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Discussion on radiation emission experiment of large equipment


 

       The detection of large-scale equipment has always been a difficult point in electromagnetic compatibility, and how to distinguish it as a large-scale equipment is also a difficult point, "GBZ 6113.205-2013 Radio Disturbance and Immunity Measurement Equipment and Measurement Method Specifications Part 2-5 Large-scale Equipment Disturbance Emission Field Measurement" The description for large equipment is as follows:

Physically large equipment】

>Commercially large equipment formed by functionally linking a group of equipment that can be clearly considered as a whole separate from its surroundings.

Note 1: When the overall size of the equipment exceeds the range that can be tested on the traditional 10m test site, it can be regarded as large equipment.

Note 2 to entry: Large equipment can be considered to be separated from the environment and other external systems by means of a disconnected imaginary interface.

Note 3: For the purpose of this guidance technical document, a component of large equipment refers to such objects as equipment, instrument units or subsystems. They are interrelated to achieve the performance goals of a function or group of functions.

       This description is relatively vague. For example, for Note 1, with the development of anechoic chamber technology, many 10-meter anechoic chambers can achieve a quiet zone size of 6 m or even 8 m. Test, in the standard "YDT 1633-2007 Field Test Method for Electromagnetic Compatibility", a test distance of 30 meters is very clearly recommended, see the following documents:

A.5.3 Test distance】

>GB4824 requires the distance between the test antenna and the device under test to be 30m.

>If the field strength cannot be measured at a distance of 30m due to too high ambient noise or other reasons, you can choose a shorter distance for testing, such as 10m or 3m.

>When the distance changes by 10 times, use a proportional coefficient 20dB that is inversely proportional to the distance change to normalize the measurement results to the distance specified by the standard to determine whether the requirements are met. (For example, reducing the antenna distance from 30m to 10m means increasing the emission limit specified by EN61000-6-4 by 10dB. Reducing the distance from 30m to 3m means increasing the corresponding emission limit by 20dB.)

>If the DUT size is larger than 3m, be very careful when measuring at 30MHz, because the near-field effect will make the measured value larger.

       The latest version of GB4824-2013 has a clear limit for the EUT size corresponding to the darkroom. In the old standard radiated emission test, Class B equipment allows 3m method testing, but Class A equipment only allows 10m method testing, because Class A equipment Most of them are used in industrial environments, and most of them are large-scale equipment. The near-field effect must exist in the 3 m method test to affect the test results. Due to the high cost of the 10 m method anechoic chamber, this provision of the standard restricts the testing of Class A equipment for many laboratories; after the implementation of the new standard, the radiation emission test of Class A equipment is more clear, allowing small equipment ( 1.2 mx 1.5 m, diameter X height) for the 3 m method test, but the Class A equipment beyond this size must be tested for the 10 m method.

From the above standards, we believe that the 3m method is recommended        for small equipment (1.2 mx 1.5 m, diameter X height), and the 10m or 30m method is recommended for large equipment (3.0 mx 3.0 m, diameter X height). For equipment beyond the definition of large equipment (3.0 mx 3.0 m, diameter X height), the 30m test should be strictly adopted.

       For the height of the test antenna, "GBZ 6113.205-2013 Radio Disturbance and Immunity Measuring Equipment and Measurement Method Specification Part 2-5 Field Measurement of Disturbance Emission of Large Equipment" also has a very clear description:

[ 6.3.3 Based on fit-for-purpose measurements]

> It is recommended to carry out radiation emission measurement according to GB/T6113.203, and conduct compliance assessment according to the corresponding limit value at the distance specified in 6.1.

Note 1: Due to the imperfection of the measurement arrangement compared with the standard test site, such as the existence of reflectors, the measured results obtained may not directly correspond to those theoretical values ​​obtained at the standard test site, which should be taken into account when evaluating the results. a little. There are still some aspects that need further consideration. It is recommended to change the height of the measurement antenna within the specified range to obtain the maximum reading. The general regulations when the measurement distance is less than or equal to 10m are as follows: when measuring the electromagnetic field, the antenna height should be changed between 1-4m, and when the measurement distance is greater than or equal to 30m When the antenna height is preferably changed between 2-6m, these changes are applicable to both horizontal polarization and vertical polarization. In extreme cases, i.e. when the device under test is installed at a high level from the ground and potential interfered-with devices are also located at a similar height, it may be necessary to take the above height into account when placing the measuring antenna during the actual test. When the position of the equipment under test and the measuring antenna are very different on the ground, it may be necessary to tilt the antenna according to the direction of the antenna to obtain the maximum reading.

Note 2: The inclination angle should not exceed 70 degrees. It is recommended to conduct tests at different locations around the EUT. The number of locations should be selected taking into account the site conditions and the physical size of the EUT.

       Based on the above standards, it can be seen that for large-scale (non-movable) equipment on site, the preferred measurement method is the 30m test, and the antenna height is moved within the range of 2-6m, including horizontal polarization and vertical polarization.

       For large mobile equipment (usually considering the transportation conditions, it is limited by the current road transportation conditions, usually the height needs to be less than 4.5m , and the size of these equipment is less than 3m*3m*3m (length*width*height)), Then the 10m method can be used for testing, and the antenna height can be moved within the range of 1-4m, including horizontal polarization and vertical polarization.

       This is also the idea of ​​the typical 10m method design, that is, considering the transportation conditions, the size of the door is less than 4m*4m, even if the size of the turntable inside the darkroom or the size of the quiet zone exceeds 3m, it is usually not recommended to test those exceeding 3m*3m* There is no need to design a 1-6m antenna tower for a product with a size of 3m (length*width*height).

       Therefore, the typical 10m method darkroom, in fact, the real utilization rate is to test products with a size below 3m*3m*3m (length*width*height). The actual situation is that the equipment exceeding this size needs to be assembled on site. These equipment Either the power exceeds the design specification of the darkroom (usually the filter design of the darkroom is within 200A), or the weight exceeds the weight that the darkroom floor can bear (usually the floor design weight of the darkroom is within 5 tons), or the height exceeds the height range that the darkroom can bear (Usually the design net height of the darkroom is less than 7m), and no matter what the case is , the 10m method darkroom cannot be used for testing.

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