GB1588698A - Lighting system supervisory apparatus - Google Patents

Description

(54) LIGHTING SYSTEM SUPERVISORY APPARATUS (71) We, MILLIGAN ELECTRONICS LiMITED., a British company of Tolworth Close, Surbiton, Surrey, KT6 7ER., 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 lighting system supervisory apparatus arranged to provide a notification of failure of any of a plurality of light sources.

In lighting systems used to illuminate extensive areas such as airfield runways or security zones surrounding locations to which access must be restricted, it is desirable to ensure that the failure of any light source may be readily ascertained, so that the defect may be rapidly corrected.

One known arrangement for this purpose depends upon a measurement of the total lamp current, a failure-denotive signal being given when this total lamp current varies predetermindly from a predetermined valuc.

This arrangement is found to be inadequately sensitive for many purposes, since where as is usual large numbers of lamps are used, the failure of a single lamp changes the total lamp current by an insignificant amount, and only when several lamps have failed will the total current vary from its nominal value by more than the tolerance range necessary to provide for fluctuations due to changes in ambient temperature. Moreover, a very substantial change in lamp brightness may result before actual cessation of lamp current occurs, and will not be detected by current measurement. Another known arrangement employs an individual monitoring means to detect that each lamp is operating, but this system, although very effective, is uneconomic in requiring individual communication channels from each lamp to a central position.

The present invention seeks to provide lighting system supervisory apparatus which will enable the continued operation of each of a large plurality of lamps to be monitored by a relatively simple apparatus not requiring to be connected with each lamp.

According to the present invention there is provided lighting system supervisory apparatus comprising a cyclically operative scanning device arranged to develop electrical signals denotive of the presence and location of light sources within its field of view; signal storage means arranged to store either signals denoting the positions of light sources within the field of view of the scanning device during a preceding scanning period or signals denoting the intended positions of light sources within said field of view and to reproduce said stored signals in synchronism with the scanning of said field of view by said scanning device; comparator means arranged to compare signals developed by said scanning means with signals relating to corresponding points within said field of view developed by said storage means and to provide a warning signal in the event of a discrepancy between said compared signals indicative of the failure of a said light source.

An embodiment of apparatus according to the invention will now be described with reference to the accompanying drawing, which is a schematic diagram illustrating the application of the invention to supervising the lights used to illuminate an airfield runway.

In the drawing there is shown a portion 11 of an airfield runway which is illuminated by eight lamps 12. The invention is in no way to be regarded as limited by this specific disclosure, since it may be employed to monitor other numbers of lamps used to illuminate other objects.

A photoelectric scanning device 13, which may be of any known kind, using either mechanical or electron-beam scanning, provided that it is capable of developing signals denotive of the presence of the light from each lamp to be supervised. A television camera of known kind may be employed, though since the purposes of the present invention do not require information to be derived at the very high rate necessary for providing a visual display of mov- ing objects, it may be advantageous to employ a camera modified to provide a relative low speed of horizontal and vertical scanning. Modifications to produce this change in performance a television camera are within the capability of any skilled television engineer.

The scanning operation performed by the scanning device 13 is controlled by synchronizing signals provided by a known synchronizing signal generating means 14.

Alternatively, if the scanning device is a known electromechanical device using one or more moving optical elements, then synchronizing signals derived from the move mcnt of these elements may be applied to a device 14' which is arranged to develop from said synchronizing signals control signals needed for other units of the apparatus, as described below.

The signals developed by scanning device 13 are, in the illustrated embodiment, fed through a known limiting means 15, yielding at its output only those signals which correspond to the presence of light from one of the lamps to be supervised. Alternatively the sensitivity of the scanning device may be controlled that it yields only output signals representative of the presence of light from a supervised lamp.

The signals representative of the presence of light from a supervised lamp are applied by way of a gate 16 to a memory or signal storage device 17, which is arranged to be operated in synchronism with the operation of scanning device 13, for which purpose control signals are applied to the memory 17 from unit 14 or 14', whichever is present in the system. The operation of memory 17 is arranged to be such that during the scanning of any specific point in each scanning cycle it will yield at its output a signal corresponding to that entered in the memory during the scanning of the corresponding point in an initial scanning cycle.

