Land Surveyor Forum

Replies

• Land Surveyor

  David Brubacher August 25, 2016 at 4:08pm

  Over what distance are you measuring?

  Certainly check your prism constant but there are many other possibilities.

  1. What measurement mode are you using? Fine will give you +/-(2mm + 2 ppm) accuracy. The other two modes are +/-(5mm + 2ppm), so if you aren't using Fine, 4mm is within the tolerance of the instrument. Likewise if you are measuring over 1000m, expect no better than +/-4mm on Fine.
  2. What about temperature correction? Over longer distances it can be significant. See page 175 of your manual. For instance at 500m, 25C to 30C is about 6 ppm!
  3. When was the last time the instrument was calibrated?
  4. When was the last time the laser you used to check the distance with was calibrated?
  5. What's the expected PPM error for both the instrument and the laser? Does 4mm fall within the expected error? I'm betting it does based on what I've read in your manual.
  6. I assume you are measuring to a prism mounted on a tribrach; set it up over a fixed spot with just the post showing (no prism) and have someone point out the nail (or whatever) and ensure the top middle of the post is directly over the spot on the ground. Now pick up the tripod, rotate 90 degrees, level it and repeat. Next, remove the post and the instrument from their tribrachs, leaving the tripods untouched. Swap the positions, check, rotate 90 and check again. This is an old school method  but really what you are trying to do is ensure your laser / optical plummets are pointing correctly 

  Hope this helps
  • Land Surveyor

    Paulo Peres > David Brubacher August 31, 2016 at 2:45am

    Hi David,

    I used in the fine mode / put the Temperature/Pressure / the baseline is a short distance in this case is 10mts.

    The prism  is in a tripod with tribrach with adapter and the total station is in a collimator( Photo of the collimator).

    I believe that problem is in the instrument, needs to be calibrated.

    In the country that I work, I think there is no Technical Assistance to Leica.

    I have counseled the client to go to a Leica representative.

    Thank you all!
  • Not a Surveyor

    William Robinson > David Brubacher August 26, 2016 at 9:05am

    I'm going back a while now but when we used to use the main Leica prisms for other instruments we used to set the prism constant at 34.4 for zero error.

    Will.
• 

  Billy Brooks August 24, 2016 at 5:08pm

  Hi Paulo, You said you have a manual,then look on page 25, But here is what to do press menu  for more than 2 sec. You will see Config, Menu,  on #1 you will see  ppm/mm, there is where you can set your prism

  constant, this is in detail on page 91 ppm / page 92 prism mm., Back to config.Menu # 2 Is CALIB instrument error,this is where to check and correct the Gun  1 is V-index and 2 is H Collim,  In this Config. Menu ,you will find all of the settings1. ppm /mm 2. Calib 3.Contrast 4.rec data 5. units 6.time /date 7.on /off.

   You also have a Main Menu with a tree under Menu and Prog menu with a tree.

  hope this helps.
• Land Surveyor

  Anthony Whitlock August 24, 2016 at 3:54pm

  Set up with a different instrument and measure an unknown distance between two random points that you have just set...measure 3 times recording each measurement...set up with your "bad instrument" and measure the same way...if the match or are extremely close then you have no "bad instrument" and there is an issue with your original field procedures or prism constants.
• 

  Timothy A Thwaites August 24, 2016 at 12:53pm

  One possibility is a prism/instrument constant issue.

  Leica instruments expect a prism with 34mm constant, and many prisms are 30mm; which would result in the 4mm that you refer to.

  Something to look into.

  Also, ensure that whatever value you are treating as the correct value is actually correct. If something was established badly there may be no problem with your measurement at all.
  • Land Surveyor

    Paulo Peres > Timothy A Thwaites August 24, 2016 at 1:17pm

    Hi Timothy,

    The CP is correct.

    I have the same error (4mm) when use laser.

    For example. I did a baseline with 10mts, with diferente total Station everything is ok with and without prism. With this TCR805 I have 4mm.

    Resume the equipment have 4mm error, I just want know if the operator can correct this error.

    I do not know very well Leica equipments.I already read the operator manual and did not see any function to correct EDM.