GB1588868A - Lighting systems - Google Patents

Description

(54) IMPROVEMENTS IN AND RELATING TO LIGHTING SYSTEMS (71) We, MILLIGAN ELECTRONICS LIMITED., a British company of Tolworth Close, Surbiton, Surrey formerly of 36 Clapham Crescent, London, SW4 7LD., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to airfield lighting systems and provides a means for monitoring the intensity of runway marker lamps.

The invention seeks to solve the problem of effecting at reasonable cost, the monitoring of the intensity of each of a large plurality of runway marker lamps, by comparing a signal representative of the brightness of each monitored lamp with a respective reference signal denotive of the expected lamp brightness and providing an indication of said discrepancy in response to discrepancy between said compared signals.

According to the present invention there is provided runway light supervisory apparatus comprising at an observation location scanning means arranged to derive in cyclic succession signals representative of the apparent brightness of each of a plurality of runway lights as viewed from that location.

means for comparing each of said signals with a respective reference signal denotive of the expected lamp brightness. means responive to any difference between the compared signals that exceeds a predetermined threshold level by providing an error signal, and display means responsive to said error signals for providing an indication of lamp defect.

One convenient manner of carrying out the invention is to provide a scanning means whereby light from each of the plurality of lamps is arranged to be incident in turn upon a device vielding an electric signal representative of the received light. The signals thus derived are each compared with a respective reference signal, derived from a selecting means arranged to operate synchronously with the scanning means, by a comparator yielding an error signal if the signals simultaneously applied thereto differ by more than a predetermined amount.

Each derived error signal may be arranged to initiate an indication of a defective lamp, but a single error signal may arise fortuitously. Preferably, therefore, it is arranged that only when error signals are derived in respect of the same lamp during each of a predetermined plurality of successive scans is a display device actuated to provide an indication of the location of the defective lamp.

Because the runway lamps are operated at different brightness in accordance with the amount of daylight and weather conditions it will be advantageous to provide a means whereby the reference signal appropriate to each lamp may be appropriately varied in accordance with the actual operating condition of the runway lamps at any time.

Preferably the means for deriving electric signals representative of the lamp brightness in respect of each of a plurality of lamps is arranged to provide a spectral response characteristic corresponding with that of the human eye. In addition. however. it is sometimes advantageous to arrange that. in respect of some at least of the scanned lamps. the response characteristic is periodically altered to respond to radiation in the rear infra-red. so that by comparing signals derived in respect of the same lamp with the two different response characteristics a measure of atmospheric absorption may be obtained.

It is convenient for the reference signals in respect of each lamp to be stored in a digital memory device provided with a respective set of reference signals for each operating condition to which the lamps can be set by the airport lamp control system.

The digital signals extracted from the memory at any one comparison operation may be converted into a corresponding analogue signal and used for comparison in a comparison amplifier with the signal derived from the lamp, or alternatively the lampderived signal may be converted into a corresponding digital signal representative of lamp brightness and this digital signal then compared in a digital comparator with the digital reference signal obtained from the memory.

In either case the comparison is arranged to yield an error signal if the brightness represented by the compared signals differ by more than a predetermined amount. In the case where provision is made for different lamp operating conditions, repeated results of comparisons that show that actual lamp brightness is greater than expected lamp brightness may be used to provide an indication that an incorrect set of reference signals is being derived from the memory.

One convenient scanning means includes a plane mirror arranged for rotation about an axis to which the miror surface is inclined, together with a linear sensor arranged in a surface over which an image, projected thereon by way of the mirror. of a field of view including lamps to be monitored is traversed as the mirror rotates.

Another advantageous scanning means includes a mirror drum as used in early television systems. or an electronic television scanner may be employed. In any case it is advantageous to provide a reference lamp which is serviced so as to ensure that it is at all times maintained at its full nominal efficiency. at least within close tolerances, the signal from this lamp being compared with the appropriate reference signal to establish a criterion for the correct operation of the apparatus.

In an advantageous mode of operating the apparatus of the invention. the threshold level which must be exceeded by an error signal to give rise to a fault indication is progressively reduced between successive scans. correlation between the threshold level and the number of fault indications will yield valuable information as to the overall condition of the lighting installation.

The invention will now be further described with reference to the accompanying drawings illustrating embodiments thereof and in which: Figitre I illustrates an embodiment of the invention in which a gyratory mirror is used; Figure 2 illustrates an embodiment of the invention in which a mirror drum is used; and Figure 3 illustrates an embodiment of the invention in which an electronic television scanner is used.

