AU4447499A - Equipment housing with humidity pump - Google Patents

Description

P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "EQUIPMENT HOUSING WITH HUMIDITY PUMP" The following statement is a full description of this invention, including the best method of performing it known to us: Technical Field This invention relates to electronic equipment housings. The invention is intended to reduce the level of humidity in such housings and is particularly applicable to housing for equipment which is exposed to the weather or is located underground.

Backa.round Art Sealed environment housings provide higher short term reliability for the electronics than vented enclosures, particularly for equipment located underground in cable pits.

However, the sealed housings suffer from a build-up of humidity and the resulting condensation can affect the reliability of the components. Previous attempts to overcome this problem have included an "Umbrella" over the components to divert condensation on the inside of the lid away from the components. This arrangement does not lower the overall humidity and condensation can still occur 15 directly on the components, particularly those which operate intermittently or at low temperatures.

Disclosure of the Invention This invention proposes the provision of a sealed enclosure with a humidity pump to reduce the humidity within the enclosure.

20 In a first embodiment, the humidity pump includes a receptacle passing through a wall of the enclosure, the receptacle having access to the internal atmosphere within the enclosure and to the external atmosphere, there being a regenerative dessicant within the receptacle, and heater means to heat at least a first part of the regenerative dessicant to drive off moisture to the external atmosphere.

Preferably a membrane which is permeable to water vapour but substantially impermeable to water separates at least the first part of the dessicant from the outer atmosphere to prevent external water from contacting the dessicant.

In one embodiment, the dessicant is divided into first and second parts and separated by a wicking material.

In a further embodiment, a cooling mechanism, such as a Peltier device is provided to cool a part of the receptacle exposed to the inner atmosphere to facilitate condensation on the cooled part.

In a modification of this embodiment, wicking material is used to draw condensate from the cooled part to the dessicant.

In a still further embodiment, the humidity pump includes condensing means within the enclosure, wicking means to draw off the condensate to the outside of enclosure, and heating means to heat at least a first part of the wicking means to drive off moisture to the outer atmosphere. Preferably a vapour permeable membrane isolates the wicking material from the external atmosphere.

Brief Description of the drawings Figure 1 is a schematic representation of an equipment housing fitted with a •o humidity pump embodying the invention.

Figure 2 shows an alternative embodiment of a humidity pump.

15 Description of Inventive Embodiments The invention will be described with reference to the embodiments shown in the drawings.

In Figure 1, an enclosed equipment housing 1 is fitted with a breather in the form of a tube 2 passing through wall 11. The ends 5 and 7 of the tube permit 20 access to the internal and external atmosphere respectively. Ends 3 and 6 of the tube are filled with a regenerative dessicant, granules 4, a first section of the dessicant being exposed to the internal atmosphere and a second section being exposed to the external atmosphere. A heater 8 is arranged to heat at least part of the dessicant to dry it out and drive at least a portion of the moisture off into the external atmosphere.

In one embodiment the tube is filled with dessicant. In the embodiment illustrated in Figure 1, first and second sections of dessicant at ends 3 and 6 are linked by wicking material In operation the inner atmosphere temperature and hence pressure fluctuates as the heat generated by the equipment varies or as the external temperature varies.

Thus air is passing in or out of the housing via the breather with these pressure fluctuations in relation to the external pressure.

As air is drawn in, the dessicants in the tube draw off some of the moisture and subsequently the dessicant at end 3 absorbs moisture from the inner atmosphere, and, when the dessicant at end 3 contains more moisture than the dessicant at end 6 some of the moisture will be drawn from end 3 to the dessicant at end 6 by the wicking material 10 or via the intermediate dessicant in the case where the tube is full of dessicant).

The heater at end 10 may be turned on intermittently or periodically via 10 switch 12 to drive off moisture at end 6 to maintain a "moisture differential" between the inner and outer dessicant. To this end, the ends 3 and 6 of the tube 2 may be perforated to enable moisture to be absorbed at end 3 and driven off at end o° 6.

In one refinement of the invention the heater 8 may be controlled by a device 15 measuring the moisture content of the dessicant. The moisture content may be measured resistively or capacitively.

In an alternative embodiment shown in Figure 2, cooling mechanism 21 such as a Peltier device may be used to cool condensation elements 22 connected to end 3 of the tube to improve the efficiency of the moisture scavenging operation. In this 20 case the tube (not shown) may be filled with dessicant (or in an alternatives it may contain only wicking material 23) to absorb the condensation and convey it to the end of the tube where the dessicant (or wicking material) is heated to drive off some of the moisture by heater 9.

The perforated end 6 of tube 2 may be covered by a vapour permeable, water resistant material Goretex TM) to enable the moisture to be driven off from end 6 and to prevent ingress of water.

However, in the embodiment shown, the end 6 of the breather is contained in a vented enclosure. In this case the vapour permeable cover need not be used.

Claims (9)

1. A humidity pump including means to draw moisture from the inner atmosphere of an enclosed housing and means to drive off moisture drawn from the inner atmosphere to the exterior atmosphere.

2. A humidity pump as claimed in claim 1, including a breather element formed of a receptacle having access to the inner atmosphere and the outer atmosphere through a wall of the housing, the humidity pump including means to draw moisture from the inner atmosphere and heater means to drive off some of the moisture to the outer 10 atmosphere. °ooo

3. A humidity pump as claimed in claim 2 wherein the means to draw moisture includes a regenerative dessicant and the heater means is arranged to heat at least *9ee part of the dessicant to cause moisture to be driven off to the outer atmosphere. gee°

4. A humidity pump as claimed in claim 3 in which the dessicant is divided into 15 a first part to absorb moisture from the inner atmosphere and a second part heated by the heater, the first and second parts being linked by wicking material.

A humidity pump as claimed in any one of claims 1 to 4, wherein the means to draw moisture includes condensation means cooled by cooling means.

6. A humidity pump as claimed in claim 5, wherein the humidity pump includes wicking means drawing moisture from the condensation means to the means to drive off moisture.

7. A humidity pump as claimed in any one of claims 1 to 6 wherein the humidity pump includes a receptacle having a first end exposed to the inner atmosphere and a second end exposed to the outer atmosphere, access to the outer atmosphere being via a vapour permeable, water resistant cover.

8. A humidity pump substantially as herein described with reference to the accompanying drawings.

9. An equipment housing fitted with a humidity pump as claimed in any one of claims 1 to 8. DATED THIS TENTH DAY OF AUGUST 1998 ALCATEL