A good first step to remove enclosure moisture is to characterize the enclosure environment utilizing a temperature/humidity data logger. These low-cost, battery-powered devices (~$200) record Low Humidity Control Cabinets. In addition they indicate the dew-point conditions inside the enclosure (Fig. 6). Maintaining enclosure temperatures above dew-point temperatures is a requirement for condensation prevention.
Pursuing this alternative can be accomplished in a number of ways, ranging from desiccant to thermoelectric dehumidifiers-the task is to select a choice that is inexpensive to both implement and keep. This type of water-absorption capacity for desiccant is determined by a number of factors (e.g., desiccant type, humidity, temperature). For example, silica gel can absorb up to 40% of their weight in water. A 4’ x 6’ x 2’ electrical enclosure in a hot/humid environment would saturate 125 g of desiccant within two air exchanges. Therefore, the resulting frequency of required desiccant change-outs (which affects maintenance costs) is largely driven by how well the enclosures are sealed. Unfortunately, in terms of desiccant regimes, each act of opening an enclosure to inspect the desiccant serves as an air exchange.
Dehumidifiers are comparatively cheap, although finding convenient available power inside an enclosure may be problematic. The positive feature is the fact that dehumidifiers remove the manual intervention associated with a desiccant regime. The negative feature of dehumidifiers is because they introduce one more piece of equipment that can ultimately fail.
Another technique is to minimize the opportunity of condensation through internal heaters (or light bulbs) to maintain the interior enclosure temperature well above dew-point temperatures. The down-side is the fact higher temperatures may be detrimental for some heat-sensitive electronic components, and also the higher temperature actually allows the air to hold more moisture. Venting and fans can aid in avoiding condensation in certain situations-although the Dry Cabinets For PCB Storage still exists. One interesting product the makers of GORE-TEX® have produced involves screw-in vents that enable enclosures to breathe, while providing a barrier to moisture and contaminants. The thought behind this sort of venting is that it cuts down on the stress on door seals when there are pressure differentials between the enclosure and the environment. By equalizing pressure, the chance of moist air at higher pressure defeating your door seals is lessened.
Moisture-hardening of electronics includes a number of techniques. With regards to connectors, using waterproof connectors or hardening existing connectors and splices with heat-shrink tubing can be useful to minimize water intrusion and corrosion. Avoiding horizontal orientation of components like printed circuit boards inside the enclosure can minimize surfaces where condensation may collect for prolonged periods of time. Conformal coatings for lower-voltage printed circuit boards and the usage of potting (see Fig. 7) of higher-voltage components greatly boost the moisture resistance of components. Potting costs vary according to the scale of order, material selection jmmhra part geometry, but representative costs for very small orders (less than 10) typically fall within the range of $18 to $45 per part. An additional benefit of potting is the added defense against shock and vibration.
Moisture protection of electronics is better approached by pursuing practices that maximize Dehumidifying Dry Cabinets during equipment installation, along with being prepared to mitigate failure through any one moisture-protection measure during operations. This strategy, in addition to tracking equipment-maintenance performance to know how well moisture-protection measures are working, can lead to long-term minimization of electronics moisture-induced problems. MT.