RU2497282C9 - Method of evaluating electromagnetic compatibility of aircraft on-board equipment in frequency range from 10 khz to 400 mhz - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: aircraft radio transmitters are interference sources, said transmitters alternately affecting through on-board transmitting antennae electrical circuits of on-board equipment with radio interference in the frequency range from 10 kHz to 400 MHz.

EFFECT: high reliability and accuracy of testing electromagnetic compatibility of aircraft equipment, which is achieved by measuring the value of current induced by on-board interference sources in electrical circuits of on-board equipment using an inductive current measurement sensor and introducing as a criterion for providing electromagnetic compatibility of the test on-board equipment, an electromagnetic compatibility safety factor, determination during testing of which enables to evaluate not only presence, but the also the impact of radio interference on aircraft on-board equipment.

2 dwg

Description

Technical field

The invention relates to the field of testing of electronic and electronic avionics equipment (BO) of aircraft for electromagnetic compatibility (EMC), and in particular, to a method for evaluating the BMS EMC in an aircraft and can be used in tests to assess the effect of radio interference on-board radio electronic equipment (Avionics) in the frequency range from 10 kHz to 400 MHz, including the extreme values of the range induced in the power supply circuits, information circuits, BO control lines.

State of the art

When an aircraft is irradiated with an electromagnetic field, on-board equipment as part of an aircraft is affected by two types of electromagnetic effects: currents induced in the on-board circuits and electromagnetic fields weakened by the aircraft fuselage. At lower frequencies (from 10 kHz to 400 MHz), the first type of electromagnetic effect in the form of induced currents in onboard electrical circuits prevails. The currents induced in the electrical circuits penetrate the electronic components and act on non-linear elements (diodes, transistors, microcircuits), which can lead to malfunctions and failures in the operation of the BO.

In the frequency range above 400 MHz, the radio noise currents quickly decay along the length of the wire of the electric circuit and practically do not reach the input circuits of nonlinear BO elements. Therefore, the EMC assessment by measuring the radio noise current in the on-board electrical circuits can only be carried out at frequencies up to 400 MHz.

During qualification tests for radio frequency susceptibility to conductivity interference in the frequency range from 10 kHz to 400 MHz for compliance with the requirements of Section 20 “Qualification requirements of KT-160D” [Qualification requirements of KT-160D. Operating and environmental conditions for avionics. (External factors - WWF). Requirements, norms and test methods. IAC Aviation Register, 2004], which are carried out prior to the installation of BOs on aircraft, the equipment is exposed to test signals generated by current injectors in BO electric circuits with levels corresponding to the selected categories of equipment. Categories of equipment are specified in the technical specifications for BO and are determined by the location of the equipment, the expected impacts, the location of the connecting wiring, the size of the aircraft and its design.

However, in addition to bench qualification tests, it is necessary to additionally carry out certification tests of on-board equipment for electromagnetic compatibility as part of the aircraft, so that during operation they do not create such electromagnetic interference to radio, radio communication equipment or electronic devices that lead to a violation of their performance or the occurrence of special situations [Aviation Rules. Part 23-29. NLGS. Requirements, norms and test methods. IAC Aviation Register, 2004].

There is a method of evaluating the EMC of ship technical equipment [RF patent for the invention No. 2374654, G01R 29/08 (2006/01) "Method for assessing the electromagnetic compatibility of ship technical equipment and the hardware complex for its implementation"], which consists in determining the electromagnetic field using a sensor ( EMF) of the characteristics of an external EMF in the immediate vicinity of the technical equipment under test (ITS) and their registration in a storage device. Based on these characteristics, parameters are set and an electromagnetic field corresponding to these parameters is formed that irradiates the ITS. The formation of EMF is carried out in cycles consisting of two parts. During the first cycle, the current discrete sequence of samples of the external EMF level is recorded, during the second cycle, the formation of the EMF irradiating the ITS is produced.

