Insulation Resistance Applied Parts to Mains. 8. IEC Leakage Measurements. Method Characteristics. Direct Leakage Provides. In-Service Test Requirements. 4 Introduction to IEC How does IEC compare. 13 with IEC ? Technical Considerations. STANDARD. IEC. CEI. NORME. INTERNATIONALE. First edition. Première édition. Medical electrical equipment –. Recurrent test and test after.
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IEC Standards for the Safety and. Efficacy of Medical Electrical Equipment . Introduction. It might, perhaps, be a little too self-evident to say that there is no. to IEc Biomed testing on the move. If you need it with you on-site, the Med -eKit Test Trolley will carry it. The Rigel Med-eKit is huge on technical features. with IEC World's smallest, automatic, electrical Contents Innovating Together. safety analyser Foreword 2 8 IEC Leakage Measurements.
High accuracy - low precision high precision high precision Low pressure applied Increased pressure high resistance low resistance 16 When using a DC Checking the protective earth during routine found in removable power cords. Restriction resistance where the conductive of film resistance which can be removed. IEC recommends that low accuracy and low precision as high readings protective earth connections are tested with a could be due to film or constriction resistance.
Cleans film resistance. High test currents might also be earth is more important during routine testing. See definition accurate way to determine the quality of the see figure Film resistance the possible resistive layer Combining a high pre-pulse to clean the film readings as a brand new good cable. Example of increased contact increased restriction resistance due to softening that accuracy must take precedence over A separate white paper on high vs low test resistance in spring loaded contacts precision as having a consistently wrong currents is available free of charge on our website measurement is precise but not very accurate.
While testing at the design a more constant reading high precision even if earth circuit due to its capability to temporarily reading will determine the pass or fail result of stage highlights the capacity of the design to cope there is a potential constriction in the protective repair constriction resistance. Figure 9: Low accuracy. Possible The test limits in IEC are set to: The highest type test approval. Lower test currents. Figures 12 and 13 below.
PE particularly older IT equipment. The risk of unacceptably high electrical fault the insulation in modern medical devices or the currents can be minimised through design connected together and enclosure protective expected leakage values that may be 7. During this test. DC insulation tests and provide no information as L During a dielectric.
An insulation resistance test exposed to a voltage it was not designed to class I and II applies a lower DC voltage.
See 7. L the mains switch as they require mains to be level. Insulation test mains parts leakage experienced in these devices rather than to protective earth. This is due to the ensuring the device operates properly. With all measurements of insulation resistance. Such insulation can be This is due to the increased use of switch mode adequately insulated from earth class I or the achieved through physical spacing creepage protective earth in class 1.
This could lead to higher leakage currents present. Results are displayed in beyond the mains switch. Figure 16 show a representation of the applied parts to mains insulation test. BF and CF equipment only. Insulation test applied parts to Figure Insulation test mains parts For both class I and class II appliances.
Free Guide to IEC 62353 Test Standard
Insulation test applied parts II and all the applied parts combined. Class II non-earthed accessible conductive parts. L For class I equipment.
The current in the live wire carries both the current readings. To consider: Each current produces a magnetic field the EUT is not required to be isolated from real n Highest accuracy compared to other Equipment leakage current. See figure As current passes IEC defines two different kinds of leakage Benefits: By subtracting both the path of the leakage current.
The net magnetic field in the primary criteria for safety due to the impact of electrical The direct leakage method is identical to the wire is equal to the leakage current as the neutral currents on the human tissues. Small amounts of method used in the IEC standard. Any voltage see 8. The current being inducted in the have a significant impact on our safety.
Opposite magnetic fields n The measurements are not influenced by n Direct comparison with measurements made Applied part leakage current.
To reflect testing at mains voltage. N equipment. In this approach. The providing a high level of safety for the test n Alternative method internal magnetic fields.
BF and CF equipment. The equipment frequency. The maximum short circuit current is leakage value up. Equipment leakage n Both direct and alternative methods provide direct. The direct method is identical to the method n The measurements have limited frequency the applied part. Example of current limited n Measurements are highly repeatable and Figure 19 and figure 20 show a representation of conductors might alter the leakage readings.
The IEC specifies three different methods n The differential leakage measurement is less leakage current is scaled in proportion to the n As live and neutral are combined. Equipment leakage Figure 21 and figure 22 show a representation of differential — class II 8.
The test is conducted with the protective earth secondary earth connections influencing the path to earth. Figure 23 and figure 24 show a representation of the alternative N M N L method. As such. EUT interrupted. Equipment leakage the differential method. The MD is part method.
PE the DUT is not required to be positioned isolated from earth. This method is in fact similar to a dielectric test alternative.
