Patent Document

CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 13/455,777, filed Apr. 25, 2012, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the detection of High Intensity Electromagnetic Fields (HIRF). More particularly, this invention relates to a detector for detecting HIRF in a line replaceable unit. 
     BACKGROUND 
     Line replaceable units (LRU) are used in commercial and military applications to provide a specific function. A line replaceable unit includes chassis and a plurality of electronic circuits. Some of the electronic components that form the electronic circuits may be sensitive to HIRF. At some level of HIRF intensity a circuit may malfunction causing the LRU to malfunction. A typical LRU has EMI protection such as EMI filter pins in the LRU connectors used to connect the LRU to external cabling and careful shielding of the chassis covers. These protection elements, however, can fail, resulting in the electronic components being subject to the HIRF. 
     LRUs are tested after assembly to verify that their operation meets specification in an Acceptance Test using factory Test Equipment. In a similar manner, LRUs that have failed and are repaired in the factory or in a test facility are tested to a similar specification using the factory Test Equipment or other test equipment that can accomplish the same testing. These tests are referred to as Continued Airworthiness tests in the case of equipment used on Civil Aircraft. 
     The testing is conducted on a closed box. That is; the unit is connected to test equipment using cabling similar to that in the vehicle with loads and inputs which simulate normal interfaces. 
     SUMMARY OF THE INVENTION 
     Accordingly, disclosed is a system, device and method for verifying the integrity of the EMI filter pin connectors or LRU shielding in a closed LRU. 
     Disclosed is a line replaceable unit (LRU) comprising at least one circuit board, each of the at least one circuit board comprising circuit components mounted thereto, a chassis; a built-in test section; an external connector having a EMI filter; and an internal high intensity radiated field (HIRF) detector. The detector comprises at least one antenna attached to the chassis. Each antenna is configured and dimensioned to pick up an electromagnetic field. The electromagnetic field induces a current in the antenna proportional to a magnitude of the electromagnetic field. The detector also comprises a circuit configured to generate a DC signal based on the induced current in the at least one antenna and a processing section configured to compare the DC signal with a threshold and output a result of the comparison to the built-in test section. 
     Also disclosed is a high Intensity radiated field (HIRF) detector installed in a line replaceable unit comprising at least one antenna attached to a chassis being configured and dimensioned to pick up an electromagnetic field. The electromagnetic field induces a current in the antenna proportional to a magnitude of the electromagnetic field. The detector also comprises a circuit configured to generate a DC signal based on the induced current in the at least one antenna; and a processing section configured to compare the DC signal with a threshold and output a result of the comparison to a built-in test section. 
     Also disclosed is a method for testing EMI filter pin connectors of a closed line replaceable unit comprising setting a selecting switch to a Test Connector position, thereby connecting a RF signal generator to a testing connection cable, the testing connection cable being attached to a Test Connector of a line replaceable unit, causing the RF signal generator to generate a test signal as input into the testing connection cable; determining if a detector has detected the test signal. If the test signal is detected, the method further comprises, for each EMI filter pin connector in the line replaceable unit, switching the selecting switch to a corresponding test cable coupled to an EMI filter pin connector, causing the RF signal generator to generate the test signal as input into the corresponding test cable and determining if the detector has detected the test signal, wherein if the test signal is detected, the associated EMI filter pin connector coupled to the test cable is not functioning properly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, benefits, and advantages of the present invention will become apparent by reference to the following figures, with like reference numbers referring to like structures across the views, wherein: 
         FIG. 1  illustrates a block diagram of an example of an internal detector in accordance with the invention; 
         FIGS. 2A and 2B  illustrate high level schematics of examples of the Receiving Section in accordance with the invention; 
         FIG. 3  illustrates an example of a circuit board having the antenna trace according to an embodiment of the invention; 
         FIG. 4  illustrates a block diagram of the Processing Section in accordance with the invention; 
         FIG. 5A  illustrates a schematic diagram of an example of an internal detector in accordance with the invention. 
         FIG. 5B  illustrates test results for the example internal detector depicted in  FIG. 5A . 
