Basic requirements for EMC standards of medical electronic equipment

With the development and use of more and more medical electronic equipment, how to solve the electromagnetic compatibility problem of medical electronic equipment and improve the reliability and safety of medical electronic equipment has become a very important and urgent research topic. This article analyzes the basic classification of electromagnetic compatibility problems, the hazards of electromagnetic compatibility phenomena, and the basic requirements for EMC standards of medical electronic devices.

Foreword

Electromagnetic Agile Computational EMC (EMC) refers to the ability of a device or system to function properly in its electromagnetic environment and does not constitute unacceptable electromagnetic disturbance to anything in the environment [1-2]. The electromagnetic compatibility standard is the requirement for this capability of the equipment or system. The implementation of electromagnetic compatibility standards for medical devices is aimed at improving the safety and effectiveness of medical devices, preventing electromagnetic interference or electromagnetic harassment during use, and causing medical devices to lose control and fail to cause harm to patients and users. When examining the electromagnetic compatibility of a device or system, it is necessary to analyze [3] the source of the disturbance, the path, the victim device or the system, as shown in Fig. 1. The harassment source generates electromagnetic harassment and acts on the victim device or system through a certain path. After the victim device or system is subjected to a certain degree of electromagnetic harassment, it may have consequences, or it may not be affected or it may only bear risks. As a result, this is the anti-jamming capability of the victim device or system. It should be noted that the disturbed device or system is also a source of harassment. Modern electronic devices or systems that use electronic technology will generate electromagnetic waves when they work normally, which will cause harassment to other devices or systems to some extent. From the path analysis, both from the air (high frequency), but also through the wire, cable (low frequency) [4].

Figure 1 Basic decomposition diagram of the EMC problem

It is generally considered that if the system meets the following three criteria, it is considered to be in electromagnetic compatibility with its environment: 1 It does not cause interference to other systems (EMI); 2 It is insensitive to emission from other systems (Electromigration Tc Susceptibility, EMS); 3 It does not interfere with itself . According to the above criteria, the EMC requirements of equipment or systems for electromagnetic compatibility are generally to limit the external harassment level of the equipment or system, that is, to limit the electromagnetic emission capability of the harassment source (limit the EMI level of the harassment source) to the equipment or The anti-jamming level of the system is the ability to withstand interference. According to the use environment and functional requirements of the equipment or system, certain requirements (improved EMS level of the disturbed equipment) are proposed. In foreign countries, the state administrative supervision departments often pay more attention to limiting the harassment of the source EMI emission capabilities. The level of immunity of the victim equipment is recommended by the company itself. In China, in order to better ensure the safety of the people's machinery, the national supervisory authorities conducted tests on EMI and EMS.

Medical Devices EMC Standards

Electromagnetic compatibility standards for medical devices include: YY 0505-2012 "Medical electrical equipment, Part 1-2: Common requirements for safety, Collateral standard: Electromagnetic compatibility requirements and tests" for medical electrical equipment and systems; Medical electrical appliances for inspection and diagnostics Equipment GB/T 18268.1-2010 Electromagnetic Compatibility Requirements for Electrical Equipment for Measurement, Control, and Laboratory Use Part 1: General Requirements and GB/T 18268.26-2010 Electromagnetic Compatibility for Electrical Equipment for Measurement, Control, and Laboratory Use Sexual Requirements Section 26: Special Requirements In Vitro Diagnostic (IVD) Medical Devices”; and some of the special requirements for electromagnetic compatibility in national and industrial standards for medical devices that have been issued and implemented, are part of these special requirements or standards, or A standard completely for electromagnetic compatibility, such as GB/T 25102.13-2010 "Electronic Acoustic Hearing Aid Part 13: Electromagnetic Compatibility (EMC)".

On December 17, 2012, the State Food and Drug Administration issued an announcement No. 74, and YY 0505-2012 will be implemented on January 1, 2014. The contents of the special standards that have been issued and implemented will also be implemented immediately. At the same time, the announcement clearly stated that the EMC testing of medical electrical equipment for inspection and diagnosis was also performed with reference to this standard. For other special standards, the implementation time and corresponding requirements of the standard shall be followed.

YY 0505 standard for medical electrical equipment and systems

YY 0505-2012 is equivalent to IEC 60601-1-2:2004 (Version 2.1) [5]. It is a parallel standard of GB 9706.1-2007 "Medical Electrical Equipment Part 1: General Requirements for Safety" and is also a general standard. It is applicable to All equipment and systems that do not specify EMC in professional or professional standards [6] do not apply to implantable medical electrical equipment. Electromagnetic compatibility standards for implantable medical electrical equipment have not yet been published. The standards specify requirements and tests for electromagnetic compatibility for equipment and systems, and serve as the basis for electromagnetic compatibility requirements and tests in specific standards. Standards specify the external marking of devices or systems, random documents, and electromagnetic compatibility levels [7].

