Electro-Visual Indicators

1. Field of the Invention

The invention relates to electro-visual indicators which present a visual output indicating whether they are electrically energized.

2. Prior Art

Known in the art are electro-visual indicators which operate via the intermediary of a mechanical part movable in response to the electrical energization of, for example, an electromagnetic coil. Movement of the mechanical part typically renders visible or not visible a display or character indicating whether the device is electrically energized. Such indicators, however, suffer from the disadvantage that movable mechanical parts are subject to wear and to effects of vibrations.

Also known in the art are electro-visual indicators which essentially comprise an electrically energizable light emitting source, light from which can either be used as an indication in itself of energization of the indicator, or to define characters representative of information requiring display. Indicators of this type are disadvantageous in that they are only able to give a positive indication when the indicator is actually energized and in that they typically have high power consumption requirements.

It is an object of the invention to provide an improved electro-visual indicator. It is a further object of the invention to provide an electro-visual indicator having no movable mechanical parts and which has a low power consumption. It is a still further object of the invention to provide an electro-visual indicator capable of providing a positive indication either when the indicator is energized or when the indicator is not energized.

According to the invention there is provided an electro-visual indicator, comprising a housing, means defining a closed-off space within the housing, a magnetic fluid partially filling the said space and having a predetermined optical characteristic, means in the housing defining a viewing window opening into part only of the said space and covered by light transmitting material, and electromagnetic means in the housing energizable to move the magnetic fluid in the space in a manner which is visually distinguishable through the said window to provide an indication of the state of energization of the electromagnetic means.

According to the invention there is also provided an electro-visual indicator, comprising a cylindrical housing of magnetic material which is closed off at one end and has a peripheral opaque flange at the other end to define a viewing window, light transmitting material sealingly fixed in the window space, a disc-shaped first pole piece mounted co-axially within the housing and having a surface closely spaced behind the said light transmitting material and sized so as to define a first gap between it and the light transmitting material and a second, annular, gap in communication with the first gap and behind the opaque flange on the housing and between the periphery of the first pole piece and the housing, an annular, second pole piece co-axially mounted around the annular gap, sealing means for sealing the annular gap such that the annular gap and the said first gap together define a closed space, a magnetic fluid partially filling the said closed space and tending to flow into the said first gap by capillary action and having a predetermined color which contrasts with the color of the said surface of the disc-shaped first pole piece behind the window, an electromagnetic coil mounted in the housing and electrically energizable to set up a radially directed magnetic flux which travels through the housing and between the first and second pole pieces to magnetically attract the magnetic fluid out of the first gap and into the second, annular gap.

An electro-visual indicator embodying the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawing in which:

FIG. 1 is a cross-section of the electro-visual indicator;

FIG. 2 is a front view of the indicator in the absence of electric power supply to the indicator; and

FIG. 3 is a front view of the indicator with electric power supplied to the indicator.

As shown in FIG. 1, the indicator comprises a housing 10 of a generally cylindrical form which is sealed at one end by a back plate 11. The housing 10 and back plate 11 are of a ferrous metal. An electromagnetic coil 12 is wound on a bobbin 13 disposed within the housing 10. The bobbin 13 has a central core 14 of a suitable magnetic material. Electric leads 15 pass through the back plate 11 to facilitate connection of the coil 12 into an external circuit. A disc-shaped pole piece 16 is disposed adjacent one end of the coil and concentric with the housing 10. The diameter of the pole piece 16 is somewhat less than the internal diameter of the housing 10. Formed on the housing 10 adjacent to and encompassing the pole piece 16 is an annular pole piece 17. The coil 12, bobbin 13, central core 14, housing 10 and pole pieces 16 and 17, together form an electromagnet.

At its end further from the back plate 11, the housing 10 has a flanged lip 18 formed around its inner edge. A thin transparent glass lens or window 19 is secured, for example by adhesive, in sealing relation with and behind the lip 17. The indicator is so constructed that the glass window 19 and the opposed front face of the disc-shaped pole piece 16 define a narrow space 20 therebetween.