         FIG. 6A  illustrate an external view of LRU,  FIG. 6B  illustrates an explode view of an LRU and  FIG. 6C  illustrate an external view of the LRU showing EMI filter pin connector slots and a Test Connector. 
         FIG. 7  illustrates a flow chart for a method of testing the EMI filter pin connectors and chassis shielding during acceptance testing; and 
         FIG. 8  illustrates a diagram of an example of an acceptance Test and Continuous Airworthiness Testing systems for testing the EMI filter pin connectors for a LRU in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Definitions 
     Line Replaceable Unit (LRU) is a modular component used in the military and commercial industries that is designed to be replaced quickly at a defined location. LRUs are designed to be removed and replaced on the flight line, hence the term “Line” Replaceable Unit. 
       FIG. 1  illustrates a block diagram of an internal High Intensity Radiated Fields (HIRF) detector  100 . The HIRF environment is applicable to equipment that is subject to extreme electromagnetic environments and/or mission critical equipment whose failure would be hazardous to human safety. As greater dependence is placed upon a vehicle&#39;s electrical and electronic systems performing functions required for safe operations, concern has increased for the protection of these systems. Concern for the protection of electrical and electronic systems in aircraft and other vehicles has increased substantially in recent years due to:
         Reduction in the electromagnetic shielding afforded by new composite materials.   Increased use of electrical and electronic systems in aircraft for flight/landing systems and in ground vehicles for propulsion and control systems.   Increased susceptibility of systems to HIRF due to increased data bus and processor operating speeds, higher density integrated circuits and cards, and greater sensitivities of electronic equipment.   Expansion of frequency usage above 1 GHz.   Increasing severity of HIRF environment because of an increase in the number of RF transmitters.       

     HIRF requirements are applied to ensure that the electrical and electronic systems are able to continue safe operation without interruption, failure or malfunction, including those in LRUs. 
     The internal detector  100  is configured to detect HIRF (“HIRF Detector”). The HIRF Detector  100  includes a Receiving Section  105 , a RF Amplifier  110 , a RF Detector/Filter  120 , and a Processing Section  125 . The Receiving Section  105  is coupled to a RF Amplifier  110 . The RF Amplifier  110  is coupled the RF Detector/Filter  120 . The Processing Section  125  is coupled to RF Detector/Filter  120 . The RF Amplifier  110 , the RF Detector/Filter  120  and Processing Section  125  are mounted on one or more Printed Wire Boards. In one embodiment, the RF Amplifier  110 , the RF Detector/Filter  120  and Processing Section  125  are mounted to the same Printed Wire Board. 
     The Receiving Section  105  is designed to a predetermined frequency range. For example, the frequency range can be 100 MHz to 1 GHZ. However, the design frequency range can be application specific, e.g., different for different types of LRUs. The Receiving Section  105  will be described in detailed with respect to  FIGS. 2A and 2B . 
     The gain of the RF Amplifier  110  can be set to account for the ambient noise caused the internal electronic components. Additionally, the gain of the RF Amplifier  110  is determined based upon the preset detection threshold stored in the Processing Section  125 . Although, the RF Amplifier  110  is depicted in the diagram ( FIG. 1 ), the RF Amplifier  110  is optional and may not be needed in all applications. The RF Detector/Filter  120  can be a circuit containing a detection diode D 1  and a RC filter section as depicted in  FIG. 5A . 
     In an embodiment, the Processing Section  125  can be programmed with two modes: a testing mode and a continuous operation mode. In the testing mode, the Processing Section  125  can output the detection bit to an external device and in the continuous operation mode, the Processing Section  125  outputs the detection bit to the internal built-in test section. 
       FIG. 1  depicts both the test input (test signal in testing mode) and the HIRF signal (continuous operation mode) as inputs to the Receiving Section  105 . Additionally,  FIG. 1  depicts both the bit detection signal output to the built-in test section (continuous operation mode) and to the Test Connector  630  (as depicted in  FIGS. 6C and 8 , in testing mode). 
