GB2275333A - Measurement of the output of a lamp - Google Patents

Abstract

The output of a lamp at P1 is measured by the use of a measuring mechanism comprising an array of sensors which may be moved through the beam B of light produced by the lamp. Means is provided for measuring the response of the sensors at successive distances longitudinally of the beam to produce output signals, which are modified to compensate for the different distances at which the response is measured. In this way the output of a lamp may be determined at relatively high speed, such as 30 to 50 kph, greatly reducing the time taken to check the quality of a linear array of lamps, e.g. bounding a runway or an airfield taxiway road. <IMAGE>

Description

Title: "Improvements relating to the measurement of the output of lamps" Description of Invention This invention is concerned with improvements relating to the measurement of the output of lamps, and in particular to the measurement of a series of lamps located in a linear array.

The invention has been devised principally in relation to the measurement of airfield lighting systems, although it is to be appreciated that the invention may be used in other situations, where similar or analogous problems arise.

Airfield lighting systems include runway centre line lighting, touchdown zone, runway edge and taxiway centre line lighting. Runway lighting systems in general and associated equipment are designed to the standards contained in CAP168, based on the International standard prepared by the ICAO.

High intensity lighting installations are designed to enable suitably equipped aircraft to take off and land safely and repeatedly under low visibility conditions.

Visibility is defined by the RVR (runway visual range). The pilot is given the RVR before starting an approach or take-off and the pilot has to confirm that the RVR exceeds the minimum specified. When landing under acceptable RVR conditions the pilot must see the minimum prescribed amount of high intensity lighting before he reaches the decision height - i.e. the height which defines the lowest height from which the landing can safely be continued or abort the landing.

Since the decision height can be very low (perhaps as low as 5 metres) it is possible to land some aircraft with an RVR of 75 metres and take-off with an RVR of 125 metres.

High light intensities are required to generate a beam that can penetrate fog of high density. To achieve these high intensities without unacceptable power consumption small concentrated beams are used, although in order to achieve the required operational performance the light output must be high enough and the beam correctly orientated.

The two major implications of poor output or incorrect orientation are reduced safety and landing success rate.

The calculation of RVR is based upon measured visibility, assuming light intensity and background luminants, beam symmetry and statistical analysis of light transmission. If the lighting unit performance is below that assumed (which in turn is based on the minimum ICAO requirements) the effective RVR perceived by the pilot will be lower than that reported. Under these circumstances the lighting system will not meet the operational requirements and will lead a pilot into starting an approach when the actual conditions of the runway are below his authorised minimum.

Conversely, a combination of sub-standard lighting and low visibility conditions is likely to result in the pilot being unable to observe the high intensity lights before the decision height is reached. This will result in the aircraft overshooting the runway, and possibly being diverted to an alternative airfield.

High Intensity Runway Lighting is designed to provide the pilot with visual aids under low visibility conditions, although in practice its quality seems to be judged by its performance as a location beacon at times of good visibility, which needs only a unique pattern of light to be visible from a large distance.

However the former implies a consistently high light output and beam orientation from each unit, since a) any abort decision will be made on information from a very limited number of lamps, since as few as five lamps (some of which are likely to be obscured by the nose of the aircraft) will be visible under the worst conditions; b) various decision heights will occur at different points in the approach to the runway; c) the calculation of RVR assumes specified lamp performance; and d) guidance for landing rollout or take-off is required throughout the length of the runway.

As airlines endeavour to improve the quality of their services they are investing in the instrumentation required to maintain schedules at low RVRs.

This trend to an increased number of low visibility movements has resulted in the need for higher uniformity in the performance of high intensity lighting rather than less.

The performance of the airfield lighting installation is measured against the following criteria: 1. Beam Intensity Beam intensity is defined by three factors: a) average intensity over the specified beam area; b) ratio of maximum/average intensity within the beam; and c) ratio of minimum/average intensity within the beam.

2. Beam Spread Beams are defined as ellipses (with the exception of the taxiway centre line) with extremities of the ellipse specified as horizontal and vertical angles.

