什么是EMC风险评估?

欧洲 EMC指令(2014/30/EU) 2014年更新, replacing the old directive (2008/108/EC), and became mandatory from April 2016 for any new product entering the EU from that date onwards. The change of directive was aimed at aligning the wording and terminology to ensure it was consistent with other CE标志 directives and implement standard text and modules laid out in the New Legislation Framework (NLF).

The principal objectives of the NLF were to:-

1. Provide legislation governing products that should be clear and more consistent across sectors
2. Clarify the obligations of all economic operators in the supply chain
3. Make provisions such that products are more traceable
4. Ensure that bodies that carry out conformity assessments should have certain attributes (e.g. independence and capability) and certain operational obligations
5. Ensure that each Member State shall have robust, 但比例, market surveillance and enforcement mechanisms in place based on a set of common requirements at the EU level.

As part of the changes that implement the above objectives, ‘risk’ was introduced into all the NLF-affected directives, 包括 EMC指令协调标准.

Risk however has multiple meanings within the directive ranging from risks associated with the product (which is the responsibility of the manufacturer); to products that present a risk which is the responsibility of the market enforcement agencies and actions required by actors in the supply chain where risks have been identified.

What does ‘risk’ mean in the context of EMC?

The EMC Directive requires that manufacturers ‘…shall include an adequate analysis and assessment of the risk(s)…’ but since the EMC directive is all about functionality and does not have any assessment of safety (including electromagnetic safety, 哪些是由其他覆盖的 CE标志 指令，例如 低压指令(LVD)、机械安全; 医疗器械指令(MDD)等.), what type of risks are being assessed?  

为了回答这个问题, it is first important to understand what a 风险分析 and risk assessment are. Risk analysis is the process of identifying all of the potential EM hazards associated with both the product and the environment in which it is going to be used. For each of the risks that have been identified, their impact has to be assessed (risk evaluation). The combination of the 风险分析 and evaluation is called the risk assessment.   

If, 作为这个过程的结果, 剩余风险很高, additional action is required to reduce the risk to a more acceptable level. This latter stage and considering information from other sources (文章 in industry publications for example) and feedback from customers, 焦点小组等. forms the risk management as illustrated in diagram 1.

EMC risk assessment vs risk management

Diagram 1 - Risk Assessment v 风险管理

Many of the hazards identified in a risk assessment will be covered by the application of an applicable ‘harmonized standard’. However, it should be noted that not all hazards and hence risk will be covered in this process.

A harmonized standard provides a ‘presumption of conformity’ to the directive for areas that the standard covers but cannot be used to simply justify that the product will meet the requirements of the directive by a simple application of the harmonized standard without further analysis.

Risk assessment example: Battery powered equipment

举个例子, battery-powered test equipment used for the logging of temperatures in a heating furnace in an industrial process may be assessed against the product-specific standard, En / iec 61326-1 Electrical equipment for measurement, 控制, and laboratory use — EMC requirements — Part 1: General requirements.

This standard contains tests to assess the functionality of the product in the presence of radiated RF fields from intentional transmitters and ISM devices in the frequency range above 80MHz (EN/IEC 61000-4-3). It also defines test requirements for the assessment of RF transmitters and ISM devices below 80MHz (down to 150kHz) and uses the standard EN/IEC 61000-4-6 for this.

The problem is that EN/IEC 61000-4-6 is performed as a conducted assessment since the wavelengths below 80MHz are very long and conduction predominates over radiation.

Does that mean that a manufacturer can simply ignore the test and all frequencies below 80MHz? 简而言之，没有.

The risk identification would (should) identify the fact that 27MHz is a well-used ISM frequency for the treatment of material and is used as the fundamental frequency for many RF heating applications. It will be known that there will be a significant EM field generated and yet there is no assessment if only the tests contained in the standard are performed. The manufacturer would identify this hazard and mitigate the risk by performing additional tests to supplement those defined in the harmonized standard, thus ensuring that the residual risk is low.

The above is just one example of where the application of a harmonized standard alone is not suitable for demonstrating EMC合规 with the EMC Directive – there will be many more, based on the type and use of the product.

风险评估示例:平板电脑

下面是另一个例子, a tablet PC can be used in an environment other than the classic ‘domestic, 商业和轻工业”. Given that a manufacturer needs to think about both the use and also foreseen misuse (part of the 风险分析), it is certainly expected that this type of product will be used on a train, 一辆车, or in much closer proximity to a cellular device than the product-specific standard (CISPR 35 / EN55035)预计. The close proximity of higher power transmitters to products results in the product being exposed to higher levels of EM radiation than the standard covers. All these situations are foreseen and should be covered in the risk assessment.

Most conducted emissions standards start from 150kHz however there is an increasing amount of electrical noise generated below this frequency. 电动汽车充电器, 光伏装置逆变器, and the like all use switching technologies in the low kHz region and produce potentially significant EM emissions. Very few EMC standards require testing below 150kHz due to the unknown compatibility levels (this is a standard body-related issue) but there is significant noise being generated and a lack of immunity tests in the standards to mitigate the risks.

It is important for EM hazards to be considered as part of the overall risk assessment of the product. The safety-related community is very familiar with safety-related risk assessments and is normally based on a wide selection of people with differing focuses. EM knowledge unfortunately is not normally well-represented meaning that EMC safety risks are often overlooked.

Before any 电磁兼容测试 is performed, it should be considered in parallel with the EM safety aspects. 电磁兼容测试 for functionality would require the product to be operating in its normal mode(s) whereas 电磁安全测试 would require a different set of parameters to be assessed (such as a product with an electronic power switch, switching ‘on’ when it should be ‘off’) which would require the standby mode to be assessed as well.

结论

Manufacturers need to ensure that an EM 风险分析 and electromagnetic risk assessment is performed as part of complying with the EMC Directive. The EMC risk assessment needs to be documented and includes the justification that leads to the overall residual risk.

Only the tests contained in harmonized standards provide a presumption of conformity for the parameters that they cover and a manufacturer should supplement these with their overall risk management to ensure that other hazards are identified and assessed accordingly.

EMC风险服务

Risk assessments are not something that can be subcontracted out from a manufacturer since the overall risk always has to lie with them. Understanding EM hazards and how to mitigate these risks however is something that can be outsourced and irrespective of who does it should be considered as part of the overall risk assessment during the product realization phase of bringing a product to market.

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