IEC 60601-1 Energy Measurement Techniques

IEC 60601-1 is an effort to make patient equipment connections safer when the patient is defibrillated.The Third Edition of the Medical Standard, IEC 60601-1, was published in 2005. However, only now are regulatory engineers beginning to examine and evaluate its requirements to determine how it will affect their evaluations of new products. Newly adopted to the 2006 Edition is the Energy Measurement Test, which was borrowed from IEC 60601-2-49, Patient Monitoring Equipment. This test is now required for any patient-connected equipment and is designed to ensure that the device under test does not absorb more than 10% of a defibrillation pulse delivered to the patient. The test equipment is specialized and specific procedures must be followed to make sure the test is correctly conducted. In addition, even if the test is conducted correctly, it is important to make sure the tester is stable before and between tests to ensure that the results will be correct.

The Energy Measurement Test uses measurement of the energy dissipated in the tester to determine if the Device Under Test (DUT) passes. First, the energy dissipated with no load attached is measured. Then, the test is repeated with the DUT connected. The two measurements cannot differ by more than 10% for a passing result. However, the tester’s resistor used for this measurement can be affected by heating during pulse delivery. Since the equation for power relies on the resistor value, the operator should measure the resistance of the tester before each test to make sure results will be accurate.

In order to make sure the Energy Measurement Test results are accurate, it is suggested that the following procedure be followed:

Measure the 100-ohm resistance value with an ohmmeter before any tests are conducted. This can be done simply by checking the resistance between the tester’s energy measurement port and the tester’s chassis ground.

Conduct the energy measurement test without the DUT connected (open circuit). All the energy developed by the tester will appear across the 100-ohm resistor; this test is the baseline for determination of the amount of power dissipated in the DUT. If it is possible to download the resulting waveform from your digital scope, insertion of the waveform into the Compliance West Excel spreadsheet will provide the energy reading directly.

Re-measure the 100-ohm resistance value and wait to proceed until it has returned to the value measured before testing started. This will allow the same power to be delivered while the DUT is connected in the next step, and will give the DUT the best chance of passing the test.

Connect the DUT to the outputs of the tester. With the DUT connected, the energy dissipated in the tester must be at least 90% of the energy dissipated with no DUT connected. 

IEC 60601-1 has tolerance limits for components within the tester, and the resistor used for the Energy Measurement Test has a tolerance of ±5%. Since the nominal value of this resistor is 100-ohms, it appears the Energy Measurement Test could be done with a resistor value of 95-ohms to 105-ohms. While this is true, care should be taken to minimize the resistor value changes during the Energy Measurement Test. Since IEC 60601-1 requires the referee test without the DUT attached to be conducted first, an unknown resistor value change because of heating (always lower) will lower the total energy delivered, and might cause a complying DUT to show failing results.

This will happen if the resistor has changed value due to heating while delivering the first pulse, with nothing connected. If the resistor is not re-measured, and the first (unheated) value is assumed for the second pulse, it will be delivered with less overall energy and it will appear that the energy reduction was due solely to the connection of the DUT. In some cases, this extra energy loss, due to the unnoticed heating of the resistor, could cause the DUT to appear to have failed the energy measurement test. To make sure the test is fair, we recommend the operator measure the resistor between tests and wait until the resistance value approaches the same value used for the first (open circuit) test.


Determining Results
Up to now, the focus has been on the possible errors that could be inadvertently introduced due to resistor heating. It is also important to address another potential problem with the Energy Measurement Test, and that is simply, determining the test results. Determination of the energy dissipated in the tester’s internal resistor requires calculation, and there are different ways to approach this problem. Some labs have data acquisition systems in place, and the energy can be directly calculated in joules. Others may not have this luxury; but with a digital oscilloscope with USB connectivity and a suitably fast, high voltage probe, the energy can be determined using Excel. In an effort to assist laboratories in performing the Energy Measurement Test, a working Excel spreadsheet can be found at compwest.com/Products/Downloads/Energy_calculation_TUV_EC13_10.75ohm_open.xls along with an explanatory video at compwest.com/YouTubeDefib-5_Setup_and_Operation.html. To incorporate this spreadsheet properly, the operator must load the oscilloscope waveform into the spreadsheet, and manually delete the pre-pulse and post-pulse data. Then, the energy contained in the waveform will be calculated and directly displayed.

IEC 60601-1 has incorporated the Energy Measurement Test, previously published in IEC 60601-2-49, in an effort to make patient equipment connections safer when the patient is defibrillated. If the Energy Measurement Test is conducted using the procedures above, the results are simple and accurate to calculate. 

Compliance West
Del Mar, CA
compwest.com