ANSI C63.18 v5.0
Revised Edition (v5.0) 10-27-07 – JLS comments as of 12-27-2007
American National Standard
Recommended Practice for an On-Site, Ad Hoc Test Method for Estimating Electromagnetic Immunity of Medical Devices to Radiated Radio- Frequency (RF) Emissions from RF Transmitters
1. Overview
ANSI C63.18 v5.0
1.1 Scope
This recommended practice is a guide to evaluating electromagnetic immunity of specific medical devices against radiated radio-frequency (RF) emissions from RF transmitters, including transmitting personal electronic devices (T-(PEDs) or any other portable RF transmitters. Importantly, this test protocol does NOT represent comprise a comprehensive test or in any way offer a gauranteeguarantee against interference risks, but is simply represents a rudimentary test that may assist in identifying medical devices that are particularly sensitive to a specific RF signal under analysis. Common T-PEDsRF transmitters for use in testing might include mobile phones, two-way radios (e.g., walkie-talkies, FRS radios), RFID readers, WiFi- enabled laptop computers, personal digital assistants, networked MP-3 players,, and two-way pagers and transmitting PEDs (e.g., mobile phones, wireless personal digital assistants (PDAs)). Thise recommended practice only applies to to T-PEDs RF transmitters with a rated power output of 8 W or less. The ad hoc test protocol can be used to evaluate existing or newly purchased medical devices with existing or newly purchased T-PED RF transmitters. The ad hoc test protocol can also be implemented for purposes of prepurchase evaluation. This recommended practice applies to medical devices used in healthcare facilities, but can also be adapted to medical devices in home-healthcare or mobile-healthcare settings. It does not apply to implantable medical devices, transport environments such as ambulances and helicopters, or to RF transmitters rated at more than 8 W. Testing with transmitters greater than 8 W in healthcare facilities is not recommended because of possible adverse effects on critical-care medical devices that are in use in other areas of the facility. This recommended practice does not address in-band RF interference on wireless networks or wireless links used by medical devices to transport medical or monitoring information.
1.2 Purpose
TWith the increase in transmitting personal electronic devices (T-PEDs) entering hospitals brought in by doctors, staff, patients, and visitors, there is a need to determine identify any problem issues that might exist with life critical medical devices as a result of specific T-PED radio-frequency (RF) emissions from transmitters used in healthcare facilities, particularly with the increase in transmitting PEDs entering hospitals brought in by doctors, staff, patients, and visitors. The purpose of this recommended practice is to provide an ad hoc test method for estimating the electromagnetic immunity of specific medical devices against the radiated RF emissions from specific T-PEDs transmitters that might be operated in proximity, such that:
ANSI C63.18 v5.0
a) The testing is relatively rapid, inexpensive, and practical;
b) The testing can be routinely performed by clinical engineers, biomedical engineers, and other technical personnel commonly associated with healthcare facilities;
c) The testing can be performed using room space and equipment that is commonly available;
d) Sufficient structure is provided in the test protocol to allow consistent and comparable results to be obtained within and across institutions;
e) Specific endpoints (i.e., effects) and thresholds (i.e., transmit power and/or distance) can be identified to providinge the basic information needed to develop an action plan;
f) The test results can be used in the formulation of policies and procedures for managing the use of T-PEDs RF transmitters within a healthcare facility.
The ad hoc test procedure is NOT expected to provide precise information on the exact threshold for EMI effects, but instead to offer a coarse test to help identify acutely sensitive medical device / T-PEDRF signal combinations that can be managed accordingly.
