GB2334599A

GB2334599A - Apparatus for providing an atmosphere of predetermined humidity

Info

Publication number: GB2334599A
Application number: GB9803637A
Authority: GB
Inventors: Fali Minocher Dadachanji
Original assignee: Protimeter PLC
Current assignee: GE Protimeter Ltd
Priority date: 1998-02-20
Filing date: 1998-02-20
Publication date: 1999-08-25
Also published as: GB9803637D0

Abstract

Apparatus is disclosed for providing an atmosphere of predetermined humidity, for example for calibrating humidity-measuring instruments or for conditioning samples. The apparatus comprises a chamber A, a heater or cooler B for controlling the temperature of the atmosphere in the chamber, a water dish D within the chamber and a cooler or heatsink P for maintaining the water in the dish at a predetermined lower temperature. The humidity within the chamber can be adjusted by adjusting the difference between the atmospheric temperature in the chamber A and the temperature of the dish D. Cooler P may be a Peltier element.

Description

DESCRIPTION OF INVENTION Title: "Apparatus for providing an atmosphere of predetermined humidity" THIS INVENTION relates to apparatus for providing an atmosphere of predetermined humidity, for example for calibrating humidity-measuring instruments and/or conditioning samples.

According to one aspect of the invention there is provided apparatus for providing an atmosphere of predetermined humidity, comprising a chamber to contain said atmosphere, means for controlling the temperature of the atmosphere in said chamber, a container for containing a volume of water with an upper surface thereof exposed to said atmosphere and means for maintaining water in said container at a predetermined lower temperature.

An embodiment of the invention is described below, by way of example, with reference to the accompanying drawings in which: FIGURE 1 is a schematic view, in vertical section, of an apparatus embodying the invention, and FIGURE 2 is a perspective view showing, by way of example, a perspective view of an apparatus embodying the invention.

Referring to the drawings, the apparatus comprises a box or container U defining a chamber A in its interior, the container U having walls, a floor and a top all of a heat insulating material or construction, the top including a removable lid J fitting closely in a complementary opening and providing access to the chamber A. The insulating material of the container U allows stable constant temperature control.

An electrical resistance heating element B extends around the wall of the chamber A adjacent its inner surface and serves as a means of controlling the temperature of the air within the chamber A. A temperature sensor T1 is provided within the chamber A to measure the temperature of the atmosphere in the chamber and suitable control circuitry, not shown incolporating sensor T1, is operable to control energisation of the heating element B so as to maintain a selected pre-set temperature of said atmosphere.

A small tray D, for example of metal, and containing a quantity of water W, is placed upon a cooling device P which is fitted into the floor of the container U. The cooling device may be a Peltier-effect device to which is fitted a heatsink or heat pipe E extending from the container U whereby heat extracted from the tray D and water W can be removed from the container U.

A fan F may be provided within the chamber operable to ensure thorough mixing of the air in the chamber and thus an even air temperature throughout the housing.

The apparatus further includes a temperature sensor T2 arranged to sense the temperature of the tray D or the water W therein. (For practical reasons, the sensor T2 may actually be embedded in the portion of the cooling device P which directly contacts the tray D rather than being immersed in the water). A further temperature sensor T3 may be provided for sensing the temperature of the wall of the container U, simply as a safety feature to prevent overheating.

This sensor T3 may simply be in the form of a thermal cut-out incorporated in the electrical circuitry energising the heating element B, or in the element itself.

In the arrangement shown, the lid J has an aperture through which, for example, a humidity sensing probe G requiring calibration, may be introduced into the chamber A.

In use of the apparatus, the tray D contains sufficient water to fully saturate the air in the chamber A at any temperature likely to be of interest and still allow some excess of liquid water remaining in the tray. In operation, the heater B regulates the overall air temperature within the chamber A to a predetermined level.

The temperature to which the water W in tray D is cooled is effectively the dewpoint of the atmosphere in the chamber A since it is the temperature at which, in the equilibrium state, the atmosphere immediately above the water and at the same temperature as the latter is saturated. Accordingly, the relative humidity within the chamber A, at equilibrium, is entirely dependant on the air temperature measured by sensor T1 and the water temperature measured by sensor T2.

Thus, for example, when the air temperature, as sensed by sensor T1, is 20 at equilibrium and the water temperature, as sensed by sensor T2 is 1 00C, the relative humidity within the chamber will be 53%. Higher relative humidity may be obtained by raising the temperature of the water W relative to the air and lower relative humidity by lowering it.

Figure 2 shows an apparatus embodying the invention and which includes an outer casing K within which is mounted the container U, together with control circuitry, a fan for cooling the heatsink E, etc. The casing K may also carry displays R for displaying relative humidity and the various temperatures sensed, and manual controls, such as selector buttons S. The upper end of container U and/or of lid J may be exposed at the top of casing K, as shown.

In operation, the chamber temperature is pre-set using one of the selector buttons. This required temperature and relative humidity can be shown on display R. The actual humidity is derived by a calculation involving the temperatures T1 and T2, such calculation being carried out by processing circuitry within the casing K and being as shown on the displays R.

The apparatus described can create, in a small volume, and in a few minutes, an atmosphere of required predetermined humidity, such as that required for multi-point calibration of humidity probes. The apparatus requires no external air supply or compressed air. If required, the chamber can be fitted with a cooling coil or placed in an artificially cooled atmosphere so that the temperature inside can be maintained at temperatures lower than ambient temperature. The range of humidities generated is limited only by the temperature to which the water W can be cooled in relation to the chamber temperature.

Claims

CLAIMS 1. Apparatus for providing an atmosphere of predetermined humidity, comprising a chamber to contain said atmosphere, means for controlling the temperature of the atmosphere in said chamber, a container for containing a volume of water with an upper surface thereof exposed to said atmosphere and means for maintaining water in said container at a predetermined lower temperature.
2. Apparatus according to claim I wherein said means for controlling the temperature of the atmosphere in said chamber is adjustable whereby different desired temperatures of said atmosphere in a range thereof may be maintained.
3. Apparatus according to claim 1 or claim 2 wherein said means for maintaining the water in said container at a predetermined temperature is adjustable whereby different desired water temperatures within a range of such temperatures may be obtained.
4. Apparatus according to any preceding claim wherein said means for controlling the temperature of the atmosphere in said chamber comprises heating means.
5. Apparatus according to claim 4 wherein said heating means is arranged to heat a wall or walls of said chamber.
6. Apparatus according to any preceding claim, wherein said means for maintaining the water in said container at a lower temperature comprises cooling means.
7. Apparatus according to claim 6 wherein said cooling means comprises a Peltier cooling device.
8. Apparatus for providing an atmosphere of predetermined humidity, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.
9. Any novel feature or combination of features described herein.