In accordance with the invention, {TAIL ~ this object} is achieved by exciting the active electrode with a HF current, measuring and combining values of the partial currents entering the partial electrodes and generating {HEAD ~ an alarm signal} which depends upon a comparison of this combination of the partial currents with a pre set limit value 
In accordance with the invention , { TAIL ~ this object } is achieved by exciting the active electrode with a HF current , measuring and combining values of the partial currents entering the partial electrodes and generating { HEAD ~ an alarm signal } which depends upon a comparison of this combination of the partial currents with a pre set limit value
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