CA1325261C - Automatic, real-time fault monitor verifying network in a microwave landing system - Google Patents
Automatic, real-time fault monitor verifying network in a microwave landing systemInfo
- Publication number
- CA1325261C CA1325261C CA000564773A CA564773A CA1325261C CA 1325261 C CA1325261 C CA 1325261C CA 000564773 A CA000564773 A CA 000564773A CA 564773 A CA564773 A CA 564773A CA 1325261 C CA1325261 C CA 1325261C
- Authority
- CA
- Canada
- Prior art keywords
- alarm
- predetermined
- stored
- monitor
- characteristic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S1/00—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
- G01S1/02—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using radio waves
- G01S1/08—Systems for determining direction or position line
- G01S1/44—Rotating or oscillating beam beacons defining directions in the plane of rotation or oscillation
- G01S1/54—Narrow-beam systems producing at a receiver a pulse-type envelope signal of the carrier wave of the beam, the timing of which is dependent upon the angle between the direction of the receiver from the beacon and a reference direction from the beacon; Overlapping broad beam systems defining a narrow zone and producing at a receiver a pulse-type envelope signal of the carrier wave of the beam, the timing of which is dependent upon the angle between the direction of the receiver from the beacon and a reference direction from the beacon
- G01S1/56—Timing the pulse-type envelope signals derived by reception of the beam
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S1/00—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
- G01S1/02—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using radio waves
- G01S1/022—Means for monitoring or calibrating
- G01S1/024—Means for monitoring or calibrating of beacon transmitters
Abstract
ABSTRACT OF THE DISCLOSURE
The fault monitoring function of an executive monitor contained in a microwave landing system is veri-fied by evaluating a history of the parametric informa-tion sampled by an executive monitor and storing in memory the number of out of tolerance parametric signals received from an antenna means over a predetermined time period, replacing the stored number of out-of-tolerance parametric signals with a predetermined number that will be beyond a second predetermined limit if another out-of-tolerance parametric signal is added to said number, adding one such internally generated out-of-tolerance parametric signal to said predetermined number, generat-ing an alarm if said sum is beyond the second predeter-mined limit, and restoring the previously stored number of out-of-tolerance parametric signals received from the antenna means if the alarm was generated, and shutting the system down if an alarm was not generated.
The fault monitoring function of an executive monitor contained in a microwave landing system is veri-fied by evaluating a history of the parametric informa-tion sampled by an executive monitor and storing in memory the number of out of tolerance parametric signals received from an antenna means over a predetermined time period, replacing the stored number of out-of-tolerance parametric signals with a predetermined number that will be beyond a second predetermined limit if another out-of-tolerance parametric signal is added to said number, adding one such internally generated out-of-tolerance parametric signal to said predetermined number, generat-ing an alarm if said sum is beyond the second predeter-mined limit, and restoring the previously stored number of out-of-tolerance parametric signals received from the antenna means if the alarm was generated, and shutting the system down if an alarm was not generated.
Description
DOCKET R4387.01 1 3 2 5 2 6 1 EA0:kaf 1 AUTOMATIC, REAL-TIME FAULT MONITOR VERIFYING
2 NETWORK IN A MICR0WAVE LANDING SYSTEM
3 BACKGROUND OF THE INVENTION
4 1. Field of the Invention The present field of the invention relates 6 to a process and network in which an executive monitor 7 is connected within a microwave landing system ("MLS") 8 to evaluate whether or not an internally-generated out-9 of-tolerance signal activates an alarm system. If the alarm system is activated, then the proper fault moni-11 toring function of the executive monitor is verified.
12 2. Description of the Prior Art 13 An instrument landing system ("ILS") has 14 served as the prior art approach and landing aid for aircraft for many years. The ILS, however, has a number 16 of basic limitations, such as being site crittcal and 17 expensive to install, being sensitive to extraneous 18 reflections, having a limited number of channels, 19 lacking the flexibilTty required for aircraft operations, and producing erroneous informat7on in rough 21 terrain and mountainous reglons. As a result of these 22 limitations, an MLS has been proposed as a standard ILS
23 replacement for world-wtde implementation since it can 24 reduce or eliminate these basic limitations.
The MLS consists of various antenna stations "' . ' ' ' ' ' ~ ' ~ .: . ' . ' ' . ' - ' ' ' " . ~ . , ',. ' : ' ' . ' 1 adJacent to a runway which transmit wave energy informa-2 tion to approaching aircraft enabling said atrcraft to 3 calculate the following data to safely land on an air-4 port runway: azimuth from an AZ station, elevation from an EL station, range from a precision distance measuring 6 equipment (DME/P) station, and back azimuth from a BAZ
7 station. The AZ station provides an aircraft with head-8 ing or approach guidance to runways or helo pads at an 9 airport. The EL station provides for a wide selection of glide slope angles needed by a pilot to land his 11 plane safely on a runway. The DME/P station provides 12 for continuous range information needed by a pilot to 13 ascertain the distance between his aircraft and the 14 airport runway on which he is landing. The BAZ station is similar to the AZ station and is intended to supply 16 guidance to a pilot for missed approaches to and depar-17 tures from an airport.
18 More specifically, the AZ station includes an 19 antenna wh7ch generates a narrow, vertical, fan-shaped beam which sweeps to and fro across the area to be 21 covered by the AZ station. Before the start of a scan a 22 test pulse is transmitted, then the "to" scan starts.
23 At the end of the scan, there Is a pause before the 24 "fro" scan starts. A second test pulse marks the end of 25 the scanning cycle. The atrcraft receives a "to" pulse 26 and a "fro" pulse. The time difference between pulses 27 is then measured by the aircraft and gives the angular ,.,, , , , ,: : :
, .
