Refrigeration – Using electrical or magnetic effect – Thermoelectric; e.g. – peltier effect
Patent
1993-11-05
1995-11-28
Wayner, William E.
Refrigeration
Using electrical or magnetic effect
Thermoelectric; e.g., peltier effect
62 93, 621766, F25B 2102, F25D 1706
Patent
active
054697077
DESCRIPTION:
BRIEF SUMMARY
THIS INVENTION relates to an apparatus for and a method of providing an atmosphere of predetermined humidity, for example for use in calibrating humidity measuring instruments or for storing items which require to be kept at a particular humidity.
A number of methods are available for providing atmospheres of known humidities. One traditional method is to mix wet air with differing quantities of dry air to produce different humidities. Another method is to maintain the volume of air concerned over a solution of saturated salts and in moisture equilibrium with the latter. These known methods are expensive and/or time consuming.
It is among the objects of the present invention to provide an improved apparatus for and method of, providing an atmosphere of predetermined humidity.
According to one aspect of the invention there is provided apparatus for providing an atmosphere of predetermined humidity, comprising a chamber for containing such atmosphere, means for supplying dry air and moist air to said chamber and means for drawing air from said chamber, control means for controlling the relative amounts of dry air and moist air supplied to the chamber to afford a coarse adjustment of humidity, and fine control means including moisture removal means for removing moisture from the atmosphere in said chamber, the apparatus including a control facility controlling said dry and moist air supplying means, and said means for drawing air from the chamber, and/or controlling said moisture removal means, said humidity sensing means providing its output signal to said control facility.
An embodiment of the invention is described below, by way of example, with reference to the accompanying schematic block diagram.
Referring to the block diagram, the apparatus includes a small chamber 10 within which are placed a reference dewpoint or relative humidity measuring probe 12 and a temperature sensing probe 14.
Exposed within the chamber, for example forming one wall of the chamber, or part of one wall, is a surface, indicated at 16, of which the temperature can be closely controlled, and which, more particularly, can be cooled with respect to its surroundings, for example thermoelectrically using a Peltier cooling device (indicated schematically at 18) or by passing a cool liquid through passages within a metal body affording the surface 16. If desired, several walls of the chamber 10 may have such surfaces 16 which can be controllably cooled in the manner indicated.
The chamber 10 is connected via a valve V2 with an air extractor or suction pump, via a valve V1 with an air saturator 20 and via a valve V3 with a source 22 of dry air. When valves V1 and V2 are open and the extractor or pump operated, dry air is drawn from the source 22, via an air conduit into the saturator 20 and, in passing through the saturator 20, becomes saturated with moisture. The saturated air then passes, via the valve V1, into the chamber 10.
The valves V1, V2 and V3 are electrically operable valves controlled by a computer 24, for example a microcomputer, having a keyboard 26 and a display 28. The humidity probe 12 and the temperature probe 14 provide electrical signals, significant of the respective values sensed to the computer 24. In practice, for precision, the humidity sensor may operate by measurement of dewpoint, for example in a repeating cycle.
The system functions as follows:
If a known humidity (or dewpoint) is required, this number is simply entered into the computer 24 by the action of the keyboard 26. The computer then determines, on the basis of the signals from the probe 12, whether the atmosphere already present in chamber 10 needs to be humidified or de-humidified. If the atmosphere needs to be humidified, then valves V1 and V2 are opened and saturated air flows into the chamber until such time as there is a slight excess of water vapour in the measuring chamber (i.e. if the required dewpoint was 5.degree. C., saturated water vapour would be allowed to flow until the dewpoint was say, 10.degree. C.). V1 and V2 are then closed. Conv
REFERENCES:
patent: 1819643 (1931-08-01), Fleisher
patent: 2754063 (1956-07-01), Kersten
patent: 3532270 (1970-10-01), Schoen, Jr.
patent: 4356834 (1982-11-01), LeMay
patent: 5056547 (1991-10-01), Brownawell
Protimeter plc
Wayner William E.
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