WO1992002802A1

WO1992002802A1 - A humidity indicator with a hygroscopic substance

Info

Publication number: WO1992002802A1
Application number: PCT/DK1991/000218
Authority: WO
Inventors: Lars Olsen; Erik Frederiksen
Original assignee: Dansk Teknologisk Institut
Priority date: 1990-07-31
Filing date: 1991-07-26
Publication date: 1992-02-20
Also published as: DK182790D0; DK168176B1; AU8322591A; DK182790A

Abstract

A humidity indicator consists of a beaker-like housing (1) with an inside pocket (6) containing a hygroscopic salt (9), a wick (8) extending from the bottom of the pocket (6), up around its top edge and down to a level below its bottom above a vessel (12) formed in the bottom part of the housing (1). When an air-tight cap (5) is removed or replaced upside-down allowing air to enter through slits (10), the humidity in the ambient air contacts the salt (9), and if the relative humidity is equal to or higher than the deliquescence threshold of the salt (9), the latter will absorb water from the air, after which this water with the salt dissolved in it will be transported by the wick (8) into the lower vessel (12). The quantity of salt or liquid transported is a measure of the total duration of those time intervals, during which the relative humidity has been at least equal to the deliquescence level of the salt (9).

Description

A HUMIDITY INDICATOR WITH A HYGROSCOPIC SUBSTANCE

TECHNICAL FIELD

The present invention relates to a humidity indicator of the kind set forth in the preamble of claim 1.

BACKGROUND ART

Humidity indicators based on hygroscopic substances being liquefied by the humidity in the air exist in a variety of types, the majority of which are intended to indicate whether the relative humidity in the air is or has been at least equal to the deliquescence threshold of the hygroscopic substance being used in each case. With these known humidity indicators, it is, however, not possible to obtain any indication of the duration of those time intervals, during which the relative humidity in the air has been equal to or exceeded a certain value.

DISCLOSURE OF THE INVENTION

Is it the object of the present invention to provide a humidity indicator of the kind referred to initially, with which it is possible to obtain an indication of the total duration of those time intervals, during which the relative humidity in the air surrounding the indicator has been equal to or has exceeded a certain value, and this object is achieved with an indicator, according to the present invention also exhibiting the features set forth in the characterising clause of claim 1.

With this arrangement, liquid is transferred from the first container to the second container substantially only during those time intervals, during which the relative humidity of the surrounding air has been equal to or has exceeded the certain value mentioned. Thus the quantity of liquid transferred, which can be measured by observing the liquid level in the second container, is an indication of said total duration. As the humidity indicator according to the present invention comprises no moving parts nor any components requiring particular precision, it can be manufactured at a very low cost.

Advantageous embodiments of the humidity indicator according to the present invention, the effects of which are explained in more detail in the following detailed portion of the present specification, are set forth in claims 2-8.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed specification, the present invention will be explained in more detail with reference to an exemplary embodiment of a humidity indicator according to the present invention shown in the drawing, in which

Figure 1 is a vertical section through the indicator in its state before being put into use, and

Figure 2 is a view similar to Figure 1, but shows the indicator after having been in operation for some time. DESCRIPTION OF THE PREFERRED EMBODIMENT

The humidity indicator shown in the drawing consists of a housing 1 in the form of an upwardly open beaker or cup with an oblique bottom 2. To enable the housing 1 to stand on a horizontal supporting surface, it is provided with a hollow base 3, the lower edge of which may rest on said supporting surface. Apart from its upwardly facing mouth, which as shown in Figure 1 may be closed by a cap 5, the housing 1 is air-tight and liquid-tight. At least some parts of the housing 1 are transparent to make it possible to see what is going on inside it.

A pocket 6 is placed in the upper part of the housing 1, there being a spacing 7 between the pocket 6 and the housing 1. The pocket 6 is formed in such a manner, that it may contain a quantity of liquid as shown in Figure 2.

A wick 8 extends from the bottom part of the pocket 6, around the upper edge of the pocket and down through the spacing 7, so as to end at a level below the level of the bottom of the pocket 6.

In its initial condition, i.e. before being put into use, the indicator is in the state shown in Figure 1, in vrtich the pocket 6 contains a quantity of hygroscopic salt 9 and the housing is closed by the cap 5 in such a manner, that no air can enter the housing, nor can any salt 9 escape from the pocket 6, as the latter is closed by the cap 5 engaging its top edge.

The following table shows examples of relatively harmless hygroscopic salts that may be used as the hygroscopic salt 9 placed in the pocket 6.

