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<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>Hi All (not sure if I have sent this message to the appropriate
forums – I’m sure you’ll let me know)<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>I’ve been the proud co-owner of a Disto-X for
about two weeks, but am almost disillusioned that to date I have been unable to
calibrate it satisfactorily.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>I have used it in a cave for a minor survey branch,
and it seemed to work fine. No pda yet, so mostly done the old fashioned
way with paper.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>Perhaps some of you out there have had similar
experiences and been able to solve them?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>On soldering together I eagerly went through a
calibration procedure in my back yard holding the disto-X by hand against my
chest and aiming roughly at a particular point for each shot. I was
standing about 3m from a steel framed trampoline (pictured in the attachment),
so of course I wasn’t expecting a perfect result. I got delta = 0.9
and compared with the ‘acceptable’ value of delta < 0.5 I
thought I’d done OK for a ‘rough enough’ attempt.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>This is the best calibration delta I have ever had,
ALL later more careful attempts have been much worse, and therefore the only
one I have ever loaded into the disto-X has been the first one.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>I then thought I’d install some lithium <u>non</u>-rechargeable
cells and do a careful calibration.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>I drove square wooden stakes into the ground in bare
grassland. There was a 230 Volt power cable buried in the ground ~35m
away. There was a steel axe 35m way, and I left my keys and cell phone
50m away. Waving my spectacles and wrist watch over the instrument
produced no effect (the bearing and clino constantly wander 0.1 to 0.2 deg with
no disturbing influences present) I figured these precautions were likely
to result in less disturbance (by at least an order or two of magnitude) than
the presence of a cavers headlight, SRT kit etc that are always likely to be
within 0.5m to 1.0m of an instrument held by a surveying caver.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>Using the stake to position the instrument carefully
I took front-rear-left-right shots aiming at specific points. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>I took up-down shots resting the instrument on the
vertical face of the stake, and used my hand to give the instrument something
to ‘read’ for the ‘up’ shots. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>For the ‘downward diagonal shots I used the same
approach as for front-rear-left-right. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>For the upward diagonal shots I held the instrument
near my belly button and aimed at my hand to give it something to read.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>Initially these calibration delta values were in
excess of 2.5, but I traced that back to a nail in the wooden peg. I went
out and bought brand new pegs and checked them for magnetic effect on the
disto-X. The new pegs enabled values of 1.5 to 2.5.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>Processing the exported calibration files I find that
the clino typically varies by 1 to 2 deg and the bearings by 2 to 6 degrees for
each of the 4 ‘roll-about-long-axis’ values. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>I studied the time it takes the bearing and clino to
stabilise when the instrument is placed on a firm surface. This is a
generous two seconds, so I always imagine a very unstable or under damped
compass while I wait before pressing the ‘dist’ button. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>I also imagine that the movement of the instrument as
I push the button is a problem – hence the wooden pegs.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>No improvement with the above approach so I made up
the wooden guide pictured in the attachments.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>It enables me, in a low tech kind of way, to ensure
the long axis of the instrument body is always pointing in the same direction
for each of the ‘roll’ shots and usually results in no detectable
movement as the button is pressed. What I found is that the laser spot
moves about 40 to 70mm as the instrument is rolled about it’s axis (after
accounting for the offset position of the laser source in the instrument) on a
target about 5m away. This equates to a misalignment of the laser of
about 0.5 to 0.8 deg relative to the body of the instrument. This seems
to me to be a reasonable construction tolerance, and one of the effects that
the first four carefully TARGETED sets of shots are intended to account for.
It also means I can not rely entirely on my wooden guide, because to do so
would be to ‘lock in’ the ‘laser-disto body’ misalignment.
I need to focus the laser spot on a particular point – and I believe this
is what is intended by the instructions.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>If I place the disto-X in the guide, and make
repeated shots with an identical orientation, I get readings for bearing and
clino that are within 0.1 deg typically, and occasionally 0.3 deg. These
compare directly with the values quoted two paragraphs above, and are an order
of magnitude smaller. So repeatability of readings is good with constant
position of instrument, but not with ‘roll-about-long-axis’.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>If I rotate the disto-X 180 deg in plan (display
upwards always) the back bearings and forward bearings are also highly
repeatable, but always about 8 deg out (ie 016 deg maps to 188 deg). The
clinos match perfectly (ie -5 deg maps to +5deg). This may be as a result of my
‘delta = 0.9’ calibration making the compass rose non-linear or something
else?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>So, any advice?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>One other thing that doesn’t have direct
bearing on the calibration, but does become annoying after a time.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>There seems to be no way to remove a calibration shot
from either the disto-X or the pocket topo calibration application. This
means that a single accidental shot screws up the whole calibration process,
and to clear it and be able to start from the beginning again it seems to have
to automatically download (at a painfully slow pace of about 1 shot per second)
into the pocket topo application so that it can be deleted/discarded.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>Also I’d be interested to learn how much more
numerical emphasis is placed on the first four calibration directions. It’s
too soon for me to detect a trend, but it seems that even a minor transgression
in the later shots can screw up what should otherwise be a reasonable
calibration attempt. This appears to be contrary to my interpretation of
the instructions.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>Beat, perhaps you could distribute a synopsis of the
calibration theory, the mathematical process and the meaning of the various
numbers produced when a calibration is exported.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>If you’ve got this far, thanks for spending the
time…<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'>Bruce<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-NZ style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
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