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.,. : , ~ . ~ , ~ 32526 1 1 location of the aircraft relative to the AZ station.
2 The EL station also includes an antenna which generates 3 a narrow horizontal fan-shaped beam which sweeps up and 4 down through the area to be covered at the airport. The time difference between receipt of the up and down 6 pulses is used by the aircraft to determine the eleva-7 tion angle of the aircraft relative to the EL station 8 and thus its displacement from the glide path angle 9 selected by the pilot to land his aircraft on a runway.
The elevation scan cycle requires much less time than 11 the azimuth scan cycle. The elevation scan cycle is 12 normally repeated 39 times per second as compared with 13 13 times per second for the azimuth cycle. The BAZ
14 station includes an antenna which generates a narrow, fan-shaped, vertical beam which sweeps to and fro 16 horizontally through the area to be covered at the 17 airport. The same angular measurement principle used 18 for determlning the approach AZ angle Ts used for 19 determining the BAZ angle. The DME/P station includes an antenna which transmits wave energy travelling at a 21 known rate. By calculatlng the tTme the wave energy 22 travels from the antenna to the aircraft and knowtng the 23 rate at which the wave energy travels, the distance or 24 range between alrcraft and the airport station can be calculated. The above information Is calculated by the 26 approaching alrcraft as a dTrect result of the 27 meantngful Information transmitted by the antenna .~
'; ' : ' ~: : ' : - ~ -- ` t :i~' ~ ' 'i 32526 1 l stations included within a given MLS at an airport.
2 The MLS is capable of operating on any one of 200 3 channels in the microwave frequency band. The present 4 microwave frequencies in use are between 5043 and 5090.7 megahertz. The AZ, BAZ and EL stations all transmit on 6 the microwave frequency. The DME/P station transmits a 7 paired frequency in L-Band. The MLS signal format has 8 the potential to transmit signals from the above-9 mentioned various stations in any desired order to approaching aircraft. A preamble or data word is trans-11 mitted by each station to approaching aircraft prior to 12 the main wave energy being transmitted in order to 13 inform the approaching atrcraft of which function (AZ, 14 EL, BAZ, DME/P) will be transmitted next. As soon as the aircraft decodes the message it waits for the wave 16 energy to be received in order to perform the desired 17 calculation. Then, the aircraft awaits the next 18 preamble to ascertain the identity of the next trans-19 mitted function. As can readily been seen, the MLS has numerous advantages over the ILS.
21 All MLS installations transmlt the following 22 basic data to approaching aircraft: facility (landing 23 runway) identlflcation; azimuth threshold distance, 24 coverage and off-set (distance from AZ antenna to fixed spot on center line of runway); beam wTdths (AZ, EL);
26 DME/P dlstance, off-set and channel (distance between : . . . . .
~, .. . . ~ , ~: . . . ~ -.: -,- - :.":;, .. . :: .
:- . : . : . . : - . . , .. .: ,:: :.. , ::, . :. . : :
- ~ :: .: . .~.:.,: : . ::
1 station and runwayj; and elevation height, off-set and 2 distance from threshold. Most of this information is 3 needed by the equipment aboard the approaching aircraft 4 to make the necessary computations for an approach to the airport. Any malfunction in the MLS equipment will 6 cause the approaching aircraft to make faulty calcula-7 tions and rely upon erroneous data. For this reason, it 8 is absolutely essential to continuously maintain the MLS
9 system and to verify that the MLS system stations are transmitting accurate information.
11 The MLS was the first system designed to utilize 12 a maintenance program. The advantages of such a mainte-13 nance program include a reduction in the time spent in 14 travel maintaining the system and a reduction in the maintenance and record-keeping for the system, which in 16 turn allows more effectlve use of a smaller number of 17 maTntenance personnel operating from a smaller number of 18 maintenance bases. Overall, such a maintenance program 19 is economtcal, reliable, and efficient.
Each MLS station is supported by an executTve 21 monitor and a maTntenance field monltor, both of which 22 are tools implementing the maintenance program. The 23 executive monltor samples the information being trans-24 mltted by each antenna station to approaching aircraft.
In other words, the executive monitor evaluates the same 26 7nformation that the antenna is transm7tting to 27 approaching aircraft to ensure that the tnformation
12 2. Description of the Prior Art 13 An instrument landing system ("ILS") has 14 served as the prior art approach and landing aid for aircraft for many years. The ILS, however, has a number 16 of basic limitations, such as being site crittcal and 17 expensive to install, being sensitive to extraneous 18 reflections, having a limited number of channels, 19 lacking the flexibilTty required for aircraft operations, and producing erroneous informat7on in rough 21 terrain and mountainous reglons. As a result of these 22 limitations, an MLS has been proposed as a standard ILS
23 replacement for world-wtde implementation since it can 24 reduce or eliminate these basic limitations.
The MLS consists of various antenna stations "' . ' ' ' ' ' ~ ' ~ .: . ' . ' ' . ' - ' ' ' " . ~ . , ',. ' : ' ' . ' 1 adJacent to a runway which transmit wave energy informa-2 tion to approaching aircraft enabling said atrcraft to 3 calculate the following data to safely land on an air-4 port runway: azimuth from an AZ station, elevation from an EL station, range from a precision distance measuring 6 equipment (DME/P) station, and back azimuth from a BAZ
7 station. The AZ station provides an aircraft with head-8 ing or approach guidance to runways or helo pads at an 9 airport. The EL station provides for a wide selection of glide slope angles needed by a pilot to land his 11 plane safely on a runway. The DME/P station provides 12 for continuous range information needed by a pilot to 13 ascertain the distance between his aircraft and the 14 airport runway on which he is landing. The BAZ station is similar to the AZ station and is intended to supply 16 guidance to a pilot for missed approaches to and depar-17 tures from an airport.
