[chbot] Wanting real data - How best to mount sensors outside in the elements?

[Henri Shustak]

With all the fibre rolling out to individual buildings you would think that they could drop the price on internet delivery. I am quite sure that even with training and equipment, if you are sending people out less frequently on faults it must cost less to maintain the network. 

Although, some of the gear they use in parts of NZ (this this bi-directional fibre) the hardware fabric is very costly. Maybe that is how they justify the cost of delivery?

> On 29/05/2020, at 9:13 PM, Stephen Irons <stephen at irons.nz> wrote:
> 
> Waterproofing is hard, really, really hard, for housings fully exposed to the weather.
> 	• IP-codes (IP-65, etc) don't mean what you think they mean [1].
> 	• Common IP-65 rated housings suck in water that collects in the groove between base and lid as the internal pressure changes with temperature.
> 	• 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.
> 	• 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].
> 	• 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].
> 	• 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).
> 		• ...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.
> 	• Otherwise, install the housing inside a cabinet sheltered from sun and rain.
> 	• Those end-user replacable batteries are also in a waterproof housing, and have exactly the same problems.
> 	• 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.
> 	• Waterproof connectors have the same issues.
> 	• 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.
> [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.
> 
> [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.
> 
> After a few weeks, it is advisable to get the intern to open the humdity chamber, preferably somewhere far away from me.
> 
> We tested 6 configurations, each with a Bluetooth environment sensor sealed inside:
> 	• ABS and PC housing screwed shut with the supplied seal and screws.
> 	• 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.
> 	• ABS and PC housing epoxied shut.
> [3] PDF file with some gas permeability of various polymers at https://www.sciencedirect.com/science/article/pii/B9781884207976500024/pdf
> 
> Good luck!
> 
> Stephen Irons
> 
> 
> On Thu, May 28, 2020 at 21:14, Andrew Sands <andrew at theatrix.org.nz> wrote:
>> 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 
>> 
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