Built in test of remote isolation

Embodiments herein relate to a system and method for detecting a degraded isolation impedance in a positively sourced remote load. The system includes a remote load driven by a direct current (DC) source, and a controller operably connected to the remote load having a positive sourcing driver interface with a dedicated return having the DC source on an output leg and a dedicated return leg. The positive sourcing driver also including a switching device configured controllably connect a DC voltage supply to the output leg of the DC voltage source, a first impedance operably connected between the output leg and ground, a second impedance operably connected between the dedicated return leg and a negative voltage supply, and a clamping and limiting device operably connected in series between the dedicated return leg and ground, the clamping device configured to limit a positive voltage on the return leg.

TECHNICAL FIELD

The present disclosure relates to a monitoring Built In Test (BIT) for Lightning Pin Injection in an aircraft application. In particular, the disclosure relates to a BIT for measuring impedance between load conductors and chassis ground.

BACKGROUND

Modern aircraft have a plurality of control surfaces, systems, actuators, torques, temperatures, and the like which need to be monitored to ensure proper operation of the aircraft. In order to be able to monitor the various aircraft parameters, sensors are used on the individual control surfaces, actuators, and engines to detect the various parameters. The values detected by the sensors can subsequently be employed for instrumentation, used to generate control commands, and for various diagnostics. With diagnostic applications, the values detected by the sensors may be compared with predetermined values for a given parameter under selected conditions and a malfunction can be identified in the event a deviation is detected by the respective sensor from the predetermined values.

A variety of sensors and actuators may be employed depending on the application. Sensors such as rotary or Linear Variable Differential Transformer sensors (RVDT or LVDT sensors), synchros and resolvers are conventionally used as sensors in aircraft because they are very robust with respect to external disturbances and have simple construction. However, in other applications, potentiometers and some low-level sensors are also commonly employed. Likewise, actuators may include valves, solenoids, relays, motors, brakes, and the like.

When sensors are used to detect various aircraft parameters, the sensors used must typically be monitored to ensure error free operation. Failures of sensors, and/or the wiring harness, or controller interfaces to sensors impact system reliability and result in a need for redundancy and overdesign to ensure operation. It is also desirable to ensure that potential failures are not only detectable, but also, preferably relegated to lesser importance and minimized impact on system reliability. Similarly, actuators are employed to move controls, control surfaces and the like to manipulate and control aircraft parameters, therefore commonly is it also desirable to monitor the operation of actuators to ensure error free operation. Failures of actuators and/or the wiring harness, or controller interfaces to them impact system reliability and result in a need for redundancy and overdesign to ensure operation. It is also desirable to ensure that potential failures are not only detectable, but also, preferably relegated to lesser importance and minimized impact on system reliability.

Some testing includes lightning protections. Qualification testing for lightning pin injection on sourced outputs permits use of an estimated ‘remote load impedance’, which is the equivalent impedance presented by the equipment between the load conductors and chassis (Earth) ground of the remote load. Furthermore, continued air-worthiness requirements dictate that lightning protection circuits should be testable, preferably by Built in Test (BIT), but at a minimum through component acceptance testing. Unfortunately, current BIT techniques do not have the capability to measure the remote load impedance, so taking advantage of its permitted use during qualification test or as part of a continued air-worthiness analysis is not available. Therefore, it is desirable to have a BIT capability that includes determination of remote load impedance where possible.

