The European Union’s (EU) Medical Device Directive (MDD) is compelling electronic equipment manufacturers to take a closer look at the electrical safety and EMC functional aspects of their products. These directives also are forcing engineers to find test equipment to help them meet the demands of the directive easily and quickly. But what is the MDD, and how does it affect you?
The MDD outlines a procedure that medical-device manufacturers must follow to obtain compliance approval to sell their products in the European Common Market. The MDD went into effect on Jan. 1, 1996, but a transition period extends until June 1998. Until then, manufacturers can use either the EMC Directive or the MDD as the basis for applying the CE Marking to medical devices.
The MDD is complex and provides a significant amount of information about the approval process. It breaks out products into four classes, I, IIa, IIb, and III. Class I contains general, typically noninvasive devices that are not used for life functions or diagnostics. Class IIa devices are considered invasive with respect to body orifices. Class IIb devices modify the biological or chemical composition of bodily fluids via the orifices. Class III devices come in contact with the heart or central nervous or circulatory systems.
The classification of medical devices determines which conformity assessment route and test procedures are appropriate. A Class I general product used for noncritical functions will have a less stringent conformity assessment route than a Class III product that performs critical patient functions.
For most product classes, the MDD also requires that an EU Notified Body approve the manufacturer’s product design, manufacture, and final inspection process. The Notified Body conducts the evaluations listed in the directive, including compliance with the essential requirements, the relevant technical standards, and the annexes associated with the routes of conformity assessment.
One of the medical EMC standards is EN 60601-1-2 Medical Electrical Equipment: General Requirements for Safety; and Collateral Standard: Electromagnetic Compatibility—Requirements and Tests. It is harmonized to the EMC and medical device directives and is identical to the IEC 601-1-2 in content and title.
EN60601-1-2 for medical electrical equipment has provisions for emissions and immunity. The emissions requirements refer to CISPR 11 Group I or II Class A or B, depending on the use of the device.
The goal of manufacturers is to make any part of the certification process easier. For example, to help you perform the tests quickly and easily, look for software that offers routines for measuring peak, quasipeak, and average detection. It allows you to set the dwell time in these routines so that noncontinuous waveforms are easily measured.
The test equipment must be easy to set up and operate, said Tom Moyer, product specialist at Amplifier Research. Even if you are new to EMC testing, the equipment should be simple to operate and provide front-panel menus with push buttons that quickly take you to the test operation of your choice. The unit should take only a few minutes to calibrate as opposed to some that can take as much as 30 minutes.
The revised IEC 601-1-2 specification calls out several IEC 1000-4-x specs for immunity testing, and any help meeting these requirements, especially at the precompliance stage, is welcome. The best test equipment should help you meet field uniformity requirements of EN 61000-4-3 and be comprised of an RF signal generator, amplifier, and a Windows-based immunity measurement program. The software also should perform conducted immunity tests and field uniformity calibration.
A common issue regarding emission and immunity testing for the medical-equipment industry revolves around the task of applying EMC filtering. Unfortunately, the medical specifications for leakage and isolation make filtering difficult.
For example, the medical leakage requirement for a device enclosure is 100 µA, and the patient leakage current for some devices is limited to 10 µA. For isolation, the patient connections routinely call for tests to 4 kV. These leakage and isolation requirements prevent the use of typical EMC filtering techniques.
Another particularly difficult device class is the patient monitor used for measuring signals ranging from microvolt to millivolt or nonoampere to microampere. To compound the problem, the signal originates from the patient and may be affected by RF in complex ways.
It is not feasible to use a human as a signal source during testing. As a result, the human-body effect is lost and the test findings must be qualified as less than perfect.
In many cases, the physiological signals can vary over several orders of magnitude. The EMC test becomes a signal-to-noise test, and the results can vary by as much as 10 dB.
Recommendations
The scope of the EU’s MDD is significant, and manufacturers must research the compliance procedures for their product if they want to meet emission and immunity requirements. Fortunately, these are well-traveled roads, and help is available.
For example, some EMC test equipment manufacturers offer intensive classes that cover the details of proper EMC board layout. Many of these courses are presented on a regular basis in different locations throughout the United States.
Help also is available for device manufacturers that need to meet the emission and immunity requirements which force them to design PCBs based on EMC guidelines, not board real estate, said Joseph Heins, senior EMC application engineer at Chase EMC. Here are some design rules to consider:
Locate crystal oscillators away from input/output buffers and drivers.
Place decoupling components near noise sources.
Route high-speed traces away from power and ground traces.
Do not filter DC-to-DC power converters.
One word of advice that epitomizes the method to meet the EMC requirement is over-design, said Mike Henry at Haefely Trench. The EU EMI susceptibility regulations are nothing more than mandated quality-control standards that you already should have in place to produce high-quality products. If you design your products to exceed the EU directives, field failures from EMI will be reduced significantly. The benefits will be customer satisfaction and loyalty.
Reference
1. Anderson, R., “The European Medical Device EMC Specifications,” IEEE International EMC Symposium on EMC, 1996, pp. 31-33.
EMI/RFI Test Equipment
Conducted Immunity Generator
Tests at 15 mW to 25 W
The CWS500 Transient Generator helps meet the requirements for the IEC 1000-4-6 specification for conducted immunity. The generator performs tests at 15 mW to 25 W from 9 kHz to 240 MHz. The voltage standing wave ratio is 1:1 at maximum power and at all phases and angles. Calibration typically takes less than 3 min. Up to four coupling/decoupling network calibration values are stored in memory. $21,100. Amplifier Research, (215) 723-8181.
