Discussion on electromagnetic interference measure

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Introduction as an automatic control element with isolation and switching functions, relay has been widely used in satellite, missile, rocket, aircraft, ship, tank, artillery, nuclear plant, radar, communication, computer and other systems. It is an essential control element in various national defense projects. The relay mainly plays the role of signal isolation and transmission, signal expansion and synthesis, automatic control and quantity and program power distribution in the military machine. For example, a new missile uses 970 relays. However, during the storage and use of the traditional contact type relay, its electromagnetic interference and reliability are affected by the poor contact between the contacts, the wear caused by the electric spark arc, the back EMF of the input coil, etc., resulting in a high failure rate of the relay, making the relay indispensable and one of the most difficult components to ensure its electromagnetic interference and reliability

electromagnetic compatibility index is the key index for the whole unit to accept the selected relay, but there is no corresponding test method at present. Generally, the test method of the whole unit is used to test the relay, which can not adapt to the working conditions of the relay as a component. Therefore, it is the purpose and background demand of this project to study the measurement methods of electromagnetic interference emission of relays and the effectiveness, applicability and preciseness of the current test methods

as entrusted by the relay development unit, our center is preliminarily studying the EMC test method for military relays. Its main purpose is to provide the military relay development unit with the basis for the EMC design of products, provide scientific data for the development and finalization of the whole machine, and fill the gap in this aspect in China

military relay is a kind of military components, so it is very necessary to develop the EMC test method for military relay, and it has the timeliness to start preparation at the end of 2016

2. General measurement requirements for emission test

2.1 measurement tolerance

unless otherwise specified for specific test, the tolerance shall be as follows:

1) distance: ± 5%

2) frequency: ± 2%

3) amplitude and measurement receiver: ± 2dB

measurement system (including measurement receiver, sensor, cable, etc.): ± 3dB

4) time (waveform): ± 5%

2.2 environmental noise of the test site

when the test is conducted in the shielding room, the electromagnetic environment level measured when the EUT is powered off and all auxiliary equipment is powered on shall be at least 6 dB lower than the specified limit value. The conductive environment level on the power line shall be measured when the fracture EUT is connected with a resistive load, which shall flow through the same rated current as the tested equipment

when testing outside the shielding room, the test shall be conducted at the time and under the condition that the electromagnetic environment level is at the lowest point

2.3 measurement requirements for radiated emission

the test site shall be flat, without overhead lines and reflective structures nearby, and have enough space to place antennas within the specified distance, and provide sufficient spacing between antennas, tested equipment and any reflective structures

Figure 1 shows the test site that meets the standard. The test site is located in an oval area with a long axis of 20m and a short axis of 17.32m. The tested equipment and the measuring equipment are respectively placed at the focal points 10m apart

Figure 1 Basic test layout of vehicle radiated emission

the natural ground of the test site shall be expanded by a conductive metal grounding plate that can cover the entire area between the tested equipment and the measuring antenna. The metal floor shall extend at least 1m beyond the boundary of the tested equipment at one end and at least 1m beyond the measuring antenna and its supporting structure at the other end. In order to meet the attenuation requirements of the site, it may be necessary to lay conductive floors larger than the surface shown to make a useful exploration on the cluster development model in some sites. The pore or gap size on the conductive metal grounding plate shall not be greater than one tenth of the maximum measured frequency wave

if the test site does not have the above characteristics, evidence shall be collected to prove that the error caused by such site will not invalidate the results obtained. An example of an alternative site is a semi anechoic chamber

the test site shall be made effective by measuring the attenuation of horizontal and vertical polarization sites. The antenna spacing used to measure the site attenuation shall be the same as that of the radiated emission antenna test

if the difference between the measured attenuation value of the horizontal or vertical site and the theoretical attenuation value of the ideal site is not greater than ± 4dB, the test site is considered acceptable

3. Test procedure

3.1 configuration of test pieces

unless otherwise specified, the layout and operation of test pieces shall be consistent with the typical application. If shielded or special cables are used during the test to meet the requirements of the limits, they shall be described in the report

