A control system alters one or more characteristics of an ablating element to ablate tissue. The barrier system includes a series of blocks at spaced intervals along the barrier system, wherein the blocks are interlinked by at least one elongate member. The capacitive sensor includes a plurality of electrodes which are arranged around the operation member, and each of which has a capacitance variable due to an approaching of a detection target, and a second detection circuit configured to detect the capacitance of each of the plurality of electrodes.