While doing a recent traverse, I stumbled upon the fact that when I plunge and take readings with the opposite face, my vertical angles tended to be off as well. I wasn't paying attention to vertical angles at the time, so gave it no thought.
But now, to measure it carefully, I set up a test shot on a level rod after uber methodically leveling the instrument; zeroed the vertical (90 00 00), read the rod, plunged and set the sight back to the same number on the level rod and find that both in this test, and many of the readings I took during the previously mentioned traverse, the readings are off by 1'-40" very consistently.
The instrument has not been recently calibrated, so that's my next step of course, but it raises some questions:
1. 1' 40" is way too much, even for an instrument with single axis compensation, correct?
2. Don't horizontal distance calculations rely on the vertical angle reading? I haven't religiously measured distances Face Right and Face Left to compare, but wouldn't one expect them to be off as well, because of the vertical angle problem?
For a traverse I always do D+R, that eliminates the vertical angle error. Topo shots (D only) would of course be affected. I don't think the presence of single or dual compensator would affect this at all. In my instrument (Trimble S6), when the calibration routines are run it stores corrections to be applied rather than having to make an adjustment as in the older instruments. For example, on a T2 one would do the D+R to a target and determine the error, which is the index error or vertical collimation error. There was an adjustment screw which you would turn until the vertical circle reading was at the mean of the two faces (accounting for the fact that the reverse reading is 360-D).
That's pretty bad. Based on this and your other posts I think you may have a bad total station. I've had the angle sensors get loose causing random problems like this. The dealer had to glue it back in because no more parts.
With a differance in collimation error of 0-01-40 would give you a mean vertical error of 0-00-50 on any topo shot or to reduce the math out a vertical error 0.025' per 100 LF of HD.
to recollimate your gun is normally a simple proceedure covered in the guide provided with the gun. If none was provided instructions can normally be downloaded.
Having said that it is my personal opinion that an instrument should be checked thoroughly every 6 months and sent in for check and calibration yearly.
If you need help finding a manual I have pdf versions of serval older guns stored somewhere in my maze of files. Let me know what inst and I may have it or my office may, If I have a copy it is availible to any who need em.
I think SC Crew Chief hit the nail on the head with his explanation.
Depending on the instrument there are other factors that go into the adjustment of the vertical angle. Above, SC Crew Chief is describing what is called the vertical indexing. In addition, some of the older instruments, especially Topcon have a vertical zero point adjustment. In addition, if you are using a Robotic Total Station there is normally a separate ATR adjustment that affects the vertical reading when being used robotically.
That is quite a bit of error but I don't believe it is due to a major problem. Sometimes the circle will lose center and must physically be moved or re-centered. This normally will happen when you are taking about the vertical error being "degrees" off and it being an older instrument.
If you will share your model instrument I would be happy to post the vertical index adjustment procedures for you. I would recommend though, if it has been a while to get the instrument in for service.
You mean RTFM?
> If you need help finding a manual I have pdf versions of serval older guns stored somewhere in my maze of files. Let me know what inst and I may have it or my office may, If I have a copy it is availible to any who need em.
Let me make sure I have this right: You mean I should READ THE MANUAL? Gee, novel concept there. You would have thought I'd have given that a try. Argh!+o(
I found the one I have (for the GTS 201D and 202...I have a GTS 203 and hope it's the same), and it advises to turn the unit on While holding the F1 key for "Adjustment of Vertical Angle 0 Datum". Then collimate, F4, Plunge, Collimate, F4 again. Assuming my model has the same function as the 201D and 202, that should solve the problem.:-D
Thank you Gentlemen. Another lesson learned. If there is a different manual for this specific unit, I'd love to get it though.
You mean RTFM?
Part of your problem may be a bad collimation in the past. Aside from that it needs to go to the shop...
Back when I was using a T2 for daily traversing, I was working on a steep mountainside in West Virginia. I always put the gun back in the bullet case to move from one point to another. I set it down for a setup, and it tipped and began rolling down the hill. After hitting several rocks and roots, it slammed into a tree. The case was dented.
I set it up, and checked the horizontal and vertical splits (that what we called them, basically the difference between D and R). The horizontal was fine, the vertical split was more than 4 minutes. Did a quick adjustment, and the instrument was fine after that. Nowadays that is of course done electronically in total stations. Not sure if a modern instrument would survive a roll down the hill like that. Of course, most instrument I have seen do NOT have round cases anymore.
Adjustment procedure worked perfectly! I did it quickly and got the difference between D and R down to a few seconds. I'll do it again tonight with a finer scale than a level rod with hundredths. I also will plan on sending it in for an overhaul.
Thanks all for the help!
