The invention concerns an HF-surgery device for cutting and/or coagulating biological tissue and a method for same, which in operation monitors the patient skin contact of a connected neutral electrode having at least two separate contact surfaces. The HF-surgery device includes at least one parallel resonant circuit arranged in a patient circuit, at least one measurement energy source arranged in a measurement circuit galvanically separated from the patient circuit for producing a measurement voltage/current acting between the contact surfaces of the neutral electrode, and at least one measuring and computing unit which in operation determines by means of the measurement voltage/current a tissue impedance which is representative of the patient skin contact and which acts between the contact surfaces. An HF-current flows in the patient circuit which is closed in the cutting or coagulation operation and the measurement voltage which is independent of the HF-current can be produced in the measurement circuit. To provide an improved HF-surgery device it is provided according to the invention that the frequency of the measurement voltage source is substantially equal to a resonance frequency of the parallel resonant circuit.本発明は、手術中に、2つのコンタクト面を備えた中性電極に対する患者の皮膚の接触状態を監視する、生物組織の切除手術または凝固手術のためのHF手術装置、ならびに、こうしたHF手術装置の制御方法に関する。HF手術装置は、患者回路に配置された少なくとも1つの並列共振回路と、患者回路から電流に関して分離された測定回路に配置され、2つのコンタクト面のあいだに測定電圧または測定電流を形成する少なくとも1つの測定エネルギ源と、手術中に測定電圧または測定電流によって2つのコンタクト面に対する患者の皮膚の接触状態を表す組織インピーダンスを求める少なくとも1つの測定計算ユニットとを有しており、手術中に閉成される患者回路をHF電流が流れ、測定電圧はHF電流から独立に測定回路内で形成される。本発明によれば、測定エネルギ源の周波数が並列共振回路の共振周波数にほぼ等しい。
