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Surge Generator Design Used for Energy Meter Test

The third version of IEC 60601-1 stipulates that when conducting the energy measurement test, the operator should do two tests. Doing the first test when the measured equipment and the surge generator are disconnected, doing the second test when the measured equipment (DUT) and the surge generator are connected. If all the two times energy measurement test results show that the pulse energy adopted by DUT is within 10% of the total pulse energy, then the measured test equipment has passed the energy measurement test. The designer and the techniques should use the special method to ensure the successful conduction of the test.

IEC 60601 stipulated the circuit diagram of the energy measurement test, but did not stipulate the wave form. Therefore, the surge tester manufacturer should ensure the accuracy of the surge generator, or it will cause inaccurate wave form. Figure 3 simulates the energy measurement test output results without the connection of DUT assuming that real components are used.

Since IEC60601 standard has stipulated the size and the variation range of the instrument, there is no need of the ISO17025 recognised standard. We must elaborately design the electrical inductance or resistor bank in order to get correct output waveform.

A surge tester of 100Ω resistor bank may pass ISO 17025 calibration, but maybe not in the margin range of tolerance after sending one surge (sharp pulse). Because the rating formula includes the resistance (quantity), if we want to get accurate result, we must ensure the resistance of the resistor will not change under the condition of heating caused by the surge. Since the energy measurement meter needs to conduct two times tests, the resistance will keep unchanged during the test. This point is very important.
The electrical resistor will emit heat in the circuit when being used; it will cause the decrease of the resistance. The electric resistance change will be defined as the temperature coefficient (T.C.) by the resistor manufacturers. The electrical resistance will change due to the influence of the surge heat effect so as to change the power measurement result. If the resistor heats to a certain degree, the resistance will have sharp movements after two times test. More pulse energy will be consumed by the resistor during the second test, the DUT energy will also decreased. If the resistor exceeds the allowable variation range after the resistor emits heat, the test result of the measured instrument will not pass the test.

If the resistance (quantity) of the resistor is wrong, the resistance heating will cause inaccurate energy measurement data during pulse transmitting. That is because that in the energy measurement formula the resistance is assumed not changed in the testing process. In the actual process, the resistance of the rated exclusion will have <5%change when it passes the pulse. In the condition of continuous pulse, the resistance value will have <5% change. Using the duty ratio of the surge tester to control 5% pulse-pulse accuracy. In order to ensure the accuracy of the energy calculation, 100Ω resistance should be tested in advance. The average value is used as the R value in the energy calculation.

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