The peripheral gap between the disc-shaped pole piece 16 and the encompassing annular pole piece 17 is sealed by an elastomeric packing gland 21, for example a rubber O-ring. The space defined by the glass window 19, the housing 10, the packing gland 21 and the pole piece 16 and which includes the narrow space 20 is partially filled with a magnetic fluid 22. One property of the fluid 22 is that it is attracted into a magnetic field.

A legend, indicating whether electric power is being supplied to the indicator, is formed, for example by painting, on the glass window 19. The front face of the disc-shaped pole piece 16 is colored in the same or similar color to that of the characters. The color of the magnetic fluid 22 is such as to contrast with the color of the characters formed on the glass window 19. Typically, the legend formed on the glass window 19 is the word `OFF` (FIG. 2) and is painted on in a durable dull black color paint which is also applied to the front face of the pole piece 16; in this case a red colored magnetic fluid 22 can be advantageously used.

In the absence of an electrical power supply to the coil 12 via the leads 15, the magnetic fluid 22 is drawn into the narrow space 20 as a result of capillary action. The characters of the legend formed on the glass window 19 will thus be contrasted against the background formed by the magnetic fluid and will be clearly visible in suitable ambient light conditions; in the example being considered, the legend OFF will be seen in black letters on a red background.

When electric power is supplied to the indicator via the leads 15, the coil 12 is energized and a radial magnetic field is set up in the space between the disc-shaped pole piece 16 and the annular pole piece 17 formed in the housing 10. The magnetic circuit is provided by the housing 10, the back plate 11, the central core 14 and the disc-shaped pole piece 16. The magnetic fluid 22 is attracted towards the radial magnetic field and is thus drawn out of the narrow space 20. The characters formed on the glass window 19 will now be viewed against a background formed on the glass window 19 will now be viewed against a background formed by the front face of the disc-shaped pole piece 16. Since there is substantially no color contrast between the characters of the legend and the front face of the pole piece 16 the characters are not visible (FIG. 3) and such a condition indicates that power is applied to the indicator.

On de-energization of the coil 12, the magnetic fluid 22 is drawn back into the narrow space 20 by capillary action thus rendering the legend visible once more.

Magnetic fluid suitable for use as the magnetic fluid 22 employed in the described indicator is known in a range of viscosities, magnetic and temperature properties, and colors. Any suitable magnetic fluid can be used as desired.

Although the described indicator operates such that when not energized a positive indication is presented (e.g., the word OFF is visible), it is possible to adapt the indicator by use of a magnetic fluid 22 of a color such that the characters on the glass window 19 are not visible when the coil 12 is de-energized and the magnetic fluid is acting as a background for the characters. In this case the front face of the pole piece 16 is painted in a color contrasting with that of the characters formed on the glass window 19 so that these characters will stand out against the background of the front face of the pole piece when the coil 12 is energized.

Further, the indicator can be constructed so that the narrow space 20 into which the magnetic fluid is drawn in the absence of energization of the coil 12 is not behind the glass window 19 and fluid will thus be drawn away from the window 19 by capillary action. In this case, the magnetic circuit of the indicator is arranged so as to produce a magnetic field on energization of the coil 12 which draws the magnetic fluid back behind the glass window 19. Contrast between characters formed on the glass window 19 and the background to the characters is provided by any of the hereinbefore described methods.

It is also possible to dispense with the characters formed on the window 19, visual indication of the state of energization of the indicator being provided solely by the color or other optical characteristic visible through the window which is determined by the presence or absense of the magnetic fluid in the field of view behind the window.

The described electro-visual indicators can be advantageously used to visually indicate electric power failure in a circuit into which the indicator is connected, for example an aircraft engine instrumentation circuit.

The indicators are advantageous in that they do not contain any mechanical moving parts which are subject to wear and to effects of vibration. The indicators are also compact, have a low power consumption and are readily adaptable to instrument display utilizing integral lighting techniques. The flat front view presentation provided by the indicators facilitates a better readability as compared with drum type indicators.