Gate 16 is controlled by signals received at an input terminal 18 in such a manner that whenever any change is made in the lighting of the runway, as when the runway lighting is first switched on, or when the number of lamps illuminated is changed at any time, the signals developed by the scanning device 13 during the next succeeding scanning cycle are entered in the memory 17. An enabling signal received at a terminal 18 from the lighting control position enables a gate 19 which is already receiving a second enabling signal from the Reset output of a bistable trigger 20. A third input of gate 19 receives a signal provided at an output of 17a of memory 17 at the end of each operating cycle, that is, at the end of each cycle of the scanning device 13.This latter signal passes through gate 19, enabled as described above, and sets the bistable trigger 20, the Set output from which is applied to enable gate 16 and allow the signals developed by scanning device 13 during the succeeding scanning cycle to enter memory 17. At the end of this scanning cycle memory 17 emits a further signal at its output 17a, which is applied to a gate 21.

Gate 21 is enabled by the signal from the Set output of bistable trigger 20 so that the signal from output 17a of memory 17 passes through the gate to the Reset input of the bistable trigger 20, which is thus reset. The signal from its Set output is thus removed from gate 16 and signals from scanning device 13 are no longer fed into the memory 17.

During each succeeding scanning cycle, until a further enabling signal is received at input terminal 18, signals developed by scanning device 13 are applied to one input of a comparator 22, to the other input of which are applied the signals fed into memory 17 during the scanning of the corresponding points in initial scanning cycle. Comparator 22 is arranged to deliver an output signal only if a signal received from memory 17 is not matched by a corresponding signal from scanning device 13, that is, if a lamp is extinguished. The signals from comparator 22 may be used directly to initiate a warning signal.

However, it is possibIe for light from an operative lamp to be temporarily screened from the scanning device by an aircraft or other vehicle moving on the runway, and it is undesirable to providing a warning of such apparent extinctions. Preferably, therefore, the signals from comparator 22 are applied to a counter device 23 which is arranged to yield an output signal only when a predetermined number of input signals have been received. Counter device 23 is arranged to be reset by the "end of cycle" signal from output 17a of memory 17. A bistable trigger 24 is arranged to be set by any output signal from comparator 22 and to be reset by each signal from output 17a of memory 17, the reset signals being delayed for a time greater than the signal duration by a delay device 25. The output signal provided at the reset output of bistable trigger 24 is used to. enable a gate 26 through which the reset signal from memory 17 may pass to reset counter device 23. Gate 26 will be inhibited unless bistable trigger 24 is in its Reset condition at the time when the reset signal reaches gate 26, that is, unless there has been no output signal from comparator 22 during the preceding scanning cycle. If there has been an output signal from comparator 22 during the preceding scanning cycle, then trigger 24 will have been set by the signal from comparator 22 and will not be returned to its Reset condition until the reset signal at gate 26 has ceased, so that the gate will not allow the passage of the reset signal to counter device 23.

The output from counter device 23, which appears after a predetermined number of comparator output signals have been counted, may be used directly to initiate an alarm signal, by application to a signalling device 27, of any preferred kind, and may also be used to initiate production of a visual display by enabling a display device 28 which is fed with display signals from scanning device 13 and with synchronizing signals from device 14 or 14' and which provides on a screen 29 a visual display representative of the signals developed by scanning device 13. Alternatively, the visual display may be continuously provided and the counter output then initiates a warning signal only.

It will be apparent that the predetermined number of signals counted by counter device 23 may occur by repetition of the same lamp failure, detected during each of a succession of scanning cycles, or may occur during a single scanning cycle if an appropriate plurality of lamp failures is detected.

In a modification of the apparatus described above the lamp-denotive signals stored in memory 17 are not derived by actual scanning of the runway but are preset at appropriate locations in the memory corresponding to the known positions of the lamps as viewed by the scanning device.

There has thus been described lamp supervisory apparatus in which signals developed by scanning a field of view comprising the lamps to be supervised are compared with signals derived from a memory and corresponding to the prior or intended condition of the lamps, and a warning signal, which may take the form of a visual display of the scanned field, is provided when the failure of a lamp is detected.

WHAT WE CLAIM IS: 1. Lighting system supervisory apparatus comprising a cyclically operative scanning device arranged to develop electrical signals denotive of the presence and location of light sources within its field of view; signal storage means arranged to store either signals denoting the positions of light sources within the field of view of the sctn- ning device during a preceding scanning period or signals denoting the intended positions of light sources within said field of view and to reproduce said stored signals in synchronism with the scanning of said field of view by said scanning device; comparator means arranged to compare signals developed by said scanning means with signals relating to corresponding points within said field of view developed by said storage means and to provide a warning signal in the event of a discrepancy between said compared signals indicative of the failure of a said light source.

