Automated lamp monitoring system for comparing light intensities with a preselected valve

Flash tube and lamp monitoring systems. The flash tube intensity monitoring system includes: a human eye spectral response photodiode for producing analog signals, each of which is directly proportional to the intensity of each flash from the flash tube; electronics for converting each of the analog signals to a digital time function proportional to the intensity of the corresponding flash; and electronics, including a microprocessor, for monitoring each of the digital time functions, for flagging those time functions which are below a preselected minimum, and for sending a fault signal when a preselected number of consecutive time functions are below the pre-selected minimum. The monitoring system and flash tube are, preferably, incorporated into single unit for easy installation in the fuselage of an aircraft. The lamp monitoring system includes: a light pickup; a photodiode for producing an analog signal which is directly proportional to the intensity of the lamp being monitored; a line transceiver; an A/D converter; and a microcontroller. The microcontroller, which has a unique identification code, sends a command to the A/D converter only upon receipt of the matching poll command.

FIELD OF THE INVENTION 
This invention relates to systems for the automatic self monitoring of the 
intensity of illumination sources, such as aircraft anti-collision flash 
tubes and incandescent lamps used in airport approach lighting systems, 
and the sending of a fault signal to a monitoring system when the 
illumination falls below a predetermined level. 
BACKGROUND OF THE INVENTION 
Xenon flash tubes are mandated for use as anti-collision lights on 
aircraft. These tubes produce sudden, brilliant flashes of light that are 
much more conspicuous than other light sources. Current FAA (i.e., Federal 
Aviation Administration) mandated airworthiness standards require that 
such flash tubes have an effective intensity of 400 candela when viewed 
within 5 degrees of horizontal for aircraft certified after 1977. For 
aircraft certified before 1977 the requirement is 100 candela. 
In a new strobe unit, the intensity of the xenon flash tube will meet or 
exceed FAA brightness standards. However, the intensity significantly 
degrades with use, long prior to actual tube failure. See: B. W. 
Henderson, "FAA: Aircraft Strobe Lights May Fall Short of Standards" 
Aviation Week & Space Technology, pp 42-43, Sep. 14, 1992; and V. M. 
Gardov, et al., "Theory of Powerful Nonsteady Xenon Discharge Taking 
Vaporization of Its Stabilizing Walls Into Account" translated from 
Teplofizika Vysokikh Temperatur, Vol. 19, No. 1., pp. 28-35, 
January-February, 1981. The result is that most flash tubes continue to 
work long after they have degraded below FAA minimum brightness 
requirements. An FAA survey showed that airlines generally rely on the 
technical manuals from the strobe light suppliers, which do not recommend 
checking brightness or regularly replacing xenon flash tubes. See 
Henderson, supra. 
Strotek (Carson City, Nev.) claims to have developed a portable optical 
measuring system which can check flash tube intensity from outside the 
aircraft while they are on the ground. However, such a system is not an 
automatic self monitoring system, as disclosed and claimed herein. 
U.S. Pat. No. 3,366,835 to H. L. Morris discloses a circuit for indicating 
a flash tube failure when the monitored tube is located where it is not 
readily visible to the operator. The failure indicator includes a light 
conducting plastic rod 48 which extends from the vicinity of the flash 
tube 14 to a photocell 49. Photocell 49 is part of a circuit including 
relay 53, capacitor 54, contacts 55 and warning light 56. If the flash 
tube fails to light for a predetermined period, capacitor 54 does not 
recharge and relay 53 is de-energized. Contact 55 then closes and the 
indicator light 56 comes on. 
A similar problem is encountered with airport runway approach lighting 
systems. -38 and -56 tungsten-halogen incandescent lamps are 
currently used. The FAA requires that all lamps in a given system be of 
even brightness. However, the lamps age with use, with the 
unacceptable result that some lamps appear dimmer than others. 