18 More specifically, the AZ station includes an 19 antenna wh7ch generates a narrow, vertical, fan-shaped beam which sweeps to and fro across the area to be 21 covered by the AZ station. Before the start of a scan a 22 test pulse is transmitted, then the "to" scan starts.
23 At the end of the scan, there Is a pause before the 24 "fro" scan starts. A second test pulse marks the end of 25 the scanning cycle. The atrcraft receives a "to" pulse 26 and a "fro" pulse. The time difference between pulses 27 is then measured by the aircraft and gives the angular ,.,, , , , ,: : :
, .
: -: :: .
.,. : , ~ . ~ , ~ 32526 1 1 location of the aircraft relative to the AZ station.
2 The EL station also includes an antenna which generates 3 a narrow horizontal fan-shaped beam which sweeps up and 4 down through the area to be covered at the airport. The time difference between receipt of the up and down 6 pulses is used by the aircraft to determine the eleva-7 tion angle of the aircraft relative to the EL station 8 and thus its displacement from the glide path angle 9 selected by the pilot to land his aircraft on a runway.
The elevation scan cycle requires much less time than 11 the azimuth scan cycle. The elevation scan cycle is 12 normally repeated 39 times per second as compared with 13 13 times per second for the azimuth cycle. The BAZ
14 station includes an antenna which generates a narrow, fan-shaped, vertical beam which sweeps to and fro 16 horizontally through the area to be covered at the 17 airport. The same angular measurement principle used 18 for determlning the approach AZ angle Ts used for 19 determining the BAZ angle. The DME/P station includes an antenna which transmits wave energy travelling at a 21 known rate. By calculatlng the tTme the wave energy 22 travels from the antenna to the aircraft and knowtng the 23 rate at which the wave energy travels, the distance or 24 range between alrcraft and the airport station can be calculated. The above information Is calculated by the 26 approaching alrcraft as a dTrect result of the 27 meantngful Information transmitted by the antenna .~
'; ' : ' ~: : ' : - ~ -- ` t :i~' ~ ' 'i 32526 1 l stations included within a given MLS at an airport.
2 The MLS is capable of operating on any one of 200 3 channels in the microwave frequency band. The present 4 microwave frequencies in use are between 5043 and 5090.7 megahertz. The AZ, BAZ and EL stations all transmit on 6 the microwave frequency. The DME/P station transmits a 7 paired frequency in L-Band. The MLS signal format has 8 the potential to transmit signals from the above-9 mentioned various stations in any desired order to approaching aircraft. A preamble or data word is trans-11 mitted by each station to approaching aircraft prior to 12 the main wave energy being transmitted in order to 13 inform the approaching atrcraft of which function (AZ, 14 EL, BAZ, DME/P) will be transmitted next. As soon as the aircraft decodes the message it waits for the wave 16 energy to be received in order to perform the desired 17 calculation. Then, the aircraft awaits the next 18 preamble to ascertain the identity of the next trans-19 mitted function. As can readily been seen, the MLS has numerous advantages over the ILS.
21 All MLS installations transmlt the following 22 basic data to approaching aircraft: facility (landing 23 runway) identlflcation; azimuth threshold distance, 24 coverage and off-set (distance from AZ antenna to fixed spot on center line of runway); beam wTdths (AZ, EL);
26 DME/P dlstance, off-set and channel (distance between : . . . . .
~, .. . . ~ , ~: . . . ~ -.: -,- - :.":;, .. . :: .
:- . : . : . . : - . . , .. .: ,:: :.. , ::, . :. . : :
- ~ :: .: . .~.:.,: : . ::
1 station and runwayj; and elevation height, off-set and 2 distance from threshold. Most of this information is 3 needed by the equipment aboard the approaching aircraft 4 to make the necessary computations for an approach to the airport. Any malfunction in the MLS equipment will 6 cause the approaching aircraft to make faulty calcula-7 tions and rely upon erroneous data. For this reason, it 8 is absolutely essential to continuously maintain the MLS
9 system and to verify that the MLS system stations are transmitting accurate information.
11 The MLS was the first system designed to utilize 12 a maintenance program. The advantages of such a mainte-13 nance program include a reduction in the time spent in 14 travel maintaining the system and a reduction in the maintenance and record-keeping for the system, which in 16 turn allows more effectlve use of a smaller number of 17 maTntenance personnel operating from a smaller number of 18 maintenance bases. Overall, such a maintenance program 19 is economtcal, reliable, and efficient.
Each MLS station is supported by an executTve 21 monitor and a maTntenance field monltor, both of which 22 are tools implementing the maintenance program. The 23 executive monltor samples the information being trans-24 mltted by each antenna station to approaching aircraft.
In other words, the executive monitor evaluates the same 26 7nformation that the antenna is transm7tting to 27 approaching aircraft to ensure that the tnformation
-5-., , ,.. :- : , - .
r .. . . .
:, ,, . :.
;"~
' . ~ ,. . . ..
''' - ~ ' ' 1 32526 t l being sent to the aircraft is reliable. For example, 2 the executive monitor checks the accuracy of the angle 3 code throughout ~he antenna coverage and thus can detect 4 when a given sample of the angle code is beyond a pre-determined limit. Examples of such transmitted param-
r .. . . .
:, ,, . :.