2. Apparatus in accordance with claim 1 wherein said storage means is arranged to store signals developed by said scanning means during a scanning cycle immediately subsequent to the application of an enabling signal to said apparatus.

3. Apparatus in accordance with claim 1 wherein the output signals of said comparator means are arranged to be applied as input signals to a counter device yielding an output signal in response to the receipt of a predetermined number.

4. Apparatus in accordance with any one of the preceding claims and including means whereby a visual display representative of the signals developed by said scanning device is provided.

5. Apparatus in accordance with claim 4 wherein said visual display is arranged to be provided in response to the development of said warning signal.

6. Apparatus in accordance with any one of the preceding claims wherein said scanning device is an electron-beam scanning device controlled by synchronizing signals developed by synchronizing signal generating means, signals from which are used also to control the reproduction of said signals by said storage means.

7. Apparatus in accordance with any one of claims 1 to 5 wherein said scanning device is an electro-mechanical device using a moving optical element and wherein synchronizing signals developed by said device are applied to a device arranged to develop from said synchronizing signals control signals used to control said storage means and, when present, said display means.

8. Lighting system supervisory apparatus substantially as herein described with reference to the accompanying drawing.

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

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. gate 26 has ceased, so that the gate will not allow the passage of the reset signal to counter device 23. The output from counter device 23, which appears after a predetermined number of comparator output signals have been counted, may be used directly to initiate an alarm signal, by application to a signalling device 27, of any preferred kind, and may also be used to initiate production of a visual display by enabling a display device 28 which is fed with display signals from scanning device 13 and with synchronizing signals from device 14 or 14' and which provides on a screen 29 a visual display representative of the signals developed by scanning device 13. Alternatively, the visual display may be continuously provided and the counter output then initiates a warning signal only. It will be apparent that the predetermined number of signals counted by counter device 23 may occur by repetition of the same lamp failure, detected during each of a succession of scanning cycles, or may occur during a single scanning cycle if an appropriate plurality of lamp failures is detected. In a modification of the apparatus described above the lamp-denotive signals stored in memory 17 are not derived by actual scanning of the runway but are preset at appropriate locations in the memory corresponding to the known positions of the lamps as viewed by the scanning device. There has thus been described lamp supervisory apparatus in which signals developed by scanning a field of view comprising the lamps to be supervised are compared with signals derived from a memory and corresponding to the prior or intended condition of the lamps, and a warning signal, which may take the form of a visual display of the scanned field, is provided when the failure of a lamp is detected. WHAT WE CLAIM IS:

1. Lighting system supervisory apparatus comprising a cyclically operative scanning device arranged to develop electrical signals denotive of the presence and location of light sources within its field of view; signal storage means arranged to store either signals denoting the positions of light sources within the field of view of the sctn- ning device during a preceding scanning period or signals denoting the intended positions of light sources within said field of view and to reproduce said stored signals in synchronism with the scanning of said field of view by said scanning device; comparator means arranged to compare signals developed by said scanning means with signals relating to corresponding points within said field of view developed by said storage means and to provide a warning signal in the event of a discrepancy between said compared signals indicative of the failure of a said light source.

2. Apparatus in accordance with claim 1 wherein said storage means is arranged to store signals developed by said scanning means during a scanning cycle immediately subsequent to the application of an enabling signal to said apparatus.

3. Apparatus in accordance with claim 1 wherein the output signals of said comparator means are arranged to be applied as input signals to a counter device yielding an output signal in response to the receipt of a predetermined number.

4. Apparatus in accordance with any one of the preceding claims and including means whereby a visual display representative of the signals developed by said scanning device is provided.

5. Apparatus in accordance with claim 4 wherein said visual display is arranged to be provided in response to the development of said warning signal.

6. Apparatus in accordance with any one of the preceding claims wherein said scanning device is an electron-beam scanning device controlled by synchronizing signals developed by synchronizing signal generating means, signals from which are used also to control the reproduction of said signals by said storage means.

7. Apparatus in accordance with any one of claims 1 to 5 wherein said scanning device is an electro-mechanical device using a moving optical element and wherein synchronizing signals developed by said device are applied to a device arranged to develop from said synchronizing signals control signals used to control said storage means and, when present, said display means.

8. Lighting system supervisory apparatus substantially as herein described with reference to the accompanying drawing.

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