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New requirements for civil avionics EMC test system


  The test level, requirements and test process try to reflect the latest progress of aviation technology and EMC electromagnetic compatibility test methods.

  RTCA/DO-160F, replacing the previous DO-160E[1] version, is a standard for environmental conditions and test procedures for aeronautical equipment developed by Special Committee 135 of RTCA and published on December 6, 2007. DO-160F covers standard procedures and environmental testing criteria for avionics electrical and electronic equipment (aviation electronics). The tests specified in DO-160F are typical tests performed to meet the requirements of the Federal Aviation Administration (FAA) or other international regulations for equipment installed on commercial aircraft.

  Tests and test levels/limits in DO-160F (see "Equipment Classification") apply to all types of aircraft in current practical use, including small general aircraft, business jets, helicopters, regional jets, and jumbo jets Aircraft such as the latest Airbus (A380) and Boeing airliners (787). The document consists of 26 parts and three appendices, but only sections 15 to 23 and section 25 contain electromagnetic compatibility. Others covered by DO-160F are: Temperature, Altitude, Vibration, Sand/Dust, Power Input, RF Susceptibility, Lightning Strike, and Electrostatic Discharge.

  The development and revision of DO-160F is in line with the EU version of RTCA: EUROCAE. A collaboration between two organizations across the Atlantic, RTCA/DO-160F is identical to its European counterpart, EUROCAE/ED-14F. This article aims to provide a brief description of each section of DO-160F related to EMC. Changes to each part after the publication of DO-160E will also be briefly described, and finally, we will also look forward to future revisions of DO-160.

  1-3 sessions

  The first three sections describe the objectives and scope of DO-160 (Section 1), provide terms and definitions used throughout (Section 2), and specify the test conditions (Section 3). The first three sections provide references to subsequent sections of DO-160 and general information and guidance on exactly how to perform specific tests.

  Where is DO-160F new?

  l In the second section, add "scope of application of test results".

  l In the third section, add "EUT settings for sensitivity testing"

  Section 15: Magnetic Effects

  MC (means magnetic compatibility and "EMC" means electromagnetic compatibility) test is used to determine the degree to which the equipment under test (EUT) affects the deflection of the compass, or the degree to which it affects the indication of the compass sensor, which is also called "magnetic valve".

  A standard compass has a large dial that reads off every degree of needle deflection, and this is the only test equipment needed. The EUT approaches the compass in an east-west direction until a one-degree shift in magnetic north is observed. Measure their spacing to determine the "device class".

  equipment class

  Equipment can be classified into five equipment classes (Y, Z, A, B and C) based on the distance between the EUT and the compass (or compass sensor) from less than 30 cm to more than 300 cm.

  Where is DO-160F new?

  l The installation distance between 0 and 30 cm is classified into the new category Y.

  l The necessary description of each equipment classification has been added to Section 15 "Test Purpose", and there is also a discussion on how to use the test results to determine the closest installation distance between the EUT and the compass (or compass sensor).

  l Added the use of "equivalent magnetic sensors" to allow the use of electronic compasses as opposed to typical "free magnetic" compasses.

  Section 16: Power Input

  While there is still debate about whether "power input" (or "power quality" as other standards call it) are true EMC tests, they are included here for two reasons. First, power/input/quality testing is often done in EMC labs by EMC testers. Second, in the latest version of DO-160, the frequency ranges for some tests have fallen within typical EMC test parameters, and the equipment used in these tests is different from many of the "true" EMC tests used in DO-160 and other EMC standards The EMC testing is similar.

  The tests in Section 16 are used to determine the normal operation of the EUT under various changes in AC and/or DC power due to normal and emergency operation of the aircraft. In addition, Section 16 includes tests to verify that the EUT does not adversely affect the aircraft power supply, thereby impairing or degrading the performance of other installed equipment.

  An interesting point about Section 16 is that it is the only one in DO-160 that covers EUT susceptibility (e.g. surges, interruptions, transients, etc.) etc.) requirements and a section of the test. The above, coupled with the increasing complexity and diversity of aviation power systems, and more than 16 sections (a total of 61 pages in DO-160), triggered SC-135 to conduct some research on the power input/quality requirements Discussion of breaking off into a completely different file -- though no imminent changes are considered at this point.