     The elements of the HIRF Detector  100  can be powered from an LRU power supply, if needed. For example, the RF Amplifier  110  can be biased using the LRU power supply. 
       FIG. 2A  illustrates an example of a Receiving Section  105 A. The Receiving Section  105 A comprises the Receiving Elements  200 , such as an antenna array, coupling wire(s), antenna traces  310 . The Receiving Element(s)  200  can be one or more antenna wires mounted or attached to the chassis, mounted along the chassis walls in a three-dimensional orientation, a circuit trace embedded or etched into a Printed Wire Board Layer  305  of a Printed Wire Board (module)  300  or one or more of the coupling wires between two Printed Wire Boards  300 .  FIG. 3  illustrates an example of Antenna Trace  310  routed along side of internal wiring from the external connectors to the mother board. One end of the Antenna Trace  310  is coupled to the Summing Element  205  (Receiving Section  105 A) or Multiplexer  215  (Receiving Section  105 B). 
     Additionally, if the Receiving Element(s)  200  is an antenna wire mounted to the chassis, a plurality of metallic wires can be used to create a  3 -dimensional mapping to generate signals representative of the fields in the x, y, and z directions. The signals are then combined to detect the HIRF. 
     In an embodiment, antenna traces  310  can be added to each Printed Wire Board  300  of an LRU. Therefore, even if the HIRF field is uneven throughout the inside of the LRU, a HIRF level high enough to cause a LRU response can be detected. 
     The Receiving Section  105  can be located in proximity to the EMI filter pin connectors  625  (an example of the EMI filter pin connectors are depicted in  FIGS. 6C and 8 ). For example, in an embodiment, the Receiving Section  105  can be an antenna trace  310  embedded in the closest Printed Wire Board  300 . Additionally, the Receiving Section  105  can be mounted on the chassis near the EMI filter pin connectors. Alternatively, the Receiving Section  105  can be located in proximity sensitive circuit components to measure the HIRF near the sensitive components such as analog circuits and high gain circuits. 
     The Receiving Section  105 A further comprises a summing element (Σ)  205  for adding the signals received from each of the Receiving Element(s)  200  and a Buffer  210  for buffering the added signals. The Receiving Section  105 A output an added signal to the RF Amplifier  110 . 
       FIG. 2B  illustrates an example of another Receiving Section  105 B. The Receiving Section  105 B comprises the same Receiving Elements  200 , however, instead of adding all of the received signals, the received signals are selected one at a time by a Multiplexer  215 . Each selected signal is successively buffered by Buffer  210 . The Multiplexer  215  repeatedly outputs one selected signal at a time to the Buffer  210 . Each signal received from the Receiving Elements  200  is selective output for each cycle. The Receiving Section  105 B outputs the currently selected signal to the RF Amplifier  110 . Receiving Section  105 B allows for each signal to be examined by the Processing Section  125 . 
       FIG. 4  illustrates a block diagram depicting an example of the Processing Section  125 . In the example of the Processing Section  125  depicted in  FIG. 4 , the Processing Section  125  comprises a Comparator  400 , a Sampler  405  and a Persistence Detector  410 . In an embodiment, the Processing Section  125  includes a storage device (not shown) for storing at least one detection threshold. Since each LRU reacts differently to a HIRF, the detection threshold varies based on the type of LRU and the electronic components mounted to the print wire boards  300 . Therefore the detection threshold can be application specific. The detection threshold also can be remotely adjusted after assembly, as necessary. In this embodiment, the storage device may also include a threshold adjustment for performing the functionality described herein. 
     The Processing Section  125  receives the output of the RF Detector/Filter  120  (showing in  FIG. 4  as input) and the Comparator  400  compares this input with the detection threshold. If the received output is higher than the detection threshold, the Comparator  400  outputs a signal indicating a positive detection to the Sampler  405 . For example, the Comparator  400  can output a “high” signal value. If the input is less than the detection threshold, the Comparator  400  outputs a signal indicating a negative detection to the Sampler  405 . For example, the Comparator  400  can output a “low” signal value. 