As connection closed to protect the user. Equipment leakage such. As live and neutral are shortened. Applied part leakage enclosure class I and non-earthed accessible direct. EUT earth and enclosure all connected together.
Due to the fact that electrical currents follow the n Equipment bolted to steel reinforced concrete MD path of least resistance much like water does. Both sources depend on a Figure Applied part leakage All floating type patient connections in each applied connection closed for protection of the user. Applied parts and patient connections not part of current limited voltage source to produce the MD the measurement shall be left floating. Each significant voltage drop.
The test is conducted with the protective earth connection closed to protect the user. Please refer according to IEC This applied part direct leakage test is thus. As is positioned between the applied part and Applied part leakage current — direct method a. AP2 8. MRI connections could influence the measurements n Equipment connected to gas or water supply of leakage currents. This is because the differential leakage on a TN system half the line voltage. Measuring leakage current with secondary earth using differential method V In case a secondary earth path exists.
Secondary earth path error 8.
In general. Example showing leakage current flowing away via a secondary Measurements under a TN terre — neutral E V earth connection system ensure the live to earth voltage is equal N to the line voltage between live and neutral. L using the alternative method which does not rely V analyser and could potentially pass a dangerous on the incoming mains configuration. Leakage measurement analyser is able to produce an internal earth at exists.
If the earth potential differs from AP the neutral potential. In this case. Leakage measurement model. See possible to test using the equipment leakage This will result in a zero reading on the safety figure L see figure Once testing. An example of such test templates is accordance with IEC Going forward.
Time saving the safety is accessed. Comparing data also makes it n Develop efficient re-test periods leakage and on the output of the medical possible to monitor leakage against expected equipment applied part leakage.
Ensure that the operator of the safety Testing to IEC has reduced the time taken n Functional testing test protocols analyser is properly trained on both the safety to conduct an electrical safety test — down from n Next inspection date n Significant time savings during routine safety analyser as well as the device under test to five minutes to less than 15 secondsv in some testing ensure that valid measurements are taken cases.
The IEC standard will provide.
Comparison with previous and To ensure proper record keeping is maintained it specialised test equipment. Ensure that leakage measurements are innovations visit www. Appreciate that secondary earth connections Equipment leakage — direct or differential method will lead to invalid measurements.
Please visit our website e. In the interests of helping to guarantee safer practice and the repeatability of test measurements, IEC defines different types of leakage current tests—one for total equipment leakage and another for applied parts leakage currents. IEC specifies three methods— direct, differential, and alternative—that can be used to determine the leakage of EM equipment. Direct Leakage Method The direct leakage method included in IEC is the same as that in IEC , measuring the true leakage through a body model measuring device to ground.
Another disadvantage is that secondary ground connections will produce a lower reading, thus potentially allowing faulty equipment to pass the test.
The direct method does therefore require a fully isolated device under test and must be performed on a terre neutral supply and in each polarity of the incoming mains supply to guarantee measurements are taken at the maximum potential leakage current. Keeping It Safe Follow this checklist for safety testing and keep all the bases covered. Ensure that the operator of safety test equipment is properly trained on both the safety analyzer and the device under test to prevent unneccessary danger during the safety test.
Stay aware of moving parts, open conductors, live components, heat, etc. Ensure that leakage measurements are performed while the equipment is in full operation mode, including its subsystems and components. Ensure high accuracy and repeatability of leakage measurement readings.
Some manufacturers might specify full-scale accuracy, which will affect the accuracy of low-leakage measurements. Contact resistance can influence the readings and cause unnecessary failures of the device under test. When determining the correct means of testing a specific medical device, ensure that the chosen safety test procedures are applicable to the device under test and are clearly documented for future use.
The main advantage of using the differential leakage method is that the ground conductor remains intact during the measurement, thus providing safer working conditions. Differential measurement of leakage also does not require an isolated device under test because it relies on comparing the difference in current between the live and neutral conductors to measure the complete leakage of the device being tested, including leakage caused by secondary connections.
Measurements can also be influenced by the presence of magnetic fields—the principle of measuring differential current—and measurements must be done in both directions to identify the worst-case scenario.
The differential leakage measurement method is also only able to measure the AC component. Alternative Leakage Method The alternative method is similar to a dielectric strength test at mains potential, using a current limited voltage source at mains frequency. The live and neutral conductors are shorted together and the current limited voltage is applied between the mains parts and other parts of the equipment. The main advantage of using the alternative method included in IEC is that the device under test is not connected to the mains supply and provides the safest possible test conditions for the operator.
In addition, this measurement is only taken in a single polarity and is similar to a dielectric test at mains potential using a current limited mains frequency supply.
