Foreseeable misuses of the equipment must also be accounted for. The risk analysis must reveal the possible consequences of the equipment being present in the electromagnetic environment in which it is expected to be used throughout its life cycle. If the equipment is affected by electromagnetic radiation, there may be a risk of the equipment not functioning as intended. Similarly, the equipment may itself interfere with other nearby equipment.
This must be accounted for in the product's design, so as to avoid harmful EMC effects. Manufacturers must remember that many electronic components become degraded over the years, and an apparatus's immunity or emissions will almost always change with time.
According to the EMC standard, producers themselves must specify the activities to be performed in relation to electromagnetic interference. Those activities must be noted in the Risk Management File. The manufacturer — not the testing laboratory — performs these activities, meaning that the manufacturers themselves must establish specific EMC testing levels and functional criteria during testing. According to the EMC standard, in the risk analysis, producers must show the likelihood of electromagnetic incompatibility occurring in the use environment, as well as any consequences of such incompatibility.
The test house must confirm that this has been accounted for by inspecting the Risk Management File. If the test house does not perform this inspection, the product cannot be considered compliant with the standard. While the test house must inspect the Risk Management File, it does not need to judge the quality of the file — only that it is present and that EMC has been considered.
New in this version of the standard, use environments are now broken up into three groups:. The standard provides suggested testing levels for each of the three environments. Formally confirming that your products and services meet all trusted external and internal standards.
The standard governing electromagnetic compatibility EMC in medical devices, IEC 4th edition has been in effect for several years. In September of , the standard was updated under Amendment 1 and after a three-year transition period, it will become required by the FDA in the USA.
In this blog we will take a look at why EMC is so important in medical devices and what does the latest amendment include. Medical EMI issues could range from mild nuisances, like an alarm going off unnecessarily, to potentially drastic effects like device malfunction. With such a wide range of potential issues, manufacturers need to mitigate risks with EMC evaluations established in IEC Edition 4.
Some of the updates to the standard include updates to reference standards, which have changed over time. Additionally, some wording changes were made without changing the meaning of the text. For example, a wording update to IEC magnetic field testing provides clarity but does not include new requirements, levels or limits. Slight changes to test voltage have also been made, with conducted emissions being changed from "any one voltage" to "minimum and maximum rated voltage" for any power frequency, requiring more testing than previously.
Another test voltage change impacts the short interruptions and voltage variations test, reducing the number of voltages required for one of the test cases. Timelines for compliance will depend on adoption and transitions specified by individual regulators. It is expected in September of this year. Gone are the requirements for tables like those in the previous edition.
However, many of the statements required to be included in the instructions for use are similar. A test laboratory can conduct a review of the product and documentation provided to an end user against these requirements. Addressing radio functions is not something that is new in the 4 th edition but it is often overlooked.
What do you do when a radio module is incorporated in a medical device? The radio function must be addressed during the testing of the complete product. Some of the tests that were likely performed on the radio module alone would still be representative of the use in the end product. However, radiated emissions and immunity tests performed on the radio module are usually not performed or the results do not consider the EMC effects of the integration, so tests must be performed on the product with the radio module operating as in normal use and in a mode to make sure no unintentional transmissions occur.
Another tip that is not new in the 4th edition addresses cycle time for each of the functions to be evaluated, which can have a significant impact on the time needed to perform radiated and conducted immunity tests. The standard requires that the dwell time at each frequency step be long enough for the product to be exercised and respond. For example, if a device processes data by taking multiple samples and averaging them and providing a result every 60 seconds, the dwell time at each frequency step would be 60 seconds.
Note that the dwell time must be specified in the test plan. Both radiated and conducted immunity tests use a frequency step size of 1 percent and a typical sweep rate of 1—3 s.
Table 2 shows the number of steps in the frequency ranges for both conducted immunity 0. The test times for conducted immunity in Table 1 are compounded by the number of interface cables, with the test typically applied to each interface cable in turn. For radiated immunity, the device is typically tested four times each side of the device facing the transmitting antenna sides, but portable devices should be tested on all six sides.
Each side is tested twice, once with the transmitting antenna vertically polarized and once with the antenna horizontally polarized. A portable device, therefore, would be tested a total of 12 times. It may be possible to implement test modes in advance of testing that use fewer samples thereby reducing the cycle time of the device or allow multiple functions to be monitored simultaneously. It must be noted that test modes have to be fully representative of the real-world application, so it may not always be possible to implement test-time-reducing features and meet the requirements of the notified body or government agency responsible for reviewing the test data.
Case 1: Infusion Pump. The essential performance of the pump was identified as providing fluid at a flow rate that remained within tolerance the tolerance was defined based on technical judgment from within the manufacturer's expertise in this specific medical application.
In addition, the pumps ability to detect certain error conditions such as air in the line or line occlusions and create an alarm was also considered a part of essential performance. This meant that two modes had be tested — normal mode with the pump infusing at a predetermined rate and alarm mode with various types of errors introduced into the system.
To address the flow-rate evaluation, the manufacturer first considered the use of a scale to determine the volume infused over a certain period of time. This method was considered inappropriate because short duration changes in the instantaneous flow rate might go unnoticed when the weight of fluid delivered was averaged over the duration of a test.
To counter this, the manufacturer developed an additional device to measure flow rate and to give a visual indication if the flow rate went out of tolerance. The flow meter had to be tested for immunity prior to performing the test to determine whether there were any susceptibilities prior to testing the final product to ensure that any flow-rate alarms were because of the device susceptibility and not due to the monitoring equipment.
The alarm conduction tests required no special test equipment since the error conditions could be recreated by manually injecting air into the line or pinching off the fluid line. As these conditions could not be recreated on a continuous basis, the manufacturer followed our recommendations to run these tests at spot frequencies for radiated and conducted immunity, with the frequencies selected based on the operating frequencies of ISM and radio devices in the hospital environment.
For transient tests ESD, surge, voltage dips, and interruptions , as the transient phenomena are all short duration events and the error condition would be a long duration event, the primary concern was that these transients did not damage the error-detection circuitry or inhibit the alarm. The ability to detect the error conditions was verified before and after applying each phenomenon, while also verifying that the transient phenomena did not reset the alarm condition.
This was not possible on the current product line but may be implemented in future products. While it may not alleviate testing in the alarm mode, it might reduce the number of tests required by allowing selection of reduced tests on the mode based on the areas where the circuits showed susceptibility.
Case 2: Telemetry System. This device contained a sensor and would periodically send data acquired by the sensor to a remote data logging device. In normal operation, the device would transmit every 2 minutes; however, the interval could be adjusted for the device to transmit every 90 seconds. It was not possible to reduce this sampling time any further because the device required this as a minimum sampling time to avoid producing invalid data.
Although there were no complicated test configuration issues with this device, the fact that the dwell time could be reduced from to 90 seconds represented a significant test time savings.
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