In the embodiment illustrated in Figure 1 an airfield runway 1 is lit by a multiplicity of lights of which two only are shown at 2, 3, though it is assumed that many others are present. It is assumed that light 2 is a reference lamp which is kept at full efficiency by careful servicing. In this embodiment the device 10 used to derive signals representative of each runway light in turn includes a plane mirror 11 mounted for rotation upon the shaft of an electric motor 12, the mirror being mounted not quite perpendicularly upon the motor shaft. The image of the field viewed by the mirror 11 is thus caused to traverse a circular path in space. A lens 13 or other suitable form of optical system produces in a plane spaced from the mirror 11 an image of a field of view including runway lights 2, 3, etc.In the image plane there is disposed on elongate light-sensitive device 14, so positioned that an image of each in turn of the runway lights 2, 3. etc. falls upon the device as the mirror 11 turns.

Signals from device 14, after amplification and modification if required, for example to exclude spurious signals originating in lights other than the runway lights. are applied to a comparator 15 in which the signal derived in respect of each light is compared with an appropriate reference signal. The necessary reference signals are advantageously derived from a read-only memory (ROM) 16, which is arranged to be addressed by an addressing means 17 so as to extract each in turn of the necessary plurality of reference signals.

Addressing means 17 is arranged to address each location in ROM 16 in turn at a rate appropriate to the speed of rotation of mirror 11, that is, to the rate at which the images of the runway lights 2, 3. etc. are projected upon light-sensitive device 14. To ensure that the correct correspondence between the light being viewed and the reference signal is always maintained a synchronizing signal may be derived from a lightsensitive device 18, upon which is projected, in one particular angular position of mirror 11. an image of a synchronizing light source 19 contained within the apparatus. This signal is arranged to cause the sequence of reference signals to be selected. starting alwavs with mirror 11 in the same angular position. If required. exact correspondence may be further ensured by providing additional light sources so that device 18 yields a train of addressing commands at appropriately timed intervals. whatever the speed of rotation of mirror ll.

Thus each signal from a runwav lamp 2. 3, etc. is compared with an appropriate reference signal in comparator 15 which is arranged to energize an alarm device 20 if the difference between the compared signals exceeds a predetermined threshold value, denoting that the light is of impermissibly low brightness.

In order to provide a defect indication only when error signals are derived during each of a plurality of successive scans, it may be arranged that each error signal derived from a particular lamp advances a counter and the defect indication is provided only when a predetermined number of error signals has been entered in the counter.

In cases where the brightness of lamps 2, 3, etc. is arranged to be varied by a control means 21, to suit the particular ambient conditions at the time, it is advantageous to arrange that device 21 provides a control signal to addressing device 17 to cause this device to address storage locations in ROM 16 which contain reference signals appropriate to the different light brightnesses set by control device 21. This arrangement may also be used in other embodiments of the invention described below.

The embodiment illustrated by Figure 2 uses a mirror drum 31 to direct upon a light-sensitive device 32 an image formed by a lens 33 of each in turn of runway lights 2, 3, etc. The signals developed bv device 32 are applied to a difference amplifier 34 in which they are each compared with a respective reference signal provided by a read-only memory 35 as commanded by an addressing means 36. Addressing means 36 is controlled by a synchronizing device driven by the same motor 38 that drives the mirror drum 31 so that derivation from ROM 35 of the correct reference signal in respect of each runway light is assured. In this embodiment the difference signals derived from difference circuit 34 are applied to a threshold device having an adjustable threshold controlled by a programme unit 40 driven by synchronizing signals from device 37.Programme device 40 is advantageously arranged to alter the threshold level set in device 39 during successive repetitions of the scanning of the runway lights performed by drum 31, thus enabling information as to ambient atmospheric conditions to be obtained bv a comparison of the number of lights failing to meet each given threshold. For this purpose it is advantageous to arrange that the output of the threshold device 39 and a signal repre sentative of the progressive change in threshold levels are applied to a display device 41 arranged to yield a comparative display.

It also may be advantageous to provide a means of modifving the response character istic of the light-sensitive device 32. This may be done by arranging alternative light sensitive means upon which the light from the runwav lights may be directed and which apply signals selectively to difference amplifier 34, and/or as illustrated in Figure 2, by providing a filter 42 that may periodically be introduced into the optical path by means of an actuator 43 controlled by programme unit 40. Thus a series of scans at progressive different threshold levels may be followed by another similar series of scans with the filter in place, yielding valuable information as to the visibility in different wavelength ranges of the spectrum and thus as to the atmospheric absorption.