  To keep up with the latest advances in aviation power system design, Section 16 has undergone dramatic changes over the past 10 years. The DO-160F has also undergone substantial revisions with the new electrical system being implemented on the latest air transport aircraft.

  The second revision of DO-160D released on June 12, 2001 greatly revised Section 16, added new tests, modified existing tests, and pointed out the part of AC harmonic current and variable frequency AC power The problem of the system [2]. In DO-160E, the entire section has been rearranged to place all AC tests in one subsection and DC tests in another subsection to make Section 16 easier to use and understand. DO-160E also introduces some new test methods, such as the DC component test for AC power equipment, and a new "Load Equipment Effects on Aircraft Power Systems" subsection. In DO-160F, more tests are required for AC and DC power systems, a new series of tests and test levels have been added including 270V DC power systems, and there is also a much expanded test list covering EUT for avionics impact on the power system.

  DC input test

  DC input tests include:

  Steady-state overvoltage and undervoltage conditions

  Ripple voltage

  momentary power interruption

  Instantaneous dips and surges

  Exposure voltage decay time (only for 270V voltage)

  instantaneous current

  AC input test

  AC input tests include:

  Steady-state overvoltage and undervoltage conditions

  Steady-state high frequency and frequency reduction

  Steady-state phase unbalance (three-phase electricity)

  Voltage and Frequency Modulation

  Voltage and Frequency Transients

  momentary power interruption

  Momentary dips and surges

  DC Bias and Voltage Distortion

  Harmonic current emission

  Phase unbalance (three-phase electrical input)

  DC power component

  instantaneous current

  current modulation

  power factor

  Equipment category

  There are three device types (A, B, D, or Z) which indicate the type of power the device uses and the type of DC and/or AC power the device can operate on. For AC powered equipment, there is an additional designator under the category designator, a two-letter designation indicating: This equipment has been tested for use in fixed frequency (CF), narrowband variable frequency (NF), or Wideband variable frequency (WF).

  There are four additional category designators for the following tests:

  AC current harmonics (H)

  AC current modulation (L)

  AC power factor (P)

  DC current ripple (R)

  AC or DC Inrush (I)

  Where is DO-160F new?

  l New categories (D), tests and test levels for EUT equipment including 270V DC drive.

  l Phase loss test for EUT equipment using three-phase alternating current.

  l Add more tests in the "Load Equipment Effects on Aircraft Power System" section.

  l Specific tolerances for all test parameters.

  l Special definition of "manual restart".

  Section 17: Spike Voltage

  This test determines whether the EUT can perform as required during and/or after a voltage spike is applied to the AC and/or DC power ports. Various methods of generating voltage spikes can be used as long as the resulting waveform has a duration of at least 10 microseconds, a rise time of less than 2 microseconds, and a source impedance of 50 ohms. Apply a peak voltage of at least 50V within 1 minute. This test is very similar to CS106 of MIL-STD-461F.

  Equipment category

  There are two device classes. The Class B test level is twice the AC (rms) and/or DC line voltage (or 200V, whichever is less). Class A test level is 600V.

  Where is DO-160F new?

  l When all input ports are connected to the same power bus, all input ports need to be tested at the same time.

  l Three-phase electrical test setup.

  l Clear the power supply impedance tolerance.

  Section 18: Conducted Audio Sensitivity------Power Input

  This test determines whether the EUT will perform as required during the injection of audio disturbances into the AC and/or DC input ports. The test configuration and steps are basically the same as the CS101 test method of MIL-STD 461F, the only difference is in the test level and frequency range. Audio interference is transformer-coupled to all power inlets, and the peak-to-peak voltage of the interference signal between the power inlets and return wires is tested. The test level is 8% of the normal AC input voltage, and the frequency range is from 10Hz to 150kHz.

  The EUT must be tested at the minimum and maximum design current (if possible), and at the limit frequency of the AC power supply if it is to be used with a variable frequency system. The frequency scanning rate is 30 steps per 10 times, and the dwell time at each step frequency point is 1 minute.

