Using IEC 60601-1-2 for Testing Medical Devices

Ensuring EMC is a vital issue for companies producing electrical and electronic medical devices. These types of devices must perform as intended and not interfere with other equipment, or the results could be catastrophic. For medical manufacturers, making sure that devices meet EMC standards is not only a marketing necessity, but also a societal concern.

There are several EMC specifications, but none of them alone will provide appropriate testing guidelines for specialized medical devices. To reduce confusion and ensure that devices will be properly tested, medical manufacturers should use an existing standard as a guide for developing a customized testing plan.

The International Electrotechnical Commission (IEC) is a worldwide body that promotes international standardization in electronics. In 1993 it released the 60601-1-2 standard, "Medical Electrical Equipment—Part 1: General Requirements for Safety, Amendment No. 2. Collateral Standard: Electromagnetic Compatibility Requirements and Tests."¹

The IEC 60601 standard offers a solid basis for medical device testing. Although they are relatively new, the IEC 60601-1-2 requirements have quickly become recognized throughout the world and are instrumental in testing to the European Medical Devices Directive. Organizations such as the American National Standards Institute (ANSI) use the IEC 60601 standard as a basis for their own requirements.

This document specifies acceptable levels for immunity and refers to other documents to specify emission levels. However, these levels may not be strict enough to ensure that equipment will operate as intended. Manufacturers should use the IEC specifications as a guide but tailor them to produce product-specific limits.

The IEC 60601-1-2 standard specifies test limits for emissions, immunity, electrostatic discharge (ESD), radiated RF electromagnetic fields, bursts, and surges.

Emissions. Equipment should comply with the conducted and radiated emissions requirements of the International Special Committee on Radio Interference (CISPR). Classification of equipment for this purpose is based on intended use and determined by the manufacturer.

Equipment may be tested for emissions at a standard test site, which would include a turntable and ground plane, and have known attenuation curves. Equipment may also be tested after it has been installed on the users' premises. It is recognized that medical equipment may have unique installation considerations and that type-testing of the installation is the only practical solution to demonstrate compliance to the requirements.

Manufacturers should refer to CISPR 11 for the appropriate requirements and amplitude levels once the class of equipment and test location have been determined.²

Currently, there are no requirements for low-frequency emissions, harmonic distortion, and voltage fluctuations, but some equipment that operate in an intermittent mode will have to meet specific variations of the CISPR 14 Click requirements.³

CISPR 11 covers a frequency range from 150 kHz to 18 GHz. Conducted emissions for low- and medium-voltage power mains (100–415 V) are performed from 150 kHz to 30 MHz. The frequency range for radiated emissions is from 150 kHz to 18 GHz. Depending on the class and use of the equipment, various frequency ranges may be defined. Only the magnetic component of the radiated field is measured from 150 kHz to 30 MHz. Above 30 MHz, both the vertical and horizontal components of the field must be measured.

Amplitude limits in general are established to protect the public broadcast services, not for equipment that may have to operate in close proximity to sensitive medical equipment.

The specification also refers to frequencies designated by the International Telecommunication Union: 2450 MHz for industrial, 5800 MHz for scientific, and 24,125 MHz for medical equipment.

Immunity. General immunity requirements are specified in IEC 60601-1-2. Test levels are given and test methods are based on the IEC 801 series of immunity requirements. If lower limits are justified, accompanying documents should explain this and describe any action that will, as a consequence, be taken by the installer or user.

Accompanying documents should include guidelines for avoiding or identifying and resolving adverse electromagnetic effects. If the use of the equipment is restricted because of its electromagnetic characteristics, relevant restrictions should be described in the accompanying documents.

Compliance with the requirements should be checked by verifying that the equipment continues to perform its intended functions as specified by the manufacturer or fails without creating a safety hazard.

ESD. Equipment should comply with the current edition of IEC 801-2.⁴ A limit of 3 kV applies for direct contact discharge to all conductive accessible parts and coupling planes. A limit of
8 kV applies for air discharge to nonconductive accessible parts.

Radiated Radio-frequency Electromagnetic Fields. Equipment should comply with the IEC 801-3 requirements, which are being updated.⁵ A limit of 3 V/m should be used over a frequency range of 26 MHz to 1 GHz. Other levels apply to equipment used in shielded locations, such as x-ray and MRI facilities. The 3-V/m requirement is decreased in proportion to the increasing shielding effectiveness of the location.

There are provisions for amplitude modulation of the signal, depending upon the passband of the equipment under test (EUT). If the EUT does not have a passband, the signal should be amplitude modulated at 1 kHz.

Bursts. Test methods and instruments specified in IEC 801-4 should be followed.⁶ A 1-kV level applies to equipment connected to the power line with a plug. For permanently installed equipment, a level of 2 kV applies. Interconnecting lines longer than 3 m should be able to withstand a 0.5-kV surge.

Surges. Test methods and instruments specified in IEC 801-5, which is currently still under consideration, should be followed.⁷ Power lines should meet levels of 1 kV for differential mode and 2 kV for common mode. Signal lines need not be tested, and telecom lines are covered by other standards. Ring wave and damped sinusoid tests are not applicable.

There are future provisions for voltage dips, short interruptions, and voltage variations on power lines, as well as for conducted immunity above 9 kHz and magnetic field immunity.

Manufacturers of electrical and electronic equipment for any use are recognizing the need for specifications that ensure compatibility among equipment. Medical electronics manufacturers also recognize that such generic standards are not necessarily appropriate; they may be too severe, or, even worse, not severe enough to protect their products. To lessen confusion and to ensure that test specifications will be appropriate, medical manufacturers should use an existing document such as IEC 60601-1-2 as a basis for creating their own product-specific standards.