2.111 major test items

In electromagnetic compatibility testing, EMI issues and EMS problems can be further divided into four basic EMC subproblems in terms of transmission of electromagnetic energy: radiation emission, radiation sensitivity, conducted emission and conduction sensitivity, as shown in Figure 2. YY 0505 has designed 11 test verification systems for electromagnetic compatibility based on four different energy transfer methods for electromagnetic energy. Among them, conducted emission, harmonic current, voltage fluctuation and flicker belong to conducted emission test; radiation emission belongs to radiation emission test; electrostatic discharge immunity, electrical fast pulse group immunity, surge immunity, voltage dip and The short-term interrupt immunity is a conducted sensitivity test; the radio-induced induced disturbance immunity, the radio frequency electromagnetic field radiation immunity, and the power frequency magnetic field immunity are radiation sensitivity experiments. Below, these 11 tests will be introduced separately. 　　

Figure 2 Four basic EMC subproblems

2.1.1 Conduction, radiation emission

In normal operation, medical electronic devices radiate electromagnetic energy through cables and surrounding space. Electromagnetic waves with a frequency of 0.15 to 30 MHz have a low frequency and radiate energy primarily through cables. Electromagnetic waves with frequencies between 30 MHz and 1 GHz and even above 1 GHz mainly radiate energy out of the space medium. If the radiated energy is received by other medical electronic devices, it may cause erroneous operation of the device and affect the work of other devices. To this end, many national standards have stipulated measurement methods and limits for electromagnetic emissions. Simple motor-driven devices or systems refer to GB 4343.1, and devices or systems that use lighting as the main function refer to GB 17743, information-technology devices or systems. Reference GB 9254, in addition to the above-mentioned other equipment or systems refer to GB 4824. And the equipment or systems that reference GB 4824 and GB 9254 must be classified according to the location of equipment use: Non-domestic and non-directly connected to residential low-voltage power supply network are Class A equipment, household equipment and directly connected to residential low-voltage power supply network For Class B, Category B emission limits are stricter than Class A.

2.1.2 Harmonic current emission, voltage flicker and fluctuation

These two requirements limit the impact of the equipment or system on the connected power network during operation.

Harmonic current emission limits refer to GB 17625.1. The fundamental reason for the harmonic generation of medical electronic devices in the power grid is due to the use of large-capacity non-linear loads in the design of medical devices. When the current flows through the load, there is no linear relationship with the applied voltage, resulting in harmonic currents in the circuit. The appearance of harmonics reduces the efficiency of the use of electrical energy, causing medical equipment to overheat, generate noise, accelerate insulation aging, shorten the service life, and even cause failure or burnout. In general, odd harmonics cause more harm than even harmonics. Therefore, the standard imposes higher requirements on odd harmonics to ensure medical equipment.

It will not cause too much impact on the public power grid. It should be noted that YY 0505 does not require equipment or systems with >16 A per phase current.

Voltage flicker and fluctuation limit reference GB 17625.2. For high-power medical electrical equipment, a large increase or decrease in the load current will cause a sharp change in the voltage, and the difference between the highest voltage and the lowest voltage root mean square value in the voltage modulated wave is called voltage fluctuation. Voltage fluctuations and sometimes the accompanying voltage flicker can lead to unstable operation of medical equipment, lighting flicker, affecting normal production, life, and even human health. Therefore, voltage fluctuations and flicker must be suppressed so that they are within the allowable range.

2.1.3 Electrostatic Discharge Immunity ESD

There are many factors that can cause the accumulation of charge, including contact pressure, coefficient of friction, and separation speed. If you touch a medical electronic device at this time, the electrostatic charge may be transferred to the device, creating an arc between the fingertip and the device. Direct transfer of charge can cause permanent damage to electronic components such as integrated circuit chips and cause system failure. Electro-Static Discharge (ESD) is a very common problem today. According to the requirements of YY 0505, the design simulates air discharge and contact discharge. The air discharge requirement equipment can withstand ±2 kV, ±4 kV and ±8 kV, and the contact discharge can withstand ±2 kV, ±4 kV and ± 6 kV. The test method refers to GB/17626.2.

2.1.4 RF electromagnetic radiation immunity

Today's environment is filled with a large number of electromagnetic fields at different frequencies, such as radio and television stations, fixed or mobile radio transmitters, and electromagnetic fields generated by various industrial radiation sources. Medical devices that operate in electromagnetic fields are affected by this electromagnetic field and affect the normal operation of the device. YY 0505 Requirement for radio frequency electromagnetic field radiation immunity level is that the non-living support equipment or system can withstand the interference field strength of 3 V/m in the frequency range from 80 MHz to 2.5 GHz, and the life support equipment or system must reach 10 V. /m. The test method refers to GB/17626.3.

