, micrometer, and standard error propogation a certain 1 sigma accuracy may be expected.
Unfortunately, the average surveyor understands little of this.
The less than ordinary surveyor will determine his height difference using his total station. He knows nothing of sigmas or error propogation, has no idea he's guessing at refraction, and is my best friend when it comes to my paycheck.
Should this guy have a stroke of genius he might perform a reciprocal observation.
Now, when it comes to measuring heights nothing beats an N3.
The achievable accuracy at 1 sigma is, considering an accuracy of +/- 8 microns at 3 meters ~ or the width of two human blood cells ~ is just magnificent.
So, now, the weak point in all of this level work is the chain.
Well, we investigated ours. Original discussion;
https://surveyorconnect.com/index.php?mode=thread&id=137361
But, we can't rely on theoretics so we tested our chain with an NA2 with micrometer at the top, just to make sure there was no shift in zero.
We then added a series of calibrated weights to the end of the tape and used the Wild N3 to observe its elongation and determine a best fit.
Just to be honest, several observers "competed" in the observation test campaign.
always great material. good to hear from you, mr. zelenak
Scott,
Always a pleasure to see what you do and how you do it!!!
I learn something new every day!!!
Jim in NH
:good: :good: :good:
Awesome tutorial Scott, thank you for posting.
It appears that you may have posted two pictures of an old N3 level and one picture of an Na2 level. Your estimated +/- error is much tighter than the Na2 is capable of consistently achieving.
Good stuff. :good: :good:
Pretty cool, Scott. I think we had a similar conversation in 2008 when I was transfering elevations across a dam, through two vertical shafts. But that was on the other board...
I am the surveyor who says, you want me to run a level up 23 floors??? Sorry I am just not going to do it, have a nice day.
Actually, the NA2 with micrometer (as shown in the pictures) is capable of achieving accuracies only several microns less than the N3.
The N3 is rated at 0.2mm per km of double run leveling.
The NA2 (with GPM3 micrometer) is rated at 0.3mm per km of double run leveling.
Actually, we anticipate running down from the 105th floor twice.
Let the hoist do the hard work...
Scott
Please help us understand these two statements:
“…The N3 is rated at 0.2mm per km of double run leveling.
The NA2 (with GPM3 micrometer) is rated at 0.3mm per km of double run leveling…”
“…The achievable accuracy at 1 sigma is, considering an accuracy of +/- 8 microns at 3 meters ~ or the width of two human blood cells ~ is just magnificent….”
Between what mileposts in time are you measuring? Does the building continue compressing after completion? ? In tall bridge pier design(300'+), compression is factored into some designs by building the piers higher than finish grade (sometimes 2-3 inches depending on the height/construction. When fully loaded, the pier theoretically compresses to finish grade. How do you factor in thermal expansion? I would venture to guess that the steel on the outside of a 1000' building experiences about 0.2' expansion this time of year. Are you running your levels at night? Just curious.
what's the other end attached to?
Thanks for the excellent posts. What is the chain(tape) attached to on the other end?
Those statements are taken directly from Wild Heerbrugg/Leica technical data sheets.
Leica NA2 Technical Data;
Wild Heerbrugg N3 Technical Data;
Wild Heerbrugg N3 short range Technical Data;
I do not see any inconsistency in the technical data.
If I have made an error, please clarify. I would appreciate it.
It looks like you're dropping your chain in the small space between the stair cases runners. If that's the case, why not just shoot a laser beam up the same void space?
Because with the N3 I expect to achieve +/- 0.02mm per run.
The best total station is 1mm +/- 1ppm.
And you still have to connect from the benches at each end to the instrument and target.
You are proclaiming a precision tighter than estimatable from their data sheet.
You also don't appear to have accounted for instability in cheap wooden tripods or temperature and calibration issues with your tape.
OK, maybe you're correct on precision. I'm not trying to be difficult here, but could you explain what you mean. Have I misunderstood something from the documentation or expressed myself incorrectly?
As to the supplemental equipment, we have GST 40 tripods and are prepared to allow them to "settle" for the required period in the Lieca White Paper on tripods (even though the White Paper doesn't test them). We have thermometers and I believe I stated my standard tape was calibrated in the original discussion link I provided. The standard tape is used strictly to compare to the field tapes.
The pictures posted were merely a trial run.
I'm not writing a thesis, merely posting on a website. I try to cover the general particulars in an interestng manner, cleanly and concisely, without littering the discussion with minutae.
I'm constantly learning and try to share what I've learned. I feel a website like this could be a valuable asset to younger surveyors and I, personally, appreciate discussions such as Kents, pictures like Moistners, and the numerous anecdotes posted here.
If I can add to a legacy like that, then I feel its a responsibilty to be borne with humility and the due diligence to get it correct.
I didn't always do my part, but I'm trying now.
To say I'm wrong, without an explaination, doesn't help me or them.
So, if you can clear up any error I may have made, I will appreciate your kindness.
My spreadsheet and formula.
What happens to your tripods when the temperature changes?
Have you checked your tapes against your standard tape at various temperatures?
Etc.?
Try to attend one of Dr. Phillips seminars on error propagation. Dr Phillips is a physicist in the Dimensional Metrology Group at NIST.
