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所谓现场测试（也称为外场测试），就是将emc测试仪器搬运到产品工作的现场进行的测试。
如风力发电机，大型工业机械设备、铁路系统、因该类产品体积庞大，且需要风力、或者相关配套系统才能正常工作，EMC测试就必须在工厂、铁路轨道或风力发电机安装的等现场进行。
EMC测试中，屏蔽室和电波暗室是必备的测试场地，但随着中国出口业的发展，越来越多大型的设备在出口时需要进行电磁兼容性的测试，如CE-EMC或者FCC。这些大型设备由于体积大，或者重量超过了屏蔽室和电波暗室的承重，或者是需要水、风等外力驱动而无法在密闭的测试室中进行正常测试，这时候，就需要用现场测试的方法来评估EMC性能。
现场测试也称为On-Site test，在CISPR/EN标准中则称为In-situ Test。现场测试对工程师的技术能力要求很高，不仅要熟悉标准的测试方法，对测试仪器也要非常熟悉，而且要有较强的协调和沟通能力，另外，还要对被测试的产品非常熟悉，才能在户外条件下尽快地完成测试。由于现场测试要将测试仪器搬运到被测产品工作的现场，仪器由于搬运和现场条件恶劣，被损坏的风险也较大，目前在国内有能力并且愿意执行现场测试的实验室还较少。
需要现场测试的产品一般工作在户外较恶劣的环境中，申请CE-EMC指令测试时，一般我们建议选择工业环境的EMC标准：EN 61000-6-2:2005，EN 61000-6-4:2007+A1:2011，涉及的测试项目简单归纳如下：
No. | Test Item | Test Requirements | 1. | Conducted Emission EN 61000-6-4 CISPR 16-1-1 as reference) | The EUT should be tested with the whole appliance active, including all modules, full load or at least appropriate load. Output lines( L1/L2/L3/N ), net cable, as well as power lines which can be connected to public power supply should be tested respectively. | 2. | Radiated Emission EN 61000-6-4 CISPR 16-1-1 as reference) | The EUT should be tested with the whole appliance active, including all modules, full load or at least appropriate load. Four surfaces (Front/Rear/Left/Right) should be checked respectively. | 3. | ESD immunity EN 61000-6-2 EN 61000-4-2 as reference) | The whole EUT should be active with appropriate load (such as 10% full load). Test Level: Conduct discharge: +/-4.0kV Air discharge: +/-2.0kV | 4. | RF Electromagnetic Field Immunity EN 61000-6-2 EN 61000-4-3 as reference) | The whole EUT should be active with appropriate load (such as 10% full load). Four surfaces (Front/Rear/Left/Right) should be checked respectively. Level: 10V/m | 5. | EFT immunity EN 61000-6-2 EN 61000-4-4 as reference) | The whole EUT should be active with appropriate load (such as 10% full load). Power supply, DC lines (>3m), net-cable (>3m) should be checked. Test Level: for input or output AC/DC lines: +/-2.0kV; other lines (Signal/net cable(>3m)): +/-1.0kV | 6. | Surge Immunity EN 61000-6-2 EN 61000-4-5 as reference) | The whole EUT should be active with appropriate load (such as 10% full load). Test Level: L/N-PE: +/-0.5kV, +/-1.0kV, +/-2.0kV L-N: +/-0.5kV, +/-1.0kV Note: The test level should be performed from low to high | 7. | Inject Currents Immunity, 0.15MHz to 80MHz EN 61000-6-2 (EN 61000-4-6 as reference) | The whole EUT should be active with appropriate load (such as 10% full load). Power supply, DC lines(>3m), net-cable(>3m) should be checked. Level: 10V/m | 8. | Voltage Dips and Interruption Immunity EN 61000-6-2 (EN 61000-4-11 as reference) | The whole EUT should be active with appropriate load (such as 10% full load). |
For conducted emission and radiated emission test, the ambient noise level should be at least 20 dB below the specified limit. For in-situ tests the ambient noise level should be at least 6 dB below the specified limit. In in-situ cases, the emission plus ambient must not exceed the limit. If the emission plus ambient exceeds the limit, then other methods need to be applied, for example, reduce the bandwidth, apply ambient cancellation, change frequency etc. The suitability of the site for the permitted ambient level may be determined by measuring the ambient noise level with the EUT in place but not operating.
Reference ground is very important for EMC test. The existing ground at the place of installation should be used as reference ground. This should be selected by taking high-frequency (RF) criteria into consideration. Generally, this is accomplished by connecting the EUT via wide straps, with a length-to-width ratio not exceeding 3, to structural conductive parts of buildings that are connected to earth ground. These include metallic water pipes, central heating pipes, lightning wires to earth ground, concrete reinforcing steel and steel beams.
1 Conducted Emission
For conducted emission test, AMN is used as a voltage probe because practical current limitations are exceeded. The principle of test setup is as follows:
NOTE: Exposed pins are made safe.
2 Radiated Emission
OATS is used as test site. Test setup is as follows:
根据同背景噪声比较，剔除背景噪声部分，采用分频段测量方法（Basing on the comparing with Background curve, eliminate the part of background and use the measurement method of discontinued range of frequency） |
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