That had been my experience as well, but one day one of the top builders
in our EAA chapter reported a problem with a water level he had never
head of, nor even seen a detectable difference. BTW: He had a degree in
Aeronautical engineering.
I don't remember what he was measuring / building but the level was way
off.
He was working in an unheated building, but I believe the temp was above
freezing.
The water level is easy to check. just bring the ends together with the
tubes vertical, side by side where you view the meniscus(sp?)
I can understand where the problem comes in when using an antifreeze as
with time and temperature, or plain water when the temperatures are
different at the ends of the tubes. The specific gravity can end up
different between the ends of even a "relatively" short tube. I have no
idea as to what caused the problem he ran into.
Using the garden hose as you do (a temporary hook up), I'd expect no
problems. I'm curious if used over time whether any volatils would leach
into the water and how temp differential would then affect the readings.
Still, if the water level is just checked (easily done) it's probably
the easiest way to level things as long as the meniscus is viewed the same.
As cheap Chinese lasers, some of the stuff they build is pretty good,
but the tolerances used in building houses doesn't require the close
tolerances we are seeking.
I spent many years as an Instrument tech, before going to college full
time. Every Monday was a calibration day, including RFI measurements
with the old Singer metrics "portable" receiver. That thing was heavy!
At any rare, I picked up a lot of experiences calibrating measurement
equipment.
73, Roger (K8RI)
On 7/23/2017 Sunday 7:02 AM, Patrick Greenlee wrote:
Roger, What did you use to measure the error in the water level. My
experience with water levels vs 4 ft and even 8 ft spirit levels shows
the water level to be as close as I could read it, essentially zero
instrument error.
I second the disparaging comment posted here regarding cheap Chinese
laser levels. I have a transit and find it no better than the water
level.
For a water level I use garden hoses with clear plastic extensions.
The extensions are sold to use for filling RV water tanks. A small
tipped marker pen can scribe a narrow line on each when the water is
not disturbed. Some of the plastic extensions have 90 degree ball
valves incorporated which makes it easier to move the hoses around
without spilling water.
Patrick NJ5G
On 7/23/2017 1:25 AM, Roger (K8RI) on TT wrote:
I've never been able to successfully use a plumb bob for more than
about 10 ft vertical outdoors. The repeat ability just isn't there
for here, at least not enough to trust it enough to make adjustments.
It may be absolutely still on the ground, but above 30 or 40 feet a
breeze so light you can hardly detect it can produce a substantial
deflection of several inches at ground level.
Be careful with water levels. I've seen as much as an inch or more in
3 feet and when the ends were paralled, there was still the same
deflection. This as in 1/4/, 3/8ths, and 1/2 inch Tygon. It was
worse when antifreeze was mixed in the water (used in some unheated
garages and sheds). Water levels are commonly used in building home
built aircraft. The big box store laser transits and levels for home
construction were close enough for 18 to 20' fuselage construction,
but on an 18 to 24" tower base?
73, Roger (K8RI)
On 7/23/2017 Sunday 1:40 AM, Clay Autery wrote:
I'll use a combination of plumb bobs and water tubes.... gravity is
remarkably more consistent than laser levels made in China. ;)
______________________
Clay Autery, KY5G
MONTAC Enterprises
(318) 518-1389
On 7/23/2017 12:00 AM, Roger (K8RI) on TT wrote:
When using laser levels there is a tolerance of +/- Something per ft,
yard, 10 feet, etc. It's often a lot more than acceptable for
leveling a tower base.
I have two, a transit and a level. Setup and calibration are
critical. I have a plain old combination bubble and 3 digit, digital
level. Two digits to the right of the decimal is more than enough.
Calibration is easy. Find something close to level (level is not
necessary, but convenient) The two points should be about the same
distance apart as the bolts. You can even use those bolts, getting
them close with the bubble. Then you simply turn on the digital mode,
set the level on the nuts and push a button, swap ends with the level
and push a button. The digital level is now zeroed.
NOTE: The calibration points must be STABLE! The nuts can not be
loose. The digital level properly zeroed is more accurate than the
laser transit or level you can purchase at the big box stores that
require much more care in calibrating. A surveying laser transit (A
lot more money) is accurate, but still takes care in calibrating.
Were I to go that route, I'd rent a surveying transit, but being
frugal (some would say cheap) and a bit lazy, I'd use my digital
level. I have it, know how to use it, and with a fresh 9V battery in
it being the only cost.
I've seen manufacturer's suggestions to use a plumb bob. Now depending
on where you live, dead calm days may be rare. We might have 3 or 4
days a year where it's dead calm long enough to use a plumb bob on a
60 - 100 ft tower and a plumb bob is far more work than these other
methods
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