A brief discussion on IEC 60601-1 surge tester calibration and inspection test analysis

In addition to describing some techniques that can help simplify surge testing, this article will also describe some easy-to-implement methods for ensuring that defibrillation-proof surge testers function properly between calibration cycles.

Energy measurement test

IEC 60601-1, the international standard for medical electrical equipment, includes several surge tests to ensure that the device under test can still operate normally when subjected to a defibrillation pulse. These tests are described in Figures 9, 10, and 11 of IEC 60601-1. Each test requires a 5000 V power supply capable of delivering 400 J of energy, which outputs approximately 360 J of energy at the tester (worst case). The three figures in the standard describe different methods of delivering this pulse to the device under test.

The two methods described in Figures 9 and 10 of IEC 60601-1:2005 are common mode and differential mode testing, which can be used to check the separation between the signal input/output parts and the patient connection parts. The voltage change of the signal input/output parts when the 360-J pulse is applied is monitored using a voltage divider network.

The 2005 edition of the IEC 60601-1 safety standard, General Requirements, added an energy measurement test that was introduced into this general medical standard from IEC 60601-2-49, Safety Requirements for Multi-Function Patient Monitoring Equipment. This new requirement states that the equipment connected to the patient shall reduce the defibrillation energy delivered through a 100 Ω load by a maximum of 10%.

The three tests mentioned above, as well as many other surge tests in AAMI and IEC medical standards, all use the 5000-V/400-J engine, with only differences in waveform components and application techniques. This similarity allows test equipment manufacturers to develop a single tester that complies with multiple standards. By reviewing the documentation for an IEC 60601 defibrillator tester, users can know exactly which standards the equipment can test against; in addition, they can view connection information for each test method.

Figure 1: IEC 60601-1:2005 Figure 9 – Application of test voltage to the PATIENT CONNECTED PARTS in a DEFIBRILLATOR APPLIED PART

As shown in the example in Figure 1 (IEC 60601-1:2005 Figure 9), by determining the circuit component values ​​and tolerances, the pulses from a 5000-V/400-J source can be controlled in the same manner as the IEC/AAMI standard. The red shaded box area of ​​the figure shows the circuit that should be provided with a defibrillation-proof surge tester. The circuit in the lower half of the red box area is a generic 5000-V/400-J surge source. Below the circuit is a list of components and tolerances; note that the surge source has tolerances of ±5%. The waveform components vary by standard, but the surge source also has component tolerances of ±5%.

Calibration ensures that component tolerances are within the specified values. For a defibrillation-proof surge tester that has not been used or calibrated, the user can be confident that the tolerances are within the above values. However, unless the surge tester is opened and the component values ​​are rechecked (which would invalidate the calibration), there is no direct way to confirm that the instrument is functioning properly between calibration cycles. Below, we will introduce some methods to check the calibration status of the surge tester without opening it.

Waveform comparison method

All three tests in the IEC 60601-1:2005 standard use a defibrillation-proof surge tester (Figures 9, 10, and 11), with pass/fail points based on pulses delivered to the device under test from a 5000-V/400-J power supply. However, without reference data (other than inaccessible component values ​​and tolerances), it is impossible to confirm the power supply output based solely on the information provided in IEC 60601-1:2005. In addition, since compliance of a surge tester to IEC 60601-1:2005 depends solely on component tolerances, even calibration to ISO 17025 only verifies component tolerances.

Figure 2: IEC60601 defibrillation waveform showing current and resulting waveform

Some manufacturers provide waveforms of the expected output type based on the test conditions anticipated by the IEC 60601-1:2005 standard. If you have access to these waveforms, it is recommended that you check the output of your new defibrillation-proof surge tester against the generated waveforms as described below. If your individual tester does not provide waveforms, consider constructing simulated waveforms using the component values ​​given in IEC 60601-1:2005 Figures 9 and 10 (see Figure 2 in this article). Due to the tolerance limitations of the IEC 60601-1:2005 standard, the simulated waveforms may not exactly simulate the output of your individual defibrillation-proof surge tester. If you do not achieve the desired results when evaluating the output, other test methods described in the Energy Measurement Test Accuracy Assessment section below may also be used.

