ILLUMINATION OF MEASURING INSTRUMENTS

Abstract: A device for the illumination, by means of light sources, of a dial of a measuring instrument provided with a protective window placed at some distance in front of the dial, the light sources being placed between the dial and the protective window.

Description: ILLUMINATION OF MEASURING INSTRUMENTS The invention relates to a device for the illumination, by means of light sources, of a dial of a measuring instrument that is provided with a protective window placed at some distance in front of the dial. Illumination devices for, for instance, dashboard instruments in vehicles; in which devices the light sources, usually common incandescent lamps, are placed behind the dial, are generally known. The disadvantage of this method of illumination is that a large propor- tion of the light emitted by the light source is lost, so that a considerable part of the energy consumption, which can be very high in the case of incandescent lamps, does not come to the benefit of the aim pursued. In the case of vehicles with a power source of their own, for instance cars, this is merely a nuisance, but with vehicles that are dependent on wind etc, for instance sailing vessels and balloons, it is a great disadvantage when energy is drawn from e.g. batteries or power packs without a useful purpose. Other known instruments are those in which on the dial light sources are fitted for the purpose of signalling, for instance warning lamps for indicating oil pressure, direction or speed limit etc. However, these light sources are not intended to illuminate the dial; they light up only if their warning function is activated. The invention aims to provide an improved system for illuminating measuring instruments that does not entail the drawbacks mentioned above. For this purpose, according to the invention, in a device of the type described in the preamble, light sources are placed between the dial and the protective window. Thus far less energy is lost and light sources with a lower luminosity and a lower energy consumption will suffice. When use is made of light sources that produce a directed beam, the loss of light will be reduced even more, since the beam can be directed such that virtu¬ ally all the light emitted will sweep across the dial. This will allow a further reduction of the luminosity and energy consumption. Preferably use is made of so-called LED's, in particular of LED's that can produce a directed beam. These LED's have a long service life, while their electricity consumption is very low. This extremely low energy consumption renders the illumination of measuring instruments according to the invention particularly suitable for vehicles that do not have a power source of their own. Moreover, by placing the directed light sources at important loca- tions on the dial, e.g. at the 50 km/h mark or at a maximum allowable RPM, an implicit signalization can be obtained. Furthermore, by using light sources of different colours the dial can be divided into clearly discernible zones, for instance a safe zone illuminated by a green light source, an approaching unsafe zone illuminated by a yellow light source, and an unsafe zone illuminated by a red light source. Further details on the invention may also be derived from the description of an example of an embodiment, with reference to the drawings. Fig. 1 shows a top view of an embodiment according to the invention, comprising five light sources; fig. 2 shows a side view in section along the line II-II in fig. 1; fig. 3 shows a different embodiment according to the invention, in cross-section; fig. 4 shows a cross-section of a pointer of a measuring instrument that is suitable for illumination according to the invention; fig. 5 shows a cross-section of a different embodiment of a pointer of an instrument that is suitable for illumination according to the invention; fig. 6 shows a cross-section of a different embodiment of a pointer of a measuring instrument that is suitable for illumination according to the invention; and fig. 7 shows an electric power supply circuit suitable for use in the device according to the invention. In fig. 1 the face of a measuring instrument is shown with indications 2 on the dial 1. A pointer 3 takes care of the indication of the measured value. On the dial 1 a rim 4 is mounted in which holes 5 are provided in such a way that the centre line of a light beam 6 emitted by an LED 7 that is placed in a hole 5, runs through the centre of the dial, whether or not perpen¬ dicular to the dial. In figures 2 and 3 two embodiments according to the invention are presented, which differ in cross-section only. Fig. 2 shows holes 5 that are directed parallel to the surface of the dial. In fig. 3 the holes are directed at an angle in such a way that the centre line of the light beam is inclined towards the dial. The rim 4 in which the holes 5 that serve to accommo¬ date the LED's 7 are provided should prevent light scattering as much as possible, so that the total amount of light produced will sweep across the dial. For this purpose the rim 4 may be made of an opaque, preferably dark, material. This material may, for instance, be a plastic in which a black, or at least dark, filler is incorporated, a suitable plastic being e.g. high-density polyethylene, or a metal or alloy. In the latter case the rim itself may also be part of the electric power supply circuit. If the rim 4 is made of a plastic, it may.be manufac¬ tured by, for instance, injection moulding, during which process the holes 5 for accommodating the LED's 7 may be formed at the same time by using mould inserts. This is also possible when the rim 4 is made of a metal or an alloy that can be suitably processed by this shaping technique, e.g. aluminium alloys. Figures 4, 5 and 6 show different embodiments of cross-sections of pointers that are suitable for use in a device according to the invention. In order to have at least one surface on which the light beam can reflect, the oblong pointer is provided with a conti- nuous or discontinuous arch or kink directed at the protective window. In fig. 4 the pointer is semi- circular, or at least provided with a rounding, while the pointer in fig. 5 shows a single kink and the pointer in fig. 6 two kinks. In fig. 7 an electric power supply circuit is depicted in which each LED 7 is connected in series to a resis¬ tor 9, so that the LED's are protected from tension peaks, while all LED's 7 are connected in parallel. It is possible to adjust the light emission of the LED's 7 by means of an adjustable resistor 10. However, it is also possible to incorporate into the electric power supply circuit a light-sensitive elec¬ tronic circuit controlling the light emission of the LED's 7, depending on the light intensity of the environment. It has been found that a combination of LED's that are arranged in such a way that they produce orange-red coloured light with a dial comprising a black back¬ ground and white indications give very good results. However, it is also possible to use LED's of other colours, or dials and indications of other colours.

Claims: CLAIMS 1. A device for the illumination, by means of light sources, of a dial of a measuring instrument provided with a protective window placed at some distance in front of the dial, characterized in that the light sources are placed between the dial and the protective window. 2. A device according to claim 1, characterized in that the light sources produce a directed beam. 3. A device according to claim 1 or 2, characterized in that the light sources are LED's with a high luminosity. 4. A device according to any one of the preceding claims, characterized in that the light sources are placed in such a way that the light beams sweep across the dial. 5. A device according to any one of the preceding claims, with at least three light sources, characterized in that the light sources are accommodated in a rim around the dial, in such a way that the centre lines of the light beams run through the centre of the dial. 6. A device according to any one of the preceding claims, characterized in that the rim is made of a plastic in which a black, or at least dark, filler is incorporated. 7. A device according to any one of the preceding claims, characterized in that the rim is made of a metal or alloy, in which case the rim itself may be part of the electric power supply circuit. 8. A device according to any one of the preceding claims, characterized in that the rim with the holes for accommodating the light sources is manufactured as a one-piece article by injection moulding. 9. A device according to claim' 3, characterized in that the LED's are intended to produce an orange- red colour and in that the dial comprises a black background with white indications. 10. A device according to any one of the preceding claims, the instrument having at least one pointer which can move freely with respect to the dial, characterized in that the pointers have an oblong shape and feature, a continuous or discontinuous arch or kink directed at the protective window.

Inventors: FISCHER WILLEM ANTONIE, FISCHER, WILLEM, ANTONIE
Applicants: FISCHER WILLEM ANTONIE, FISCHER, WILLEM, ANTONIE
Application year: 1985
Main classification: G01D11
IPC codes: G01D11, G12B11