Design for EMC Test: An Interdisciplinary Approach

Designing a medical device to meet the IEC 60601-1-2 4th edition Electromagnetic Compatibility (EMC) standards is notoriously difficult. Making matters worse, the details of what goes on during EMC testing is cloaked in mystery to many engineers. Regardless of the difficulty, every electronic device must pass formal EMC testing before it can be sold commercially.


Design for EMC Test is the interdisciplinary design of the support features required to perform formal EMC device testing at a testing laboratory


Design for EMC Compliance is the process of designing a device so that it will meet EMC requirements. Design for EMC Test is the interdisciplinary design of the support features required to perform formal EMC device testing at a Nationally Recognized Testing Laboratory (NRTL). While there is a wealth of information on EMC compliance design, little has been written about design for EMC test.

What is Design for EMC Test?

Design for EMC Test is the process of designing the special device software and hardware features, configurations, custom test fixtures and test equipment required to support EMC testing. A smooth, efficient and successful EMC test requires the participation of an interdisciplinary team of electrical, software and mechanical engineers.

Waiting until the end of a project to incorporate the features needed to support EMC testing is time consuming and sometimes prohibitively disruptive and expensive. Using a Design for EMC Test approach at the beginning of a project allows features to be incorporated into the device architecture that will support EMC testing at little upfront cost.

Design for EMC Test Process

A useful method of flushing out the software and hardware features needed to support EMC testing is to create an EMC test plan outline with details on test setup, hardware and software configuration, monitoring requirements and support equipment requirements for each type of EMC test. The radiated RF emissions test support requirements will be different from the support requirements for radiated RF immunity and radiated spurious emissions. During radiated RF emissions testing the device software needs to continuously exercise all functions and modes of operation to maximize electromagnetic emissions. During radiated immunity testing the device must be exercised while being continuously monitored to check for immunity problems such as resets, signal corruption and functional failures. During radiated spurious emissions testing the wireless radios must be configured to continuously transmit using special radio test AT Commands.

Creating a sketch of the device in the EMC test chamber with all the required cables and support equipment is a surprisingly useful tool for discovering design details that might otherwise be forgotten.

Software Considerations

Next a list of software EMC test support features is created to start the collaboration discussion on how to modify the software to meet the needs and how much time will be required to add the new features. It’s important that even if the list isn’t complete that at least some rough outline is shared with the software team early in the design process before it’s too late to change the design architecture.

Typically, the software team will need to 1) add EMC test support to the embedded device software, and 2) create a Windows/Linux software application to monitor and control the device remotely from a laptop outside the EMC test chamber. Since the EMC test software features needed for RF emissions testing, RF immunity testing and radiated spurious emissions testing will all be different, a means of switching between the different modes needs to be considered.

Hardware Considerations

While collaborating with the software team, the hardware team can develop a list of needed device hardware features, custom test fixtures and support and monitoring equipment. In order to continuously monitor the device during immunity testing there must be a communication connection to the device. It’s often necessary to get creative with how to accomplish this while not unintentionally adding a new antenna that introduces a new failure point on an otherwise good design.

During RF immunity testing, all wireless radios must be enabled and actively communicating. For an RFID reader, this can be as simple as placing a passive RFID tag adjacent to the reader antenna. For a Wi-Fi radio a wireless router must be placed inside the EMC test chamber to establish a wireless local-area network connection. For a cellular radio the network connection is more complicated, and it is best to consult with the test lab to find out their preferred approach. For radiated spurious emissions testing a means of sending special radio test AT commands to the wireless radio(s) must be considered.

Summary

  • Design for EMC Test is the process of designing the special features required to perform EMC testing.
  • Start Design for EMC Test early in the design process beginning with an EMC test plan outline.
  • Use an EMC test plan outline to start an interdisciplinary discussion with the design team on how to incorporate the features needed to support EMC testing into the device architecture.
  • Don’t underestimate the time and effort required to support EMC testing.

Tensentric is a team of highly experienced engineers developing a wide range of medical devices and in vitro diagnostic systems. Tensentric has completed over 300 development projects for clients in the medical device and IVD space since the company’s inception in 2009 and is ISO 13485:2016 certified for design and manufacturing. With capabilities for BSL-2 lab use, manufacturing process development, rapid prototyping, human factors validation and consulting, and in-house design for injection molding expertise, Tensentric is uniquely suited to a wide variety of medical device design, development, and manufacturing application.

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