The embodiment illustrated in Figure 3 employs an electronic scanning tube 51 of the type commonly used in television applications. An image of a field of view including the runway lights. 2, 3, etc. is projected upon the target electrode within tube 51 by a lens 52, so that the illumination at respective points on the target represents the apparent brightness of the individual lights.

It is possible to derive successive signals representative of these light brightnesses by deflecting the electron beam of scanner tube 51 in a normal television type scan pattern and deriving the necessary reference signals, as before, from a ROM controlled in accordance with the scan development.

However, as shown in Figure 3 it is more convenient to derive successive pairs of deflection signals from a ROM 53 and applying them to deflection generator circuits in a deflection unit 54 providing appropriate deflection controlling signals to tube 51. By this means the scanning beam may be directed in turn to the images of the respective runway lights and the ROM is conveniently arranged to yield the respective reference signal to a difference circuit 55 to which also the signal from scanner tube 51 representative of the light brightness is applied.

As in Figure 2. signals from difference circuit 55 are applied to a threshold device 56 of which the threshold level is set by a program device and which yields signals to a displav device 58. also controlled by program device 57 to yield a display relating number of lights failing to pass each threshold to the threshold level. Program device 57 is also arranged to control an actuator 59 by which a filter 60 is introduced into the optical path, thus enabling further information as to atmospheric absorption to be obtained. ROM 53 and program device 57 are controlled by respective signals from a clock generator 61 so that appropriate sequences of scans may be completed under the required different conditions.

It will be appreciated that the signals derived from the photosensitive means will be an analog signal. whereas that stored in the ROM will necessarilv be a digital signal.

It is possible to deal with this minor problem in either of two different ways; either the signal derived from the memory may be converted into a corresponding analog signal which is then compared with the signal from the light sensitive device in an analog difference circuit, most conveniently a differential amplifier, or the signal from the photosensitive device may be converted into a corresponding digital signal and this is then compared with the reference signal from the ROM in a digital difference circuit.

Figures 1 and 2 illustrate the former of these alternatives, the signal derived from ROM 16 or 35 being converted into a corresponding analog signal in a digital to analog converter 16a or 35a, respectively, while Figure 3 illustrates the second alternative, with the signals from scanning tube 51 being converted into corresponding digital signals by an analog to digital converter 51a.

In the embodiment of Figure 1 a filter may be arranged to be introduced into the optical path, as described in relation to Figure 2 or 3, while in Figures 2 and 3 display device 41 or 58 may be supplemented or replaced by an alarm device arranged to give warning when any light yields a very anomalous signal. In the case of the embodiment of Figure 3 it may be arranged that any such warning signal arrests the progress of the scanning operation and thus enables a defective light to be immediately signalled.

WHAT WE CLAIM IS: 1. Runway light supervisory apparatus comprising at an observation location scanning means arranged to derive in cyclic succession signals representative of the apparent brightness of each of a plurality of runway lights as viewed from that location, means for comparing each of said signals with a respective reference signal denotive of the expected lamp brightness. means responsive to any difference between the compared signals that exceeds a predetermined threshold level by providing an error signal, and display means responsive to said error signals for providing an indication of lamp defect.

2. Apparatus in accordance with claim 1 and including means wherebv said indication is given only when a plurality of scannings of a particular lamp yield error signals.

3. Apparatus in accordance with claim 2 and including means whereby each said error signal is caused to advance a counter and said indication is provided when a predetermined number of error signals has been entered in said counter.

4. Apparatus in accordance with any one of claims 1 to 3, wherein said scanning means includes a rotating mirror inclined at an angle other than ()() to its axis of rotation and optical means arranged to project an image of a field of viexv including said runway lights by way of said mirror in a plane containing a light-sensitive means upon which an image of each of said lights falls in turn to derive said succession of signals.

5. Apparatus in accordance with any one of claims 1 to 3, wherein said scanning means includes a rotatable mirror drum including a plurality of mirrors, each of which is differently inclined to the axis of rotation, and optical means arranged to project an image of a field of view including said runway lights by way of said miror drum into a plane containing a lightsensitive device, said mirrors being arranged to cause an iniage of each of said lights in turn to fall upon said light-sensitive device thereby to derive said succession of signals.