The formation is carried out by setting its level by reproducing the registered discrete sequence of samples of the external EMF level converted into analog form. Then, a sequential increase in the level of the irradiating EMF is carried out until the response of ITS to the effect of EMF is fixed. The EMC of the technical means with the adjacent technical means of the ship is estimated by the ratio of the EMF level, which leads to the appearance of the response of the ITS to the initially registered EMF level.

This method of evaluating EMC requires the creation of a special hardware test suite, which includes an electromagnetic field sensor, a control device, a storage device, an amplifier with a gain control, an electromagnetic field emitter, and an indicator that displays the characteristics of the electromagnetic field. In addition, when using this method to assess the degree of influence of EMF, it is required during the experiment to increase the level of EMF until a response is obtained from each tested ship’s technical equipment. This increases the test time and cost of their implementation.

A known method for evaluating EMC at a separate object [patent GB 2256057 (A) "Testing electrical systems for electromagnetic compatibility"] by injecting a high level current into the electrical circuits of the tested equipment with simultaneous monitoring of the performance of the tested equipment according to the selected criteria. However, to conduct such tests at the facility, the transfer characteristics of the electrical circuits of the equipment under test should be previously measured by the low-level scanning current method, then the electromagnetic field around the object created by the radio interference sources is determined. Using data on the magnitude of the electromagnetic field and the numerical values of the current transfer characteristics, a large level current is injected into the electrical circuits of the equipment during testing. This test method is expensive and time-consuming - it requires laborious preliminary measurements of the current transfer characteristics of electric circuits and an additional assessment of the electromagnetic environment around the test object.

Closest to the proposed method, adopted as a prototype, is a method for evaluating the EMC BO as part of an aircraft, which consists in assessing the state and parameters of the BO before and after turning on the radio noise on board the aircraft [Typical method for assessing the electromagnetic compatibility of on-board radio equipment installed on aircraft GA. Gos. Research Institute "Air Navigation", State. SC "LII them. M.M. Gromova. " Moscow, 1995]. At the same time, the presence of failures or malfunctions in the BO operation is recorded according to the indications of the means of visual display of information (indicators, control devices, etc.) and by changing equipment parameters recorded using standard on-board devices for recording flight parameters or using a specially set for the time test system on-board measurements.

However, this method of testing BOs for electromagnetic compatibility requires lengthy preparation — development of a list of registered parameters, software for primary and secondary processing of test results, development and installation of an on-board measurement system on an aircraft. Evaluation of the effect of radio interference on the BO by the crew using the means of visual display of information is subjective and does not exclude the presence of errors. In addition, this test method only allows you to identify the presence of influence, not allowing you to quantify the degree of this influence, does not provide a quantitative assessment of the margin of electromagnetic compatibility of the tested BO.

The technical result, to which the claimed invention is directed, consists in increasing the reliability and improving the accuracy of the BO tests for EMC in the composition of the aircraft.

In order to achieve the indicated technical result in the method for evaluating the EMC of on-board equipment as part of an aircraft in the frequency range from 10 kHz to 400 MHz, including the extreme values of the range, which consist of sequentially switching on electromagnetic radiation sources of radiation - radio transmitters of on-board electronic equipment that are transmitted through on-board transmitting antennas sequentially affect radio interference on the test BO, in assessing its performance before and after switching on the radio interference on board L And, additionally, after switching on the radio noise source, the interference currents induced in the electrical circuits of the equipment under test are measured — I room, for which an induction measuring current sensor is located at a distance of five centimeters from the input connector on the electrical circuit of the aircraft under test equipment (the distance corresponds to the requirements of Section 20 “Qualification Requirements” KT-160D "). An induction measuring current sensor is connected via a high-frequency cable to a spectrum analyzer that measures the level of interference voltage. The induced current level is determined in each electric circuit BO taking into account the transfer impedance of the current sensor Z according to the formula:

I room = U pom. - Z, where (1)

I room - measured level of interference current, expressed in dB mA.

I room [dB mA] = 201g I aux. [mA];

U room - the level of interference voltage measured by the spectrum analyzer at the operating frequency, expressed in dB mV,

U room [dB mV] = 201g U aux. [mV];

Z is the transfer impedance of the current sensor, expressed in dB Ohm.

