| Suunto
Clinometer Testing |
Edward
Frank |
| Sep
14, 2005 18:00 PDT |
You can test the level accuracy of a clinometer or instrument.
Sight from a
marked height at some object- tree of pole at a distance. Have
an assistant
mark the point on the distant object the clinometer or
instrument says is
level. Move to that spot and sight back to your
original position. If it
is perfectly accurate the backsight will be right on the point
you shot from
originally. If it is reading high, then the angle it is off will
be
under-reading by arc tan [1/2 (error)/distance]. If
it is pointing lower
than the starting point, then it is readin high, calculations
are the same.
In this way you can tell at least if the original level line is
actually
level or not.
Ed
|
| Response
to Ed on clinometer testing |
Robert
Leverett |
| Sep
15, 2005 10:02 PDT |
Ed:
Thanks for describing this simple, but elegant
test. We can add it to
our repertoire. I own a laser level, so I can quickly spot level
on a
target and then test my clinometer reading accordingly.
I just sent you and others an off list email
showing the basic
design of an experiment I want to conduct to check on the
calibration of
both my Suunto clinometer and my RD 1000's tilt sensor that
calculates
the impact of out-of-calibration instrument. I used this method
once in
the past on a clinometer that I already knew was out of
calibration. But
I quickly learned that the darned thing was so far out of
calibration
that my solution was to buy a new clinometer rather than develop
a
calibration compensation chart. Over the years, I have owned 5
Suunto
clinometers. Phooey on them. I'm ready to try a different brand.
Bob
|
| Clinometer
Accuracy |
Edward
Frank |
|
Sep
16, 2005 01:12 PDT |
Bob,
I have been considering your comments about problems with the
Suunto
Clinometers. As you know from past posts, you know I am a caver.
I
personally have been involved in the survey of dozens of caves,
with
hundreds of people around the country and in the Caribbean. [
New Mexico,
Texas, Kentucky, Tennessee, Pennsylvania, West Virginia,
Virginia, The
Bahamas, Dominican Republic, Puerto Rico] The standard
instruments used for
these cave surveys are Suunto Compasses, Suunto Clinometers, and
tapes.
When you survey in a cave, you sight from one station to the
next. Measured
are the azimuth (compass angle), inclination (vertical angle),
and the
distance is taped. In tough situations both front shots and
backshots are
taken at every station. These surveys have involved dozens of
different
sets of instruments - everyone using Suuntos in the mud, water,
crawlways.
There are three basic types of error involved. Random error -
reading a
number slightly off one way one time and another way another
time. These
tend to even out over the course of a survey. Systematic error -
something
is being measured incorrectly in a single direction over and
over again.
These errors are cumulative. And Busts - significant
non-repeating errors
caused by misreading the instrument incorrectly at some point by
a
significant amount or an example being exchanging a + sign for a
- sign for
an inclination. The point is that when surveying one goal is to
run long
loops ending back at a common point of origin. Typically closure
errors
from loops of hundreds of feet are less than a foot or two at
the most.
If a clinometer was reading high for example, that would be a
cumulative
error that would be repeated at every station and added
together. When the
loop was closed then there would be a significant vertical error
either
higher or lower because of the addition of all of the cumulative
errors. In
my entire experience I have never came across a SINGLE example
of this type
of a cumulative error in ANY cave survey I have ever been
involved with.
This is with dozens of different instrument sets being used.
Cave mapping
is serious business in terms of instrumentation, computer
modeling software,
etc, that allows three dimensional virtual reality maps of these
caves. In
over twenty-five years of caving and cave mapping, I have never
came across
a single example in a trip report or survey report talking about
problems
measuring the inclination during cave surveys with the Suunto
clinometers.
From my experience, if my Suunto said something was level and a
laser level
said it was off, I would believe the Suunto.
With that word of caution, try my experiment to test the
accuracy of the
level on your laser level and see if it is really true or not.
You talked about a calibration curve for a clinometer. The
clinometer is
purely mechanical. A weighted wheel spins so that its heavy side
points
down. It works on the principle that gravity pulls downward.
There are no
calculations involved, no interpolations. It is possible that
the weight
does not line perfectly with the scale, but that error would be
a constant
error at all angles - there would be not calibration curve
because the error
would be constant. The wheel could be out of round, but that
would not make
any real difference in the reading so long at the heavy side
pointed down.
Without a doubt a Suunto can stick, you need to make sure it is
turning
freely when doing a measurement. This is an uncommon problem as
well. The
fluid can leak out when you drop it down a pit, but they are one
of the most
reliable instruments I have ever used in the field. Not even
hammers work
as well because I break or bend the handles pounding on rocks.
The more high tech an instrument is, the more things that can go
wrong with
the measurement. If you are going to base the interpretation
that the
clinometer is misaligned, based upon a reading from a laser
level.
Definitely check to make sure the laser level is actually
producing a level
line.
I don't know what to tell you about the problems with the
Suunto's you have
cited. Suunto's are the best in the business. These problems are
totally
unfathomable to me.
|
| RE:
Clinometer Accuracy |
Robert
Leverett |
| Sep
16, 2005 05:33 PDT |
Ed:
I carefully read your description of the
Suunto clinometer's
reliability and concede to your point that the more
sophisticated the
instrument, the more things that can go wrong. You have a talent
for
bringing me back to point after I've shot from the hip. Yes, the
Suunto
clinometer is a simpler instrument. Sticking and being off scale
on the
zero mark are the two conditions I, and several others,
experience with
the Suunto, but those problems are understandable, as opposed to
numeric
routines built into the circuitry that one cannot get at. The
sticking
problem with the Suunto happens fairly regularly with my main
instrument, but I'm learning to jostle it into compliance. John
Eichholz
quickly mastered the technique. I've been much slower to catch
on.
I like your method of checking for accuracy of
the level point on the
clinometer and will incorporate it into my regimen. As
mentioned, I've
been using a laser level and am starting to see it as an
integral part
of my equipment reperatoire. My laser level has 3 features to
indicate
level, an audio indicator, a light indicator, and the manually
manipulated bubble. At the distances, I've been working, I
haven't had
reason to doubt that it is accurate, but should run some checks
on it,
per your cautions. Maybe get a second level. One cannot have too
many
laser rangefinders, clinometers, dendrometers, and levels. I
want to get
myself a good plumb bob next. At some point I need to consider
procuring
a wheelbarrow to care all my gadgets.
Bob
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