  Equipment category

  The three DC power equipment categories (R, B, and Z) indicate the category of electrical power used by the equipment and the type of DC power supply that the equipment is compatible with. Two (R and K) categories of AC power equipment have been developed. Class R is described with an additional indication (a two-letter symbol), the symbol in brackets after the category indication, indicating that this equipment has been tested and can be used in fixed frequency (CF), narrowband variable frequency (NF), wideband Variable Frequency (WF), Class K is used to indicate that the EUT has been tested for use with any AC power input and at higher voltage distortion than Class R.

  Where is DO-160F new?

  l Three-phase electrical test configuration.

  l Add (Figure 1) 270V DC test category/level.

  l 270V DC Class Z common mode test (at 2x differential mode level).

  l When all input ports are connected to the same power bus, all input ports need to be tested at the same time.

 

  Figure 1 Class Z, 270V DC conduction susceptibility test level

  Section 19: Inductive Signal Sensitivity

  This section of the electromagnetic compatibility test is used to determine whether the equipment and interconnection cables can operate as required under the action of audio electric fields, magnetic fields, and transient peak voltages. The test level for interconnecting cables is determined by the length of the cable exposed to the radiation. For the inductive switching transient current (inductive spike) test, the exposure length can be 1.2 or 3.0 meters, and the spike voltage applied to the radiating cable must reach at least 600V peak-to-peak.

  For the case of electromagnetic field induction into the cable, the test level is determined by the length of interconnection cable where the product is exposed to the radiating cable and the RMS voltage or current applied to the radiating cable. Test levels are expressed in "Volts x meters" (Vm) or "Amperes x meters" (Am). For example, class Z requires an electric field strength of 1800V-m, which corresponds to a 3 meter long cable exposed to the electromagnetic field generated by a radiating cable with an applied voltage of 600Vrms. If, due to space constraints, only less than 3 meters of the cable is exposed to the radiating cable, the voltage applied to the radiating cable should be increased to achieve a test level of 1800V-m. When the test encounters a special case where the last cable is less than 3m, special handling is required. In this case, the test level may be reduced in proportion to the coupling length.

  The frequency range for sweep testing is determined by the equipment class. The frequency scanning rate is 30 steps per 10 times, and the dwell time at each step frequency point is 10 seconds.

  Equipment category

  The equipment category is indicated by two letters, the first letter (A, B, C or Z) indicating the test performed and the level of the test. The second letter (C, N or W) indicates the operating frequency (static, variable narrowband, or variable wideband) of the AC power system compatible with the EUT.

  Where is DO-160F new?

  l No significant changes.

  Section 20: Electromagnetic Compatibility Testing RF Susceptibility (Radiated and Conducted)

  This electromagnetic compatibility test is used to determine whether the EUT will perform as required when the EUT and its interconnecting cables are exposed to radio frequency interference. Continuous wave (CW), amplitude modulated square wave (SW), and pulse modulated (PM) RF signals are required. A linear impedance stabilization network (LISN) must be connected in series with each power line and ungrounded power return, and a 10µF capacitor should be connected between the LISN's power input and the ground plane. Unless otherwise specified, interconnect cables must be at least 3.3 meters long and power cables must not exceed 1 meter.

  Electromagnetic Compatibility Test Conducted Susceptibility

  The RF conduction susceptibility test procedure is similar to the CS114 method in MIL-STD-461F. Radio frequency interference is coupled into the EUT's interconnection cables and power lines using injection probes that are first calibrated to the test level (in a 50 ohm fixture) prior to testing. Record the RF power value required to reach the specified RF current at each frequency point in the calibration fixture, and the resulting frequency-power calibration table will be used in the actual test.

  During the test, the RF induced current introduced into the tested cable or power line is monitored by a calibrated RF current probe, and the RF power injected into the probe is gradually increased until it reaches the appropriate current level (determined by the type of equipment used). The RF energy injected into the probe must not exceed the power level recorded when calibrated in a 50 ohm calibration jig by more than 6dB. Test frequencies range from 10KHz to 400MHz, and each test typically requires two scans—one with the CW signal and then with the SW modulated signal.

  EMC Test Radiation Susceptibility

  The steps of RF radiation susceptibility test are similar to RS103 in MIL-STD-461E. The EUT, its interconnection cables and power cables are exposed to RF radiation fields in the frequency range of 100MHz to 18GHz.

