Evaluation and comparison of 50 Hz current threshold of electrocutaneous sensations using different methods |
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| Authors: | G Lindenblatt J Silny |
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| Institution: | (1) Centre for Optical and Electromagnetic Research, Department of Optical Engineering, Zhejiang University, Hangzhou, 310027, China;(2) Research Center for Bioelectromagnetic Interaction (femu), University Hospital, Aachen University, 52074 Aachen, Germany |
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| Abstract: | Leakage currents, tiny currents flowing from an everyday-life appliance through the body to the ground, can cause a non-adequate
perception (called electrocutaneous sensation, ECS) or even pain and should be avoided.
Safety standards for low-frequency range are based on experimental results of current thresholds of electrocutaneous sensations,
which however show a wide range between about 50 μA (rms) and 1000 μA (rms). In order to be able to explain these differences,
the perception threshold was measured repeatedly in experiments with test persons under identical experimental setup, but
by means of different methods (measuring strategies), namely: direct adjustment, classical threshold as amperage of 50% perception
probability, and confidence rating procedure of signal detection theory. The current is injected using a 1 cm2 electrode at the highly touch sensitive part of the index fingertip.
These investigations show for the first time that the threshold of electrocutaneous sensations is influenced both by adaptation
to the non-adequate stimulus and individual, emotional factors. Therefore, classical methods, on which the majority of the
safety investigations are based, cannot be used to determine a leakage current threshold.
The confidence rating procedure of the modern signal detection theory yields a value of 179.5 μA (rms) at 50 Hz power supply
net frequency as the lower end of the 95% confidence range considering the variance in the investigated group. This value
is expected to be free of adaptation influences, and is distinctly lower than the European limits and supports the stricter
regulations of Canada and USA.
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| Keywords: | Electrocutaneous sensation Non-adequate stimulation Adaptation Psychophysics Cutaneous mechanoreceptors Human hand Safety guidelines |
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