The legislator imposes a multitude of requirements on all electrical devices and systems that must be met for successful CE conformity. An approval process therefore includes at least the three major chapters "electrical safety," "electromagnetic compatibility (EMC)," and "Restriction of Hazardous Substances (RoHS)“.
EMC compliance consists of a wide range of tests designed to ensure a defined maximum emission level and a minimum immunity to external interference receivers or sources – either wired or electromagnetic. The design of the system being tested and the required measuring equipment in the test laboratory can sometimes differ quite significantly. Safe behavior in the event of electrostatic discharge (ESD), which can occur unintentionally and unnoticed by the user when touching the system, is also an important part of EMC testing.
In collaboration with accredited EMC test houses, an "EMC test plan" has already proven successful in the past. This clearly defines the procedure for system and module tests. Since the test engineers in EMC test houses are generally not involved in product development and are unlikely to be familiar with the thought processes of the development teams, the EMC test plan ensures that all individual tests can be set up, conducted, evaluated, and documented as required. This minimizes misunderstandings that could result in valuable time being lost, or the need for regular consultations with the responsible developers. Since reproducibility in EMC tests is often already very difficult, the EMC test plan offers the opportunity to describe the test in great detail to avoid unpleasant surprises during repeat tests.
Until recently, the EMC test plan was a "secret" efficiency tool in my daily EMC practice. Since the 4th edition of IEC 60601-1-2, it has been mandatory for all developers and testers of medical electrical equipment. While the standard doesn't provide a form for this, Appendix G lists all the recommended information for the EMC test plan.
In the following article, I describe my best practice for a test plan to make the tests clearer, more structured, more reproducible, and, of course, compliant with standards.
Contents of the test plan
The structure of the test plan is roughly based on Table G of IEC 60601-1-2. Many chapters can be summarized, as this improves the structure and clarity of the test plan. The chapter numbers are taken from IEC 60601-1-2 for clarity.
1.) Testing laboratory
Name, address and contact details of the EMC test house where the tests are carried out.
2.) Device structure and accessories
List of accessories available for the test subject:
All electrical accessories and cables should be listed here, for example, international power cords or all variants of patient cables. If the device under test consists of multiple electrical components (possibly non-ME devices), even if they are connected wirelessly, they should be listed here.
This chapter specifies which of the cables mentioned above will be used for testing. This could, for example, be just a specific power cable or the most sensitive patient cable variants, since a comprehensive test of all possible system variants is rarely economically viable and technically meaningful. However, if the patient cables differ significantly, you should definitely consider testing several variants or at least provide a plausible explanation for why only some of the cables are being tested.
This chapter can also include the contents of Chapters 18–23 of Table G, as this configuration typically does not change across EMC tests. Should one or more points change, they can be described individually for each test in Chapter 12.
3.) Essential performance features and basic security
The essential performance characteristics are the crucial part of the test plan, as they describe which influences are acceptable and which are not. In addition to the essential performance characteristics of the product standards, the basic safety characteristics, the additionally defined performance characteristics of the device are also listed. This gives the tester a clear overview of all the characteristics that must be monitored during testing.
4.+5.+6.) Description of the test specimen
The device under test should be described as precisely as possible. The hardware and software versions are mandatory, and any manual modifications to a device under test should also be documented. The serial number and additional information, such as the exact supply voltage level for a wide-range input or special test conditions, should also be recorded. The number of devices under test should also be defined.
7.) Intended purpose and intended environment
This chapter specifies the intended purpose and all the environments in which the device under test can be used. These environments are professional and/or domestic, but may also include additional specialized environments. These environments can be found in Chapter 8.9.
Different requirements may arise for devices (e.g. a blood pressure monitor) if, for example, it is to function during an operation with an electrosurgical device, is used in a home environment, or is used in a helicopter.
