无线模块对 EMC 测试布局的影响

结论：无线功能让「测什么状态」变成一个需要专门设计的问题

现在很多康复辅具和医疗设备带无线功能——蓝牙连接手机应用、无线数据上传、无线遥控。无线模块的存在给 EMC 测试带来几个新问题：

设备自己在发射。 无线模块工作时的发射与设备的无意发射叠加，测发射时要处理这个问题。

设备自己的发射可能干扰自己。 无线模块对设备其他部分的影响。

抗扰度测试中无线链路可能中断。 链路中断算不算失效，取决于它是否属于基本性能。

测试状态的组合变多。 无线开/关、连接/未连接、传输/空闲，各状态的表现可能不同。

所以带无线功能的设备，测试方案的设计比不带无线的复杂得多，而方案不清楚会导致测试反复或者结果不可信。

布局的原则

无线设备的测试布局要处理几件事：

通信对端的位置。 与设备通信的另一端（手机、接收器）放在哪里，距离多少，是否在测试场地内。

对端设备的影响。 对端本身也是电子设备，它的发射可能被计入测量。

线缆布置。 与非无线设备相同的布置要求，但无线设备可能线缆更少，布置的自由度反而带来一致性问题。

天线方向。 设备内置天线的方向性影响发射测量结果。

辅助设备的隔离。 用于维持通信的辅助设备应当尽量隔离或远离。

「对端设备的位置」是最需要明确记录的一项。 位置不同，测出的结果可能差别明显，而且别人按你的记录复现时，位置不明确就复现不了。

测试状态的设定

建议按以下思路确定测试状态：

列出所有的工作模式。 无线的开关、连接状态、数据传输状态、以及设备的功能模式。

分析各模式的发射特性。 哪个模式的发射最大，通常选该模式做发射测试。

分析各模式的敏感性。 哪个模式最容易受干扰，选该模式做抗扰度测试。

确认是否需要多模式测试。 如果不同模式的特性差别大，可能需要分别测。

记录选择的理由。 为什么选这些状态，理由要写下来。

「选最不利状态」是通用原则，但前提是知道哪个状态最不利。这需要预先做一些摸底测量，而不是凭猜测。

发射测试的处理

无线模块的有意发射与设备的无意发射要分开看待：

有意发射。 无线模块按其自身的要求考察（通常是无线电方面的要求）。

无意发射。 设备的 EMC 发射要求。

测量时的处理。 无线模块的工作频段在 EMC 发射测量中的处理方式要明确——通常有相应的规定，但需要在方案中说清楚。

谐波与杂散。 无线模块的谐波可能落在 EMC 关注的频段内。

建议在测试前先做一次预扫，看清楚哪些峰来自无线模块的有意发射，哪些是设备的无意发射。分不清楚就无法正确判定。

抗扰度测试的处理

抗扰度测试中，无线设备的核心问题是：通信链路中断算不算失效？

答案取决于链路是否承载基本性能。 如果无线链路传输的是关键的控制指令或监测数据，中断就是基本性能的丧失；如果只是传输非关键的统计数据，短暂中断可以接受。

所以这个判断要回到基本性能的定义上 ——而基本性能的定义应当在测试之前就明确。

判定准则要具体。 不是笼统说「通信正常」，而是说清楚：允许中断多久、中断后是否应当自动恢复、恢复需要多长时间、中断期间设备的行为是什么。

「中断后自动恢复」的验证值得强调。 抗扰度测试中链路中断后，设备能否在干扰消失后自动重连，是实际使用中很重要的特性。

共存方面的考虑

无线设备在实际使用中会遇到其他无线设备，共存是实际问题：

同频段的其他设备。 常用频段上设备密集。

医院环境的特殊性。 医疗机构中无线设备很多。

干扰下的降级行为。 通信质量下降时设备应当如何表现。

重连机制。 链路中断后的恢复。

共存方面的验证不完全属于 EMC 的范围，但它对应实际使用中的问题，值得考虑。特别是对依赖无线链路实现关键功能的产品。

送检准备的建议

提供完整的无线参数。 频段、功率、调制方式、天线特性。

提供通信对端。 送检时把配套的手机、接收器一起送，并说明配置。

说明各工作模式。 以及如何切换。

明确基本性能。 包括无线链路的地位。

提供监测方法。 测试中如何判断设备工作正常、链路是否正常。

准备演示软件或工具。 便于在测试中观察设备状态。

「监测方法」这一项如果准备不足，测试会很低效。 实验室需要在干扰施加过程中判断设备是否正常，如果没有便捷的监测手段，判断就很困难。

各类无线功能的差异

不同的无线用途，在测试上的侧重不同：

无线遥控是风险较高的一类。 干扰可能导致遥控失灵（设备不响应）或者误动作（设备执行了未发出的指令）。后者的风险更大，设计上应当有措施防止——比如指令校验、超时机制、以及需要持续信号才动作的逻辑。

