Trimble Business Center

 View Only
Back to discussions
Expand all | Collapse all

Distance measurement accuracy (SX12 and others)

  • 1.  Distance measurement accuracy (SX12 and others)

    Posted 03-28-2022 00:07
    Good day!
    I am Latvia University of Life Sciences and Technologies 3rd Year student and I am collecting information for my diploma project. One part of my interesting information is about DR mode accuracy. In SX12 datasheet for DR mode have written 2mm + 1.5ppm, but in prism mode 1mm + 1.5ppm. (Other total stations similar situation)

    In DR mode 2mm + 1.5ppm most likely are for measurments to building and other non reflective objects, but is this accuracy stay 2mm + 1.5ppm when measurments are to reflective mark (topo surveying to reflective mark ...)? Or there in reality has other accuracy?

    ------------------------------
    Karlis Lepa
    ------------------------------


  • 2.  RE: Distance measurement accuracy (SX12 and others)

    Posted 03-29-2022 18:46
    Hi Karlis
    You probably would have been better most this on the Trimble Access ad Survey Field Solutions Community. On a SX12, if you are in DR Mode, the stated accuracy is 2mm+1.5ppm regardless of what you are shooting too. A reflective target may help with the return signal however it, not going to make distance any more accurate.

    ------------------------------
    James McWha
    ------------------------------

    Original Message


  • 3.  RE: Distance measurement accuracy (SX12 and others)

    Posted 03-29-2022 22:29
    There are multiple reasons for different accuracy values. Direct reflex to any natural surface reflects a much smaller amount of light, making the return signal much weaker. The spread of multiple distance readings will be much wider than readings to a good reflecting surface.
    In some instruments the DR mode also uses a different method than the prism mode to compute the distance.
    In some high precision models the EDM measures the phase difference of the reflected beam whereas DR is always time of flight. Different method -> different accuracy, even if you measure to a good reflecting surface.
    From the S-Series User Guide (https://forms.trimble.com/globalTRLTAB.asp?nav=Collection-125380):


    SX10 and SX12 are always time of flight, but they have a "brute force" approach. The EDM is taking 26600 readings per second and averages them, resulting in a very high repeatability.
    I only found the video for the SX12 on the webinars page. Haven't watched it yet. At some point you have to enter your name and email address, but otherwise those videos are all for free.
    https://go2.trimble.com/2021-04-06-GEO-TS-WB-SX12-Inside-Session-1_LandingPage-Replay.html?_ga=2.93184093.1766418360.1648616748-418228924.1648616748

    The old SX10 video had also information about the magdrive, tilt sensor, angle readings/encoding, production and calibration. Those might be missing here.

    In the SX12 spec-sheet it says that the measure time in DR mode is only 1.2 sec but in prism mode 1.6 sec.
    0.4 sec shorter reading time, or 31920 averaged readings instead of 42560 probably lead to the lower accuracy for DR mode.


    ------------------------------
    Ronny Schneider
    ------------------------------

    Original Message