3. Beam Orientation Beam orientation is defined by the vertical and horizontal positions of the centre of the ellipse (elevation and azimuth/toe-in respectively).

Additionally since airfield lighting systems also include lamps of specified colour, it is desirable to check that the colour of each lamp is maintained at a desired colour value and that the colour sequence is correct.

Whilst it is common practice to check that a lamp when manufactured meets the criteria (1) and (2) by testing under factory conditions, and that the criteria (3) is complied with during installation, considerable difficulty is encountered when checking that the criteria are maintained during use. In particular, the following difficulties may be encountered; 1. the tungsten filament of a lamp may move during use; 2. the alignment of a lamp may be upset by a particularly heavy landing; 3. the lenses of a lamp may be partly obscured with rubber, oil or other detritus; 4. the power supply to a group of lamps may become faulty, and supply power at reduced output.

The conventional way of checking lamps in operation is to place a device, comprising a number of sensors for measuring illuminants, at a known distance from the lamp. With a large number of sensors (say 68) placed on a defined grid located at a specified distance from the light source it is possible to measure the beam at one degree intervals both horizontally and vertically, thereby covering the specified beam area.

Such a method is very time consuming. Additionally it is in general desirable to carry out such testing at night, to eliminate variable daytime background illumination.

The result is that airfield lamps are not checked as frequently as may be desired, and/or involve a checking procedure which is unduly expensive.

According to this invention there is provided a method of measuring the output of a lamp which produces a beam of light, involving the use of a sensor, and measuring the response of the sensor at successive distances longitudinally of the beam.

Preferably, said method involves the use of an array of sensors, said array being moved away from the lamp whilst being maintained generally in the beam, whereby the sensors will respond to progressively inner regions of the beam.

In this manner by compensating the response of the sensors for the change in distance from and the angular position to the lamp, an array comprising a relatively small number of sensors may be utilised to measure the output of the lamp over a majority of the cross-sectional area.

Thus where the beam is generally of elliptical cross-section, preferably the array of sensors comprises a group of sensors (hereinafter being referred to as the first group) arranged in a similar ellipse, or at least part thereof. By sensing the output of the first group of sensors when the array is relatively close to the lamp, and where the outline or footprint of the beam (or part thereof) generally coincides with the outline of the first group, the output of the lamp may be measured over an outer region of the elliptical cross-section thereof.

By movement of the array away from the beam but maintaining the array generally at right angles to a vertical plane containing the vertical axis of the ellipse, progressively inner regions of the elliptical cross section of the beam will fall upon said first group.

However whilst said first group of sensors will respond to successive inner regions of the beam, it will not respond to the centre of the beam, and thus the array of sensors preferably comprises at least one additional sensor located generally centrally of the first group.

Thus a measuring device comprising such an array may be tracked over the lamp with the beam in line with the vertical axis of the beams ellipse, and a measurement of the output of the sensors taken at a specific (e.g. 5 metre) distance from the lamp, at which the footprint of the beam coincides generally with the first group of sensors. Further measurements may be taken at successive 10cm intervals, at each time the output of the sensors being compensated for the further distance from the lamp by the inverse square ratio so that, for a beam of uniform lux density over its cross-section, identical readings will be obtained.

In this manner by continuing the measurements over a distance of about 3 metres (e.g. up to 8 metres from the lamp) the output of substantially the whole of the cross-section of the beam may be taken.

It has been found that this method of measurement may be carried out a relatively high speed, such as 30 to 50 kph, greatly reducing the time taken to check the quality of the linear array of lamps, e.g. bounding a runway, or an airfield taxiway road.

Under the normal output conditions of a lamp operating at a desired output, the effect on the array of sensors of an adjacent lamp will be minimal, and may be ignored. Preferably however, because the characteristics of the previous lamp are known, its effect on the array of sensors is compensated for.

By averaging the outputs of all of the readings taken, an average output may be obtained, in determination as to whether the criteria a), b) and c) are met.

Similarly the array of sensors may comprise one or more colour responsive sensor, in order to provide one or more of the following: a) a correction factor (eye response) if broad band sensors are used; b) confirmation of the correct colour sequence of the lamps; c) determination of the type of fault.