  Section 20 allows the use of two RF radiation susceptibility test methods. The first method is the same as the RS103 test method mentioned in MIL-STD-461F, using a standard semi-anechoic chamber. The anechoic room must be laid with radio frequency absorbing materials, and the minimum performance of the absorbing materials is specified. The minimum distance between the antenna and the EUT is 1 meter, and when the beam width of the antenna cannot cover the entire system, multiple antennas need to be placed. If the EUT contains holes, connectors, seams or other penetration points on the casing, all these parts must be directly exposed to the test antenna, and it is necessary for the EUT to change its position several times during the test.

  Calibration of the RF field is required prior to EUT placement. The RF power required to achieve the specified test level shall be recorded for each antenna used. During EUT testing, a calibrated power level is applied to the antenna at each test frequency. The second method is to use the mode conditioning reverberation chamber, field uniformity calibration and maximum chamber load verification must be performed before using the chamber for the first time or after any modification to the chamber. Field uniformity and maximum electric field strength measurements require the use of a triaxial electric field probe at nine different locations in the chamber. Also, the passive linear antenna needs to be moved to different locations in the chamber to calibrate the antenna before the test. This calibration allows the antenna to be used to measure chamber Q, time constant and chamber load factor during EUT testing. As with the test method using an anechoic chamber, the calibration power level corresponding to each test frequency can be added to the antenna during the test.

  Equipment category

  Section 20 equipment classes are designated by two letters. Conducted sensitivity test levels are indicated by the first classification letter, and radiated sensitivity test levels are indicated by the second classification letter. There are 7 equipment classes for conducted susceptibility and 10 equipment classes for radiated susceptibility. These classifications indicate the level of severity with which the test was performed, and/or the modulation used. The 1V/m of S class is the least severe level, and the L class is the most severe level, which needs to reach 7200V/m. 

  Where is DO-160F new?

  l Reduced number of device classes

  l There is only one test method for conduction sensitivity

  l In the anechoic chamber test method, a clear description has been added for the requirements of the gaps and openings that need to expose the EUT.

 

  Figure 2 Radiation susceptibility test levels (CW and SW) for categories B, D, F, G, and L

  Figure 3 Radiation susceptibility test levels (pulse) for categories B, D, F, G, and L

  Section 21: Electromagnetic Compatibility Test Radio Frequency Emissions

  The tests carried out in this section are used to determine whether the radio frequency interference emitted by the EUT exceeds the specified limit. Tests for conducted RF emissions present in interconnecting cables and power lines. RF radiated emissions from the EUT, interconnecting cables and power lines also need to be tested.

  Testing must be performed using a test instrument having the peak detector, IF bandwidth, frequency step size, and dwell time requirements specified in Section 21, Table 1.

  Each power line and non-ground power return line needs to be connected in series with a LISN, and a 10μF capacitor is connected between the power input terminal of the LISN and the ground plane. Unless otherwise specified, the interconnection cable shall be at least 3.3 meters long and the power cord shall not exceed 1 meter when tested. The ambient radiation level must be at least 6dB below the applicable limit, and any signal within 3dB of the applicable limit needs to be measured and recorded.

  Electromagnetic Compatibility Test Conducted Emissions

  Use clamp-on current probes to test for conducted RF currents in interconnect cables and power lines. The probe is placed at a distance of 5 cm from the EUT, and the measurement frequency range is from 150 kHz to 152 MHz.

  EMC Test Radiated Emissions

  Radiated RF fields are measured using linearly polarized antennas over the frequency range 100MHz to 6GHz. Like the RF radiation susceptibility test in Section 20, there are two RF radiation emission test methods in Section 21: the anechoic chamber method and the reverberation chamber method.

  The anechoic chamber requires the laying of absorbing materials indoors, and the minimum performance of the absorbing materials is stipulated. The distance of the test antenna is 1 meter. When the beam of the antenna cannot cover the whole system, multiple antenna positions are required. If the EUT contains holes, connectors, seams or other leak points on the enclosure, all of these must be directly exposed to the test antenna, and the EUT needs to change multiple positions during the test.

  The second method is to use a reverberation chamber, which requires field uniformity verification as described in Section 20. The EUT load measurement is carried out after the EUT is installed in the anechoic chamber, and these data are used as correction factors in the radiation emission measurement. For each frequency range tested, a minimum of 200 sweeps are required by the analyzer or test receiver per rotation of the tuner.