Several optional methods for ad hoc testing are outlined in this recommended practice to allow flexibility with regard to the time, personnel, and resources available to perform the testing. As a result, these different options provide different levels of accuracy and comprehensive testingness. The most appropriate ad hoc test strategy will depend upon the specific needs and resources available to the end userof the end-user of this recommended practice. Each methodThe tests can be used performed with or without an electromagnetic electric-field- strength (E-field) meter, although the use of an E-field meter is recommended. The preferred method for evaluation in most circumstances, given limited time and resources, a small number of life-critical medical devices to be tested, and a single or a limited small number of RF signals as a test sources, involves the use of a an actual T-PED RF transmitters placed in constant transmit (i.e., test mode) and the use of an E-field strength meter to measure the approximate electric field strength incident on the medical device at the threshold distance for observed effects. For transmitting PEDs, the preferred method is to place the transmitter in constant transmit (i.e., test mode). Many factors can influence the choice of optimal test strategy, however, including the size of the area and the number of medical devices and/or RF signals to be analyzed. The appropriate trade-off between practicality, cost, time, and accuracy of the results is left to the end- user to determine. This recommended practice also provides guidance for selection of the medical devices to be tested, selection and operation of transmitters used as RF test sources, and assessment of the test results.
Policies and procedures for mitigation of electromagnetic interference (EMI) in healthcare facilities (i.e., allowing or restricting the use of specific RF transmitters within specific areas) should be based on objective information, such as that which can be obtained by the use of this test method. Ideally, in order to mitigate EMI in medical devices, each healthcare organization would:
ANSI C63.18 v5.0
a) Fully characterize its electromagnetic environment;
ANSI C63.18 v5.0
b) Fully characterize the EMC of its existing inventory of electrical and electronic medical devices with all RF transmitter signal types that might enter the building; and
c) Ensure that any new electrical and electronic equipment purchased is compatible with this environment and with the existing inventory of medical devices.
Such comprehensive evaluation, however, may not always be practical. As a result, many clinical and biomedical engineers have traditionally performed their own rudimentary (“ad hoc”) EMC testing using in-house RF transmitters and medical devices. Differences in methodology, however, can make comparison of results between different institutions impractical. Item c) is a prospective activity that, in theory, could be implemented in a purchasing policy. However, such complete information about the environment or the medical device is seldom available. Conformance to voluntary EMC standards may provide some information, although many T-PEDs RF transmitters are able to greatly exceed these immunity levels when nearby or in the very near field. AnnexA lists EMC standards and guidelines that contain radiated RF immunity requirements applicable to medical devices. This recommended practice can be used to supplement the information that is obtained by testing to existing voluntary EMC standards. The results of ad hoc testing should be considered in the development of EMC/EMI policies and procedures for each healthcare facility.
Background information and further recommendations for mitigation of EMI in healthcare facilities are presented in the annexes.
2 Caveats and limitations
This recommended practice is not intended to substitute for rigorous laboratory electromagnetic compatibility (EMC) testing (e.g., IEC 60601-1-2) in which the test conditions are more fully controlled and the response of the medical device is characterized over a wide range of frequencies. This ad hoc test cannot fully characterize the radiated RF immunity of a medical device to all T-PED RF signals, and only offers a rudimentary evaluation for the narrow frequency and signal specific to the T-PEDtransmitter under evaluation. Performing the ad hoc test does NOT in any way offer a gauranteeguarantee against interference risks, but can assist in identifying medical devices that are particularly sensitive to the RF signal under evaluation.
If the test methods described are implemented without the use of an electromagnetic E-field strength meter, there can be considerable uncertainty and variability in the test results. This uncertainty and variability is due to:
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a) Manufacturer vVariance in the RF output characteristics of the RF transmitter due to e.g., manufacturing differences, battery charge;
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b) The specific type and small changes in orientation of the antenna with respect to the medical device;
c) Ambient RF fields;
d) Reflection and absorption of RF energy by people, objects, and structures in the test area; and
e) Small changes in cable placement and the relative position of the RF test source and the medical device.
Test results for each medical device apply only to that medical device unit and to the frequency, modulation, and field strength characteristics of the RF transmitter source. The medical device may be either susceptible or immune to other frequencies, modulations, and/or field strengths. Results for the same medical device may vary in the short term due to variability in the test method, movement of people or equipment, and/or variations in local ambient RF fields. The results may also vary over time as the medical device ages and/or undergoes service or maintenance. Results for different units of the same model may vary for these reasons as well as differences in design or manufacture (e.g., design revisions, component substitutions, tolerances, physical location of components and wires, assembly).
