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RE: [PSUBS-MAILIST] Papenberg Depth Gauge #5
Jens,
I agree that the instrument is very worthwhile and that water levels are
great when at eye level. I have used them in many applications when I
prefer them to gauges. One aspect is that gauges can tend to stick when at
the lower part of the scale after a lot of use. Some gauges such as 3D
instruments etc have fool proof gauges but you pay for them. Digital I
prefer. Accuracy is not as important as repeatability and sensitivity and
should not be confused. It is normal to have deviation charts for most
instruments in a quality environment but we are talking practical
environment. Unfortunately I deleted most of your emails before I thought
about it but would appreciate seeing a projects page with the info on it.
If they have been used for subs before then they have an application.
However it seems to me that the ratio of airchamber to water column diameter
and length is fairly critical. As the thread has dragged on for a bit I
would appreciate you sending me your info again offline. Regards, Hugh
-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jens Laland
Sent: Saturday, 13 March 2010 1:35 a.m.
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Papenberg Depth Gauge #5
This all started by Michael asking me 'how do I make one at home?'. Such a
question required (my assumption) something else than a set of drawings and
a few tips on how to machine the parts.
It was my intention - should my fragmented inputs spur any interest for the
instrument - that we all, collectively, could come up with something useful
for the PSUBS website in the end (as a result of a final rewriting of my own
fragments by including other people's opinions, questions, proposals,
advice, comments, etc., etc.).
I believe that we could get some very interesting web site material using
this approach. But it requires that the originator of a topic take the
responsibility upon himself to do the final editing (re-writing), then issue
this draft for comments prior to have a document of "instructional"
format officially published on the PSUBS website.
** For what its worth, I found the posts up until #4, to be
** lacking enough detail to comment on.
** It probably would have been better if you started with the
** overall sketch and then showed the details in subsequent posts.
I'll try to introduce my next topic in a more inspirational manner, and also
be very clear (up front) on why I think it would be useful for other people,
and not only myself.
** The unit you are describing is very similar to what we call a
** "water level" in the States.
I agree that the Papenberger could be misinterpreted to be nothing more than
a "water level".
However, it's far from it!
It is a very precise depth gauge used at shallow depths. Together with it's
operational companion, the trim indicator, this unity (see attached
image) provides you with an excellent tool that you can use to bring your
boat to a perfect diving trim. Besides, it will even tell you how close you
are at neutral buoyancy as soon as you dive.
** It is the curvature of the water surface within this thin tube
** that gives an early indication of direction the boat will travel.
I could not say it any better than what David just did [in the above quote],
but I would still recommend everyone to check up the fourteen text lines and
two images available at Wikipedia on the same subject, ref
http://en.wikipedia.org/wiki/Meniscus
** internal PSI rating of the glass tube and where do you find that
information.
I would simply determine its pressure rating by performing realistic bench
tests.
And I would probably use an "unbreakable" plexiglass instead of glass tubing
to avoid splinters all over the place should the gauge burst open due to
excessive depth with the instrument open to sea (ignore to shut down the sea
cock valve). Maybe even furnish the assembly with a small rupture disk at
the very top of the air chamber, this to prevent any view glass bursting at
all.
** Also, is the depth indication (graduations) as shown by the water
** column linear, or does it vary as the air bubble is compressed?
As Frank just pointed out, the variations will gradually get smaller as the
pressure increases.
To avoid a lot of tedious, repetitive calculations, I made a program that
generate a table required to make a proper graduated (non-linear) depth
scale. The same software is also a great help to determine the optimal
volume (length of scale versus air-cushion volume) for a final design of
such an instrument.
Finally, please note, that the attached image can be found in full size, at
my ftp server, ref
ftp://ftp.artematrix.org/instrumentation/papenberg_and_trimmzeiger/S302.jpg
Best regards,
Jens Laland
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