Leakage measurements achieved using the alternative method are highly repeatable and provide a good indication of deterioration in the dielectrics of the medical device under test. The disadvantages of using the alternative method are that measurements cannot be compared with previous IEC tests, and those active parts of the circuitry that require mains potential between live and neutral cannot be tested for possible leakage.
For this reason, the alternative leakage method is only relevant for certain types of EM devices. IEC defines two different kinds of leakage current tests for applied parts—equipment leakage current that tests for total leakage deriving from the applied parts, enclosure, and mains parts combined to real ground; and applied part leakage current that checks for total leakage deriving from the combined patient connections within an applied part to ground and any conductive or nonconductive parts on the enclosure.
Measurements are done in both polarities of the incoming mains, excluding alternative method. Figures 1, 2, and 3 provide a schematic representation of the equipment leakage test on Class I grounded ME equipment. Applied Part Leakage The applied part leakage test measures the RMS deriving from the combined patient connections within an applied part to ground and any conductive or nonconductive parts on the enclosure.
Unlike low test currents, high test currents do provide a practical problem during preventive maintenance, leading to potential damage to functional ground circuits and masking of poor contact resistance in older mains cabling. Protective ground problems are common, caused by either partial or complete restriction in the current path due to mechanical damage or wear and tear.
It is taken for granted, and its benefits far outweigh the dangers. And so it must be accepted that electrical currents—referred to as functional current—are a necessary part of modern medical devices. Figure 4. Applied part leakage, direct method, class 1 equipment.
See Figure 3 for abbreviation keys. Increased leakage currents can occur due to reduced insulation quality as a result of component failure inevitable , mechanical damage leading to reduced creepage distances, evident and nonevident spillage of liquids inside the medical device, degrading of insulation materials due to aging or abrasion and environmental conditions, and unintentional misuse of the medical device.
Unintentionally high leakage currents can lead to macro shocks, current path between two different skin areas eg, hand-to-hand or hand-to-foot , and micro shock eg, current flow is introduced across or near the heart. Considering that electrically conductive parts can be placed in close proximity to the heart, and that electrically conductive parts from a medical device can be connected to a patient for hours, even up to several days or weeks during treatment or monitoring, the risk of micro and macro shocks cannot be understated, especially when considering that the patient might be vulnerable or have impaired ability to move or communicate.
Figure 1 provides an overview of the different means of protection against electrical shock and how the effectiveness is tested. Figure 5. Equipment leakage, differential method, class 1 equipment.
Human skin acts as an electrical insulator and can limit the amount of current passing through the muscle tissues and vital organs like the heart. To standardize the leakage measurements, a common measuring device body model is specified in IEC and IEC See the graphs, figure 2 above. IEC defines two different kinds of leakage current tests: The equipment leakage current and the applied part leakage current.
The equipment leakage current is the total leakage deriving from the applied parts, chassis, and mains parts combined to ground. This can also be referred to as leakage on the input of the medical device, as leakage is predominately generated in the power supply.
The applied part leakage current is the total leakage deriving from the combined patient leads within an applied part to ground and any conductive or nonconductive parts on the chassis. This can also be referred to as leakage on the output of the medical device.
During this test, the effectiveness of the dielectrics of the floating applied parts is determined. Figure 6. Equipment leakage, alternative method, class 1 equipment. The strength of IEC is that leakage measurements are done primarily under single fault condition, reducing the need for repeated measurements—as is done under IEC Furthermore, IEC measurements in patient environments are always ideal.
Secondary ground due to functional grounding or connections in a medical system can lead to invalid readings false pass caused by the internal resistance of the measuring device.
Leakage currents are primarily referenced to ground, as this is the most common danger to humans. When measuring on an isolated mains supply, the line isolators in hospitals can mask high leakage currents in medical devices. As such, a false pass might occur when a medical device has generated a fault. This will only become apparent when the medical device leaves the isolated mains location. Testing Leakage Testing leakage under these conditions is not covered by IEC but is considered in IEC by offering different methods for testing leakage: the direct leakage, differential leakage, and the alternative methods.It is clear that most commonly used electrical which vary between types of equipment.
Although all reasonable care has been taken to ensure accuracy of the information and reference figures and data have been taken from the latest versions of various standards, guidance notes and recognised best practices to establish the recommended testing requirements, Rigel Medical, their agents and distributors, accept no responsibility for any error or omissions within this booklet, or for any misinterpretations by the user.
Conclusion 24 This is now possible with IEC , providing concise information for manufacturers and operators, which can lead to improvements in product and design and provide an important reference when evaluating new medical devices. Insulation test.
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