What are the exact leakage currents? (SECUTEST SIII)

Influence of the patient connection cables on the SECUTEST SIII.

Problem: Accuracy of patient leakage currents is not sufficient.

The direct leakage current measurement is practically identical to a measurement with a multimeter in the µA range with a shunt of 1 kOhm and a frequency response up to 1 KHz( 3dB limit). In this measurement, there is practically no influence from any connecting cables or cable lengths or cable routing, since the whole thing is relatively low impedance (there is only an influence via the frequency of the current).

The situation is different for the substitute patient leakage current measurement or for the mains measurement on the application part. (The two measurements are almost identical in terms of measurement, only the name is different, since the measurement is defined once in IEC 601 and once in DIN VDE 0751).

In these measurements, the connection cables have an immense influence on the measured value The cause lies in the method itself.

During the substitute measurement, the test instrument generates its own test voltage of approx. 250V (the value can also be up to 300 V). However, the test voltage must be current limited for safety reasons (to 3.5 mA, because the user can touch the leads) this means that the actual test voltage at the DUT is between 0V and 280V, depending on the load. The test voltage is an AC voltage with 50Hz - therefore the measurement is frequency independent. However, depending on the number, position, length and thickness of the connecting leads, there is a more or less significant crosstalk.

Example: only channel A activated

• nothing connected to the sockets, approx. 0.5 µA
• standard cable connected to channel A 1.1 µA
• PA4 whip connected 5.8 µA

Example: all channels activated

• nothing connected to the sockets, approx. 0.7 µA
• standard cable connected to channel A 1.5 µA
• standard cable connected to A to K 2.1 µA
• PA4 whip connected 14.5 µA

So if the accuracy of the measurement in the µA range is important the standard cables and only the used inputs should be used if possible. If adapters or terminal boards are used, care must be taken to use the thinnest possible cables and the greatest possible distance between the cables and between the connection sockets.