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''' - ~ ' ' 1 32526 t l being sent to the aircraft is reliable. For example, 2 the executive monitor checks the accuracy of the angle 3 code throughout ~he antenna coverage and thus can detect 4 when a given sample of the angle code is beyond a pre-determined limit. Examples of such transmitted param-
6 eters which are checked by the executive monitor to
7 ascertain whether or not they are out-of-tolerance are
8 (a) scanning beam mean angle error, (b) function
9 preamble, (c) effective radiated po~er (whether it be for the function preamble, the EL and BAZ scanning 11 beams, clearance pulses, or an out of coverage 12 indicator), (d) timing error in signal format, (e) 13 synchronization error in time division multiplexing, (f) 14 digital phase shift keying ("DPSK") data transmission, (9) interstation synchronization, (h) array integrity 16 parameters (such as dynamtc sidelodes, channel failures, 17 frequency channels, etc.), and (i) clearance angle. If 18 any of these transmitted parameters a-J are out-of-19 tolerance, then the executive monitor automatically initiates an alarm, the stat10n is shut down, and the 21 approach7ng aircraft does not recelve information from 22 that station. The AZ, EL, BAZ, and DME/P antenna sta-23 tions each contaln an executTve monitor. If the EL or 24 BAZ station is shut down, the other statlons are still operable and transmit information to the approachlng 26 airçraft. If the AZ station is shut down, however, all 27 stations are disabled and do not transm7t tnformation to ,.
;.: ; : .-. .. ...
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.. .. . . ... . . . .
l approaching aircraft. Since the executive monitor 2 initiates an alarm and shuts down a station or the 3 system when an out-of-tolerance parameter Ts detected 4 over a predetermined period of time it is necessary to verify that ~he fault monitoring function of the execu-6 tive monitor is operating properly and will provide such 7 an alarm when such an out-of-tolerance parameter is 8 detected over that predetermined period of time. Other-9 wise an approaching aircraft may be erroneously relying on MLS supPlied information which should have generated 11 an alarm and shut down the station or the MLS without 12 transmitting information to approaching aircraft.
14 An obJect of the invention is automatic real-time verification of the fault monitoring operation of an 16 executive monitor so that an alarm is generated and 17 declared valid when an internally generated out-of-18 tolerance or erroneous signal is detected by the 19 monitor.
A further object of the inventton is to provide 21 for the veriflcation of the fault monitoring operatlon 22 of an executive monitor in which a station control board 23 is connected on line with the executive monitor and 24 provides a signal thereto representative of erroneous or out-of-tolerance data in order to initiate an alarm in 26 the executive monitor. Another obJect of the invention - , . . .
: .: - :. ~ : : ....................................... :
.
~i 32~261 1 is to store the actual data obtained by the executive 2 monitor until proper fault monitoring verification 3 occurs.
4 Another obJect of the invention is to employ a filter counting means to record a history of the out-of-6 tolerance data received by the executive monitor so that 7 the filter counting means can be preconditioned during 8 the verification process to receive one additional out-9 oftolerance sample to thereby generate an alarm within the executive monitor.
11 Another object of the invention is to employ a 12 switch which will permit an internally generated out-of-13 tolerance sample to be analyzed instead of the sampled 14 information generated by the antenna system.
For a better understanding of the present inven-16 tion together with other and further obJects, reference 17 is made to the following description in conjunction with 18 the accompanying drawTngs.
19 BRIEF DESCRli'TlON OF THE DRAWINGS
Figure 1 is a schematic block diagram of a cir-21 cuit for verlfying proper operatTon of the fault moni-22 toring function of the executlve monTtor accordlng to 23 the Inventlon.
24 Flgure 2 is a flow-chart Illustratlng a sequence of operatTons for verifylng proper operatlon of the 26 fault monitorlng functlon of the executive monitor.
. : : .: . - : :
2 Figure l illustrates the EL station 14 components 3 of an MLS system whlch are used to process one of many 4 MLS parameters transmitted to approaching aircraft and to verify the proper functioning of a fault monitor 6 system within the MLS should an out-of-tolerance param-7 eter be detected by the MLS system.
8 Since many parameters are verified in an MLS (see 9 parameters a-J listed above), the one chosen to best illustrate the invention and the one shown in Figure 1 11 is the scanning beam mean angle error parameter.
12 Although the scanning beam mean angle error parameter is 13 illustrated, it is to be understood that any of the 14 other parameters verified by the landing system could have been chosen to illustrate the invention, and in 16 this regard, the invention is not to be limited to the 17 illustrated parameter. The scanning beam mean angle 18 error from an EL sta~ion provides the difference between 19 the actual height of the approaching aircraft in angular degrees and the height the approaching aircraft already 21 calculated. The EL station transmtts scanning beam mean 22 angle error Information to approaching a7rcraft by an 23 array antenna means 1. The antenna means 1 also samples 24 this transmisslon Internally wlthin the MLS system by providing an output of hlgh frequency RF voltage signals 26 to an RF receiver detector means 2. The detector means .: . , - ' . : :
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:. . :
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~ 325261 l 2 in conventional fashion converts the voltage 5 i gnals 2 into a series of D-C video pulses and outputs them to an 3 executive monitor means 3 over a manifold video llne.
4 The executive monitor means 3 contains a local CPU 4, local memory means 5, and a memory means 6 shared with a 6 control means 9, called a station control board.
