I recently acquired an early 2000's total station, Nikon DTM-332, for cheap. It was seriously out of mechanical adjustment, but it works and I've readjusted things. I'm using a poor substitute for the dead battery right now, but managed to get a distance measurement on a pair of points I had previous measured.
I have a prism that looks like it is set up for what most of the non-Leica world would call -30 mm, i.e., the plumb point is below the body, not behind it. But I match the old data better with +30 mm setting, like I should specify opposite of the correction. Also, the manual gives some discussion which refers to "30 mm" never "-30 mm".
Am I just confused, or does this machine really use the opposite sign from Topcon, Trimble, etc?
I've used a different Nikon total station where the offset was always assumed to be negative so you had to put in 30 for -30.
Thanks. Your reply reduced the amount of checking and thinking I have to do.
I suppose, though, I should some day go through the process to measure the precise value for this gun/prism combination. I don't think there is an official cal baseline near me that is complete or checked in a long time.
Irrespective of the TS/Prism combination it's important to truth them before using them. Regardless of the manual provided this step can't be ignored. The good thing is that this step is trivial and extremely easy to do. We do our checks on a conference table, simply set up the TS and the prism, measure the distance with a tape and shoot them. We also have a set of monuments in the parking lot to set up over with a known distance. Same process, this checks the tribrach and the prism offsets. So, the 360 prism, the normal rod prism, the peanut all get the same treatment. Always have. As far as a calibrated base, that's a good idea but unnecessary for the prism constant. It induces the same error at 10, 100, 1000'.
Moe - that's pretty much what I did, using two "known" points.
Lurker - I don't suppose there is any way to get past the "Tilt Telescope" message without doing so, if I'd rather not disturb the pointing? I'm guessing there is a sensor that has to initialize to that known position before it can measure vertical angles.
I only have a vague recollection of always moving the scope up and down after turning on the total station and before beginning any work but I can't remember why that was always done. I don't remember any specific prompt. It just became a habitual task.
when using onboard software with Nikon total stations any offset you enter is a negative value by defualt. When you enter "30" the Nikon software treats that as "-30" hence your results working out with the "30" setting.
The 'plunging' of the scope through 90 degrees initializes/sets the vertical index. On later models XS/XF (maybe the Nivo as well?) the indexing is done automatically.
To check prism offsets it's about measuring with a tape measure. It's always done to be sure the proper offset is entered for each prism TS combination. Any established control points could have error that's not easily detected. Even when set, they could have been done with the wrong prism offsets so the result may close precisely but they can compensate for a good closure. Using a tape measure is SOP for this procedure. And why not, it's trivially simple.
Use a proper steel tape. Cloth tapes vary too much to check your prism constant.
Next silly question about the Nikon. It has options for Curvature and Refraction of OFF, 0.132, and 0.200 but I can't relate those numbers to any values I find in textbooks.
Does somebody have an explanation of what their units are, how they relate to the classical textbook numbers, or which one is better under what circumstances?
This is of no real help to your question, but you should be aware many data collectors will also apply the curvature and refraction correction so one should be sure that it is not applied by both the data collector and the instrument.
So I think this explains it. The refraction correction is typically 1/7th that of the curvature and opposite. Thus the following that I found adds context to the coefficients offered.
The coefficient of refraction is assumed to be 0.13 or 0.14 under standard conditions, but it fluctuates quite considerably.
The biggest influence on the value of the coefficient is the vertical temperature gradient
I assume there exists some situation that one would expect a lot of refraction in your sighting and thus the option for .20 but I don't know what that might be. We've always used the 0.14 coefficient for refraction.
From my days in uni, it's possible to determine the prism constant by doing a three peg test. You place three pegs in a line. You then measure the distance between them and over all using the same prism, the subtract the longer distance from the sum of the two shorter ones and that should give you the prism constant for whatever you were using.