A common solution to the foregoing problem with approach lighting systems 
is, per FAA regulations, to replace all the lamps in the system on a 
periodic basis (e.g., every 400 hours at major airports) even though many 
of the lamps still meet illumination requirements. Alternately, indirect 
monitoring systems are used which are subject to false indications caused 
by variances in loop current and lamp impedance, aging effects and by 
shorting devices intended to protect the system when a lamp fails. U.S. 
Pat. No. 5,105,124 to K. Futsuhara, et al., discloses a system in which a 
feedback signal consisting of a unique frequency for each lamp flows 
through the lamp circuit. Thus, any failed lamp can be detected by 
checking this feedback signal. Unfortunately, this system does not detect 
lamps which have not failed, but are below FAA brightness requirements. 
Numerous other lamp failure indicators are disclosed in the prior art. See, 
for instance: U.S. Pat. No. 3,541,504 to R. H. Bush, which is described as 
a vehicle burn-out indicator; U.S. Pat. No. 3,588,816 to R. H. Himes; U.S. 
Pat. No. 3,624,629 to C. A. Donaldson; U.S. Pat. No. 4,572,987 to D. M. 
Embrey, et al.; and U.S. Pat. No. 4,376,910 to J.P. Pieslier. 
In view of the foregoing, it is an object of the present invention to 
provide systems for the continuous monitoring of flash tubes and 
continuous illumination sources, which systems provide a fault signal or 
other indication when the intensity of the source being monitored falls 
below a predetermined (sometimes mandated) value (e.g., a minimum set by a 
regulatory agency such as the FAA). 
It is also an objection of the invention to improve airport runway approach 
lighting by providing a system capable of monitoring, either continuously 
or on command, each of the lamps used therein and providing a fault signal 
or other indication when the intensity falls below the required minimum 
(even though the lamp has not failed). 
It is a further object of the invention to use the existing runway approach 
lamp power grid to avoid the requirement for any additional wiring. 
It is another object of the invention to provide a system which can be used 
to monitor both high intensity constant current and medium intensity 
constant voltage runway approach lighting systems. 
The foregoing improves both aircraft and runway safety and, at least in the 
case of runway approach lights, reduces the unnecessary replacement of 
lights in those systems where, for lack of applicant's monitoring system, 
all lamps are replaced on a periodic basis regardless of their individual 
intensities. In addition, the monitoring capability can statistically 
record average bulb lifetimes, thus allowing an accurate forecasting of 
bulb purchases. 
SUMMARY OF THE INVENTION 
A flash tube intensity monitoring system including: a human eye spectral 
response photodiode for producing analog signals, each of which is 
directly proportional to the intensity of each flash from the flash tube; 
electronics for converting each of the analog signals to a digital time 
function proportional to the intensity of the corresponding flash; and 
electronics, including a microprocessor, for monitoring each of the 
digital time functions, for flagging those time functions which are below 
a preselected minimum, and for sending a fault signal when a preselected 
number of consecutive time functions are below the pre-selected minimum. 
The monitoring system and flash tube are, preferably, incorporated into 
single unit for easy installation in the fuselage of an aircraft. The unit 
includes structure, interposed between the flash tube and the photodiode 
for at least partially blocking heat from the flash tube from reaching the 
photodiode. The unit also includes a light pipe which samples the light 
from the flash tube and transmits this sampled light to the photodiode. 
The electronics for converting the analog signals includes an analog 
integration circuit and a calibration circuit. The microprocessor looks 
for variations in flash intensity as seen by the photodiode. 