BRIEF DESCRIPTION

According to one embodiment of the invention, described herein is a system and method for detecting a degraded isolation impedance in a positively sourced remote load. The system includes a remote load driven by a direct current (DC) source, and a controller operably connected to the remote load having a positive sourcing driver interface with a dedicated return having the DC source on an output leg and a dedicated return leg. The positive sourcing driver also including a switching device configured controllably connect a DC voltage supply to the output leg of the DC voltage source, a first impedance operably connected between the output leg and ground, a second impedance operably connected between the dedicated return leg and a negative voltage supply, and a clamping and limiting device operably connected in series between the dedicated return leg and ground of the controller, the clamping device configured to limit a positive voltage on the return leg.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first impedance and the second impedance is selected so that an appreciable voltage may be measured at the voltage divider.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first impedance and the second impedance is selected to be about 10% of the expected value of the isolation impedance of the remote load.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first and the second impedance is a resistor of at least one of 50 kΩ, 100 kΩ, 200 kΩ, 500 kΩ and one Mega Ohm.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the clamping and limiting device is at least one of a diode, Zener diode, and transistor.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the positive voltage supply is 28 VDC.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the switching device is at least one of a switch, relay, contactor, transistor, FET, MOSFET, thyristor, and triac.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the remote load is at least one of an actuator, valve, solenoid, and brake.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the controller is configured to execute a method including applying a first high impedance pull down to ground on the output leg of a positive sourcing driver interface of the controller, applying a second high impedance pull down to a negative voltage supply on the return leg of a positive sourcing driver interface, clamping and limiting the return leg of the positive sourcing driver interface to a fixed positive voltage, measuring a voltage across the first high impedance pulldown with the positive sourcing driver inactive, determining if a degradation or loss of the isolation impedance at the remote load based on the measured voltage, and identifying the isolation impedance as degraded based on the determining.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the controller includes a data acquisition system.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the controller is configured to execute a built in test function.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the built in test function includes a step of the controller applying a known stimulus as excitation to the remote load and monitoring a response.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the built in test function identifies at least one of: a short circuit and an open circuit.

Also described herein in an embodiment is a method of detecting a degraded isolation impedance in a positively sourced remote load operably connected to a controller with positive sourcing driver interface and a dedicated return having the DC source on an output leg and a dedicated return leg, the controller configured to execute a method. The method includes applying a first high impedance pull down to ground on the output leg of a positive sourcing driver interface of the controller, applying a second high impedance pull down to a negative voltage supply on the return leg of a positive sourcing driver interface, clamping and limiting the return leg of the positive sourcing driver interface to a fixed positive voltage, measuring a voltage across the first high impedance pulldown with the positive sourcing driver inactive, determining if a degradation or loss of the isolation impedance at the remote load based on the measured voltage, and identifying the isolation impedance as degraded based on the determining.

In addition to one or more of the features described above, or as an alternative, further embodiments may include operably connecting the first impedance and second impedance to form a voltage divider with the remote load and the isolation impedance thereof.

In addition to one or more of the features described above, or as an alternative, further embodiments may include generating an excitation signal and transmitting it to the remote load.

In addition to one or more of the features described above, or as an alternative, further embodiments may include executing the method as part of a built in test function.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of this disclosure is thereby intended. The following description is merely illustrative in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the term controller refers to processing circuitry that may include an Application Specific Integrated Circuit (ASIC), an electronic circuit, an electronic processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable interfaces and components that provide the described functionality.

Although similar reference numbers may be used in a generic sense, various embodiments will be described and various features may include changes, alterations, modifications, etc. as will be appreciated by those of skill in the art, whether explicitly described or otherwise would be appreciated by those of skill in the art.

In general, embodiments herein relate generally to a non-invasive Built In Test (BIT) that measures load impedance of a remotely connected load e.g. an actuator while an output is not activated. In particular, on a positive sourcing output driver with dedicated ground returns, a circuit configuration that facilitates determination of the driver load isolation impedance or at least, an evaluation that the impedance is high e.g., on the order of 100 KOhms. Turning now toFIG. 1, a simplified diagram of a control or data acquisition system10on an aircraft12(partially shown) is depicted. The control system10includes, but is not limited to a control surface16depicted in this instance, on an aircraft wing20. The control system10includes one or more sensors22a,22b. . .22nconfigured to measure any of a variety of aircraft parameters or actuators24a,24b. . .24n. For example, in this instance, sensors22a,22b. . .22nmay measure displacement or displacement speed of the control surface16. Other parameters include, but are not limited to, temperatures, pressures, strains, and the like. The sensors22a,22b. . .22ncould be any configured to measure the aircraft parameter including RVDTs, LVDTs, potentiometers, thermocouples, bimetallic thermocouples, strain gauges, and the like. Likewise, the actuators24a,24b. . .24nmay include motors, valves solenoids and the like for controlling various devices on the aircraft12. For example, an actuator24a,24b. . .24nmay control the position of a control surface16or flow of fuel and the like. While the following descriptions of the embodiments will be made with respect to application of positive sourcing outputs, such as28Volts Direct Current (VDC) output drivers, it will be appreciated that the described embodiments may readily be applied to other output drivers and voltage levels and particularly any DC drivers. In an embodiment the sensors22a,22b. . .22nand actuators or loads24a,24b. . .24nmay be interconnected with a controller100. The interconnection30could be a simple wiring harness, bus configuration or any form of wireless communication as is known in the art.