Waveform comparison test method

This method compares the new waveform generated by the defibrillation-proof surge tester to the waveform in the initial calibration packet when the instrument was received. If the above information is not available, the generic analog waveform provided in Figure 2 can be used. This is a simple and quick way to verify the output of the surge tester. Figure 3 in this article is an example of an initial reference waveform for reference during testing.

One final note: The 5% component tolerances specified by the IEC 60601-1:2005 standard may seem tight, but our experience is that even when all tolerances are met, some output variation is likely. If your defibrillator-proof surge tester output data is not ideal, no conclusions can be drawn immediately about the instrument's current calibration status and further testing is required. When using a defibrillator-proof tester that complies with the standard, the output peak voltage will be between 4500 V and closer to 5000 V, due to differences in tolerance and quality of the components used.

1. Use a high voltage, high frequency oscilloscope probe. We have had very good results using a Tektronix P6015 (available on the used market at a reasonable price).

2. Use a digital oscilloscope and set the input signal to 1.00 kV/vertical division and 500.0 μSec/horizontal division.

3. If your defibrill-proof surge tester has multiple waveform networks, make sure it is set to 50 ohms, 500 μH.

4. Set the front panel meter to 5000 V, which indicates that the internal supply is charged to 5000 V (the output will be lower than this; see Figure 2 of this article).

5. Power on the defibrillation-proof surge tester so that current is delivered to the open-circuit output with only the high-voltage probe connected.

6. Observe the oscilloscope display. The output peak should be between 4500 and 4900 V (not 5 kV).

7. Find the midpoint of the voltage peak waveform on the waveform duration side. This waveform should match the initial waveform, located around 2.42 milliseconds.

8. If the peak value of the waveform or its duration is slightly lower than expected, the defibrillation-proof surge tester may not be able to deliver the required 360 J of energy. Further testing should be performed (see the Energy Measurement Test Accuracy Assessment section below), or maintenance should be scheduled.

Energy measurement test (IEC 60601-1, ): Resistance measurement

The energy measurement test requires two measurements: a reference measurement to determine the exact output of the defibrillation-proof surge tester, and a second measurement where the device under test is connected to the defibrillation-proof surge tester output. The two measurements must be within 10% of each other to pass.

Figure 3: Sample waveform received during the defibrillation surge tester test

The order in which the above tests are performed is important. As the resistor heats up, its resistance decreases. As the resistance decreases, less energy is transferred. This is important because when the device under test is connected to the defibrillator-proof surge tester, the change in resistance caused by the increase in temperature will affect the 10% change in energy allowed. Therefore, it is important to ensure that both tests are completed at the same resistance value. Although the resistor banks provided by the manufacturers of defibrillator-proof surge testers will not change in resistance more than 5% of the nominal value when used according to the recommended duty cycle, it is recommended that resistance measurements be made between tests. The time it takes for the resistor to return to the initial resistance value used in the reference test may exceed the manufacturer's published duty cycle time. [page]

Energy measurement test: resistance value measurement

1. Before the energy measurement test, place a resistor with a cold resistance value of 100Ω into the defibrillation-proof surge tester.

2. Ensure that the defibrillation-proof surge tester is not charged. This requirement can be ensured by following the manufacturer's specified procedures. Normally, the instrument should power on and the front panel voltmeter should read close to 0 volts.

3. Turn off the defibrillation-proof surge tester.

4. Place the ohmmeter between the energy measurement port and the defibrillation-proof surge tester ground lead. The measurement should be within ±5% of 100 Ω.

5. Perform an energy measurement reference test; that is, according to IEC 60601-1:2005 standard, without connecting any instrument to the output of the defibrillation-proof surge tester. Confirm the output energy and record the result.

6. Repeat steps 2 and 3 above.

7. Place the ohmmeter between the energy measurement port and the ground lead of the defibrillation-proof surge tester. If the value is slightly lower than the value measured in step 4, wait for the resistor bank to cool so that the value is close to the value measured in step 4.

8. Connect the instrument under test to the anti-defibrillation surge tester and perform an energy measurement test. If the difference between the above two results is less than 10%, it is qualified.