The lamp monitoring system, for incandescent or other continuous light 
sources, includes a light pickup, a photodiode for producing an analog 
signal which is directly proportional to the intensity of the lamp being 
monitored, a line transceiver for sending and receiving digital data and 
instructions over the lamp's power line, means for converting the analog 
signals to a digital function proportional to the intensity of the lamp, 
and a microcontroller connected to the line transceiver and the converting 
means. The converting means is connected to the photodiode and the line 
transceiver. The microcontroller includes a unique identification code and 
is adapted to receive a poll command over the power line, whereby when the 
microcontroller receives the poll command which matches the unique 
identification code it sends a command to the converting means and the 
converting means converts the analog signals to said digital function. The 
monitoring system also includes apparatus for amplifying and conditioning 
the analog signals from the photodiode so as to fit the input range of the 
converting means (preferably an A/D chip). The monitoring system further 
includes an optical pickup bezel for collecting visible light from the 
lamp, which bezel contacts at least a portion of the perimeter of the lamp 
without degrading or interfering with the lamp's projected beam path. The 
monitoring system also further includes an optical coupling which 
separates the photodiode, the line transceiver, A/D chip, and 
microcontroller from the intense heat generated by the lamp.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With referenced to FIG. 1, flash intensity self monitoring system 11 
includes an anti-collision light flash tube 13 (such as a made by Grimes, 
Hella and Flight Components), a light pipe 15, a photodiode 17, an optic 
board 19 (for the integration and conversion of analog electric signals to 
a digital time function), and a microcontroller 21. Light pipe 15 is, 
preferably, made of pyrex or other suitable light transmitting material. 
For the reasons set forth below, each end of light pipe 15 is hemispheric. 
For aircraft anti-collision flash tubes, the photodiode 17 is a human eye 
spectral response photodiode. 
The above-identified components are housed in anti-collision light unit 25, 
as illustrated in FIGS. 2 and 3. Unit 25 includes an external housing 27, 
an internal housing 29, a fuselage mounting plate 31, and a glass flash 
tube cover 33. External housing 27 includes a flash tube unit mounting 
plate 35, and a gasket 37. The flash tube unit includes a mounting plate 
39, a shield 41, conventional mechanical apparatus (not shown) for 
attaching cover 33 and conventional flash tube electrical connectors (also 
not shown). Flash tube mounting plate 35 includes an opening 43 (see FIG. 
3) for supporting light pipe adaptor 45. Plate 31 includes a plurality of 
mounting holes, such as illustrated at 47, to secure unit 25 to the 
fuselage of an aircraft, and an opening (not shown) for supporting the 
sensor portion of photodiode 17 within housing 27 and beneath light pipe 
15. Diode 17 does not have to be aligned with light pipe 15. Housing 29 
supports optic board 19 and MPU board 51 (which includes microcontroller 
21), circuit board 53 (of conventional design, for energizing flash tube 
13), and conventional electric connector 55. 
Electrical wiring (partially shown) interconnects the various boards and 
electrical components. Light pipe 15 is positioned laterally from flash 
tube 13 and photodiode 17 is positioned below plate 35 a distance 
sufficient to prevent photodiode 17 from being adversely affected by the 
intense heat generated by flash tube 13. The end of light pipe 15 exposed 
to flash tube 13 is rounded so that there is no alignment requirement when 
it is screwed into place. The opposite end is also rounded to provide 
diffused light. The use of such diffused light attenuates the intensity of 
the light from flash tube 13 on photodiode 17, to a level below that which 
would overdrive or saturate photodiode 17. 
The design of optic board 19 and MPU board 51 could, as those skilled in 
the art will appreciate, take a number of forms. As illustrated 
schematically in FIG. 4, optic board 19 is powered from the regulated +15 
volts coming in through pin 1 of J301. Resistors R306, R307 and R308 are 
used to create a reference voltage of 5 volts and a bias voltage of 3 
volts. The 3 volt bias voltage is applied across photodiode 17 by op amp B 
of U301. This bias voltage is necessary to speed up the response time of 
photodiode 17. Potentiometer R304 is used to adjust the gain of op amp B 
of U301. Due to normal manufacturing tolerances, there will be variations 
in the optical light path between flash tube 13 and photodiode 17. This 
will cause variations in the light intensity of the strobe flash as seen 
by the photodiode. There will also be slight variations in the 
photodiode's sensitivity. Gain potentiometer R304 is used to calibrate the 
optic board and to correct for any differences in the optical path. 
Resistor R303 and capacitor C301 form the analog integration network. Op 
amp A of U301, wired as an comparator to the 5 volt reference, changes 
this analog signal from C301 to a time function binary signal which is 
output through R305. This signal goes off the board through pin 2 of J301 
and goes directly to microcontroller 21. 