Z [dB Ohm] = 201gZ [Ohm].

Measured using an induction measuring sensor induced in the electrical circuits of the equipment under test interference current I aux. compare in the frequency band of the source of radio interference with the maximum allowable interference current I add., corresponding to the level of conductivity susceptibility tests for a given category of the investigated BO before installation on the plane. The category of equipment is set before the installation of the BO on the aircraft in the terms of reference for the BO in accordance with the requirements of section 20, "Qualification requirements of CT-1 60D."

If the requirement for each measured electrical circuit is satisfied by the following conditions:

$$Id\mathrm{about}P.-IP\mathrm{about}m.>0\text{where (2)}$$

I add. - permissible interference current level, expressed in dB mA,

I add. [dB mA] = 201g I add. [mA];

I room - measured level of interference current, expressed in dB mA; and at the same time there are no disturbances in the performance of the equipment under test, then they conclude that the EMC is provided in the frequency range from 10 kHz to 400 MHz and the margin of safety EMC A in decibels is calculated from the current measurements by the formula:

$$\Delta \left[dB\right]=Id\mathrm{about}P.-IP\mathrm{about}m.(3)$$

Based on the results of this assessment, they judge the need to develop additional measures to ensure EMC.

Thus, the proposed method improves the reliability of tests by measuring the current of radio interference in the frequency range from 10 kHz to 400 MHz in the electrical circuits of the equipment under test in the real electromagnetic environment of the aircraft with simultaneous monitoring of the operability of the tested onboard equipment. In addition, the accuracy of the tests is improved due to the introduction of an EMC safety factor tested by the BO as a criterion for ensuring EMC, the determination of which during the test process allows us to evaluate not only the presence, but also the degree of exposure to radio interference on the BO LA.

The invention is illustrated by the drawings shown in figure 1 and figure 2.

Figure 1 shows the structural diagram of the EMC tests of onboard equipment as part of the aircraft.

Figure 2 shows the control line (9), corresponding to the maximum allowable induced current I add. for a given category of equipment, and the results of measurements of the induced current I pom. (10) when tested for electromagnetic compatibility of BO.

The method is as follows.

The tested equipment (1) as part of an aircraft is exposed to radio interference from sources (7), on-board radio transmitters, connected in series to the radiation, from which, through the on-board transmitting antennas (8), radio interference affects the on-board electrical circuits and induces interference currents penetrating into the blocks of the tested equipment.

Since the occurrence of possible failures and failures in the operation of the BO depends on the level of the interference current induced in the on-board circuits at the input of the equipment blocks, to assess the influence of radio interference, an induction measuring current sensor (2) is used, installed at a distance of about five centimeters from the input connector of the equipment under test on an on-board electrical circuit (5) suitable for the equipment under test (1) from the load (6) (the distance complies with the requirements of section 20 “Qualification requirements of KT-160D”). An induction sensor is connected via a high-frequency cable (3) to a spectrum analyzer (4). A spectrum analyzer (measuring receiver) and an induction measuring current sensor of serial production are used.

The magnitude of the induced interference current - I pom. (10) is measured using an induction current sensor connected through a high-frequency cable (3) to a spectrum analyzer (4), which measures the level of interference voltage U pom. Level of induced current I apt. determine in each electric circuit BO taking into account the transfer impedance Z of the current sensor at the operating frequency according to the formula 1.

Compare I pom. (10) in the frequency band of the radio interference source with the control line of the current of the maximum permissible interference current - I add. (9), which corresponds to the level of conductivity susceptibility tests for a given category of the investigated BO before being installed on an airplane, by formula 2 and determine the EMC safety factor by formula 3.

During the tests, the equipment operability is also monitored. The measurement results during the tests are shown in figure 2.

