(Optical) bonding with your panel PC
Panel PCs and industrial displays marketed as conforming to IP65 and/or being waterproof naturally lead one to surmise a sealed, airtight unit. Whether this is true could be irrelevant, but in certain operational environments it can be very relevant indeed. Here I discuss how system integrators often overlook environmental suitability criteria and assume IP65 is sufficient for usage in outside environments with heavily varying temperature and humidity conditions.
IP rating translating
First, we should understand what is meant by IP65. Whilst “IP,” denoting “Ingress Protection,” is fairly self-explanatory, the numbers that follow are not. Our interest lies with the second number, which defines the protection against liquid ingress, where “5” is protection against low-pressure jets of water. We should note the rating does not express that no ingress is possible, moreover that any ingress cannot be harmful to the functionality of the panel PC. To achieve a product that is immersible in water, thus considered “watertight” – though not “airtight,” – you will need a minimum of an IP67/68 rated unit.
Now for the interesting part: In any interior environment, temperatures and humidity tend to stay fairly constant. Whilst of course there are fluctuations, they are nothing compared to what the unit will experience al fresco. It is probably valid to argue that unless you are required to wash down your panel PC with a pressure washer or immerse it in water (indoors), standard IP65 will meet your needs entirely. Unfortunately, issues can arise when one believes such a unit is equally suitable for being left to the wrath of the great outdoors.
Here I concentrate on IP65, as this is the most common rating, but what follows is equally true of anything less than a special type of IP68.
Two issues exist with such units outside the “phenomenon” of condensation.
Most users’ first reaction to seeing condensation on the inside of the display is “How did the water get in there?” which initially seems a valid question. Actually, when one considers the units are far from airtight, this becomes far easier to understand.
Water molecules are far larger than air molecules, so, as mentioned, a watertight system isn’t necessarily airtight – though vice versa, of course, this does hold true. For a system to be airtight, it must be hermetically sealed, which even for IP68 certified panel PCs isn’t common, and the additional costs involved aren’t really necessary.
Now we understand that almost no unit is airtight nor contains a vacuum; it’s easy to see how water can exist in the air inside. Some will be trapped at build time, though these units tend to be built in dehumidified rooms to minimise this. Also, because of the change in external air pressure when units are flown across the world at high altitude, air – and the moisture contained within – is pulled into the unit.
In a fairly constant temperature environment, this humidity stays “hanging” in the air inside of the unit; this isn’t evident on systems located indoors, or a significant quantity outside, actually. If they are exposed to the full elements, they experience often freezing nights and relatively hot days, possibly in direct sunlight. In these conditions, the moisture separates from the air and finds the coolest surface to condense upon, which is the inside of the glass of the display; there it rests to form the condensation.
It’s worth mentioning that this is usuallytemporary. Once the ambient temperature rises sufficiently, the condensation will again evaporate. Interestingly, the compass orientation in which the unit faces varies the severity of the effect, because of the angle of the sun.
The other issue when sitting these units outside is reflection, given the layer of air between display glass and touch screen. A resultant zigzag effect of reflecting light can render a display illegible.
Thankfully, a solution exists for both the condensation and reflection issues – a solution that does not require the level of seal a nuclear sub would be proud of.
Optical bonding is the process of gluing the touch-screen membrane directly to the display, using optical-grade adhesive to avoid any image distortion. This solves the condensation issue, as no layer of air exists that the moisture can use to access the glass front and thus condense. The reflection issue is also solved, as no zigzagging of light can occur between the two layers. Also, optical bonding strengthens the display from breakage as it has universal support across its face from the layer behind.
“Why isn’t this standard?” Of course there is a cost attached to this that isn’t insignificant, and which would be an extraneous cost to the majority using such systems in a more temperature-controlled environment. It’s also down to user experience: The condensation and reflection don’t cause any functional detriment to the unit; it will work perfectly well without optical bonding, so it really becomes a decision based on the application.