The variability of this ad hoc test can be minimized by using an RF E-field strength meter to more accurately determine incident E-field strength and by controlling the test variables as much as possible. If it is necessary to deviate from the recommendations herein, deviations should be kept to a minimum and the testing should be done as consistently as possible.
3 Preparation for testing
Preparation for ad hoc testing includes selection of the medical devices to be tested, selection of the RF signal and transmitters to be used as test sources, and selection of the test area.
3.1 Selection of medical devices to be tested
Healthcare organizations should use their judgment in prioritizing medical devices for ad hoc electromagnetic immunity testing. However, the following factors should be considered:
a) If the medical device is critical (e.g., life-supporting, used to monitor critical patient parameters, provides a diagnosis, delivers drugs);
b) If the medical device has not been tested for compliance with applicable EMC standards;
c) If failure or malfunction of the medical device could adversely affect the patient (e.g., if there is potential for patient injury or death);
d) If there are known EMI problems with similar medical devices due to insufficient RF immunity;
e) If RF transmitters are frequently used in the vicinity of the medical device (e.g., in emergency rooms);
f) If the medical device uses sensitive components or circuitry (e.g., circuits with high-gain amplifiers, patient lead wires and cables, and microprocessors can be particularly sensitive);
g) If the medical device has been noted to perform erratically; and
h) If the medical device is repeatedly referred for service, yet when the performance of the medical device is tested, no problem is found, particularly when tested in a service location which that may be elsewhere in the building (e.g., the basement) or off-site.
Medical devices that have proven in the past to be somewhat more susceptible in the past to RF emissions from T-PEDs RF transmitters include some EEG and ECG monitors, some oxygen meters, and some fetal heart monitors. Critical medical devices include infusion pumps and ventilators.
Electronic medical devices that exhibit one or more of the characteristics listed above are good candidates for ad hoc electromagnetic immunity testing. Ad hoc testing should be considered for existing equipment, pre-purchase evaluation, and, if pre-purchase evaluation was not performed, after purchase of new electronic medical devices.
3.2 Selection of RF transmitters
Any T-PED or other RF transmitter that will be used in or near the healthcare facility, has an output power up to 8 W, and can be conveniently relocated to the test area is a candidate for using use as a test transmitter. Hand-held transceivers (e.g., walkie-talkies), telemetry transmitters and repeaters, mobile phones, WiFi- enabled laptops, access points and other RF wireless communication and data information technology (IT) equipment can be used as an RF test source. For further information on T-PEDs and related RF transmitters, see Annex B.
3.3 Selection of the test area
The area in which ad hoc testing is to be performed should be located away from critical-care areas. It should be selected such that there are no critical medical devices in use in adjacent rooms and on the floors above and below that would be adversely affected by the test. Conversely, no other RF transmitters should be operating in the test room or in adjacent rooms or on the floors above or below that could affect the testing.. See 5.1 for precautions regarding electronic medical devices in use in nearby areas.
A location that meets the test facility requirements of IEC 61000-4-3 (2002-096) (see Annex A) is preferred. However, if such a facility is not available, the test should be performed in an area that is as free as possible of structures and metallic objects. Approximately 6 m x 6 m (20 ft x 20 ft)[1] of clear area is recommended. Ideally there should be at least 1.5 m (5 ft) between the medical device (including its cables) and the nearest wall or structure, as well as sufficient available room to back away from the medical device if an interaction is observed. If the available test area is smaller than these recommendations, the test setup may be moved or rotated as described in 5.3. If there are metal venetian blinds on the windows, they should be fully raised or opened during the test. This is because prior testing has found that such metallic blinds can act as a phased array and have a tuning effect that can distort the RF field pattern in the test room. The basement of a facility is often a good location for the test area because it can offer significant attenuation of the outside RF signals getting in entering the test area (i.e., provide a quieter lower ambient RF environment for the test) and can likewise attenuate the RF signals generated by the ad hoc test transmitters exiting the test area inside from getting out (i.e., reducing liklihood of interference with licensed networks). In addition, basement rooms are often remote from critical patient care and treatment areas. When selecting an indoor test area, B.1.11 B.1.8 should be considered. If no suitable indoor facility is available, the test can be performed in a vacant area of a parking lot.