     The Sampler  405  periodically samples the output of the Comparator  400 . The sample rate is preset. The sample rate can be every  30  seconds. However, the sample rate can be application specific. Furthermore, in an embodiment, the sample rate can be remotely adjusted after assembly, as necessary. In this embodiment, the storage device (not shown) may also include a sample rate adjustment for performing the functionality described herein. If the Sampler  405  receives a positive detection signal during the sample period, e.g., a “high” signal, the Sampler  405  outputs a positive detection signal to the Persistence Detector  410 . If the Sampler  405  receives a negative detection signal during the sample period, e.g., a “low” signal, the Sampler  405  outputs a negative detection signal to the Persistence Detector  410 . 
     The Persistence Detector  410  is configured to determine if the positive detection signal received from the Sampler  405  occurs for a period of time where the HIRF signal can cause damage. In an embodiment, the Persistence Detector  410  counts the number of consecutive positive detection signals received from the Sampler  405  and compares the counted number with a threshold. If the counted number is greater than the threshold, the Persistence Detector  410  outputs a positive detection bit to the built-in test section (in continuous operation mode) or to the Test Connector  630  (in testing mode). The built-in test section can be mounted on the same Printed Wire Board  300 . In another embodiment, the Persistence Detector  410  counts the number of positive detection signals received from the Sampler  405  within a preset period of time. If the counted number is greater than the threshold, the Persistence Detector  410  outputs a positive detection bit to the built-in test section or the Test Connector  630 . In another embodiment, the Persistence Detector  410  tracks the number of positive detection signals received in a period of time and the number of negative detection signals received within the same period of time. The Persistence Detector  410  separately adds the number of positive detection signals and the negative detection signals and then subtracts the total number of negative detection signals from the total number of positive detection signals to obtain a net positive detection value. If the net positive detection value is greater than the threshold, the Persistence Detector  410  outputs a positive detection bit to the built-in test section (or the Test Connector  630 ). 
     While  FIG. 4  depicts the Comparator  400 , Sampler  405  and the Persistence Detector  410  separately, these components can be integrated into a single processor. The processor can be a microprocessor or a CPU. Additionally, the functionality of the Comparator  400 , Sampler  405  and persistence detection  410  can be implemented using a PAL, PAL, FPGA or an ASIC. 
     The Processing Section  125  is powered from the LRU Power Supply (not shown). 
     The HIRF Detector  100  can be used during initial testing, such as acceptance testing, during continuous operation and during maintenance procedure such as continued airworthiness (CAW) tests. 
       FIG. 5A  illustrates a schematic diagram of an example of HIRF Detector  100 .  FIG. 5B  depicts simulated and measured test results for this detector. A signal having a known signal strength was input. The output voltage was measured using a voltmeter. The simulated results substantially correlate with the measure voltages. As can be seen from  FIG. 5B , the frequency response for the detector is relatively flat over measured frequency range. 
       FIG. 6A  illustrates an external view of an example of an LRU  600 .  FIG. 6A  depicts the external chassis shielding  605 .  FIG. 6B  illustrates an external exploded view of the same LRU  600 . The external view illustrates multiple Printed Wire Boards  300 . The front panel  610  and rear panel assembly  615  and the side panels  620  form a housing for the Printed Wire Boards  300 . The front panel  610 , rear panel assembly  615 , and side panels  620  collectively form the chassis shielding  605 . The Printed Wire Boards  300  attached to slots in the rear panel assembly  615 . 
       FIG. 6C  illustrates an external view of the rear panel of a second example of an LRU  600 A. The rear panel comprises a plurality of EMI filter pin connectors  625  and a Test Connector  630 . During testing, the Test Connector  630  is covered with a metallic cover  635 . 
     The HIRF Detector  100  is sensitive to higher than normal intruding EMI fields from external sources. Each LRU  600  also includes a built-in test section (not shown). 