  Equipment category

  There are four device categories (B, L, M, H or P) that define the location of the device and the distance of the device from the aircraft antenna. In general, the closer the device is to the aircraft antenna, and the closer it is "in direct view" to the aircraft antenna, the stricter the radiation limits.

  Where is DO-160F new?

  l The frequency range of conducted emission has been expanded to 150kHz-152MHz, and the frequency range of radiated emission test has been narrowed to 100MHz-6GHz.

  l Added a new test method in the reverberation chamber for the radiated emission test.

  l In the anechoic chamber method, a clear description has been added for all pores and open parts that need to expose the EUT.

  • Added a new limit category - Class P - that provides additional protection for specific receivers with deeper "dimpled" limits (Figures 4 and 5).

  • The special limit notches included in the radiated emission limits for Class P equipment were added at the last minute at the insistence of the RTCA 159 Special Committee to provide special protection for GPS receivers.

  Figure 4 Class P Conducted RF Emissions Limits - Power Lines

  Figure 5 Class P radiated radio frequency emission limits

  Section 22: Transient sensitivity introduced by lightning

  This type of testing utilizes pin and cable bundle injection into EUT connector pins, interconnection cables and power lines of various types of simulated lightning-induced transient waveforms to determine whether the equipment will perform as specified during or after that period. Pin injection methods are typically used to show damage tolerance and cable bundle tests are typically used to show disturbance tolerance. The third revision of DO-160D released on December 5, 2002, made a lot of revisions to Section 22, mainly adding test procedures, waveforms and test levels to the multi-burst and multi-impact cable harness test method . New waveform group designations (G to K) are also used to cover multi-burst shock and multi-pulse tests.

  pin injection

  In the pin injection test, the EUT is powered normally, so that the circuit under test can operate normally. The test level is defined as the open circuit voltage (Voc) of the specified source impedance of the signal source. For example, waveform 3, test level 2 stipulates that Voc is 250V, short-circuit current (Isc) is 10 amperes, and the required signal source impedance can be calculated as 25Ω from the ratio of Voc to Isc. Adjust the signal source to generate the specified waveform 3, and this transient wave is directly injected into the interface pin. After the test, it is evaluated whether there is any performance degradation of the EUT.

  Cable bundle test

  Cable bundle testing can use cable entry or ground injection to couple transient waveforms into interconnecting cable bundles and power lines.

  The cable entry test method uses injection probes to inject transient waveforms into interconnecting cables and power lines. The ground injection method is very similar to the cable entry method, except that the transient waveform is added between the EUT chassis and the ground plane.

  The EUT is isolated from the ground plane by raising all local grounds and returns, and insulating the equipment box from the ground plane. This step forces transients injected into the cable shield and any other returns back to the ground plane.

  Each power line and ungrounded power circuit must be connected in series with a Line Impedance Stabilization Network (LISN). The AC power supply equipment is connected to the power input terminal of the LISN and the ground plane through a 10 microfarad capacitor, while the DC power supply equipment uses a 33000 microfarad capacitor. capacitance. Unless otherwise specified, this test requires interconnection cables to be at least 3.3 meters long and power cords to be no longer than 1 meter.

  For each waveform, each specified voltage or current test level has a corresponding current or voltage limit. For example, Waveform 2, Test Level 3, specifies a test level (VT) of 300V and a current limit (IL) of 600A. These requirements mean that the signal source output level is increased during the test until the peak-to-peak voltage measured on the single-turn monitoring ring of the injection probe strap is 300V, or until the current introduced into the cable or power line is 600 amps until.

  The cable harness test can be performed using only the single-shock method, or a combination of single-shock, multiple-shock, and multiple-burst methods.

  The single-shock test method is used to characterize the effect of aircraft interior wiring on the harshest aircraft exterior lightning strikes. A single trigger (shock) of the specified test waveform is injected into the cable bundle or cable under test, and each polarity is applied repeatedly for a total of 10 times.

  The multi-burst test method is used to characterize the inductive effect of the internal wiring of the aircraft on the lightning pulse of the multi-shock nature outside the aircraft (Figure 6). The specified test waveform is injected into the bundle or cable under test and repeated for at least 5 minutes for each polarity.