2.1.5 Electrical fast burst immunity

When high-power inductive loads, switches or relays on the power supply network are switched, rapid transient pulse interferences with considerable energy are generated and coupled to the power ports, signals and control ports to affect the operation of the device or system. YY 0505 level requirements for electrical fast burst immunity are AC and DC power lines can withstand ± 2kV, signal cables and interconnect cables exceeding 3m can withstand ± 1kV. The test method refers to GB/17626.4.

2.1.6 Surge immunity

Lightning-induced electromagnetic fields induce high-energy transient voltages on transmission lines. High-power loads also produce the same behavior during switching. This high-energy transient voltage can affect equipment or systems along the power line. YY 0505's rating requirements for surge immunity are that the AC power line ground can withstand ±0.5 kV, ±1 kV and ±2 kV, and the line-to-line can withstand ±0.5 kV and ±1 kV. The test method refers to GB/17626.5.

2.1.7 RF induced conducted disturbance immunity

If the equipment or system is exposed to electromagnetic radiation with a low frequency, electromagnetic waves will cause conductive disturbances on the cable and affect the operation of the equipment or system. YY 0505 immunity to radio frequency induced disturbance immunity level requirements in the frequency range of 150 kHz to 80 MHz: non-life support equipment or systems can withstand 3 Vrms interference, life support equipment or systems in addition to Technicians suffer 10 Vrms interference on the frequency band. The test method refers to GB/17626.6.

2.1.8 Voltage Dips and Short Interrupts Immunity

If the power grid fails or the load changes drastically, it will cause the phenomenon that the power supply is interrupted after a short time or the voltage will be reduced for a short time, which will affect the normal operation of the equipment or system. YY 0505 analyzes the voltage sag of the equipment through the test system under three different conditions: voltage dip 95%, duration 10 ms, voltage dip 60%, duration 100 ms, voltage dip 30%, and duration 500 ms. Immunity. The short-term interrupt immunity of the device was analyzed by testing the results of the system in the event of a voltage interruption of 5 s. The test method refers to GB/17626.11.

2.1.9 Power frequency magnetic field immunity

When the conductor passes the power frequency current, it will generate a certain magnetic field around it, which will affect some equipment or systems with high sensitivity to the magnetic field. YY 0505's level of immunity to power frequency magnetic fields is required to withstand magnetic field strength of 3 A/m. The test method refers to GB/17626.8.

Although the above 11 requirements of the test all reference the corresponding national standards, but YY 0505 according to the specificity of the medical device on the test put forward some specific requirements, such as the standard requirements, if necessary, provide physiological simulation of the patient signal to simulate the test For the normal operation of the equipment or system, an analog hand should be used for the coupling point of the patient, and the coupling point of the patient must be in the test environment or the like so as to more fully and accurately examine the electromagnetic compatibility of the equipment or system during normal operation. The requirement of YY 0505 to resist the level of disturbance not only reached the higher level of the cited standard, but also put forward a higher level requirement for some items of life support equipment. However, standards also allow equipment or systems to have immunity levels below the standard, but they must be accepted for important physical, technical, or physical limitations. For the determination of immunity test results, YY 0505 uses 36.202.1 j as a general compliance criterion to list the phenomena that a series of devices or systems are not allowed to encounter when they are subject to a specified level of interference, including device failures and programmable Changes in parameters, changes in operating modes, false alarms, waveform noise or image distortion that can interfere with diagnostic treatment or monitoring.

2.2 Requirements for External Markers and Random Files

It should be noted that YY 0505 places a high degree of emphasis on the requirements for external tags and random files. The tag can play a role of prompting and warning for the user, and the random file has an irreplaceable role for the user in understanding, using, and maintaining the device or the system.

YY 0505 has 3 requirements for external markings, namely: 1 Marking non-ionizing radiation, indicating that the device or system will actively generate RF electromagnetic waves, and should pay attention to the impact on peripheral devices during use; 2 Free of static electricity in devices and systems The tested connectors are marked to indicate that the connectors are susceptible to static electricity. During the operation, precautions must be taken in the form of random documents. 3 The equipment and systems that are required to be used only in the shielded area must have warning instructions to explain the equipment and system requirements. Can be used only at designated shielded locations.

YY 0505's requirements for random documents include prompt instructions, warning instructions, and several forms. The random file needs to explain the location where the equipment or system is used, the application of radio frequency, the accessories that affect the electromagnetic compatibility, etc., as well as some warnings about the use process, understand and comply with these information and warnings, and ensure the equipment or system. Electromagnetic compatibility plays an important role.