Preferably said array of sensors comprises a further group of sensors in a generally horizontal line, preferably at a lower region of the array. In this manner by detecting a continued imbalance of sensed readings between a subgroup of said further group on one side of the vertical axis and the other subgroup on the other side of the vertical axis, assuming that the measuring device is maintained in alignment with a desired vertical axis orientation (i.e. straight) then a displacement of skew of the lamp from the desired orientation may be determined.

Preferably the array comprises a group of sensors in line vertically of said array, said vertical group if desired including sensors of another group, e.g.

the first group, the central sensor, or the further group. In this manner misalignment of the beam from a desired horizontal inclination may be detected.

Preferably the measurement obtained from the vertical group is compensated for known variations in the runway from the horizontal. Thus, if the runway is known to incline at 1.5 degrees in the direction of movement of the measuring device, the array of sensors will also be inclined at 1.5 degrees from the vertical, and the variation of response seen by the vertical group of sensors may be compensated for, ensuring that the recorded measurements indicate misalignment of the beam from a desired horizontal alignment.

According to this invention there is also provided a mechanism for measuring the output of a lamp, said mechanism comprising: a) at least one sensor; b) means for moving the sensor longitudinally of the beam; c) means for measuring the response of the sensor at successive distances longitudinally of the beam to produce output signals; and d) means for producing a modified output signal from the output signal, compensating for the different distances at which the response is measured.

A specific example of the execution of the invention will now be given, with reference to the accompanying drawings.

FIGURE 1 illustrates a vehicle V carrying an array of sensors of a measuring device M, the array being at a position P2 in relation to a lamp located at P1. The array of sensors is generally shown in Figure 2, and position P2 the footprint of the beam B, generally shown in dotted lines in Figure 2, coincides approximately with the outline of an upper group of sensors, provided by the sensors 1, 2, 3, 4, 5, 6, 7, 8 and 9.

As the vehicle is moved towards position P3, the sensors 1 to 9 will respond to progressively inner regions of the beam B, and further output measurements are taken at positions P3, P4, P5 and P6 etc..

A second group of sensors, consisting of the sensors 10, 11 and 12, are arranged in a generally horizontal line, and these sensors will respond to a generally constant, lower portion of the beam as the vehicle is tracked through successive positions. This second group of sensors may be utilised to provide position information, both in relation to the longitudinal position in relation to the lamp, and any lateral offset from the desired vertical plane.

The distance through which measurements are taken will be determined by the elliptical cross-section of the beam, together with the density of sensors of the measuring device, but the sensors as shown in Figure 2 are arranged in an array having a major horizontal axis of approximately 800mm and a minor vertical axis of approximately 600mm, measurements being taken every 10mm between a distance of 5mm from point P1 and 8 metres from P1. The output of all of the sensors, together with a colour sensor 13 will under these circumstances provide output readings covering approximately the whole of the cross-section of the beam.

In this manner the average, maximum and minimum output values may be obtained, and beam orientation and other performance criteria calculated.

If desired, additional sensors may be located at positions X, Y and Z (Figure 2).

Alternatively measurements may be averaged over a short time (say 10 milliseconds) and sampled continually from one lamp to the next.

The use of individual samples in the calculation of the beam characteristics is determined by the longitudinal and lateral offset from the lamp as determined by the second group of sensors, together with preferably a distance transducer.

Thus, the second group of sensors may be utilised in determining the distance from the lamp, said second set determining when the lamp is passed over, and the lateral offset at this position. Thus, a sensor on a tachograph (or similar device) may provide an output from which the distance from the lamp is continuously monitored.

In Figure 3 ellipse X indicates the situation when the output from the beam is correctly aligned longitudinally of the runway, ellipse Y showing an offset to one side, ellipse Z showing an offset to the other side. Thus, a continuously higher reading obtained from sensors 6, 7, 8 and 9, compared with the output readings of the sensors 1, 2, 3 and 4, will indicate an offset to one side, whilst the opposite will indicate an offset to the other side.