  Equipment category

  Class definitions consist of 5 characters and describe the pin and cable test waveform group and test class.

  The three-pin injection test waveforms are divided into two waveform groups (A and B). The 5 cable bundle test waveforms are divided into 4 groups of single-shock waveforms (C to F), and 4 groups of combined single-shock, multi-pulse, and multi-burst waveforms (G to K).

  Where is DO-160F new?

  • No significant changes in test levels and methods.

  l A clear definition of waveform parameters has been added.

  l Reorganized and improved readability by moving annotations to appropriate paragraphs below icons in test steps.

  l Added guidance for determining test levels for "noise" waveforms.

  Section 23: Lightning Direct Effects

  The tests in this section are used to determine the ability of externally mounted electrical and electronic equipment to withstand severe lightning strikes. The equipment is usually not powered during the tests, and these tests often cause damage (sometimes severely) to the EUT. High voltages of thousands of kilovolts and/or currents of hundreds of kiloamperes are required.

  Equipment category

  The category definition consists of 4 characters and describes the characteristics and severity level of the test waveform used. The first two characters indicate the high voltage impulse additional test category, and the last two characters indicate the high current physical damage test category. The determination of the EUT category should correspond to the lightning impact area where the EUT is installed on the aircraft.

  Where is DO-160F new?

  l A clear definition of test waveforms and methods is added throughout the section, which greatly enhances the practicability.

  l Added tables and improved (increased) illustrations to make the test steps easier to understand.

  l Added category definitions for voltage and current tests.

  l The category definition is clarified, and category F is deleted.

  Section 25: Electromagnetic Compatibility Testing Electrostatic Discharge (ESD)

  This test is used to determine whether the EUT can still operate normally according to the regulations during and after the air electrostatic discharge test. The test procedures and signal sources used are similar to most other international ESD standards, except that the EUT is placed on a grounded plane and that only air discharges are specified. The test points are selected based on the parts in contact with the human body, and 10 positive and 10 negative 15kV discharge tests are required at each place.

  Equipment category

  There is only one category (A), and the test level is 15kV.

  Where is DO-160F new?

  l Apart from the correction of typographical errors in figures and figures, there are no significant updates.

  The latest developments of SC-135:

  From the most recent (March 2008) SC-135 meeting, some examples of items that may change in the future are as follows:

  After many sections of DO-160F, add a "User's Guide" appendix (informative only).

  Section 16 will have more tests and power types.

  Section 20 reintroduces the "stirred mode" as an option to the reverberation chamber test method.

  Section 21 will be revised to include special limits and procedures to focus on the protection of airborne GPS receivers used for navigation.

  Section 25 will be revised to include more test level classifications, contact discharge and indirect discharge tests.

  These revisions, and many more, have been proposed for inclusion in the new DO-160G to be published in December 2020.

  Summarize

  RTCA/DO-160 and its European counterpart—EUROCAE/ED-14, are the world standards required by the electromagnetic compatibility test system for avionics and electrical equipment. The test levels, requirements and steps reflect the latest developments in aviation technology and EMC test methods. In view of the rapid development of aviation technology and EMC electromagnetic compatibility test methods, the next revision RTCA/DO-160 will continue to be studied.

  references

  1. RTCA/DO-160E, "Environmental Conditions and Test Methods for Aviation Equipment", RTCA, Inc., December 9, 2004

  2. RTCA/DO-160D, "Environmental Conditions and Test Methods for Aviation Equipment", RTCA, Inc., July 29, 1997

  3. MIL-STD-461F, "Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems and Equipment", Interface Standards Division, Department of Defense, December 10, 2007


 

  Erik Borgstrom has been working in the field of EMC testing for over 21 years. He is currently an EMC project manager at Environ Laboratories, an expert in EMC testing in the defense and aerospace industries. Mr. Borgstrom is active in IEEE as a member of the Standards Advisory and Communications Committees. He is also the liaison to RTCA of IEEE's EMC chapter. Mr. Borgstrom is also active on SAE Committees AE-2 and AE-4 (HIRF) and is Environ's representative at RTCA, whereby he is a member of RTCA Specific Committee 135 for DO-160 Section 25 (ESD) The modification coordinator for .

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