3.2 working state of the test piece

the test piece shall operate under the rated working voltage and typical load conditions according to the design requirements. Actual loads shall be used whenever possible; If an analog load is used, it shall be resistive

the test piece shall work under the working condition of maximum radiation emission. That is, during the test, the rated values of auxiliary excitation and input excitation shall be applied to the corresponding circuits of the tested equipment. When the tested equipment is in the transient action state, the measurement and cleaning method is to adjust its electromagnetic emission

note: the input excitation quantity and auxiliary excitation quantity circuit shall not affect the electromagnetic emission of the test piece

4. Measurement of radiation emission

this test method is used to test the electric field emission of EUT and related wires and cables. During the test, the EUT shall maintain the basic test configuration specified in 3.1, and ensure that the side where the EUT produces the maximum radiation emission faces the measuring antenna

4.1 antenna ground lapping

measured in the shielding room, use a solid core metal strip with the same width as the ground to lap the rod antenna ground to the grounding plate, and the maximum DC lapping resistance between the ground and the grounding plate is 2.5m Ω. Use the test bench of the metal grounding plate and lap the ground to the metal grounding plate

4.2 antenna positioning

(1) determine the EUT and its related cable test configuration boundary for antenna positioning

(2) use the geometric reference point on the antenna shown in figure re102-2 in gjb152a-97 to measure the height and distance from the antenna to the edge of the test configuration

1) for all configurations, the antenna shall be LM from the leading edge of the test configuration boundary

2) except for the 1040 rain pull rod antenna, the antenna shall be 1200ram higher than the ground grounding plate

3) ensure that any part of the antenna is not less than LM from the wall of the shielding room and not less than 0.5m from the top plate

4) for the test configuration using the test bench, the additional positioning requirements for the rod antenna and the distance to the grounding plate of the test bench shall meet the requirements of re102-2 in gjb152a-97

4.3 test method

(1) check the electromagnetic environment level according to 2.2 in this standard, and draw the electromagnetic environment curve if necessary

(2) the test equipment is powered on and preheated to make it reach a stable working state

(3) according to the system inspection path in Figure 1, evaluate the entire system from each antenna to the data output device at its highest frequency point. For the rod antenna using passive matching network, the center frequency of each frequency band is used for evaluation

1) apply a calibration signal to the coaxial cable at the antenna connection point, and its level is 6dB lower than the limit value of GJB151A minus the antenna coefficient

2) scan the measuring receiver according to the normal data scanning method, and check whether the indication level of the data recording device is within the range of -i-3db of the injected signal level

3) for the 1040mm pull rod antenna, remove the pull rod and apply a signal to the antenna matching network through a 10PF capacitor connected to the base

4) if the reading deviation obtained exceeds ± 3dB, find out the cause of the error and correct it

(4) using the measurement path of the basic test layout for radiation emission measurement, the following evaluation shall be conducted for each antenna to confirm that the antenna is intact and available

1) use the antenna or short rod radiator to radiate signals at the highest use measurement frequency point of each antenna

2) adjust the measuring receiver to the added signal frequency and check whether the received signal is appropriate

(5) EUT is powered on for preheating. Make it work stably

(6) determine the radiation emission of EUT and its related cables according to the measurement path arranged for the basic test of radiation emission measurement

1) use the bandwidth and minimum measurement time specified in Table 2 of article 4.9.3 of gjb152a-97 General requirements to make the measurement receiver scan within the whole applicable frequency range

2) for frequencies above 30MHz, the antenna shall be horizontally polarized and vertically polarized

(7) data provision

1) continuously and automatically draw the relationship curve between amplitude and frequency, and do not accept manually collected data except for verifying the curve

2) each curve shall reach at least 1% or twice the frequency resolution of the snapshot receiver bandwidth (whichever is lower) of go and go-pda models with different moisture content and at least LDB amplitude resolution

3) provide two groups of curves for EUT test and measurement system calibration and inspection in the test method

4) provide the description of checking the integrity of the measuring antenna determined in Clause 4.3.4. (end)

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