In operation, flash tube 13 is energized via conventional electronics such 
as located on board 53 (not shown). A portion of the light emitted from 
each flash is transmitted, via light pipe 15, to photodiode 17 which, in 
turn, sends an analog signal to optics board 19. The effective intensity 
of a strobe light is defined as an integral of the instantaneous intensity 
taken over the flash duration. With reference to FIGS. 5A and 5B, the 
analog signal from photodiode 17 is integrated and converted into a 
digital time function. Specifically, the analog signal is integrated by 
optic board 19 into a binary function in which the time duration of the 
binary signal represents the effective intensity of the flash. 
Microcontroller 21 samples the binary signal after each flash at a 
predetermined point (as indicated in FIG. 5B). If the flash intensity is 
above the acceptable intensity (e.g., at or above 400 candela), 
microcontroller 21 will see a binary 1. If the flash intensity falls below 
the required minimum, microcontroller 21 will see a binary 0. Repeated 
flashes (e.g. 250; 50 flashes per minute for 5 minutes) at output levels 
below the predetermined minimum will cause microcontroller to send a fault 
signal indicating that flash tube 13 should be replaced. 
With reference to FIG. 6, the major components of an automatic incandescent 
lamp monitoring system 71 for, for instance, airport runway approach 
lighting systems, is illustrated. System 71 includes a plurality of 
approach lamps 73 (typically -56 or -38 lamps), each of which 
includes an optical pickup bezel 75, fiber optic line 77, and monitor 
module 79. Bezel 75 is made of pyrex or other similar material to pick up 
light from around the entire perimeter of lamp 73, without degrading or 
interfering with the lamp's projected beam path. By internal reflection a 
portion of the light picked up is directed to pick up point 80. Line 77 
includes standard couplers 81, 83 and exposed fiber ends 85, 87. Coupler 
81 mates with threaded adaptor 89 to position end 85 within bezel 75 at 
pick-up point 80. Coupler 83 mates with threaded adaptor 91 to position 
tip 87 within the housing of monitor module 79. 
The basic internal components of module 79, which are illustrated in FIG. 
7, include a photodiode 93, a signal conditioning stage 95, and A/D 
converter 97, a power line transceiver 99, and a microcontroller 101. 
Photodiode 93 is a human eye spectral response photodiode. Signal 
conditioning stage 95 amplifies and conditions the analog signal from 
photodiode 93 so that it fits the input range of A/D converter 97. The 
conditioning includes calibration and temperature compensation circuits. 
A/D converter 97 may be a serial output 5.6.sup..mu.s 12-bit A/D converter 
such as the Maxim Max 170. A/D converter 97 only reads the signal from 
conditioning stage 95 in response to a command from microcontroller 101. 
Transreceiver 99 may be a commercial grade FM line transmitter/receiver 
unit, which includes a transformer to electronically couple the components 
of module 79 to the power line (not shown) for lamp 73. This permits the 
lamp monitoring system to send the digital information along the power 
lines which have already been put in place to run the lamps being 
monitored. Finally, MPU 101 is, preferably, a single chip programmable 
microcontroller such as a PIC16C56. 
In operation, each MPU 101 is programmed to respond only to a unique poll 
command. A master computer (not shown) at a remote location monitors all 
lamps in the array by polling each lamp (in sequence or as otherwise 
directed). When MPU 101 receives its unique poll command, via the 
associated lamp's power line, it commands A/D converter 97 to function. In 
response to this command, A/D converter 97 reads the voltage signal from 
conditioner 95, converts this signal to a 12 bit digital word, which is 
then output to transceiver 99. Transceiver 99 then sends the digital 
signal over the power line of lamp 73 to the master computer which 
processes the signal with a lookup table or equivalent to determine if the 
brightness of lamp 73 is within range. 
Whereas the drawings and accompanying description have shown and described 
the preferred embodiment of the present invention, it should be apparent 
to those skilled in the art that various changes may be made in the form 
of the invention without affecting the scope thereof.