     Each Printed Wire Board  300  has electronic component mounted thereto. These electronic components are configured to perform the functionality of the LRU, e.g., LRU  600 . Additionally, according to certain aspects of the invention, one or more of the Printed Wire Boards  300  also includes electronic components that are dedicated to detect HIRF and output a signal to a built-in test section. If a HIRF is detected, there is a high likelihood that either one of the EMI filter pin connectors  625  and/or the chassis shielding  605  have failed. The HIRF Detector  100  provides a closed-box testing. 
     A typical LRU, e.g., LRU  600 , is tested using an extensive qualification and acceptance testing that exposes the units and a model of their interconnections cabling to high amounts of electromagnetic energy (RF energy), representative of a real world exposures that the units can and will be exposed during service. The tests use various test equipment to evaluate the levels of energy and the response of the unit. 
     The test implements an Acceptance Test Procedure (ATP)/Continuous Airworthiness Procedure. The tests are required to be performed with the LRUs  600  closed and in a ready-for-delivery configuration. The HIRF Detector  100  is used to determine the integrity of the LRU  600  related to an exposure of the RF energy. 
       FIGS. 7 and 8  illustrate the testing procedure and test setup, respectively. 
     The test setup  800  comprises an external test RF Signal Generator  805 , a Connector Switch  810 , a plurality of External Test Cables  815   N  and a Test Connector  630 . The Connector Switch  810  comprises a plurality of switching positions and will selectively couple the test signal generated by the RF Signal Generator  805  to each of the External Test Cable  815  and the Test Connector  630  via the connector testing cable  631 . As depicted in  FIG. 8 , the Connector Switch  810  has four switch positions (illustrates by the dots). Three of the switching positions are used to couple the three External Test Cables  815  (three EMI filter pin connectors  625   N ) to the RF Signal Generator  805 . One of the switching positions is used to couple the Test Connector  630  to the RF Signal Generator  805 . The Connector Switch  810  will need to have one more switching position than the number of EMI filter pin connectors  625   N . Each EMI filter pin connector  625  has a corresponding External Test Cable  815  coupled to it. As depicted, there are three EMI filter pin connectors  625   1-3  and three external test cables  815   1-3 .  FIG. 8  illustrates a portion of the External Test Cable being exposed to show the internal test cable wires and the coupling resistors (test cable wires  816 ). The External Test Cables  815   1-3  have LRU connectors at one end and at the other end each wire in the cable is terminated in a coupling resistor. The other terminal of each of the isolation resistors associated with a given cable is connected together and connected to the output amplifier. Each external test cable  815  is similarly fitted. 
     The Test Connector  630  is coupled to the internal HIRF Detector  100 . The Test Connector  630  is not fitted with EMI filters. When not in use, the area where the Test Connector  630  is located is capped with the metallic cover  635  for EMI shielding. The Test Connector  630  is capped during testing to present the test frequency signal being leaked into the LRU, e.g.,  600 A. 
     The output of the internal HIRF Detector  100  is sent to a test equipment computer (the computer is not shown in  FIG. 8 ). However, the output of the internal HIRF Detector  100  is illustrated as Detection Signal  830 . 
     As depicted in  FIG. 8 , the LRU under test, e.g., LRU  600 A, comprises three internal circuit modules (wire boards  300   1-3 ), three EMI filter pin connectors  625   1-3  and a rear panel assembly  615 . The EMI filter pin connectors  625   1-3  are coupled to the rear panel assembly  615  via cables  817   1-3 . 
       FIG. 7  illustrates a flow chart of an example of a testing method. The testing method will be described in conjunction with the test setup depicted in  FIG. 8 . However, the testing method is not limited to the test setup  800  depicted in  FIG. 8  and can be conducted using other testing setups. 
