IEC 60601-2-34 Issue 3: Changes to Recovery Test
The IEC has made a change to the Recovery Test, 60601-2-34. Issue 3 offers modifications that make it more beneficial for engineers as a custom test system is no longer required for this specific test. This article reviews the full breadth of the test and how it can impact medical device manufacturers.
IEC 60601-2-34:2011 (Issue 3) has been published as a replacement Standard, replacing and making obsolete the previous Standard, IECD 60601-2-34:2001 (Issue 2). The IEC has made this change stating that it “constitutes a technical revision in order to align structurally with the 2005 edition of IEC 60601-1.”
Because of the technical and alignment nature of this revision, the IEC has immediately withdrawn Issue 2 and the requirements of Issue 3 are in force immediately.
The Recovery Test illustrated in Figure 1 has undergone an alignment change, and this has a critical impact on the tests conducted. In Issue 2, the Recovery Test used a limiting resistor of 50 kohm in the 5,000 V line to the saline, resulting in a test current of around 100 mA. Issue 3 has changed the limiting resistor value to 50 ohms, which could allow a current of up to approximately 100 A to flow through the saline and to the transducer.
This change was made to align the test setup to the requirements of the Defibrillation-Proof Common-Mode and Differential-Mode Tests in IEC 60601-1, Section 8.5.5. In general, the alignment concerns itself chiefly with making the 5,000 V power supply the same as that used in IEC 60601-1 Figures 9 and 10; using 50 and 100 ohm resistors and replacing the 50 k and 100 k<ohm> resistors that were used in -2-34 Issue 2. This surge generator configuration also appears in IEC 60601-2-25 and -2-27; and similar wave-shaping networks are used in many medical standards and tests in IEC and AAMI Standards. The 50 kohm limiting resistor was specific to IEC 60601-2-34, and with the change to Issue 3, testing in IEC 60601-2-34 can use standardized defibrillator test equipment, instead of custom equipment used only for this substandard.
This change will benefit manufacturers because a separate machine or option is no longer required to conduct the Recovery Test. Now, the tester used for the Defibrillation-Proof Tests of IEC 60601-1 and -49 can be used for the -2-34 Recovery Test as well.
Analysis of the circuit shows some interesting behavior. Although the available current is many times higher in the new Standard, the sums of the two circuits show that more voltage is generated and is available for a longer period of time when the test in Issue 2 is conducted. Another way to look at this is to see what impedance of the DUT will pass in the new test vs. the old test. Under the requirements of Issue 2, the DUT needed an insulation resistance of approximately 4 M<ohm> to pass the test, while in Issue 3, a DUT with a resistance of 139 k<ohm> will now pass.
In essence, the change in surge generator topology has changed the Recovery Test from an insulation resistance type of test into a surge test.
UL also considers the change as a reduction in requirements, as a check of their website list of open File Reviews does not list any Reviews currently open for Medical Equipment.
Manufacturers of invasive blood pressure monitoring equipment should start testing using the standard 100 ohm and 50 ohm values when performing the Recovery Test to ensure their practices are in accordance with Issue 3, which is now currently in force. It seems that any constructions that passed the Recovery Test in Issue 2 will have no problems passing the Issue 3 version.
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