Hello surveyors
I have encountered a frustrating problem that has me bamboozled.
A bit of background. I am an archaeologist using a Nikon NPR362 linked to a laptop running a CAD program to collect my field data. The link is facilitated by a piece of software called TheoLT.
Today I noticed that I was getting the odd erroneous measurement - i.e. bricks were ending up looking more triangular than rectanglar. The error was random and I could not narrow it down.
This evening I set up the system and took a whole series of calibration points to see if I could narrow down the problem - whether it was a Total Station problem, CAD or the linking software. After taking a few hundred points at different distances (from about 5m to 30m) and angles radiating from the TS I have found that the TS is generating a random error, usually every 25 or so shots, but sometimes only after three. I have found that the random error point is generated on a straight line between the TS and the accurate points, always at a horizontal distance of 0.19m from the actual point location.
If it helps I have a the dwg file with the calibration shots to better demonstrate what I am talking about.
Have any of you experienced this weirdness before? It is an error being generated by the TS. It is not due to the presence of reflective material near the prism either, which was one of my initial thoughts. The TS was calibrated last month.
Any suggestions on what to do next would be gretly appreciated.
Weakwilled
you may want to start by resetting/rebooting all of your electronics; some component may be changing a prism offset.
the straight line part i do not understand, but maybe try the above idea to start your troubleshooting.
i used a nikon total station that occasionally would blow a distance measurement from two way radio interference, but that was about 18 years ago, so take that with a small grain of salt
Hi Moe. Thanks for the reply. Do you mean the software running on the laptop? I wondered that, but when I was doing my testing I noted that the Nikon was outputting that random error coord (as in, I noted what it was reading consistently on the Nikon for the accurate points and noted that when the error shot occurred the Nikon was outputting a different coord)
It has been a number of years since we've used a Nikon TS, but I did experience something similar.
The unit would regularly record point data with an erroneous horizontal distance, while the azimuth angle record would be correct. Like what you described, the error would be in the recorded horizontal distance. Sometimes the unit would perform flawlessly for a good long time, and then return several erroneous distances spasmodically.
The gremlin was in the vertical angle sensing mechanism. Since the zenith angle of the telescope is necessary to calculate a horizontal distance, the error was only showing up there. I don't remember if it was a physical "short" or whether the pendulum itself was bad, but we finally had it repaired. The malfunction was random and didn't seem to be tied to anything tangible like temperature or how often the instrument was moved about.
Unlike what you've described the deviation was not a constant distance, but was never over 1' if I remember correctly.
If the error is always a constant at 0.19m and in the direct line of the measurement, that sounds to me like the instrument is calculating the wrong number of wavelengths of the beam; it would be interesting to know what the wave length of that EDM is. It could be a problem with the shutter in the scope randomly sticking, I'd have it checked out by a (highly) qualified Nikon service center.
paden cash, post: 352265, member: 20 wrote: It has been a number of years since we've used a Nikon TS, but I did experience something similar.
The unit would regularly record point data with an erroneous horizontal distance, while the azimuth angle record would be correct. Like what you described, the error would be in the recorded horizontal distance. Sometimes the unit would perform flawlessly for a good long time, and then return several erroneous distances spasmodically.
The gremlin was in the vertical angle sensing mechanism. Since the zenith angle of the telescope is necessary to calculate a horizontal distance, the error was only showing up there. I don't remember if it was a physical "short" or whether the pendulum itself was bad, but we finally had it repaired. The malfunction was random and didn't seem to be tied to anything tangible like temperature or how often the instrument was moved about.
Unlike what you've described the deviation was not a constant distance, but was never over 1' if I remember correctly.
I had the same thing happen with a Topcon 3005w a few years ago. Initially it would only do it about once every 1000 shots. I learned to scan the data file before moving the instrument looking for elevations that were off by hundreds of feet. As the OP described, my shots would be on the correct horizontal angle but significantly short of their correct horizontal distance from the instrument. Looking at the raw data I would see that the slope distance would be correct but the vertical angle would be screwy. Sent it to my dealer with a description of what was happening and they blamed my data collector, cables, etc. Finally I convinced them to set it up to continuously shoot a static prism and record the data. Once they had a few hours of continuous data it was easy to spot the erroneous shots. After a couple of failed repair attempts we got rid of the instrument because we were concerned that it might be generating less obvious errors that might slip through undetected.
It sounds like you are outputting coordinates from the TS and you can see the erroneous coordinates on the TS display screen when the error occurs. So it's a TS measurement or calculation error.
You didn't say whether your observations are generally level or looking steeply up or down. Taking some steep test shots might reveal some clues. Also, look at the point elevations. Do they vary when the coordinate error shows up?
I'd think that tracking this down would be best done by observing the raw measurement data, comparing what shows up on the TS display screen with the output to your device, and even with the coordinates displayed on the TS.
Hi all. Thanks for your quick and erudite comments/suggestions. Triple-checking with just the machine (no data logger) has confirmed that it is a TS problem. It is now going to go to a friendly qualified doctor...