Referring now toFIG. 2as well, where a simplified diagram of a positive sourcing output driver interface110in the controller100in accordance with an embodiment is depicted. When an actuator24a-24nis employed in application as a remote load on the aircraft12, the controller100typically provides (sources) a direct current (DC) excitation voltage on an output leg112to control or actuate the actuator24a-24n. In addition, in an embodiment, a dedicated return leg114provides the ground path for the current sourced to the remote load e.g., the actuator24a-24n. The voltage sourced may be provided via a switching device or controller116(also labeled as S1or via amplifier and the like connected to a voltage bus or supply115, in an embodiment, 28 Vdc. The switching device116may be any sort of controllable electromechanical devices such as a switch, relay, contactor and the like, or the switching device116may be or include a semiconductor type device such as a transistor, FET, MOSFET, thyristor, triac, and the like.

The remote load or actuator24a-24nexhibits an impedance presented to the controller output. This impedance is typically very small, for example on the order of ohms for a conventional coil, and the like. However, also of importance to the testing of a positive sourcing output driver110for a controller100, are the isolation impedances26(identified as ZISOLATION) exhibited by the remote load (actuator24a-24n)) with respect to its chassis ground. Typically, isolation impedance26is on the order of mega Ohms (MΩ) are expected. Ensuring that these isolation impedances26are maintained and their relative magnitude to the load impedance are important for equipment level lightning testing. Qualification testing for lightning pin injection, where voltage transients are introduced simulating lightning strikes on the aircraft12, on sourced outputs110permits use of an estimated ‘remote load impedance’, which is the equivalent impedance presented by the actuator24a-24nbetween the load conductors and chassis (Earth) ground of the remote load or the actuator24a-24n. In addition, lightning protection circuits should be testable, preferably by Built in Test (BIT). Therefore identifying during testing or BIT the relative magnitude of these impedances is advantageous for testing the system and ensuring correct functional testing and satisfactory airworthiness testing. To not consider the remote load impedance may have negative effect on testing and result in overdesigning protection circuits to withstand the injected voltage and current transients required by the lightning tests.

Continuing withFIG. 2, in an embodiment the positive sourcing driver interface110of the controller100also includes two impedances, first impedance118and second impedance120, as well as a voltage clamp122. In an embodiment, the first impedance118is connected as a pull down from positive sourced voltage as provided by the switching device116to a first voltage supply. In an embodiment, the first impedance118is fairly large to avoid loading the voltage source and supply115and dissipating excessive currents, but also smaller than the expected magnitude of the expected isolation impedance26. In one embodiment the first impedance and the second impedance is selected so that an appreciable voltage may be measured at the voltage divider. Moreover, the first impedance and the second impedance may be selected to be about 10% of the expected value of the isolation impedance of the remote load. For example, in an embodiment where the expected isolation impedance is on the order of MΩ, the impedance118is on the order of kilo Ohms (kΩ). In an embodiment a 100 kΩ resistance is employed, however other values such as 50 kΩ, 100 kΩ, 200 kΩ s, 500 kΩ and one MΩ are possible. Likewise, a second impedance120is employed as a pull down from the return leg114to a second supply voltage121. Once again in an embodiment, where the expected isolation impedance26is on the order of MΩ, the second impedance120is on the order of kilo Ohms (kΩ). In an embodiment a 100 kΩ resistance is employed, however other values such as 50 kΩ, 100 kΩ, 200 kΩ, 500 kΩ and one MΩ are possible. In an embodiment, the first voltage supply is typically ground and the second voltage supply is typically a negative voltage, (e.g., shown in the figure as −15 Vdc). In another embodiment they could be reversed and the first voltage supply could be a negative voltage and the second voltage supply could be ground or zero volts. It should be appreciated that the exact values of the first and second impedances are not critical, only that they be sufficiently large to facilitate establishing a voltage divider with the isolation impedance26of the remote load (e.g., actuator24a-24n) such that the voltage is detectable. In addition a voltage clamp122employed in series with the return leg114. In an embodiment a forward biased diode operates as the voltage clamp122to ground of the controller100ensuring that in operation the positive sourcing driver110is not impacted. In another embodiment the voltage clamp could be a diode, Zener diode, transistor and the like as would be well understood in the art.