7 The shared memory means 6 contains two filter 8 counters 7. Like the executive monitor means 3, the 9 control means 9 also contains a local CPU 11 and memory means 10. CPUs 4 and 11 are thus able to read from or 11 write into the shared memory means 6. CPUs 4 and 11 12 perform comparisons and calculations. The two filter 13 counters 7 are used in the executive monitor means 3 14 (together wlth an angle decoder not shown) to detect the time of occurrence of the rising and falling edges of 16 the video pulses and thus an out-of-tolerance scanning 17 beam angle. If a small scanning beam angle error is 18 detected, one of the two filter counters 7 lncrements.
19 If a large scanning beam angle error is detected the other filter counter 7 increments. If the calculated 21 scanning beam angle is withln a first predetermlned 22 limit, then the filter counters 7 decrement, but never 23 below a value of zero. The approachlng aircraft detects 24 the same timing tnformatlon as the executlve monltor means 3. The pulse edges are defined as the 3dB points 26 of each pulse and are detected when the video pulse 27 amplitude equals a first reference voltage corresponding 1 to 0.707 times a second reference voltage which is 2 stored in the executive monitor s local memory means 5 3 in digital form. The comparison of the video pulses 4 with said second reference voltage eliminates the counting of spurious false alarm signals and thus the erroneous calculation of guidance information.
7 As another safeguard at least two rising and two 8 falling edges (two pulses) are analyzed in real-time by 9 the CPU 4 in the executive monitor to determine the scanning beam angle error. Thirty-one samples of these 11 paired video pulses must be fed to the two filter 12 counters over a 0.8 second time period in order for the 13 executive monitor to accurately and reliably determine 14 if an out of tolerance scanning beam mean angle error exists. Such determination is made by comparing the 16 number of incremented counts in each filter counter with 17 a second predetermined limit for each stored in 18 memory. If the number of incremented counts exceeds the 19 second predetermined limit for either filter counter then the filter counter output indicates that mean 21 erroneous guidance - the scanning beam mean angle error 22 is beyond acceptable limits`- exists for the prescribed 23 0.8 second time period; an alarm 8 is therefore 24 generated in the executive monitor and noted in the memory means 6 shared by the monitor means 3 and the 26 control means (station control board) 9 when such 27 erroneous guidance is detected. Under these conditions ~1 .. , - 1 1 -~:, ~ ,, :;." ' '. ' ' ~ ' ' ' ' :', ' ' . ' ~ :, '' ':'';' ' ' '' 1 3~52~
1 an alarm signal is then fed by the station control board 2 9, to the transmitter of the array antenna means 1 3 shutting the system down. Of course, if erroneous 4 guidance is not indicated by eTther filter counter, then the alarm system will not be activated and the system 6 will not be shut down. The approaching aircraft 7 realizes that a fault condition has been detected in a 8 particular station when it does not receive any 9 information from that station.
The real-time, automatic operation of the present 11 fault monitoring verificatton scheme will now be 12 explained with reference to Figure 2. Figure 2 shows 13 through logic the manner in which the proper operation 14 of the fault monitoring function performed by the executive monitor is verified. Using the scanning beam 16 mean angle error parameter by way of example only, 17 verification is accomplished by having the contents of 18 the two filter counters 7 saved in the shared memory 19 means 6 in a location separate and apart from the filter counters 7. Between antenna scans the two filter 21 counters 7 are then provided with a predetermined count 22 that will cause the generation of a real-time, automatic 23 alarm If one more sample outsTde scanning beam mean 24 angle error limits is recelved. Thls precondltioning of the two fllter counters is accomplished in the memory 26 means 6 shared by the control means (station control 27 board) 9 and executive monitor means 3 shown in ~.
' , , :, , '':
. . . ' ' ." ' ' ' 'i 325261 1 Figure l. During the next antenna scan, the control 2 means CPU ll sends a signal over the MV SEL-Gl and G2 3 line activating switch 12 which replaces the parametric 4 video output received by the executive monitor means 3 with one out-of-tolerance pulse pair sample generated 6 internally. The internally genera~ed out-of-tolerance 7 pulse pair sample is sent by CPU 11 over the MV pulse 8 generator line to the executive monitor which then 9 increments the filter counters 7. The internally generated pulse pair represents a sample outside filter 11 counter limits and when summed with the predetermined 12 count in filter counters 7 should activate alarm 8.
13 If an alarm is generated as a result of the 14 introduction of the internally-generated out-of-tolerance pulse pair to the filter counters 7, then the 16 test is determined to be valid, i.e. the fault monitor-17 ing function of the executive monitor is working 18 properly. Under these conditions, the previously saved 19 contents of both filter counters are restored in order for normal operation of the system to be resumed on the 21 next antenna scan. If elther filter counter does not 22 generate an alarm, then an executive monitor failure Is 23 declared in the statlon control board 9, and the actual, 24 real-time alarm ts activated. Under these circumstances the station or system is automatically shut down by the 26 station control board 9 and In need of repaTr. This 27 7nforms maintenance personnel that the system is not ,: : , ' ' ': , '':
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l properly monitoring fault conditions when scanning beam 2 mean angle errors Tn excess of a second predetermined 3 limit are detected. The above real-time verification 4 process is automatic software controlled and conducted every 15 minutes in an MLS. The MLS system also can 6 request the performance of a verification test from 7 human sources~
8 Specific structural details for the shared memory 9 means 6 and local memories 5 and 10 would be apparent to one skilled in the art. Although the alarm 8 and 11 filter counters 7 are shown in Figure 1 to be contained 12 in the shared memory means 6 those functions could 13 be performed by separate hardware or in local memories 14 5 and 10 with assistance from processors 4 and 11. An ari~hmetic logic unit could be used in combination 16 with the memories and processors to perform calcula-17 ttons with intermediate and final results stored in 18 memories 5 6 or lO. The verTficatTon process 19 although described in reference to an MLS may be used with any type of landing system. All of the above 21 changes could be made without departlng from the true 22 scope of the inventlon.