The second group of sensors, comprising sensors 10, 11, and 12, which are retained in the bottom of the beam throughout their tracking movement, may be used to calculate the offset of the beam from the vertical centre line. Thus if desired the outputs of the sensors may be compensated for this offset, to provide an output close to that which is actually provided by the lamp, ignoring the offset.

In this manner, the output values will not be seen as being unduly low, and the error of the beam may be noted as simply being one of offset, allowing the orientation of the beam to be corrected, without the need for changing the bulb of the lamp.

Similarly as illustrated in Figure 4, ellipse A shows the situation with a correct alignment of the beam to the horizontal, ellipse B shows the situation when the beam is offset upwardly, and ellipse C showing an offset downwardly.

For an upward offset, some sensor readings will initially be higher than expected, but will fall off more rapidly.

Sensor 3 is a colour responsive sensor, and produces an output signal from which the desired colour information may be determined.

In a typical tracking situation, in which the measuring device is tracked over a number of lamps A to Z at approximately 30 metres separation, the following results were obtained: Course: RUNWAY CENTRE LINE (from 09) Distance Status Colour Avg Offset Max Min Azim Elev Cumulative 7.4m X 0.20 20% 209 -0.16 302 136 -60 48 0 37.4m OK Red 4% 818 -0.08 1090 537 -31 58 1 67.6m X Red 13% 219 -0.11 298 143 -53 47 1 97.9m X 0.19 14% 218 -0.10 293 95 -28 62 2 127.9m OK Red 5% 615 -0.10 777 427 -23 53 3 157.7m OK 0.19 5% 888 -0.06 1363 90 -14 29 3 188.0m OK Red 7% 665 -0.04 1032 447 2 48 4 218.2m X 0.20 16% 221 -0.08 306 124 -33 42 5 248.2m OK Red 4% 465 -0.11 833 99 -37 82 5 278.3m X Red 24% 109 -0.07 179 45 -27 30 6 309.7m X 0.69 7% 610 -0.06 909 265 -26 35 7 338.5m X 0.20 13% 256 -0::07 504 75 -26 2 7 368.7m X White 3% 1805 -0.10 2308 1290 -41 46 8 398.8m OK Red 5% 965 -0.04 1223 802 -5 53 9 429.6m OK White 8% 4218 0.07 7290 750 44 36 9 458.9m OK Red 13% 533 -0.02 800 138 -11 33 10 489.0m OK White 5% 6333 -0.01 8283 1847 -1 41 11 519.lm OK Red 11% 794 0.00 991 559 15 55 11 549.2m OK White 7% 4411 0 03 7668 762 36 16 12 579.3m ? Red 13% 411 0.08 769 129 49 20 13 610.0m OK White 2% 5292 0.05 7864 1980 24 40 13 639.5m OK Red 11% 472 -0.05 809 131 -33 22 14 668.4m ? White 11% 2488 -0.01 8199 463 -7 -58 15 699.7m OK Red 10% 915 -0.01 1456 171 -9 24 15 728.7m OK White 4% 2967 0.00 3801 1923 -11 52 16 759.8m OK Red 13% 584 -0.03 1015 74 -22 1 17 790.8m OK White 7% 4516 -0.15 6767 1675 -62 54 17 820.lm OK White 6% 4754 -0.06 6287 3056 -14 52 18 851.4m OK White 4% 5308 -0.08 8935 471 -20 15 19 880.2m X White 8% 857 -0.04 3412 274 4 2 19 910.3m OR White 7% 4726 -0.06 7778 524 -33 31 20 940.lm OK White 5% 4088 -0.03 7363 736 -18 7 21 970.5m OK White 9% 6427 -0.04 9159 626 -13 31 21 1000.6m OK White 5% 3819 -0.03 5122 2227 1 43 22 1030.6m X White 5% 1119 -0.02 2212 326 27 34 23 1060.7m OK White 4% 5088 -0.05 7347 956 -18 27 23 1090.8m X White 7% 1531 -0.12 3801 456 -57 -7 24 1120.9m ? White 5% 2431 -0.13 4276 448 -28 14 25 1151.0m X White 6% 1465 -0.09 2175 540 -17 49 25 1181.2m OK White 9% 3065 -0.11 6562 544 -51 -7 26 1211.lm OK White 8% 2839 -0.03 7055 384 21 -13 27 1241.4m OK White 3% 3474 -0.07 5563 1057 -46 45 27 1271.2m OK White 9% 4796 0.04 7857 1133 28 40 28 From the table, the following abnormalities are apparent: 7.4 metres This lamp fails because the output is low and the orientation (azimuth) is too large.