     At step  700 , the Connector Switch  810  is set to the Test Connector  630 , which couples the RF Signal Generator  805  to the Test Connector  630 . At step  705 , the LRU, e.g.,  600 A having the internal HIRF Detector  100  is excited with the test frequency signal the internal HIRF Detector can be one or more of the Internal Circuit Modules  300   1-3  (Printed Wire Board). The power level of the test frequency signal is predetermined and controlled. The RF Signal Generator  805  is set to the predetermined frequency and amplitude for the Test Connector input. At step  710 , the Processing Section  125  compares the output of RF Filter/Detector  120  with the preset threshold. The Processing Section  125  compares a digital value of the test frequency signal with the preset threshold. The digital value is generated from the received test frequency signal. The HIRF Detector  100  should indicate that HIRF has been detected. At step  715 , a determination is made if the HIRF Detector  100  detected the HIRF by evaluating the Detection Signal  830  on the test equipment computer. If the HIRF Detector  100  detected the HIRF, then the testing proceeds (“Y” at step  715 ). This test validates that the HIRF Detector  100  functions properly. 
     At step  720 , the Connector Switch  810  is set to one of the External Test Cables, e.g.,  815   1 , which couples the RF Signal Generator  805  to the external test cables  815   1 . For each external test cable  815 , the LRU with the internal HIRF Detector  100  is excited with the test frequency signal at step  725 . At step  730 , the Processing Section  125  compares the output of RF Filter/Detector  120  with the preset threshold. At step  730 , the Processing Section  125  outputs the Detection Signal  830 . At step  735 , a determination is made if the HIRF Detector  100  detected the HIRF by evaluating the Detection Signal  830  on the test equipment computer. If all of the EMI filter pin connectors  625  are functioning properly no response from the HIRF Detector  100  is expected (“N” at step  735 ). If the HIRF Detector  100  registers a HIRF intrusion, the EMI filter pin connector  625  is faulty (“Y” at step  735 ) and must be replaced or repaired (step  737 ). 
     Steps  720 - 735  are repeated for each EMI filter pin connection  625 . After step  735 , a determination is made if there are any untested EMI filter pin connectors  625  (step  740 ). If there are untested EMI filter pin connectors (“Y” at step  440 ), the process returns to step  720 . If not, (“N” at step  740 ), the process is done and all of the EMI filter pin connectors  625  are functioning properly (step  742 ). 
     If at step  715 , the test signal is not detected by the HIRF Detector  100 , the HIRF Detector  100  is faulty (“N” at step  715 ) and should be examined for further evaluation (step  717 ). 
     Various aspects of the present disclosure may be embodied as a program, software, or computer instructions embodied or stored in a computer or machine usable or readable medium, which causes the computer or machine to perform the method when executed on the computer, processor, and/or machine. A computer readable medium, tangibly embodying a program of instructions executable by the machine to perform various functionalities and methods described in the present disclosure is also provided. 
     The computer readable medium could be a computer readable storage medium or a computer readable signal medium. Regarding a computer readable storage medium, it may be, for example, a magnetic, optical, electronic, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing; however, the computer readable storage medium is not limited to these examples. Additional particular examples of the computer readable storage medium can include: a portable computer diskette, a hard disk, a magnetic storage device, a portable compact disc read-only memory (CD-ROM), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an electrical connection having one or more wires, an optical fiber, an optical storage device, or any appropriate combination of the foregoing; however, the computer readable storage medium is also not limited to these examples. Any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device could be a computer readable storage medium. 
     The computer instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means, devices, units, or sections for implementing the functionality specified. 
     The Detector may be any type of known or will be known systems such as, but not limited to, a virtual computer system and may typically include a processor, memory device, a storage device, input/output devices, internal buses, and/or a communications interface for communicating with other computer systems in conjunction with communication hardware and software, etc. 
     The terms “element”, “interface” “section”, “device” or “unit” as may be used in the present disclosure may include a variety of combinations of fixed and/or portable computer hardware, software, peripherals, and storage devices. The Detector or system may include a plurality of individual components that are networked or otherwise linked to perform collaboratively, or may include one or more stand-alone components. 
     The function(s) described herein may occur out of the order noted in the figures or text including in the reverse order or concurrently (or substantially concurrently) depending upon the functionality involved. 
     The embodiments described above are illustrative examples and it should not be construed that the present invention is limited to these particular embodiments. Thus, various changes and modifications may be effected by one skilled in the art without departing from the spirit or scope of the invention as defined in the appended claims.

Technology Category: 3