' '' ' . ~;" ~ .
:. :
~, .
.-: . ~ . : . -. . .
;.: ; : .-. .. ...
.; , . . ~ - : - . -.r .:. . .
.. .. . . ... . . . .
l approaching aircraft. Since the executive monitor 2 initiates an alarm and shuts down a station or the 3 system when an out-of-tolerance parameter Ts detected 4 over a predetermined period of time it is necessary to verify that ~he fault monitoring function of the execu-6 tive monitor is operating properly and will provide such 7 an alarm when such an out-of-tolerance parameter is 8 detected over that predetermined period of time. Other-9 wise an approaching aircraft may be erroneously relying on MLS supPlied information which should have generated 11 an alarm and shut down the station or the MLS without 12 transmitting information to approaching aircraft.
14 An obJect of the invention is automatic real-time verification of the fault monitoring operation of an 16 executive monitor so that an alarm is generated and 17 declared valid when an internally generated out-of-18 tolerance or erroneous signal is detected by the 19 monitor.
A further object of the inventton is to provide 21 for the veriflcation of the fault monitoring operatlon 22 of an executive monitor in which a station control board 23 is connected on line with the executive monitor and 24 provides a signal thereto representative of erroneous or out-of-tolerance data in order to initiate an alarm in 26 the executive monitor. Another obJect of the invention - , . . .
: .: - :. ~ : : ....................................... :
.
~i 32~261 1 is to store the actual data obtained by the executive 2 monitor until proper fault monitoring verification 3 occurs.
4 Another obJect of the invention is to employ a filter counting means to record a history of the out-of-6 tolerance data received by the executive monitor so that 7 the filter counting means can be preconditioned during 8 the verification process to receive one additional out-9 oftolerance sample to thereby generate an alarm within the executive monitor.
11 Another object of the invention is to employ a 12 switch which will permit an internally generated out-of-13 tolerance sample to be analyzed instead of the sampled 14 information generated by the antenna system.
For a better understanding of the present inven-16 tion together with other and further obJects, reference 17 is made to the following description in conjunction with 18 the accompanying drawTngs.
19 BRIEF DESCRli'TlON OF THE DRAWINGS
Figure 1 is a schematic block diagram of a cir-21 cuit for verlfying proper operatTon of the fault moni-22 toring function of the executlve monTtor accordlng to 23 the Inventlon.
24 Flgure 2 is a flow-chart Illustratlng a sequence of operatTons for verifylng proper operatlon of the 26 fault monitorlng functlon of the executive monitor.
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2 Figure l illustrates the EL station 14 components 3 of an MLS system whlch are used to process one of many 4 MLS parameters transmitted to approaching aircraft and to verify the proper functioning of a fault monitor 6 system within the MLS should an out-of-tolerance param-7 eter be detected by the MLS system.
8 Since many parameters are verified in an MLS (see 9 parameters a-J listed above), the one chosen to best illustrate the invention and the one shown in Figure 1 11 is the scanning beam mean angle error parameter.
12 Although the scanning beam mean angle error parameter is 13 illustrated, it is to be understood that any of the 14 other parameters verified by the landing system could have been chosen to illustrate the invention, and in 16 this regard, the invention is not to be limited to the 17 illustrated parameter. The scanning beam mean angle 18 error from an EL sta~ion provides the difference between 19 the actual height of the approaching aircraft in angular degrees and the height the approaching aircraft already 21 calculated. The EL station transmtts scanning beam mean 22 angle error Information to approaching a7rcraft by an 23 array antenna means 1. The antenna means 1 also samples 24 this transmisslon Internally wlthin the MLS system by providing an output of hlgh frequency RF voltage signals 26 to an RF receiver detector means 2. The detector means .: . , - ' . : :
. , ~, . . . ' :. ~
., .
:. . :
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~ 325261 l 2 in conventional fashion converts the voltage 5 i gnals 2 into a series of D-C video pulses and outputs them to an 3 executive monitor means 3 over a manifold video llne.
4 The executive monitor means 3 contains a local CPU 4, local memory means 5, and a memory means 6 shared with a 6 control means 9, called a station control board.
7 The shared memory means 6 contains two filter 8 counters 7. Like the executive monitor means 3, the 9 control means 9 also contains a local CPU 11 and memory means 10. CPUs 4 and 11 are thus able to read from or 11 write into the shared memory means 6. CPUs 4 and 11 12 perform comparisons and calculations. The two filter 13 counters 7 are used in the executive monitor means 3 14 (together wlth an angle decoder not shown) to detect the time of occurrence of the rising and falling edges of 16 the video pulses and thus an out-of-tolerance scanning 17 beam angle. If a small scanning beam angle error is 18 detected, one of the two filter counters 7 lncrements.
19 If a large scanning beam angle error is detected the other filter counter 7 increments. If the calculated 21 scanning beam angle is withln a first predetermlned 22 limit, then the filter counters 7 decrement, but never 23 below a value of zero. The approachlng aircraft detects 24 the same timing tnformatlon as the executlve monltor means 3. The pulse edges are defined as the 3dB points 26 of each pulse and are detected when the video pulse 27 amplitude equals a first reference voltage corresponding 1 to 0.707 times a second reference voltage which is 2 stored in the executive monitor s local memory means 5 3 in digital form. The comparison of the video pulses 4 with said second reference voltage eliminates the counting of spurious false alarm signals and thus the erroneous calculation of guidance information.