天线与结构的影响

内置天线的产品，结构对无线性能和 EMC 都有影响：

天线位置。 靠近金属件会影响性能，也改变发射分布。

外壳材料。 金属外壳屏蔽电磁波，天线需要开窗或外置。

接地设计。 天线的接地面积和形式影响辐射特性。

内部布线。 高速信号线靠近天线会增加干扰。

这几项在设计阶段处理成本低，产品定型后再改成本高。 建议在结构设计时就把天线位置和周边环境考虑进去。

我们的做法

承接带无线功能的设备时，我们会先确认三件事：无线链路是否承载基本性能、通信对端的配置、以及各工作模式的差异。 这三点明确之后，测试状态和判定准则才能定下来。

测试布局方面，我们会完整记录对端位置、天线朝向、线缆布置，因为这些是结果可复现的前提。 记录不全的测试，复测时可能得到不同结果。

如果你有带无线功能的产品需要安排 EMC 测试，想先理清测试状态怎么定，可以把无线参数和功能说明发过来一起讨论，或者直接联系：132 4819 8029。能力范围见服务介绍，送检要求见送检要求，流程见检测流程。

English version

Conclusion. Many rehabilitation and medical products now include wireless functions, connecting to phone applications by Bluetooth, uploading data wirelessly or accepting wireless control. A wireless module introduces several new problems for electromagnetic compatibility testing. The equipment transmits intentionally, so the module's emissions overlay the equipment's unintentional emissions and must be handled during emission measurement. The equipment may interfere with itself, through the module's effect on other parts. The wireless link may drop during immunity testing, and whether that counts as a failure depends on whether the link carries essential performance. And the number of test states multiplies, since wireless on or off, connected or not, transmitting or idle may all behave differently. Test plans for wireless equipment are therefore considerably more complex, and an unclear plan leads to repeated testing or untrustworthy results.

Layout principles. Several matters need settling. The position of the communication partner, meaning where the phone or receiver sits, at what distance, and whether it is inside the test area. The partner's own influence, since it is an electronic device whose emissions may be included in the measurement. Cable arrangement, following the same requirements as for wired equipment, though wireless equipment often has fewer cables and the resulting freedom creates consistency problems of its own. Antenna orientation, since an internal antenna's directivity affects emission measurements. And isolation of auxiliary equipment used to maintain communication, which should be separated or kept distant. The partner's position is the item most needing explicit recording: results can differ markedly with position, and anyone reproducing your work cannot do so if it is unstated.

Setting test states. Work through it as follows. List every operating mode, covering wireless on and off, connection state, data transmission state and the equipment's functional modes. Analyse emission characteristics per mode and select the highest-emission mode for emission testing. Analyse susceptibility per mode and select the most susceptible for immunity testing. Confirm whether multiple modes need testing where characteristics differ substantially. And record the reasons for the selection. Choosing the least favourable state is the general principle, but it presupposes knowing which state is least favourable, which requires preliminary survey measurements rather than guesswork.

Handling emission testing. Intentional emissions from the module and unintentional emissions from the equipment must be treated separately. Intentional emissions are assessed against the module's own requirements, generally radio requirements. Unintentional emissions are assessed against the equipment's emission requirements. How the module's operating band is treated during emission measurement must be explicit; provisions generally exist but the plan must state them. And harmonics and spurious emissions from the module may fall within the bands of EMC interest. Run a preliminary scan before testing to establish which peaks are the module's intentional emissions and which are the equipment's unintentional ones; without that distinction, correct assessment is impossible.

Handling immunity testing. The central question is whether a dropped link counts as a failure, and the answer depends on whether the link carries essential performance. Where it carries critical control commands or monitoring data, a drop is loss of essential performance; where it carries non-critical statistics, a brief interruption is acceptable. The judgement therefore returns to the definition of essential performance, which must be settled before testing. Acceptance criteria must be specific: not simply that communication is normal, but how long an interruption is permitted, whether automatic recovery is required, how long recovery may take and how the equipment behaves during the interruption. Automatic recovery deserves emphasis: whether the equipment reconnects once the disturbance ceases is an important characteristic in real use.

Coexistence. Wireless equipment encounters other wireless equipment in service, making coexistence a practical matter. Other devices share the common bands, which are crowded. Hospital environments are particularly dense in wireless devices. Degraded behaviour under interference must be defined, meaning how the equipment should behave as link quality falls. And reconnection mechanisms must work after a drop. Coexistence verification falls outside strict EMC scope but addresses real problems and is worth considering, particularly for products whose critical functions depend on a wireless link.

Preparing for submission. Provide complete wireless parameters covering band, power, modulation and antenna characteristics. Provide the communication partner, submitting the matching phone or receiver with the equipment and describing the configuration. Describe the operating modes and how to switch between them. State essential performance explicitly, including the status of the wireless link. Provide monitoring methods, explaining how normal operation and link status are to be judged during testing. And provide demonstration software or tools for observing equipment state. Inadequate monitoring provision makes testing very inefficient: the laboratory must judge whether the equipment is operating normally while disturbance is applied, and without convenient means that judgement is difficult.

How we handle it. For wireless equipment we establish three things first: whether the link carries essential performance, the configuration of the communication partner, and how the operating modes differ. With those settled, test states and acceptance criteria can be fixed. On layout we record the partner's position, antenna orientation and cable arrangement in full, because those are what make results reproducible; incompletely recorded testing can yield different results on repetition.

Send us the wireless parameters and functional description and we will work out the test states. Phone or WeChat: +86 132 4819 8029.