On most expeditions I've been on, Distos are calibrated, or at least
checked, on site. At Carlsbad Caverns a couple of years ago, we
calibrated the Distos _in_ the cave at the beginning of survey. We got
great backsight agreement and awesome closures. One very large loop
closed with under a foot of error. We've had similar closure success in
Warm River Cave, where we closed a 2300-foot loop with 0.1% error. Of
course if the data are good, large loops should close better than small
ones because minor random errors will tend to cancel out. Not so for
systematic errors like from miscalibrated instruments.
The current DistoX2 firmware has a feature that compares the last three
shots and if they agree to within 2 degrees (or whatever), the
instrument beeps and displays three dots. That way you know whether your
shots are good without having to look back and compare manually. If you
rotate the unit between shots it uses different sensors, and is good for
catching calibration errors. Of course taking actual backsights is still
advisable because that's the only way to detect possible magnetic
anomalies.
In actual practice we find that if treated well, the DistoX2 generally
stays within calibration over long periods of time and from one place to
another, within reason.
Mark Minton
On 2019-07-23 14:07, Pete Lindsley wrote:
DIsto X2s are great in a cave when they are calibrated. I have
modified 6 units so far with 2 more on the bench. One of those I
suspect has a bad daughterboard. I found out the other Disto had an
issue before I took it apart. It helps to calibrate the units before
going into a cave. At Stanton we have found bad calibrations both
during a survey or afterwards. Ditto for Bruntons & Suuntos. So you
need to be able to calibrate the DIsto X2 in the cave, which means you
need to carry in your Android phone or tablet. (The Brunton is more
rugged than those smart devices, and may be a worthy backup unit.)
All of the Suuntos I have bought have only lasted for 3-4 years before
you have to replace the clouded up “smart part”, at just slightly
less cost than a brand new Suunto. The Suuntos can also have compass &
inclination errors (like Disto & Bruntons) but few people bother to
check calibration. At least the Suuntos are waterproof. Suuntos &
Bruntons work well in the daylight, not so much the Distos.
For the Disto units where the laser does not align with the sides of
the unit, you certainly need to carefully run a calibration that
rotates the unit on all 4 sides. Some of the calibration videos out
there don’t do that.
I started off with a used tripod-mounted quadrant Brunton using the
Shadow Method. We ran the closure data in Carlsbad against Tom
Rohr’s theodolite and precision level survey using the
Hardy-Corcoran Fortran program on an IBM 360. Overkill for your
smaller caves, but we made pretty good FS/BS measurements out to ~ 100
feet. Over the last 15+ years the Fort Stanton Snowy River surveys
have used all of these devices and our sketching techniques have
improved 200%, partially because it is so easy to use the Disto to
accurately shoot in the key sketched items. The Suuntos apparently
introduced blunders, and perhaps lazy FS/BS techniques, because some
of those older surveys appear to show that water runs uphill.
Our new trick is an Arduino controlled data logging barometer that we
hope will help sort out these past elevation errors. I am hoping we
can kill off some of our 20 foot elevation closure errors from old
Suunto surveys with the baro units quickly checking the route. When
your 12 mile long stream passage has an average inclination of ~0.2
degrees, careful backsights become very important. It might even help
to mount your Disto-X2 on a tripod and take instrument height / light
height data like we were doing 50 years ago with the lowly Brunton.
Hand-held 200 foot Disto shots usually have quite a bit of
“wiggle” if you are trying for 0.5 degree precision.
- Pete
_______________________________________________
Texascavers mailing list | http://texascavers.com
Texascavers@texascavers.com | Archives:
http://www.mail-archive.com/texascavers@texascavers.com/
http://lists.texascavers.com/listinfo/texascavers
