Influence of patient connection cables on the SECUTEST SIII
Problem: Accuracy in patient leakage is not enough.
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 virtually no interference from any leads or line lengths or wirings, as the whole is relatively low impedance (there is only one influence over the frequency of the current).
The situation is different with the replacement of the patient with leakage current measurement or with the measuring network 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 connecting cables have an immense influence on the measured value. The cause lies in the method itself.
In the replacement measurement, the tester generates its own test voltage of about 250V (the value can also be up to 300V). For safety reasons, however, the test voltage must be current-limited (to 3.5 mA, because the user can touch the wires), which means that the actual test voltage at the test object is between 0V and 280V, depending on the load. The test voltage is an alternating voltage with 50Hz - therefore the measurement is frequency independent. Depending on the number, position, length and thickness of the connection leads but results in 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 μA range plays a role, 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 ensure the thinnest possible cables and the greatest possible distance between the cables and between the connection sockets.