6. Apparatus in accordance with any one of claims 1 to 3, wherein said scanning means comprises a television camera tube upon the photo-sensitive target member of which an optical system is arranged to project an image of a field of view including said runway lights, and means for scanning said target member with an electron beam to derive said succession of signals.

7. Apparatus in accordance with claim 6, wherein means are provided for controlling the deflection of said electron beam so that it moves in turn to that portion of the target upon which an image of each of said lights is projected under the control of signals derived from a memory used also to contain said reference signals.

8. Apparatus in accordance with claim 7 wherein said difference circuit is a digital circuit and said succession of lamp brightness representative signals are applied to said difference circuit by way of an analog/ digital converter.

9. Apparatus in accordance with any one of the preceding claims, wherein means are provided for altering the level of said threshold between the derivation of said successions of signals whereby to derive information as to ambient atmospheric conditions.

10. Runway light supervisory apparatus substantially as herein described with reference to Figure 1, Figure 2 or Figure 3 of the drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. signal derived from the memory may be converted into a corresponding analog signal which is then compared with the signal from the light sensitive device in an analog difference circuit, most conveniently a differential amplifier, or the signal from the photosensitive device may be converted into a corresponding digital signal and this is then compared with the reference signal from the ROM in a digital difference circuit. Figures 1 and 2 illustrate the former of these alternatives, the signal derived from ROM 16 or 35 being converted into a corresponding analog signal in a digital to analog converter 16a or 35a, respectively, while Figure 3 illustrates the second alternative, with the signals from scanning tube 51 being converted into corresponding digital signals by an analog to digital converter 51a. In the embodiment of Figure 1 a filter may be arranged to be introduced into the optical path, as described in relation to Figure 2 or 3, while in Figures 2 and 3 display device 41 or 58 may be supplemented or replaced by an alarm device arranged to give warning when any light yields a very anomalous signal. In the case of the embodiment of Figure 3 it may be arranged that any such warning signal arrests the progress of the scanning operation and thus enables a defective light to be immediately signalled. WHAT WE CLAIM IS:

1. Runway light supervisory apparatus comprising at an observation location scanning means arranged to derive in cyclic succession signals representative of the apparent brightness of each of a plurality of runway lights as viewed from that location, means for comparing each of said signals with a respective reference signal denotive of the expected lamp brightness. means responsive to any difference between the compared signals that exceeds a predetermined threshold level by providing an error signal, and display means responsive to said error signals for providing an indication of lamp defect.

2. Apparatus in accordance with claim 1 and including means wherebv said indication is given only when a plurality of scannings of a particular lamp yield error signals.

3. Apparatus in accordance with claim 2 and including means whereby each said error signal is caused to advance a counter and said indication is provided when a predetermined number of error signals has been entered in said counter.

4. Apparatus in accordance with any one of claims 1 to 3, wherein said scanning means includes a rotating mirror inclined at an angle other than ()() to its axis of rotation and optical means arranged to project an image of a field of viexv including said runway lights by way of said mirror in a plane containing a light-sensitive means upon which an image of each of said lights falls in turn to derive said succession of signals.

5. Apparatus in accordance with any one of claims 1 to 3, wherein said scanning means includes a rotatable mirror drum including a plurality of mirrors, each of which is differently inclined to the axis of rotation, and optical means arranged to project an image of a field of view including said runway lights by way of said miror drum into a plane containing a lightsensitive device, said mirrors being arranged to cause an iniage of each of said lights in turn to fall upon said light-sensitive device thereby to derive said succession of signals.

6. Apparatus in accordance with any one of claims 1 to 3, wherein said scanning means comprises a television camera tube upon the photo-sensitive target member of which an optical system is arranged to project an image of a field of view including said runway lights, and means for scanning said target member with an electron beam to derive said succession of signals.

7. Apparatus in accordance with claim 6, wherein means are provided for controlling the deflection of said electron beam so that it moves in turn to that portion of the target upon which an image of each of said lights is projected under the control of signals derived from a memory used also to contain said reference signals.

8. Apparatus in accordance with claim 7 wherein said difference circuit is a digital circuit and said succession of lamp brightness representative signals are applied to said difference circuit by way of an analog/ digital converter.

9. Apparatus in accordance with any one of the preceding claims, wherein means are provided for altering the level of said threshold between the derivation of said successions of signals whereby to derive information as to ambient atmospheric conditions.

10. Runway light supervisory apparatus substantially as herein described with reference to Figure 1, Figure 2 or Figure 3 of the drawings.