67.6 metres This lamp fails because the output is too low.

97.9 metres This lamp fails because the output is too low.

218 metres This lamp fails because the output is too low.

278.3 metres This lamp fails because the colour value is wrong.

309.7 metres The colour value of this lamp suggests white, but the output is too low for a white light.

338.5 metres This lamp fails because the output is too low.

668.4 metres This lamp is queried, because the ratio of max/average is too high, and minimum/average is too low. The elevation value suggests that the beam is pointing too high.

1120.9 metres This lamp is queried. Probably the minimum is too low because the lamp is dirty. When cleaned, the minimum value would increase, increasing the average, taking the maximum/average and minimum/average values to acceptable conditions.

It will be appreciated that in the use of this invention, each sensor collects data as it moves through the ellipse, and therefore can reduce the number of sensors required, or, where the same number of sensors is maintained, increase the number of points over which the beam is measured.

The sensors do not have to be positioned on a specific grid, and thus a single array may be used on different lamp types with different beam densities.

The calculation of intensity is based on the square of the distance from the centre, i.e. candela = lux/distance squared. Thus as the sensor moves away from the light source the effect of any error in locating the position of the light source becomes significantly less. It should be noted that although the impact of ambience light becomes more important as the sensors move away from the light, the present invention allows this to be taken into account.

By the location of two or more additional sensors mounted close together which measure energy at different spectrums it is possible to a) determine the correct colour of the light sequence; b) determine the correct operating characteristics of the light source; c) determine the type of fault.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims (13)

1. A method of measuring the output of a lamp which produces a beam of light, involving the use of a sensor, and measuring the response of the sensor at successive distances longitudinally of the beam.

2. A method according to Claim 1 involving the use of an array of sensors, said array being moved away from the lamp whilst being maintained generally in the beam.

3. A method according to one of Claims 1 and 2 for the measurement of a beam of generally elliptical cross section, involving the use of a group of sensors arranged in a similar ellipse, or at least part thereof.

4. A method according to Claim 3 wherein during movement of the arrav away from the beam, the array is maintained generally at right angles to a vertical plane containing the vertical axis of the ellipse.

5. A method according to one of Claims 3 and 4 involving the use of at least one additional sensor located generally centrally of the first group.

6. A method according to any one of the preceding claims involving the use of a measuring device comprising an array of sensors which may be tracked over the lamp with the beam in line with the vertical axis of the beam's ellipse involving the taking of a measurement of the output of the sensors at a specific distance from the lamp, and taking further measurements at successive intervals.

7. A method according to Claim 6 wherein the mechanism comprises one or more colour responsive sensors.

8. A method according to any one of the preceding claims involving the use of a group of sensors in a generally horizontal line.

9. A method according to any one of the preceding claims involving the use of a group of sensors in a line generally vertically of the array.

10. A mechanism for measuring the output of a lamp which produces a beam, said mechanism comprising: a) at least one sensor; b) means for moving the sensor longitudinally of the beam; c) means for measuring the response of the sensor at successive distances longitudinally of the beam to produce output signals; and d) means for producing a modified output signal from the output signal compensating for the different distances at which the response if measured.

11. A method of measuring the output of a lamp which produces a beam of light, when carried out substantially as hereinbefore described with reference to the accompanying drawings.

12. A mechanism for measuring the output of a lamp, constructed and arranged substantially as hereinbefore described with reference to the accompanying drawings.

13. Any novel feature or novel combination of features hereinbefore described and/or shown in the accompanying drawings.