7 As another safeguard at least two rising and two 8 falling edges (two pulses) are analyzed in real-time by 9 the CPU 4 in the executive monitor to determine the scanning beam angle error. Thirty-one samples of these 11 paired video pulses must be fed to the two filter 12 counters over a 0.8 second time period in order for the 13 executive monitor to accurately and reliably determine 14 if an out of tolerance scanning beam mean angle error exists. Such determination is made by comparing the 16 number of incremented counts in each filter counter with 17 a second predetermined limit for each stored in 18 memory. If the number of incremented counts exceeds the 19 second predetermined limit for either filter counter then the filter counter output indicates that mean 21 erroneous guidance - the scanning beam mean angle error 22 is beyond acceptable limits`- exists for the prescribed 23 0.8 second time period; an alarm 8 is therefore 24 generated in the executive monitor and noted in the memory means 6 shared by the monitor means 3 and the 26 control means (station control board) 9 when such 27 erroneous guidance is detected. Under these conditions ~1 .. , - 1 1 -~:, ~ ,, :;." ' '. ' ' ~ ' ' ' ' :', ' ' . ' ~ :, '' ':'';' ' ' '' 1 3~52~
1 an alarm signal is then fed by the station control board 2 9, to the transmitter of the array antenna means 1 3 shutting the system down. Of course, if erroneous 4 guidance is not indicated by eTther filter counter, then the alarm system will not be activated and the system 6 will not be shut down. The approaching aircraft 7 realizes that a fault condition has been detected in a 8 particular station when it does not receive any 9 information from that station.
The real-time, automatic operation of the present 11 fault monitoring verificatton scheme will now be 12 explained with reference to Figure 2. Figure 2 shows 13 through logic the manner in which the proper operation 14 of the fault monitoring function performed by the executive monitor is verified. Using the scanning beam 16 mean angle error parameter by way of example only, 17 verification is accomplished by having the contents of 18 the two filter counters 7 saved in the shared memory 19 means 6 in a location separate and apart from the filter counters 7. Between antenna scans the two filter 21 counters 7 are then provided with a predetermined count 22 that will cause the generation of a real-time, automatic 23 alarm If one more sample outsTde scanning beam mean 24 angle error limits is recelved. Thls precondltioning of the two fllter counters is accomplished in the memory 26 means 6 shared by the control means (station control 27 board) 9 and executive monitor means 3 shown in ~.
' , , :, , '':
. . . ' ' ." ' ' ' 'i 325261 1 Figure l. During the next antenna scan, the control 2 means CPU ll sends a signal over the MV SEL-Gl and G2 3 line activating switch 12 which replaces the parametric 4 video output received by the executive monitor means 3 with one out-of-tolerance pulse pair sample generated 6 internally. The internally genera~ed out-of-tolerance 7 pulse pair sample is sent by CPU 11 over the MV pulse 8 generator line to the executive monitor which then 9 increments the filter counters 7. The internally generated pulse pair represents a sample outside filter 11 counter limits and when summed with the predetermined 12 count in filter counters 7 should activate alarm 8.
13 If an alarm is generated as a result of the 14 introduction of the internally-generated out-of-tolerance pulse pair to the filter counters 7, then the 16 test is determined to be valid, i.e. the fault monitor-17 ing function of the executive monitor is working 18 properly. Under these conditions, the previously saved 19 contents of both filter counters are restored in order for normal operation of the system to be resumed on the 21 next antenna scan. If elther filter counter does not 22 generate an alarm, then an executive monitor failure Is 23 declared in the statlon control board 9, and the actual, 24 real-time alarm ts activated. Under these circumstances the station or system is automatically shut down by the 26 station control board 9 and In need of repaTr. This 27 7nforms maintenance personnel that the system is not ,: : , ' ' ': , '':
,: , , ~. , , ' .
'. - ' '': , ~ , ' 1 32526~
l properly monitoring fault conditions when scanning beam 2 mean angle errors Tn excess of a second predetermined 3 limit are detected. The above real-time verification 4 process is automatic software controlled and conducted every 15 minutes in an MLS. The MLS system also can 6 request the performance of a verification test from 7 human sources~
8 Specific structural details for the shared memory 9 means 6 and local memories 5 and 10 would be apparent to one skilled in the art. Although the alarm 8 and 11 filter counters 7 are shown in Figure 1 to be contained 12 in the shared memory means 6 those functions could 13 be performed by separate hardware or in local memories 14 5 and 10 with assistance from processors 4 and 11. An ari~hmetic logic unit could be used in combination 16 with the memories and processors to perform calcula-17 ttons with intermediate and final results stored in 18 memories 5 6 or lO. The verTficatTon process 19 although described in reference to an MLS may be used with any type of landing system. All of the above 21 changes could be made without departlng from the true 22 scope of the inventlon.
' '' ' . ~;" ~ .
:. :
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.-: . ~ . : . -. . .
