EMI

Troubleshooting

The American Radio Relay League (ARRL) defines electromagnetic interference (EMI) as any unwanted signal or noise that distorts or disrupts a desired signal or an electrical disturbance that interferes with a device’s normal operation.

We have all talked about and seen much done about EMI that causes problems with medical devices, usually as it relates to radio frequency (RF) transmissions. Most hospitals have taken precautions when it comes to cell phones, but EMI can travel via other pathways.

According to ARRL, there is always a source for the interference, a device that is the victim of the interference, and a transmission path that allows the interference to get to the victim.

Stopping the interference at any of the three points prevents a device from becoming a victim. If EMI is stopped at its source, it cannot spread. Removing the pathway prevents EMI from getting to a device. Preventing EMI from entering a device stops that device from becoming a victim.

EMI can travel through the air from a source to a victim by RF transmission. It can also travel by conduction and induction. EMI travels by conduction when the source and victim have a common conductive pathway. This pathway can be a wire or even conductive tubing. Induction occurs when the source couples EMI to the victim through the pathway provided by the proximity of their separate wires.

Since working on a special project to reduce EMI, I became more aware of EMI and its prevention and include the possibility of problems due to EMI whenever I troubleshoot equipment problems. I look more closely at how cables and power cords have been managed, especially when I am unable to find a problem with a device after a user has reported one.

Following are some cable-management problems I found that allow EMI by either conduction or induction to occur:

• Cords and cables mixed up and twisted with one another. The proximity of the cords and cables to one another enabled EMI to occur.
• Cords plugged into outlets but not connected to any equipment. The unconnected cords, wound up in a mass of cables, acted as a source of interference.
• AC outlet strips that caused interference on ECG monitors.
• Coiled cables and cords. The coiled wires set up fields that enabled EMI to occur.

I solved some device problems by correcting the above items. Therefore, I expanded my EMI prevention program to include my areas of responsibility. Now, I look more closely at cable management and take steps to prevent EMI problems.

I believe all technicians should pay much more attention to EMI prevention by following simple cable-management procedures:

• Keep cords and cables as short as possible. Run them directly to each device.
• Route cords and cables away from one another. Make sure the cords and cables do not become intertwined.
• Ensure cords are securely plugged into outlets and equipment and cable connectors are securely connected at both ends.
• Disconnect and remove all unused power cords.
• Keep cords and cables away from other equipment and power sources.
• Replace suspected power strips.
• Do not coil excessive lengths of cords and cables. Instead, tightly bundle them and secure them with tie-wraps, being careful not to create sharp bends that can crease the cord and cable ends.

EMI problems can also be due to a building’s electrical system. Try using a premium surge suppressor, not a cheap one. Periodically check the indicator lights and, if the lights go out and remain out, replace the surge protector. Use an isolation transformer to eliminate noise on an AC line. Get help from an electrician, who can check electrical panels for loose or faulty connections and defective parts.

Remember to follow proper policies and procedures. Use medical-grade electrical components when required.

Keep in mind that solving an EMI problem can be a recurring job. Equipment is moved or replaced and renovations occur—all meaning EMI can reappear.

EMI prevention is beneficial. If BMETs will take responsibly for proper cable management, that effort will contribute to device uptime, patient well-being, and overall customer satisfaction.

Ray Taft is senior BMET in the biomedical engineering department at Texas Children’s Hospital in Houston.