Radiated Emission Test
The Radiated Emission test is to measure the radiated disturbance field strength transmitted by the EUT through space. It can be divided into magnetic field radiation and electric field radiation. The former is aimed at lamps and induction cookers, while the latter is widely used. In addition, home appliances, power tools, and auxiliary equipment of AV products have requirements for power radiation (called disturbance power).
1. Radiated emission test standard:
a) Electric field radiation: CISPR22, CISPR13, CISPR11, CISPR14-1, CISPR15 (specific categories of toys);
b) Magnetic field radiation: CISPR15 (lamps whose working current frequency exceeds 100Hz), CISPR11 (induction cooker);
c) Disturbance power: CISPR14-1 (except for some equipment whose operating frequency does not exceed 9kHz), CISPR13 (only for auxiliary equipment).
2. Radiated emission test method
1) Radiated emission testing instruments and equipment:
a) Electric field radiation: receiver (below 1G), spectrum analyzer (above 1G), anechoic chamber, antenna (below 1G generally use dual
Combination of cone and logarithmic period or broadband composite antenna, horn antenna above 1G);
b) Magnetic field radiation: receiver, three-loop antenna or single small-loop remote antenna;
c) Disturbance power: receiver, power absorption clamp.
The receiver follows the requirements of CISPR16-1-1, the antenna and site follow the requirements of CISPR16-1-4, and the absorption clamp follows the requirements of CISPR16-1-3.
2) Radiated emission test Test arrangement:
a) Electric field radiation: it is also divided into desktop and floor type, which is the same as conducted emission (because the relationship between radiation emission results and product layout
It is particularly close, so it is necessary to arrange the tested samples including products, auxiliary equipment, all cables in strict accordance with the standard);
b) Magnetic field radiation: Three-loop antennas of different sizes have limitations on the maximum size of the EUT that can be tested. Taking a ring-shaped three-loop antenna with a diameter of 2m as an example, the EUT with a length of less than 1.6m can be placed in the center of the three-loop antenna for testing; In CISPR11, the induction cooker with a diameter of more than 1.6m is measured at a distance of 3m with a single-loop far antenna with a diameter of 0.6m, and the minimum height is 1m;
c) Disturbance power: It is divided into desktop and floor type. The desktop equipment is placed on a non-metallic table of 0.8m, and it is at least 0.8m away from other metal objects (usually the metal inner wall of the shielded room. This distance is required to be at least 0.8m in CISPR14-1). 0.4m); the floor-standing equipment is placed on a non-metallic support of 0.1m; the cable under test (LUT) is arranged on the guide rail of the power absorption clamp with a height of 0.8m and a length of 6m, the absorption clamp is sleeved on the cable, and the current transformer end towards the device under test. If the device under test has other cables, disconnect those that can be disconnected without affecting the function, and isolate those that cannot be disconnected with ferrite absorbing clamps.
3) Radiated emission test frequency band: The electric field radiation is generally 30MHz-1GHz (some products need to be measured over 1G, according to specific standards), the magnetic field is 9kHz-30MHz, and the disturbance power is 30-300MHz.
4) Radiated emission test limit: with different standards, the site is 3m, 10m or other sizes, different product classifications (Group 1/2, Class A/B) have different limits.
5) Radiated emission test process:
a) 30MHz-1GHz electric field radiation: carried out in a semi-anechoic chamber, the EUT rotates 360 degrees with the turntable, and the antenna is at a height of 1-4m
Go up and down and look for the radiation maximum. The result is represented by the QP value. Both vertical and horizontal antenna polarization directions are measured.
b) Electric field radiation greater than 1G: ITE equipment whose operating frequency exceeds 108MHz and ISM equipment whose operating frequency exceeds 400MHz need to be tested at a 3m site using a spectrum analyzer. The test method of ITE equipment is basically the same as 30MHz-1GHz, and the results are expressed by Peak and AV values. The products of ISM are a little different and need to be measured in a full anechoic chamber. The antenna is at the same height as the product and does not rise and fall, and the turntable still rotates to find the maximum radiation value;
c) Substitution method: use ERP (effective transmit power) instead, and then convert it into a field strength value. This is often used in RF testing, and conventional EMC is rarely used. The purpose of the substitution method test is to test the shell radiation of the EUT, and all detachable cables need to be removed, and the non-detachable cables are covered with ferrite rings. First use antenna A and receiver to measure the maximum disturbance value of EUT, then replace EUT with antenna B, adjust the output power of the signal generator until the measurement receiver reaches the same value. Record the input power of the substitute antenna B, which is the shell radiated power of the EUT. The selection of the antenna is determined according to the test frequency;
d) Magnetic field radiation: There is nothing to say about the magnetic field radiation test using the three-loop antenna. The sample is placed in the center of the antenna, and a set of magnetic field radiation results are measured in each of the three directions of X/Y/Z. When using a single small loop antenna, the antenna is placed vertically on the ground, and the lowest part is 1m higher than the ground. Because it is a near-field measurement and the reflection of the ground is considered, the measured value reflects the horizontal and vertical magnetic field components of the EUT;
e) Disturbance power: All cables with a length of more than 25cm (including cables of auxiliary equipment) need to be carried out. Because the disturbance at different frequency points within 30-300MHz is distributed in the form of standing waves in the tested cable. Therefore, in the measurement, it is necessary to pull the power absorption clamp along the guide rail to find the position where the disturbance power of each final measurement frequency point is the largest (approximately at a distance of half wavelength from the device).
3. Judgment of radiation emission test results:
Still comparing with the limit line. Below PASS, above FAIL.
4. Precautions for Radiated Emission Test:
Test placement is still the most required part of testing. In addition, because it is a high-frequency test, the venue, equipment, etc. are all very important factors that will affect the final result.
5. Radiated emission test range 30MHz-18.5GH