Thus, by measuring the amount of radio noise current I aux. Induced in the on-board electrical circuits of the BO, and then comparing it with the qualification requirements - I add., We can conclude that the EMC of the equipment under test is provided. If the level of induced currents in the on-board circuits is less than the qualification requirements for the equipment, the EMC safety factor Δ [dB] is greater than zero and there is no disturbance in the performance of the equipment under test, then it is concluded that the EMC of the airborne equipment is provided with the EMC safety factor Δ [dB ].

Based on the results of all measurements, a numerical assessment of the effect of radiation from on-board sources of unintentional interference on the electrical circuits of the equipment under test is made and a general assessment is made to ensure the EMC of the aircraft equipment. Based on the results of this assessment, they judge the need to develop additional measures to ensure EMC.

Example

In this way, we evaluated the EMC of an on-board radio station (7) in the meter wavelength range (118-137 MHz) with an on-board air signal system (SHS) (1), which was tested before being installed on an aircraft for susceptibility to conductivity interference in category W, which corresponds to the maximum permissible interference current I add., equal to 43.5 dB mA. Control line I add. (9) is shown in FIG.

During EMC tests as part of the aircraft, an Fischer type F-55 induction current measuring sensor (2) was installed on the on-board electrical circuit (5) connected to the tested SHS system (1) from the load (6) at a distance of five centimeters from the input connector system and connected to a spectrum analyzer (4) from Rohde & Schwarz type FSH8. Then the radio station (7) was turned on for radiation at its operating frequency. On the screen of the spectrum analyzer (4), at a given operating frequency, the measured interference voltage was recorded and determined, in accordance with formula 1, the level of the induced interference current in the electric circuit of the BOF I room, equal to 35.5 dB mA. Current I room (10) is shown in FIG. In accordance with formula (3), the EMC safety factor was determined.

Since the induced current is less than the permissible and at the same time there is no disturbance in the performance of the equipment under test, we conclude that the EMC of the air signal system and radio station at the operating frequency is provided with an EMC margin of 8 dB.

Claims (1)

A method for assessing the electromagnetic compatibility (EMC) of on-board equipment in an aircraft in the frequency range from 10 kHz to 400 MHz, including the extreme values of the range, comprising sequentially turning on the radio transmitters of the on-board radio-electronic equipment to radiation, acting through the on-board transmitting antennas with radio interference on the tested on-board equipment (BO) ), evaluation of the operational efficiency of the BO before and after turning on the radio noise on board, characterized in that, in addition, after turning on the source of radiation the interference in the electrical circuit of the equipment under test sequentially measures the induced interference currents Im, for which an induction measuring current sensor is located at a distance of five centimeters from the input connector on the electrical circuit of the equipment under test, connected via a high-frequency cable to a spectrum analyzer that measures the level of interference voltage , and taking into account the transient impedance of the current sensor Z, the induced current level in the electric circuit is estimated by the formula
I room = U room-Z,
where I pom. - the level of the induced interference current in the electrical circuit, expressed in dB mA, I pom. [dB mA] = 201g I aux. [mA];
U room - the interference voltage level measured by the spectrum analyzer, expressed in dB - mV, U aux. [dB mV] = 201g U aux. [mV];
Z is the transient impedance of the current sensor, expressed in dB Ohm,
Z [dB Ohm] = 201g Z [Ohm];
compare I pom. at the operating frequency of the radio noise source with the maximum allowable current I add., I add. [dB mA] = 201g I add. [mA] corresponding to the level of susceptibility tests to conductivity interference depending on a given category of the investigated BO before installation on the aircraft, while the category of equipment is set before the installation of the BO on the aircraft in the technical task on the BO, and if the requirement for each measured electric circuit of the BO is satisfied the following conditions
I extra-I room> Oh,
and at the same time there are no disturbances in the operability of the equipment under test, then they conclude that the EMC is provided in the frequency range from 10 kHz to 400 MHz and, according to the results of current measurements in the electric circuits of the BO, the EMC safety factor is calculated by the formula
Δ [dB] = I extra-I pom., Where Δ EMC safety factor, expressed in decibels;
according to the results of this assessment, they judge the need to develop additional measures to ensure EMC.

Images