Interpretation of IEC60601, a general standard for safety testing of medical electrical equipment(5).
Leakage current measurement.
A small amount of current can have very serious consequences. Studies have shown that it is often the current, not the voltage, that is responsible.
When an electric current flows through the human body, its effect is affected by two main factors: first, the magnitude of the current, and second, how long the current flows.
For example, if the current lasts for 250ms at 40mA, 100ms at 100mA, or 50ms at 200mA, the heart will stop beating.
Consider the following example of the effect on the human body when an electric current is applied to ** (non-invasive):
0.9 - 1.2mA is just enough to perceive the current.
15.0 - 20.0mA cannot be released. Endure for no more than 15 minutes.
50.0 - 100.0mA ventricular fibrillation. Respiratory arrest, which leads directly to death.
100.0 - 200.0mA severe burns and muscle contractions, to the extent that the chest muscles contract the heart.
Compare these values to the 250mA current required to power a 25W lamp.
As a result, the IEC 60601 committee has established strict rules for the design of medical devices to prevent any patient or operator from being exposed to currents that are not functionally operated by the device. These currents are known as leakage currents.
IEC 60601 defines three different types of leakage currents:
Leakage current to ground: Current flows through the PE protection ground wire in the power supply wire.
Enclosure leakage (contact current): An electric current that flows to earth through a person touching a medical device system or part of it.
Application Section or Patient Leakage: An electric current flowing from the application section through the human body to the earth, or an unexpected voltage flowing from the human body to the application section by an external power source.
Application section Patient leakage can be divided into multiple measurements, such as:
Patient leakage (see appropriate paragraph).
Patient type F leak (see appropriate paragraph).
Patient-assisted leakage (see appropriate paragraph).
Application section or patient leakage is the most important part of any medical device leak measurement. The application part is in direct contact with the patient, or an invasive device is placed under the patient's **. *forms our natural protection against currents, but the currents applied under **, can lead to even greater consequences, with currents as low as 15 A leading to death.
The leakage current limit in IEC 60601-1 is designed to reduce the probability of ventricular fibrillation to 0002 – The limit for CF application parts is 10 A under normal circumstances. See Appendix A for a complete overview of IEC 60601-1 test limits.
The following tests are derived from IEC 60601-1, but are specifically required by the AAMI and NFPA 99 standards (USA).
Patient leakage (application part to ground): Similar to patient leakage (see description above).
Patient Leakage (Application Part to Enclosure): Similar to patient leakage (described above), the leakage current path passes from the application part through the patient to the enclosure of the EUT DUT.
Patient Assist Current (Application Part to Application Part or Lead-to-Wire): Similar to Patient Assist Current (see description above).
Patient Assist Current (Application Part to All): Similar to Patient Assist Current. In this manual, the focus will be on the direct correlation leakage measurement as specified in IEC 60601-1.
Warning: The power supply voltage applied to the device.
It is important to verify that medical devices with moving parts, such as motors or pumps, are safely installed to allow movement without causing damage to personnel or equipment. The secondary ground path will affect the leak measurement and may give an incorrect pass reading. When measuring leaks, always ensure that the device under test is in a safe position and isolated from ground.
The German GMC-I Group's comprehensive medical electrical safety tester SecuLife ST Pro has the latest IEC60601 version 3 automatic test sequence, which can measure ground leakage current, contact current, patient leakage current and patient auxiliary current.
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