<html>
<head>
<meta http-equiv="Content-Type" content="text/html;
charset=windows-1252">
</head>
<body text="#000000" bgcolor="#FFFFFF">
<div class="moz-cite-prefix">Wow Stephen, thank you. This is
fascinating.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">I have seen some commercial products
that had a vent at the bottom, allowing water to escape and
conformally coat the assembly inside, to keep the electrics safe.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Military product milled out of block
aluminium, with O ring seals and hermetically sealed connectors
suddenly doesn't seem quite as much overkill as it did once.<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">-Mark<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<br>
<div class="moz-cite-prefix">On 29/05/2020 9:13 PM, Stephen Irons
wrote:<br>
</div>
<blockquote type="cite" cite="mid:5N53BQ.K3OSOPZI03ZY1@irons.nz">
<meta http-equiv="content-type" content="text/html;
charset=windows-1252">
<div id="geary-body" dir="auto">
<div>Waterproofing is hard, really, really hard, for housings
fully exposed to the weather.<br>
<ul>
<li>IP-codes (IP-65, etc) don't mean what you think they
mean [1].</li>
<li>Common IP-65 rated housings suck in water that collects
in the groove between base and lid as the internal
pressure changes with temperature.</li>
<li>PTFE pressure-relief vents prevent this, as long as
water does not pool on the vent mebrane. PTFE is the magic
stuff in outdoor clothing that claims to keep the water
out, yet lets your skin breathe.</li>
<li>PTFE pressure-relief vents are permeable to gas,
including water-vapour. The humidity inside the housing
will approach the ambient humidity in about a week [2].</li>
<li>All polymers (including ABS and PC) are permeable to
gases, including water-vapour [3]. The humidity inside the
housing will approach the ambient humidity in about a
month [2].</li>
<li>If at all possible, use a potting compound to exclude
gas. This solves the pressure-change problem, and many
epoxies and polyurethanes are waterproof (polyester resins
were not quite waterproof enough, as older boats with
osmosis blisters show).</li>
<ul>
<li>...but you need to find a compound that will stick to
the insulation of all of the cables that penetrate the
potting. Some cable jackets are made of polymers that
resins don't likt to stick to.</li>
</ul>
<li>Otherwise, install the housing inside a cabinet
sheltered from sun and rain.</li>
<li>Those end-user replacable batteries are also in a
waterproof housing, and have exactly the same problems.</li>
<li>It is really tricky to seal the battery-compartment lid
properly. Too loose, and water gets in. Too tight, and the
lid bends and water gets in.</li>
<li>Waterproof connectors have the same issues.</li>
<li>Multi-core cables and with braided screens have voids
between the strands. Capilliary action will draw water
into these voids, corroding the conductors. If this it not
enough, they are subject to the same pressure variations
as the main housing which helps to draw water into the
cable.</li>
</ul>
<div>[1] IP-codes apply to the product as a whole, not to the
housing. Water might be acceptable inside an IP-67 or IP-68
rated product, as long as the product still works.
Obviously, it will be easier to make a water-resistant
product using a 'waterproof' housing.</div>
<div><br>
</div>
<div>[2] IP-65 rated ABS and PC housings from Jaycar, with
Bluetooth environment sensors sealed in them, installed in a
100% humidity chamber (a plastic crate with a bowl of water)
with its own Bluetooth environment sensor to monitor the
humidity chamber itself. Temperature, pressure and humidity
were measured hourly for 2 months. The humidity chamber was
indoors, but not temperature controlled so it was subject to
daily temperature variation.</div>
<div><br>
</div>
<div>After a few weeks, it is advisable to get the intern to
open the humdity chamber, preferably somewhere far away from
me.</div>
<div><br>
</div>
<div>We tested 6 configurations, each with a Bluetooth
environment sensor sealed inside:</div>
<div>
<ul>
<li>ABS and PC housing screwed shut with the supplied seal
and screws.</li>
<li>ABS and PC housing screwed shut with the supplied seal
and screws, with PTFE vent installed. PTFE vent on a
vertical edge to avoid water pooling.</li>
<li>ABS and PC housing epoxied shut.</li>
</ul>
<div>[3] PDF file with some gas permeability of various
polymers at <a
href="https://www.sciencedirect.com/science/article/pii/B9781884207976500024/pdf"
moz-do-not-send="true">https://www.sciencedirect.com/science/article/pii/B9781884207976500024/pdf</a></div>
</div>
<div><br>
</div>
<div>Good luck!</div>
<div><br>
</div>
<div>Stephen Irons</div>
</div>
<div><br>
</div>
</div>
<div id="geary-quote" dir="auto"><br>
On Thu, May 28, 2020 at 21:14, Andrew Sands
<a class="moz-txt-link-rfc2396E" href="mailto:andrew@theatrix.org.nz"><andrew@theatrix.org.nz></a> wrote:<br>
<blockquote type="cite">
<div class="plaintext" style="white-space: pre-wrap;">Hey all list dwellers,
I'm looking for advise, suggestions and general pointers to what other have done in order to get various types of sensors working out in the real world - that is beyond the bench.
What sensors perform better / marginal, what methods provide the best mechanical / environmental protection.
Where should I position say an outdoors temperature sensor?
Mostly I'm after less of the theory and more of the I tried this but it mutated a spider which ate my cat kind of thing. So don't do that.
Thanks for reading, stay safe. Wash your hands.
Regards,
Andrew
</div>
</blockquote>
</div>
</blockquote>
<br>
</body>
</html>