Turnkey System Measures
Emissions to 2 GHz
The EMI PAK EMC testing package measures emissions from 10 kHz to 2 GHz, meeting the requirements of all international EMC standards. Included with accessories, cables, and software, EMI PAK assesses radiated and conducted emissions to international standards. The system has a wideband antenna for open-site testing, a LISN, a spectrum analyzer, a transient limiter, a 30-dB preamplifier, magnetic near-field probes, and a PC-based emission-measurement software package. A memory card with preprogrammed test setups also is available. $17,950. Chase EMC, (201) 252-8001.
Precompliance Test System
Locates Noise Sources
The PC-112 Precompliance Test System is used to perform radiated and conducted emission tests. Included with the PC-112 are the Model SA-510 Spectrum Analyzer for radiated and conducted testing, the Model AB-100 Biconical Antenna, the Model AL-100 Log Periodic Antenna, the Model PA-102 Preamplifier, and an antenna tripod for radiated emissions. The system also includes a near-field probe set to locate noise sources, a comb generator used as a reference source, and a line-impedance stabilization network. $8,895. Com-Power, (714) 528-8800.
Two Methods Offered
To Inject Current Into Cables
Common-mode current disturbance signals are injected into unscreened cables, shielded cables, balanced cables, coaxial cables, and power main cables via direct- capacitive and inductive coupling The direct-capacitive coupling method uses a coupling/decoupling network (CDN). The inductive method has an RF bulk-current injection probe. More than 35 CDNs are offered that maintain 150-W impedance from 150 kHz to 230 MHz. Power-line configurations are offered in current ratings of 16 A, 25 A, 32 A, 50 A, 100 A, 200 A, and 300 A. The injection-clamp or bulk-current injection methods provide a nominal 50-W impedance to the disturbance signal and are supplied in 23-mm and 32-mm clamp sizes. Call company for price. Fischer Custom Communications, (310) 891-0635.
Power-Frequency Tester Meets
IEC 1000-3-3 Requirements
The PHF 555 Single-Phase Power Frequency Test System meets the IEC 1000-3-2 and 1000-3-3 requirements for harmonic and flicker measurements. It also generates voltage and frequency fluctuations, interharmonics, and harmonics. The system features a linear AC power source. The Windows-based software helps analyze measurements and compares them to regulatory requirements. Approximately $22,000. Haefely Trench, (703) 494-1900.
RF Amplifier Performs
Conducted Immunity Tests
The M75 RF Amplifier helps perform tests to meet IEC-1000-4-6 requirements. It provides 75 W of power from 10 kHz to 230 MHz and has a bandpass flatness of ±1.0 dB and nominal harmonics of -30 dBc. The flat response and low harmonics ensure the equipment under test is not subjected to undesirable fields. Applications include radiated susceptibility, EMP simulations, broadband communications, antenna testing, and power-meter calibration. $4,995. Instruments For Industry, (800) 467-7705.
Immunity Test System Meets
IEC, ANSI, CCITT, UL Standards
The EMCPro™ EMC Immunity Test System meets the requirements for EN, IEC, ANSI, CCITT, and UL standards. It performs ESD, EFT, surge, dips, interrupts, and magnetic-field immunity tests. The system can be configured for the IEC 1.2/50-µs combination surge waveform and the 10/700-µs telecomm waveform or 100-kHz ring wave. A 6.6-kV surge-test capability is provided. Starting at $15,000. KeyTek, Division of Thermo Voltek, (508) 275-0800.
Simulator Generates
Repeatable Pulses to 30 kV
The ESS-200AX ESD Simulator generates repeatable ESD pulses up to 30 kV in the contact and air-discharge modes and complies with IEC 1000-4-2. It features a 5″ display, a 10-button keypad, a lightweight probe, and room-temperature and humidity sensors. A variety of capacitor and resistor units is optional. The menu-driven simulator offers manual, IEC-severity, sweep, and program modes. Watahan Nohara International, (800) 366-3515.
EMI Measurement System
Software Is Windows-Based
The 27120A EMI Measurement System performs pre- and post-certification testing. It incorporates the company’s EMC120 Windows™-based software package to help create and modify EMI tests. The system includes the company’s spectrum analyzer, a quasipeak adapter, a set of CISPR filters, an internal preamp, an RF preselector, five near-field probes, an LISN with a transient limiter, antennas, and RF cables for performing conducted and radiated testing. $25,950. Tektronix, (800) 426-2200.
Portable Analyzer
Measures to 1,000 MHz
The SCOPE 4600 is a portable spectrum analyzer for use in the field or laboratory. It performs broadband measurements with selectable resolution bandwidths to 1,000 MHz. The instrument has a lighted graphical LCD, built-in batteries and a charger, a PC interface for remote control, and a noise generator. The software keeps track of the calibrated test components attached to SCOPE 4600 and provides the appropriate display for each test. Antenna Research, (301) 937-8888.
Immunity Test System Meets
Requirements for CE Marking
The EMCPro™ EMC Immunity Test System meets the requirements for the CE Marking and other international standards. It performs tests for ESD, EFT, surge, dips, interrupts, and magnetic-field immunity for the IEC and EN standards. The system also checks surge levels up to 6.6 kV to meet ANSI, CCITT, and UL requirements. In addition to the 1.2/50-µs surge waveforms required by the IEC standard, a 10/700-µs telecom waveform or a 100-kHz ring wave can be added. KeyTek, (508) 275-0800.
Copyright 1997 Nelson Publishing Inc.
October 1997