Energy measurement test (IEC 60601-1 Figure 11): Accuracy assessment

If your defibrillation-proof surge tester is already IEC 60601-1:2005-ready, it can be equipped with an energy port to perform the test shown in Figure 11. This port can also be used to confirm the exact energy output of the defibrillation-proof surge tester. The output energy for any test should be greater than 360 J using a 5000-V source and a 32-μF capacitor (see Figure 1 in this article). This reference test is performed in the same manner as the first part of the energy measurement test. Because the method for transferring waveform data from an oscilloscope to an Excel spreadsheet varies depending on the oscilloscope used, the following is a brief procedure. Alternatively, the spreadsheet is available free of charge on our website. A link to the website is provided at the end of this article.

Energy measurement test brief process

1. Remove the load from the defibrill-proof surge tester output.

2. If necessary, set the defibrillation-proof surge tester to 25-mH, 400-Ω.

3. Measure the resistance of the 100-Ω resistor using the above resistance measurement method.

4. Using a suitable high-voltage probe (for example, a Tektronix P6015), connect the oscilloscope across the 100-Ω resistor bank inside the tester. For most testers, this location is between the energy measurement output and the tester ground lead.

5. Use a digital oscilloscope that can transfer the waveform data to an Excel spreadsheet. Set up the oscilloscope to capture the entire waveform. Set the vertical axis to 1000 V/division and the horizontal axis to 2 msec/division.

6. Charge the Defibrill-proof Surge Tester until its internal power supply is charged to 5000 V. (In most cases, the power supply voltage is shown on the front panel display.) Then, power on the Defibrill-proof Surge Tester.

7. The display should show the full oscilloscope waveform, starting at 0 V and ending at 0 V. Go to http://www.compwest.com/Products/Downloads/Energy_calculation_TUV_

EC13_10.75ohm_open.xls to view an ideal waveform representation contained in the Excel spreadsheet. If the complete waveform is not obtained with the recommended settings, adjust the settings until the complete waveform is displayed on the oscilloscope display.

8. Transfer the waveform data to an Excel spreadsheet. How you do this depends on the type of oscilloscope you are using.

9. Open the Excel spreadsheet. Delete the waveform data outside the start and end range of the waveform. (The noise component of this data will cause the energy result to be too large.)

10. Calculate the result using an Excel spreadsheet. The result should be greater than 360 J.

If the result is significantly less than 360 J, the defibrillator-proof surge tester should be checked and the cause of the low output energy corrected.

Defibrillator-proof parts testing (IEC 60601-1 Figures 9 and 10): Accuracy assessment

All of the above methods and discussions refer to the power supply of the defibrillation-proof surge tester. A laboratory that follows the above guidelines should ensure that the tester is operating properly and is suitable for energy measurement tests. However, for the common mode and differential tests shown in Figures 9 and 10 of IEC 60601-1:2005, it is also necessary to ensure that the voltage divider network is operating properly (as shown in the upper part of the red strip in Figure 1 of this article).

One way to do this verification is to substitute known values ​​for the instrument under test, which means replacing all the white parts in Figure 1 of this article. This is the most effective verification method; additionally, if the expected output values ​​are obtained, it also proves that the entire test setup is correct.

Some manufacturers offer a defibrillation-proof pass/fail measurement tool that can be inserted into the above test setup. This pass/fail measurement tool is shipped with a specific defibrillation-proof surge tester because the tolerance specifications of the IEC 60601-1:2005 standard do not allow for the same setup for all testers. However, if necessary, an uncalibrated pass/fail measurement tool can be used to obtain useful information and verify the overall integrity of the test setup and the defibrillation-proof surge tester.

in conclusion

This article introduces the new surge test in the IEC 60601-1:2005 standard and describes some procedures and suggestions to simplify the test and ensure correct test results. In addition, this article describes some simple methods to ensure that your defibrillator-proof surge tester is operating properly between calibration cycles. These methods can be used to understand the overall condition of the defibrillator-proof tester and ensure that the tester connections are valid. We hope that these methods will help ensure that all tests are completed with the equipment in good working condition.