GB2129128A

GB2129128A - Moisture detector

Info

Publication number: GB2129128A
Application number: GB08328377A
Authority: GB
Inventors: Thomas Clifford Hedges
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1982-10-28
Filing date: 1983-10-24
Publication date: 1984-05-10
Also published as: GB8328377D0; GB2129128B

Abstract

A moisture detector, for enclosed electronic equipment, of the kind having, for example, cobalt chloride (4) which changes from blue when dry to pink when moist, is characterised in that a light source such as a photodiode (1) causes light to be transmitted or reflected from the cobalt chloride to a light detector such as a phototransistor (3). A blue light filter (5) may be included in the light path, which is related to the colour changes of the cobalt chloride (4) to accentuate these changes. Preferably both failure to function of the detector and high moisture level give an alarm signal. <IMAGE>

Description

SPECIFICATION Moisture detectors This invention relates to moisture detectors.

One form of moisture detector, which finds particular application in association with moisture sensitive electronic equipment, comprises a screwed plug containing a disc of cobalt chloride impregnated paper exposed to the atmosphere inside the equipment and visible from outside of the equipment through a sealed glass window.

The paper is dried to a blue colour at the time that the electronic equipment is sealed. If the paper disc turns pink owing to increased humidity, the equipment can be opened and corrective measures taken to remove the moisture.

The above-mentioned moisture detector has a number of disadvantages, being that, regular inspection of the sealed equipment is necessary, the sealed equipment may be in an inaccessible or hazardous place and because the blue/pink indicator must be visible, the physical structure of the containment for the equipment is subjected to constraints.

Another known form of moisture detector comprises a capacitor which has a di-electric which is sensitive to moisture. The capacitor is part of a tuned circuit so that when the di-electric properties change, the frequency of the tuned circuit changes. Unfortunately, this form of moisture detector is relatively expensive when compared with the first above-mentioned type of known moisture detector and incorporation of the capacitor moisture detector may involve substantial modifications to the equipment in which moisture is to be detected.

Arr object of the present invention is to provide an improved moisture detector.

According to the present invention, a moisture detector for enclosed equipment, such as enclosed electronic equipment, of the kind in which moisture sensitive material changes its optical properties in response to moisture is characterised in that a light emitting source is disposed to cause light to fall on the material and then pass to a light receiver disposed to detect said changes in optical properties and thereby detect moisture changes.

The light source may comprise a light emitting diode and the light detector may comprise a photo transistor.

Preferably, the moisture detector is arranged to be fail-safe. In the present context, fail-safe is meant to indicate that detector malfunction and excess moisture detection both result in an alarm signal.

An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagram of a first embodiment of the invention, and Figure 2 is a diagram of a second embodiment of the invention.

Reference is directed firstly to Figure 1, in which a light source is generally indicated by 1.

The light source typically comprises a light emitting diode. An optical path for light emitted by the light source is indicated by a dotted line 2. The light path 2 is from the light source 1 to a light detector 3, which detector typically comprises a photo transistor. Between the light source 1 and the light detector 3, there is disposed cobalt chloride moisture sensitive material 4 and a blue pass optical filter 5.

Reference is now directed to Figure 2, in which like reference numerals to Figure 1 are used for like parts. The embodiment of the invention shown in Figure 2 differs from that shown in Figure 1 in that light is reflected from the moisture sensitive material 4 rather than being transmitted through it.

The moisture sensitive material 4 typically comprises gelatine containing cobalt chloride. Dry cobalt chloride has a blue colour which changes to pink in the presence of moisture. By selecting an appropriate choice of wave length of light to be transmitted through or reflected by the moisture sensitive material 4, the material passes or reflects more or less light to the detector 3 as the humidity of its environment changes. Wave length of the light may be determined by choosing an appropriate light source or by use of the filter 5.

The system may be arranged such that any malfunction or electrical disconnection is selfindicating, ie fail-safe operation is provided. As referred to above, this arrangement can be achieved by using a light emitting diode as a light source transmitting blue light through a blue pass filter to a moisture sensitive medium containing cobalt chloride which is blue when dry and pink when wet. In a dry environment the blue light passes through the medium to a silicon photo transistor causing a current to flow to a monitoring point, which might be on the front panel of electrical equipment with which the moisture sensitive material is associated or may be at a remote monitoring point. When the moisture sensitive material becomes pink, very little blue light is passed to the detector and the signal current to the panel warning light or remote monitor falls.Any disconnection or obscuring of the light in this arrangement would be evident, since the current would change to the moisture alarm situation.

When remote indication of moisture is given, the indicating signal may also be recorded or may control associated apparatus to carry out an operating function. When an indication that moisture is too great is given, silica gel used for keeping equipment dry may be changed. The moisture sensitive material can be chosen so as to be cheap to produce and manufacture and can therefore be used on a throw-away basis. Damp pink samples could be replaced with new dry blue samples.

Optical properties of the moisture sensitive material include those properties sensitive in the spectrum from ultra-violet through visible light to infra-red. Any desired optical property within this rahge may be used. While the change in optical property described above is a change in colour caused by moisture affecting the transmission through or reflection from the sensitive material, in other embodiments of the invention, the change in optical property may be an effect due to light scattering within the material.

The light source might in some embodiments of the invention be an incandescent lamp, a gaseous discharge lamp, an electro-luminescent diode or, indeed, any other known source of light. In other embodiments of the invention, the means of detecting the light can be semi-conductor photo diodes, photo transistors, photo conductive cells, or integrated circuit light actuator switches.

Moisture sensitive material may be impregnated in any suitable medium such as silica gel, gelatine, organic plastics or paper.

Addition of hydroscopic materials such as sodium chloride to the light sensitive material enables the sensitivity and speed of response of the moisture sensitive material to be adjusted. If disposable moisture sensitive material units are not employed then the material is arranged to be reversible. It could follow ambient conditions or it may need to be reset by an operator to an initial state. The device may be designed in a fail-safe manner such that open circuits in the detector give the same indication as any condition that is being detected.

The electrical signal generated by the light detector may itself be processed to give a precise indication of percentage humidity in the moisture sensitive material environment. Such processing may be effected by a comparator arrangement which switches at preselected levels, corresponding to calibrated moisture levels. In some embodiments, there may need to be a number of moisture sensitive materials and detectors, so that relative humidity in different ranges can be determined by different detectors, giving an exact determination over a wider range than is possible with only one detector.

Claims

1. A moisture detector for enclosed equipment.

such as enclosed electronic equipment, of the kind in which moisture sensitive material changes its optical properties in response to moisture characterised in that a light emitting source is disposed to cause light to fall on the material and then pass to a light receiver disposed to detect said changes in optical properties and thereby detect moisture changes.

2. A detector as claimed in claim 1 in which the light source is a light-emitting diode and the light receiver is a phototransistor.

3. A detector as claimed in claim 1 or 2 in which both failure of the detector to function and increased moisture changes above a threshold produce an alarm signal.

4. A detector as claimed in any preceding claim in which the moisture sensitive material is cobalt chloride and a blue pass filter is located between the light source and said material.

5. A detector as claimed in any preceding claim including comparator arrangements so that the detector is calibrated at various moisture levels.