3 GB/T 18268.1 and GB/T 18268.26 for inspection and diagnostic medical electrical equipment

The diagnostic and diagnostic medical electrical equipment mainly includes biological microscopy, PCR amplification instruments, microplate readers and other equipment used in clinical laboratories or clinical laboratory departments. For this kind of equipment, it does not apply to YY 0505, but it requires the use of GB/T 18268.1 and GB/T 18268.26. The GB/T 18268.1 [8] standard stipulates the electromagnetic compatibility test configuration, working conditions, test requirements, and harassment limits and immunity requirements of medical electrical equipment for inspection and diagnosis. The electromagnetic compatibility standards quoted are basically consistent with YY 0505. GB/T 18268.1 proposes different requirements for the level of immunity test to be used in places such as industrial sites and controlled electromagnetic environments; at the same time, performance criteria are clearly defined for each immunity test. Determine its compliance. GB/T 18268.1 classifies the performance criteria into A, B, and C types, corresponding to normal, biased, but self-recovering, operator-intervented, or system-reset. The C phenomenon is not allowed to be used in equipment that is used in a controlled electromagnetic environment.

The GB/T 18268.26 [9] standard is applicable to in vitro diagnostic (IVD) equipment and is a specific requirement for electromagnetic compatibility of IVD products. It is different from GB/T 18268.1 in terms of immunity requirements. This is because the risk of using IVD medical equipment is similar to the risk of non-life support medical equipment. Therefore, similar immunity test requirements as those of non-living support medical equipment are given in this standard. For the content of the level of immunity level, readers can consult the relevant standards.

4 Discussions and Conclusions

4.1 Some Special National Standards and Industrial Standards

Up to now, a total of 31 national and industry standards, including those that have not yet been released, have made electromagnetic compatibility requirements different from YY 0505 for electromagnetic compatibility [10] involving high-frequency, microwave, ultrasound, and endoscopes. Mirror, hearing aid, ventilator, ECG, monitoring, defibrillation, X-ray, nuclear magnetic and other equipment. These standards are either different from the requirements of YY 0505 in terms of limits, or put forward specific requirements on the criteria, or make specific provisions on the test layout. Due to the large number, this article does not describe one by one.

4.2? EMC's on-site testing technology

Electromagnetic compatibility field test (also called outfield test) is the test conducted on the site where the EMC test instrument is moved to the product work. In the EMC test, shielded rooms and anechoic chambers are necessary test sites. However, with the development of electronic technologies, more and more large-scale medical devices need to be tested for electromagnetic compatibility, such as PT, PET-CT, and NMR. Because these large-scale equipments are bulky, or their weight exceeds the load-bearing capacity of shielded rooms and anechoic chambers, or they are permanently connected to a power source and cannot be tested in a closed test room, field tests are required to evaluate EMC. performance.

On-site testing is faced with complex conditions such as the complexity of the electromagnetic environment and the diversity of system components. This makes it possible to assess the presence of serious environmental disturbances, difficulty in evaluation, unstable results, low utilization of test data, and difficult identification of interference sources. Therefore, sufficient attention needs to be given.

4.3 Basic Performance in EMC Testing

YY 0505-2012 introduces the concept of "basic performance", that is, the anti-interference test and assessment of medical electrical equipment is only for "basic performance", and YY 0505-2012 clearly states that manufacturers should specify the "basic performance" of the product. Should be determined by the manufacturer and should be stated in a random document, for products that do not specify "basic performance", all functional considerations should be considered as basic performance for immunity testing. However, for a wide variety of medical device devices with increasingly integrated functions, the establishment of basic performance is a problem that needs to be considered. Taking multi-parameter monitors as an example, currently mainstream devices on the market include electrocardiogram, heart rate, non-invasive/positive The measurement of parameters such as blood pressure, single/double conductor temperature, blood sample saturation, and respiration is performed. Therefore, the basic performance needs to be based on the intended use of the product and the use environment, and is derived through the method of risk analysis and emphasizes that these properties are expected. The electromagnetic environment used can be satisfactorily achieved without degradation and loss of performance.

4.4 Model and Unit Coverage Issues

As with electrical safety, electromagnetic compatibility also has the problem of whether the model and component modules can cover other models. However, due to the invisibility of the electromagnetic field, the electromagnetic compatibility model coverage is more difficult than the electrical safety, and there is no experience to follow. Therefore, this issue requires further research and discussion.

The YY 0505 standard and related electromagnetic compatibility standards that began in 2014 are of great significance to the medical device industry. It will surely promote the quality of medical device products, promote product upgrading, and protect the safety of product use. In this process, both the manufacturer, the testing unit, and the user of the equipment or system need to work together to contribute to the smooth implementation of the electromagnetic compatibility standards for medical devices.