In operation, in an embodiment, when the positive sourcing driver interface110is not operating, the first and second impedance118and120operate in conjunction with the isolation impedance26of the remote load, e.g., actuator24a-24nand the impedance of the actuator24a-24nitself to formulate a voltage divider. As stated earlier it is expected that the impedance of the remote load, e.g., the actuator24a-24nis much smaller than the isolation impedance26. For example, the impedance of the load Zloadis on the order of ohms, while the isolation impedance Zisolation26is on the order of MΩ. When the voltage source is not operating the voltage divider is formed that results in a voltage at Vx=−15(R1//Zisolation)/(R2+R1//Zisolation). It should be noted that because Zisolationis so large compared to Zload, and it could be on either side of Zload, (as shown in the figure) it is only used once in the equation.

If the Zisolationis large as expected, (˜MegaOhms), indicating a good isolation between Zloadand chassis of the remote load or actuator24a-24n, then, the voltage divider of the interconnected circuit simplifies to; Vx=−15(R1)/(R2+R1)=−7.5 V; when the supply voltage on the pull down for resistor120(R2) is −15 Vdc. Furthermore, under a potential fault condition when the isolation impedance26at the remote load is low, indicating a degradation in the isolation (i.e., a fault at the actuator24a-24n), the voltage divider is impacted and detectable. For example, if Zisolationis small (<100 kΩ) or on the order of 10 kΩ, when R1=R2=100 KOhms, then the voltage divider yields: Vx=−15(10 k//100 k)/(100 k+100 k//10 k)=−1.25 V. Therefore a change in the isolation impedance at the actuator24a-24nis detectable. In an embodiment a degradation in the isolation impedance of a remote load26e.g. actuator24a-24ncan be detected/measured by the controller during its initialization by means of BIT. In an embodiment the voltage Vxmeasured across the first impedance118e.g., pulldown resistor (R1) exhibits a broad range sufficient for detection and evaluation. In an embodiment, a 10:1 ratio is possible, identifying sufficient isolation vs. degraded isolation. As a result of the testing as may be conducted as part of a BIT, a failure or warning may be reported by the controller to ensure continued airworthiness and to validate the use of series resistance during the pin injection lightning testing per current standards.

It will be appreciated that while the embodiments herein have been described with respect to detecting/mitigating degradation or loss of isolation impedance at a remote load, detection of other potential failure modes is also possible. For example, during power on or initiated built in test (PBIT, IBIT), when the sensors22a-22nare not being used in application, an external wiring, sensor or open circuity may optionally be detected. For example, applying known stimulus to the sensor22a-22nor actuator24a-24nand monitoring the voltage developed across the resistors118and120to yield an expected response. Moreover, during an PBIT, IBIT, test voltages and currents may be applied to the sensors and actuators to ensure no other failures are detected. For example, during PBIT, IBIT fault modes that may be detected by conventional BIT methods include, but may not be limited to: an open circuits shorted wiring.

Turning now toFIG. 3, a flowchart of the method200of detecting degradation in an isolation impedance at a remote load is depicted. In accordance with the embodiments described herein the method is initiated at process step205of applying a first high impedance pull down to ground on an output leg of a positive sourcing driver interface110of a controller100. As depicted at step210, the method also includes applying a second high impedance pull down to a negative voltage supply on a return leg of a positive sourcing driver interface110. The method continues at process step215, with clamping and limiting the return leg of the positive sourcing driver interface110to a fixed positive voltage. With the positive sourcing driver110inactive, measuring a voltage across the first high impedance pulldown as depicted at process step220. Based on the measured signal, a determination is made if a degradation or loss of the isolation impedance26at the remote load e.g., actuator24a-24nis present as depicted at process step225. The degradation can be determined based of conventional voltage divider techniques to characterize the voltage signal measured. In one embodiment the voltage is equivalent to about half the negative supply is indicative of good isolation impedance26at the remote load e.g. actuator24a-24n, while a voltage equivalent to about 10% of the negative supply voltage is indicative to a loss or degradation of isolation impedance26. In this manner the controller100can identify the presence of an degradation or short in the isolation impedance26of the remote load. The controller100can then characterize, identify, and manage the failure as appropriate, such as annunciating the detected failure, identifying the remote load e.g., actuator24a-24nfor service, attempting corrective action, and/or electing to ignore the remote load exhibiting the degraded condition as depicted at process step230.