8.) Applicable standards
All standards used for testing should be listed here. In addition to the EMC standard (IEC 60601-1-2) and any additional environmental standards, such as those for automotive or aviation, these include applicable product standards that provide additional requirements or exceptions for EMC testing. Due to the relatively long transition periods for standards, the respective version to which the tests refer should also be precisely documented.
9.) Deviations from the EMC basic standard
This chapter lists the standards that contain exceptions to the basic EMC standards (IEC 61000-xx-) or IEC 60601-1-2. These are primarily product standards that require modifications to the standard structure or that define PASS/FAIL criteria.
Optional: 10.) Applicable tests that are not performed.
If tests should or must not be performed, this should also be documented in the test plan. The reason why a test was not performed should also be recorded in bullet points for the test engineer (and for future generations).
(The electronics wisdom also applies in technical documentation: Undefined states are bad states :-P )
11.) Test conditions for special environments
This point is not needed for most products and, if applicable, would certainly result in an entire blog entry.
12.) Test conditions
This chapter specifies the limits and test conditions for all tests. If a higher test severity is required by a standard, it is listed here. In the case of interference, the modulation frequency and the 27.) Length of stay be specified.
The limitations, such as which SIPs/SOPs (digital input and output lines, e.g. USB) or patient lines are tested differently, should be described here. This chapter should also include 16.) Input voltages and frequencies be specified, as it may be useful to check several voltages and/or frequencies in a particular test.
13.) Immunity-related criteria regarding “pass/fail”
The pass/fail criteria required to evaluate the test results can be found in IEC 60601-1-2 or the respective product standards. Additional, self-defined criteria may also be required as part of the risk management process.
You can also start this chapter with 3.) , as these are directly related to the essential performance characteristics. Depending on the test, there are also different pass/fail criteria for the respective application part or essential performance characteristic. It's best to assign the criteria a number or abbreviation so that they can be linked directly in the respective tests (described in Chapter 12).
14.) Operating modes and settings
All operating modes should be listed here. If you don't want to test all operating modes or modes, you should justify your selection. For economic or technical reasons, in practice, you usually limit yourself to modes that are considered "worst-case" (e.g., full-load operation) or in which you can monitor as many functions as possible (key performance characteristics, communication via interfaces, displays, etc.).
15.) Test setup
This chapter should describe how the device under test is set up and terminated with all connections and simulators. Here, you can decide how the patient line(s), supply lines, and SIP/SOP lines should be routed. It is usually the peripheral lines that have a significant impact on the test results or, if the test is performed with a different test setup, can even result in barely reproducible results. Simple sketches or photos round out this chapter and simplify the tester's work in the lab.
24.) Documentation of additional hardware or software
If additional devices such as PCs, patient simulators, or special EMC testing software are used, this can be documented in this chapter. In my practice, simulators from well-known manufacturers have already proven unsuitable for EMC immunity measurements, making proper EMC measurements impossible. Such devices should also be kept under close scrutiny in case of bizarre test results.
25.) Alarm limit settings
The default alarm limits should be recorded here so that the tester can set and check them as needed. If a threshold is set at 90% during a test, the alarm could suddenly trigger during a repeat test if the threshold is different this time.
26.) List of planned ESD test points
In this chapter, you can include some images or a drawing and define the test points for the electrostatic discharge tests. Air and contact discharge can be marked in different colors. Alternatively, you can use a list by naming the test points. However, since the tester usually has limited knowledge of the system, this can sometimes lead to confusion.
Closing words
Practice has shown that a timely handover of the EMC test plan, the operating instructions and the risk analysis to the EMC test house – even if these documents are currently only available in draft form – enables rapid testing without many queries.
Depending on the number of applicable standards and application parts, the test plan can become a very extensive document. If you regularly approve medical devices, a corresponding document template with a structure, checklist-like device classification, and the required standard tests can be very time-saving.
It is also recommended to write the test plan in English, as EMC test houses usually copy and paste some chapters directly into their English-language test reports.