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Apparatus for automatically verifying in real-time the proper operation of a fault monitor in an aircraft landing system, comprising:
antenna means for periodically transmitting aircraft guidance signals intended to have a predetermined characteristic during said transmission periods;
monitor means for receiving said transmitted signals and determining whether said characteristic exceeds a predetermined limit;
control means connected to the monitor means for replacing said received signals with a supplied signal having said characteristic and wherein said characteristic exceeds said predetermined limit;
memory means for storing a first number representing the number of times said characteristic of said transmitted signal exceeds said predetermined limit in a selected time period;
alarm means associated with said monitor means and said memory means for generating an alarm when said stored number represents a predetermined number;
preconditioning means for replacing said stored first number with a second number between selected transmission periods of said antenna means, said second number being one less than said predetermined number; and means for causing said control means to supply said supplied signal during the next transmission period following the replacement of said stored first number with said second number by said preconditioning means, thereby causing said stored number to become equal to said predetermined number, as a result of which said alarm means should generate an alarm.
antenna means for periodically transmitting aircraft guidance signals intended to have a predetermined characteristic during said transmission periods;
monitor means for receiving said transmitted signals and determining whether said characteristic exceeds a predetermined limit;
control means connected to the monitor means for replacing said received signals with a supplied signal having said characteristic and wherein said characteristic exceeds said predetermined limit;
memory means for storing a first number representing the number of times said characteristic of said transmitted signal exceeds said predetermined limit in a selected time period;
alarm means associated with said monitor means and said memory means for generating an alarm when said stored number represents a predetermined number;
preconditioning means for replacing said stored first number with a second number between selected transmission periods of said antenna means, said second number being one less than said predetermined number; and means for causing said control means to supply said supplied signal during the next transmission period following the replacement of said stored first number with said second number by said preconditioning means, thereby causing said stored number to become equal to said predetermined number, as a result of which said alarm means should generate an alarm.
2. The apparatus as claimed in claim 1 wherein the alarm means generates an alarm and causes the antenna means to terminate transmission when said stored number represents said predetermined number and an alarm was not generated as a result thereof.
3. The apparatus as claimed in claim 1 wherein the memory means is read into and written from both the monitor means and control means.
4. The apparatus as claimed in claim 1 wherein said memory means restores said stored first number after said alarm has been generated and causes said control means to discontinue replacing said received signals with said supplied signal, thereby causing said monitor means to resume normal monitoring of said received signals.
5. A method of automatically verifying in real-time the proper operation of a fault monitor in an aircraft landing system, comprising:
receiving and evaluating signals periodically transmitted by said landing system and intended to have a predetermined characteristic during said transmission periods, and storing in memory a first number representing the number of items said characteristic of said received signals exceeds a predetermined limit within a predetermined time period;
replacing said stored first number in memory with a second number between selected transmission periods of said landing system, said second number being one less than a predetermining number;
replacing said received signals with a supplied signal during the next transmission period following the replacement of said stored first number in memory by said second number, said supplied signal having said characteristic and wherein said characteristic excess said first predetermined limit;
generating an alarm when said stored number represents a number equal to said predetermined number;
restoring said stored first number if said alarm was generated; and generating an alarm and rendering the system inoperative if an alarm was not generated when the number represented by said stored number exceeds said predetermined number.
receiving and evaluating signals periodically transmitted by said landing system and intended to have a predetermined characteristic during said transmission periods, and storing in memory a first number representing the number of items said characteristic of said received signals exceeds a predetermined limit within a predetermined time period;
replacing said stored first number in memory with a second number between selected transmission periods of said landing system, said second number being one less than a predetermining number;
replacing said received signals with a supplied signal during the next transmission period following the replacement of said stored first number in memory by said second number, said supplied signal having said characteristic and wherein said characteristic excess said first predetermined limit;
generating an alarm when said stored number represents a number equal to said predetermined number;
restoring said stored first number if said alarm was generated; and generating an alarm and rendering the system inoperative if an alarm was not generated when the number represented by said stored number exceeds said predetermined number.
Priority Applications (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/040,505 US4823127A (en) | 1987-04-20 | 1987-04-20 | Automatic, real-time fault monitor verifying network in a microwave landing system |
| GB8809191A GB2203915B (en) | 1987-04-20 | 1988-04-19 | Automatic, real-time fault monitor verifying network in a microwave landing system |
| JP63098048A JPS6426176A (en) | 1987-04-20 | 1988-04-20 | Automatic and real time disturbance monitoring/checking circuit network for microwave landing system |
| CA000564773A CA1325261C (en) | 1987-04-20 | 1988-04-21 | Automatic, real-time fault monitor verifying network in a microwave landing system |
| DE3885092T DE3885092T2 (en) | 1988-04-21 | 1988-05-27 | Automatic real-time verification circuit for a fault monitor in a microwave landing system. |
| EP88304871A EP0343295B1 (en) | 1988-04-21 | 1988-05-27 | Automatic, real-time fault monitor verifying network in a microwave landing system |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/040,505 US4823127A (en) | 1987-04-20 | 1987-04-20 | Automatic, real-time fault monitor verifying network in a microwave landing system |
| CA000564773A CA1325261C (en) | 1987-04-20 | 1988-04-21 | Automatic, real-time fault monitor verifying network in a microwave landing system |
| EP88304871A EP0343295B1 (en) | 1988-04-21 | 1988-05-27 | Automatic, real-time fault monitor verifying network in a microwave landing system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1325261C true CA1325261C (en) | 1993-12-14 |
Family
ID=27167933
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000564773A Expired - Fee Related CA1325261C (en) | 1987-04-20 | 1988-04-21 | Automatic, real-time fault monitor verifying network in a microwave landing system |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1325261C (en) |
| GB (1) | GB2203915B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3885092T2 (en) * | 1988-04-21 | 1994-05-19 | Hazeltine Corp | Automatic real-time verification circuit for a fault monitor in a microwave landing system. |
| GB2282292B (en) * | 1993-09-28 | 1997-12-17 | Siemens Plessey Electronic | Improvements in or relating to aircraft landing systems |
-
1988
- 1988-04-19 GB GB8809191A patent/GB2203915B/en not_active Expired - Fee Related
- 1988-04-21 CA CA000564773A patent/CA1325261C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| GB2203915A (en) | 1988-10-26 |
| GB8809191D0 (en) | 1988-05-25 |
| GB2203915B (en) | 1991-05-22 |
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