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How to deal with damaging condensation

How to deal with damaging condensation Water and humidity are the constant enemies of equipment cabinets - or rather their contents. Brownell manufactures a complete set of moisture control 'tools' for cabinet/housing designers because of concern over two trends - the advanced electrical and electronic components can be more sensitive to moisture levels than their predecessors and that moisture control is too often regarded as an inexact science.

There are two methods of moisture reduction, for two types of moisture control needs. Molecular sieve desiccators like the Brownell panel mounting units are extremely efficient at extracting water vapour from the atmosphere. They are for applications where virtually dry atmospheres are essential for component protection, for example against electrical short-circuiting, insulation breakdown, visibility loss, etc. Because atmospheric moisture levels may be critical, units incorporate an indicator showing when the desiccant is reaching, and has reached, its absorption capacity.

The one disadvantage with molecular sieve desiccators is that the desiccant itself cannot be reactivated. Alternative silica gel based desiccators are more general purpose. Their moisture absorption rate is not as powerful as that of molecular sieve types but the desiccant can be reactivated by oven-drying and cooling in a container sealed to prevent the crystals absorbing moisture during cooling. An indicator shows that the silica gel is absorbing moisture and when reactivation is due.

Brownell silica gel desiccators are designed for protection against corrosion and mould growth hazards in electrical and electronic equipment or, indeed, any storage container the contents of which would deteriorate with dampness.

Having decided which type of desiccator is best, one can then calculate the optimum size of unit. Brownell units are all sized according to the typical volume of air they will protect in litres - from 10 to 50 litres per unit. Allowance must also be made for non-typical ambient conditions or conditions which are less foreseeable, as in portable equipment.

Sometimes water is the enemy instead of humidity, in which case a drain plug is the answer. The new Brownell unit for this includes a dust filter allowing liquid flow no contamination. A two-way flow of air will be required where air pressures outside the cabinet change, for instance in portable equipment again, especially as used in air transport. Membrane keyboards are particularly sensitive to air pressure changes. The antidote for these gradual pressure changes is a breather valve, but one which is immersion proof. The Brownell immersion proof breather valve withstands immersion to 1m for up to 15 min.

Where an accurate continuous indication of humidity levels is required to make sure all these measures are coping, Brownell has complementary relative humidity indicator plugs, for either 30/50% with silica gel desiccant or 15/30% using molecular sieves.
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