An ultrasonic surgical system enables connection of a hand switch as well as a foot switch, which is used to operate a driving signal generator, without the necessity of retrofitting a main unit including the driving signal generator used to drive an ultrasonic transducer incorporated in a connected handpiece. A frequency emphasis circuit with an overall high pass transfer characteristic selectively emphasizes higher frequency signal components over lower frequency signal components. The converted codeword is compared to an initially set target codeword to detect an amount of non-identical bits. Thus as the blades of the fan turn, the cloth swipes off any dust.