I'd like to welcome Dara McLain again as our guest blogger. What's great is that she's not only willing to write a couple of guest blogs, but she's also open to speaking at your biomed association – time permitting of course. Thank you Dara and to all of you who have embraced the blog – we appreciate it! Read on for Dara's latest.

By Dara McLain: I understand the frustration involved when it comes to Electromagnetic Compatibility. It’s what I do for a living. No story of interference ever surprises me. I’ve been in thousands of healthcare environments, all unique, and still see something new every day. Calm and logical investigation is how I get through them. Sadly, 90% of them can be avoided through simple management.

Manufacturers are VERY concerned about immunity and emissions of any device they make, and the devices that might be used with them. If they weren’t, they would lose business faster than they could sell. Many test their products beyond IEC standards in an effort to beat the odds of encountering something new. Some only test right up to current standards set by IEC. Some will take ownership of leakage or immunity problems and take the necessary steps to correct it, if possible, even when the user has not, or cannot, follow practical guidelines, or exceptions, or the device meets test standards already. Everyone makes mistakes, and correcting one is a credit to them. Going above and beyond is the mark of a manufacturer who practices due diligence.


When I am investigating, I do my homework, and not just on Philips products. A good understanding of the specifications on any product is most of what I need. A quick Google search almost always gets me the specs on any device, or a number I can call, since I rarely can get the user manual from the hospital. I have never been turned down by another manufacturer when asking for information (and I never tell them who I am either, so that is not a factor here).

Yes, I do know Philips products pretty well, but I didn’t 8 years ago. I’ve never designed one, or been involved with their design. My knowledge about them comes from reading what is available to anyone, and the vast number of ways they are used. If I don’t understand, I ask. That’s why I’m successful.

Knowing what can go wrong, or has, in any environment from experience, is a bonus, yes, but the interfering source is almost always something new, especially when it is incidental (unintentional) and most of those interferers are non-medical devices. Many of those events can be avoided through good management practices (maintaining lighting ballasts and motor brushes, limiting the use of mobile transmitters, etc.).

Proximity is an important factor, even when a device meets test standards. Interference between two intentional transmitters on the same operating frequency can always be avoided through frequency management, or proximity management. I am continually amazed at the number of issues that still arise in this respect. I still find hospitals running two different telemetry systems operating on the same frequencies in the same facility, and the Biomed dept has no knowledge of it. Those that do, look me straight in the eye and ask WHY they can't do that. Some of you may chuckle at that, but it happens.

There are some immunity issues that cannot be resolved through shielding or hardware changes, such as filtering of an intended pass band of frequencies. Just as the intended frequency of a transmitter is necessary to device functionality, so are intended pass bands; the band of frequencies the device is designed to receive. Good shielding will only do so much. Do you know the intended pass band for Ultrasound? You should. It’s readily available. Can you filter its pass band? No, or you would have no image. The user manual clearly states that use of Ultrasound imaging during electro-surgery coagulation will produce image artifacts, yet hospitals still complain about it. It is a limitation of the product’s use.

System specifications play an important role in EMC management. For example; a paging system company is asked to boost their system power to allow more range of paging. Will the power level of the final boosted signal exceed the input specifications of another system’s receivers, such as Telemetry? Do you know the specifications on those Telemetry receivers? Blindly allowing the installation of this booster system and not limiting its output power, causing failures as a result, is mismanagement of device usage in your environment. If you didn’t ask, or research it, you have yourself to blame when a malfunction occurs as a result. Similarly, allowing a high powered mobile transmitter in the area of sensitive equipment is also mismanagement.

In a perfect world, all devices would be immune to everything. And hospitals would have an unlimited budget to purchase those that are. Should you pay millions for a device that currently costs $50k with usage limitations, so you don’t have to worry about managing anything? I’m guessing no, even if the manufacturer would agree to develop it.

My wireless surround-sound system at home comes with EMC guidelines explaining what might interfere with it, and what I have to do to prevent that. Do I call them and say they need to make their 2.4 GHz speaker system immune to my microwave, or my 2.4GHz cordless phone? Should I go out and buy a $1000 microwave with absolutely no leakage? No. Or another phone set? Maybe. Instead, I have a $65 microwave that leaks emissions like a sieve, and I keep it separated with enough distance so it won’t have any effect on my speakers. And when I’m on the phone, I leave the room, because I know that two signals cannot occupy the same frequency at the same time. It costs me far less to have all, and costs me nothing to manage.

What EMC management does NOT involve is retesting products by the hospital, to see if they comply. I would never expect any hospital to conduct testing such as labs do. Not only is it cost prohibitive, but the equipment and facilities required to do it with any substantial accuracy are not at their disposal. Manufacturing test labs are already experts. Don’t reinvent the wheel. Test labs, as well as test results, are controlled and audited for integrity. Manufacturers do everything possible to assure EMC, and when there are known unavoidable exceptions to test limits, they are disclosed in the EMC guidelines.

From a hospital’s perspective, EMC management involves summarily:

•    taking the time to read and understand the EMC guidelines/exceptions, that come with a device;
•    asking questions about compatibility, and disclosing what you already have in operation in the intended usage area, when considering a purchase;
•    understanding the specifications of a product and how they interact with others, and
•    maintaining the integrity of your equipment, medical and non-medical

This will take care of nearly all interference problems.

Manufacturers also make a valiant attempt to predict what will be used with, or near, their devices. People like you (and me!) can help provide feedback on the true environment as it is today, but some things will still be missed. Humans aren’t perfect, and the products they make aren’t either.

Yes, manufacturers DO expect users to manage the use of their medical equipment within reason. And in most cases, the guidelines are right at your fingertips, if you will but look for them.

Thus, management of devices in any environment, by understanding their operating parameters, is essential to compatible use, based on limitations, immunity or emissions specs. Some devices are too sensitive to tolerate a cell phone placed on top of it, or the use of a high powered transmitter within one meter. The answer is managing the use of those interferers around your sensitive devices.

Rather than asking why a device is not immune to everything, which is not technologically possible in some cases and cost prohibitive in others, ask how to manage them. If you don’t have the specifications on a device, ask for them. If you don’t understand those specifications, ask the manufacturer for an explanation. If they won’t tell you, ask me.

For everything unknown, RF Surveys will tell you what’s in the environment; maybe not what some things are, but that unknown signals are there and might cause a problem.

There are many online seminars that cover RF phenomena, and I regularly teach classes to Biomeds along these lines, at no charge. There are many ways to overcome incompatibility issues that do not require an engineering degree, only common sense, a little effort, and very little money, if any at all.

Feel free to contact me if you and your peers would like to learn more. I'm sure I can arrange something for you, or your local Biomed Society. I can teach you how to manage your environment successfully. And in the course of such practice, your feedback to manufacturers will help them develop better products for you. Compatibility involves both the maker, and the user.

By Dara McLain, EMC engineer, Program Manager Interference Investigations, Philips Healthcare. E-mail: [email protected]



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