I'm designing an equipment that will be in a rural area exposed to heavy rains. I already got an IP67 rated enclosure with IP67 connectors and it's working as expected.
I need to measure the ambient pressure so I found this sensor for the task. The issue is, I need to drill a hole for the pressure inside the enclosure be the same as the pressure outside. But this hole will be an entrance for water during heavy rains. I found this image from a mesh used in the iPhone 7 that allows air to pass through but not water:
But I couldn't find the name of this meshes or something similar. I'm thinking that I could protect the hole with a mesh like that to prevent water entrance.
Does this meshes has any special name? What other approach is used to measure ambient pressure in this conditions?
Best Answer
That looks like a hydrophobic membrane. These have low surface energies and the force of attraction to the water is less than the surface tension of the water. Because of this the water is able to "ball-up".
Figure 1. Surface energy measurement. Source: Rame-Hart.
Surface energy is a problem in printing on plastic substrates, for example, as water-based inks won't wet. Solutions to the problem include corona treatment to increase the surface energy by knocking out some hydrogen atoms from the polymers and replacing them with oxygen atoms. This, in simple terms, provides more molecular hooks for the water.
I would be afraid that thermal cycling will expel air from the enclosure and then, on contraction, suck water through the membrane. I would look for a sensor that could be mounted through the outside of the enclosure or read through a tube terminated on the casing.
Figure 2. A pnuematic bulkhead fitting.
Figure 3. A bellows diaphragm. Source: AP Racing
On further thought, if your pressure variation is modest a bellows diaphragm would allow the pressure to equalise while maintaining weatherproofing. Put the bellows on the inside. The photo is some sort of car part but it might get you started on a search.