TABLE

Liquefies Ml H2O at rel. supplied to hum. liquefy (20°C) 100 g salt (0-20°C)

Anhydrous copper chloride 68.4% 142 Dihydrate of copper chloride 68.4% 90.6

Sodium chloride 75.5% 280

Ammonium sulphate 81.0% 142

Potassium chloride 86.0% 288 Potassium nitrate 93.2% 752

Potassium sulphate 97.1% 833

When the humidity indicator is to be put into use, it is placed in the location, in which it is desired to monitor the relative humidity of the air, after which the cap 5 is removed, inverted and replaced, so that it protects the inside of the housing 4 against dust or falling debris, but at the same time allowing the space inside the housing 1 to communicate with the surrounding air through a number of ventilating slits 10 formed in the periphery of the "crown" of the cap 5. The air inside, the housing 1 will now come into equilibrium with the air outside, so that any humidity in the latter will act upon the hygroscopic salt 9. If the relative humidity of the air contacting the hygroscopic salt 9 is equal to or higher than the deliquescence threshold for the particular salt 9 being used, the salt will absorb moisture from the air and dissolve in this moisture, so that the pocket 6 will now contain a quantity of liquid 11 being a solution of the salt 9 in the water absorbed from the air.

As soon as the level of the liquid 11 has reached a level, at which the wick 8 is able to absorb it and transfer it through the spacing 7 and to the lower end of the wick, liquid will be transferred from the pocket 6 along the wick 8, leaving the latter in the form of drops falling down into a vessel 12 formed by the lower part of the housing 1 including the oblique bottom 2.

After a period of time, a greater or lesser quantity of liquid will have collected in the vessel 12. The quantity of liquid collected in the vessel 12 will now be a measure of the total duration of the time inter¬ vals, during which the humidity has been equal to or greater than the deliequenscence level of the hygro¬ scopic salt 9. The oblique bottom 2 makes it easier to measure small quantities of liquid, such as by reading a scale (not shown) on the outside wall of the housing 1.

The housing 1 and the pocket 6 are preferably made of transparent plastic material, such as acrylic resin, so that it can be seen, whether the hygroscopic salt 9 is still dry in the state before use, and to observe the level of the liquid in the vessel 12, when the indicator is in use.

During storage before use, it is, of course, important to prevent humidity from the surrounding air from acting upon the hygroscopic salt 9. This could be achieved by mounting a cartridge (not shown) contain¬ ing a drying agent, such as silica gel, on the inside of the cap 5, or by placing the whole indicator in a suitable bag or container also containing a suitably enclosed portion of such a drying agent.

The cap 5 may be made of suitable impermeable and resilient material, such as synthetic rubber or another elastomeric substance.

The wick 8 may consist of any suitable material capable of being moistened by water, such as fine tissue paper or so-called cigarette paper. Other materials, including textiles, may also be used.

The humidity indicator may be quite small, as its ability to function does not depend on its size. A total height of between 10 and 30 mm has been contemplated.

Claims

CLAIMS :

1. A humidity Indicator for indicating air humidity and of the kind, the effect of which is based upon a hygroscopic substance, which when acted upon by air with at least a predetermined degree of humidity absorbs water from the air and is dissolved in said water, c h a r a c t e r i z e d by a) a first container (6), the inner space of which is in open communication with the surrounding air during use, said first container being liquid- tight at least up to a certain level and before use of the indicator contains a predetermined quantity of said hygroscopic substance, b) a second container (12), which during use is situated at a lower level than said first container (6), said second container equally being liquid-tight at least up to a certain level, and c) liquid-transferring means (8) adapted by capillary effect to transfer liquid from a first region in said container (6) adjacent or close to its bottom to a second region outside of said first container and at a lower level that its bottom level, from which second region said liquid-transferring means (8) may deliver liquid to said second container (12).

2. An indicator according to claim 1, c h a ¬ r a c t e r i z e d in that said liquid-transferring means comprise(s) at least one wick (8) capable of being moistened by water.

3. An indicator according to claim 1 or 2, c h a r a c t e r i z e d in that said second container is constituted by the region close to the bottom of an envelope (1) being liquid-tight downwards and towards the sides, in which envelope said first container (6) is situated in the form of an upwardly • open pocket, and in which said liquid-transferring means (8) extend(s) through at least one gap (7) between said pocket and a wall in said envelope spaced from said pocket.

4. An indicator according to claim 3, c h a - r a c t e r i z e d in that said envelope (1) is adapted to be sealed in a vapour-tight manner from the surrounding air, e.g. by means of a removable, close- fitting cap or stopper (5).

5. An indicator according to claim 4, c h a - r a c t e r i z e d in that said cap or stopper (5) is adapted to close said first container (6) in a manner to substantially prevent communication with the remainder of the internal space of said envelope (1).

6. An indicator according to any one or any of the claims 1-5, c h a r a c t e r i z e d in a) that the sectional area of said second container (12) being horizontal in use diminishes downwardly from a finite magnitude to substantially zero, and b) that said second container (12), at least in or near its lowermost part, is at least partly translucent or transparent.

7. An indicator according to any one or any of the claims 4-6, c h a r a c t e r i z e d in that said first container (6) comprises at least one transparent wall region, through which its contents (9, 11) may be seen.

8. An indicator according to any one or any of the claims 1-7, c h a r a c t e r i z e d in that said hygroscopic substance is selected from the group of salts consisting of anhydrous copper chloride, dihydrate of copper chloride, sodium chloride, ammonium sulphate, potassium nitrate, potassium chloride, and potassium sulphate.